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LabVIEW Data Acquisition Basics Manual

1. Figure 8 5 Analog Triggering with Your DAQ Device Analog Triggering Examples A common example of analog triggering in LabVIEW is the Acquire N Scans ATrig VI located in examples daqlanlogin anlogin 11b This VI as shown in Figure 8 6 uses the AI Waveform Scan VI to perform buffered acquisition where data is stored in a memory buffer during acquisition After the acquisition National Instruments Corporation 8 7 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers completes the VI retrieves all the data from the memory buffer and displays it time limit 5 sec oftware tigger TITEN pS pretrigger cans 0 Be GLA a trigger level 0 eeu input limits no change number of scars to acquire 1000 can rate 1000 scanssec Figure 8 6 Block Diagram of the Acquire N Scans ATrig VI For more information on buffered acquisition read Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 8 8 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers You must tell your device the conditions on which to start acquiring data The following shows the trigger and clock cluster input where you specify the triggering conditions on the AI Waveform Scan VI trigger and clock no trig int clk trigger type no trig 0 La a no trigger o pretrigger edge or sl
2. Non buffered handshaking takes place when your program transfers one digital value after receiving a digital pulse on the handshaking lines LabVIEW does not store these digital values in computer memory You should only use non buffered handshaking when you expect only a few digital handshaking pulses For multiple pulsed applications you should use buffered handshaking which you can learn about in the next section of this chapter Figure 15 3 shows an example of non buffered handshaking using the Intermediate VI DIO Single Read Write In this example LabVIEW reads the data from the digital port s Figure 15 3 Non buffered Handshaking Using the DIO Single Read Write VI Typically you want to put the DIO Single Read Write VI inside a loop You can use the iteration input the terminal where the loop iteration is connected to optimize your digital operation When iteration is 0 default LabVIEW calls the Advanced VI DIO Group Config to configure the port s If iteration is greater than zero LabVIEW uses the existing configuration which improves performance Every time your program calls the DIO Group Config VI the digital line values are reset to their default values If you want to set the digital line values once and keep the same values from one loop iteration to the next set iteration to 0 on the first iteration of the loop then set iteration to 1 When group direction is equal to 1 default all the ports listed in port
3. LabVIEW Data Acquisition Basics Manual January 1996 Edition Part Number 320997A 01 Copyright 1996 National Instruments Corporation All Rights Reserved Internet Support GPIB gpib support natinst com DAQ daq support natinst com VXI vxi support natinst com LabVIEW lv support natinst com LabWindows lw support natinst com HiQ hiq support natinst com E mail info natinst com FTP Site ftp natinst com Web Address http www natinst com Bulletin Board Support BBS United States 512 794 5422 or 800 327 3077 BBS United Kingdom 01635 551422 BBS France 1 48 65 15 59 FaxBack Support 512 418 1111 or 800 329 7177 Q gt Telephone Support U S Tel 512 795 8248 Fax 512 794 5678 or 800 328 2203 D International Offices Australia 03 9 879 9422 Austria 0662 45 79 90 0 Belgium 02 757 00 20 Canada Ontario 519 622 9310 Canada Qu bec 514 694 8521 Denmark 45 76 26 00 Finland 90 527 2321 France 1 48 14 24 24 Germany 089 741 31 30 Hong Kong 2645 3186 Italy 02 48301892 Japan 03 5472 2970 Korea 02 596 7456 Mexico 95 800 010 0793 Netherlands 0348 433466 Norway 32 84 84 00 Singapore 2265886 Spain 91 640 0085 Sweden 08 730 49 70 Switzerland 056 200 51 51 Taiwan 02 377 1200 U K 01635 523545 National Instruments Corporate Headquarters 6504 Bridge Point Parkway Austin TX 78730 5039 Tel 512 794 0100 Important Information Warranty Copyright Tra
4. In this picture you can see the difference between the ideal reading and the actual reading This difference is called V or the binary offset before the two readings intersect The difference between the actual and ideal readings after they intersect is called the gain error One point calibration removes the V binary offset by measuring a O volt signal and comparing the actual reading to it Two point calibration removes the V binary offset and corrects gain error by first performing a one point calibration Then you measure a voltage at x volts and compare it to the actual reading The x must be as close as possible to the full scale range The following sections explain how to perform a one point and two point calibration LabVIEW Data Acquisition Basics Manual 20 4 National Instruments Corporation Chapter 20 SCX Calibration Increasing Signal Measurement Precision One Point Calibration These steps show you how to perform a one point calibration calculation in LabVIEW You should use one point calibration when you only need to adjust the binary offset in your module If you need to adjust both the binary offset and the gain error of your module read the Two Point Calibration section later in this chapter Open SCXI 1100 One Point Calibration example in examples daq analogin SCXI 11b for an example application that demonstrates one point calibration Note If you are using an AT MIO 16F 5 AT MIO 64F 5 AT MIO 16
5. Pin or wire lead to which you apply or from which you read the analog or digital signal Analog signals can be single ended or differential For digital signals you group channels to form ports Ports usually consist of either four or eight digital channels The clock controlling the time interval between individual channel sampling within a scan Boards with simultaneous sampling do not have this clock Input output operation that reads or writes more data points than can fit in the buffer When LabVIEW reaches the end of the buffer LabVIEW returns to the beginning of the buffer and continues to transfer data Hardware component that controls timing for reading from or writing to groups A set of ordered unindexed data elements of any data type including numeric Boolean string array or cluster The elements must be all controls or all indicators The smallest detectable change in an input voltage of a DAQ device A way to organize the data in a 2D array by columns G 3 LabVIEW Data Acquisition Basics Manual Glossary common mode voltage conditional retrieval conversion device counter 1llb counter timer group coupling D A DAC daqconf data acquisition data flow default input LabVIEW Data Acquisition Basics Manual Any voltage present at the instrumentation amplifier inputs with respect to amplifier ground A method of triggering in which you to simulate an analog trigger using software
6. Chapter 2 Installing and Configuring Your Data Acquisition Hardware requires When you change the system configuration you need to run daqconf to update the system so it reflects the new configuration When running daqconf displays a window that shows the current system configuration The box on the left side of the window displays a list of the configured devices and their ID numbers that you use whenever calling NI DAQ functions You can assign a device to any given ID number On the right side of the window daqconf displays the settings for the selected device You set the device type and the device file The device file is the file in the dev directory that acts as the interface between applications and the driver When an application needs to make a driver call the application writes to the device file The system automatically creates these files The system names the device files in the form dagX where X is 0 through 15 The system starts numbering device files with daq0 and adds one for each non data acquisition device you install The system numbers each device in the order the computer probes the slots when it boots For instance if in a three slot computer you install a device in slot 1 and another device in slot 3 the computer names the device file for the device in slot 1 daq0 and the device file for the device in slot 3 daq1 Refer to the user manual for your computer to determine what order your computer probes the slot
7. Note INFO Get DAQ Device Information VI This chapter will get you up and running using data acquisition with LabVIEW The chapter contains hardware installation and configuration instructions and some general information and techniques If you are using Windows 95 please refer to the NI DAQ Configuration Utility online help file for installation instructions Windows The LabVIEW installer prompts you to have the NI DAQ driver software already installed All National Instruments data acquisition DAQ devices are also packaged with NI DAQ driver software The version of NI DAQ packaged with your DAQ device may be newer than the version installed by LabVIEW If you select the LabVIEW upgrade option in the NI DAQ installation program it will compare the NI DAQ versions and it will only install the NI DAQ drivers again if they are newer You can determine the NI DAQ version in LabVIEW by running the Get DAQ Device Information VI located in Functions Data Acquisition Calibration and Configuration After installing LabVIEW follow the steps in Figure 2 1 to install your hardware and complete the software configuration LabVIEW uses the National Instruments Corporation 2 1 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware software configuration information to recognize your hardware and to set default DAQ parameters Install Plug in Devices y Use Yo
8. 9 4 external conversion pulses 9 4 scan clock control 9 6 to 9 7 AI Config VI basic circular buffered analog input 7 13 to 7 14 basic non buffered application 6 4 hardware timed analog I O control loops 6 8 interchannel delay 9 2 multiple channel single point analog input 6 5 multiple waveform acquisition 7 5 one point calibration 20 5 simple buffered analog input with multiple starts 7 7 to 7 9 AI Continuous Scan VI 7 11 to 7 12 LabVIEW Data Acquisition Basics Manual Index AI Read One Scan VI 6 7 AI Read VI advantages and disadvantages of reading backlog A 1 basic circular buffered analog input 7 13 to 7 14 conditional retrieval cluster 8 11 to 8 12 continuous acquisition from multiple channels 7 12 to 7 13 controlling startup times note 7 8 multiple waveform acquisition 7 5 one point calibration 20 5 scan clock control 9 7 SCXI temperature measurement 19 6 to 19 7 simple buffered analog input with multiple starts 7 7 to 7 9 AI Sample Channel VI multiple channel single point analog input 6 3 single channel single point analog input 6 1 to 6 2 AI Single Scan VI basic non buffered application 6 4 hardware timed analog I O control loops 6 8 to 6 9 improving control loop performance 6 9 to 6 10 multiple channel single point analog input 6 4 one point calibration 20 5 software timed analog I O control loops 6 6 AI Start VI basic circular buffered analog input 7 13 to 7 14 continuous ac
9. Analog Output Buffer 2D Array Now that you have read some basic LabVIEW DAQ concepts you can go to the section s that discuss your specific application In the following chapter Chapter 4 Where You Should Go Next you can answer questions about your application to narrow down where you should go next for help in this manual LabVIEW Data Acquisition Basics Manual 3 16 National Instruments Corporation Where You Should Go Next This section directs you to the chapter in the manual best suited to answer questions about your data acquisition application You answer a series of questions that help determine the purpose of your application The questions start very broad and narrow in scope until you are referred to a specific section in the manual dealing with your type of application Note You should always read the Things You Should Know chapter preceding the chapter specific to your application The Things You Should Know chapters teach you about basic concepts dealing with your application Use the following flowchart as a guide as you answer the questions that follow it The questions should pinpoint the sections in the manual that you should read for your particular application National Instruments Corporation 4 1 LabVIEW Data Acquisition Basics Manual Chapter 4 Where You Should Go Next Plug in DAQ Device Only Type of Measuring Device cin Seni Digital Read Part 5 SCX Getting Signals Your
10. If you have a channel list array you can use one channel entry per array element specify the entire list in a single National Instruments Corporation 3 9 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts element or use any combination of these two methods For instance if 0 1 and 2 are your channels you can specify a list of channels in a single element by separating the individual channels by commas for example 0 1 2 Or because 0 refers to the first channel in a consecutive channel range and 2 refers to the last channel you can specify the range by separating the first and last channels with a colon for example 0 2 cz Note Keep in mind that some Macintosh devices require either 1 or an even number of channels Some Easy and Advanced Digital VIs and Intermediate Counter VIs only need one port or counter to be specified Refer to the LabVIEW Data Acquisition VI Reference Manual for more information or choose Help Show Help and put your cursor on the VI to view the VI Help window for the VI you intend to use LabVIEW recognizes three types of analog channels on a DAQ device onboard AMUX 64T and SCXI channels It recognizes two types of digital ports and counters onboard and SCXI This section discusses addressing onboard channels ports and counters AMUX 64T addressing is discussed later in Chapter 5 Things You Should Know about Analog Input SCXI channel port and counte
11. Limit Settings 0 to 5V Limit Settings 0 to 5V Figure 5 6 The Effects of Limit Settings on ADC Precision Considerations for Selecting Analog Input Settings The resolution and device range of a DAQ device determine the smallest detectable change in the input voltage You can calculate the smallest detectable change called the code width using the following formula device range resolution 2 LabVIEW Data Acquisition Basics Manual 5 6 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input For example a 12 bit DAQ device with a 0 to 10 V input range detects a 2 4 mV change while the same device with a 10 to 10 V input range detects only a change of 4 8 mV device range_ 10 24 mV gresolunon g device TEREE 4 8 mV 2 2 A high resolution A D converter provides a smaller code width given a device voltage ranges shown above device range 10_ 15 mV g esolution 2 6 2 2 The smaller your code width the more accurate your measurements will be There are times you must know if your signals are unipolar or bipolar Unipolar signals are signals that range from 0 to a positive voltage i e 0 to 5 V Bipolar signals are signals that range from a negative to a positive voltage 5 to 5 V To achieve a smaller code width if your signal is unipolar specify that the device voltage range is unipolar as shown previously If your signal range is smal
12. When you connect any type of SCXI module to a DAQ device certain digital lines are reserved Refer to Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual for more information When operating in parallel mode with analog input SCXI modules certain lines on the DAQ device are reserved Refer to Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual for more information For the fastest performance in parallel mode on digital modules you can use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs Note SCXI modules provide higher analog input gains than those available on most DAQ plug in devices Before reading this section you should have already read the Limit Settings section in Chapter 3 Basic LabVIEW Data Acquisition Concepts It is important to follow the basic rules for setting SCXI gains If your module has jumper selectable gains enter those gains in the configuration utility If your module has programmable gains LabVIEW selects a gain for you when you use the input limits parameter to the analog input VIs If you do not use the input limits parameter LabVIEW uses the gain setting in the configuration utility as the default Enter the gain jumper settings in the configuration utility for each channel on each module with jumpered gains LabVIEW stores these gain settings and uses them to scale the input data
13. hardware You should read any unique installation instructions for your platform in Chapter 2 Installing and Configuring Your Data Acquisition Hardware 2 Learn Basic Data Acquisition Concepts Chapter 3 Basic LabVIEW Data Acquisition Concepts shows you the location of DAQ example VIs DAQ VI organization VI parameter conventions default and current value conventions common VI parameter definitions error handling channel port and counter addressing limit settings and data organization for analog applications 3 Goto Your Specific Application Section Chapter 4 Where Should You Go Next shows you where to find information in this manual for your application 4 Review LabVIEW Example Application The remaining chapters teach you basic concepts in analog input and output digital I O counters and SCXI Each application section first lists example VIs then discusses the basic concepts needed to understand these example VIs Whenever possible you should have the VI open as you refer to these examples 5 Learn How to Debug Your Application Chapter 27 Debugging Techniques discusses the different ways you can debug your application This chapter helps you trouble shoot for common programming errors Now you can begin the rewarding adventure of data acquisition with LabVIEW National Instruments Corporation 1 3 LabVIEW Data Acquisition Basics Manual Installing and Configuring Your Data Acquisition Hardware cP Note
14. list are treated as inputs The number of elements in the data read National Instruments Corporation 15 5 LabVIEW Data Acquisition Basics Manual Chapter 15 Shaking Hands with a Digital Partner parameter will be the same as the product of the number of ports in the group and the number to read parameter Figure 15 4 shows how you can use non buffered handshaking to write data The programming flow resembles the read operation above The updates to write array must contain as many elements as the number of ports multiplied by the number of values to write Figure 15 4 Non buffered Handshaking Using the DIO Single Read Write VI Buffered Handshaking Buffered handshaking allows you to store multiple points in computer memory Use this technique if multiple pulses are expected on the handshaking lines Buffered handshaking comes in two forms simple and circular You can use simple buffered handshaking on all DAQ devices that support handshaking but you can perform circular buffered handshaking only on the AT DIO 32F You can think of a simple buffer as a storage place in computer memory where buffer size equals the number of updates multiplied by the number of ports A circular buffer differs from a simple buffer only in the way your program places the data into it and retrieves data from it A circular buffer fills with data the same as a simple buffer but when it gets to the end of the buffer LabVIEW returns to the beginning of
15. located in examples daq anlogin anlogin 11b You connect analog trigger signals to the analog input channels the same channels where you connect analog data Your DAQ device monitors the analog trigger channel until trigger conditions are met You configure the DAQ device to wait for a certain condition of the analog input signal like the signal or voltage level or slope either rising or falling Once the device identifies the trigger conditions it starts an acquisition In Figure 8 4 the analog trigger is set to start the data acquisition on the rising slope of the signal when the signal reaches 3 2 volts Level and Slope of Signal Initiates Data Capture Figure 8 4 Diagram of an Analog Trigger LabVIEW Data Acquisition Basics Manual 8 6 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers Figure 8 5 explains analog triggering for post triggered data acquisition using a timeline You configure your DAQ hardware in LabVIEW to begin taking data when the incoming signal is on the rising slope and when the amplitude reaches 3 2 volts Your DAQ device receives this message waits until the pulse reaches the starting point you designated and then begins capturing data External Analog Trigger Device Signal DAQ Device continues checking signal until analog trigger conditions are met Then External Analog Data DAQ Device Device
16. you must do so from the SCXI Configuration window 2 23 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual Cabled Device or Logical Device for SCXI 1200 If the module is an SCXI 1200 WOAQCONF selects a logical device number Otherwise if the module in the current slot is directly cabled to a DAQ device in your computer set this field to the device number of that DAQ device Leave the Cabled Device field at None if the module in the current slot is not directly cabled to a DAQ device If you are operating your modules in multiplexed mode you only need to cable one module in each chassis to your DAQ device If you are not using multiplexed mode refer to the SCXI Operating Modes section of Chapter 17 Hardware and Software Setup for Your SCXI System for instructions about module cabling Operating Mode The system defaults to the multiplexed operating mode which is recommended for almost all SCXI applications The operating modes available for each SCXI module type are discussed in the SCXI Operating Modes section of Chapter 17 Hardware and Software Setup for Your SCXI System For the SCXI 1200 two modes are available SCXI multiplexed and stand alone In the SCXI multiplexed mode you can use the SCXI 1200 to communicate with other modules in the same chassis In stand alone mode you can use the SCXI 1200 only as a stand alone
17. 0 eee eeceeeceeceseeeeeeseeeseseeeeseeseeeaeeseens 7 6 Simple Buffered Analog Input with Graphing eee eeeeeeeeeeereeees 7 6 Simple Buffered Analog Input with Multiple Starts 00 eee 7 7 Simple Buffered Analog Input with a Write to Spreadsheet File 0 0 00 7 9 Triggered Analog Input o cic ccs sscscscessitasesssesibecdssssvossatisegsstescasssccbeasageseasedigeass 7 10 Do You Need To Access Your Data during Acquisition 2 0 eee eeeeeseeeeeereeeeees 7 10 Continuously Acquiring Data from Multiple Channels 0 eee 7 11 Circular Buffered Analog Input Examples 000 0 eee eecceeeecseceeeeseeeseteeeeseeseeeseesees 7 13 Basic Circular Buffered Analog Input eee ee ee eeeeeeeeeeeeseeeseeeeeeseeseees 7 14 Other Circular Buffered Analog Input Examples 00 eee eee eeeeereeeeees 7 14 Cont Acq amp Chart buffered Vi oe eee eeeeeseeceeeceseeceeecennersaeeeseeeenees 7 15 Cont Acq amp Graph buffered Vi oo ec eceee eee eseeeeeceeceseeseeeneeseees 7 15 Cont Acq to File binary Vii oe ec eeceeeeeeeeseceeececeseeseeeaeeseees 7 15 Cont Acq to File Scaled Vi cee ieeseceeeeceseeceeeeeneeceneeenessaeeeseeeenees 7 15 Cont Acq to Spreadsheet File Vi oo eee eee eeeceeesseceseeseeeaeeeees 7 15 Chapter 8 Controlling Your Acquisition with Triggers Hardware Trio Serine ooe Soscde scents ines cotuantect E AEA R RR E AE 8 1 Digital Trepering eii aat oo Sie A a a E ERE O Eaa 8 2 Digital Triggering Examples oo eee cece eeeeseceeeseeeesee
18. 22 8 measuring frequency and period high frequency signals 24 6 low frequency signals 24 4 to 24 5 multiple channel single point analog input 6 3 multiple waveform acquisition 7 4 to 7 5 non buffered handshaking 15 5 to 15 6 overview 3 5 to 3 6 SCXI temperature measurement examples 19 6 to 19 9 simple buffered handshaking 15 7 single immediate updates 11 1 to 11 2 single square pulse generation 22 4 to 22 5 strain gauge application 19 13 waveform generation 12 2 to 12 3 interval scanning 5 17 T O page lock limit changing 2 14 to 2 15 National Instruments Corporation IRQ jumper settings note 2 5 ISA bus computers configuring 2 6 to 2 9 isolation of transducer signals 16 4 J jumper settings 2 5 2 13 L LabVIEW software basic LABVIEW data acquisition concepts 3 1 to 3 16 See also VIs data organization for analog applications 3 13 to 3 16 location of common DAQ examples 3 1 to 3 2 common questions about LabVIEW A 1 to A 5 data acquisition hardware support Macintosh systems table 2 5 Windows environment table 2 4 data types xx relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 Windows NT considerations 2 14 to 2 15 changing I O page lock limit 2 14 to 2 15 user privilege level 2 15 latched digital I O See handshaking latched digital I O limit settings 5 5 to 5 6 considerations for selecting analog input settings 5 6 to 5 8 description 5 5 to 5 6 effec
19. 51 48 49 50 51 48 49 50 51 13 52 53 54 55 52 53 54 55 52 53 54 55 14 56 57 58 59 56 57 58 59 56 57 58 59 15 60 61 62 63 60 61 62 63 60 61 62 63 National Instruments Corporation 5 15 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input Table 5 4 Scanning Order for Each DAQ Device Input Channel with Four AMUX 64Ts DAQ AMUX 64T Channels Device Channel Device 1 Device 2 Device 3 Device 4 0 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 1 phen nae Senor 4 5 6 7 2 8 9 10 1 8 9 10 1 8 9 10 1 8 9 10 11 3 12 13 i 15 12 13 Pi 15 12 13 z 15 12 13 14 15 4 16 17 18 19 16 17 18 19 16 17 18 19 16 17 18 19 5 20 21 22 23 20 21 22 23 20 21 22 23 20 21 22 23 6 24 25 26 27 24 25 26 27 24 25 26 27 24 25 26 27 7 28 29 30 31 28 29 30 31 28 29 30 31 28 29 30 31 8 32 33 34 35 32 33 34 35 32 33 34 35 32 33 34 35 9 36 37 38 39 36 37 38 39 36 37 38 39 36 37 38 39 10 40 41 42 43 40 41 42 43 40 41 42 43 40 41 42 43 11 44 45 46 47 44 45 46 47 44 45 46 47 44 45 46 47 12 48 49 50 51 48 49 50 51 48 49 50 51 48 49 50 51 13 52 53 54 55 52 53 54 55 52 53 54 55 52 53 54 55 14 56 57 58 59 56 57 58 59 56 57 58 59 56 57 58 59 15 60 61 62 63 60 61 62 63 60 61 62 63 60 61 62 63 To determine which AMUX 64T channels LabVIEW scans a
20. Also called software triggering Device that transforms a signal from one form to another For example analog to digital converters ADCs for analog input digital to analog converters DACs for analog output digital input or output ports and counter timers are conversion devices A LabVIEW DAQ library containing VIs that count the rising and falling edges of TTL signals generate TTL pulses and measure the frequency and period of TTL signals A collection of counter timer channels You can use this type of group for simultaneous operation of multiple counter timers The manner in which a signal is connected from one location to another Digital to analog Digital to analog converter An electronic device often an integrated circuit that converts a digital number into a corresponding analog voltage or current The NI DAQ configuration utility on the Sun Process of acquiring data typically from A D or digital input plug in boards Programming system consisting of executable nodes in which nodes execute only when they have received all required input data and produce output automatically when they have executed LabVIEW is a dataflow system The default value of a front panel control G 4 National Instruments Corporation default setting device device number DIFF differential measurement system digital digital input group digital output group digital trigger DIP National Instrument
21. As you can see the ability to handshake gives you the ability to synchronize digital data transfer between your DAQ device and instrument The following list shows the DAQ devices that support digital handshaking e AT MIO 16D e AT MIO 16DE e DAQPad 1200 e DAQCard 1200 e DIO 24 DAQCard NB and PC e DIO 32F NB and AT e DIO 96 PCI NB and PC e SCXI 1200 e Lab Series devices NB LC and PC e PCI 1200 Another example of where you could use handshaking might be if you wanted to test the durability of a product prototype Each durability test would be performed with a different piece of machinery for the same amount of time For each test you could turn the machinery on and off with a specific variation of handshaked digital I O known as pattern National Instruments Corporation 15 1 LabVIEW Data Acquisition Basics Manual Chapter 15 Shaking Hands with a Digital Partner generation Internal counters would serve to generate the handshaking signal that initiates a digital transfer Counters output digital pulses at a steady frequency Thus you could generate and retrieve patterns at a constant rate because the handshaking signal would be produced at a constant rate However you could use this rate only if the instrument or external hardware does not work with or require communication signals for its data transfers Only the DIO 32F devices support pattern generation If you have an external signal controlling yo
22. Basic LabVIEW Data Acquisition Concepts Now that you know which kind of ADC to use and what settings to use for your signal you can connect your signals to be measured On most LabVIEW Data Acquisition Basics Manual 5 8 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input DAQ devices there are three different ways to configure your device to read the signals Differential Referenced Single Ended RSE and Non Referenced Single Ended NRSE Differential Measurement System In a differential measurement system you do not need to connect either input to a fixed reference such as earth or a building ground DAQ devices with instrumentation amplifiers can be configured as differential measurement systems Figure 5 7 depicts the 8 channel differential measurement system used in the MIO 16 series devices Analog multiplexers AMUX increase the number of measurement channels while still using a single instrumentation amplifier For this device the pin labeled AIGND the analog input ground is the measurement system ground Instrumentation Amplifier Figure 5 7 8 Channel Differential Measurement System National Instruments Corporation 5 9 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input In general a differential measurement system is preferable because it rejects not onl
23. DAQ device s onboard channels for these modules SCXI 1100 1 SCXI 1120 15 use referenced single ended mode SCXI 1121 4 SCXI 1122 1 For example you can run the Getting Started Analog Input VI found in examples daq run_me 11b with the channel string ob0 sc1 md1 mtemp to read the temperature sensor on the terminal block that is connected to the module in slot 1 of SCXI chassis 1 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications SCXI terminal blocks have two different kinds of sensors either an Integrated Circuit IC sensor or a thermistor For terminal blocks that have IC sensors such as the SCXI 1300 and the SCXI 1320 multiply by 100 to get the ambient temperature in degrees Centigrade at the terminal block For terminal blocks that have thermistors such as the SCXI 1303 SCXI 1322 SCXI 1327 and SCXI 1328 use the Thermistor Conversion VI from Functions Data Acquisition Signal Conditioning to convert the raw voltage data into units of temperature You cannot sample other SCXI channels from the same module while you are sampling the mtemp sensor However if you are in parallel mode you can sample the dt emp sensor along with other channels on the same module at the same time because you are not performing any multiplexing on the SCXI module You can also sample the cj temp sensor along with other channels on the SCXI 1102 but cj temp must be the first channel in the channel list For great
24. DAQ device You cannot communicate with other modules in stand alone mode but using this mode does make the digital ports normally reserved for SCXI operation available If the module in this slot is an SCXI 1200 you must also configure the following fields Connected To The parallel port address to which the SCXI 1200 is cabled You must select which parallel port you have cabled the module to LPT1 LPT2 and so on and WDAQCONF will detect the addresses of the parallel ports in your system IRQ Level The interrupt level used by the parallel port During a data acquisition or waveform generation on the SCXI 1200 NI DAQ services parallel port interrupts to transfer data between the SCXI 1200 and your PC memory This IRQ level must correspond to the IRQ level used by the parallel port to which the SCXI 1200 is connected On most PCs LPT1 uses IRQ Level 7 and LPT2 uses IRQ Level 5 If you are using an EPP parallel port card you can choose the 2 24 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware IRQ level by setting a jumper on the card then enter the IRQ Level in this field If the module in the slot is not an SCXI 1200 you must configure the following fields Terminal Block Select the terminal block you are using with this module if any If the module is an analog input module enter the gain settings and the filter settings if applicable for your module
25. DAQ palettes You can run these VIs from the front panel or use them as subVIs in basic applications These VIs are stand alone in that you only need one Easy VI to perform each basic DAQ operation Unlike intermediate and advanced level VIs Easy VIs automatically alert you to errors with a dialog box that asks you to stop the execution of the VI or to ignore the error The Easy VIs are actually composed of Intermediate VIs which are in turn composed of Advanced VIs The Easy VIs provide a basic convenient interface with only the most commonly used inputs and outputs For more complex applications you should use the intermediate or advanced level VIs for more functionality and better performance Refer to your particular type of VI in the LabVIEW Data Acquisition VI Reference Manual for specific VI information The Intermediate VIs have more hardware functionality and efficiency in developing your application than the Easy VIs Actually the National Instruments Corporation 3 5 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts Utility Vis Advanced Vis Intermediate VIs contain groups of Advanced VIs but they use fewer parameters and do not have some of the more advanced capabilities Intermediate VIs give you more control over error handling than the Easy VIs With each VI you can check for errors or pass the error cluster on to other VIs The Utility VIs found in many of the Lab
26. DIO Group Config VI 15 5 DIO Port Config VI digital input application example 19 16 immediate digital I O 14 2 DIO Single Read Write VI 15 5 to 15 6 DIO Start VI 15 7 to 15 8 DIO Wait VI 15 7 Divide Config VI 26 1 to 26 2 dividing frequencies See frequency division DMA jumper settings note 2 5 documentation conventions used in manual xviii xx flowchart for finding information 4 2 how to use this book 1 1 to 1 3 organization of manual xvii xviii related documentation xxi down counter 26 1 Down Counter VI 26 1 to 26 2 LabVIEW Data Acquisition Basics Manual Index E e mail support B 2 Easy VIs See also VIs addressing OUT and IN pins on DIO 32F board A 2 continuous pulse train generation 22 6 counting events or elapsed time 25 3 to 25 5 digital input application 19 15 digital output application 19 16 to 19 18 finite pulse train generation 22 7 grouping two or more ports A 2 immediate digital I O 14 1 to 14 2 limitations 6 3 measuring frequency and period high frequency signals 24 5 to 24 6 low frequency signals 24 4 multiple channel single point analog input 6 3 multiple immediate updates 11 2 to 11 3 multiple waveform acquisition 7 3 overview 3 5 single channel single point analog input 6 1 to 6 2 single immediate updates 11 1 to 11 2 single square pulse generation 22 4 single waveform acquisition 7 2 to 7 3 strain gauge application 19 13 waveform generation 12 1 to 12 2 edges of
27. Devices e All DAQPad Devices e National Instruments Plug and Play devices National Instruments Corporation 2 9 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware Refer to the Configuring Your DAQ Device for ISA and PCMCIA Bus Computers section of this chapter for instructions on non switchless devices For Plug and Play or switchless devices read the next section Configuring Plug and Play Switchless DAQ Devices in Windows National Instruments MIO E Series devices support switchless and jumperless configuration All resources on these devices including base address DMA channels and IRQ levels are fully software configurable No dip switches or jumpers are needed to configure any resources on these devices When you begin installation the NI DAQ installer installs a stand alone executable called NI PNP EXE in the root directory of your boot drive This program detects and configures any Plug and Play devices you have in your computer The program runs every time you boot from your AUTOEXEC BAT file After configuring the Plug and Play hardware in your system the program generates a NI PNP INI file in the same directory This file contains information about all the National Instruments devices in your system including Plug and Play devices The DAQ configuration utility WOAQCONF reads this NI PNP IN file for information and au
28. If you want to acquire or generate digital signals read the next question 3 Digital or Counter Interfacing Digital I O interfaces primarily control events such as turning external equipment on or off or sense logic states such as the on off position of the switch Counters generate individual digital pulses or waves and count digital events like how many times a digital signal rises or falls in value National Instruments Corporation 4 3 LabVIEW Data Acquisition Basics Manual Chapter 4 Where You Should Go Next If you are performing digital I O refer to question 7 If you need to use counters read question 8 4 Single Point or Multiple Point Acquisition Do you want to acquire a voltage value s at one time or over a period of time at a certain rate If you read a value at a given instant of time you are performing single point acquisition If you read values over a period of time at a certain rate then you are performing multiple point or waveform acquisition If you want single point acquisition refer to Chapter 6 One Stop Single Point Acquisition If you answered multiple point acquisition read question 6 5 Single Point or Multiple Point Generation Are you outputting a steady DC voltage or voltages are you generating a changing signal at a certain rate A constant or slowly changing voltage output is called single point generation The output of a changing signal at a certain rate is called multiple point or
29. In order to perform continuous acquisition you need to set up a buffer In this case the buffer is 10 times the number of points acquired for each channel After your device averages the voltage data from the AI Read VI it converts the National Instruments Corporation 19 13 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications voltage values to strain values After completing the acquisition remember to always clear the acquisition by using the AI Clear VI When measuring strain gauge data there are some parameters on the Convert Strain Gauge Reading VI you should know Rg 120 GF 2 05 v 00 0 Ysg 0 0 Bridge Configuration 3 Hal Wex 3 23 Vinit 0 0 R100 Vsg the strain gauge value is the only parameter wired in the previous VI diagram The other parameters for this VI have default values but those values may not be correct for your strain gauge You should check the following parameters Vinit the voltage across the strain gauge before strain is applied always measure at the beginning of the VI Bridge Configuration Vex the excitation voltage RI the lead resistance and Rg the resistance of the strain gauge before strain is applied Usually you can ignore the lead resistance RI for strain gauges unless the leads are several feet For more information on any of the parameters for this VI look in Chapter 14 Data Acquisition Utility VIs in the LabVIEW Data Acquisition VI Refer
30. Instruments Corporation Table of Contents Figure 16 1 Common Types of Transducers Signals and Signal Conditioning 16 3 Figure 16 2 Amplifying Signals Near the Source to Increase Signal to Noise Rafo prenin ei a EEA sts steed tasdtes E 16 4 Figure 17 i SCXLSYSten nennen uena E E EE ERNEA 17 1 Figure 17 2 Components of an SCXI System ssessseesseessersrrerssreresrsresrssreresrrersese 17 2 Figure 17 3 SOX Chassis reier iee o Eae AEE E EOE E EEE E ATE 17 3 Figure 19 1 Measuring a Single Module with the Acquire and Average VI 19 6 Figure 19 2 Measuring Temperature Sensors Using the Acquire and Average V Edanaren Seeds a e a a a eA 19 7 Figure 19 3 Continuously Acquiring Data Using Intermediate VIs 0 0 0 0 19 8 Figure 19 4 Half Bridge Strain Gauge seeeseeeeseseseeseeersrrsrrersrrsresrsresresrsresrerrseese 19 12 Figure 21 1 CTR Control VI Front Panel and Block Diagram eseeeeesseeeeeee 21 5 Figure 22 1 Pulse Created with Positive Polarity and Toggled Output 0 22 2 Figure 22 2 Pulse Duty Cycles eni mrn in a E E E 22 3 Figure 22 3 Physical Connections for Generating a Square Pulse 22 4 Figure 22 4 Using the Generate Delayed Pulse VI oo eee eee eeeeeneteeeeneeeeees 22 4 Figure 22 5 Generating a Single Delayed Pulse Using Intermediate Vis 22 5 Figure 22 6 Physical Connections for Generating a Square Pulse 22 6 Figure 22 7 Generating a Continuous Puls
31. Instruments Corporation XV LabVIEW Data Acquisition Basics Manual Table of Contents Figure 24 5 Figure 24 6 Figure 24 7 Figure 24 8 Figure 25 1 Figure 25 2 Figure 25 3 Figure 25 4 Figure 25 5 Figure 26 1 Figure 26 2 Figure 27 1 Figure 27 2 Tables Table 2 1 Table 2 2 Table 5 1 Table 5 2 Table 5 3 Table 5 4 Table 9 1 Table 16 1 Table 18 1 Table 25 1 Measuring Low Frequency Signals with Measure Pulse Width or Period VE o Ate ht ek ee Ae lie a tant ised 24 4 Measuring Low Frequency Signals Using Intermediate VIs 24 5 Measure Frequency Viesienas nanea a n aoa ai 24 6 Measuring High Frequency Signals Using Intermediate VIs 24 6 Connecting Counters to Your Device to Count Events or Time 25 1 Using the Count Events or Time VI to Count External Events 25 3 Using the Count Events or Time VI to Measure Elapsed Time 25 4 Using the Intermediate VIs to Count External Events 0 0 0 25 5 Using the Intermediate VIs to Measure Elapsed Time 25 6 Wiring Your Counters for Frequency Division 0 0 0 eee 26 1 Programming a Single Divider for Frequency Division 26 2 Error Checking Using the General Error Handler VI eee 27 3 Error Checking Using the Simple Error Handler VI e 27 3 LabVIEW DAQ Hardware Support for Windows sses 2 4 LabVIEW DAQ Hardware Support for Macintosh eee 2 5 Measureme
32. LabVIEW Data Acquisition Basics Manual Chapter6 One Stop Single Point Acquisition Figure 6 2 shows how you program the AI Sample Channel VI in LabVIEW to acquire data Al Sample Channel Figure 6 2 Acquiring Data Using the Al Sample Channel VI This example continuously calls the AI Sample Channel VI in a While Loop until you press the Power control button on the front panel Each time around the loop the AI Sample Channel VI initiates an A D conversion on the DAQ device and returns the scaled voltage as an output The high limit is the highest expected voltage level of the signals you want to measure The low limit is the lowest expected voltage level of the signals you want to measure Single channel acquisition makes acquiring one channel very basic but what if you need to take more than one channel sample For instance you might need to monitor the temperature of the fluid as well as the fluid level of the tank In this case two transducers must be monitored You can monitor both transducers using a multiple channel single point acquisition in LabVIEW Multiple Channel Single Point Analog Input With a multiple channel single point read or scan LabVIEW returns the voltage on several channels at once Use this type of operation when you have multiple transducers to monitor and you want to LabVIEW Data Acquisition Basics Manual 6 2 National Instruments Corporation Chapter 6 One Stop Single Point Acquisition ret
33. Like the other Easy VIs you cannot use any advanced programming features with the AI Acquire Waveforms VI The built in error checking of this VI alerts you to any errors that occur in the program National Instruments Corporation 7 3 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition A second method for acquiring multiple waveforms uses the Intermediate Analog Input VI AI Waveform Scan as shown in Figure 7 4 An example using this VI is the Acquire N Scans VI found in labview examples daq analogin anlogin 11b This VI acquires multiple waveforms just like the AI Acquire Waveforms VI but you can set different input limits for different channels This VI can also specify inputs for triggering coupling and additional hardware Coupling affects the value of the DC offset in your analog signal AC coupling subtracts the average value of this signal from the signal before measurement while DC coupling leaves DC offset voltages in your signal measurements If you want to know if your DAQ device supports coupling check in the tables in Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual trigger and clock no trig int clk coupling amp input config no change 0 input limits no change number of scans to acquire 1000 scan rate C1000 scans sec Figure 7 4 Using the Al Waveform Scan VI to Acquire Multiple Waveforms You can als
34. MIO 16F 5 Em any Base address hex 220 ae DMA channels le 7 F Empty IRQ levels 11 Empty Em Ep x Confiqure Test Device 1 l Device Number 1 bi Configuration Device DMA IRQ Test Hardware Help Device Base address DMA IRQ AT MIO 16F 5 hex 220 6 11 On Off Figure 2 6 Device Configuration Window inWDAQCONF on an ISA Bus Computer LabVIEW Data Acquisition Basics Manual 2 12 National Instruments Corporation ce Note Chapter 2 Installing and Configuring Your Data Acquisition Hardware Clicking on the Hardware menu opens a Hardware Configuration window as shown in the Figure 2 7 DeviceNumbert Configuration Device DMA IRQ Test Hardware Help Device Base address DMA IRQ AT MIO 16F 5 hex 220 bff 11 On Off Device 1 AT MIO 16F 5 Configuration Modify Help ANALOG INPUT CONFIGURATION Polarity Range Selected Yalues 5 tothy Polarity BIPOLAR Range 10 Mode Differential Accessory None Figure 2 7 Hardware Configuration Window inWDAQCONF In this window you can establish default settings for parameters such as analog input polarity and range on a per device basis You can also specify if you have an SC 2040 SC 2042 RTD or SC 2043 SG device or up to four AMUX 64
35. Manual Table of Contents Appendix A LabVIEW Data Acquisition Common Questions Appendix B Customer Communication Figures Figure 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 2 6 Figure 2 7 Figure 2 8 Figure 2 9 Figure 2 10 Figure 2 11 Figure 2 12 Figure 2 13 Figure 2 14 Figure 3 1 Figure 3 2 Figure 3 3 Figure 3 4 Figure 3 5 Figure 3 6 Figure 3 7 Figure 3 8 Figure 3 9 Figure 3 10 Figure 3 11 Figure 3 12 Figure 5 1 Figure 5 2 Figure 5 3 Installing and Configuring DAQ Devices eee ee eeceeeeeeeeeeeeeees 2 2 How NI DAQ Relates to Your System and DAQ Devices 2 3 Locating WDAQConf in Windows eeeeeeeeceseeeseeceeeeteeceaeeeseeeeaeeees 2 6 NI DAQ Configuration Utility Window ssesssesseesseeeeeeseerrsrseesresreees 2 7 Device Number N Window sssssssseessssesesreresreresresrsresresrsresrrsrsresresrsres 2 8 Device Configuration Window in WDAQCONF on an ISA Bus COMPUTE see RAR Bees We So MIRE ANR R 2 12 Hardware Configuration Window in WDAQCONE eee 2 13 NI DAQ Device Window Listing eee eeeeseeseeneeeeeeeeneeeeeeaes 2 16 Accessing the Device Configuration Window in NI DAQ 2 17 Device Configuration and I O Connector Windows in NI DAQ 2 18 SCXI Configuration Window in WDAQCONE 0 ee eeeeeeseeeeeseereeees 2 22 SCXI Module Configuration Window in WDAQCONF cesses 2 23 Accessing the NI DA
36. Setup for Your SCX System lines on the DAQ device are reserved for SCXI chassis communication To find out which lines are reserved on your device refer to the tables in Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual Figure 17 3 SCXI Chassis When you use SCXI as an external DAQ system only some of the digital I O lines of the DAQ device are reserved for SCXI chassis communication when other modules are present The DAQ device digitizes any analog input data and transfers it back to the computer through the parallel port SCXI Operating Modes The SCXI operating mode determines the way that DAQ devices access signals There are two basic operating modes for SCXI modules multiplexed and parallel You designate the mode in the operating mode parameter in the configuration utility Also you may have to set up jumpers on the module for the correct operating mode Check your SCXI module user manual for more information Note National Instruments recommends that you use the multiplexed mode for most purposes National Instruments Corporation 17 3 LabVIEW Data Acquisition Basics Manual Chapter 17 Hardware and Software Setup for Your SCX System Multiplexed Mode for Analog Input Modules cP Note Note When an analog input module operates in multiplexed mode all of its input channels are multiplexed to one module output When you cable a DAQ device to a multiplexed analog input
37. Signals in Great Condition Digital Digital or Counter Counter Interfacing Read Chapter 21 Things You Should Know about Counters Latched or Non Latched 7 Non Latched Digital Read Chapter 22 Generating a 1 0 Square Pulse or Pulse Train Read Chapter 15 Shaking Hands Read Chapter 14 When You Need Read Chapter 23 Measuring with a Digital Partner It Now Immediate Digital I O Pulse Width Read Chapter 24 Measuring i Frequency and Period Generation Read Chapter 25 Counting Signal Highs and Lows Read Chapter 26 Dividing Frequencies Acqauisiti Signal Acquisition or Generation Single Point Multiple or Multiple Point Generation Read Chapter 11 One Stop Read Chapter 12 Buffering Your Single Point Generation Way through Waveform Generation Single Point Multipl or Multiple Point uipa Acquisition Read Chapter 6 One Stop Single Point Acquisition Yes Triggering a Signal External Internal Using an Internal or External Clock Read Chapter 8 Controlling Read Chapter 7 Buffering Your Read Chapter 9 Letting an Outside Your Acquisition with Triggers Way Through Waveform Acquisition Source Control Your Acquisition Rate LabVIEW Data Acquisition Basics Manual 4 2 National Instruments Corporation Chapter 4 Where You Should Go Next Questions You Should Answer 1 Measuring Device DAQ Device or SCXI Module Are you wor
38. VI After determining the average amplifier offset and cold junction compensation you can acquire data using the Intermediate VIs as shown in Figure 19 3 This example continually acquires data until an error occurs or the user stops the execution of the VI In order to perform continuous hardware timed acquisition you need to set up a buffer In this case the buffer is 10 times the number of points acquired for each channel Before you initiate the acquisition with the AI Start VI you need to set up the binary to voltage scaling constants by using the Scaling Constant Tuner VI This VI which you can find in Functions Data Acquisition Signal Conditioning passes the amplifier offset to the DAQ driver so that LabVIEW accounts for the amplifier offset as the AI Read VI retrieves the data After the compensated voltage data from the AI Read VI is averaged the voltage values are converted to temperature and linearized by using the Convert Thermocouple Reading VI in Functions Data National Instruments Corporation 19 7 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications number of samples to average for each data point 100 Acquisition Signal Conditioning After completing the acquisition remember to always clear the acquisition by using the AI Clear VI previous errors seu binary amplifier offset gt scan rate gt e T lt number of chans lt lt eror cluster lt lt taskID gt
39. VI 6 7 multiple immediate updates 11 2 to 11 3 single immediate updates 11 1 to 11 2 AO Write VI circular buffered output 12 4 to 12 5 waveform generation 12 3 arrays transposing 7 7 two dimensional 2D arrays 3 13 to 3 16 AUTOEXEC BAT file 2 10 base address switch settings note 2 5 breakpoints setting 27 4 buffered analog input 7 1 to 7 15 buffer overflow problems with Macintosh systems A 5 circular buffered analog input continuous acquisition from multiple channels 7 11 to 7 13 determining adequate buffer capacity A 1 examples basic circular buffered analog input 7 13 to 7 14 LabVIEW Data Acquisition Basics Manual Cont Acq to File scaled vi 7 15 Cont Acq to Spreadsheet File vi 7 15 Cont Acq amp Chart buffered vi 7 14 Cont Acq amp Graph buffered vi 7 15 overview 7 10 to 7 11 how buffers work 7 2 simple buffered analog input data buffer overview 7 1 to 7 2 examples displaying waveforms on graphs 7 6 to 7 7 sampling with multiple starts 7 7 to 7 9 writing to spreadsheet file 77 9 multiple waveform acquisition 7 3 to 7 5 single waveform acquisition 7 2 to 7 3 waiting to analyze data 7 1 to 7 2 buffered analog output choosing between single point or multiple point generation 4 4 circular buffered output 12 3 to 12 5 eliminating errors 12 5 overview 10 1 to 10 2 waveform generation 12 1 to 12 3 buffered handshaking 15 6 to 15 10 circular buffered examples 15 9 to 15 10
40. You can find NI DAQ in your control panels folder The NI DAQ icon looks like the one shown to the left Double click on this icon to launch NI DAQ When you launch the program NI DAQ displays a list of all of the devices in your computer Each device has a small list of attributes as shown in Figure 2 8 The number specified in the device line is the logical device number that NI DAQ assigned to the device You will use this number in LabVIEW a for any operation s the device number to select the device Active Devices dew j ce 4 name HB AZ000 type 112 bus HuBus socket C address Ox fecooooo DHA socket E ATSI bus 1 dew joe 22 name PCI 1200 type 353 bus PCI socket F2 address Ox9000 1000 Figure 2 8 NI DAQ Device Window Listing LabVIEW Data Acquisition Basics Manual 2 16 National Instruments Corporation National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware Now show the Device Configuration window by selecting the Device Configuration option from the menu as shown in Figure 2 9 N Gap dew joe name type bus socket address DHA socket ATSI bus dew j ce name type bus socket address 4 3 0 Devices Device Configuration SCHI Configuration Errors i 112 HuBus C Ox fecoon E 1 22 PCl 1200 353 PC F2 Ox 9000 1000 Figure 2 9 Accessing the D
41. Your Way to High Precision Timing Chapter 21 Things You Should Know about Counters Knowing the Parts of Your Counter cece eesecesecseeeseesseeseceeeesecnseeseeesecseensesaeenaes 21 2 Knowing Your Counter Chip moroene ii T r pi che stets conyet tents seve AE A 21 4 Counting Operations When All Your Counters Are Used ooo eee eeeeseeeeeneeeeeees 21 5 Chapter 22 Generating A Square Pulse or Pulse Trains Generating Square Pulse s ccccscssecesccsashascssdeedencassaecedseesesdsssabiedascave siden saenitasesvapededashses 22 1 Generating a Single Square Pulse ie ceeeeeeseceecesecseeeeesseesecseeeaecnseeseessesaeseseeeenaes 22 3 Generating a Pulse Traini cunning a E E a ERRE 22 5 Generating a Continuous Pulse Train esesseeesseesseeeseeeresresesresreeesresrssrsresresese 22 5 Generating a Finite Pulse Train ssesseseseeseeesseersersrrsrsresresesresrerrsresrssreresrerese 22 7 LabVIEW Data Acquisition Basics Manual X National Instruments Corporation Table of Contents Knowing the Accuracy of Your Counters ceeeecceeeecssceeeeseeeseseeeeseseeeaeeseeeaeeseens 22 9 Stopping Counter Generations o oo eeceescceseeseeeseceecesecseceseseeeeaeseeesseesaeeseeeaeeseens 22 9 Chapter 23 Measuring Pulse Width Measuringa Pulse Width sororius akaa deasiisanies e a R 23 1 Determining Pulse Width wie 3 23 scuigtievd sensei ore E E a E a ia 23 2 Controlling Your Pulse Width Measurement s esseseseseeesseesssesseerse
42. acquisition boards A 3 Input Buffer Full IBF line 15 2 input range and input setting selection 5 6 to 5 8 installation and configuration debugging software configuration errors 27 1 to 27 2 installing and configuring DAQ devices figure 2 2 LabVIEW data acquisition hardware support Macintosh systems table 2 5 Windows environment table 2 4 Macintosh systems 2 16 to 2 18 National Instruments devices 2 5 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 SCXI chassis hardware configuration 2 20 to 2 21 software configuration Macintosh systems 2 25 to 2 27 Windows environment 2 21 to 2 25 UNIX operating systems 2 18 to 2 20 Windows environment changing I O page lock limit 2 14 to 2 15 EISA bus computers 2 9 LabVIEW Data Acquisition Basics Manual inserting PCMCIA cards note 2 5 ISA and PCMCIA bus computers 2 6 to 2 9 LabVIEW for Windows NT 2 14 to 2 15 multiple DAQ devices note 2 5 Plug and Play switchless DAQ devices 2 10 Plug and Play software 2 10 to 2 11 user privilege level 2 15 WDAQCONE utility 2 11 to 2 14 Intermediate VIs See also VIs advantages 6 4 to 6 5 circular buffered output 12 3 to 12 5 continuous acquisition from multiple channels 7 11 to 7 13 continuous pulse train generation 22 6 to 22 7 controlling pulse width measurement 23 3 counting events or elapsed time 25 6 to 25 7 dividing frequencies 26 1 to 26 2 finite pulse train generation 22 7 to
43. ast ek Sane ia lee ev 16 5 ATANSAUCEr EXCILALLON S ino e o de culgub euteones sueus te tad eases cesevss teed Weavducweath eee 16 5 Linearization ees teeriieee n een lest aes Heathen ed Sans 16 5 Chapter 17 Hardware and Software Setup for Your SCXI System SCX Operating MOdeS s csscecssvessntenteasstevagvaasteettenassaessaeecdansedeuita R pussteveeeaes 17 3 Multiplexed Mode for Analog Input Modules 0000 0 eee eeeceeeseceseeeeeeeneeeenees 17 4 Windows Multiplexed Mode for the SCXI 1200 0 eee 17 4 Multiplexed Mode for Analog Output Modules 0 ee 17 4 Multiplexed Mode for Digital and Relay Modules 2 000 eee eeseeeeeeeeeeees 17 5 Parallel Mode for Analog Input Modules 00 0 ect eee eee seeeeeeeeeeeeeeeeeseeeeees 17 5 Windows Parallel Mode for the SCXI 1200 17 6 Macintosh and Windows Parallel Mode for Digital Modules 17 6 SCXI Software Installation and Configuration 00 0 cies eecessceeeseeeseeeeeeseeseeeseeeens 17 6 Chapter 18 Special Programming Considerations for SCXI SCXT Channel Addressing aciei oerrint n e n E eatheaede E Ee iR 18 1 SEIKEL AE Aguhaiinskiatel tides hand cui widaun Al liitindy 18 2 SCX Settling TIME s 3s sic estes pr e EE EE E E ERE 18 5 National Instruments Corporation ix LabVIEW Data Acquisition Basics Manual Table of Contents Chapter 19 Common SCXI Applications Analog Input Applications for Measuring Temperature 000 0 eee eee eeeeeeeneeeeeeee 19 2 Measuring Temperature
44. but you first must figure out a few more signal characteristics before you can begin For example to what is your signal referenced How fast does the signal vary with time The rate at which you sample determines how often the A D conversions take place A fast sampling rate acquires more points in a given time and therefore can often form a better representation of the original signal than a slow sampling rate According to the Nyquist Theorem you must sample at greater than twice the rate of the maximum frequency component in that signal The frequency at one half the sampling frequency is referred to as the Nyquist frequency You must have answers like this to all of your questions so that you can use the proper tools to acquire the signal To What Is Your Signal Referenced Signals come in two forms referenced and non referenced signal sources More often referenced sources are said to be grounded signals and non referenced sources are called floating signals Grounded Signal Sources Grounded signal sources have voltage signals that are referenced to a system ground such as earth or a building ground Devices that plug into a building ground through wall outlets such as signal generators and power supplies are the most common examples of grounded signal sources as shown in Figure 5 2 Vs Ground Figure 5 2 Grounded Signal Sources LabVIEW Data Acquisition Basics Manual 5 2 National Instruments Corporation Cha
45. can be any number less than the buffer size If you do not retrieve data from the circular buffer fast enough your unread data will be overwritten by newer data You can resolve this problem in one of three ways by adjusting the buffer size scan rate or the number of scans to read parameters If your program overwrites data in the buffer then data is coming into the buffer faster than your VI can read all of the previous buffer data and LabVIEW returns an error code number 10846 You can increase the size of the buffer so that it takes longer to fill up which leaves your VI with more time to read data from it If you slow down the scan rate you reduce the speed at which the buffer fills up which also leaves more time for your program to retrieve data You can also increase the number of scans to read which will retrieve more data out of the buffer each time and effectively reduce the number of times to access the buffer before it becomes full Check the output scan backlog to see how many data values remain in the circular buffer after the read Read amp process data until all data acquired an error occurs or the stop button pressed Figure 7 12 Continuously Acquiring Data with the Al Continuous Scan VI Because this is an Intermediate VI you can also control parameters such as triggering coupling and additional hardware National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition You
46. controls the initiation of the pulse train An example of this if you want to generate a continuous pulse train as a result of meeting certain conditions If you used the Easy VI the VI would configure and then immediately start the pulse train generation With the Intermediate VIs you can configure the counter long before the conditions are met Then as soon as the conditions are met you can begin pulse train generation In this situation using Intermediate VIs would improve performance If the duty cycle is 0 0 or 1 0 the closest achievable duty cycle is used to generate a train of positive or negative pulses You must stop the counter if you want to use it for other purposes For more information on stopping counters refer to the Stopping Counter Generations section at the end of this chapter Generating a Finite Pulse Train You can set the Easy I O VI Generate Pulse Train or a stream of Intermediate VIs to generate a finite pulse train With either technique you must use two counters as shown in the connection diagram in Figure 22 9 Refer to Chapter 25 Counting Signal Highs and Lows for more information on how to determine counter 1 and how to use the adjacent counter VI The maximum number of pulses in the pulse train is 216 1 for Am9513 devices and 274 1 for DAQ STC devices Figure 22 9 shows how you can produce a finite pulse train on the OUT pin of a counter counter generates the finite pulse train with high level
47. drection inpay drecton inpwlh handzhaking mode parameters Figure 15 7 Reading Data with the Digital Vis Using Digital Handshaking DIO 32F Devices For the other devices that support digital handshaking the example would be the same as above except the handshaking mode input would be deleted from the DIO Config VI and the DIO Start VI would be replaced with the DIO Buffer Control VI Also you do not need the handshake source and clock frequency inputs for most devices LabVIEW Data Acquisition Basics Manual 15 8 National Instruments Corporation Chapter 15 Shaking Hands with a Digital Partner because of the external handshaking signal source Figure 15 8 shows the VI used for all DAQ devices other than the DIO 32F direction inpu Port data read Figure 15 8 Reading Data with the Digital VIs Using Digital Handshaking Circular Buffered Examples Circular buffered handshaking is similar to simple buffered handshaking in that both types of handshaking place data in a buffer however a circular buffer application returns to the beginning of the buffer when it reaches the end and fills the same buffer again Note Remember that circular buffered handshaking works only on the AT DIO 32F Figure 15 9 shows an example of a circular buffered application In this example you are continually reading or writing digital values until you stop the VI or an error occurs In order to create a circular buffer you must create
48. falling edge For more information look at the Down Counter or Divide Config VI description in Chapter 18 Intermediate Counter VIs of the LabVIEW Data Acquisition VI Reference Manual National Instruments Corporation 26 3 LabVIEW Data Acquisition Basics Manual Debugging Your Data Acquisition Application This section contains an explanation of ways you can debug your data acquisition application to make sure your application is accurate and runs smoothly Part 7 Debugging Your Data Acquisition Application contains the following chapters e Chapter 27 Debugging Techniques shows you some tips to help figure out why your VI is not working Debugging Techniques Is your VI not working as you expected it would Well this chapter shows you some tips to help figure out why your VI is not working First find your LabVIEW User Manual and LabVIEW Tutorial Manual because these manuals are references in this section With LabVIEW data acquisition DAQ applications you may find errors in hardware connections software configuration or VI construction The goal of this chapter is to help you narrow down where the problem is in your program flow Hardware Connection Errors When no error occurs but the data is not what you expected then you may want to check your hardware connections and jumper settings For instance if you have an analog input application make sure your signals are properly grounded For
49. for obtaining measurements 24 2 high frequency signals 24 5 to 24 7 how and when to measure 24 1 to 24 2 low frequency signals 24 4 to 24 5 National Instruments Corporation physical connections for period measurement high frequency signals figure 24 3 low frequency signals figure 24 3 square wave period measurement figure 24 2 frequency division 26 1 to 26 3 FTP support B 1 Function Generator VI 12 5 Functions palette illustration 3 3 locating VIs 3 2 to 3 4 G gain definition 3 13 gains SCXI description 18 2 to 18 4 SCXI 1100 channel arrays input limits array and gains table 18 4 GATE input 21 2 to 21 3 gating levels figure 21 3 GATE input pin 21 2 General Error Handler VI 27 2 to 27 3 Generate Continuous Sinewave VI 12 3 Generate Delayed Pulse VI single square pulse generation 22 4 stopping counter generations 22 9 Generate N Updates example VI 12 2 Generate Pulse Train VI continuous pulse train generation 22 6 finite pulse train generation 22 7 to 22 8 stopping counter generations 22 9 to 22 10 Get DAQ Device Information VI 2 1 Getting Started Analog Input example VI channel clock control 9 3 to 9 4 reading amplifier offset 19 4 to 19 5 reading channels from different SCXI chassis 19 19 scan clock control 9 6 to 9 7 temperature sensor 19 3 Getting Started Counters VI 25 3 Getting Started Digital I O VI 14 1 to 14 2 National Instruments Corporation Index gr
50. generate TTL pulses TTL pulses can be used as clock signals gates and triggers You can also use a generated pulse with a known timebase to determine an unknown TTL signal frequency or use a square pulse to trigger an analog acquisition There are two basic types of counter signal generation toggled and pulsed When a counter reaches a certain value a counter configured for a toggled output changes the state of the output signal from high to low or from low to high while a counter configured for a pulsed output outputs a pulse The width of the pulse is equal to one cycle of the counter s SOURCE signal When generating a pulse or pulse train you must define the polarity of the signal as positive or negative In the following illustration you can see that for a signal with a positive polarity the initial state is low while for a signal with a negative polarity the initial state is high Positive Polarity Negative Polarity Each counter generated pulse consists of two parts phase 1 and phase 2 If the counter is configured to output a signal with positive polarity and toggled output as shown in the following diagram the period of time from when the counter starts counting to the first rising edge is called phase 1 The time between the rising and the following National Instruments Corporation 22 1 LabVIEW Data Acquisition Basics Manual Chapter 22 Generating A Square Pulse or Pulse Trains falling edge is called phase 2 I
51. going through a system In this illustration 1000 scans of channels 0 and 1 are taken at the rate of 5000 scans per second The Actual Scan Period output displays in the actual timebase on the x axis of the graphs Remember that each column of the 2D array contains the information for each channel device 19 Column Figure 7 6 Simple Buffered Analog Input Example If you want to display the data on the same graph look at the Acquire N Scans example VI found in labview examples daq anlogin LabVIEW Data Acquisition Basics Manual 7 6 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition anlogin 11b Figure 7 7 shows a simple buffered input application that uses graphing input limits ne change channels EOJ pon number of scans to acquire 1000 scan rate 1000 scans sec Figure 7 7 Simple Buffered Analog Input with Graphing For a 2D array to be displayed on a waveform graph each row of data must represent a single plot This is because waveform graphs are in row major order Because the channel data is in each column you must transpose the 2D array Transposing the array can easily be done by popping up on the front panel of the graph and choosing Transpose Array Simple Buffered Analog Input with Multiple Starts In some cases you may not want to acquire contiguous data like in an oscilloscope application In this case you would only want to take a specified number of
52. illustrates these Help window parameter conventions for the AI One Scan VI As the window text for this VI indicates you should wire the device channels error in and iteration input parameters and the voltage data and error out output parameters In LabVIEW Data Acquisition Basics Manual 3 6 National Instruments Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts order to pass error information from one VI to another connect the error out cluster of the current VI to the error in cluster of the next VI The coupling amp input config input limits and output units input parameters and the binary data output parameter are optional parameters You rarely need to use the number of AMUX boards parameter coupling amp input config no change 0 e input limits no change m device voltage data channels 0 2 a binary data output units volts 1 Aa error in no error iteration Cinit 0 number of AMUX boards 0 sooxoerror out Figure 3 4 LabVIEW Help Window Conventions for the Al Single VI Default and Current Value Conventions To use the DAQ VIs you should know the difference between a default input a default setting and a current setting A default input is the default value of a front panel control When you do not wire an input to a terminal of a VI the default input for the control associated with that terminal passes to the driver In the Help window default inputs appear in p
53. in an update is equal to the number of channels in the output group For example one pulse from the update clock produces one update which sends one new sample to every analog output channel in the group The number of output updates per second The number of channels in the channel list or number of ports in the port list you use to configure an analog or digital output group volts Volts direct current Virtual instrument A LabVIEW program so called because it models the appearance and function of a physical instrument Voltage reference G 16 National Instruments Corporation W waveform WDAQCONF EXE wire write mark National Instruments Corporation Glossary Multiple voltage readings taken at a specific sampling rate The NI DAQ configuration utility in Windows Data path between nodes Points to the update at which a write operation begins Analogous to a file I O pointer the write mark moves every time you write data into an output buffer After the write is finished the write mark points to the next update to be written Because multiple buffers are possible you need both the buffer number and the update number to express the position of the write mark G 17 LabVIEW Data Acquisition Basics Manual A ACK Acknowledge line 15 2 ACK Acknowledge Input line 15 2 Acquire amp Proc N Scans Trig example VI 8 6 8 10 Acquire amp Process N Scans VI 7 11 Acquire and Ave
54. input polarity and input gain s Similarly if you wire the input limits range and polarity the VIs can infer the onboard gains when you do not use SCXI The difference between the maximum and minimum voltages an analog input channel can measure at a gain of 1 The input range is a scalar value not a pair of numbers By itself the input range does not uniquely determine the upper and lower voltage limits An input range of 10 V could mean an upper limit of 10 V and a lower of 0 V or an upper limit of 5 V and a lower limit of 5 V The combination of input range polarity and gain determines the input limits of an analog input channel For some boards jumpers set the input range and polarity while you can program them for other boards Most boards have programmable gains When you use SCXI modules you also need their gains to determine the input limits A signal indicating that the central processing unit should suspend its current task to service a designated activity Scanning method where there is a longer interval between scans than there is between individual channels comprising a scan Input output The transfer of data to or from a computer system involving communications channels operator interface devices and or data acquisition and control interfaces G 8 National Instruments Corporation ISA isolation Kwords L LabVIEW latched digital I O limit settings linearization LSB MB memory buff
55. level administrator level However you may not want to always run your LabVIEW DAQ application in the highest privilege level To change the default behavior you need to change the NI DAQ driver load option in the Control Panel palette as follows 1 Choose Control Panel Devices 2 Use the scroll bar and scroll down the driver list until you see NIDAQNT Highlight NIDAQNT by clicking on it once Click on the Startup button on the right Change the startup type to Automatic and press OK D Pin RS Close the Devices window and the Control Panel palette The next time you reboot and restart Windows NT the program automatically loads the NI DAQ driver when it boots You can then log in as any type of user and run LabVIEW DAQ applications ce Note WDAQCONF needs to be able to load and unload the NI DAQ device driver on the fly in order to configure DAQ devices After you change the driver load option to automatic you will not be able to configure any DAQ devices through WDAQCONF You can run WDAQCONF only in read only mode If you need to configure a DAQ device you must change the NIDAOQNT driver Startup button back to Manual and reboot Windows NT National Instruments Corporation 2 15 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware Configuring Your DAQ Device Using NI DAQ on the Macintosh Turn your computer back on
56. loaded from the module EEPROM The SCXI 1141 has only gain adjust constants in the EEPROM it does not have the binary zero offset All other analog input modules excluding the SCXI 1102 SCXI 1122 and SCXI 1141 do not have calibration constants by default and do not assume any binary offset and ideal gain settings This means you must use one of the procedures described in the SCXI Calibration Methods for Signal Acquisition section below to store calibration constants for your module if it is not an SCXI 1102 SCXI 1122 or SCXI 1141 You can determine calibration constants based specifically on your application setup which includes your type of DAQ device your DAQ device settings and your cable assembly all combined with your SCXI module and its configuration settings ce Note If your SCXI module has independent gains on each channel the calibration constants for each channel are stored at each gain setting National Instruments Corporation 20 3 LabVIEW Data Acquisition Basics Manual Chapter 20 SCX Calibration Increasing Signal Measurement Precision SCXI Calibration Methods for Signal Acquisition There are two ways you can calibrate your SCXI module through one point calibration or two point calibration The following illustration explains why you may need to calibrate your SCXI module Binary Reading Ideal Reading aw Actual Reading Gain Error Actual Voltage in Binary Representation Binary Reading
57. more information on analog input configuration issues refer to Chapter 5 Things You Should Know about Analog Input For SCXI modules you must verify that gain jumpers are set up properly To verify how a DAQ device gets set to a certain gain or limit setting as noted in the software refer to Chapter 3 Basic Data Acquisition Concepts Another common SCXI hardware error is using digital lines on your DAQ device that are reserved for communication with the SCXI modules In order to test that your hardware has not been damaged connect a known voltage to the channels you are using To check the location of any hardware connections refer to your hardware user manual Software Configuration Errors As you check hardware connections it is a good idea to verify that the NI DAQ software configuration reflects your hardware setup For possible difficulties with software configuration read the Installation National Instruments Corporation 27 1 LabVIEW Data Acquisition Basics Manual Chapter 27 Debugging Techniques and Configuration section of this manual the chapter of this manual that discusses your specific application or the NJ DAQ User Manual Windows In the NI DAQ configuration you can use the utilities under the test menu to take single point measurements for analog I O and digital I O applications These utilities are helpful in testing for damaged hardware VI Construction Errors Error Handling The various
58. on your machine try setting the board to use programmed I O interrupts only with the Set Device Information vi in DAQ gt Calibration and Config Analternative is to switch to an EISA bus machine The DMA controller can address up to 4 GB of RAM on FISA machines Windows 3 1 am having problems running Windows for Workgroups with my data acquisition program Remark out nivisrd 386 inthe 386 Enhanced section of your system ini file To mark out the line place a number sign at the beginning of the line which reads device c windows system nivisrd 386 nivisrd 386 normally improves performance by reducing interrupt latencies in Windows enhanced mode Windows 3 1 bought LabVIEW for Windows and also have a slightly older DAQ device from National Instruments installed the entire LabVIEW package but should I go ahead and install my NI DAQ for Windows drivers that originally got with the board In most cases the answer is no The LabVIEW installer installs a set of DAQ driver files that are guaranteed to work with LabVIEW whereas if you happen to install an older version of the drivers you may run into many problems You may even end up crashing your computer every time you do any data acquisition If you buy a new DAQ device and if you already have LabVIEW installed it is safe to LabVIEW Data Acquisition Basics Manual A 4 National Instruments Corporation Appendix A LabVIEW Data Acquisition Common Ques
59. reading Al Read s backlog rather than a fixed amount of data Reading the backlog is guaranteed not to cause a synchronous wait for the data to arrive However it adds more delay until the data is processed because the data was really available on the last call and it can require constant reallocation or size adjustments of the data acquisition read buffer in LabVIEW How can tell when a continuous data acquisition operation does not have enough buffer capacity The scan backlog rises with time either steadily or in jumps or takes a long time to drop to normal after an interrupting activity like mouse movement If you can open another VI during the operation without receiving an overrun error you should have adequate buffer capacity National Instruments Corporation A 1 LabVIEW Data Acquisition Basics Manual Appendix A LabVIEW Data Acquisition Common Questions want to group two or more ports using my DIO32F DI024 or DIO 96 board but do not want to use handshaking just want to read one group of ports just once How can set it up in software Use Easy I O VIs Write to Digital Port or Read from Digital Port or Advanced Digital VIs DIO Port Config DIO Port Write or DIO Port Read and set multiple ports in the port list For Easy I O VIs you can specify up to four ports in the port list Whatever data you try to output to each port of your group will correspond to each element of the data array This also appl
60. samples as a snapshot of what the input looks like periodically For an example using the AI Waveform Scan VI open the Acquire N multi Start VI found in Labview examples daqianlogin anlogin 11b The AI Waveform Scan VI shown in Figure 7 8 is similar to the Acquire N Scans example except the National Instruments Corporation 7 7 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition acquisition only occurs while the start button on the front panel is pressed Acquire and display M scans until stop button i pressed or an error occurs Wait for start button between acquisitions Note for analog input input limits no change with group O waveform taskID is the graph same as device device 13 channels CO number of scans to acquire 1000 scan rate 1000 scans free start stop LTE small asynchronous delay while waiting for button R 100 Figure 7 8 Taking a Specified Number of Samples with the Al Waveform Scan VI This example is similar to the standard simple buffered analog input VI but now both the AI Start and AI Read VIs are in a While Loop which means the program takes a number of samples every time the While Loop iterates Note The AI Read VI returns 1000 samples taken at 5000 samples per second every time the While Loop iterates however the duration of the iterations of the While Loop can vary greatly This means that with this
61. scan The program then passes the returned data to the My Single Scan Processing VI With this VI you can program whatever processing needs your application calls for such as looking for a limit to be exceeded or performing an average The VI then passes the data through the build array function to a waveform chart for display on the front panel The Wait Until Next ms multiple VI controls the loop timing You enter a scan rate the application converts the value into milliseconds and passes the converted value to the Wait Until Next ms multiple VI The loop then executes at the rate of scanning The loop ends when you press the stop button or an when error occurs Once the loop finishes the Simple Error Handler VI displays any errors that occurred on the screen Read amp chart data until an error occurs or the stop button pressed transposed waveform chart i o buffer interchannel delay in secs 1 hw default Figure 6 6 The Cont Acq amp Chart immediate VI Block Diagram The previous examples use software timed acquisition With this type of acquisition the CPU system clock controls the rate at which you acquire data Your system clock can be interrupted by user interaction so if you do not need a precise acquisition rate use software timed analog input National Instruments Corporation 6 5 LabVIEW Data Acquisition Basics Manual Chapter6 One Stop Single Point Acquisition Using Analog Input Output Control Loo
62. stop bit no parity United Kingdom 44 635 551422 Up to 9 600 baud 8 data bits 1 stop bit no parity France 1 48 65 15 59 Up to 9 600 baud 8 data bits 1 stop bit no parity FTP Support To access our FTP site log on to our Internet host ftp natinst com as anonymous and use your Internet address such as joesmith anywhere com as your password The support files and documents are located in the support directories National Instruments Corporation B 1 LabVIEW Data Acquisition Basics Manual FaxBack Support FaxBack is a 24 hour information retrieval system containing a library of documents on a wide range of technical information You can access FaxBack from a touch tone telephone at the following numbers 512 418 1111 or 800 329 7177 E Mail Support currently U S only You can submit technical support questions to the appropriate applications engineering team through e mail at the Internet addresses listed below Remember to include your name address and phone number so we can contact you with solutions and suggestions GPIB gpib support natinst com DAQ daq support natinst com VXI vxi support natinst com LabWindows lw support natinst com Telephone and Fax Support National Instruments has branch offices all over the world Use the list below to find the technical support number for your country If there is no National Instruments office in your country contact the source from which you purchase
63. syntax Use the iteration input to optimize your digital operation When iteration is 0 default LabVIEW calls the DIO Port Config VI an Advanced VI to configure the port If iteration is greater than zero LabVIEW bypasses reconfiguration and remembers the last configuration which improves performance You can wire this input to an iteration terminal of a loop With the DIO 24 and DIO 96 devices every time you call the DIO Port Config VI the digital line values are reset to default values If you want to maintain the integrity of the digital values from one loop iteration to another do not set iteration to O except for the first iteration of the loop For an example on SCXI digital input refer to SCXI 1162 1162HV Digital Input VI located in examples dag digital digio 11b Even though this VI uses Advanced VIs it is functionally equivalent to the Easy I O Digital VI Read from Digital Port The DIO Port Config VI resets output lines on adjacent ports on the same 8255 chip for DIO 24 DIO 96 MIO 16D MIO 16DE and Lab Series devices If you are also using SCXI analog input modules make sure your cabling DAQ device is cabled to one of them National Instruments Corporation Chapter 19 Common SCX Applications Digital Output Application Example To output digital signals through an SCXI chassis you can use the SCXI 1160 SCXI 1161 SCXI 1163 and SCXI 1163R modules and the digital Easy Digital VI Write to Digital Port
64. the LabVIEW User Manual and the LabVIEW Tutorial Manual for more information on using the probe Setting Breakpoints and Showing Advanced DAQ Vis Once you have narrowed down the location of an error to a subVI you can set a breakpoint on that subVI to cause VI execution and pause before executing the subVI You can now see what values get passed in or are generated by the Advanced VIs single step through the subVI s execution probe wires to see data or change values of front panel controls Refer to Chapter 5 Executing and Debugging in the LabVIEW User Manual and the LabVIEW Tutorial Manual for more information on how to set a breakpoint LabVIEW Data Acquisition Basics Manual 27 4 National Instruments Corporation LabVIEW Data Acquisition Common Questions Where is the best place to get up to speed quickly with data acquisition and LabVIEW Read the LabVIEW Data Acquisition Basics Manual and look at the run_me 11b examples in examples gt daq included with the package What is the easiest way to address my AMUX 64T board with my MIO board Set the number of AMUX boards used in the configuration utility wdaqconf exe on Windows or NI DAQ control panel on Macintosh Then in the channel string inputs specify the onboard channel For example with one AMUX 64T board the channel string 0 1 will acquire data from AMUX channels 0 through 7 and so on What are the advantages disadvantages of
65. the Measure Pulse Width or Period VI description in Chapter 17 Easy Counter VIs of the LabVIEW Data Acquisition VI Reference Manual for further information regarding the input parameters Controlling Your Pulse Width Measurement Figure 23 4 describes how to measure pulse width using the following Intermediate Counter VIs Pulse Width or Period Meas Config Counter Start Counter Read and Counter Stop Use this set of VIs to control when the measurement of the pulse width begins and ends The Pulse Width or Period Meas Config VI configures a counter to count the number of cycles of a known internal frequency or timebase The Counter Start VI begins the measurement The Counter Read VI determines if the measurement is complete and displays the count value With Am9513 devices the Counter Read VI also alerts you if an overflow occurs when the counter reaches terminal count TC Overflows do not occur in continuous counter operations Once you press the stop button the Counter Stop VI stops the counter operation And finally the Simple Error Handler VI notifies you of any errors timebase Hz device counter type of measurement Figure 23 4 Measuring Pulse Width Using Intermediate VIs When measuring pulse width make sure you start the counter before your device measures the first pulse Otherwise LabVIEW returns an error or an incorrect measurement LabVIEW Data Acquisition Basics Manual 23 3 National Instruments Co
66. the Measure Pulse Width or Period VI located in Functions Data Acquisition Counter as shown below in Figure 24 5 Set the type of measurement parameter to a period or pulse measurement The frequency is the reciprocal of the period value returned The valid parameter indicates if the frequency was measured without overflow Overflow occurs when the counter reaches its highest value or terminal count TC You only need to check the valid parameter if you are using an Am9513 chip The DAQ STC does not use the valid parameter to set the overflow so you do not need to check this parameter with this chip device pulse width period C5 Figure 24 5 Measuring Low Frequency Signals with Measure Pulse Width or Period VI If you need more control over when frequency period measurement begins and ends use the Intermediate VIs instead of the Easy VIs Figure 24 6 shows you how to measure the period and frequency for low frequency signals The Intermediate VIs described in Figure 24 6 include the Pulse Width or Period Meas Config Counter Start Counter Read and the Counter Stop VIs The Pulse Width or Period Meas Config VI configures the counter for period measurement The Counter Start VI begins the counting operation Counter Read returns the count value from the LabVIEW Data Acquisition Basics Manual 24 4 National Instruments Corporation Chapter 24 Measuring Frequency and Period counter which is used to determine the frequenc
67. the SCXI 1121 module with RTDs because it easily performs all the signal conditioning listed previously You must set up the excitation level gain and filter settings on the SCXI 1121 module with jumpers as well as in your system s configuration utility For information on how to connect and configure the RTD with the SCXI 1121 module look at the Getting Started with SCXT manual or the RTD application note mentioned previously The SC 2042 RTD device is a signal conditioning device designed specifically for RTD measurement This device can be used as an alternative to SCXI modules For more information look at the National Instruments catalog You do not have to worry about cold junction compensation with RTDs as you do when measuring thermocouples To build an application in LabVIEW you can use the Easy I O analog input VIs If you are measuring multiple transducers on several different channels you will need to scan the necessary channels with little overhead Because the Easy I O VIs reconfigure your SCXI module every time your application performs an acquisition it is recommended that you use the Intermediate analog input VIs as well as the RTD conversion VI as shown in the following example The Convert RTD Reading VI LabVIEW Data Acquisition Basics Manual 19 10 National Instruments Corporation channels device i Ge buffer size f Chapter 19 Common SCXI Applications in Functions Data Acquisition Signal Conditioni
68. the buffer and fills up the same buffer again You should use simple buffered handshaking when you have a predetermined number of values to acquire or generate Use circular buffered handshaking when you want to acquire or generate data continuously LabVIEW Data Acquisition Basics Manual 15 6 National Instruments Corporation Chapter 15 Shaking Hands with a Digital Partner Simple Buffered Examples The example in Figure 15 5 uses the Intermediate VIs to perform pattern generation using the DIO 32F devices An example VI that ships with LabVIEW similar to the diagram below is the Digital Buffered Handshaking VI found in examples daq digio 11b Notice the port list contains more than one port number which means the ports are grouped together number of updates 1000 handshake source 1 internal 1000 updates sec Figure 15 5 Pattern Generation Using the DIO 32F Devices The For Loop generates the digital data to output The amount of data generated equals the number of ports in the port list multiplied by the number of updates The direction input specifies whether the ports are configured for input or output The DIO Wait VI waits until the digital buffered input or output operation completes before returning to the main VI The DIO Clear VI halts any transfers and clears the group port configuration If you want an external source to supply the handshaking signals you can specify the handshake source to be an external s
69. the number of times the trigger conditions are met The hysteresis parameter displays the range of voltage levels you will use to meet retrieval conditions For more information on the conditional retrieval input cluster look at the AI Read VI description in Chapter 4 Intermediate Analog Input VIs in the LabVIEW Data Acquisition VI Reference Manual Conditional Retrieval Examples You can use the AI Waveform Scan VI to perform conditional retrieval just as you use it for hardware analog triggering Actually the AI LabVIEW Data Acquisition Basics Manual 8 12 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers Waveform Scan VI calls the AI Read VI to perform conditional retrieval as discussed in the previous section The Acquire N Scans ATrig example located in examples daq anlogin anlogin 11b uses the AI Waveform Scan VI as shown in Figure 8 9 time limit 5 sec software tigger TCE XE pretrigger scans 0 trigger level 04 ga sua number of scars to acquire 1000 scan rate 1000 scanssec Figure 8 9 Block Diagram of the Acquire N Scans ATrig VI The main difference between the trigger condition inputs for conditional retrieval and hardware triggering is the type of trigger You set up trigger channel slope and voltage level the same way for both triggering methods The pretrigger scans value will be negated and connected to the offset value in the conditional retri
70. the other items you need You can compare this scenario to circular buffered data acquisition shown in Figure 7 11 Using a circular buffer you can set LabVIEW Data Acquisition Basics Manual 7 10 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition up your device to continuously acquire data in the background while LabVIEW retrieves the acquired data Buffer Being Filled gt gt Number to Read ke gt Current Read Mark Buffer Size Figure 7 11 How a Circular Buffer Works A circular buffer differs from a simple buffer only in how LabVIEW places the data into it and retrieves data from it A circular buffer is filled with data just as a simple buffer however when it gets to the end of the buffer it returns to the beginning and fills up the same buffer again This means data can read continuously into computer memory but only a defined amount of memory can be used Your VI must retrieve data in blocks while the data enters the circular buffer so that data is not overwritten by newer data Because of the buffer maintenance you can only use the Intermediate or Advanced VIs with this type of data acquisition While a circular buffer works well in many applications there are two possible problems that can occur with this type of acquisition your VI could try to retrieve data from the buffer faster than data is placed into it or the program might not retrieve data from the b
71. this appendix contains forms to help you gather the information necessary to help us solve your technical problems and a form you can use to comment on the product documentation When you contact us we need the information on the Technical Support Form and the configuration form if your manual contains one about your system configuration to answer your questions as quickly as possible National Instruments has technical assistance through electronic fax and telephone systems to quickly provide the information you need Our electronic services include a bulletin board service an FTP site a FaxBack system and e mail support If you have a hardware or software problem first try the electronic support systems If the information available on these systems does not answer your questions we offer fax and telephone support through our technical support centers which are staffed by applications engineers Electronic Services Bulletin Board Support National Instruments has BBS and FTP sites dedicated for 24 hour support with a collection of files and documents to answer most common customer questions From these sites you can also download the latest instrument drivers updates and example programs For recorded instructions on how to use the bulletin board and FTP services and for BBS automated information call 512 795 6990 You can access these services at United States 512 794 5422 or 800 327 3077 Up to 14 400 baud 8 data bits 1
72. to voltage When you LabVIEW Data Acquisition Basics Manual 18 2 National Instruments Corporation Chapter 18 Special Programming Considerations for SCX use the input limits parameter of the analog input VIs LabVIEW chooses onboard gains that complement the jumpered SCXI gains to achieve the given input limits as closely as possible For analog input modules with programmable gains LabVIEW uses the gain setting you enter in the configuration utility for each module as the default gain for that module LabVIEW uses the default gain for the module whenever you leave the input limits terminal to the analog input VIs unwired or if you enter 0 volts for your upper and lower input limits You can experiment with the default gain setting by using the original Getting Started Analog Input VI found in examples daq run_me 11b This VI does not use input limits After you execute the VI you can open the configuration utility while Lab VIEW is open and change the default gain setting there Be sure to save your change by choosing File Save for the Macintosh save changes by closing the utility before switching back to LabVIEW to run the VI again Remember that the larger the gain setting the more precise your measurements will be as long as the signal is within the resulting range of the channel The Easy I O VIs for analog input always pass default input limits of 10 V to 10 V to the analog input VIs Therefore if your module has programma
73. triggers an event such as A D conversion A first in first out memory buffer In a FIFO the first data stored is the first data sent to the acceptor A type of signal conditioning that allows you to filter unwanted signals from the signal you are trying to measure Signal sources with voltage signals that are not connected to an absolute reference or system ground Also called nonreferenced signal sources Some common example of floating signal sources are batteries transformers or thermocouples G 6 National Instruments Corporation G gain GATE input pin grounded measurement system grounded signal sources group H handle handshaked digital I O hardware triggering hex Hz National Instruments Corporation Glossary The amplification or attenuation of a signal A counter input pin that controls when counting in your application occurs See referenced single ended measurement system Signal sources with voltage signals that are referenced to a system ground such as the earth or a building ground Also called referenced signal sources A collection of input or output channels or ports that you define Groups can contain analog input analog output digital input digital output or counter timer channels A group can contain only one type of channel however You use a task ID number to refer to a group after you create it You can define up to 16 groups at one time To erase a group you pa
74. values you want to transfer in a buffer Only one value will be transferred after each handshaked pulse If you want to use non latched immediate digital I O refer to Chapter 14 When You Need It Now Immediate Digital I O If you need to perform latched handshaked digital I O refer to Chapter 15 Shaking Hands with a Digital Partner 8 Counters Counting or Generating Digital Pulses If you want to generate digital pulses from a counter at a certain rate read Chapter 22 Generating a Square Pulse or Pulse Trains If you want to measure the width of a digital pulse refer to Chapter 23 Measuring Pulse Width If you want to measure the frequency or period of a digital signal refer to Chapter 24 Measuring Frequency and Period If you just want to count how many times a digital signal rises or falls refer to Chapter 25 Counting Signal Highs and Lows To learn how to slow the frequency of a digital signal refer to Chapter 26 Dividing Frequencies National Instruments Corporation 4 5 LabVIEW Data Acquisition Basics Manual Catching the Analog Input Wave with This section contains basic information on acquiring data with LabVIEW including acquiring a single point or multiple points triggering your acquisition and using outside sources to control acquisition rates Part 2 Catching the Wave with Analog Input contains the following chapters Chapter 5 Things You Should Know about Analog Input explains b
75. waveform generation If you want to perform single point generation refer to Chapter 11 One Stop Single Point Generation If you answered multiple point generation refer to Chapter 12 Buffering Your Way through Waveform Generation 6 Triggering a Signal or Using a Clock You can start an analog acquisition when a certain analog or digital value occurs by triggering the acquisition If you want to trigger an analog acquisition refer to Chapter 8 Controlling Your Acquisition with Triggers Multiple Point Acquisition with an Internal or External Clock Multiple point or waveform acquisition can be done at a rate set by an internal DAQ device clock or an external clock The external clock will be a TTL signal produced at a certain rate If you want to acquire a waveform at the rate of an external signal refer to Chapter 9 Letting an Outside Source Control Your Acquisition Rate If not read Chapter 7 Buffering Your Way through Waveform Acquisition LabVIEW Data Acquisition Basics Manual 4 4 National Instruments Corporation Chapter 4 Where You Should Go Next 7 Non Latched or Latched Digital 1 0 If you want your program to read the latest digital input or immediately write a new digital output value you should use non latched immediate digital I O When a DAQ device accepts or transfers data after a digital pulse has been received it is called latched handshaked digital I O With latched digital I O you can store the
76. will wait until the slope and voltage level conditions are met before starting a buffered acquisition The Acquire N Scans ATrig example VI located in examples dagq anlogin anlogin 11b holds the data in a memory buffer until the device completes data acquisition The number of data points you want to acquire must be small enough to fit in memory This VI only views and processes the information after the acquisition If you need to view and process information during the acquisition use the Acquire amp Proc N Scans Trig VI located in examples daq anlogin anlogin 11b If you expect multiple analog trigger signals that will start multiple acquisitions use the example Acquire N multi ATrig located in examples dag anlogin anlogin 11b Software Triggering Software triggering allows you to simulate an analog trigger using software This form of triggering is often used in situations where hardware triggers are not available Another name for software triggering signals specifically analog signals is conditional retrieval With conditional retrieval you set up your DAQ device to collect data but the device does not return any data to LabVIEW unless the data meets your retrieval conditions LabVIEW scans the input data and performs a comparison with the conditions but does not store the data until it meets your specifications Figure 8 7 shows a timeline of events that typically occur when you perform conditional retrieval The re
77. with Thermocouples 000 0 cc eecesceseeseeseeeeeeseeeeetees 19 2 Temperature Sensors for Cold Junction Compensation 19 3 Amplifier Offset sies Ge iiaee a a a sbett des 19 4 VIExamples Sn ni A tated eed ee ee Bedi ees 19 5 Measuring Temperature With RTDs 0 eee ec cecceseeeeeeeceeetseeesesseesaeeeeeaeeseeeaeeseeens 19 9 Measuring Pressure with Strain Gauges 00 cee cee eseeeeeeceeeceeeseeeeeaesseeeaesseeeaeeeeeas 19 11 Analog Output Application Example 0 0 ee eeccesseeceeseceeeeseeeseeseeeaesseeeaeeseeeaeeeeens 19 14 Digital Input Application Example ooo ceccessceceeseceeecseeeseeseeeaesseeesesseeeaeeeeeas 19 15 Digital Output Application Example 0 0 0 ccc eeeeseeeeeeseceeecseeesesseeeaecseeeaesseeeaeeseeas 19 17 Multi Chassis Applications 2 0 cece eee eseseesecseceseesecesecseeeseceeessecesesseesaeseeeaesseeeaeeseeegs 19 18 Chapter 20 SCXI Calibration Increasing Signal Measurement Precision EEPROM Your System s Holding Tank for Calibration COMStaMtS sssri e a inva Ena ARE NE EAE R a 20 1 Calibrating SCXD Modules oivicsiussscssisecesassesecscsssccsctecussaeivesidessasesossessdeuseds a aS 20 3 SCXI Calibration Methods for Signal Acquisition eee eeeeeeeeeeeeee 20 4 One Point Calibration isisisi eee ceeeceeeeeceeeeseseeeeseseeeeseesaeeeeeaee 20 5 Two Point Calibration iesenii ieietu noiiire 20 6 Calibrating SCXI Modules for Signal Generation 2 00 0 eee eee eects eeeeeeee 20 7 Part 6 Counting
78. 0 eee eeeeeeeeeeeeees 5 4 Figure 5 5 The Effects of Range on ADC Precision 0 eeeseeeeeeeeeeeeeeeneeneeeees 5 5 Figure 5 6 The Effects of Limit Settings on ADC Precision oe eee 5 6 Figure 5 7 8 Channel Differential Measurement System eee eeeeeeeeeee 5 9 Figure 5 8 Common Mode Voltage 0 cece ec eeceeseesscesecseeeseeseeeseseeeeseeneeeaeenaes 5 10 Figure 5 9 16 Channel RSE Measurement System o00 eee eee eeeeeeseeeeeeseeeees 5 11 Figure 5 10 16 Channel NRSE Measurement System 0 eee ee eeeeeeseeeeeereeeees 5 12 Figure 6 1 The AI Sample Channel VI Help Window o oo eee eeeeeeeereeeees 6 1 Figure 6 2 Acquiring Data Using the AI Sample Channel VI s es 6 2 Figure 6 3 Acquiring a Voltage from Multiple Channels with the AI Sample Channels Vianen cele a aes tees tere ites 6 3 Figure 6 4 The AI Single Scan VI Help Diagram 00 eee eee ceeeeseeeeeeneeeees 6 4 Figure 6 5 Using the Intermediate VIs for a Basic Non Buffered APPLICATION o erer eevee vos 8d ee E aA deepest estes sts E S EEEE E 6 4 Figure 6 6 The Cont Acq amp Chart immediate VI Block Diagram 6 5 Figure 6 7 Software Timed Analog VO wee eececeeseeeseeseceseeneenseeseeeseseeeeseeeees 6 7 Figure 6 8 Analog IO Control Loop hw timed VI Block Diagram 0 6 8 Figure 7 1 How Butters Work toecchkiad duhedhs atta it E esti 7 2 Figure 7 2 The AI Acquire Waveform VI o oo cece eeeeceeseceeceeceeeeseseeetseseeeeaeenees 7 3 Figure 7 3 T
79. 0 us delay it configures the acquisition but does not return a warning You can set your channel clock rate with the interchannel delay input of the AI Config VI which calls the Advanced AI Clock Config VI to actually configure the channel clock The simplest method to select an interchannel delay is to gradually increase the delay or clock period until the data appears consistent with data from the previous delay setting Refer to your hardware manuals for the required settling time for your channel clock You can also find the interchannel delay by running the low level AI Clock Config VI for the channel clock with no frequency specified Externally Controlling your Channel Clock There are times when you might need to control the channel clock externally The channel clock rate is the same rate at which analog conversions occur For instance suppose you need to know the strain value at an input every time an infrared sensor sends a pulse Most DAQ devices have an EXTCONV pin on the I O connector for providing your own channel clock This external signal must be a TTL level signal where the actual conversion occurs on the falling edge of the signal as shown in Figure 9 3 With devices that have a RTSI connector you can get your channel clock from other National Instruments DAQ devices rising edge falling edge TTL Signal Figure 9 3 Example of a TTL Signal Figure 9 4 shows you the Getting Started Analog Input example
80. 1 SOURCE GATE2 OuTzZ SOURCES GATES OUTS FOUT HB AIO 16 Figure 2 10 Device Configuration and 1 0 Connector Windows in NI DAQ You can also find helpful information by clicking on the Help button If at any time during configuration you need to view a list of the LabVIEW DAQ error codes and their meanings you can do so by pulling down on the NI DAQ menu bar located to the right of the Help button and choosing Errors cep Note Some DAQ devices such as the Lab NB and NB MIO 16 devices require hardware jumper changes in addition to software configuration Consult your DAQ device hardware reference manual for more information Installing and Configuring Your DAQ Device in Unix Your operating system creates an entry in the dev directory For example dev daq0 would mean that your first DAQ device would be device 1 dev daql1 would be device 2 and so on All you have to do is assign a device number to the device You do this by editing the daqconf cfg file in the daq or the install directory For example if you wanted to assign dev daq0 to device 3 you would type in LabVIEW Data Acquisition Basics Manual 2 18 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware device 3 SB A2200 daq 0 where SB A2200 is your device type Installing NI DAQ Software in Unix This section contains instructions for installing and configuring the NI DAQ UNIX software f
81. 2 3 NI DAQ software deciding which driver version to use A 4 installing in UNIX 2 19 Macintosh device drivers 2 3 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 user privilege level in Windows NT 2 15 versions of NI DAQ drivers note 2 1 Windows device drivers 2 3 Windows NT device drivers 2 3 NI PNP EXE utility 2 10 NI PNP INI file 2 10 NIDAQ DLL file 2 3 NIDAQNT DLLI file 2 3 nivisrd 386 device A 4 non buffered handshaking 15 5 to 15 6 non referenced signal sources 5 2 nonlatched digital I O 14 1 to 14 3 nonreferenced single ended NRSE measurement system 5 11 to 5 12 16 channel NRSE system figure 5 11 when to use 5 12 Nyquist frequency 5 2 Nyquist Theorem 5 2 0 OBF Output Buffer Full line 15 2 one point calibration 20 4 to 20 6 one shots 22 6 OUT output pin 21 2 OUT signal 21 3 to 21 4 Output Buffer Full OBF line 15 2 P parallel mode SCXD analog input modules 17 5 channel addressing 18 1 to 18 2 LabVIEW Data Acquisition Basics Manual digital modules Macintosh and Windows 17 6 SCXI 1200 Windows 17 6 parameters for VIs common DAQ VI parameters 3 7 to 3 8 conventions 3 6 to 3 7 pattern generation 15 2 PCMCIA bus computers configuring 2 6 to 2 9 PCMCIA cards inserting with computer running note 2 5 period measurement See frequency and period measurement Plug and Play switchless DAQ devices configuring 2 10 Plug and Play software f
82. 20 7 SCXI modules components chassis figure 17 3 illustration 17 2 overview 17 2 hardware configurations LabVIEW Data Acquisition Basics Manual illustration 17 1 overview 17 1 Windows or Macintosh systems 2 20 to 2 21 software configuration Macintosh systems 2 25 to 2 27 Windows environment 2 21 to 2 25 when to use 4 3 SCXI operating modes 17 3 to 17 6 multiplexed mode analog input modules 17 4 analog output modules 17 4 channel addressing 18 1 to 18 2 digital and relay modules 17 5 SCXI 1200 Windows 17 4 parallel mode analog input modules 17 5 channel addressing 18 1 to 18 2 digital modules Macintosh and Windows 17 6 SCXI 1200 Windows 17 6 SCXI programming considerations 18 1 to 18 5 channel addressing 18 1 to 18 2 gains 18 2 to 18 4 SCXI 1100 channel arrays input limits array and gains table 18 4 settling time 18 5 SCXI Temperature Monitor VI 19 8 SCXI Voltage example 19 5 settling time SCXD 18 5 SETUP program for ISA bus computers 2 9 signal conditioning amplification 16 3 to 16 4 common transducers table 16 1 to 16 2 common types of signal conditioning 16 2 conditioning for common types of transducers signals figure 16 3 definition 16 2 filtering 16 5 National Instruments Corporation isolation 16 4 linearization 16 5 transducer excitation 16 5 signal divider 26 1 signal edges 21 2 signal voltage range See limit settings signals See also analog
83. 2D array use the Index Array function from Functions Array amp Cluster Add a dimension so that you have two black rectangles in the lower left corner The top rectangle selects the row and the bottom rectangle selects the column Pop up on the row rectangle and select Disable National Instruments Corporation 3 15 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts Indexing Now when you select a column or channel by wiring your selection to the bottom rectangle the Index Array function produces the entire column of data as a 1D array as shown in Figure 3 11 Column major 2D Array Index Array Single Channel Channel Figure 3 11 Extracting a Single Channel from a Column Major 2D Array Analog output buffers that contain data for more than one channel are also column major 2D arrays To create such an array first make the data from each output channel a 1D array Then select the Build Array function from Functions Array amp Cluster Add as many input terminals rows to the Build Array terminal as you have channels of data Wire each 1D array to the Build Array terminal to combine these arrays into a single row major 2D array Then use the Transpose 2D Array function to convert the array to a column major array The finished array is ready for the AO Write VI as shown in Figure 3 12 Channel 0 Transpose l 2D Array Column major Build Array 20 Array Channel 1 Figure 3 12
84. 51 100 To set the module to use the second half of the ribbon cable set the operating mode in the configuration utility to Parallel secondary SCXI Software Installation and Configuration After you assemble your SCXI system you must run the configuration utility to enter your SCXI configuration LabVIEW needs the configuration information to program your SCXI system correctly Refer to Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Basics Manual 17 6 National Instruments Corporation Special Programming Considerations for SCXI When you want LabVIEW to acquire data from SCXI analog input channels you use the analog input VIs in the same way that you acquire data from onboard channels You also read and write to your SCXI relays and digital channels using the digital VIs in the same way that you read and write to onboard digital channels You can write voltages to your SCXI analog output channels using the analog output VIs The following sections discuss special programming considerations for SCXI in LabVIEW which include channel addressing gains limit settings and settling time SCXI Channel Addressing If you operate a module in parallel mode you can specify an SCXI channel either by specifying the corresponding onboard channels or by using the SCXI channel syntax described in this section If you operate the modules in multiplexed mode you must use the SCXI cha
85. 6F 5 AT MIO 64F 5 or AT MIO 16X device or an MIO E series device you should calibrate your DAQ device first using either the MIO Calibrate VI or E Series Calibrate VI Follow steps 1 through 5 in the previous section One Point Calibration 6 Now apply a known stable non zero voltage to your input channel at the terminal block This input voltage should be close to the upper limit of your input voltage range for the given gain setting For example if your input voltage range is 5 to 5V you would want to apply an input voltage that is as close to 5 volts as possible but not exceeding 5 volts 7 Take another binary reading or average of readings If your binary reading is the maximum binary reading for your DAQ device you should try a smaller input voltage This is your second volt binary measurement LabVIEW Data Acquisition Basics Manual 20 6 National Instruments Corporation Chapter 20 SCXI Calibration Increasing Signal Measurement Precision 8 Use the SCXI Cal Constants VI with the first volt binary measurement from step 4 as Volt Amp 1 and Binary 1 inputs and the second measurement from step 7 as Volt Amp 2 and Binary 2 inputs of the VI The following illustration shows how you should enter the values into these inputs in LabVIEW if your volt binary measurements are 0V 0 and 5V 2045 Keep in mind that your input names may vary depending on your application setup volt Amp 1 Binary 1 Volt Amp 2 Binary 2 9 Ifyou
86. 6X you can use the MIO Configure VI to enable dithering which makes your averaged data more accurate The dither mode is always enabled on MIO E series devices By using the Al Start and AI Read VIs instead of the AI Single Scan VI you can average over an integral number of 60Hz or 50Hz power line cycles sine waves to eliminate line noise You now have your first volt binary 20 5 LabVIEW Data Acquisition Basics Manual Chapter 20 SCXI Calibration Increasing Signal Measurement Precision measurement volt 0 0 or the applied voltage at your input channel and binary is your binary reading or binary average 5 Use the SCXI Cal Constants VI with your volt binary measurement from step 4 as the Volt Amp 1 and Binary 1 inputs in your VI respectively These input names may vary depending on your application setup For example if your volt binary measurement from step 4 was 0 00 volts and 2 then you would enter the values into your front panel controls as shown in the following illustration Volt amp 1 Binary 1 Two Point Calibration These steps show you how to perform a two point calibration calculation in LabVIEW You should use two point calibration when you need to correct both the binary offset and the gain error in your SCXI module Open SCXI 1100 two point calibration example in examples daq anlogin SCXI 11b for an example application that demonstrates a two point calibration Note If you are using an AT MIO 1
87. AQCONE CFG file 2 6 Wheatstone bridge 19 12 Windows environment installation and configuration EISA bus computers 2 9 inserting PCMCIA cards note 2 5 ISA and PCMCIA bus computers 2 6 to 2 9 multiple DAQ devices note 2 5 Plug and Play switchless DAQ devices 2 10 Plug and Play software 2 10 to 2 11 SCXI hardware 2 20 to 2 21 SCXI software 2 21 to 2 25 using WDAQCONF 2 11 to 2 14 NI DAQ drivers 2 3 questions and answers A 3 to A 4 Windows 95 users note 2 1 Windows NT environment LabVIEW considerations 2 14 to 2 15 changing I O page lock limit 2 14 to 2 15 user privilege level 2 15 NI DAQ drivers 2 3 Write N Updates example VI multiple immediate updates 11 2 to 11 3 single immediate updates 11 1 to 11 2 Write to Digital Line VI 14 2 Write to Digital Port VI digital output application 19 16 to 19 17 immediate digital I O 14 2 Write to Spreadsheet File VI 7 9 National Instruments Corporation Index 35 Index LabVIEW Data Acquisition Basics Manual
88. ATIONAL INSTRUMENTS MAKES NO WARRANTIES EXPRESS OR IMPLIED AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE CUSTOMER S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA PROFITS USE OF PRODUCTS OR INCIDENTAL OR CONSEQUENTIAL DAMAGES EVEN IF ADVISED OF THE POSSIBILITY THEREOF This limitation of the liability of National Instruments will apply regardless of the form of action whether in contract or tort including negligence Any action against National Instruments must be brought within one year after the cause of action accrues National Instruments shall not be liable for any delay in performance due to causes beyond its reasonable control The warranty provided herein does not cover damages defects malfunctions or service failures caused by owner s failure to follow the National Instruments installation operation or maintenance instructions owner s modification of the product owner s abuse misuse or negligent acts and power failure or surges fire flood accident actions of third parties or other events outside reasonable control Under the copyright laws this publication may not be reproduced or transmitted in any form electronic or mechanical including photocopying recording storing in an inform
89. Acquisition Basics Manual 2 22 National Instruments Corporation National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware Leave the Communication Mode and Communication Path fields alone WOAQCONF sets these fields automatically after you enter the module information in step 5 Enter the configuration for each slot in the chassis The fields in the Slot Configuration sections of the window reflect the settings for the selected Chassis Slot number Refer to your SCXI chassis hardware manual to determine how the slots in a chassis are numbered You must set the following fields for each SCXI module you install Module Type Select the correct module type for the module installed in the current slot If the current slot does not have a module leave this field set to empty and advance the Chassis Slot number to the next slot Click on the Configure Module n where nis your module number button to bring up the Module Configuration window for the remaining fields Figure 2 12 shows this window Configuring chassis slot 1 Module Type Cabled Device Dev 1 AT MIO 16F 5 Operating Mode Multiplexed hannel Configuration Filter No Filter LabVIEW only Figure 2 12 SCXI Module Configuration Window in WDAQCONF a Module Type This number reflects the number of the SCXI Module that you chose in the main SCXI Configuration window If you want to change the Module Type
90. As with single point analog output you can use the Analog Output Utility VI AO Waveform Gen for most of your programming needs This VI has several inputs and outputs that the Easy I O VI does not have You have the option of having the voltage array generated once several times or continuously through the generation count input Figures 12 2 shows an example diagram of how to program this VI Generation count device channels abc Update rate ywoltages Figure 12 2 Waveform Generation Using the AO Waveform Gen VI In this example LabVIEW generates the voltages in the array five times before stopping The Generate N Updates example VI located in examples daq anlogout 11b uses the AO Waveform Gen VI Putting this VI ina loop and wiring the iteration terminal of the loop to the iteration input on the VI optimizes the execution of this VI When iteration is 0 LabVIEW configures the analog output channels appropriately If iteration is greater than 0 LabVIEW uses the existing configuration which improves performance With the AO Waveform Gen VI you can also specify the limit settings input for each analog output channel For more information on limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts LabVIEW Data Acquisition Basics Manual 12 2 National Instruments Corporation Chapter 12 Buffering Your Way through Waveform Generation If you want even more control over your analog output applicatio
91. Calibration example 20 5 SCXI 1100 Two point calibration example 20 6 SCXI 1124 Update Channels VI 19 14 SCXI 1162 1162HV Digital Input VI 19 16 SCXI 1200 module multiplexed mode Windows 17 4 parallel mode Windows 17 6 SCXI application examples 19 1 to 19 19 analog input application for measuring LabVIEW Data Acquisition Basics Manual Index temperature 19 2 to 19 5 analog output application 19 14 to 19 15 digital input application 19 15 to 19 16 digital output application 19 16 to 19 18 multi chassis applications 19 18 to 19 19 overview 19 1 to 19 2 pressure measurement with strain gauges 19 11 to 19 14 temperature measurement applications amplifier offset 19 4 to 19 5 sensors for cold junction compensation 19 3 to 19 4 using RTDs 19 9 to 19 11 using thermocouples 19 2 to 19 5 VI examples 19 5 to 19 9 SCXI Cal Constants VI automatic calculation of calibration constants 20 3 calibrating SCXI modules for signal generation 20 8 loading saved calibration constants 20 7 20 8 one point calibration 20 5 overwriting default constants in EEPROM 20 2 two point calibration 20 6 to 20 7 SCXI calibration 20 1 to 20 8 EEPROM for storing calibration constants 20 1 to 20 3 default load area 20 2 factory area 20 2 user area 20 2 to 20 3 one point calibration 20 4 to 20 6 reasons for calibrating 20 3 to 20 4 signal acquisition 20 3 to 20 7 signal generation 20 7 to 20 8 two point calibration 20 6 to
92. Config VI finite pulse train generation 22 8 measuring frequency and period 24 6 single square pulse generation 22 4 delays for improving control loop performance 6 9 to 6 10 device voltage range 5 4 to 5 5 considerations for selecting analog input settings 5 6 to 5 8 description 5 4 to 5 5 effect on ADC precision figure 5 5 measurement precision for various device ranges and limit settings table 5 8 differential measurement system 5 9 to 5 10 channel differential system figure 5 9 common mode voltage figure 5 10 when to use 5 10 digital and relay SCXI modules 17 5 Digital Buffered Handshaking VI 15 7 Digital Clock Config VI 15 7 to 15 8 digital DAQ example file 3 2 digital I O buffered handshaking 15 6 to 15 10 choosing between digital or counter interfacing 4 3 to 4 4 choosing between non latched or latched digital I O 4 5 National Instruments Corporation Index handshaking latched digital I O 15 1 to 15 2 immediate non latched digital I O 14 1 to 14 3 non buffered handshaking 15 5 to 15 6 overview 13 1 to 13 2 SCXI application examples digital input 19 15 to 19 16 digital output 19 16 to 19 18 sending out multiple digital values 15 2 to 15 5 Digital Mode Config VI 15 8 digital ports and lines 13 1 digital SCXI modules 17 6 digital triggering definition 8 2 description 8 2 to 8 3 examples 8 3 to 8 6 DIO Buffer Control VI 15 7 to 15 9 DIO Clear VI 15 7 DIO Config VI 15 8
93. Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts settings contained in the last entry of the limit settings cluster array Figure 3 7 illustrates this case Tow limit Figure 3 7 Limit Settings Case 2 In this example channels 0 1 2 and 3 have limits of 10 00 to 10 00 volts There are more channels left but the limit settings cluster array is exhausted Therefore the remaining channels 4 5 6 and 7 are also assigned limits of 10 00 to 10 00 volts The Easy I O Analog Input VIs have only one pair of input limits This pair forms a single cluster element All channels scanned with these VIs have identical limit settings The Easy Analog Output VIs do not have limit settings All the Intermediate VIs both analog input and output have the channel string array and the limit settings or input limits cluster array on the same VI Assignment of limits to channels works exactly as described above Refer to the LabVIEW Data Acquisition VI Reference Manual for more information on how to assign limit settings to a particular analog channel using the Advanced VIs the Group Config VI and the Hardware Config VI In analog applications you not only specify the voltage range of the signal you must also specify the voltage range and the polarity of the device A unipolar voltage range is a range containing either positive or negative voltages but never both A bipolar voltage range is a range that has both positive and n
94. DAQ functions error in no error error out code code source source C YE Figure 3 5 The Error In Input and Error Out Output Error Clusters in LabVIEW For more information on error handling refer to Part 7 Debugging Your Data Acquisition Application in this manual Channel Port and Counter Addressing The Analog Input and Analog Output VIs have a channel list parameter where you can specify the channels from which the VIs read or to which they write The Digital Input and Output VIs have a similar parameter called port list and the equivalent value is called counter list for the Counter VT s For ease of understanding of channel addressing concepts the channel list port list and counter list parameters are referred to as channel list in this section Any special exceptions for these parameters will be noted Each channel you specify in the channel list becomes a member of a group For each group you can acquire or generate data on the channels listed in the group VIs scan during acquisition or update during generation the channels in the same order they are listed To erase a group pass an empty channel list and the group number to the VI or assign a new channel list to the group Changing groups can only be done at the Advanced VI level Refer to the LabVIEW Data Acquisition VI Reference Manual for more information The channel list can be an array of strings or as with the Easy VIs a scalar string control
95. Digital I O contains the following chapters e Chapter 13 Things You Should Know about Digital I O basic concepts on digital I O e Chapter 14 When You Need It Now Immediate Digital I O explains how to use digital lines to acquire and generate data immediately e Chapter 15 Shaking Hands with a Digital Partner shows you how you can synchronize digital data transfers between your DAQ devices and instruments Things You Should Know about Digital 1 0 Digital I O interfaces are often used to control processes generate patterns for testing and communicate with peripheral equipment like heaters motors and lights Digital I O components on DAQ devices and SCXI modules consist of hardware parts that generate or produce on off signals As shown in the diagram below all digital lines are grouped into ports on DAQ devices and banks on SCXI modules The number of digital lines per port or bank is specific to the particular device or module used but most ports or banks consist of four or eight lines Except for the TIO 10 and E Series devices all lines within the same port or bank must all be of the same direction either input or output as shown in Figure 13 1 By writing to or reading from a port you can set or retrieve simultaneously the states of multiple digital lines Refer to Appendix B Hardware Capabilities of the LabVIEW Data Acquisition VI Reference Manual or your hardware user manual for port information on y
96. I 1 1 LabVIEW Data Acquisition Basics Manual Chapter 1 How To Use This Book Part 6 Part 7 Hardware and Software Setup for Your SCXI System Special Programming Considerations for SCXI Common SCXI Applications SCXI Calibration Increasing Signal Measurement Precision Counting Your Way to High Precision Timing Things You Should Know about Counters Generating a Square Pulse or Pulse Train Measuring Pulse Width Measuring Frequency and Period Counting Signal Highs and Lows Dividing Frequencies Debugging Techniques If you have already started a LabVIEW DAQ application please refer to Chapter 2 Installing and Configuring Your Data Acquisition Hardware to check your configuration the appropriate application section for information on common errors and Part 7 Debugging Techniques The following flowchart shows the steps you should follow before running your application LabVIEW Data Acquisition Basics Manual Install and Configure Your Hardware Learn Basic Data Acquisition Concepts Go to Your Specific Application Section Review LabVIEW Example Applications Learn How to Debug Your Application 1 2 National Instruments Corporation Chapter 1 How To Use This Book 1 Install and Configure Your Hardware When you install LabVIEW the program prompts you to have the data acquisition DAQ drivers already installed This manual guides you through setting up NI DAQ software with your DAQ device and SCXI
97. IEW and some common SCX applications What is Signal Conditioning Electrical signals can be generated by transducers to measure physical phenomena such as temperature force sound or light Table 16 1 lists some common transducers Table 16 1 Phenomena and Transducers Phenomena Transducer Temperature Thermocouples Resistance temperature detectors RTDs Thermistors Integrated circuit sensor Light Vacuum tube photosensors Photoconductive cells Sound Microphone Force and pressure Strain gauges Piezoelectric transducers Load cells Position displacement Potentiometers Linear voltage differential transformer LVDT Optical encoder National Instruments Corporation 16 1 LabVIEW Data Acquisition Basics Manual Chapter 16 Things You Should Know about SCX Table 16 1 Phenomena and Transducers Continued Phenomena Transducer Fluid flow Head meters Rotational flowmeters Ultrasonic flowmeters pH pH electrodes In order to measure signals from transducers you must convert them into a form that a data acquisition DAQ device can accept For example the output voltage of most thermocouples is very small and susceptible to noise Therefore you may need to amplify and or filter the thermocouple output before digitizing it The manipulation of signals to prepare them for digitizing is called signal conditioning The following are some common types of signal condi
98. In this case internal counters are inefficient for your needs You must control your acquisition rate by some other external source You could compare a scan of your channels to taking a snapshot of the voltages on your analog input channels If you set your scan rate to 10 scans per second you are taking 10 snapshots each second of all the channels in your channel list In this case an internal clock within your device the scan clock sets the scan rate which controls the time interval between scans Also remember that most DAQ devices those that do not simultaneously sample proceed from one channel to the next depending on the channel clock rate Therefore the channel clock is the clock controlling the time interval between individual channel samples within a scan which means the channel clock proceeds at a faster rate than the scan clock The faster the channel clock rate the more closely in time your system samples the channels within each scan as shown in Figure 9 1 National Instruments Corporation 9 1 LabVIEW Data Acquisition Basics Manual Chapter 9 Letting an Outside Source Control Your Acquisition Rate Note For devices with both a scan and channel clock lowering the scan rate does not change the channel clock rate O12 3 0 r LLTI x channel interval scan interval Figure 9 1 Channel and Scan Intervals Using the Channel Clock Some DAQ devices do not have scan clocks but rather use round ro
99. M could be compared to a holding tank for calibration constant information in your module s memory There are 3 parts to this holding tank the factory area the default load area and the user area National Instruments Corporation 20 1 LabVIEW Data Acquisition Basics Manual Chapter 20 SCXI Calibration Increasing Signal Measurement Precision ie Note Only the SCXI 1122 SCXI 1124 SCXI 1102 and SCXI 1141 have EEPROMs All other SCXI modules do not store calibration constants Electronically Erasable Programmable Read Only Memory EEPROM Default Load Area e The factory area has a set of factory calibration constants already stored in it when you receive your SCXI module You cannot write into the factory area but you can read from it so you can always access and use these factory constants if they are appropriate for your application e The default load area is where LabVIEW automatically looks to load calibration constants the first time you access the module When the module is shipped the default load area contains a copy of the factory calibration constants we Note You may overwrite the constants stored in the default load area of EEPROM with a new set of constants using the SCXI Cal Constants VI To learn more about this VI refer to Chapter 20 Calibration and Configuration VIs in the LabVIEW Data Acquisition VI Reference Manual e The user area is an area for you to store your own calibration constants that
100. NF and LabVIEW You can obtain the Error Messages and Crashes Common Questions document from the NI FaxBack system Windows am having problems accessing ports 2 or higher on the AT MIO 16D or PC DIO 96 A problem was found in version 3 0 with addressing the higher numbered ports on these boards To fix the problem get the updated version of atwdaq d11 and use the updated DIO Port Read vi These updated files are included with LabVIEW for Windows version 3 0 1 LabVIEW for Windows version 3 0 users can obtain these files by downloading the file win30up2 zip from the NI BBS or FTP sites The file is in the directory support labview windows LVWin3 0 updates National Instruments Corporation A 3 LabVIEW Data Acquisition Basics Manual Appendix A LabVIEW Data Acquisition Common Questions Windows While performing analog input get memory allocation errors 10444 even though I have a large amount of memory on my machine Buffers for data acquisition arrays unlike arrays for LabVIEW buffers must be available in physical RAM not in virtual memory For example assume the machine has 32 MB of RAM and LabVIEW is allocated 8 MB of RAM The memory allocated to LabVIEW wires will come out of the 8 MB however data acquisition buffers will be allocated out of the remaining 24 MB of RAM On an AT style machine ISA using DMA the DMA controller can only address the first 16 MB of RAM If you get out of memory errors
101. National Instruments Corporation 22 7 LabVIEW Data Acquisition Basics Manual Chapter 22 Generating A Square Pulse or Pulse Trains gating counter 1 provides counter with a long enough gate pulse to output the number of desired pulses counter 1 counter Figure 22 9 Physical Connections for Generating a Finite Pulse Train A gated pulse train using the Easy Counter VI Generate Pulse Train as shown in Figure 22 7 requires the frequency duty cycle and number of pulses controls to be set Instead of setting the number of pulses to 0 as you would for a continuous pulse train set the number of pulses to a value greater than 0 Figure 22 10 describes how to create a finite pulse train using the Intermediate VIs gate mode fedge gating gate mode evel gating aes Pu Counter Counter counter Start Start tab te ee pulse polarity frequency 1 0 counter 1 duty cycle Figure 22 10 Creating a Finite Pulse Train Using the Intermediate VIs In this operation you use counter to generate a continuous pulse train with level gating while using counter 1 to generate a minimum delayed pulse to gate the counter long enough to generate the desired number of pulses The Continuous Pulse Generator Config VI configures counter to generate a continuous pulse train Then the Delayed Pulse Generator Config VI configures counter 1 to generate a single delayed pulse The first Counter Start VI in the flow begins the continuous pulse gene
102. Pe cold junction voltage Figure 19 3 Continuously Acquiring Data Using Intermediate VIs Another temperature acquisition example using the SCXI 1100 module is SCXI Temperature Monitor VI located in examples daq anlogin scxi 11b This VI continually acquires thermocouple readings and sets an alarm if the temperature readings go above a user defined limit You can use the SCXI 1100 examples with the SCXI 1122 module Both modules have the capability to programmatically measure the amplifier offsets and both modules need the cold junction compensation to linearize thermocouple measurements The main difference between the two modules is the type of temperature sensors available on their terminal blocks The main difference between the two modules is in the way module channels are multiplexed The SCXI 1100 uses a CMOS multiplexer which is capable of fast channel multiplexing whereas the SCXI 1122 uses a electromechanical relay LabVIEW Data Acquisition Basics Manual 19 8 National Instruments Corporation Chapter 19 Common SCX Applications to switch one of its 16 channels Because the SCXI 1122 uses a relay this module imposes a minimum interchannel delay of 10 ms However scanning multiple SCXI 1122 channels many different times can quickly wear out the relay To avoid this acquire data from the SCXI 1122 module a single channel at a time For further information refer to the SCXI 1122 User Manual or the SCXI 1122 Voltage exampl
103. Q SCXI Configuration Window on the Macintosh innin anaia alates ec ave a ee 2 26 SCXI Configuration Window in NI DAQ occ eeeeseeseeeeeneeees 2 26 Accessing the Data Acquisition Palette eee ee eeeeeeeseeereeeeeenees 3 3 Data Acquisition Palette Description 0 eee ee ceeeseeeeeereeseeenees 3 4 Analog Input VI Palette Organization 0 eee ee ee eeeeceeeereeseeenees 3 5 LabVIEW Help Window Conventions for the Al Single VI 3 7 The Error In Input and Error Out Output Error Clusters in ab VIEW are avis ened ida battle Sav ies 3 9 Limit Settings Case F sects cesta ccseetvensssgesientystssyseeusietecectuisesveutees cd 3 12 Limit Settings Cas Zi a eesti ten ee AeA ais 3 13 Example of a Basic 2D Array occ eeeeceeeeeseeseeeseceeeeseseeeeaeeeeeeaeeeens 3 14 2D Array in Row Major Order oo eee seeceseeseeeseeeeeeseeseeeaeeeeens 3 15 2D Array in Column Major Order eee eee eseeseeseeeeeeeeseeeseesseens 3 15 Extracting a Single Channel from a Column Major 2D Array 3 16 Analog Output Buffer 2D Array occ eee ec eeeeseceeceeeeeeeeseeeeeeseeeeees 3 16 Dypes Of Analog Sigttal scivecicosceccenvonesossntesiesunsserens aaea 5 1 Grounded Signal Sources oo eee ec eeeeseeseceeesseceseeseeeseeseeeaeeseeeaeeeeens 5 2 Floating Signal SOUrCES tea aeeoa en e r a a EE E E RA 5 3 LabVIEW Data Acquisition Basics Manual xii National Instruments Corporation Table of Contents Figure 5 4 The Effects of Resolution on ADC Precision 00
104. RE A EO E E 3 8 Channel Port and Counter Addressing sesesseseesesesesseeeeessssressersrestessessesstessesseessesese 3 9 Limit Setting S eeh E A A A N R E 3 11 Data Organization for Analog Applications essseeseseesessssesseerseestesrsrrsresesresreersresresenes 3 14 Chapter 4 Where You Should Go Next Questions You Should Answer cccesccsscccssceescecseeeseecsaeesseecsaeeeeecsaeesseeceaeesseeenaeenses 4 3 Part 2 Catching the Wave with Analog Input Chapter 5 Things You Should Know about Analog Input Defining Your Sisal yenne Sve seostis intend os Aosta lute esrateetete a nid autin gegen 5 1 To What Is Your Signal Referenced oo eee cece ceeeseeeseteeeeseeseeeseeeeens 5 2 Grounded Signal Sources eee eeceseeeeeseceeeeseseeeeseeseeeseseeetaeeesees 5 2 Floating Signal Sources oo ee eee eseceeeeseeeeeeseeeseeseceeeeaeeneeeaeenaes 5 3 Choosing Your Measurement System ccc ecseseeescnseecsesssssessesseseessessensesseseeas 5 3 Resolution einna a a wine te ei ea inna sete Ak 5 3 Device Voltage Range iss orrien eer desuececetocers su scaceeeses aret EEEa VAERE AEE Ee 5 4 Signal Voltage Range Limit Settings 0 eee eeeesecseeneeeseeeeeseeeenaes 5 5 Considerations for Selecting Analog Input Settings cece eeeeneeeeeeeeeeeeee 5 6 Differential Measurement System oe ec ee eee ceeceeceeeeseeeseseeeseeseeeaeeeeeas 5 9 Referenced Single Ended Measurement System 00 0 eeeeseeetseeeeeeees 5 10 LabVIEW Data Acquis
105. Square Pulse or Pulse Trains the GATE input pin Instead of having an internal timebase as your SOURCE you can connect an external signal counter Source out gate Your Your device device Figure 22 6 Physical Connections for Generating a Square Pulse Besides generating continuous pulse trains the How to Generate Pulses and Pulse Trains example VI configures counters to generate retriggerable pulse trains which behave like one shots Figure 22 7 shows how to generate a continuous pulse train using the Easy Counter VI Generate Pulse Train This VI requires you to specify the frequency and the duty cycle inputs The number of pulses parameter defaults to 0 for the generation of a continuous pulse train device counter number of pulses cont Figure 22 7 Generating a Continuous Pulse Train with the Generate Pulse Train VI If you are generating a pulse train and you want more control over when the counter actually begins the operation use the Intermediate LabVIEW Data Acquisition Basics Manual 22 6 National Instruments Corporation Chapter 22 Generating A Square Pulse or Pulse Trains VIs instead of the Easy VIs Figure 22 8 demonstrates how to generate a simple pulse train using Intermediate level VIs device counter Figure 22 8 Generating a Continuous Pulse Train Using Intermediate VIs The Continuous Pulse Generator Config VI configures the counter for the operation and the Counter Start VI
106. T devices cabled to your MIO device If you have an SC 2043 SG device cabled you can click on the Configure Accessory button and select gains on a per channel basis LabVIEW uses these settings when initializing the devices instead of the default settings listed in the descriptions of the hardware configuration VIs You can use the hardware configuration VIs to override any settings already recorded by WOAQCONF EXE Some DAQ devices such as the Lab PC AT MIO 16 and AT MIO 16D require hardware jumper changes in addition to software configuration Consult the hardware reference manual for your device for more information National Instruments Corporation 2 13 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware You can use the Test menu in the Device Number window to verify the configuration or perform single point analog input or output operation a digital input or output to specified port or grouping of digital channels and or counter measurements When you select Test Analog I O a Test window appears as shown in the following figure Device Numbert f Configuration Device DMA IRQ Test Hardware Help Device AT MIO 16F 5 Analog I0 Tests for AT MIO 16F 5 Analog Input Analog Output Channel Voltage The errors returned by the Test window are NI DAQ status codes not LabVIEW status codes Y
107. Utility Window cquisition Hardware Device name AT MIO 16F 5 The Select a Device Number box to the left of the window shows all the available device numbers you can use to configure your device Initially all the boxes next to the device numbers read have DAQ devices in your system that are already config show up in the Select a Device Number box When you Empty If you ured they will highlight a particular device number the settings for that device appear in the Device Selected area to the right To configure your device highlight the device in the Select a Device Number box and click on the Configure Test Device n button n is the number of the device you National Instruments Corporation 2 7 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware have selected Figure 2 5 shows the Device Number n window that should appear Device Number 1 Configuration Device DMA IRQ Test Hardware Help Device Base address DMA IRQ AT MIO 16F 5 hex 220 6 7 11 On Off Figure 2 5 Device Number V Window Select your device type from the Devices menu If you are using an AT MIO 16 AT MIO 16D or AT MIO 16DE 10 device be sure to select the correct device subtype If your base address DMA or IRQ settings have changed from the factory defaults select the correct settings Select the base address by clicking the dip switch box until the switch positions
108. VI located in examples daq run_me 11b This example demonstrates how to set up your acquisition for an externally controlled channel National Instruments Corporation 9 3 LabVIEW Data Acquisition Basics Manual Chapter 9 Letting an Outside Source Control Your Acquisition Rate clock The Getting Started Analog Input VI places acquired data in a buffer For purposes of this discussion the VI was slightly altered and now includes the AI Clock Config VI and the clock source was connected to the I O connector Which Clock Channel Clock Timeout 5 seconds transposed voltage graph device 1 number of scans to acquire 1000 scan rate CO gt disables scan clack Figure 9 4 Getting Started Analog Input Example VI You can enable external conversions by calling the Advanced level AI Clock Config VI Remember that the AI Clock Config VI which is called by the AI Config VI normally sets internal channel delay automatically or manually with the Interchannel Delay control However calling the AI Clock Config VI after the AI Config VI resets the channel clock so that it comes from an external source for external conversion Also notice that the scan clock is still set internally on those devices that have a scan clock If you want round robin scanning for those devices that support both scan and channel clocks change the scan rate to 0 CP Note Dynamic signal acquisition DSA devices like the AT A2150 do not support ext
109. VI found in the examples daq run_me 11b with the channel string ob0 sc1l md1 calgnd to read the grounded amplifier of the module in slot 1 of SCXI chassis 1 The voltage reading should be very close to very close to 0 V The AI Start VI grounds the amplifier before starting the acquisition and the AI Clear VI removes the grounds from the amplifier after the acquisition completes The SCXI 1141 has a separate amplifier for each channel so you must specify the channel number when you ground the amplifier To specify the channel number attach the channel number to the end of the string calgnd For example calgnd2 grounds the amplifier inputs for channel 2 and reads the offset You can also specify a range of channels The string calgnd0 7 grounds the amplifier inputs for channels 0 through 7 and reads the offset for each amplifier Use the Scaling Constant Tuner VI from Functions Data Acquisition Signal Conditioning to modify the scaling constants so that LabVIEW automatically compensates for the amplifier offset when scaling binary data to voltage The SCXI 1100 Voltage example found in examples daq anlogin scxi 11b shows you a way to use the Scaling Constant Tuner VI This section discusses how to measure temperature with the SCXI 1100 and SCXI 112x modules using thermocouples The temperature examples below use both cold junction measurements and amplifier offsets In SCXI analog input examples you cannot set the scaling constants w
110. VI you can control the rate at which samples are taken but you may not be able to designate exactly when your application starts acquiring each set of data If this start up timing is important to your program read the Do You Need To Access Your Data during Acquisition section in this chapter to see how to control acquisition start up times To increase control over your DAQ process use the Intermediate Analog Input VIs AI Config AI Start AI Read and AI Clear as shown in Figure 7 9 LabVIEW Data Acquisition Basics Manual 7 8 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition device 1 Graph Display No of Samples 1000 Figure 7 9 Controlling the Sampling Rate in a Simple Buffered Acquisition Simple Buffered Analog Input with a Write to Spreadsheet File If you want to write the acquired data to a file there are many file formats in which you can store the data The spreadsheet file format is used most often because you can read it using most spreadsheet applications for later data graphing and analysis In LabVIEW you can use VIs to send data to a file in spreadsheet format or read back data from such a file You can locate these VIs in Functions Utility File I O The VI used in this example is the Write to Spreadsheet File VI shown in Figure 7 10 In this exercise the Intermediate analog input VIs acquire an array of data graph the data using the actual sample perio
111. VIEW DAQ palettes are also intermediate level VIs and thus have more hardware functionality and efficiency in developing your application than the Easy VIs Read the previous Intermediate VIs section for more information on how these operate The Advanced VIs are the lowest level interface to the DAQ driver Very few applications require the use of the Advanced VIs Use the Advanced VIs when the Easy or Intermediate VIs do not have the inputs necessary to control an unusual DAQ function Advanced VIs return the greatest amount of status information from the DAQ driver This manual primarily focuses on applications using the Easy or Intermediate VIs VI Parameter Conventions In each LabVIEW DAQ VI front panel or Help window the appearance of the control and indicator labels denote the importance of that parameter Control and indicator names in bold typically must be wired to a node on the block diagram for your application to run Controls and indicators not necessary for your program to operate appear in plain text You rarely need to use the parameters with labels in square brackets Keep in mind that these conventions apply only to the information in the Help window and on the front panel Both this manual and the LabVIEW Data Acquisition VI Reference Manual list all parameter names in bold to distinguish them from other elements of the text The default inputs appear in parentheses to the right of the parameter names Figure 3 4
112. VIs that generate single values or multiple values waveforms to output through analog channels counter 11b contains VIs that count the rising and falling edges of TTL signals generate TTL pulses and measure the frequency and period of TTL signals digital contains VIs that perform immediate digital I O and digital handshaking run_me 1lb contains VIs that perform basic operations concerning analog I O digital I O and counters Each chapter in this manual teaches the basic concepts behind several of the DAQ examples For a brief description of any example open the example VI and choose Windows Show VI Info for a text description of the example You can also choose Help Show Help to open the Help window When the Help window is open you can put your cursor over any front panel or block diagram item and see a description of that item in the window Locating the Data Acquisition Vis in LabVIEW You can find the Data Acquisition VIs in the Functions palette from your block diagram in LabVIEW When you put your cursor over each of the icons in the Functions palette LabVIEW displays the palette name you are about to access at the top of the Functions palette You LabVIEW Data Acquisition Basics Manual 3 2 National Instruments Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts can find the Data Acquisition icon near the bottom of the Functions palette as shown in Figure 3 1 O Functions Data Acquisition D
113. X device or an MIO E series device you should calibrate your DAQ device first using either the MIO Calibrate VI or E Series Calibrate VI 1 Al CONFIG Cl 2 3 Al 4 5 5CAH wa National Instruments Corporation Make sure you set the SCXI gain to the gain you want to use in your application If your modules have gain jumpers or DIP switches they must be set appropriately Refer to your SCXI module user manual for jumper or switch setting information If your modules have software programmable gain use the input limits parameter in the AI Config VI to set gain Program the module for a single channel operation by using the AI Config VI with the channel that you are calibrating as the channels parameter in the VI Ground your SCXI input channel to determine the binary zero offset You should ground inputs because offset can vary at different voltage levels due to gain error If you are using an SCXI 1100 or SCXI 1122 you can ground your input channels without external hookups by substituting the channel string with calgnd as the channel number For other modules you need to wire the positive and negative channel inputs together at the terminal block and wire them to the chassis ground Use the AI Single Scan VI to take several readings and average them for greater accuracy Set the DAQ device gain settings to match the settings you plan to use in your application If you are using an AT MIO 16F 5 AT MIO 64F 5 or AT MIO 1
114. XI 1140 AT MIO 16F 5 DIO 24 SCXI 1141 AT MIO 16X SCXI 1160 AT MIO 16XE 50 SCXI 1161 AT MIO 64E 3 SCXI 1162 AT MIO 64F 5 SCXI 1162HV SCXI 1163 SCXI 1163R SCXI 12007 LabVIEW for Windows NT does not work with the SCXI 1 102 SCXI 1122 SCXI 1124 SCXI 1141 SCXI 1162HV SCXI 1163R SCXI 1200 DAQPad 1200 PC AO 2DC PCMCIA cards E Series devices SC 2040 SC 2042 RTD SC 2043 SG and PC OPDIO 16 2The SCXI 1200 DAQPad MIO 16XE 50 and DAQPad 1200 do not work with NEC PC 9800 Series computers LabVIEW Data Acquisition Basics Manual 2 4 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware Table 2 2 LabVIEW DAQ Hardware Support for Macintosh Plug In Devices External SCXI Modules Devices DAQCard 500 NB DIO 32F NB AO 6 AMUX 64T SCXI 1000 SCXI 1140 DAQCard 700 NB DIO 96 NB A2150 SC 2040 SCXI 1001 SCXI 1141 DAQCard 1200 NB DMA 8 G NB A2100 SC 2042 RTD SCXI 1100 SCXI 1160 DAQCard DIO 24 NB DMA2800 NB A2000 SC 2043 SG SCXI 1102 SCXI 1161 DAQCard AO 2DC NB MIO 16 PCI 1200 SCXI 1120 SCXI 1162 Lab LC NB MIO 16X PCI DIO 96 SCXI 1121 SCXI 1162HV Lab NB NB TIO 10 PCI MIO 16XE 50 SCXI 1122 SCXI 1163 NB DIO 24 SCXI 1124 SCXI 1163R If you have any other questions regarding hardware support for LabVIEW refer to Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual Installing Your National Instr
115. a 32 bit counter on the Am9513 chip The Am9513 chip has a set of five counters numbered 1 5 that can be connected in a circular fashion For example the next higher counter to counter is counter 2 called counter 1 and the next lower counter is counter 5 called counter 1 The TIO 10 device contains two Am9513 chips so the device has 10 counters two sets of five counters which can be accessed in a circular fashion Table 25 1 identifies the adjacent counters for the Am9513 one and two chips Note You cannot cascade counters with devices that have the DAQ STC chip Table 25 1 Adjacent Counters for Counter Chips Device Next Lower Counter Next Higher Type Counter Counter 5 1 2 1 2 3 2 3 4 3 4 5 4 5 1 S 5 10 6 7 6 7 8 7 8 9 8 9 10 9 10 6 LabVIEW Data Acquisition Basics Manual 25 2 National Instruments Corporation Chapter 25 Counting Signal Highs and Lows For more information on adjacent counters refer to the Adjacent Counters VI description in Chapter 18 Intermediate Counter VIs of the LabVIEW Data Acquisition VI Reference Manual Counting Events or Elapsed Time In order to count events or elapsed time you can use Easy I O and Intermediate VIs You should only use the Advanced VIs if the Easy I O and Intermediate VIs do not satisfy your needs One example in LabVIEW that uses the Advanced VIs is the How To Count VI found in examples daq counter 11b In the discu
116. a buffer that is at least twice as large as the number of scans updates you want to read at a time You can have an internal or external handshake source If your handshake source is internal remember to specify the rate at which you read values with the clock frequency Scan backlog specifies how many values are left in the buffer after you read The number read parameter indicates the total National Instruments Corporation 15 9 LabVIEW Data Acquisition Basics Manual Chapter 15 Shaking Hands with a Digital Partner number of values that have been read from the buffer because the VI started executing number of scans updates buffer size number read number of ecarns updates Figure 15 9 Digital Handshaking Using a Circular Buffer Digital handshaking whether non buffered or buffered inputs or outputs digital patterns only after your computer receives a digital pulse Not all DAQ devices support digital handshaking The DIO 32F devices have internal as well as external handshaking signals and support circular buffered I O Other DAQ devices that support handshaking accept only external handshaking signals You should use digital handshaking when you need to generate or retrieve a digital pattern after a digital event or pulse is detected LabVIEW Data Acquisition Basics Manual 15 10 National Instruments Corporation SCXiI Getting Your Signals in Great Condition This section contains basic inform
117. a step voltage to your data acquisition DAQ device after the heating process completes If you have no way to begin measuring data immediately after your device receives the step voltage then you must acquire more points some before the step voltage and some after it in order to capture the data you need As you can see this solution is an inefficient use of computer memory and disk space because you must allocate and use more than is necessary Sometimes the data you need may be closer to the front of the buffer and other times it may be closer to the end of the buffer However there is a way to start an acquisition based on the condition or state of an analog or digital signal This technique is commonly called triggering Generally a trigger is any event that causes or starts some form of data capture There are two basic types of triggering hardware and software triggering In LabVIEW you can use software triggering to start acquisitions or use it with an external device to perform hardware triggering Hardware Triggering Hardware triggering lets you set the start time of an acquisition and gather data at a known position in time relative to a trigger signal External devices produce hardware trigger signals In LabVIEW you specify the triggering conditions that must be reached before acquisition begins Once the conditions are met the acquisition begins immediately You can also analyze the data before trigger There are tw
118. acintosh 2 16 Installing and Configuring Your DAQ Device in Unix 0 eee 2 18 Installing NI DAQ Software in Unix oo eeeeeeeeeeeeteeeeaees 2 19 Configuring Your DAQ Device in UNIX wo eeeeeeeeeeeeee 2 19 Installing and Configuring Your SCXI Chassis in Windows or on the Macintoshien ai aE E R E E Geiveics EE EE 2 20 National Instruments Corporation v LabVIEW Data Acquisition Basics Manual Table of Contents Hardware Configuration 0 0 ccc eececseesseesecsceeseceseeseeeseeeenseeseenaes 2 20 Software Configuration in Windows 0 0 0 ceeeceseeeeseeeeeseeeeeeeeeesees 2 22 Software Configuration on the Macintosh 00 eee eee eeeeeees 2 25 Chapter 3 Basic LabVIEW Data Acquisition Concepts Location of Common DAQ Examples o e ccc eececcesseeeeseseeeceeeeseeseeesesseeesesseeeaeeseeens 3 1 Locating the Data Acquisition VIs in LabVIEW ooo eee cece eseeseeseeeseeneeeeeeseenaeees 3 2 DAQ Vi Organization iiss sel atest ciate neil Ae hae ae yA eS Lake 3 4 Easy VIS eroe e eaea E EE N E see E E EE E E 3 5 Intermediate VIS sirare e EEE E E E iia 3 5 UUNI S heene enne ss tox E EEEE E E AO 3 6 Advanced VIs ceco neh alee hate ieee e TE EEEN EEEE oE E Ea RS 3 6 VI Parameter Conventions sessioner eren r repie Panes eae iE ass 3 6 Default and Current Value Conventions ssssosseesesesssessssesseersetessresssresssresseressresseressee 3 7 Common DAQ VI Parameters sorcerien ais p iE ae i Eais 3 7 Error Hand ang eoa ae a a
119. ack of the SCXI 1200 and connect the other end of the cable to the parallel port on your PC Turn on your chassis power 2 21 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware Software Configuration in Windows To use SCXI with LabVIEW you must enter the configuration for each SCXI chassis using WOAQCONF Click on the SCXI menu in the WI DAQCONF to bring up the SCXI Configuration window shown in Figure 2 11 SCXI Configuration ia Chassis ID Chassis Type scxI 1001 Chassis Address O Communication Mode Serial using DIO port B Communication Path Dev 1 AT MIO 16F 5 lot Configuratio Chassis Slot Configure Module 1 Figure 2 11 SCXI Configuration Window in WDAQCONF Leave the Chassis ID set to 1 if you have only one chassis Use this number to access the SCXI chassis from your application If you have multiple chassis advance the Chassis ID to the next chassis every time you finish configuring a chassis Select the appropriate Chassis Type for your chassis This enables the remaining fields on the panel The Chassis Address field applies only to the SCXI 1001 chassis If you have only one chassis leave this field and the address jumpers on your SCXI 1001 set to 0 If you have additional chassis you need to select a unique hardware jumpered address for each chassis and enter it in the Chassis Address field LabVIEW Data
120. ad search position pointer traverses the buffer until it finds the scan location where the data has met the retrieval conditions Offset indicates the scan location from which the VI begins reading data relative to the read search position A negative offset indicates that you need pretrigger data data prior to the retrieval conditions If offset is LabVIEW Data Acquisition Basics Manual 8 10 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers greater than 0 you should need posttrigger data data after retrieval conditions Signal Checked for i 7 a External Trigger Conditions DAQ Device Device Rest of Data When trigger conditions are met read search position When Offset 0 Scan Scan 3 4 xX Start reading data When Offset lt 0 read search position Scan Scan Scan Scan 1 2 3 4 Offset Start reading data When Offset gt 0 read search position Scan Scan Scan Scan 1 2 3 4 Offset x Start reading data Figure 8 7 Timeline of Conditional Retrieval National Instruments Corporation 8 11 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers The conditional retrieval cluster of the AI Read VI specifies the analog signal conditions of retrieval as shown in Figure 8 8 cond
121. al Data Capture Initiated Figure 8 1 Diagram of a Digital Trigger Figure 8 2 shows a timeline of how digital triggering works for post triggered data acquisition In this example an external device sends a trigger or TTL signal to your DAQ device As soon as your DAQ LabVIEW Data Acquisition Basics Manual 8 2 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers device receives the signal and your trigger conditions are met your device begins taking data External Digital Trigger DAQ Device Device Signal DAQ Device continues checking signal until digital trigger conditions are met Then External Analog Data DAG Device nas Figure 8 2 Digital Triggering with Your DAQ Device Digital Triggering Examples A common example of digital triggering in Lab VIEW is the Acquire N Scans DTrig VI found in examples daq anlogin anlogin 11b This VI as shown Figure 8 3 uses the AI Waveform Scan VI to perform a buffered acquisition where LabVIEW stores data in a memory buffer during acquisition After the acquisition completes the National Instruments Corporation 8 3 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers VI retrieves all the data from the memory buffer and displays it Figure 8 3 shows the block diagram of this example VI time limit 5 sec pone e
122. al 24 2 National Instruments Corporation Chapter 24 Measuring Frequency and Period frequency you should wire the signal to be measured to the GATE input pin and a timebase of known frequency to the SOURCE input pin counter Source your device Figure 24 3 Physical Connections for Period Measurement of Low Frequency Signals For high frequency signals you have a greater potential for a larger counting range Counters are cascaded together to increase the counting range as shown in Figure 24 4 Here counter 1 creates a gating pulse for an even counter counter and for increased resolution you can concatenate an additional counter counter 1 counter counter 1 counter 1 32 bit Figure 24 4 Physical Connections for Period Measurement of High Frequency Signals ce Note You cannot cascade counters together with devices that use the DAQ STC chip Refer to Chapter 25 Counting Signal Highs and Lows for further information regarding adjacent counters A LabVIEW example that measures the frequency and period of high and low frequency signals is the How to Measure Frequency and Period VI located in examples daq counter 11b Refer to this example as you read the following sections National Instruments Corporation 24 3 LabVIEW Data Acquisition Basics Manual Chapter 24 Measuring Frequency and Period Measuring the Frequency and Period of Low Frequency Signals For low frequency signals you can use
123. all of the different types of analog output signals e Chapter 11 One Stop Single Point Generation shows you which VIs to use in LabVIEW to perform single point updates e Chapter 12 Buffering Your Way through Waveform Generation shows you which VIs to use in LabVIEW to perform buffered analog updates Things You Should Know about Analog Output Some measuring systems require that analog signals be generated by a data acquisition DAQ device This analog signal can be a steady or slowly changing voltage or a continuously changing waveform The next few sections show you how to use LabVIEW to produce all of these different types of signals First you should learn about the various situations in which you might need to produce an analog signal Single Point Output When the voltage level at the output is more important than the rate at which the output voltage changes you need to generate a steady DC voltage You can use the single point analog output VIs to produce this type of output Any time you want to change the voltage on an analog output channel you must call one of the VIs that produces a single update a single voltage change Therefore you can change the output voltage only as fast as LabVIEW calls the VIs This technique is called software timing You should use software timing if you do not need high speed generation or very accurate timing Refer to Chapter 11 One Stop Single Point Generation for more inf
124. ange limit settings 5 5 to 5 6 types of analog signals figure 5 1 analog input with LabVIEW See AMUX 64T devices Analog IO Control Loop VI 6 6 to 6 7 Analog IO Control Loop hw timed VI 6 8 analog multiplexers AMUX 5 9 See also AMUX 64T devices analog output buffered analog output overview 10 1 to 10 2 waveform generation 12 1 to 12 3 circular buffered output 12 3 to 12 5 multiple immediate updates 11 2 to 11 3 SCXI analog output application example 19 14 to 19 15 single immediate updates 11 1 to 11 2 single point output 10 1 analog output SCXI modules 17 4 analog to digital converter ADC See ADC analog triggering description 8 6 to 8 7 examples 8 7 to 8 10 anlogin DAQ example file 3 1 anlog_io llb DAQ example file 3 1 anlogout llb DAQ example file 3 2 AO Clear VI circular buffered output 12 4 to 12 5 waveform generation 12 3 LabVIEW Data Acquisition Basics Manual Index AO Config VI analog output SCXI example 19 14 circular buffered output 12 4 to 12 5 waveform generation 12 3 AO Continuous Gen VI 12 3 to 12 4 AO Generate Waveforms VI 12 1 to 12 2 AO Group Config VI 19 14 AO Hardware Config VI 19 14 AO Single Update VI analog output SCXI example 19 15 calibrating SCXI modules for signal generation 20 8 AO Start VI circular buffered output 12 4 to 12 5 waveform generation 12 3 AO Update Channels VI 11 1 AO Wait VI 12 3 AO Waveform Gen VI 12 2 AO Write One Update
125. anning support for example the AT MIO 16F 5 this clock gates the channel clock on and off On boards with simultaneous sampling for example the EISA A2000 this clock clocks the track and hold circuitry The number of times or scans per second that LabVIEW acquires data from channels For example at a scan rate of 10Hz LabVIEW samples each channel in a group 10 times per second The number of channels in the channel list or number of ports in the port list you use to configure an analog or digital input group Signal Conditioning eXtensions for Instrumentation The National Instruments product line for conditional low level signals within an external chassis near sensors so only high level signals in a noisy environment are sent to data acquisition boards Seconds The amount of time required for a voltage to reach its final value within specified limits The manipulation of signals to prepare them for digitizing Performing frequency division on an external signal G 13 LabVIEW Data Acquisition Basics Manual Glossary simple buffered I O single ended inputs software trigger software triggering SOURCE input pin STC strain gauge subVI switchless device syntax LabVIEW Data Acquisition Basics Manual Input output operation that uses a single memory buffer big enough for all of your data LabVIEW transfers data into or out of this buffer at the specified rate beginning at the start of the buff
126. aphing simple buffered analog input example 7 6 to 7 7 grounded signal sources 5 2 H handshaking latched digital I O 15 1 to 15 10 buffered handshaking 15 6 to 15 10 circular buffered examples 15 9 to 15 10 simple buffered examples 15 7 to 15 9 connecting signal lines digital input figure 15 3 digital output figure 15 4 DAQ devices supporting digital handshaking 15 1 grouping ports for DIO 32F devices note 15 4 non buffered handshaking 15 5 to 15 6 overview 15 1 to 15 2 sending out multiple digital values 15 2 to 15 5 hardware See also installation and configuration debugging connection errors 27 1 LabVIEW data acquisition hardware support Macintosh systems table 2 5 Windows environment table 2 4 relationship between LabVIEW NI DAQ and DAQ hardware figure 2 3 hardware timed analog input output control loops 6 7 to 6 9 hardware triggering 8 1 to 8 10 analog description 8 6 to 8 7 examples 8 7 to 8 10 digital description 8 2 to 8 3 examples 8 3 to 8 6 overview 8 1 LabVIEW Data Acquisition Basics Manual Index How to Count VI 25 3 How to Generate Pulses and Pulse Trains VI dividing frequencies 26 1 generating pulse train 22 5 to 22 6 generating single square pulse 22 3 How to Measure Frequency and period VI 24 3 IBF Input Buffer Full line 15 2 immediate digital I O 14 1 to 14 3 immediate updates multiple 11 2 to 11 3 single 11 1 to 11 2 initialization of data
127. are using SCXI 1102 or SCXI 1122 inputs you can save the constants in the module user area in EEPROM Store constants in the user area as you are calibrating and then use SCXI Cal Constants VI again at the end of your calibration sequence to copy the calibration table in the user area to the default load area in EEPROM Remember that constants that are stored in the default load area can be overwritten If you want to use a set of constants later you should keep a copy of the constants stored in the user area in EEPROM Note If you are storing calibration constants in the SCXI 1102 or SCXI 1122 EEPROM your binary offset and gain adjust factors must not exceed the ranges given in the respective module user manuals For other analog input modules you must store the constants in the memory Unfortunately calibration constants stored in the memory are lost at the end of a program session You can solve this problem by creating a file and saving the calibration constants to this file You can load them again in subsequent application runs by passing them into the SCXI Cal Constants or the Scale Constant Tuner VIs Repeat the above procedure for any additional channel or gain settings you want to calibrate Calibrating SCX Modules for Signal Generation When you output a voltage or current value to your SCX analog output module LabVIEW uses the calibration constants loaded for the given module channel and output range to scale the voltage o
128. arentheses to the right of the parameter names A default setting is a parameter value recorded in the driver The current setting is the value of a control at any given moment The default setting of a control becomes the current setting and remains so until you change the value of the control In many cases a control input defaults to a certain value most often 0 which means you can use the current setting For example the default input for a parameter may be do not change the current setting and the current setting may be no AMUX 64T boards If you change the value of such a parameter the new value becomes the current setting Common DAQ VI Parameters The device input on analog I O digital I O and counter VIs specifies the number assigned to your DAQ device in the DAQ configuration software Your software assigns a unique number to each DAQ device National Instruments Corporation 3 7 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts The device parameter usually appears as an input to the configuration VIs Another common configuration VI output task ID assigns your specific I O operation and device a unique number that identifies it throughout your program flow The task ID can also contain group information about the channels and gain used in your operation For basic tests and calibrations you can wire the device parameter into the task ID Some DAQ VIs perform either the devic
129. as shown below Cluster to array to number conversion The port number is a string expressed in the SCX MOY 0 format where you are trying to output from the digital output module on slot y of chassis x The last identifier is always port 0 because the whole module is considered one port The port width should be the number of lines on your SCXI module if you are operating in multiplexed mode The SCXI 1160 has 16 relays the SCXI 1161 has 8 relays and the SCXI 1163 1163R have 32 relays You can do not use the SCXI 1160 or SCXI 1161 in parallel mode For the SCXI 1163 1163R the port width in parallel mode should be the number of lines on your DAQ device or SCXI 1200 module The DIO 32F device can access all 32 lines of the SCXI 1163 1163R modules at once by using the SCXI 1348 cable assembly The DIO 24 and the DIO 96 devices can only access the first 24 lines of the SCXI 1163 1163R when configured in parallel mode For the fastest performance in parallel mode you can use the appropriate onboard port numbers instead of the SCXI channel string syntax Use the iteration input to optimize your digital operation When iteration is 0 default LabVIEW calls the DIO Port Config VI an Advanced VI to configure the port If iteration is greater than zero LabVIEW bypasses reconfiguration and remembers the last configuration which improves performance You can wire this National Instruments Corporation 19 17 LabVIEW Data Acquisition Basics Man
130. asics concepts on using analog input with LabVIEW Chapter 6 One Stop Single Point Acquisition shows you how to acquire one data point from a single channel and then one data point from each of several channels using Lab VIEW and explains how software timing and or hardware timing affects the performance of analog I O Chapter 7 Buffering Your Way through Waveform Acquisition reviews the different methods of reading multiple channels and explains how LabVIEW stores the acquired data with each method Chapter 8 Controlling Your Acquisition with Triggers explains how to set your analog acquisition to occur at a certain time using either software or hardware triggering methods Chapter 9 Letting an Outside Source Control Your Acquisition Rate shows you how to control your data acquisition rate by some other external source in your system Things You Should Know about Analog Input Hunting has been a part of man s survival from the beginning of time People used to hunt for the things they needed to survive like food and water Today engineers and scientists use data acquisition to hunt down the information they need to survive in the information age This chapter focuses on defining the tools you need to be a successful hunter in the world of data acquisition Defining Your Signal Analog Signal DC You and your friends plan a hunting trip for this weekend What do you plan to bring with you This questio
131. ation and configuration National Instruments Corporation Index Cont Acq to File scaled vi 7 15 Cont Acq to Spreadsheet File vi 7 15 Cont Acq amp Chart buffered vi 7 14 Cont Acq amp Graph buffered vi 7 15 Cont Acquire amp Chart immediate vi 6 4 to 6 5 continuous acquisition from multiple channels 7 11 to 7 13 Continuous Generation example VI 12 4 Continuous Pulse Generator Config VI 22 6 22 8 control loops See analog input output control loops Convert RTD Reading VI 19 10 to 19 11 Convert Strain Gauge Reading VI 19 13 to 19 14 Convert Thermocouple Reading VI 19 6 to 19 7 Count Events or Time VI 25 3 to 25 5 counter addressing for VIs 3 9 to 3 11 Counter Read VI 25 6 to 25 7 controlling pulse width measurement 23 3 measuring frequency and period high frequency signals 24 6 low frequency signals 24 4 to 24 5 Counter Start VI 25 6 to 25 7 controlling pulse width measurement 23 3 dividing frequencies 26 1 to 26 2 finite pulse train generation 22 8 measuring frequency and period high frequency signals 24 6 low frequency signals 24 4 to 24 5 single square pulse generation 22 4 Counter Stop VI controlling pulse width measurement 23 3 counting external events 25 6 to 25 7 dividing frequencies 26 1 to 26 2 measuring frequency and period high frequency signals 24 6 low frequency signals 24 4 to 24 5 LabVIEW Data Acquisition Basics Manual Index stopping counter generations 22 9 coun
132. ation on setting up and using SCXI modules with your data acquisition application special programming considerations common SCXI applications and calibration information Part 5 SCXI Getting Your Signals in Great Condition contains the following chapters Chapter 16 Things You Should Know about SCXT includes basic concepts on how to use SCXI modules with LabVIEW for data acquisition Chapter 17 Hardware and Software Setup for Your SCXI System explains how to set up your SCXI hardware to work with data acquisition in LabVIEW Chapter 18 Special Programming Considerations for SCXI discusses special programming considerations for SCXI in LabVIEW which include channel addressing gains limit settings and settling time Chapter 19 Common SCXI Applications cover example VIs for analog input analog output and digital SCXI module Chapter 20 SCXI Calibration Increasing Signal Measurement Precision teaches you how to calibrate SCXI modules and shows you where LabVIEW stores your calibration constants Things You Should Know about SCXI Signal Conditioning eXtensions for Instrumentation SCXI is a highly expandable signal conditioning system In the next few chapters you will learn the basic concepts of signal conditioning the setup procedure for SCXI hardware the hardware operating modes the procedure for software installation and configuration the special programming considerations for SCXI in LabV
133. ation retrieval system or translating in whole or in part without the prior written consent of National Instruments Corporation DAQ STC LabVIEW NI DAQ National Instruments and RTSI are trademarks of National Instruments Corporation Product and company names listed are trademarks or trade names of their respective companies WARNING REGARDING MEDICAL AND CLINICAL USE OF NATIONAL INSTRUMENTS PRODUCTS National Instruments products are not designed with components and testing intended to ensure a level of reliability suitable for use in treatment and diagnosis of humans Applications of National Instruments products involving medical or clinical treatment can create a potential for accidental injury caused by product failure or by errors on the part of the user or application designer Any use or application of National Instruments products for or involving medical or clinical treatment must be performed by properly trained and qualified medical personnel and all traditional medical safeguards equipment and procedures that are appropriate in the particular situation to prevent serious injury or death should always continue to be used when National Instruments products are being used National Instruments products are NOT intended to be a substitute for any form of established process procedure or equipment used to monitor or safeguard human health and safety in medical or clinical treatment About This Manual Organi
134. bVIEW Data Acquisition Basics Manual xviii National Instruments Corporation About This Manual AT MIO 16 AT MIO 16F 5 AT MIO 16X AT MIO 16D AT MIO 64F 5 in Windows bold Bold text denotes menus menu items or dialog box buttons or options In addition bold text denotes VI input and output parameters In the Help window pictures of VI inputs and outputs boldfaced parameters are parameters whose values you must specify bold italic Bold italic text denotes a note caution or warning configuration utility Configuration utility refers to NI DAQ on the Macintosh WOAQCONF EXE in Windows and daqconf on the Sun driver Driver refers to the NI DAQ data acquisition device driver DIO devices DIO devices refer to all devices with the letters DIO in their name unless otherwise noted italic Italic text denotes emphasis a cross reference or an introduction to a key concept monospace Text in this font denotes text or characters that you should enter literally using the keyboard Sections of code programming and syntax examples and the proper names of files also appear in this font Warning This icon to the left of bold italicized text denotes a warning which alerts s7 you to the possibility of damage to you or your equipment Wy Caution This icon to the left of bold italicized text denotes a caution which alerts you to the possibility of data loss or a system crash gt Note This icon to the left of
135. bVIEW will take the samples From this information LabVIEW allocates a buffer in memory to hold a number of data points equal to the number of samples per channel multiplied by the number of channels As the data acquisition continues the buffer fills with the data however the data may not actually be accessible until LabVIEW acquires all the samples N Once the data acquisition is complete the data that is in the buffer can be analyzed stored to disk or displayed to the screen by your VI Acquiring a Single Waveform You can acquire a waveform from a single channel by using the AI Acquire Waveform VI shown in Figure 7 2 You can find this VI in Functions DAQ Analog Input Because AI Acquire Waveform is an Easy Analog Input VI it has the minimal number of inputs needed to acquire a waveform from a single channel These minimal inputs are the device channel string number of samples from the channel and the sample rate You can programmatically set the gain by setting the high limit and the low limit Using only the minimal set of inputs makes programming the VI less problematic but the VI lacks more advanced capabilities such as triggering Built in error handling is another LabVIEW Data Acquisition Basics Manual 7 2 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition useful feature of the Easy VIs If an error occurs the program stops running and notifies you with a dialog box explaini
136. begins the actual generation at the update rate The AO Write VI in the while loop writes new data to the buffer until you LabVIEW Data Acquisition Basics Manual 12 4 National Instruments Corporation Chapter 12 Buffering Your Way through Waveform Generation press the stop button Then the AO Clear VI unconfigures the analog channels new woltages Figure 12 5 Circular Buffered Waveform Generation Using Intermediate VIs The Function Generator VI located in examples daq anlogout 11b is amore advanced example of Figure 12 5 This VI changes the output waveform on the fly responding to changing signal types i e sine square amplitude offset update rate and phase settings on the front panel Eliminating Errors from Your Circular Buffered Application If you get an underflow error error number 10843 while performing circular buffered output it means your program could not write data fast enough to the buffer to output the data at the update rate To solve this problem decrease the speed of the update rate If adjusting the update rate does not get rid of the error in your application increase the buffer size National Instruments Corporation 12 5 LabVIEW Data Acquisition Basics Manual Getting Square with Digital 1 0 This section describes basic concepts on how to use digital signals with data acquisition in LabVIEW including immediate and handshaked digital I O Part 4 Getting Square with
137. bin scanning Figure 9 2 shows an example of round robin scanning channel interval Figure 9 2 Round Robin Scanning Using the Channel Clock The devices that always perform round robin scanning include NB MIO 16 PC LPM 16 DAQCard 500 DAQCard 700 Lab NB Lab SE and Lab LC With no scan clock the channel clock is used to switch between each channel at an equal interval The same delay exists between all channel samples as well as between the last channel of a scan and the first channel in the next scan For boards with scan and channel clocks round robin scanning occurs when you disable the scan clock by setting the scan rate to zero and using the interchannel delay of the AI Config VI to control your acquisition rate Finally remember that LabVIEW is scan clock oriented In other words when you select a scan rate LabVIEW automatically selects the channel clock rate for you LabVIEW selects the fastest channel clock rate that allows adequate settling time for the Analog to Digital Converter ADC LabVIEW adds an extra 10 us to the interchannel delay to compensate for any unaccounted factors However LabVIEW does not consider this additional delay for purposes of warnings If you have specified a scan rate that is adequate for acquisition but too fast for LabVIEW to LabVIEW Data Acquisition Basics Manual 9 2 National Instruments Corporation Chapter 9 Letting an Outside Source Control Your Acquisition Rate apply the 1
138. ble gains the Easy I O VIs do not use the gain settings from the configuration utility unless you explicitly set the input limits to 0 volts When you use the input limits to specify non zero voltage limits for a module with programmable gains LabVIEW chooses the most appropriate SCXI gain for the given limits LabVIEW selects the highest SCXI gain possible for the given limits and then selects additional DAQ device gain if necessary If your module has programmable gains and only one gain for all channels and you are using an MIO DAQ device you can specify different input limits for channels on the same module by splitting up your channel range over multiple elements of the channel array and using a different set of input limits for each element LabVIEW selects one module gain suitable for all of the input limits for that module then chooses different MIO gains to achieve the different input limits The last three examples in Table 18 1 illustrates this method The last example shows a channel list with two modules You can open the advanced VI AI Hardware Config to see the gain selection After running this VI the group channel settings cluster National Instruments Corporation 18 3 LabVIEW Data Acquisition Basics Manual Chapter 18 Special Programming Considerations for SCX Table 18 1 SCXI 1100 Channel Arrays Input Limits Arrays and Gains Array SCXI 1100
139. bold italicized text denotes a note which alerts you to important information National Instruments Corporation X X LabVIEW Data Acquisition Basics Manual About This Manual LabVIEW Data Types Each VI description gives a data type picture for each input and output parameter as illustrated in the following table Control Indicator Data Type Signed 8 bit integer Signed 16 bit integer Signed 32 bit integer LEJ Unsigned 8 bit integer Unsigned 16 bit integer Unsigned 32 bit integer Single precision floating point number Double precision floating point number Extended precision floating point number a EB BEE String Boolean Array of signed 32 bit integers He EEE B A BEBEEEE HH EE Cluster File Refnum Abbreviations acronyms metric prefixes mnemonics symbols and terms are listed in the Glossary LabVIEW Data Acquisition Basics Manual XX National Instruments Corporation About This Manual Related Documentation The following documents contain information that you may find helpful as you read this manual e The user manuals for the data acquisition boards you use e LabVIEW Data Acquisition VI Reference Manual e LabVIEW Tutorial e LabVIEW User Manual e LabVIEW Networking Reference Manual e Application Note 025 Field Wiring and Noise Considerations for Analog Signals e Application Note 005 Therm
140. can also perform this function using the four Intermediate Analog Input VIs AI Start AI Read and AI Clear as shown in Figure 7 13 The only adjustment that you must make to these VIs for circular buffered analog input is to set the number of scans to acquire in the AI Start VI to 0 which indicates continuous data acquisition in the AI Start VI The buffer size input of the AI Config VI determines the circular buffer size and the number of scans to read input of the AI Read VI sets the size of the blocks of data to retrieve from the buffer The only differences between this method and the previously discussed method used with the AI Continuous Scan VI is the versatility of having more control over your DAQ processes continuous i number to read at a time a CLEAR i ine buffer size z oe te CS g pg nll f l Config vi Al Stari vi Al Clear Simple al n Error 7 Handler scan rate Figure 7 13 Using Intermediate VIs to Continuously Acquire Time Sampled Data There are two ways that you can read data from the circular buffer using the AI Read VI If you already know the total number of samples you want to acquire you can call the AI Read VI so that after several loops you will have acquired all the desired data If you do not know exactly how much data you want to acquire then set your program up to call the AI Read VI from a continuous loop within your VI and place a stop button on the front panel so that you ca
141. can find the Wait ms VI in Functions Time amp Dialog The previous methods can be used National Instruments Corporation 22 9 LabVIEW Data Acquisition Basics Manual Chapter 22 Generating A Square Pulse or Pulse Trains so that the counter can be used for another operation without resetting the entire board Generate Delayed Pulse vi Waite ma wi Figure 22 12 Using the Generate Delayed Pulse and Stopping the Counting Operation To stop a generated pulse train another Generate Pulse Train VI can be concatenated to the diagram and have the Number of Pulses input set to 1 as shown in Figure 22 13 Humber of Pulses Generate Pulse Train i Generate Delayed Pulse vi Figure 22 13 Stopping a Generated Pulse Train LabVIEW Data Acquisition Basics Manual 22 10 National Instruments Corporation Measuring Pulse Width This chapter describes how you can use a counter to measure pulse width There are several times you may need to determine pulse width For example if you wanted to determine the duration of an event you would want your application to measure the width of a pulse that occurs during that event Another example would be if you wanted to determine the interval between two events In this case you would measure the pulse width between the two events An example of when you might use this type of application is if you wanted to determine the time interval between two boxes on a conveyor belt or t
142. ce 3 is 01020003 The following table shows how the configuration VIs encode the bits of the task ID Bits Purpose 31 through 28 Reserved Function code Reserved Group number Device number The following table gives the function code definitions Function Code T O Operation 1 analog input analog output digital port I O digital group I O counter timer I O Terminal count The highest value of a counter A form of counter signal generation by which the output changes the state of the output signal from high to low or low to high when the counter reaches a certain value G 15 LabVIEW Data Acquisition Basics Manual Glossary top level VI track and hold transducer excitation trigger U unipolar update update rate update width VDC VI Vref LabVIEW Data Acquisition Basics Manual VI at the top of the VI hierarchy This term is used to distinguish the VI from its subVIs A circuit that tracks an analog voltage and holds the value on command A type of signal conditioning that uses external voltages and currents to excite the circuitry of a signal conditioning system into measuring physical phenomena Any event that causes or starts some form of data capture A signal range that is either always positive or negative but never both for example 0 to 10 V not 10 to 10 V One or more analog or digital output samples Typically the number of output samples
143. cquisition DAQ VIs located in the examples daq anlogin anlogin 11b or the Getting Started Analog Input VI found in examples daq run_me 11b to acquire data from the SCXI 1140 module For analog output you will learn how to output voltage or current values using the SCXI 1124 module For digital I O you will learn how to input values on the SCXI 1162 1162HV modules and output values on the SCXI 1160 SCXI 1161 and SCXI 1163 1163R modules Besides looking at the following sections other sources of information are the following application notes and support documents e SCXI Hardware Specific Common Questions e Common Questions about Transducers e Common Questions about Signal Issues National Instruments Corporation 19 1 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications All of these notes can be accessed on the NI FaxBack system or by accessing the BBS World Wide Web or FTP site the numbers for which are located in the front of this manual Analog Input Applications for Measuring Temperature Two common transducers for measuring temperature are thermocouples and RTDs Read the following sections on special measuring considerations needed for each transducer Measuring Temperature with Thermocouples In this section you will learn how to use analog input SCXI modules with thermocouples to measure temperature If you want to measure the temperature of the environment you can use the temp
144. cquisition with an AMUX 64T a counter on the DAQ device switches the DAQ device multiplexers When you connect a single AMUX 64T device to the DAQ device you must scan four AMUX 64T input channels for every DAQ device channel If you attach two AMUX 64T devices to the DAQ device LabVIEW scans eight AMUX 64T channels for every DAQ device input channel For example assume that channels 0 through 3 on AMUX 64T device 1 and channels 0 through 3 on AMUX 64T device 2 are multiplexed together into DAQ device channel 0 In this case LabVIEW scans the first four channels on AMUX 64T device 1 followed by the first four channels on AMUX 64T device 2 If you attach four AMUX 64T devices to the DAQ device LabVIEW scans 16 AMUX 64T channels for every DAQ device input channel For example channels 0 through 3 on AMUX 64T device 1 2 3 and 4 are multiplexed together into DAQ device channel 0 In this case LabVIEW scans the first four channels on device 1 followed by the first four channels on device 2 the first four channels on device 3 and then the first four channels on device 4 The order in which LabVIEW scans channels depends on the channel list you specify in the AI Group Config VI You specify this channel list as an array of DAQ device channel numbers indicating the order in which LabVIEW scans the DAQ device channels When scanning multiple channels list only the device channels not the AMUX 64T channels You only use the AMy x synta
145. csasesschcecedesessestasesvestscaescteocssabeasescesssbivesvesestasceseseseoseseass 12 1 Changing the Waveform during Generation Circular Buffered Output concien ononaria aa A E E 12 3 Eliminating Errors from Your Circular Buffered Application 0 eeeeeeee 12 5 Figure 12 5 Circular Buffered Waveform Generation Using Intermediate VIs 12 5 Part 4 Getting Square with Digital 1 0 Chapter 13 Things You Should Know about Digital 1 0 LabVIEW Data Acquisition Basics Manual viii National Instruments Corporation Table of Contents Chapter 14 When You Need It Now Immediate Digital 1 0 Chapter 15 Shaking Hands with a Digital Partner Sending Out Multiple Digital Values oe eee ceeceeecseeeseeseeesesneetsessseeseeeaeeseees 15 2 Non Buffered Handshaking c c sc ccssscetseses cesses csssccscuscssssssuecabeas o a aA 15 5 Buffered Handshaking sciens cis ooien thsetedaseg saeia caan ascend even a aroan a E Sa iais 15 6 Simple Buffered Examples anan norssi apa aie 15 7 Circular Buffered Examples ssseseseesseesseessseessrsresresesrestresrestnrrsresreresrenrnreses 15 9 Part 5 SCXI Getting Your Signals in Great Condition Chapter 16 Things You Should Know about SCXI What is Signal Conditioning cresien a a 16 1 Amplification isete ne evcadacs seus Ses iv els shad yen sag te ua aud atte A ghey salts 16 3 Isolation 52 esse civ h soe ec honed duit ee reat Heap erate teen See eae betes Ben ee 16 4 Filtering sin catia nist See ee a
146. d for the x axis timebase and create a spreadsheet file containing the data National Instruments Corporation 7 9 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition device 1 sean rate 5000 Transpose Figure 7 10 Writing to a Spreadsheet File after Acquisition Triggered Analog Input For information on starting your acquisition with triggers go to Chapter 8 Controlling Your Acquisition with Triggers Do You Need To Access Your Data during Acquisition You can apply the simple buffering techniques in many DAQ applications but there are some applications where these techniques are not appropriate If you need to acquire more data than your computer s memory can hold or if you want to acquire data over long periods of time you should not use these simple buffered techniques For these types of applications you should set up a circular buffer to store acquired data in memory In the previous section buffered input was compared to shopping for groceries You typically use a cart or bag your buffer to hold as many groceries your acquired data as possible so that you only have to make one trip to the store In this case imagine that you must prepare a meal and you are unable to go shopping yet periodically you need things from the store for your recipe If you send someone else to the store for you you can continue to prepare dinner while someone else retrieves
147. d mean that each row holds data from one channel Selecting a row selects a channel Selecting a column selects a scan of data This ordering method is often referred to as row major order When you create data in a nested For Loop the inner loop creates a row for each iteration of the outer loop If you were to label your index LabVIEW Data Acquisition Basics Manual 3 14 National Instruments Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts selectors for a row major 2D array the array might look like Figure 3 9 Figure 3 9 2D Array in Row Major Order You can also organize 2D array data by columns The Analog Input VIs in LabVIEW are organized in this way Each column holds data from one channel so selecting a column selects a channel Selecting a row selects a scan of data This ordering method is often called column major order If you were to label your index selectors for a column major 2D array the array might look like Figure 3 10 scan channel Figure 3 10 2D Array in Column Major Order To graph a column major order 2D array you must configure the waveform chart or graph to treat the data as transposed by turning on this option in the graph pop up menu cP Note This option appears in gray until you wire the 2D array to a graph If you need to convert the data to row major order select Functions Array amp Cluster Transpose 2D Array If you want to extract a single channel from a column major
148. d of TTL signals e You can count TTL signal transitions edges or elapsed time e You can divide the frequency of TTL signals The counter chapters that follow this chapter discuss each one of these counter functions National Instruments Corporation 21 1 LabVIEW Data Acquisition Basics Manual Chapter 21 Things You Should Know about Counters Knowing the Parts of Your Counter The following illustration shows a basic model of a counter Counter Register A counter consists of aSOURCE input pin a GATE input pin an OUT output pin and a count register In plug in device diagrams and in the LabVIEW Data Acquisition VI Reference Manual these counter parts are called SOURCE n GATE n and OUT n where n is the number of the counter Typically acounter counts the signal transitions at the SOURCE input You can configure the counter to count either the low to high or the high to low transition of the SOURCE input These signal transitions are sometimes referred to as edges For each counted edge the counter increments or decrements the internal count register The count register value always reflects the current count of the signal edges Reading the count register does not change its value The GATE input can control when counting in your application occurs You can enable and disable counting according to GATE signal transitions or levels There are four different gating modes rising edge falling edge high level and l
149. d to the SOURCE input to occur Refer to the How to Measure Frequency and Period VI Case 4 for a detailed description of the block diagram It is a good idea to know what type of signal you are measuring so you can use the best approach for measuring the frequency signal National Instruments Corporation 24 7 LabVIEW Data Acquisition Basics Manual Counting Signal Highs and Lows Counters can count external events like the rising and falling edges on the SOURCE input pin or elapsed time like the rising and falling edges of an internal timebase When might you need to count external events or elapsed time One case is if you are in charge of figuring out the throughput of a production line You have a bar code reader which reads the serial number of every product The bar code reader outputs a digital pulse every time it reads a serial number You could use a counter counter A to count the number of digital pulses or events from the barcode reader If you only needed to count the digital pulses for a certain amount of time you can gate the operation of the counter In order to produce the gate signal for the counter you can use another counter counter B to count the pulses of an internal clock for the amount of time needed to count the number of products So counter B would measure elapsed time and the output pulse s of counter B would turn counter A on and off As you can see time or event based counting can be ve
150. d your software to obtain support Australia Austria Belgium Canada Ontario Canada Quebec Denmark Finland France Germany Hong Kong Italy Japan Korea Mexico Netherlands Norway Singapore Spain Sweden Switzerland Taiwan U K gt Telephone 03 9 879 9422 0662 45 79 90 0 02 757 00 20 519 622 9310 514 694 8521 45 76 26 00 90 527 2321 1 48 14 24 24 089 741 31 30 2645 3186 02 48301892 03 5472 2970 02 596 7456 5 202 2544 03480 33466 32 84 84 00 2265886 91 640 0085 08 730 49 70 056 20 51 51 02 377 1200 01635 523545 LabVIEW lv support natinst com HiQ hiq support natinst com VISA visa support natinst com Fax 03 9 879 9179 0662 45 79 90 19 02 757 03 11 519 622 9311 514 694 4399 45 76 71 11 90 502 2930 1 48 14 24 14 089 714 60 35 2686 8505 02 48301915 03 5472 2977 02 596 7455 5 520 3282 03480 30673 32 84 86 00 2265887 91 640 0533 08 730 43 70 056 20 51 55 02 737 4644 01635 523154 Technical Support Form Photocopy this form and update it each time you make changes to your software or hardware and use the completed copy of this form as a reference for your current configuration Completing this form accurately before contacting National Instruments for technical support helps our applications engineers answer your questions more efficiently If you are using any National Instruments hardware or software products related to this problem include the configuration forms from their us
151. demarks The media on which you receive National Instruments software are warranted not to fail to execute programming instructions due to defects in materials and workmanship for a period of 90 days from date of shipment as evidenced by receipts or other documentation National Instruments will at its option repair or replace software media that do not execute programming instructions if National Instruments receives notice of such defects during the warranty period National Instruments does not warrant that the operation of the software shall be uninterrupted or error free A Return Material Authorization RMA number must be obtained from the factory and clearly marked on the outside of the package before any equipment will be accepted for warranty work National Instruments will pay the shipping costs of returning to the owner parts which are covered by warranty National Instruments believes that the information in this manual is accurate The document has been carefully reviewed for technical accuracy In the event that technical or typographical errors exist National Instruments reserves the right to make changes to subsequent editions of this document without prior notice to holders of this edition The reader should consult National Instruments if errors are suspected In no event shall National Instruments be liable for any damages arising out of or related to this document or the information contained in it EXCEPT AS SPECIFIED HEREIN N
152. dow Figure 25 3 shows how to use the Easy Counter VI Count Events or Time VI to measure elapsed time counter size DHr start Figure 25 3 Using the Count Events or Time VI to Measure Elapsed Time The only difference between measuring events or time is the type of source signal When measuring events you have an external signal connected to the SOURCE input When measuring time you use an internal timebase signal produced by the counter chip With the Am9513 chip you can choose from the timebases of 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz With the DAQ STC chip you can choose from the timebases of 20 MHz and 100 kHz How do you know which timebase frequency to use Suppose you want to count the rising edges of the internal signal for 1 minute The maximum counted value for a LabVIEW Data Acquisition Basics Manual 25 4 National Instruments Corporation Chapter 25 Counting Signal Highs and Lows 16 bit counter is 65 535 If you use the 100 Hz signal your counter would count 100 edges in a minute If you use the 100 kHz signal then the counter counts 100 000 edges in a minute This means you would need to cascade two counters in order to count the necessary edges using the 100 kHz signal You should use a higher frequency for smaller time measurements and use a slower frequency for longer time measurements If you do not choose one of the above frequencies then the counter will give you error 10403 which informs you that
153. dule that connects directly to the parallel port on the PC The SCXI 1200 can control several SCXI signal conditioning modules installed in the same chassis The functionality of the SCXI 1200 module is similar to the plug in Lab devices Terminal Signal SCXI Chassis SCXI Personal Blocks Conditioning Cable Assembly DAQ Board Computer and or or Parallel Port Optional Data Acquisition Cable Modules Figure 17 2 Components of an SCX System Refer to the SCXI tables in Appendix B Hardware Capabilities of the LabVIEW Data Acquisition VI Reference Manual for tables containing specifications for all the SCXI modules This appendix also includes a list of all the SCXI modules and the compatible terminal blocks How do you connect the transducers to the SCXI modules How do you set the jumpers on the SCXI modules before they are placed in the chassis For information on how to set up each module and transducer consult your hardware user manuals and the Getting Started with SCXI manual How do you transfer data from the SCXI chassis to the DAQ device or parallel port Figure 17 3 shows a diagram of an SCXI chassis When you use SCX as a front end signal conditioning system the analog and digital bus backplane also known as the SCXIbus transfers analog and or digital data to the DAQ device Some of the analog and digital LabVIEW Data Acquisition Basics Manual 17 2 National Instruments Corporation Chapter 17 Hardware and Software
154. e first clock pulse on the EXTCONV pin configures the acquisition but does not cause a conversion However all subsequent pulses cause conversions Externally Controlling your Scan Clock External scan clock control may be more useful than external channel clock control if you are sampling multiple channels but may not be as obvious to find because it does not have the input on the I O connector labeled ExtScanClock the way the EXTCONV pin does National Instruments Corporation 9 5 LabVIEW Data Acquisition Basics Manual Chapter 9 Letting an Outside Source Control Your Acquisition Rate Note Some MIO devices have an output on the I O connector labeled ScanClock This cannot be used as an input The appropriate pin to input your external scan clock can be found in the Table 9 1 Table 9 1 External Scan Clock Input Pins Device External Scan Clock Input Pin AT MIO 16 Out2 AT MIO 16F 5 AT MIO 16X AT MIO 16D AT MIO 64F 5 All E Series Devices Any PFI Pin Lab PC OutB 1 SCXI 1200 DAQPad 1200 DAQCard 1200 we Note Some devices do not have internal scan clocks and therefore do not support external scan clocks These devices include NB MIO 16 PC LPM 16 DAQCard 700 DAQCard 500 Lab NB Lab SE and Lab LC After connecting your external scan clock to the correct pin set up the external scan clock in software For example in the Getting Started Analog Input Example VIs located in
155. e leave this field set to None and advance the Module number to the next slot b Cabled Device If the module in the current slot is directly cabled to a DAQ device in your computer set this field to the device number of that DAQ device Leave the Cabled Device field set to None if the module in the current slot is not directly cabled to a DAQ device If you are operating your modules in Multiplexed mode you need to cable only one module in each chassis to your DAQ device If you are not using multiplexed mode refer to the SCXI Operating Modes section of Chapter 17 Hardware and Software Setup for Your SCXI System for instructions about module cabling c Operating Mode The system defaults to the multiplexed operating mode which is recommended for almost all SCXI applications The operating modes available for each SCXI module type are discussed in the SCXI Operating Modes section of Chapter 17 Hardware and Software Setup for Your SCXI System 2 27 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware If the module is an analog input module enter the gain and filter settings for each channel in the bottom section of the window The system disables the Channel control for any modules that use only one gain and filter setting for the entire module Now that you have successfully installed and configured your DAQ hardware for LabVIEW read Chapter 3 Basic Data Acquisition Conce
156. e AI Config VI Figure 6 5 shows a simplified block diagram for non buffered applications LabVIEW calls the AI Config VI which configures the channels selects the input limits the high limit and low limit parameters in the Easy VIs and generates a taskID The program passes the taskID and the error cluster to the AI Single Scan VI which returns the voltage data in an array one point for each channel specified Al Configi Al Single Scan vi buffer size 0 channels 0 Figure 6 5 Using the Intermediate VIs for a Basic Non Buffered Application Figure 6 6 shows how you can program the AI Config and AI Single Scan VIs to perform a series of single scans by using software timing a While Loop and processing each scan This example shows the Cont Acquire amp Chart immediate vi which you can find in examples daq anlogin anlogin 11b LabVIEW Data Acquisition Basics Manual 6 4 National Instruments Corporation Chapter6 One Stop Single Point Acquisition The advantage to using the intermediate level VIs is that you do not have to configure the channels every time you want to acquire data as you do when using the Easy VIs To call the AI Config VI only once put it outside of the While Loop in your program The AI Config VI configures channels selects a high low limit and generates a taskID Then the AI Config VI passes the taskID and error cluster into the While Loop where LabVIEW calls the AI Single Scan VI to retrieve a
157. e Immediate Update Using the AO Update Channels VI 11 1 Single Immediate Update Using Intermediate VI oe 11 2 Multiple Immediate Updates Using Intermediate VI 0 11 3 Waveform Generation Using the AO Generate Waveforms VI 12 1 Waveform Generation Using the AO Waveform Gen VI essees 12 2 Waveform Generation Using Intermediate VIs 0 lee eeeeeeeee 12 3 Circular Buffered Waveform Generation Using the AO Continuous Gen Vi esep arre ne testene E RE eedbees 12 4 Circular Buffered Waveform Generation Using Intermediate VIs 12 5 Digital Ports and Lines sisirodnorecirina n nanea EE EN 13 1 The Easy Digital VIs sistas ecouiesetis n an n a a I 14 2 Connecting Signal Lines for Digital Input sseeseseeseeeseseeresesesreersees 15 3 Connecting Digital Signal Lines for Digital Output 0 15 4 Non buffered Handshaking Using the DIO Single Read Write VI 15 5 Non buffered Handshaking Using the DIO Single Read Write VI 15 6 Pattern Generation Using the DIO 32F Devices cee eee 15 7 Pattern Generation Using DAQ Devices Other Than DIO 32F DEVICES acca neh ides hectic EEUE E E E Eana 15 8 Reading Data with the Digital VIs Using Digital Handshaking DIO 32F Devices sto bee ssies ceeds lashes n a ti N ERE aR 15 8 Reading Data with the Digital VIs Using Digital Handshaking 15 9 Digital Handshaking Using a Circular Buffer eee 15 10 LabVIEW Data Acquisition Basics Manual xiv National
158. e Train with the Generate Pulse Train VE arranoen n dt tavaaa rs euses ha E stig te eee ees 22 6 Figure 22 8 Generating a Continuous Pulse Train Using Intermediate VIs 22 7 Figure 22 9 Physical Connections for Generating a Finite Pulse Train 22 8 Figure 22 10 Creating a Finite Pulse Train Using the Intermediate VIs 0 0 0 0 22 8 Figure 22 11 Uncertainty of One Timebase Period o0 eee ec eeeeeeeeeeereteeeereeeeees 22 9 Figure 22 12 Using the Generate Delayed Pulse and Stopping the Counting Operaton ee sand coe Bite elied lee ett D nteien 22 10 Figure 22 13 Stopping a Generated Pulse Train eee ee eeceeeeeeeesseeeeeseeeaeeeees 22 10 Figure 23 1 Counting Input Signals to Determine Pulse Width o oo 23 1 Figure 23 2 Physical Connections for Determining Pulse Width 0 23 2 Figure 23 3 Determining Pulse Width Using the Pulse Width or Period VI 23 2 Figure 23 4 Measuring Pulse Width Using Intermediate VIs 00 23 3 Figure 24 1 Measuring Square Wave Frequency 0 c cee eeeeeeseseeseeseeeseteeeeseeneees 24 1 Figure 24 2 Measuring a Square Wave Period 0 0 0 eee eeeeseeeeeeeeteeeeseeseeeaeeseees 24 2 Figure 24 3 Physical Connections for Period Measurement of Low Frequency SION AIS sess ct sveis coche E E E E a memes 24 3 Figure 24 4 Physical Connections for Period Measurement of High Frequency IGM ALS aise aeea eae aene a ONA E E suyesteyssasdeveboniges ds 24 3 National
159. e Used MIO series devices feature an FOUT output and E Series devices feature a FREQ OUT output where your device can generate a square wave without using any of the available counters The CTR Control VI found in Functions Data Acquisition Counters Advanced Counters enables and disables the FOUT signal and sets the square wave frequency The square wave frequency is defined by FOUT timebase signal FOUT divisor The front panel and block diagram below show an FOUT output configured to generate a 25 000 Hz square wave Front Panel FOUT port F FOUT port 1 FOUT timebase source ra i internal frequency in Hz Block Diagram CTR Control wi Figure 21 1 CTR Control VI Front Panel and Block Diagram Now that you have read about the basic operations of a counter go to the chapter that discusses your particular counter application For specific information about the Counter VIs in LabVIEW refer to Chapter 16 Introduction to the Counter VIs in the LabVIEW Data Acquisition VI Reference Manual National Instruments Corporation 21 5 LabVIEW Data Acquisition Basics Manual Generating A Square Pulse or Pulse Trains This chapter describes the ways you can generate a square pulse or multiple pulses called pulse trains using the counters available on your data acquisition DAQ device with the Easy and Intermediate Counter VIs in LabVIEW Generating a Square Pulse There are many times that you may need to
160. e VI in examples daq analogin scxi 1122 voltage vi If you are measuring temperature with the SCXI 1120 and the SCXI 1121 modules then you can refer to the example VI SCXI 112x Thermocouple located in examples daq anlogin scxi 11b This VI is similar to the VI used to measure temperature on the SCXI 1100 Both VIs average and linearize temperature data using the Intermediate analog input VIs The two main differences between the VIs are that the SCXI 112x VI does not measure the amplifier offset and the input limits for the module and the temperature sensor are different from the input limits for the SCXI 1100 The SCXI 1120 and SCXI 1121 modules do not have the internal switch used to programmatically ground the amplifiers as in the SCXI 1100 for the amplifier offset measurement If you want to determine the amplifier offset you have to manually wire the amplifier terminals to ground and use a separate VI to read the offset voltage You can also manually calibrate the SCXI 1120 and SCXI 1121 to remove any amplifier offset on a channel by channel basis Refer to the SCXI 1120 or SCXI 1121 user manuals for specific instructions Measuring Temperature with RTDs Resistance Temperature Detectors RTDs are temperature sensing devices whose resistance increase with temperature They are known for their accuracy over a wide temperature range RTDs require current excitation to produce a measurable voltage RTDs are available in 2 wire 3 w
161. e configuration or the I O operation while other DAQ VIs perform both configuration and the operation The VIs that handle both functions have an iteration input When your VI has the iteration set to 0 LabVIEW configures the DAQ device and then performs the specific I O operation For iteration values greater than 0 LabVIEW uses the existing configuration to perform the I O operation You can improve the performance of your application by not configuring the DAQ device every time an I O operation occurs Typically you should wire the iteration input to an iteration terminal in a loop as shown in the following illustration l Waveform Scan vi Wiring the iteration input this way means the device is only configured on the first I O operation Subsequent I O operations use the existing configuration Error Handling Each Easy VI contains an error handling VI A dialog box appears immediately if an error occurs in an Easy VI Every Intermediate and Advanced VI contains an error in input cluster and an error out output cluster as shown in Figure 3 5 The clusters LabVIEW Data Acquisition Basics Manual 3 8 National Instruments Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts contain a Boolean that indicates whether an error occurred the code for the error and source or the name of the VI that returned the error If error in indicates an error the VI passes the error information to error out and does not execute any
162. e to separate modules in an SCXI chassis For example you can use two Lab NB or AT MIO 16E 2 devices operating in parallel mode and cable each one to a separate SCXI 1120 module in the chassis You must be sure to enter the correct device numbers in the Cabled Device field of the configuration utility for each module you operate in parallel mode For more information on the Cabled Device field read the Installing and Configuring Your SCXI Chassis in Windows or on the Macintosh section in Chapter 2 Installing and Configuring Your Data Acquisition Hardware By default when a module operates in parallel mode the module sends its channel 0 output to differential analog input channel 0 of the DAQ device the channel 1 output to analog input channel of the DAQ device and so on Note The SCXI 1200 only reads channels from another analog input module in multiplexed mode not in parallel mode When you use the analog input VIs specify the correct onboard channel for each parallel SCXI channel If you are using a range of SCXI channels LabVIEW assumes the onboard channel numbers match the SCXI channel numbers Refer to the SCXI Channel Addressing section in Chapter 18 Special Programming Considerations for SCXI for the proper SCXI channel syntax National Instruments Corporation 17 5 LabVIEW Data Acquisition Basics Manual Chapter 17 Hardware and Software Setup for Your SCX System Windows Parallel Mode for the SCXI 1200 In parall
163. e you try to read this manual If you have never worked with LabVIEW please read through the LabVIEW Tutorial Manual before you begin This manual shows you how to configure your software teaches you basic concepts needed to accomplish your task and refers you to common example VIs in LabVIEW If you have used LabVIEW for data acquisition before you can use this book as a troubleshooting guide The following outline shows you what kind of information you can find in this manual Part 1 Part 2 Part 3 Part 4 Part 5 National Instruments Corporation Before You Get Started How to Use This Book Installing and Configuring Your Data Acquisition Hardware Basic Data Acquisition Concepts Where You Should Go Next your map to this manual Catching the Wave With Analog Input Things You Should Know about Analog Input One Stop Single Point Acquisition Buffering Your Way through Waveform Acquisition Taking Control of Your Acquisition with Triggers Letting an Outside Source Control Your Acquisition Rate Using Analog I O Control Loops Making Waves with Analog Output Things You Should Know about Analog Output One Stop Single Point Generation Buffering Your Way through Waveform Generation Getting Square with Digital I O Things You Should Know about Digital I O When You Need It Now Immediate Digital I O Shaking Hands with a Digital Partner SCXI Getting Your Signals in Great Condition Things You Should Know about SCX
164. easure the amplifier offset of many modules at once but in Figure 19 1 it only measures one module input limits no change Jeyice output units binar Teor offset channel ure binary amplifier offset d ob0 sc1 md calgnd average Figure 19 1 Measuring a Single Module with the Acquire and Average VI After measuring the amplifier offset measure the temperature sensor for cold junction compensation Both the amplifier offset and cold junction measurements should be taken before any thermocouple measurements are taken To measure temperature sensors you use the Acquire and Average VI The main differences between the amplifier offset measurement and temperature sensor measurement are the channel string and the input limits If have set the temperature sensor in mtemp mode the most common mode you access the temperature LabVIEW Data Acquisition Basics Manual 19 6 National Instruments Corporation Chapter 19 Common SCX Applications by using mtemp If you have set the temperature season in dtemp mode then you would read the corresponding DAQ device onboard channel Make sure you use the temperature sensor input limits which are different from your acquisition input limits To read from a temperature sensor based on an IC sensor or a thermistor set the input limit range from 2 to 2 V The temperature sensor voltage will range from2V to 2 Figure 19 2 Measuring Temperature Sensors Using the Acquire and Average
165. ect the counter on your device to measure pulse width counter Source your device Figure 23 2 Physical Connections for Determining Pulse Width Determining Pulse Width You can measure the pulse width using the Measure Pulse Width or Period VI located in Functions Data Acquisition Counter This VI automatically notifies you with a dialog box if an error occurs Figure 23 3 shows how to program your counters to determine the pulse width using this Easy Counter VI pulse width period s counter type of measurement Measure Pulse width or Period vi timebase 100 Hz Figure 23 3 Determining Pulse Width Using the Pulse Width or Period VI The Measure Pulse Width or Period VI counts the number of cycles of the specified internal timebase between the starting and ending events that you designate in the type of measurement input You can measure the pulse width from rising to falling edge or from falling to rising edge The valid parameter indicates whether the frequency measured the data without overflow Overflow occurs when the counter reaches its highest value or terminal count TC You only need to check the valid parameter if you are using an Am9513 chip The DAQ STC National Instruments Corporation 23 2 LabVIEW Data Acquisition Basics Manual Chapter 23 Measuring Pulse Width does not use the valid parameter to set the overflow so you do not need to check this parameter with this chip Refer to
166. ediately to the right of the module that you will cable to the DAQ device Otherwise the cable connectors may not fit together conveniently If you have more than one chassis select a unique jumpered address for each additional chassis by using the jumpers directly behind the front panel of the chassis Plug the appropriate terminal blocks into the front of each module and screw them tightly into the chassis frame If you are using a DAQ device in your computer to control your SCXI chassis connect the mounting bracket of the SCXI 134x where x is a number cable assembly to the back of one of the modules and screw it into the chassis frame Connect the other end of the cable to the DAQ device in your computer In multiplexed mode you only need to cable one module to the DAQ device In most cases it does not matter which module you cable The following are two special cases where you should cable a specific module to the device a Ifyou are using SCXI 1140 modules along with other types of modules you need to cable one of the SCXI 1140 modules to the DAQ device b If you are using analog input modules and other types of modules you need to cable one of the analog input modules to the DAQ device Refer to the Getting Started with SCXI manual for more information on related topics such as multichassis cabling Windows If you are using the SCXI 1200 module to control your chassis connect one end of the parallel port cable to the b
167. ef explanation of ways you can debug your data acquisition application to make sure your application is accurate and runs smoothly Appendix A Common LabVIEW Data Acquisition Questions lists answers to questions frequently asked by LabVIEW users Appendix B Customer Communication contains forms you can use to request help from National Instruments or to comment on our products and manuals The Glossary contains an alphabetical list and description of terms used in this manual including abbreviations acronyms metric prefixes mnemonics and symbols The Index contains an alphabetical list of key terms and topics in this manual including the page where you can find each one Conventions Used in This Manual The following conventions are used in this manual In Help window pictures of VI inputs and outputs square brackets enclose parameters whose values you rarely need to set Angle brackets enclose the name of a key on the keyboard for example lt shift gt A hyphen between two or more key names enclosed in angle brackets denotes that you should simultaneously press the named keys for example lt shift delete gt Key names are lowercase AI device An analog input device that has AI in its name such as the NEC AI 16E 4 Am9513 based These MIO devices do not have an E in their device names These devices include the NB MIO 16 NB MIO 16X NB A2000 NB TIO 10 and NB DMA2800 on the Macintosh and the La
168. efinition 8 1 triggers definition 8 1 two dimensional 2D arrays 3 13 to 3 16 two point calibration 20 6 to 20 7 U UNIX operating system installation and configuration of DAQ devices DAQ device configuration 2 19 to 2 20 NI DAQ software 2 19 overview 2 18 to 2 19 user privilege level Windows NT 2 15 Utility VIs 3 6 See also VIs LabVIEW Data Acquisition Basics Manual V VIs See also specific VIs Advanced VIs 3 6 channel port and counter addressing 3 9 to 3 11 common DAQ VI parameters 3 7 to 3 8 crashing VIs in Windows A 3 data organization for analog applications 3 13 to 3 16 debugging 27 1 to 27 4 default and current value conventions 3 7 Easy VIs 3 5 error handling 3 8 to 3 9 finding VIs in LabVIEW 3 2 to 3 4 Intermediate VIs 3 5 to 3 6 limit settings 3 11 to 3 13 organization 3 4 to 3 5 parameter conventions 3 6 to 3 7 SCXI examples 19 5 to 19 9 Utility VIs 3 6 W Wait Until Next ms Multiple VI improving control loop performance 6 10 multiple channel single point analog input 6 5 software timed analog I O control loops 6 6 Wait ms VI 6 10 22 9 waveform generation See buffered analog output WDAQCOMF utility configuring DAQ devices EISA bus computers 2 9 ISA and PCMCIA bus computers 2 6 to 2 9 testing and configuring in Windows 2 11 to 2 14 icon in Windows figure 2 6 locating in Windows figure 2 6 National Instruments Corporation WD
169. egative voltages When a device uses jumpers or dip switches to select its voltage range and polarity you must enter the correct jumper setting in the configuration utility In DAQ hardware manuals and in the configuration utility you may find the word gain Gain is the amplification or attenuation of a signal National Instruments Corporation 3 13 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts Most National Instruments DAQ devices have programmable gains no jumpers but some SCXI modules require the use of jumpers or dip switches For all DAQ devices used with LabVIEW the gain is determined by limit settings so you never have to figure out the gain However for some SCXI modules you must enter the gain in the configuration utility Data Organization for Analog Applications If you acquire data from more than one channel multiple times the data is returned as a two dimensional 2D array If you were to create a 2D array and label the index selectors on a LabVIEW front panel the array might looks like Figure 3 8 Figure 3 8 Example of a Basic 2D Array The two vertically arranged boxes on the left are the row and column index selectors for the array The top index selects a row and the bottom index selects a column You can organize data for a 2D array in one of two ways First you can organize the data by rows If the array contained data from analog input channels this woul
170. el inputs Cont Acq amp Graph buffered vi The Cont Acq amp Graph buffered vi is similar to Cont Acg amp Chart buffered vi except this VI displays data in a waveform graph Cont Acq to File binary vi Inthe Cont Acq to File binary vi your program acquires data through circular buffered analog input and stores it in a specified file as binary data This process is more commonly called streaming to disk Cont Acq to File scaled vi The Cont Acq to File scaled vi is similar to the previous binary VI with the exception that this VI writes the acquired data to a file as scaled voltage readings rather than binary values Cont Acq to Spreadsheet File vi The Cont Acq to Spreadsheet File vi continuously reads data that LabVIEW acquires in the circular buffer and stores this data to a specified file in spreadsheet format You can view the data stored in a spreadsheet file by this VI in any spreadsheet application National Instruments Corporation 7 15 LabVIEW Data Acquisition Basics Manual Controlling Your Acquisition with Triggers The single point and waveform acquisitions discussed in the previous sections start at random times relative to the data But there are times that you may need to be able to set your analog acquisition to start at a certain time An example of this would be if you wanted to measure the temperature of an object after applying heat to it An electrical thermometer sends
171. el mode Make sure that you change the jumper in the SCXI 1200 to the ground position to connect the SCXI 1200 and SCXIbus grounds together Refer to the SCXI 1200 User Manual for more details Multiplexed Mode for Analog Output Modules Because LabVIEW communicates with the multiplexed modules over the SCXIbus backplane you must only cable one multiplexed module LabVIEW Data Acquisition Basics Manual 17 4 National Instruments Corporation Chapter 17 Hardware and Software Setup for Your SCX System in each chassis to a DAQ device to communicate with any multiplexed modules in the chassis Multiplexed Mode for Digital and Relay Modules Multiplexed mode is referred to as serial mode in the digital and relay module hardware manuals When you operate your digital or relay module in multiplexed mode LabVIEW communicates the module channel states serially over the SCXIbus backplane Parallel Mode for Analog Input Modules When an analog input module operates in parallel mode the module sends each of its channels directly to a separate analog input channel of the DAQ device cabled to the module You cannot multiplex parallel outputs of a module on the SCXIbus You must cable a DAQ device directly to a module in parallel mode to access its input channels In this configuration the number of channels available on the DAQ device limits the total number of analog input channels In some cases however you can cable more than one DAQ devic
172. el mode the SCXI 1200 reads only its own analog input channels The SCXI 1200 does not have access to the analog bus on the SCXI backplane in parallel mode You should use parallel mode if you are not using other SCXI analog input modules in the chassis with the SCXI 1200 Macintosh and Windows Parallel Mode for Digital Modules Note When you operate a digital module in parallel mode the digital lines on your DAQ device directly drive the individual digital channels on your SCXI module You must cable a DAQ device directly to every module operated in parallel mode You may want to use parallel mode instead of multiplexed mode for faster updating or reading of the SCXI digital channels For the fastest performance in parallel mode you can use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs Refer to the hardware tables in Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual for the digital ports used in parallel mode on each DAQ device If you are using a DIO 96 an AT MIO 16D or an AT MIO 16DE 10 device you can also operate a digital module in parallel mode using the digital ports on the second half of the NBS or R1005050 ribbon cable lines 51 100 Therefore the DIO 96 can operate two digital modules in parallel mode one module using the first half of the ribbon cable lines 1 50 and another module using the second half of the ribbon cable lines
173. ence Manual Analog Output Application Example With the SCXI analog output module SCXI 1124 you can output voltages or currents Refer to the example analog output VI SCXI 1124 Update Channels VI located in examples daq anlogin scxi 11b This VI uses the analog output Advanced VIs because the output mode whether you have voltage or current data must be accessible in order to change the value as shown below The program calls the AO Group Config VI to specify the device and output channels The AO Hardware Config VI specifies the output mode and the output voltage range or limit settings for all the channels specified in the channels string This advanced level VI is the only place where you can specify a voltage or current output mode LabVIEW Data Acquisition Basics Manual 19 14 National Instruments Corporation Chapter 19 Common SCX Applications If you are going to output voltages only you may want to use the AO Config VI an Intermediate VI instead of the AO Group Config and AO Hardware Config VIs You can program individual output channels of the SCXI 1124 for different output ranges by using the arrays for channels output mode and limit settings The AO Single Update VI initiates the update of the SCXI 1124 output channels To help debug your VIs it is always helpful to display any errors in this case using the Simple Error Handler VI we Note LabVIEW for Windows NT does not support the SCXI 1124 module AO Gro
174. ent of O specifies channels 0 through 3 on each AMUX 64T device Table 5 2 shows the number of channels available on a DAQ device with an external multiplexer Table 5 2 Analog Input Channel Range Number of Channel Range Channel Range AMUX 64Ts Single Ended Differential 0 0 through 15 O through 7 1 AM1 0 through AM1 0 through AM1 63 AM1 31 2 AM1 0 through AM1 0 through AM1 63 AM1 31 AM2 0 through AM2 0 through AM2 63 AM2 31 4 AM1 0 through AM1 63 AM1 0 through AM2 0 through AM2 63 AM1 31 AM3 0 through AM3 63 AM2 0 through AM4 0 through AM4 63 AM2 31 AM3 0 through AM3 31 AM4 0 through AM4 31 National Instruments Corporation 5 13 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input You specify the number of AMUX devices through the configuration utility or the AI Hardware Config VI Refer to the LabVIEW Data Acquisition VI Reference Manual for more information on this VI The AMUX 64T Scanning Order This section explains how LabVIEW scans channels from the AMUX 64T You must know this scanning order so that you can determine which analog input channel LabVIEW scanned during a data acquisition operation The scanning counters on the AMUX 64T and on the DAQ device perform automatic scanning of the AMUX 64T analog input channels When you perform a multiple channel scanned data a
175. equencies and periods using the counters on your data acquisition DAQ device The period of a signal is equal to one cycle of the signal Frequency is the inverse of period An example of when you would want to know the frequency of a signal is when you have a signal that controls how often a meter takes measurements like a flow meter measuring flow rates or a thermometer measuring temperature Knowing How and When to Measure Frequency and Period A common way to measure the frequency of a signal is to measure the number of pulses that occur during a known time period For example Figure 24 1 illustrates the measurement of a waveform of an unknown frequency f by a pulse of a known pulse width Teo The frequency of the waveform equals the count divided by the period of known pulse width frequency count T The period is always the reciprocal of the measured frequency period 1 f Tg pulse of known width count register SOURCE input of unknown frequency fs Figure 24 1 Measuring Square Wave Frequency For period measurement you count the number of pulses of a known frequency f during one period of the signal to be measured As shown in Figure 24 2 the signal of a known frequency is connected to the National Instruments Corporation 24 1 LabVIEW Data Acquisition Basics Manual Chapter 24 Measuring Frequency and Period SOURCE and the signal to be measured is connected to the GATE The peri
176. er multibuffered I O National Instruments Corporation Glossary Industry Standard Architecture A type of signal conditioning in which you isolate the transducer signals from the computer for safety purposes This protects you and your computer from large voltage spikes and makes sure the measurements from the DAQ device are not affected by differences in ground potentials 1 024 words of memory Laboratory Virtual Instrument Engineering Workbench A type of digital acquisition generation where a device or module accepts or transfers data after a digital pulse has been received Also called handshaked digital I O The maximum and minimum voltages of the analog signals you are measuring or generating A type of signal conditioning in which LabVIEW linearizes the voltage levels from transducers so the voltages can be scaled to measure physical phenomena Least significant bit megabytes of memory See buffer Input operation for which you allocate more than one memory buffer so you can read and process data from one buffer while the acquisition fills another G 9 LabVIEW Data Acquisition Basics Manual Glossary multiplexed mode multiplexer NB NI DAQ NI PNP EXE NI PNP IN nodes nonlatched digital I O non referenced signal sources NRSE Non referenced single ended NRSE measurement system LabVIEW Data Acquisition Basics Manual An SCXI operating mode in which analog
177. er accuracy you should take several readings from the temperature sensor and average those readings to yield one value If you do not want to average several readings you can take a single reading using the Easy Analog Input VI AI Sample Channel You should look at the SCXI Thermocouple example VIs found in examples daq anlogin scxi 11b The VIs use the mtemp string to read the temperature sensor and use the reading for thermocouple cold junction compensation Amplifier Offset The SCXI 1100 SCXI 1122 and SCXI 1141 have a special calibration feature that enables LabVIEW to ground the module amplifier inputs so that you can read the amplifier offset For the other SCXI analog input modules you must physically wire your terminals to ground The measured amplifier offset is for the entire signal path including the SCXI module and the DAQ device To read the grounded amplifier on the SCXI 1100 or SCXI 1122 use the standard SCXI string syntax in the channels array with calgnd LabVIEW Data Acquisition Basics Manual 19 4 National Instruments Corporation VI Examples Chapter 19 Common SCX Applications substituted for the channel number Refer to the following table for an example of this Channel List Element Channel Specified ob0 scx mdy calgnd SCXI 1100 and SCXI 1122 only The grounded amplifier of the module in slot y of the chassis with ID x For example you can run the Getting Started Analog Input
178. er and stopping at the end of the buffer You use simple buffered I O when you acquire small amounts of data relative to memory constraints Analog inputs that you measure with respect to a common ground A programmed event that triggers an event such as data acquisition A method of triggering in which you to simulate an analog trigger using software Also called conditional retrieval An counter input pin where the counter counts the signal transitions System timing controller A thin conductor which is attached to a material that detects stress or vibrations in that material VI used in the block diagram of another VI comparable to a subroutine Devices that do not require dip switches or jumpers to configure resources on the devices also called Plug and Play devices The set of rules to which statements must conform in a particular programming language G 14 National Instruments Corporation T task task ID TC toggled output National Instruments Corporation Glossary A timed I O operation using a particular group See task ID A number generated by LabVIEW which encodes the device number and group number after you configure a group You use the group configuration VIs in each function group to create the task ID which you use when you run other VIs to specify the boards or channels on which the VIs operate For example the task ID in hex for an analog input task that uses group 2 and devi
179. er manuals Include additional pages if necessary Name Company Address Fax ___ Phone __ Computer brand Model Processor Operating system include version number Clock speed MHz RAM MB Display adapter Mouse ___ yes ___no Other adapters installed Hard disk capacity MB Brand Instruments used National Instruments hardware product model Revision Configuration National Instruments software product Version Configuration The problem is List any error messages The following steps reproduce the problem Documentation Comment Form National Instruments encourages you to comment on the documentation supplied with our products This information helps us provide quality products to meet your needs Title LabVIEW Data Acquisition Basics Manual Edition Date January 1996 Part Number 320997A 01 Please comment on the completeness clarity and organization of the manual If you find errors in the manual please record the page numbers and describe the errors Thank you for your help Name Title Company Address Phone Mail to Technical Publications Fax to Technical Publications National Instruments Corporation National Instruments Corporation 6504 Bridge Point Parkway 512 794 5678 Austin TX 78730 5039 Prefix Meaning
180. erature sensors in the terminal blocks But if you want to measure the temperature of an object away from the SCXI chassis you must use a transducer like a thermocouple A thermocouple is a junction of two dissimilar metals that gives varying voltages based on the temperature However when using thermocouples you need to compensate for the thermocouple voltages produced at the screw terminal because the junction with the screw terminals itself forms another thermocouple You can use the resulting voltage from the temperature sensor on the terminal block for cold junction compensation The cold junction compensation voltage is used when linearizing voltage readings from thermocouples into temperature values The SCXI modules that will be used to measure temperature in this section are SCXI 1100 SCXI 1102 SCXI 1120 SCXI 1121 SCXI 1122 and SCXI 1141 All of the terminal blocks used with these modules have temperature sensors which can be used as cold junction compensation In addition the SCXI 1100 SCXI 1141 and SCXI 1122 offer a way for you to ground the module amplifier inputs so you can read the amplifier offset You can subtract the amplifier offset value to determine the actual voltages For more information on temperature sensors and amplifier offsets look at the following two sections You can also refer to Application Note 005 Thermocouples and Temperature Measurements for more information on measuring temperature with thermocoupl
181. erform these updates Single Immediate Updates The most basic way to program single point updates in LabVIEW is by using the Easy Analog Output VI AO Update Channels Figure 11 1 shows a diagram of a VI that writes voltages to one or more output channels on the output data acquisition DAQ device Device Figure 11 1 Single Immediate Update Using the AO Update Channels VI Notice that an array of voltages is passed as an input to the VI The first element in the array corresponds to the first entry in the channel string and the second array element corresponds to the second channel entry For more information on channel string syntax refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts Remember that Easy VIs already have built in error handling If you want more control over the limit settings for each channel you can also program a single point update using the Intermediate Analog National Instruments Corporation 11 1 LabVIEW Data Acquisition Basics Manual Chapter 11 One Stop Single Point Generation Output VI AO Write One Update Figure 11 2 shows an example of using this VI limit settings Figure 11 2 Single Immediate Update Using Intermediate VI In this example your program passes the error information to the Simple Error Handler VI The iteration input optimizes the execution of this VI if you wanted to place it in a loop For more information look at the next section With Intermediate VIs you
182. ernal conversion pulses On most devices external conversions occur on the falling edge of the EXTCONV line Consult your hardware reference manual for timing diagrams On the MIO E series devices you can set the Clock Source Code input of AI Clock Config VI to the PFI pin with either falling or LabVIEW Data Acquisition Basics Manual 9 4 National Instruments Corporation Chapter 9 Letting an Outside Source Control Your Acquisition Rate rising edge or use the default PFI2 Convert pin where the conversions occur on the falling edge as shown in Figure 9 5 clock source no change clock source cade clock source string vf no change i E internal WO connector ETSI connection FFI pin low to high FFI pin high to low ETSI pin low to high ETSI pin high to low GPCTR output low to high GPCTR output high to low ATCOUT low to high ATCOUT high to low Figure 9 5 Setting the Clock Source Code for External Conversion Pulses for E Series Devices we Note The AT MIO 16 AT MIO 16D NB MIO 16 and NB MIO 16X cannot support both an external channel clock and a digital trigger signal at the same time You must choose one or the other Because LabVIEW determines the length of time before the AI Read VI times out based on the interchannel delay and scan clock rate you may need to force a time limit for the AI Read VI as shown previously in Figure 9 4 ie Note On the Lab PC SCXI 1200 DAQPad 1200 and DAQCard 1200 th
183. es You can access this note on the NI Fax Back system as well as the BBS World Wide Web or ftp site the numbers for which are located in the front of this manual LabVIEW Data Acquisition Basics Manual 19 2 National Instruments Corporation cr National Instruments Corporation 19 3 Note Chapter 19 Common SCX Applications Temperature Sensors for Cold Junction Compensation The temperature sensors in the terminal blocks for the analog input modules can be used for cold junction compensation If you are operating your SCXI modules in multiplexed mode as recommended you should leave the cold junction sensor jumper on the terminal block in the mt emp factory default position If you are using parallel mode you can use the dtemp jumper setting The SCXI 1102 only uses the cjtemp string in multiplexed mode To read the temperature sensor use the standard SCXI string syntax in the channels array with mt emp substituted for the channel number like the one shown in the following table Channel List Element Channel Specified ob0 scx mdy mtemp The temperature sensor configured in mtemp mode on the multiplexed module in slot y of the chassis with ID x ob0 scx mdy cjtemp The temperature sensor configured in cj temp mode on the multiplexed module of the SCXI 1102 in slot y of the chassis with ID x If you want to read the cold junction temperature sensor in dtemp mode you can read the following
184. escribes the ways you can generate a square pulse or multiple pulses called pulse trains using the counters available on your data acquisition DAQ device with the Easy and Intermediate Counter VIs in LabVIEW e Chapter 23 Measuring Pulse Width describes how you can use a counter to measure pulse width e Chapter 24 Measuring Frequency and Period describes the various ways you can measure frequencies and periods using the counters on your data acquisition DAQ device e Chapter 25 Counting Signal Highs and Lows teaches you how to use counters to count external events or elapsed time e Chapter 26 Dividing Frequencies shows you how to divide the available device frequencies to get the frequency you need for your data acquisition application Things You Should Know about Counters Counters add counting or high precision timing to your data acquisition DAQ system Counters respond to and output Transistor Transistor Logic TTL signals square pulse signals that are OV low or 5V high in value The following diagram shows a TTL signal Signal Transitions or Edges Even though counters just count the signal transitions edges of a TTL source signal you can use this counting capability in many ways e You can generate square TTL pulses for clock signals and triggers for other DAQ applications e You can measure the pulse width of TTL signals e You can measure the pulse frequency and perio
185. eval cluster of the AI Read VI When the trigger conditions are met the VI will return the requested number of scans If you need to control your acquisition buffer size or if you need to acquire data continuously then you should use the Intermediate VIs AI Config AI Start AI Read and AI Clear The Acquire N National Instruments Corporation 8 13 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers Scans SWTrig example VI located in examples daq anlogin anlogin 11b uses these VIs Because the AI Read VI is used in this example the triggering conditions are specified in the conditional retrieval input cluster The acquisition is continuous in this example so your device stores the acquired data in a circular buffer As the data is being applied the VI searches the trigger channel data for data that meets the trigger conditions When a trigger condition is met or a timeout occurs the acquisition is stopped LabVIEW Data Acquisition Basics Manual 8 14 National Instruments Corporation Letting an Outside Source Control Your Acquisition Rate Typically a data acquisition DAQ device uses internal counters to determine the rate to acquire data but sometimes you might need to capture your data at the rate of particular signals in your system For example you can also read temperature channels every time a pulse occurs which represents pressure rising above a certain level
186. evice Configuration Window in NI DAQ Figure 2 10 shows the NI DAQ Device Configuration window When you are in the Device Configuration window of the utility you can edit the default settings for parameters such as analog input polarity bipolar negative and positive voltages and unipolar only positive voltages and range on a per device basis If you are using AMUX 64T or signal conditioning devices with your DAQ device select the appropriate device with the Accessories menu LabVIEW uses these settings when initializing the device instead of the default settings listed in the descriptions of the hardware configuration VIs You can use these VIs to change any setting recorded by NI DAQ When you 2 17 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware click on the name of the device NI DAQ displays the I O connector for the device as shown in Figure 2 10 Al GMO if Al GNO ACHO ACHE 4 8 0 ACHZ Ste ACH 10 Device Configuration g ACH4 11 12 ACH12 F 2 ACHS FICH 13 lt _3_ eJNByMto Tene ACHE 15 16 ACH 14 1 0 Subsystem ADC 0 ACH 17 18 ACH15 Al SENSE 19 20 DACO OUT Polarity Bipolar Mode Differ DACI OUT EXTREF y AQ GND DIG GHD Range 20U Speed 42 usec AD 100 BD 0c ADO 27 28 JEDIOI Accessories None ADIDZ BDIOZ ADO BOO DIG GHD 5 4 5 4 SCANCLE EXTSTROBE STARTTA G STOPTRIG EXTCON SOURCE 1 GATE 1 OUT
187. examples daq run_me 11b you would configure the external scan clock by setting the Scan Clock Source control to 2 I O connector in the AI Start VI as shown in Figure 9 6 This disables the internal scan clock from driving the scan clock circuitry You do not need to specify a scan rate value because LabVIEW Data Acquisition Basics Manual 9 6 National Instruments Corporation Chapter 9 Letting an Outside Source Control Your Acquisition Rate your device ignores this value when you set it up to use an external scan clock Timeout seconds transposed voltage graph device 1 Al COHFIG number of scans to acquire 1000 Sean Clack Source 1 0 Connector Scan rate Cinput ignored with external clack Figure 9 6 Externally Controlling Your Scan Clock with the Getting Started Analog Input Example VI The NB MIO 16X cannot support external scan clocks as the other devices can The device layout does not allow you to directly provide an external scan clock Instead you can offer a timebase to the internal counter counter 5 that generates the scan clock Do this by sending a timebase into the source 5 pin and calling the Advanced VIs used by the AI Clock Config VI In addition you need to wire the alternate clock rate specifications as shown below into the AI Clock Config VI Remember that the which clock input of the AI Clock Config VI should be set to scan clock 1 alternate clock rate specification no change cl
188. f the SCXI modules have lowpass filters with cutoff frequencies at 4Hz and 10 kHz A lowpass filter eliminates all signal frequency components above the cutoff frequency The SCXI 1141 module has lowpass filters that have a cutoff frequencies from 10 Hz to 25 kHz Transducer Excitation Linearization Signal conditioning systems can generate excitation for some transducers Strain gauges and RTDs require external voltage and currents respectively to excite their circuitry into measuring physical phenomena This type of excitation is similar to a radio which needs power to receive and decode audio signals Some plug in DAQ devices and SCXI modules including the SCXI 1121 and SCXI 1122 modules provide the necessary excitation for transducers Many transducers such as thermocouples have a nonlinear response to changes in the physical phenomena being measured LabVIEW can linearize the voltage levels from transducers so the voltages can be scaled to the measured phenomena LabVIEW provides simple scaling functions to convert voltages from strain gauges RTDs thermocouples and thermistors For specific information about the VIs you can use with your SCXI module in LabVIEW refer to Chapter 20 Calibration and Configuration VIs in the LabVIEW Data Acquisition VI Reference Manual National Instruments Corporation 16 5 LabVIEW Data Acquisition Basics Manual Hardware and Software Setup for Your SCXI System SCXI ha
189. f you configure the counter to generate a continuous pulse train the counter repeats this process many times as shown on the bottom line of Figure 22 1 counter starts phase 1 phase 2 Single Pulse l phase 1 phase 2 phase 1 phase 2 Pulse Train Figure 22 1 Pulse Created with Positive Polarity and Toggled Output The following is a list of terms you should know before outputting a pulse or pulse train using LabVIEW Phase 1 refers to the first phase or delay to the pulse Phase 2 refers to the second phase or the pulse itself Period is the sum of Phase 1 and Phase 2 Frequency is the reciprocal of the Period 1 Period In LabVIEW you can adjust and control the times of phase 1 and phase 2 in your counting operation You do this by specifying a duty cycle The duty cycle equals Phase2 where Period Phase 1 Phase 2 Period Examples of various duty cycles are shown in Figure 22 2 The first line shows a duty cycle of 0 5 In this case phase 1 and phase 2 are the same duration A signal with a 0 5 duty cycle acts as a SOURCE for counter operations The second line shows a duty cycle of 0 1 In this case phase 1 has been increased and phase 2 has been decreased The LabVIEW Data Acquisition Basics Manual 22 2 National Instruments Corporation Chapter 22 Generating A Square Pulse or Pulse Trains final line shows a large duty cycle of 0 9 In this example phase 1 is very short and the phase 2 duration
190. g Your DAQ Device for ISA and PCMCIA Bus Computers Turn your computer back on LabVIEW DAQ software comes with a configuration utility for establishing all of the configuration parameters on ISA and PCMCIA bus computers This utility WOAQCONF saves the configuration parameters in a file named WDAQCONF CFG In Windows NT WDAQCONF saves the configuration parameters in the system registry Use WDAQCONF to assign a device number and set the base address interrupt level and DMA channels for your device When you install LabVIEW the software puts WOAQCONF in the same directory as the LabVIEW executable Figure 2 3 shows how your LabVIEW program window might look in Windows after installing WDAQCONF LabVIEW 8 g uninstall Update DAG Vie NI DAQ Read Me LabVIEW e Power Down Figure 2 3 Locating WDAQConf in Windows Run WDAQCONF by double clicking on its icon in Windows Figure 2 4 shows the NI DAQ Configuration Utility window which appears on your screen after you run WDAQCONF LabVIEW Data Acquisition Basics Manual 2 6 National Instruments Corporation Chapter 2 Installing and Configuring Your Data A NI DAQ Version 4 8 5 Configuration Utility Configuration Options Resources SCI Help Select A Device Number AT MIO 16F 5 Device Selected Base address DMA channels 6 F IRQ levels mo Contigure Test Device 1 1 2 3 4 5 B T a g Figure 2 4 NI DAQ Configuration
191. g in the driver You can set the AI Single Scan VI time limit in sec to zero Then the VI reads the DAQ Device FIFO and immediately returns whether the next scan was acquired or not The AI Single Scan VI voltage data output array will be empty if the scan was not yet acquired Poll for your analog input by using a Wait ms or Wait Until Next Ms Multiple VI together with the AI Single Scan VI ina while loop within your control loop diagram Set the wait time for a smaller time than your control loop interval at least twice as smaller If the voltage data output array is not empty exit the polling loop passing out the voltage data array and execute the rest of your control loop diagram This method does not return data as soon as the scan has been acquired as in the example discussed previously but provides ample time for other VIs and loops to execute This method is a good technique for balancing the CPU load between several loops and VIs running in parallel In the previously discussed techniques if you are using software delays for control loop speeds gt 1 Hz turn the Use Default Timer option off in the Performance dialog box in your LabVIEW Preferences Turning this off gives you around ms software timer resolution instead of the default 55 ms timer resolution LabVIEW Data Acquisition Basics Manual 6 10 National Instruments Corporation Buffering Your Way through Waveform Acquisition If you want to take more tha
192. gain more control over when you can check errors Multiple lmmediate Updates Figure 11 3 shows the block diagram of a VI that performs multiple updates The Write N Updates example VI located in examples daq analogout 11b is similar to Figure 11 3 The diagram shown in Figure 11 3 resembles the one shown in Figure 11 2 except that the While Loop executes the subVI repeatedly until either the error status or the stop boolean is TRUE You could use the Easy Analog Output VI AO Write One Update in a loop but this is inefficient because the Easy I O VIs configure the device every time they execute The AO LabVIEW Data Acquisition Basics Manual 11 2 National Instruments Corporation Chapter 11 One Stop Single Point Generation Write One Update VI configures the device only when the value of the iteration input is set to 0 timit settings Simple Error Handler vi voltage data Figure 11 3 Multiple Immediate Updates Using Intermediate VI Figure 11 3 shows an immediate software timed analog output VI application This means that software timing in a loop controls the update rate One good reason to use immediate software timed output is that your application calculates or processes output values one at a time however you should remember that software timing is not as accurate as hardware timed analog output For more information on hardware timed analog output refer to Chapter 12 Buffering Your Way through Waveform Gene
193. gital converter ADC otherwise known as a digitizer Your system should amplify low level signals at the DAQ National Instruments Corporation 16 3 LabVIEW Data Acquisition Basics Manual Chapter 16 Things You Should Know about SCX Ce Note Isolation device or at the SCXI module located nearest to the signal source as shown in Figure 16 2 Noise Instrumentation Ss Amplifier Lead Wires Low Level Signal External DAQ Board Amplifier Figure 16 2 Amplifying Signals Near the Source to Increase Signal to Noise Ratio You can minimize noise that lead wires pick up by using shielded cables or a twisted pair of cables and by minimizing wire length Also keeping signal wires away from AC power cables and monitors will help reduce 50 Hz or 60 Hz noise If you amplify the signal at the DAQ device the signal is measured and digitized with noise that may have entered the lead wires However if you amplify the signal close to the signal source with an SCXI module noise has a less destructive effect on the signal In other words the digitized representation is a better reflection of the original low level signal For more information consult Application Note 025 Field Wiring and Noise Considerations for Analog Signals You can access this note on the NI Fax Back system as well as the BBS World Wide Web or FTP site the numbers for which are located in the front of this manual Another common way to use SCXI is to
194. han the required accuracy of the data You can use single ended measurement systems when all input signals meet the following criteria e High Level Signals normally greater than 1 V e Short or Properly Shielded Cabling Wiring Traveling through a Noise Free Environment e All Signals Can Share a Common Reference Signal at the Source Use differential connections when your system violates any of the above criteria Until now you have learned about analog input in general Now you should focus on some analog input concepts that are specific to LabVIEW The following section discusses these Lab VIEW specific issues LabVIEW Data Acquisition Basics Manual 5 12 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input LabVIEW and Analog Input Channel Addressing with the AMUX 64T An AMUX 64T external multiplexer device expands the number of analog input signals a plug in DAQ device can measure You can address AMUX 64T channels when you attach one two or four AMUX 64T devices to a plug in DAQ device You can multiplex four eight or 16 AMUX 64T channels into one device channel The scanning order of these AMUX 64T channels is fixed To specify a range of AMUX 64T channels enter the device channel into which the range is multiplexed in the channel list For example if you have no AMUX 64T devices a channel list element of 0 specifies device channel 0 If you have a AMUX 64T device a channel list elem
195. he AI Acquire Waveforms VI ooo ce eceeceeseeeeeeceeeeseeeeetseeeeeeaeenees 7 3 Figure 7 4 Using the AI Waveform Scan VI to Acquire Multiple Wavelorins ner tds oes d ta ae iste E eh eee ented 7 4 Figure 7 5 Using the Intermediate VIs to Acquire Multiple Waveforms 7 5 Figure 7 6 Simple Buffered Analog Input Example 0 eee eee eeeeeeeeees 7 6 Figure 7 7 Simple Buffered Analog Input with Graphing 0 0 00 7 7 Figure 7 8 Taking a Specified Number of Samples with the AI Waveform Scam Vio oeo e aeara E aS E EE shavers T E ENT 7 8 Figure 7 9 Controlling the Sampling Rate in a Simple Buffered Vaea LAETTE TO p EEEE E EE E EEEO 7 9 Figure 7 10 Writing to a Spreadsheet File after Acquisition 2 0 0 eee 7 10 Figure 7 11 How a Circular Buffer Works 000 cece eee eeeeeeceeeteeeesesseeeaeeseees 7 11 Figure 7 12 Continuously Acquiring Data with the AI Continuous Scan VI 7 12 Figure 7 13 Using Intermediate VIs to Continuously Acquire Time Sampled Data panenan a E asec eset a aoe sted 7 13 Figure 7 14 Basic Circular Buffered Analog Input Using the Intermediate VIS eosin o eu AEE E E E 7 14 Figure 8 1 Diagram of a Digital Trigger eesesesseeeeeeseersresesresreerssreresrsresresesreses 8 2 Figure 8 2 Digital Triggering with Your DAQ Device ssessesseeesserseesrseesrrerseeees 8 3 Figure 8 3 Block Diagram of the Acquire N Scans DTrig VI seee 8 4 Figure 8 4 Diagram of an Analog Trigger eeseessereeeessersrese
196. he DAQ device for analog input and output only on the first iteration of the loop The loop rate as well as the acquisition rate is specified by loop rate The reason why the actual loop period is important is because user interaction affects the loop and acquisition rate When a user presses the mouse button for instance that action interrupts the system clock which controls the loop rate If your analog acquisition rate for control loops does not need to be consistent then use software timed control loops Using Hardware Timed Analog 1 0 Control Loops For a more precise timing of your control loops and more precise analog input scan rate use hardware timed control loops National Instruments Corporation 6 7 LabVIEW Data Acquisition Basics Manual Chapter6 One Stop Single Point Acquisition device 1 An example of hardware timed non buffered control loops is the Analog IO Control Loop hw timed VI located in examples daq anlog_io 1lb With hardware timed control loops your acquisition is not interrupted by user interaction Hardware timed analog input automatically places the data in your DAQ device FIFO buffer at an interval determined by the analog input scan rate You can synchronize you control loop diagram to this precise analog input scan rate by repeatedly calling the AI Single Scan VI to read the oldest data in the FIFO The AI Single Scan VI returns as soon as the next scan has been acquired by the DAQ De
197. he time it takes one box to be processed through an operation The event would be an edge every time a box goes by a point which prompts a digital signal to change in value Measuring a Pulse Width You can measure pulse width by determining the number of pulses of known frequency that are generated during the period to be measured As illustrated in Figure 23 1 connect the pulse you want to measure to the GATE input pin and a signal of a known frequency to the SOURCE input pin Your counter must be configured for high level mode gating which means the counter starts counting when the gated signal goes high and stops counting at the end of the pulse Figure 23 1 describes how a pulse of an unknown width Tpw gates a counter configured to count a timebase clock of a known period Ts The pulse width equals the timebase period times the count or T p T Xxcount V S count register frequency SOURCE Source Figure 23 1 Counting Input Signals to Determine Pulse Width National Instruments Corporation 23 1 LabVIEW Data Acquisition Basics Manual Chapter 23 Measuring Pulse Width The SOURCE input can be an external or internal signal An internal signal or clock is based upon the type of counter chip on your device With Am9513 devices you can choose frequencies or timebases of 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz DAQ STC devices have internal timebases of 20 MHz and 100 kHz Figure 23 2 shows how to physically conn
198. he user area as you are calibrating and then use SCXI Cal Constants VI again at the end of your calibration sequence to copy the calibration table in the user area to the default load area in EEPROM Remember that constants that are stored in the default load area can be overwritten If you want to use the constants later you should store a backup copy of the constants in the user area in EEPROM Repeat the procedure above for each channel and range you want to calibrate Subsequent analog outputs will use your new constants to scale voltage or current to the correct binary value For more information on the SCXI Cal Constants VI refer to Chapter 20 Calibration and Configuration VIs in the LabVIEW Data Acquisition VI Reference Manual LabVIEW Data Acquisition Basics Manual 20 8 National Instruments Corporation Want Precision Timing Use Counters This section describes the different ways you can use counters with your data acquisition application including generating a pulse or pulses measuring pulse width frequency and period counting events and dividing frequencies for precision timing Part 6 Want Precision Timing Use Counters contains the following chapters e Chapter 21 Things You Should Know about Counters shows you how to add high precision timing to your data acquisition DAQ system by using counters and explains basic counter concepts e Chapter 22 Generating a Square Pulse or Pulse Trains d
199. ies for input want to use the OUT1 OUT 2 OUT3 and IN1 IN2 IN3 pins on my DIO 32F board How do address those pins using the Easy 1 0 Digital Vis in LabVIEW These output and inputs pins are addressed together as port 4 OUT1 and IN1 are referred to as bit 0 OUT2 and IN2 are referred to as bit 1 and OUT3 and IN3 are referred to as bit 2 Only the NB DIO 32F has 3 pins for each direction If you use the Write To Digital Port VI you will output on the OUT pins and if you use the Read From Digital Port VI you will input from the IN pins want to use a TTL digital trigger pulse to start data acquisition on my DAQ device noticed there are two types of triggers Digital Trigger A and Digital Trigger A amp B Which digital trigger setting should use and where should connect the signal You should use Digital Trigger A which stands for first trigger to start a data acquisition Digital Trigger B which stands for second trigger should only be used if you are doing both a start AND a stop trigger for your data acquisition Connect your trigger signal to either STARTTRIG pin 38 if you are using an AT MIO 16 AT MIO 16D NB MIO 16X or EXTTRIG or DTRIG for any other board that has that pin The only analog input boards on which you cannot do a digital trigger are the PC LPM 16 DAQCard 700 and the DAQCard 500 Refer to the AI Trigger Config description in Chapter 6 Advanced Analog Input VIs in the LabVIEW Data Acq
200. ignal entering through the I O connector handshake source 2 which is the default value or the RTSI connector handshake source 3 You only need to use the clock frequency if you are performing pattern generation having an internal handshake source For DAQ devices other than the DIO 32F devices you can use a VI similar to the one above to output digital data The main difference is that you use an Advanced Digital VI like DIO Buffer Control instead of the DIO Start VI as shown in Figure 15 6 The reason for using the DIO Buffer Control VI is because the DIO Start VI contains Digital Clock Config and Digital Mode Config VIs that work only with the National Instruments Corporation 15 7 LabVIEW Data Acquisition Basics Manual Chapter 15 Shaking Hands with a Digital Partner DIO 32F devices You do not need to use the Handshake source and clock frequency inputs because of the external handshaking signal source number of updates 1000 feed Fore aTe direction output Figure 15 6 Pattern Generation Using DAQ Devices Other Than DIO 32F Devices Reading information is similar to writing data when using digital handshaking In the example shown in Figure 15 7 the VI is reading data into the DIO 32F devices while using external handshaking For the DIO 32F devices the DIO Config VI can set or change the handshaking mode for instance whether you trigger digital communication on an edge or at a certain level
201. indows A 3 to A 4 multiple channel single point analog input 6 2 to 6 5 multiple waveform acquisition 7 3 to 7 5 scan clock control 9 5 to 9 8 SCXI application for measuring temperature example 19 2 to 19 5 selecting input settings 5 6 to 5 12 calculating code width 5 6 to 5 7 considerations for selecting 5 6 to 5 12 differential measurement system 5 9 to 5 10 measurement precision for various device ranges and limit settings table 5 8 nonreferenced single ended measurement system 5 11 to 5 12 referenced single ended measurement system 5 10 to 5 11 signals See analog input signals single buffered analog input examples 7 6 to 7 10 single channel single point analog input 6 1 to 6 to 6 2 single waveform acquisition 7 2 to 7 3 software triggering 8 10 to 8 14 terminology 5 17 to 5 18 triggering 8 6 to 8 10 analog input output control loops 6 6 to 6 10 hardware timed control loops 6 7 to 6 9 improving performance 6 9 to 6 10 overview 6 6 software timed control loops 6 6 to 6 7 analog input SCXI modules multiplexed mode 17 4 parallel mode 17 5 National Instruments Corporation Index analog input signals choosing a measurement system 5 3 to 5 6 choosing between analog and digital signals 4 3 defining signals 5 1 to 5 2 device voltage range 5 4 to 5 5 floating signal sources 5 3 grounded signal sources 5 2 referenced and non referenced 5 2 resolution of ADC 5 3 to 5 4 signal voltage r
202. ing Using the Simple Error Handler VI The following shows an example of the dialog box the Error Handler VIs display if an error occurs Error 10005 occurred at Al Group Config Possible reasons DAQ or DSP badDeviceEn The device ts invalid Please refer to the LabVIEW Function Reference Manual for more information on the error handler VIs Single Stepping through a VI Single stepping through a VI allows you to execute one node at a time in the block diagram A node can be subVIs functions structures formula nodes and attribute nodes Refer to Chapter 5 Executing and Debugging in the LabVIEW User Manual and the LabVIEW Tutorial Manual for more information on single stepping Execution Highlighting Execution highlighting shows you how the data passes from one node to another in your program When you turn execution highlighting on data movement is marked by bubbles moving along the wires Refer to National Instruments Corporation 27 3 LabVIEW Data Acquisition Basics Manual Chapter 27 Debugging Techniques Chapter 5 Executing and Debugging in the LabVIEW User Manual and the LabVIEW Tutorial Manual for more information on execution highlighting Using the Probe Tool If your VI is producing questionable results you may want to use the Probe tool to check intermediate values in a VI The Probe tool will help you narrow down where the incorrect results are occurring Refer to Chapter 5 Executing and Debugging in
203. input channels are multiplexed into one module output so that your cabled DAQ device has access to the module s multiplexed output as well as the outputs on all other multiplexed modules in the chassis through the SCXI bus Also called serial mode A set of semiconductor or electromechanical switches with a common output that can select one of a number of input signals and that you commonly use to increase the number of signals measured by one ADC NuBus The NI DAQ configuration utility on the Macintosh A stand alone executable that NI DAQ installs in your NI DAQ root drive that detects and configures any Plug and Play devices you have in your computer A file generated by the NI PNP EXE that contains information about all the National Instruments devices in your computer including Plug and Play devices Execution elements of a block diagram consisting of functions structures and subVIs A type of digital acquisition generation where LabVIEW updates the digital lines or port states immediately or returns the digital value of an input line Also called immediate digital I O Signal sources with voltage signals that are not connected to an absolute reference or system ground Also called floating signal sources Some common example of non referenced signal sources are batteries transformers or thermocouples Nonreferenced single ended All measurements are made with respect to a common reference but the
204. input limits LabVIEW LabVIEW Index channel list Array Selected Selected Array SCXI Gain MIO Gain 0 ob0 scl md1 0 7 0 01 to 0 01 1000 1 0 ob0 scl md1 0 7 0 001 to 0 001 2000 5 0 scl md1 0 7 0 001 to 0 001 2000 1 0 ob0 scl md1 0 3 0 1 to 0 1 100 1 1 ob0 scl md1 4 15 0 01 to 0 01 100 10 0 ob0 scl md1 0 15 0 01 to 0 01 10 100 1 ob0 scl md1 16 31 1 0 to 1 0 10 1 0 ob0 scl md1 0 3 1 0 to 1 0 10 1 1 ob0 scl md1 4 15 0 1 to 0 1 10 10 2 ob0 scl md2 0 7 0 01 to 0 01 1000 1 Applies if the MIO device supports a gain of 5 some MIO devices do not This case forces a smaller gain at the SCXI module than at the MIO device because the input limits for the next channel range on the module require a small SCXI gain This type of gain distribution is not recommended because it defeats the purpose of providing amplification for small signals at the SCXI module The small input signals are only amplified by a factor of 10 before they are sent over the ribbon cable where they are very susceptible to noise To use the optimum gain distribution for each set of input signals do not mix very small input signals with larger input signals on the same SCXI 1100 module unless you are sampling them at different times LabVIEW Data Acquisition Basics Manual array at the right side of the panel shows the settings for each channel The gain indicator displays the total gain for the channel which is the product of the SCXI gain and
205. input signals choosing between analog and digital signal analysis 4 3 simple buffered analog input data buffer overview 7 1 to 7 2 examples displaying waveforms on graphs 7 6 to 7 7 sampling with multiple starts 7 7 to 7 9 writing to spreadsheet file 77 9 multiple waveform acquisition 7 3 to 7 5 single waveform acquisition 7 2 to 7 3 waiting to analyze data 7 1 to 7 2 Simple Error Handler VI analog output SCXI example 19 15 debugging VIs 27 2 to 27 3 multiple channel single point analog input 6 5 single channel single point analog input choosing between single point and multi point acquisition 4 4 description 6 1 to 6 2 single ended measurement system nonreferenced 5 11 to 5 12 referenced 5 10 to 5 11 single immediate updates 11 1 to 11 2 single point analog output choosing between single point or multiple point generation 4 4 overview 10 1 single stepping through VIs 27 3 single waveform acquisition 7 2 to 7 3 software configuration errors debugging 27 1 to 27 2 software timed analog input output control loops 6 6 to 6 7 National Instruments Corporation Index software timing 10 1 software triggering description 8 10 to 8 12 examples 8 12 to 8 14 timeline of conditional retrieval figure 8 11 SOURCE input increasing measurable width range 23 4 measuring pulse width 23 1 to 23 2 SOURCE input pin 21 2 spreadsheet files Cont Acq to Spreadsheet File vi 7 15 simple buffered analog input e
206. ion does not use a buffer created in CPU memory but instead uses the DAQ device FIFO The input limits parameter also known as limit settings affects the expected voltage LabVIEW Data Acquisition Basics Manual 6 8 National Instruments Corporation Chapter6 One Stop Single Point Acquisition range of the input signals For more information on input limits limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts The AI Start VI begins the analog acquisition at the loop rate scan rate parameter On the first iteration of the loop the AI Single Scan VI reads the newest data in the FIFO Some data may have been acquired between the execution of the AI Start and the AI Single Scan VIs On the first iteration of the loop the application reads the latest data acquired between the AI Start and the AI Single Scan VIs On every subsequent iteration of the loop the application reads oldest data in the FIFO which is the next acquired point in the FIFO If more than one value was stored in the DAQ device FIFO when you read it your application was not able to keep up with the control loop acquisition and you have not responded with one control loop interval After the application completes analog acquisition and generation then the AI Clear VI clears the analog input task Figure 6 7 also includes a waveform chart in the control loop This reduces your maximum loop rate You can speed up the maximum rate of the control loop b
207. ire or 4 wire configuration The lead wires in the 4 wire configuration are resistance matched If you use a 2 wire or 3 wire RTD they are unmatched Resistance in the lead wires that connect your RTD to the measuring system will add error to your readings If you are using lead lengths greater than 10 feet you will need to compensate for this lead resistance RTDs are also classified by the type of metal they use The most common metal is platinum National Instruments Corporation 19 9 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications Note You should only use the RTD conversion function in LabVIEW for platinum RTDs If you do not have a platinum RTD the voltage temperature relation will be different so the LabVIEW conversion function cannot be used For more information on how the lead wires affect RTD measurements as well as general RTD information look at the Measuring Temperature with RTDs application note You can find this note on the NI FaxBack system or by accessing the BBS World Wide Web or FTP site the numbers for which are in the front of this manual Signal conditioning is needed to interface an RTD to a DAQ device or an SCXI 1200 module Signal conditioning required for RTDs include current excitation for the RTD amplification of the measured signal filtering of the signal to remove unwanted noise and isolation of the RTD and monitored system from the host computer Typically you would use
208. is ID The string ob1 sc2 md1 0 means channel 0 on the module in slot 1 of SCXI chassis 2 multiplexed into onboard channel 1 Remember to use the correct chassis ID number from the configuration utility and to put the jumpers from the power supply module in the correct position for each chassis When an MIO Series device is cabled to multiple chasses the number of reserved analog input channels depends on the number of chasses Refer to Table B 14 Reserved DAQ Device Analog Input Channels in Appendix B Hardware Capabilities of the LabVIEW Data Acquisition VI Reference Manual for more channel information When you access digital SCXI modules you do not use onboard channels Therefore if you have multiple chassis you only have to choose the correct SCXI chassis ID and module slot LabVIEW Data Acquisition Basics Manual 19 18 National Instruments Corporation Chapter 19 Common SCX Applications You can perform DAQ operations on channels in multiple SCXI chassis at the same time For example the first element of your channels array could be ob0 sc1 md1 0 31 and the second element of the channels array could be 0b1 sc2 md1 0 31 Then LabVIEW would scan 32 channels on module 1 of SCXI chassis 1 using onboard channel 0 then the 32 channels on module 1 in SCXI chassis 2 using onboard channel 1 Remember that the scan rate you specify is how many scans per second LabVIEW performs For each scan LabVIEW reads every channel in the cha
209. is longer counter starts 4 phase 1 phase 2 Duty Cycle 0 5 F Duty Cycle 0 1 Duty Cycle 0 9 Figure 22 2 Pulse Duty Cycles Note A high duty cycle denotes a long pulse phase relative to the delay phase Now that you know the terms involving generating a single square pulse or a pulse train you can learn about the LabVIEW VIs and the physical connections needed to implement your application Generating a Single Square Pulse When do you need to generate a single square pulse A single pulse could be used to trigger analog acquisition or to gate a counter operation especially if you are triggering off an edge of the pulse Refer to the How to Generate Pulses and Pulse Trains VI located in examples daq counter 11b as you read this section Figure 22 3 illustrates how to connect your counter and device to generate a square pulse The edges of the internal SOURCE signal are counted to generate the output signal You get the pulse signal for your external device from the counter s OUT pin and you can optionally gate the operation with the signal connected to the GATE Instead of National Instruments Corporation 22 3 LabVIEW Data Acquisition Basics Manual Chapter 22 Generating A Square Pulse or Pulse Trains using an internal timebase as your SOURCE you could connect an external signal Basic Connection Optional Connection OUT gt SOURCE OUT DAQ Device Y Cou
210. isolate the transducer signals from the computer for safety purposes When the signal being monitored contains large voltage spikes that could damage the computer or harm the operator you should not directly connect the signal to a DAQ device without some type of isolation Another reason for isolation is to make sure that the measurements from the DAQ device are not affected by differences in ground potentials When the DAQ device and the signal are not referenced to the same ground potential a ground loop may occur Ground loops can cause an inaccurate representation of the measured signal If the potential difference between the signal ground and the DAQ device ground is LabVIEW Data Acquisition Basics Manual 16 4 National Instruments Corporation Filtering Chapter 16 Things You Should Know about SCX large then damage may even occur to the measuring system Using isolated SCXI modules will eliminate the ground loop and ensure that the signals are accurately measured Signal conditioning systems can filter unwanted signals or noise from the signal you are trying to measure You can use a noise filter on low rate or slowly changing signals like temperature to eliminate higher frequency signals that can reduce the accuracy of the digitized signal A common use of a filter is to eliminate the noise from a 60 Hz AC power line A lowpass filter of 4 Hz is best for removing the 60 Hz AC noise from signals sampled at low rates Most o
211. isplay of Palette Name Figure 3 1 Accessing the Data Acquisition Palette National Instruments Corporation 3 3 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts The Data Acquisition palette contains six subpalette icons that take you to the different classes of DAQ VIs Figure 3 2 shows what each of the icons in the Data Acquisition palette means Analog Output VIs Digital I O VIs Analog Input VIs Counter VIs Calibration and Configuration Vis Signal Conditioning VIs Figure 3 2 Data Acquisition Palette Description DAQ VI Organization In most of the DAQ subpalettes the VIs are arranged in different levels according to their functionality You can find some of the following four levels of DAQ VIs within the DAQ VI subpalettes e Easy VIs e Intermediate VIs e Utility VIs e Advanced VIs LabVIEW Data Acquisition Basics Manual 3 4 National Instruments Corporation Easy VIs Intermediate Vis Chapter 3 Basic LabVIEW Data Acquisition Concepts A good example of a palette that contains all of the available levels of DAQ VIs is the Analog Input palette Figure 3 3 shows this palette HL Analog Input Easy Analog Input VIs Intermediate Analog Input Vis Advanced Analog Input Vis Analog Input Utility Vis Figure 3 3 Analog Input VI Palette Organization The Easy VIs perform simple DAQ operations and are typically the first row of VIs in the
212. ith the Easy VIs determined by the amplifier offset With the Intermediate VIs you can change the scaling constants before acquisition begins while the Advanced VIs include functions that are not necessary to accurately measure temperature National Instruments Corporation 19 5 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications with SCXI modules The examples discussed in this section use Intermediate VIs along with transducer specific VIs First you should learn how to measure temperature using the SCXI 1100 with thermocouples You can use the example SCXI 1100 Thermocouple VI located in examples daq anlogin scxi 11b Open the VI and continue reading this section In order to reduce the noise on the slowly varying signals produced by thermocouples you can average the data and then linearize it For greater accuracy you can measure the amplifier offset which helps scale the data and lets you eliminate the offset error from your measurement The diagram below shows how you can program the Acquire and Average VI to measure the amplifier offset You can find this VI in vi lib dag zdaqutil 11b This VI acquires 100 measurements from the amplifier offset designated in the offset channel input by calgnd and then averages the measurements When you determine the amplifier offset you must always use the same input limits and clock rates that you will be using in the acquisition The Acquire and Average VI can m
213. ition Basics Manual 5 10 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input building ground Figure 5 9 depicts a 16 channel RSE measurement system Instrumentation Amplifier AIGND O Figure 5 9 16 Channel RSE Measurement System Nonreferenced Single Ended Measurement System DAQ devices often use a variant of the RSE measurement technique known as the nonreferenced single ended NRSE measurement system In an NRSE measurement system all measurements are made with respect to a common reference because all of the input signals are already grounded Figure 5 10 depicts an NRSE measurement system where AISENSE is the common reference for taking measurements and AIGND is the system ground All signals must share a common reference at AISENSE National Instruments Corporation 5 11 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input Instrumentation Amplifier AISENSE Figure 5 10 16 Channel NRSE Measurement System In general a differential measurement system is preferable because it rejects not only ground loop induced errors but also the noise picked up in the environment to a certain degree On the other hand the single ended configuration allows for twice as many measurement channels and is acceptable when the magnitude of the induced errors is smaller t
214. ition Basics Manual vi National Instruments Corporation Table of Contents Nonreferenced Single Ended Measurement System eee eeeeeeeeeeees 5 11 LabVIEW and Analog Input 00 aen iieii ea E E E A 5 13 Channel Addressing with the AMUX 64T sssesesseessseseeesseesssrsresreresresrsreses 5 13 The AMUX 64T Scanning Order oo cece ceceseceeeceeeeeseeeaeeseeeaeeeeees 5 14 Important Terms You Should Know oo cece eseeseesecececeeceeeeseeeseseeeesesseesseeseeeseeseees 5 17 Chapter 6 One Stop Single Point Acquisition Single Channel Single Point Analog Input 20 0 eee ee eeceseceeeeeeceeesseeesetseeeaeeseens 6 1 Multiple Channel Single Point Analog Input eee cece eeeeeeceeeeseseeeeseeseeeseeeeees 6 2 Using Analog Input Output Control Loops oo eee eee eesceeeeeeeseseeeesereeeseeseeeseeeees 6 6 Using Software Timed Analog I O Control Loops cece ee eeeeseeeereeeeees 6 6 Using Hardware Timed Analog I O Control Loops 00 0 cece eeeeereeeeees 6 7 Improving Control Loop Performance 000 0 ec eeee eee eseeeeeeeeeeeeeeeseeseeeaeeeees 6 9 Chapter 7 Buffering Your Way through Waveform Acquisition Can You Wait for Your Data ee cee esccneeereeneeeseceeecsesneessesseesnesenesseseseeseseesensees 7 1 Acquiring a Single Waveform 0 eee eeeeseceeceseceeeeseeesecseeesesseeeseeeeeaeeseens 7 2 Acquiring Multiple Waveforms 0 ceceeeseeceseceeeeseeesecseseseseeeseeseeeseeseees 7 3 Simple Buffered Analog Input Examples 20 0
215. itional retrieval off mode off channel index 0 mu rising kel 0 0 PeT Figure 8 8 The Al Read VI Conditional Retrieval Cluster ce Note Remember that the actual data acquisition is started by running your VI and that the conditional retrieval just controls the returning of data already being acquired When acquiring data with conditional retrieval you typically store the data in a memory buffer similar to hardware triggering applications After you start running the VI the data is placed in the buffer Once the retrieval conditions have been met the AI Read VI searches the buffer for the desired information As with hardware analog triggering you specify the analog channel called channel index of the triggering signal as well as the slope rising or falling and the level The AI Read VI begins searching for the retrieval conditions in the buffer at the read search position another input of the AI Read VI Once the slope and level conditions on channel index have been found the read search position indicates the location where the retrieval conditions were met The offset a value of the conditional retrieval input cluster indicates the scan locations from which the VI begins reading data relative to the read search position A negative offset indicates data prior to the retrieval condition pretrigger data and a positive offset indicates data after the retrieval condition posttrigger data The skip count parameter shows
216. k control to channel clock 1 and set the clock frequency to 1 00 no change Now run the VI The actual clock rate specification cluster is on the right side of the panel National Instruments Corporation 18 5 LabVIEW Data Acquisition Basics Manual Common SCXI Applications Now that you have your SCXI system set up and you are aware of the special SCXI programming considerations you should learn about some common SCX applications This section will cover example VIs for analog input analog output and digital modules For analog input you will learn how to measure temperature with thermocouples and RTDs and strain with strain gauges using the SCXI 1100 SCXI 1102 SCXI 112x and SCXI 1141 modules If you are not measuring temperature or pressure you can still gain basic conceptual information on how to measure voltages with an analog input module Read these sections and then apply the information to measuring your transducer Another analog input module the SCXI 1140 is a simultaneous sampling module All the channels acquire voltages at the same time which means you can preserve interchannel phase relationships After all channel voltages are sampled by going into hold mode the software will read one channel at a time When a scan of channels is done the SCXI 1140 module returns to track mode until the next scan period Both of these operations are performed by the analog input VIs You can use any of the data a
217. king in a noisy environment If you are then you may have Signal Conditioning eXtensions for Instrumentation SCXI modules connected to your DAQ device or the parallel port of your computer SCXI modules can filter and isolate noise from signals They can also amplify low voltage or current signals SCXI modules expand the number of channels to acquire or generate data DAQ devices are primarily used alone when extra signal conditioning is not necessary If you are using a DAQ device then read question 2 If you are using SCXI go to Part 5 SCX Getting Your Signals in Great Condition 2 Analog or Digital Signal Analysis Does your signal have two discrete values that are TTL logic signals If so then you have a digital signal Otherwise you have an analog signal The type of information you would need to know from an analog signal is the level discrete value shape and frequency content Analog or Digital Signal Acquisition or Generation If you want to measure and analyze signals from a source outside the computer you want to acquire signals If you want to send signals to an outside instrument to control its operation then you want to generate signals If you want to acquire analog signals go to question 4 If you want to generate analog signals refer to question 5 If you want to acquire and generate analog signals refer to the Using Analog I O Control Loops section of Chapter 6 One Step Single Point Acquisition
218. l Instruments Corporation One Stop Single Point Acquisition This chapter shows you how to acquire one data point from a single channel and then one data point from each of several channels using LabVIEW Single Channel Single Point Analog Input A single channel single point analog input is an immediate non buffered operation In other words the software reads one voltage from an input channel and immediately returns the value to you This operation does not require any buffering or timing You should use single channel single point analog input when you need one data point from one channel and when the information you seek an analog voltage A good example of when you might want to use this would be if you needed to periodically monitor the fluid level in a tank You could connect the transducer that produces a voltage representing the fluid level to a single channel on your DAQ device and initiate a single channel single point acquisition whenever you want to know the fluid level For most basic operations use the AI Sample Channel VI located in Functions DAQ Analog Input The Easy Analog Input VI AI Sample Channel measures the signal attached to the channel you specify on your DAQ device and returns the scaled voltage Figure 6 1 shows how you can wire this VI device channel 0 high Tirnit C104 low limit 104 Figure 6 1 The Al Sample Channel VI Help Window National Instruments Corporation 6 1
219. ler than the device voltage range then you should set your limit settings to values that more accurately reflect your signal range Table 5 1 shows how the National Instruments Corporation 5 7 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input code width of the 12 bit DAQ devices vary with device ranges and limit settings Table 5 1 Measurement Precision for Various Device Ranges and Limit Settings Device Voltage Limit Settings Precision Range 0 to 10V 0 to 10 V 2 44 mV Oto5 V 1 22 mV 0to2 5 V 610 uV 0 to 1 25 V 305 uV Otol V 244 uV 0to0 1 V 24 4 uV OmV to 20 mV 4 88 uV 5 to 5V 5 to 5V 2 44 mV 2 5 to 2 5 V 1 22 mV 1 25 to 1 25 V 610 uV 0 625 to 0 625 V 305 uV 0 5 to 0 5 V 244 uV 50mV to 50 mV 24 4 uV 10mV to 10 mV 4 88 uV 10 to 10V 10 to 10 V 4 88 mV 5to5 V 2 44 mV 2 5 to 2 5 V 1 22 mV 1 25 to 1 25 V 610 uV ltolV 488 uV 0 1 to 0 1 V 48 8 uV 20mV to 20 mV 9 76 UV The value of 1 LSB of the 12 bit ADC In other words the voltage increment corresponding to a change of 1 count in the ADC 12 bit count For more information on the device range and limit settings for your device refer to the tables in Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual In these tables there is information on gain settings for each device For more information on gain refer to the Limit Settings section of Chapter 3
220. limit setting voltages forms a cluster Analog output limits have a third member the reference source but for simplicity LabVIEW refers to limit settings as a pair of voltages LabVIEW uses an array of these clusters to assign limits to the channels in your channel string array National Instruments Corporation 3 11 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts As the previous Channel Port and Counter Addressing section explains LabVIEW uses an array of strings to specify which channels belong to a group Also remember LabVIEW lists as few as one channel to as many as all of the device s channels in a single array element in the channel string array LabVIEW also assigns all the channels listed in a channel string array element the same settings in the corresponding limit settings cluster array element Figure 3 6 illustrates one case of this Channel String Array Limit high limit qs 00 Settings Cluster Array imi Tow limit low limit Figure 3 6 Limit Settings Case 1 In this example channels 0 3 or 0 1 2 and 3 are assigned limits of 10 00 to 10 00 volts Channel 4 has limits of 5 00 to 5 00 volts Channels 5 6 and 7 have limit settings of 1 00 to 0 00 volts If the limit settings cluster array has fewer elements than the channel string array LabVIEW assigns any remaining channels the limit LabVIEW Data Acquisition Basics Manual 3 12 National Instruments
221. lts as shown in Figure 5 5 the same ADC now separates a 20 volt range into eight divisions The LabVIEW Data Acquisition Basics Manual 5 4 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input smallest detectable voltage increases from 1 25 to 2 50 volts and you now have a much less accurate representation of the signal E Range OV to 10V Range 10V to 10V Figure 5 5 The Effects of Range on ADC Precision Signal Voltage Range Limit Settings Limit settings are the maximum and minimum voltages of the signal you are measuring A more precise limit setting allows the ADC to use more digital divisions to represent the signal For example using a 3 bit ADC and a device range setting of 0 00 to 10 00 volts Figure 5 6 shows the effects of a limit setting between 0 and 5 volts and 0 and 10 volts With a limit setting of 0 to 5 volts the ADC uses only four of the eight divisions in the conversion By changing the limit setting to the device s range setting the ADC now has access to all eight digital divisions This makes the digital representation of the signal more accurate National Instruments Corporation 5 5 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input Limit Settings 0 to 10V F
222. match those on your device Select your DMA and IRQ settings from the choices listed in the DMA and IRQ menus Save these settings by choosing Configuration Save WDAQCONF tests your settings at this time If a test fails a message appears explaining the reason for the failure If all tests are successful LabVIEW saves your settings and the device you selected appears in the Select a Device Number box in the NI DAQ Configuration Utility window You have now configured your DAQ device and saved the information When using WDAQCONF you cannot assign a base address DMA or IRQ setting that conflicts with another DAQ device unless you disable the resource checking feature Disable this feature by selecting Options Resource Checks which removes the check mark beside this menu item You should never share base address space between devices You can share DMA and IRQ resources as long as the devices sharing a resource do not attempt to use it simultaneously LabVIEW Data Acquisition Basics Manual 2 8 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware cz Note You cannot change the Resource Checks option if you are currently changing the configuration of any device including SCXI modules Make sure all your Device Number windows and your SCXI Configuration windows are closed before you select this option Refer to the Configuring and Testing Your DAQ Devices with WDAQCONF in Windows sec
223. mbined with the SCXI hardware form a diamond shaped configuration of resistors know as a Wheatstone bridge When you apply a voltage to the bridge the differential voltage Vm varies as the resistor values in the bridge change The strain gauge usually supplies the resistors that change value with strain DC Voltage Excitation Physical strain gauge Supplied by signal Rg is value at rest conditioning hardware Figure 19 4 Half Bridge Strain Gauge Strain gauges come in full bridge half bridge and quarter bridge configurations For a full bridge strain gauge the four resistors of the Wheatstone bridge are physically located on the strain gauge itself For a half bridge strain gauge the strain gauge supplies two resistors for the Wheatstone bridge while the SCXI module supplies the other two resistors as shown above For a quarter bridge strain gauge the strain gauge only supplies one of the four resistors for a Wheatstone bridge For more information on how to connect your strain gauge to SCXI refer to the Getting Started with SCXI manual The SCXI 1121 and the SCXI 1122 modules are commonly used with strain gauges because they include voltage or current excitation and internal Wheatstone bridge completion circuits You can also use the signal conditioning device SC 2043SG as an alternative to SCXI modules The device is designed specifically for strain gauge measurements For more information on this device look in your Natio
224. met The technique you use on a data acquisition board to keep a continuous buffer filled with data so that when the trigger conditions are met the sample includes the data leading up to the trigger condition Multiple pulses A form of counter signal generation by which a pulse is outputted when a counter reaches a certain value G 11 LabVIEW Data Acquisition Basics Manual Glossary R read mark read mode referenced signal sources Points to the scan at which a read operation begins Analogous to a file I O pointer the read mark moves every time you read data from an input buffer After the read is finished the read mark points to the next unread scan Because multiple buffers are possible you need both the buffer number and the scan number to express the position of the read mark Indicates one of the four reference marks within an input buffer that provides the reference point for the read This reference can be the read mark the beginning of the buffer the most recently acquired data or the trigger position Signal sources with voltage signals that are referenced to a system ground such as the earth or a building ground Also called grounded signal sources referenced single ended RSE All measurements are made with respect to a common reference measurement system RMS row major order RSE RTD RTSI run_me llb LabVIEW Data Acquisition Basics Manual or a ground Also called a grounded measuremen
225. module the DAQ device has access to that module s multiplexed output as well as all other 44 modules in the chassis through the SCXIbus The analog input VIs route the multiplexed analog signals on the SCXIbus for you transparently So if you operate all modules in the chassis in multiplexed mode you only need to cable one of the modules directly to the DAQ device The SCXI 1200 module MIO devices and Lab PC devices support multiple channel and multiple scan acquisitions in multiplexed mode The Lab NB and Lab LC PC LPM 16 and DAQCard 700 support only single channel or single scan acquisitions in multiplexed mode When you cable a DAQ device to a multiplexed module the multiplexed output of the module and all other multiplexed modules in the chassis appears at analog input channel 0 of the DAQ device by default Windows Multiplexed Mode for the SCXI 1200 In multiplexed mode the SCXI 1200 can access the analog signals on the SCXI bus The DAQ VIs can multiplex the channels of analog input modules and send them on the SCXI bus This means that if you configure the SCXI 1200 for multiplexed mode you can read the multiplexed output from other SCXI analog input modules in the chassis In fact during the same scanning operation you can have analog input channels from the SCXI 1200 with input channels from other analog input modules The SCXI 1200 only reads analog input module channels configured in multiplexed mode not in parall
226. n addressing AMUX 64T channels Refer to the AMUX 64T User Manual for more information on the external multiplexer device Important Terms You Should Know The following are some definitions of common terms and parameters that you should remember when acquiring your data A scan is one acquisition or reading from each channel in your channel string The number of scans to acquire parameter refers to the number of data acquisitions or readings to acquire from each channel in the channel string The number of samples is the number of data points you want to sample from each channel The scan rate determines how many times per second LabVIEW acquires data from channels The scan rate parameter enables interval scanning a longer interval between scans than between individual channels comprising a scan on devices that support this feature The channel clock rate parameter defines the time between the acquisition of consecutive channels in your channel string For more information on scan and channel clock rates refer to Chapter 9 Letting an Outside Source Control Your Acquisition Rate National Instruments Corporation 5 17 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input For specific information about the Analog Input VIs refer to Chapter 2 Introduction to the Analog Input VIs in the LabVIEW Data Acquisition VI Reference Manual LabVIEW Data Acquisition Basics Manual 5 18 Nationa
227. n use the set of Intermediate DAQ VIs as shown in Figures 12 3 device voltages update rate Figure 12 3 Waveform Generation Using Intermediate VIs With these VIs you can set up an alternate update clock source such as an external clock or a clock signal coming from another device or return the update rate The AO Config VI sets up the channels you specify for analog output The AO Write VI places the data in the buffer the AO Start VI begins the actual generation at the update rate and the AO Wait VI waits until the waveform generation completes Then the AO Clear VI unconfigures the analog channels The Generate Continuous Sinewave VI located in examples daq anlogout 11b is similar in structure to Figure 12 3 This example VI continually outputs a sine waveform through the channel you specify Changing the Waveform during Generation Circular Buffered Output When your waveform data is too large to fit in a memory buffer or is constantly changing you should use a circular buffer to output the data You also could use the Easy Analog Output VIs in a loop to create a circular buffered output but this sacrifices efficiency because Easy VIs configure allocate and deallocate a buffer every time they execute When you spend time configuring allocating and deallocating a buffer there are time gaps between the data output Figures 12 4 and 12 5 show two different ways to perform circular buffered analog output using the In
228. n is really not valid because you must know first what you will be hunting before you pack your fishing pole or elephant rifle The same idea applies to scientists and engineers engaged in the quest for information You must know the defining characteristics of what you want to hunt be it a wild animal or an analog signal You cannot just say I will hunt voltages or even I will hunt analog voltages Voltages come in various forms This chapter gives you the terms tools and techniques designed to help show you the best way to catch your wave You can break down analog signals into three categories DC time domain and frequency domain You must ask yourself Is the information I seek primarily contained in the level the shape or the frequency content of my signal Figure 5 1 illustrates what signals correspond to certain types of signal information ADC DAC A 0985 Level slow gt t Time Domain ADC DAC A MANA Shape fast gt Frequency Domain ADC wol a Aa Freq Content Analysis Figure 5 1 Types of Analog Signals National Instruments Corporation 5 1 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input You may be saying to yourself I know that I have a thermocouple and that the primary information temperature is contained in the level of the analog voltage Now I am ready to go hunting Well you are almost ready to hunt
229. n of the event source timebase input as well as any other parameters on any VI use the Help window The Counter Start VI initiates the counter to begin counting the edges of the SOURCE input The Counter Read VI reads the latest edge count from the counter register and displays the value on the front panel Once the stop button has been pressed the Counter Stop VI stops the counter operation It is a good idea to always check for errors at the end of an operation to see if the operation was successful If you want to trigger TTL event counting then set up your gate mode input on the Event or Time Counter Config VI With this VI you can perform level or edge triggering Refer to the Event or Time Counter Config VI description in Chapter 18 Intermediate Counter VIs of the LabVIEW Data Acquisition VI Reference Manual for more information When you use Easy I O VIs to measure external events or elapsed time the only difference between the two block diagrams is the counting source The same is true when you use Intermediate VIs For the Event or Time Counter Config VI the default event source timebase input is the signal connected to the SOURCE input a value of 0 If you want to use an internal timebase as your source then you need to enter an internal frequency available on your DAQ device Figure 25 5 shows how to measure elapsed time using Intermediate VIs count continuouesl elapsed time Figure 25 5 Using the Intermediate VIs
230. n one reading on one or more channels there are two techniques that you can use depending on what you want to do with the data after you acquire it This chapter reviews these different methods and explains how LabVIEW stores the acquired data with each method You will discover which method you should use by answering the following questions e Do you want to analyze your data as it is being acquired or after it has been acquired e Do you want to acquire a predetermined or indefinite number of data points If you want to analyze your data as it is being measured and the number of data points does not matter read the Do You Need to See Your Data during the Acquisition section in this chapter If you acquire a predetermined number of data points and you want to analyze the data after it has been acquired refer to the Can You Wait for Your Data section in this chapter Also throughout the chapter there are some basic examples of some common data acquisition DAQ applications that use these two methods Can You Wait for Your Data One way to acquire multiple data points for one or more channels is to use the non buffered methods described in the previous chapter in a repetitive manner For example you could compare this method to a trip to the grocery store You need to get 20 items from the store but because you can t carry all 20 items at once you decide you must make 30 separate trips to the store Grocery shopping in this manner w
231. n stop your VI Circular Buffered Analog Input Examples The only differences between the simple buffered applications and circular buffered applications in the block diagram is the number of scans to read input of the AI Start VI is set to 0 and now we must call the AI Read VI repeatedly to retrieve your data These changes can be applied to many of the examples in the previous section on simple buffered analog input however we will review the basic National Instruments Corporation 7 13 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition circular buffered analog input VI here and discuss some other example VIs that are included with LabVIEW Basic Circular Buffered Analog Input Buffer Size 1000 scans sec Figure 7 14 shows an example VI that brings data from channel 0 at a rate of 1000 samples s into a buffer that can hold 4000 samples This type of example might be handy if you wanted to watch the data from a channel over a long period of time but you could not store all the data in memory at once The AI Config VI sets up the channel specification and buffer size then the AI Start VI initiates the background data acquisition and specifies the rate Inside the While Loop the AI Read VI repeatedly reads blocks of data from the buffer of a size equal to either 1000 scans or the size of the scan backlog whichever one is larger The VI does this by using the Max amp Min f
232. n utility to configure all National Instruments devices in your system Subsequently you must run the DAQ configuration utility to assign an NI DAQ device number to the new device You must run the DAQ configuration utility after running the Plug and Play configuration utility or you cannot configure any system resources for the device Your Plug and Play configuration utility assigns the system resources for the device Examples of Plug and Play software that might be already in your system are the Plug and Play BIOS or the Intel Plug and Play Kit which includes the Intel Configuration Manager and has its own configuration utility Configuring and Testing Your DAQ Devices with WDAQCONF in Windows This section describes how to use WDAQCONF to configure and test your plug in DAQ hardware before you write a VI This information applies to ISA and EISA bus computers only National Instruments Corporation 2 11 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware If you have an ISA bus computer you should have just finished saving your device settings A Test and Hardware menu should now be activated in the Device Number n menu bar as shown in Figure 2 6 NI DAQ Yersion 4 8 5 Configuration Utility Configuration Options Resources SCI Help Select A Device Number Device Selected 1 _AT MIO 16F 5 Empty Device 1 Empty Empty Device name AT
233. nal Instruments catalog LabVIEW Data Acquisition Basics Manual 19 12 National Instruments Corporation Chapter 19 Common SCX Applications You can set up your SCXI module to amplify strain gauge signals or filter noise from signals In order to set up the excitation level gain and filter settings you must consult your Getting Started with SCXI manual for the necessary hardware configuration and Chapter 2 Installing and Configuring Your Data Acquisition Hardware for software configuration To build a strain gauge application in LabVIEW you can use the Easy T O analog input VIs If you are measuring multiple transducers on several different channels you will need to scan the necessary channels as quickly as possible Because the Easy I O VIs reconfigure your SCXI module every time the VI is called you should use the Intermediate analog input VIs as well as the strain gauge conversion VI as shown in the following example The Convert Strain Gauge Reading VI located in Functions DAQ DAQ Utilities converts the voltage read by the strain gauge to units of strain input limits no change channels abc pf ens sere DEH oaas ao buffer size STOP Gao sean rate bs weet dF alse bf i FEA mimber of samples to average for cach data point 100 latest t ture dat ata i laa Temper ature Strip Chart This example continually acquires data until an error occurs or the user stops the VI from executing
234. nano micro milli kilo mega Numbers Symbols 1D 2D A A AC A D ADC ADC resolution Al AIGND National Instruments Corporation One dimensional Two dimensional amperes Alternating current Analog to digital Analog to digital converter An electronic device often an integrated circuit that converts an analog voltage to a digital number The resolution of the ADC which is measured in bits An ADC with 16 bits has a higher resolution and thus a higher degree of accuracy than a 12 bit ADC Analog input The analog input ground pin on a DAQ device G 1 LabVIEW Data Acquisition Basics Manual Glossary amplification AMUX devices analogin analog_io 1llb analog input group analog multiplexer analogout 1lb analog output group analog trigger LabVIEW Data Acquisition Basics Manual A type of signal conditioning that improves accuracy in the resulting digitized signal and to reduce noise See analog multiplexers A LabVIEW DAQ library containing VIs that perform analog input with DAQ devices and SCXI modules and can write or stream the acquired data to disk A LabVIEW DAQ library containing VIs for analog I O control loops A collection of analog input channels You can associate each group with its own clock rates trigger and buffer configurations and so on A channel cannot belong to more than one group Because each board has one ADC only one gro
235. nd the scanning order perform the following steps 1 Locate the channel for each DAQ device channel in your channel list in the DAQ Device Channel column in Table 1 3 or 1 4 Start with the first device channel and continue through the list in your specified channel order 2 Read from left to right along the table row where you located the channel number to find the AMUX 64T scanning order To read a single AMUX 64T channel use channel specifier AMy x This specifier returns data from channel x of the AMUX 64T with ID y To read more than one AMUX 64T channel use channel specifier OBx y This specifier returns data from the AMUX 64T channels that correspond to device channel x through device channel y LabVIEW Data Acquisition Basics Manual 5 16 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input When the channel list contains a single AMUX 64T channel you must also specify the number of the AMUX 64T device as shown in the following table channel list Channel Specified parameter AMy x Channel x on AMUX 64T device y AM4 8 Channel 8 on AMUX 64T device 4 You refer to AMUX 64T channels only when a single AMUX 64T channel comprises the entire list Otherwise you refer to them indirectly through the device channels that you use to scan the AMUX 64T channels Refer to Appendix B Hardware Capabilities of the LabVIEW DAQ VI Reference Manual for more information o
236. ng converts the voltage read from the RTD to a temperature representation input limits no change O means continuous acq l START wa sean rate number of samples to number of chans Temperature Strip Chart This example continually acquires data until an error occurs or the user stops the VI from executing In order to perform continuous hardware timed acquisition you need to set up a buffer In this case the buffer is 10 times the number of points acquired for each channel After your device averages the voltage data from the AI Read VI it converts the voltage values to temperature After completing the acquisition remember to always clear the acquisition by using the AI Clear VI Measuring Pressure with Strain Gauges Strain gauges give varying voltages in response to stress or vibrations in materials Strain gauges are thin conductors attached to the material to be stressed Resistance changes in parts of the strain gauge to indicate deformation of the material Strain gauges require excitation generally voltage excitation and linearization of their voltage measurements Depending on the strain gauge configuration another requirement for using strain gauges with SCXI is a configuration of National Instruments Corporation 19 11 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications resistors As shown in Figure 19 4 the resistance from the strain gauges co
237. ng the error device waveform channel 0 actual sample period sec number of samples sample rate 1000 samples sec high lirnit C1049 low timit k 10 Figure 7 2 The Al Acquire Waveform VI Acquiring Multiple Waveforms You can acquire more than one waveform at a time with another of the Easy Analog Input VIs AI Acquire Waveforms shown in Figure 7 3 This VI also has minimal set of inputs but it allows inputs of more than one channel to read and returns data from all channels read device Al waveforms channels 0 3 oe actual scan period sec number of samples ch scan rate 1000 scans sec high limit 104 Tow limit 1049 Figure 7 3 The Al Acquire Waveforms VI The channel input for this VI is a string where you can enter a list of channels Refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts for more information on channel specification in LabVIEW LabVIEW outputs a two dimensional 2D array in the waveforms output for this VI where each channel has a different column and the sample are on each row Refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts for more information on how data is organized for analog applications You can set the high limit and low limit inputs for all the channels to the same value You cannot have different limit settings for different channels when you use this VI For more information on gain specifications go to Chapter 3 Basic LabVIEW Data Acquisition Concepts
238. nnel syntax An SCXI channel number has four parts the onboard channel optional the chassis ID the module slot and the module channel In the following table of examples x is any chassis ID y is any module slot a is any module channel and b is any module channel greater than a Channel List Element Channel Specified OBO SCx MDy a Channel a on the module in slot y of the chassis with ID x is multiplexed into onboard channel 0 OBO SCx MDy a b Channels a through b inclusive on the module in slot y of the chassis with ID x are multiplexed into onboard channel 0 National Instruments Corporation 18 1 LabVIEW Data Acquisition Basics Manual Chapter 18 Special Programming Considerations for SCX LF Note LF Note CF Note SCXI Gains The channel input for DAQ VIs is either a string with the Easy I 0 VIs or an array of strings Each string value can only list the channels for one module With the array structure for channel values you can list the channels for several modules In other words for one scanning operation you can scan several modules You can scan an arbitrary number of channels for each module but the channels of each module must be scanned in consecutive ascending order You do not need the SCXI channel string syntax to access channels on the SCXI 1200 module Use 0 for channel 0 1 for channel 1 and so on The SCXI 1200 module is identified by its logical device number
239. nnels array One restriction is that the channel list for each module must be consecutive You can practice reading channels from different chassis by using the channel strings explained above in the Getting Started Analog Input VI found in examples daq run_me 11b we Note Only the SCXI 1001 chassis can be used in multi chassis applications with MIO Series devices other than the DAQPad MIO 16XE 50 Lab Series LPM DAQCard 500 DAQCard 700 DAQCard 1200 and DIO 24 devices do not support multi chassis applications National Instruments Corporation 19 19 LabVIEW Data Acquisition Basics Manual SCXI Calibration Increasing Signal Measurement Precision Your SCXI module ships to you pre calibrated for the specified accuracy at the factory You only need to recalibrate the module if the precision of your signal measurement is not acceptable because of shifts in environmental conditions Before learning about how to calibrate you should understand where LabVIEW stores your calibration constants This chapter does not apply to the SCXI 1200 For calibration on the cr SCXI 1200 you should use the 1200 Calibrate VI which you can find in Functions Data Acquisition Calibration and Configuration EEPROM Your System s Holding Tank for Calibration Constants When you calibrate your SCXI module in LabVIEW the calibration constants can be stored in Electronically Erasable Programmable Read Only Memory EEPROM EEPRO
240. nt Precision for Various Device Ranges and Limit DOUUIN GS Ha yeeissessseeoes asdbeativeas A ea eat et eee eve costs 5 8 Analog Input Channel Range ooo cee eeeeeceeereceeeeeeeseeaeenseeseenaes 5 13 Scanning Order for Each DAQ Device Input Channel with Four AMUX GATS oe widest E A R teas bese cde A E EES 5 15 Scanning Order for Each DAQ Device Input Channel with Four AMUX OATS oe enini cet ssctnsciescostedea tiepuaseneadsesi cleavtnducavedseuivsoded ER 5 16 External Scan Clock Input Pins 00 eee eeeeseceeeeeeeseesenseeseenaes 9 6 Phenomena and Transducers 0 0 ee eeceeseeeeseceeeeseesseeeeeseeseenseeseenaes 16 1 SCXI 1100 Channel Arrays Input Limits Arrays and Gains 18 4 Adjacent Counters for Counter Chips 0 0 0 eee eseeceeseeeeeseeeseeseenees 25 2 LabVIEW Data Acquisition Basics Manual Xvi National Instruments Corporation The LabVIEW Data Acquisition Basics Manual includes the information you need to get started with data acquisition and LabVIEW This manual supplements the LabVIEW User Manual and assumes that you are familiar with that material You should also be familiar with the operation of LabVIEW your computer your computer s operating system and your data acquisition DAQ board Organization of This Manual The LabVIEW Data Acquisition Basics Manual is organized by parts which in turn are made up of chapters The parts in this manual are as follows National Instruments Corporati
241. nter Register DAQ Device Dees Counter Register GATE Figure 22 3 Physical Connections for Generating a Square Pulse The Generate Delayed Pulse VI found in Functions Data Acquisition Counter tells your device to generate a single delayed pulse This VI is self contained and checks for errors automatically With the Generate Delayed Pulse VI you must connect the pulse delay phase 1 and pulse width phase 2 controls to define the output pulse as shown in Figure 22 4 Sometimes the actual pulse delay and pulse width are not the same as you specified actual pulze delay or cycles Figure 22 4 Using the Generate Delayed Pulse VI If you need more control over when the counter actually begins generating a single square pulse use Intermediate VIs instead of the Easy VIs Figure 22 5 shows how to generate a single pulse using the intermediate level VIs The Delayed Pulse Generator Config VI configures the counter and the counter using the Counter Start VI generates the TTL signal An example of this is if you wanted to generate a pulse as a result of meeting certain conditions If you used the Easy Counter VI the VI would configure and then immediately start the pulse generation With the Intermediate VIs you can LabVIEW Data Acquisition Basics Manual 22 4 National Instruments Corporation Chapter 22 Generating A Square Pulse or Pulse Trains configure the counter l
242. number of divisions into which your system can break down National Instruments Corporation 5 3 LabVIEW Data Acquisition Basics Manual Chapter 5 Things You Should Know about Analog Input the ADC range and therefore the smaller the detectable voltage change A 3 bit ADC divides the range into 2 or 8 divisions A binary or digital code between 000 and 111 represents each division The ADC translates each measurement of the analog signal to one of the digital divisions Figure 5 4 shows a sine wave and its corresponding digital image as obtained by a 3 bit ADC Clearly the digital signal does not represent the original signal adequately because the converter has too few digital divisions to represent the varying voltages of the analog signal By increasing the resolution to 16 bits however the ADC s number of divisions increases from 8 to 65 536 2 The ADC can now obtain an extremely accurate representation of the analog signal 3 Bit ADC 16 Bit ADC Figure 5 4 The Effects of Resolution on ADC Precision Device Voltage Range Range refers to the minimum and maximum analog voltage levels that the ADC can digitize Many DAQ devices feature selectable ranges so you can match the ADC range to that of the signal to take best advantage of the available resolution For example in Figure 5 5 the 3 bit ADC has eight digital divisions in the range from 0 to 10 volts If you select a range of 10 00 to 10 00 vo
243. o B 2 D daisy chaining SCXI chassis 19 18 to 19 19 DAQ examples list of example files 3 1 to 3 2 locations 3 1 to 3 2 DAQ hardware See hardware DAQ VIs See VIs daqconf utility UNIX 2 19 to 2 20 daqconf cfg file 2 20 data acquisition See also analog input analog input output control loops 6 6 to 6 10 basic LabVIEW data acquisition concepts 3 1 to 3 16 See also VIs data organization for analog applications 3 13 to 3 16 limit settings 3 11 to 3 13 location of common DAQ examples 3 1 to 3 2 buffered See buffered analog input common questions about LabVIEW data acquisition A 1 to A 5 important terms 5 17 multiple channel single point 6 2 to 6 5 single channel single point 6 1 to 6 2 triggered See triggered data acquisition data acquisition hardware See hardware Data Acquisition palette 3 4 data organization for analog applications 3 13 to 3 16 column major order 3 14 to 3 16 National Instruments Corporation row major order 3 14 two dimensional 2D arrays 3 13 to 3 16 data types for LabVIEW xx debugging VIs 27 1 to 27 4 error handling 27 2 to 27 3 execution highlighting 27 3 to 27 4 hardware connection errors 27 1 setting breakpoints and showing advanced DAQ VIs 27 4 single stepping through VIs 27 3 software configuration errors 27 1 to 27 2 using Probe tool 27 4 VI construction errors 27 2 to 27 4 default input for VIs 3 7 default setting for VIs 3 7 Delayed Pulse Generator
244. o expand the AI Waveform Scan VI into four separate Intermediate VIs which may make your VI diagram look more complicated but it provides more control over your data acquisition processes like being able to read any part of the buffer An example similar to Figure 7 5 is the Getting Started Analog Input VI located in labview examples daq run_me 11b With these Intermediate Analog Input VIs you must wire a taskID to identify the DAQ LabVIEW Data Acquisition Basics Manual 7 4 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition operation and the set of channels used in the acquisition and to make sure the VIs execute in the correct order woltage data pet device 1 7 Ee channels 0 my it ee i buffer size scan rate 4000 scans sec Ga Figure 7 5 Using the Intermediate VIs to Acquire Multiple Waveforms With these VIs you not only have the ability to configure triggering coupling acquisition timing retrieval and additional hardware but you also can control when each step of the data acquisition process occurs With the AI Config VI you can configure the different parameters of the acquisition such as the channels to be read and the size of the buffer to use In the AI Start VI you specify parameters used in your program to start the acquisition such as number of scans to acquire the rate at which your VI
245. o specific types of hardware triggers digital and analog In the following two sections you will learn about the necessary conditions to start an acquisition with a digital or an analog signal National Instruments Corporation 8 1 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers Digital Triggering A digital trigger is usually a transistor transistor logic TTL level signal having two discrete levels a high and a low level When moving from high to low or low to high a digital edge is created There are two types of edges rising and falling You can set your analog acquisition to start as a result of the rising or falling edge of your digital trigger signal In Figure 8 1 the acquisition will begin after the falling edge of the digital trigger signal Usually digital trigger signals are connected to STARTTRIG EXTTRIG or DTRIG pins on your DAQ device If you want to know which pin your device has look at your hardware manual or at the AI Trigger Config VI description in Chapter 10 Advanced Analog Input VIs of the LabVIEW Data Acquisition VI Reference Manual Digital signals that are connected to STARTTRIG and EXTTRIG pins are inverted meaning high level signals become low and falling edges become rising Make sure you account for this situation when specifying your triggering conditions TTL Signal Connect to STARTTRIG EXTTRIG or DTRIG Pins Falling Edge of Sign
246. ock period timebase signal timebase source no change National Instruments Corporation 9 7 LabVIEW Data Acquisition Basics Manual Chapter 9 Letting an Outside Source Control Your Acquisition Rate Note You must divide the timebase by some number between 2 and 65535 or you will get a bad input value error Because LabVIEW determines the length of time before AI Read times out based on the interchannel delay and scan clock rate you may need to force a time limit into AI Read In Figure 9 6 the time limit is 5 seconds Externally Controlling the Scan and Channel Clocks You can control the scan and channel clocks simultaneously by combining the two previous sections However make sure that you follow the proper timing Figure 9 7 demonstrates how you can set up your application to control both clocks Which Clock Channel Clock Timeout 5 seconds transposed voltage graph device 1 number of scans to acquire 1000 Figure 9 7 Controlling the Scan and Channel Clock Simultaneously LabVIEW Data Acquisition Basics Manual 9 8 National Instruments Corporation Making Waves with Analog Output This section contains basic information on generating data with LabVIEW including generating a single point or multiple points Part 3 Making Waves with Analog Output contains the following chapters e Chapter 10 Things You Should Know about Analog Output explains how to use LabVIEW to produce
247. ocouples and Temperature Measurements Customer Communication National Instruments wants to receive your comments on our products and manuals We are interested in the applications you develop with our products and we want to help if you have problems with them To make it easy for you to contact us this manual contains comment and configuration forms for you to complete These forms are in Appendix B Customer Communication at the end of this manual National Instruments Corporation xxi LabVIEW Data Acquisition Basics Manual Before You Get Started This section contains all the information you should know before you start learning about data acquisition with LabVIEW Part 1 Before You Get Started contains the following chapters Chapter 1 How to Use This Book explains how this manual is organized Chapter 2 Installing and Configuring Your Data Acquisition Hardware gets you up and running with LabVIEW and your Data Acquisition hardware Chapter 3 Basic LabVIEW Data Acquisition Concepts explains key concepts in understanding how data acquisition works with LabVIEW Chapter 4 Where You Should Go Next serves as your map to this manual directing you to the chapter or chapters that discuss your particular application How To Use This Book This manual includes the basic information you need to get started with data acquisition and LabVIEW You should have a basic knowledge of LabVIEW befor
248. od is the count divided by the known frequency count f count register SOURCE input of known frequency fs Figure 24 2 Measuring a Square Wave Period You typically would use frequency measurement for high frequency signals because the signal to be measured is faster than most available internal timebases Period measurement is commonly used with low frequency signals because the signal to be measured is slower than most internal timebases For the Am9513 chip the possible internal timebases are 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz For the DAQ STC chip the possible internal timebases are 20 MHz and 100 kHz Remember that whether you use the frequency or period measurement you can always obtain the other measurement by taking the inverse of the current one as shown in the following equations 1 period measurement frequency measurement 1 frequency measurement _ period measurement Connecting Counters to Measure Frequency and Period For low frequency signals your counting range should not exceed the range of one counter 65 535 for the AM9513 chip and more than 4 billion for the DAQ STC chip If the counting range does exceed one counter pick a faster timebase Connect your device and counter as indicated in Figure 24 3 to measure low frequency signals To measure pulse period and LabVIEW Data Acquisition Basics Manu
249. on Part 1 Before You Get Started contains all the information you should know before you start learning about data acquisition with LabVIEW Part 2 Catching the Wave with Analog Input contains basic information on acquiring data with LabVIEW including acquiring a single point or multiple points triggering your acquisition using outside sources to control acquisition rates and using control loops for analog input and output Part 3 Making Waves with Analog Output contains basic information on generating data with LabVIEW including generating a single point or multiple points Part 4 Getting Square with Digital I O describes basic concepts on how to use digital signals with data acquisition in LabVIEW including immediate and handshaked digital I O Part 5 SCXI Getting Your Signals in Great Condition contains basic information on setting up and using SCXI modules with your data acquisition application special programming considerations common SCX applications and calibration information Part 6 Counting Your Way to High Precision Timing describes the different ways you can use counters with your data acquisition xvii LabVIEW Data Acquisition Basics Manual About This Manual application including generating a pulse or pulses measuring pulse width measuring frequency and period counting events and dividing frequencies for precision timing Part 7 Debugging Your Data Acquisition Application contains a bri
250. onal Instruments Corporation 14 1 LabVIEW Data Acquisition Basics Manual Chapter 14 When You Need It Now Immediate Digital 1 0 digital testing purposes All of the Easy Digital VIs have error reporting port width port width device channels Tine port width device device channels port number pattern iteration iteration Read from Digital Port VI Write to Digital Port VI Figure 14 1 The Easy Digital Vis The device input identifies the DAQ device you are using The port number input specifies the port of digital lines that you will use during the digital operation The line parameter is an individual port bit or line in the port number The pattern or line state is the value s you want to read from or write to a device Pattern values can be displayed in decimal default hexadecimal octal or binary form Refer to Chapter 10 Numeric Controls and Indicators in your LabVIEW User Manual for instructions on how to change the display of a numeric control or indicator The iteration input optimizes your digital operation When iteration is zero the default value LabVIEW calls the DIO Port Config VI an Intermediate VI to configure the port If iteration is greater than zero LabVIEW uses the existing configuration which improves performance You can wire this input to an iteration terminal of a loop Every time iteration is zero you call the DIO Port Config VI which resets the digital line values to their defaul
251. onal Instruments DAQ devices contain one of three different counter chips the Am9513 the DAQ STC and the 8253 8254 chip To find out which counter chip your device uses refer to your hardware manual or Chapter 19 Advanced Counter VIs in the LabVIEW Data Acquisition VI Reference Manual All counter information discussed in this manual refers to the Am95 13 chip a 16 bit counter with a counting range of 0 to 65 535 and the DAQ STC chip a 24 bit counter with a counting range of 0 to 24 1 For information on the 8253 8254 chip refer to the ICTRControl VI in Chapter 19 Advanced Counter VIs of the LabVIEW Data Acquisition VI Reference Manual If you have the DAQ STC chip LabVIEW provides a buffer to perform counter operations Typically you should use buffered counter operations when you have a GATE signal that may trigger the counter to count several times or if you want to save data from different counters count several times If you have the DAQ STC chip and want to perform buffered counter operations you can alter any of the counter examples that ship with LabVIEW For information on buffered counter operations or how to alter the examples refer to the CTR Mode Config VI in Chapter 19 Advanced Counter VIs of the LabVIEW Data Acquisition VI Reference Manual LabVIEW Data Acquisition Basics Manual 21 4 National Instruments Corporation Chapter 21 Things You Should Know about Counters Counting Operations When All Your Counters Ar
252. ong before the actual pulse generation begins As soon as you want a pulse to be generated the counter can immediately begin without having to configure the counter In this situation using Intermediate VIs would improve performance device counter Figure 22 5 Generating a Single Delayed Pulse Using Intermediate Vis You must stop the counter if you want to use it for other purposes For more information on stopping counters refer to the Stopping Counter Generations section at the end of this chapter Generating a Pulse Train There are two types of pulse trains continuous and finite You may use a continuous pulse train as the SOURCE of another counter or as the clock for analog acquisition or generation You may use a finite pulse train as the high level gate signal for another counter For a LabVIEW example on generating continuous and finite pulse trains look at the How to Generate Pulses and Pulse Trains VI located in examples daq counter 11b Generating a Continuous Pulse Train Figure 22 6 describes how to connect your counter and device to generate a continuous pulse train The edges of the internal source signal are counted to generate the output signal You obtain the continuous pulse train for your external device from the counter s OUT pin You can optionally gate the operation with a signal connected to National Instruments Corporation 22 5 LabVIEW Data Acquisition Basics Manual Chapter 22 Generating A
253. ope scans 0 Cno change Alo ve orange JE analog chan 3 amp level CO v trigger channel empty level 0 scan clock Source no change 0 no change p In this example trigger type should be set to analog trigger The Acquire N Scans ATrig VI has the option to use condition retrieval to simulate a hardware trigger in software Conditional retrieval is discussed in the next section In LabVIEW you can acquire data both before and after an analog trigger signal If the pretrigger scans is gt 0 your device acquires data before the triggering conditions and subtracts the number of scans parameter value from the pretrigger scans parameter value to determine the number of scans to collect after the triggering conditions are met If pretrigger scans is 0 then the number of scans will be acquired after the triggering conditions are met Before you start acquiring data you must specify in the edge or slope input if the acquisition is going to be triggered on the rising or falling edge of the analog trigger signal Aside from specifying the slope you must determine the channel where the analog triggering signal will be connected as well as the voltage level on the triggering signal needed National Instruments Corporation 8 9 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers to begin acquisition In other words once you specify the channel of the triggering signal LabVIEW
254. or configuring devices 2 10 to 2 11 polling for analog input 6 10 ports digital ports and lines 13 1 grouping ports without handshaking A 2 problems accessing ports 2 or higher Windows A 3 VI port addressing 3 9 to 3 11 pressure measurement with strain gauges example 19 11 to 19 14 Probe tool 27 4 Pulse Generator Config VI 24 6 pulse train generation 22 5 to 22 8 continuous pulse train 22 5 to 22 7 duty cycles 22 2 to 22 3 finite pulse train 22 7 to 22 8 illustration 22 2 physical connections for generating continuous pulse train figure 22 5 finite pulse train figure 22 7 terminology related to 22 2 pulse width measurement 23 1 to 23 4 controlling pulse width measurement 23 3 counting input signals figure 23 1 determining pulse width 23 2 to 23 3 National Instruments Corporation increasing measurable width range 23 4 measuring pulse width 23 1 to 23 2 overview 23 1 physical connections for determining pulse width figure 23 2 Pulse Width or Period Meas Config VI controlling pulse width measurement 23 3 measuring frequency and period 24 4 to 24 5 pulsed counter signal generation 22 1 Q questions about using DAQ devices 4 3 to 4 5 LabVIEW data acquisition common questions A 1 to A 5 R range of device voltage 5 4 to 5 5 considerations for selecting analog input settings 5 6 to 5 8 description 5 4 to 5 5 effect on ADC precision figure 5 5 measurement precision for vari
255. or the Sun SPARCstation for SunOS 4 x and Solaris 2 x Before you install the NI DAQ consider the following e You must have super user privilege to install the software e The distribution disk is in TAR format Perform the following steps to install NI DAQ 1 Log on as a super user root 2 Create a directory by entering the following command mkdir usr daqg lt Enter gt 3 Change to this directory by entering the following command cd usr daq lt Enter gt 4 Copy the files from the distribution disk to this directory by entering the following command tar xvf dev rfd0a lt Enter gt 5 Load the Solaris driver Because the Solaris driver is loadable you do not need to link the driver with the kernel object files rebuild the kernel or restart the system Run daqinstall in your working directory and follow the instructions in the shell script Enter the following command dagqinstall lt Enter gt ie Note If there is a problem with the driver software you must unload the driver To unload the driver you must have super user privilege and the driver must not be in use Unload the driver by entering the following command daq_remove lt Enter gt Configuring Your DAQ Device in UNIX NI DAQ includes a configuration utility daqconf to create and modify the system configuration file that the NI DAQ software National Instruments Corporation 2 19 LabVIEW Data Acquisition Basics Manual
256. ormation on single point output Buffered Analog Output Sometimes in performing analog output the rate that your updates occur is just as important as the voltage level This is called waveform generation or buffered analog output For example you may want your DAQ device to act as a function generator You can do this by storing one cycle of sine wave voltage data in an array and programming the DAQ device to continuously generate the voltages in the array one point at a time at a specified rate This is known as single buffered analog output But what if you want to generate a continually changing waveform For example you may have a large file stored on disk that contains data that you want to output Because LabVIEW cannot store the entire waveform in a single buffer you must continually load new data into the buffer during the generation This National Instruments Corporation 10 1 LabVIEW Data Acquisition Basics Manual Chapter 10 Things You Should Know about Analog Output process requires the use of circular buffered analog output in LabVIEW To learn more about single or circular buffering read Chapter 12 Buffering Your Way through Waveform Generation LabVIEW Data Acquisition Basics Manual 10 2 National Instruments Corporation One Stop Single Point Generation In the preceding chapter you learned the appropriate time to use single point updates This chapter shows you which VIs to use in LabVIEW to p
257. ou can acquire data both before and after a digital trigger signal If the pretrigger scans is gt 0 your device will acquire data before the triggering conditions are met and subtract the number of scans parameter value from the pretrigger scans parameter value to determine the number of scans to collect after the triggering conditions are met If pretrigger scans is 0 then you will acquire the number of scans after the triggering conditions are met Before you start acquiring data you must specify in the edge or slope input when the acquisition should be triggered on the rising or falling National Instruments Corporation 8 5 LabVIEW Data Acquisition Basics Manual Chapter 8 Controlling Your Acquisition with Triggers Analog Triggering edge of the digital trigger signal The analog chan and level and scan clock source inputs are not used for digital triggering Digital Triggering Examples The Acquire N Scans DTrig example VI holds the data in a memory buffer until your device completes the acquisition The number of data points you need to acquire must be small enough to fit in memory This VI only views and processes the information after the acquisition If you need to view and process information during the acquisition use the Acquire amp Proc N Scans Trig VI found in examples daq anlogin anlogin 11b If you expect multiple digital trigger signals that will start multiple acquisitions use the example VI Acquire N multi DTrig
258. ou can find the explanation for both kinds of codes in Appendix C Error Codes of the LabVIEW Data Acquisition VI Reference Manual Special Considerations for LabVIEW for Windows NT Changing 1 0 Page Lock Limit Windows NT limits the total amount of memory that is non swappable page locked The default amount of memory is determined according to the total amount of physical memory available in your system If you are working with large DAQ buffers you can increase the default I O page lock limit in WOAQCONF EXE To change the page lock limit LabVIEW Data Acquisition Basics Manual 2 14 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware select Options IOPageLockLimit and enter a new page lock limit Your changes will go into effect when you reboot and restart Windows NT User Privilege Level When Using NI DAQ Windows NT provides different security levels for different kinds of users Depending on your privilege level you have limitations on what you can do with NI DAQ in LabVIEW By default LabVIEW DAQ applications load the NI DAQ kernel mode device driver on demand Windows NT loads the NI DAQ device driver when you run your first LabVIEW DAQ application Windows NT unloads the driver when you exit LabVIEW This default behavior saves memory when you are not running LabVIEW DAQ applications Loading and unloading device drivers require the highest privilege
259. ould be very inefficient and time consuming The same applies for when you are acquiring a single data point from one or more channels over and over Also with this method of acquisition you do not have accurate control over the time between each sample or channel Going back to the example of grocery shopping it would be much more efficient to use a shopping bag to hold all 20 food items at once so that you only National Instruments Corporation 7 1 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition have to make one trip In the same sense you can use a data buffer in computer memory as your shopping bag with which you acquire data With buffered I O LabVIEW transfers data taken at timed intervals from a DAQ device to a data buffer in memory Figure 7 1 illustrates how the data fills up the buffer only once however the overall size of the buffer is specified in your VI In this illustration think of N as the number of scans or updates the buffer can hold and T as the trigger occurrence whether the trigger is due to our external signal or the start of the execution of your VI Refer to Chapter 8 Controlling Your Acquisition with Triggers for more discussion on triggering your acquisition from another signal T gt writing and reading N Figure 7 1 How Buffers Work In your VI you must specify the number of samples to be taken and the number of channels from which La
260. our device Output Lines Output Port Data latches x and drivers Input Port Data latches and drivers lt l Input Lines Device or Module Figure 13 1 Digital Ports and Lines There are two types of digital acquisition generation nonlatched or immediate and latched or handshaked With nonlatched or immediate digital I O your system updates the digital lines National Instruments Corporation 13 1 LabVIEW Data Acquisition Basics Manual Chapter 13 Things You Should Know about Digital 1 0 immediately Latched or handshaked digital I O is when a device or module accepts or transfers data after a digital pulse has been received There are two types of latched handshaked digital I O non buffered and buffered Not all the devices and modules support latched handshaked digital I O Again you should refer to the hardware tables in Appendix B Hardware Capabilities of the LabVIEW Data Acquisition VI Reference Manual or refer to your hardware manual to see if your device or module supports it For specific information about the Digital I O VIs refer to Chapter 12 Introduction to the Digital I O VIs in the LabVIEW Data Acquisition VI Reference Manual LabVIEW Data Acquisition Basics Manual 13 2 National Instruments Corporation When You Need It Now Immediate Digital 1 0 The most common way to use digital lines is with nonlatched immediate digital I O All DAQ devices and SCXI mod
261. ous device ranges and limit settings table 5 8 Read from Digital Line VI 14 2 Read from Digital Port VI 14 2 referenced signal sources 5 2 referenced single ended RSE measurement system 5 10 to 5 11 16 channel RSE system figure 5 11 relay SCXI modules 17 5 REQ Request line 15 2 Resistance Temperature Detectors RTDs 19 9 to 19 11 resolution of ADC 5 3 to 5 4 effects on ADC precision figure 5 4 round robin scanning figure 9 2 row major order 3 14 RSE See referenced single ended RSE measurement system National Instruments Corporation Index RTDs for measuring temperature 19 9 to 19 11 run_me llb DAQ example file 3 2 S SC 2042 RTD device 19 10 Scale Constant Tuner VIs 20 7 Scaling Constant Tuner VI 19 7 scan clock 9 5 to 9 8 channel and scan intervals using channel clock figure 9 2 devices without scan clocks note 9 6 input pins table 9 6 lack of external scan clock support in NB MIO 16X board 9 7 MIO device ScanClock output note 9 6 scan clock orientation of LabVIEW 9 2 simultaneous control of scan and channel clocks 9 8 scans channel clock rate parameter 5 17 definition 5 17 interval scanning 5 17 maximum scan rate calculating 7 5 number of samples parameter 5 17 number of scans to acquire parameter 5 17 round robin scanning figure 9 2 scan rate parameter 5 17 SCXI 112x Thermocouple example VI 19 9 SCXI 116x Digital Output VI 19 18 SCXI 1100 One Point
262. ow level The following diagram illustrates the four gating modes The numbers represent how many low to high transitions rising edges occur at the SOURCE input after the counter has been gated You also can count the high to low transitions falling edges on the SOURCE input but it is not shown in the diagram below LabVIEW Data Acquisition Basics Manual 21 2 National Instruments Corporation Chapter 21 Things You Should Know about Counters g gt Note The gating levels shown below are not available with devices that use the DAQ STC chip Rising Edge Gating SOURCE ILI LPL Le Counter Value 2 934 567 8910 count rising SOURCE edge l eare T Lo T Lo Z y Falling Edge Gating SOURCE LU LILU LLL Lyre Le LL te Counter Value 1 2 3 4 5 6 7 8 count rising SOURCE edge GATE High Level Gating SOURCE Counter Value count rising SOURCE edge GATE Low Level Gating SOURCE Counter Value 12 34 5 6 count rising SOURCE edge eae Lo TS LOTS By default counters count up in value but you can change your counter to count down in value You can use the count direction input on the Advanced VI CTR Mode Config to configure a counter to count up or down in value For more information refer to the description of the CTR Mode Config VI in Chapter 19 Advanced Counter VIs in the LabVIEW Data Acquisition VI Reference Manual Note If a GATE edge or level change occurs after the specified tran
263. ps You should use analog input output I O control loops when you want to output analog data after receiving some analog data With control loops this process is repeated over and over again For instance you want to control the fluid flow into several tanks If the present flow rate causes the tank to fill up then you open a valve so the fluid can flow to another tank You acquire information about the fluid flow rate at a constant rate The single point analog input and output VIs support several analog T O control loops at once because you can acquire analog inputs from several different channels in one scan and write all the analog output values with one update You perform a single analog input call process the analog output values for each channel and then perform a single analog output call to update all the output channels The following sections discuss the two different types of analog I O control loop techniques software timed and hardware timed analog I O Using Software Timed Analog 1 0 Control Loops With software timed analog control loops the analog acquisition rate and subsequent control loop rate are controlled by a software timer such as the Wait Until Next Millisecond multiple timer The acquisition is performed during each loop iteration when the AI Single Scan VI is called and the control loop is executed once for each time interval Your loop timing can be interrupted by any user interaction which means your acq
264. pter 5 Things You Should Know about Analog Input Floating Signal Sources Floating signal sources contain a signal whose voltage signal is not connected to an absolute reference such as earth or a building ground Some common examples of floating signals are batteries battery powered sources thermocouples transformers isolation amplifiers and any instrument that explicitly floats its output signal Notice that in Figure 5 3 neither terminal of the floating source is connected to the electrical outlet ground Vs Ground Figure 5 3 Floating Signal Sources Now that you know how your signal is referenced read on to learn the different systems available to acquire these signals Choosing Your Measurement System Resolution Now that you have defined your signal you must choose a measurement system You have an analog signal so you must convert the signal with an ADC measurement system which converts your signal into information the computer can understand Some of the issues you must resolve before choosing a measurement system are your ADC bit resolution minimum and maximum device voltage levels and minimum and maximum signal voltage levels The number of bits used to represent an analog signal determines the resolution of the ADC You could compare the resolution on a DAQ device to the marks on a ruler The more marks you have the more precise your measurements Similarly the higher the resolution the higher the
265. pts for more information on data acquisition with LabVIEW LabVIEW Data Acquisition Basics Manual 2 28 National Instruments Corporation Basic LabVIEW Data Acquisition Concepts Before you start building your data acquisition DAQ application you should know some of the following basic LabVIEW DAQ concepts e Location of Common Examples e Locating the Data Acquisition VIs in LabVIEW e DAQ VI Organization e DAQ VI Parameter Conventions e Default and Current Value Conventions e Common DAQ VI Parameters e Error Handling e Channel Port and Counter Addressing e Limit Settings e Data Organization for Analog Applications If you do not already understand basic programming concepts in LabVIEW refer to your LabVIEW Tutorial Manual and LabVIEW User Manual for help with programming in LabVIEW Location of Common DAQ Examples The DAQ examples address many common applications involving data acquisition in LabVIEW You can find these examples in labview examples daq The following list briefly describes the VI libraries designated by library name 11b and directories located in the daq directory anlog_io llb contains VIs for analog I O control loops anlogin contains VIs that perform analog input and can write or stream the acquired data to disk National Instruments Corporation 3 1 LabVIEW Data Acquisition Basics Manual Chapter 3 Basic LabVIEW Data Acquisition Concepts anlogout 11b contains
266. quisition from multiple channels 7 12 to 7 13 hardware timed analog I O control loops 6 9 multiple waveform acquisition 7 5 one point calibration 20 5 LabVIEW Data Acquisition Basics Manual scan clock control 9 6 to 9 7 SCXI temperature measurement 19 6 to 19 7 simple buffered analog input with multiple starts 7 7 to 7 9 AI Waveform Scan VI analog triggering examples 8 7 to 8 8 conditional retrieval examples 8 12 to 8 14 multiple waveform acquisition 7 4 amplification increasing signal to noise ratio figure 16 4 methods for minimizing noise note 16 4 amplifier offset reading 19 4 to 19 5 AMUX 64T devices addressing with MIO boards A 1 analog input channel range figure 5 13 channel addressing with AMUX 64T 5 12 to 5 13 scanning order for DAQ devices 5 13 to 5 17 four AMUX 64Ts table 5 16 one or two AMUX 64Ts table 5 15 specifying number for AMUX 64T device table 5 17 analog input AMUX 64T external multiplexer device 5 12 to 5 17 analog input output control loops See analog input output control loops channel clock control 9 3 to 9 5 9 8 circular buffered analog input examples 7 13 to 7 15 continuous acquisition from multiple channels 7 11 to 7 13 defining signals 5 1 to 5 3 digital triggering 8 2 to 8 6 external control of acquisition rate 9 1 to 9 3 National Instruments Corporation hardware triggering 8 1 to 8 10 measurement systems 5 3 to 5 6 memory allocation errors W
267. r addressing is discussed in Chapter 16 Things You Should Know about SCXI Onboard channels refer to analog or digital I O channels provided by the plug in DAQ device If x is an onboard channel you can specify this by entering x or OBx as the channel list element Refer to the description of your device in your hardware user manual for restrictions on channel order The following illustration shows several ways you can address onboard channels 0 1 and 2 The top three examples apply to VIs whose channel parameters are string arrays The LabVIEW Data Acquisition Basics Manual 3 10 National Instruments Corporation Chapter 3 Basic LabVIEW Data Acquisition Concepts bottom two examples apply to VIs whose channel parameters are scalar strings Channel String Array Control Channel String Control gt Note Refer to Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual for the number of channels your device can acquire data from at one time Limit Settings Limit settings are the maximum and minimum voltages of the analog signal s you are measuring or generating The pair of limit setting voltages can be unique for each analog input or output channel For analog input applications the limit setting voltages must be within the voltage range for the device For more information on the voltage range for your device refer to Chapter 5 Things You Should Know about Analog Input Each pair of
268. r current value to the appropriate binary value to write to the output channel By National Instruments Corporation 20 7 LabVIEW Data Acquisition Basics Manual Chapter 20 SCXI Calibration Increasing Signal Measurement Precision default calibration constants for the SCXI 1124 will be loaded into the memory from the EEPROM default load area You can recalibrate your SCXI analog output module by following these steps 1 Use the AO Single Update VI to output a binary value If you are tingle Update calibrating a voltage output range enter 0 in the binary array Ek input of the VI If you are calibrating current range enter 255 into the binary array input of the VI 2 Measure the output voltage or current at the output channel with a voltmeter or ammeter This is your first volt binary measurement Binary 1 0 and Volt Amp 1 is the voltage or current you measured at the output 3 Use the AO Single Update VI to output a binary value of 4 095 4 Measure the output voltage or current at the output channel This is your second volt binary measurement Binary 2 should be 4 095 and Volt Amp 2 is the voltage or current you measured at the output 5 Use SCXI Cal Constants VI with the first voltage binary measurement from step 2 as the Volt Amp 1 and Binary 1 inputs and the second measurement from step 4 as the Volt Amp 2 and Binary 2 inputs of the VI You can save the constants on the module in the user area in EEPROM Use t
269. rage VI 19 6 to 19 7 Acquire N multi ATrig example VI 8 10 Acquire N multi DTrig example VI 8 6 Acquire N multi Start example VI 7 7 Acquire N Scans ATrig example VI 8 7 to 8 8 8 10 8 12 to 8 13 Acquire N Scans DTrig example VI 8 3 to 8 4 8 6 Acquire N Scans example VI 7 6 Acquire N Scans SWTrig example VI 8 13 acquisition rate See external control of acquisition rate ADC limit settings effects figure 5 6 measurement precision for various device ranges and limit settings table 5 8 range effects figure 5 5 resolution 5 3 to 5 4 effects on precision figure 5 4 adjacent counters for counter chips table 25 2 to 25 3 Advanced VIs See also VIs analog output SCXI example 19 14 to 19 15 external control of channel clock 9 4 non buffered handshaking 15 5 overview 3 6 simple buffered handshaking 15 7 to 15 9 National Instruments Corporation AI Acquire Waveform VI simple buffered analog input with multiple starts 7 7 to 7 9 single waveform acquisition 7 2 to 7 3 AI Acquire Waveforms VI multiple waveform acquisition 7 3 simple buffered analog input with graphing 7 6 to 7 7 AI Clear VI continuous acquisition from multiple channels 7 12 to 7 13 hardware timed analog I O control loops 6 9 multiple waveform acquisition 7 5 SCXI temperature measurement 19 6 to 19 7 simple buffered analog input with multiple starts 7 7 to 7 9 AI Clock Config VI external control of channel clock
270. ration National Instruments Corporation 11 3 LabVIEW Data Acquisition Basics Manual Buffering Your Way through Waveform Generation In Chapter 10 Things You Should Know about Analog Output you learned when to use buffered analog updates This chapter shows you which VIs to use in LabVIEW to perform these updates Buffered Analog Output You can program single buffered analog output in LabVIEW using an Easy Analog Output VI AO Generate Waveforms as shown in Figures 12 1 This VI writes an array of output voltages to the analog output channels at a rate specified by the Update Rate parameter For example if Channels is 0 1 and the Voltages array consists of two columns containing voltage data for the two channels LabVIEW writes voltages from each column to the corresponding channels at every update interval After LabVIEW writes all of the voltages in the array to the channels the VI stops The voltage level on the output channel maintains the value of the final voltage in the array until another voltage value is generated Easy VIs contain error handling If an error occurs in the AO Generate Waveforms VI a dialog box appears displaying the error number and description and the VI stops running voltages Figure 12 1 Waveform Generation Using the AO Generate Waveforms VI National Instruments Corporation 12 1 LabVIEW Data Acquisition Basics Manual Chapter 12 Buffering Your Way through Waveform Generation
271. ration and the next Counter Start VI generates a pulse after a specified time The gate mode must be specified as level gating on the Continuous Pulse Generator Config VI in order for the counter to wait for the gate signal from counter 1 The gate mode for the Delayed Pulse Generator Config VI can be set to a single or multiple edges In LabVIEW Data Acquisition Basics Manual 22 8 National Instruments Corporation Chapter 22 Generating A Square Pulse or Pulse Trains other words you could produce one finite pulse train or multiple pulse trains The GATE signal for counter 1 can be from an external device or from another counter on your DAQ device Knowing the Accuracy of Your Counters When you generate a waveform there can be an uncertainty of up to one timebase period between the start signal and the first counted edge of the timebase This is due to the uncertainty in the exact relation of the start signal which the software call or the gate signal supplies to the first edge of the timebase as shown in Figure 22 11 YUU eS phase 2 I uncertainty of v1 timebaze period Figure 22 11 Uncertainty of One Timebase Period Stopping Counter Generations You can stop the counting operation in several ways such as starting the counter again after it has generated a pulse reconfiguring the counter to do something else or calling the Wait ms VI and Counter Stop function as shown in Figure 22 12 You
272. rdware provides signal conditioning close to the signal source and increases the number of analog and digital signals that can be analyzed by a data acquisition DAQ device With PC compatible computers SCXI can be configured in two ways a front end signal conditioning system for plug in DAQ devices or an external data acquisition and control system For Macintosh computers SCXI hardware can only be used as a front end signal conditioning system for plug in DAQ devices Figure 17 1 demonstrates these configurations PC Plug In Data Acquisition Board Conditioned Signals SCXI Signal ne Conditioning 4 j Modules SCXI Signal Conditioning and Data Acquisition Modules SCXI 1200 12 Bit Data Acquisition and Control Module External Data Acquisition and Control System Figure 17 1 SCXI System National Instruments Corporation 17 1 LabVIEW Data Acquisition Basics Manual Chapter 17 Hardware and Software Setup for Your SCX System Figure 17 2 shows the components of an SCXI system An SCXI system consists of an SCXI chassis that houses signal conditioning modules terminal blocks that plug directly into the front of the modules and a cable assembly that connects the SCXI system to a plug in DAQ device or the parallel port of a computer If you are using SCXI as an external DAQ system where there are no plug in DAQ devices you can use the SCXI 1200 module which is a multifunction analog digital and timing I O counters mo
273. rforming frequency division on a internal signal is called a down counter whereas frequency division on an external signal is called a signal divider Figure 26 1 shows how to wire counters to perform frequency division your device Frequency Division for a Signal Divider counter counter Frequency Division for a Down Counter Figure 26 1 Wiring Your Counters for Frequency Division In order to divide down frequencies you must use Intermediate VIs instead of Easy VIs For a LabVIEW example on frequency division refer to How to Generate Pulses and Pulse Trains VI pulse generation method 5 in examples daq counter 11b The diagram in National Instruments Corporation 26 1 LabVIEW Data Acquisition Basics Manual Chapter 26 Dividing Frequencies Figure 26 2 shows how you can program a signal divider using the Down Counter or Divide Config Counter Start and Counter Stop VIs timebase divisor Figure 26 2 Programming a Single Divider for Frequency Division The Down Counter or Divide Config VI configures the specified counter to divide the SOURCE signal by the timebase divisor value and output a signal when the counter reaches its terminal count TC Using Down Counter or Divide Config VI you can configure the type of output to be pulse or toggled The diagram above outputs a high pulse lasting one cycle of the source signal once the counter reaches its TC For more information on the different types of signal output
274. rieve data from each transducer at the same time Your DAQ device executes a scan across each of the specified channels and returns the voltage values when finished Refer to Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual for the number of channels your device can scan at one time The Easy I O VI AI Sample Channels acquires single voltage values from multiple channels The AI Sample Channels VI performs a single A D conversion on the specified channels and returns the scaled voltages in a 1 dimensional 1D array The expected voltage range for all the signals specified by high limit and low limit inputs applies to all the channels Figure 6 3 shows how you can acquire a voltage from multiple channels with this VI Note Remember to use commas to delimit individual channels in the channel string or use a colon to indicate an inclusive list of channels Al Sample Channels vi Index Array A Al device ONE PT 2 channel O voltage 408 channels high limit low limit channel 1 voltage Figure 6 3 Acquiring a Voltage from Multiple Channels with the Al Sample Channels VI You can benefit from using the Easy Analog Input VIs because you only need one icon in your diagram to perform the task there are only a few basic inputs to the VIs and the VIs have built in error checking however the lack of programming flexibility with these VIs can be a limitation Because Easy VIs have only a few inp
275. rporation Chapter 23 Measuring Pulse Width Increasing Your Measurable Width Range The maximum value for counters determines the internal timebases you can use to measure the pulse width of a signal Remember the internal timebase acts as the SOURCE When measuring the pulse width of a signal you count the number of SOURCE edges that occur during the measured pulse The counted number of SOURCE edges cannot exceed the counting range of the counter Slower internal timebases allow for a greater range in possible pulse widths because it takes a longer period of time to reach the maximum counter value Because the Am9513 counters are 16 bit count registers the maximum count value is 65 535 2 6 1 For example if you use a 1 us internal timebase the counter has a pulse width range of 65 ms or 655 s at 100 Hz The DAQ STC counter has a pulse width range of about 840 ms at 20MHz and 167ms at 100 kHz Therefore if you produce an overflow error decrease the timebase frequency to increase your range of measurable width Instead of using an internal timebase you can set up an additional counter for pulse train generation and use the output of that counter as the source of the counter measuring pulse width You can also use FOUT or FREQ OUT for this purpose National Instruments Corporation 23 4 LabVIEW Data Acquisition Basics Manual Measuring Frequency and Period This chapter describes the various ways you can measure fr
276. rsresrsresresrsresrrersese 23 3 Increasing Your Measurable Width Range 00 0 eee cece ceeeseeeseceeceseseeeeseeseeeaeeeees 23 4 Chapter 24 Measuring Frequency and Period Knowing How and When to Measure Frequency and Period 0 ceeseeseeeereeeseeeeeees 24 1 Connecting Counters to Measure Frequency and Period 00 0 eee eeeeseeeeeereeeeees 24 2 Measuring the Frequency and Period of Low Frequency Signals 0 0 0 0 eee 24 4 Measuring the Frequency and Period of High Frequency Signals eee 24 5 Chapter 25 Counting Signal Highs and Lows Counting Events or Elapsed Time ipene aa A a a a 25 3 Gaining More Control over Your Counting Operations sssessseesseressersrrsreersrrerrereee 25 5 Chapter 26 Dividing Frequencies Part 7 Debugging Your Data Acquisition Application Chapter 27 Debugging Techniques Hardware Connection Errors siiesnisnenr nerina ineeie ess 27 1 Software Configuration Errors essseseessseessersesesrestsrtsresterestesterestesrsresrerentesrnsrstesresestes 27 1 VI Construction Errors sanaca Sod aires eid elev 27 2 Error Handling neses oen e E EE E T 27 2 Single Stepping through a VI oo cee eeeeeseceeeeseceeeeseesaeeaeeeseeasenseeaeenas 27 3 Execution High obtain gy oe aeea e oeer s ooon eeN PEPE EEE E AREE 27 3 Using the Probe Tool mesen See te ieee as eee i ia oaa 27 4 Setting Breakpoints and Showing Advanced DAQ VIS seese 27 4 National Instruments Corporation xi LabVIEW Data Acquisition Basics
277. ry useful with data acquisition Figure 25 1 shows how to connect the counter on your device to measure events left diagram and elapsed time right diagram The GATE signal can be produced by your device or another counter like in the example mentioned above counter counter yaur device source source your source i fsource required agti out deaiee out out optional gate gate q q internal eounter 1 counter 1 connections count events 32 bit count time 32 bit cP Note Figure 25 1 Connecting Counters to Your Device to Count Events or Time Am9513 chips only Make sure to use counters that are not being used in any other data acquisition DAQ applications If you try to use a counter that is already being used by another DAQ application LabVIEW returns error number 10009 Refer to Appendix B Hardware Capabilities in the National Instruments Corporation 25 1 LabVIEW Data Acquisition Basics Manual Chapter 25 Counting Signal Highs and Lows LabVIEW Data Acquisition VI Reference Manual for information on which counters are already used for analog and digital applications As shown in Figure 25 1 you can extend the counting range of a counter chip by connecting to the next higher counter called counter 1 This is called cascading counters By cascading counters you can increase your counting range from 65 535 the maximum number for a 16 bit counter to almost 4 3 billion the maximum number for
278. s The configuration file daqconf cfg must be in a place when executing NI DAQ functions in an application From an application NI DAQ searches for the configuration file in the following places in the order listed 1 current working directory 2 usr daq Installing and Configuring Your SCXI Chassis in Windows or on the Macintosh Hardware Configuration Your SCXI hardware kit includes the Getting Started with SCXI manual which contains detailed instructions for assembling your SCXI system module jumper settings cable assemblies and terminal blocks The following are the basic steps to assemble your SCXI system 1 Check the jumpers on your modules Generally you will leave the jumpers in their default positions However the Getting Started LabVIEW Data Acquisition Basics Manual 2 20 National Instruments Corporation National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware with SCXI manual has a section for each module type that lists cases where you may want to change the jumper settings Turn off the chassis power Plug your modules in through the front of the chassis You can put the modules in any slot For simplicity start with slot 1 on the left side of the chassis and move right with each additional module Be sure to screw the modules tightly into the chassis frame If you are using an SCXI 1180 feedthrough panel you must install the SCXI 1180 in the slot imm
279. s refer to the Down Counter or Divide Config VI description in Chapter 18 Intermediate Counter VIs of the LabVIEW Data Acquisition VI Reference Manual The diagram above counts the rising edges of the SOURCE signal the default value of the source edge input In order to figure out where the inputs and outputs are located on this VI remember to use the Help window Open this window by choosing Help Show Help The Counter Start VI tells the counter to start counting the SOURCE signal edges The counter only stops the frequency division when the stop button is pressed The Counter Stop VI stops the counter immediately and clears the count register It is a good idea to always check your errors at the end of an operation to see if the operation was successful You can alter the Down Counter or Divide Config VI to create a down counter To do this change the timebase value from 0 0 external SOURCE to a frequency available on your counter With the Am9513 chip you can choose timebases of 1 MHz 100 kHz 10 kHz 1 kHz and 100 Hz With the DAQ STC chip you can choose timebases of 20 MHz and 100 kHz LabVIEW Data Acquisition Basics Manual 26 2 National Instruments Corporation Chapter 26 Dividing Frequencies Instead of triggering frequency division for signal dividers and down counters by software as was previously discussed you can trigger using the GATE signal You can trigger while the GATE signal is high low or on the rising or
280. s Corporation Glossary A default parameter value recorded in the driver In many cases the default input of a control is a certain value often 0 that means use the current default setting For example the default input for a parameter may be do not change current setting and the default setting may be no AMUX 64T boards If you do change the value of such a parameter the new value becomes the new setting You can set default settings for some parameters in the configuration utility A DAQ device inside your computer or attached directly to your computer through a parallel port Plug in boards PCMCIA cards and devices such as the DAQPad 1200 which connects to your computer s parallel port are all examples of DAQ devices SCXI modules are distinct from devices with the exception of the SCXI 1200 which is a hybrid The slot number or board ID number assigned to the board when you configured it Differential A differential input is an analog input consisting of two terminals both of which are isolated from computer ground and whose difference you measure A way you can configure your device to read signals in which you do not need to connect either input to a fixed reference such as the earth or a building ground A LabVIEW DAQ library containing VIs that perform immediate digital I O and digital handshaking with DAQ devices and SCXI modules A collection of digital input ports You can associate each group with its o
281. s not use the valid parameter to set the overflow so you do not need to check this parameter with this chip frequency Hz Figure 24 7 Measure Frequency VI If you need more control over when frequency period measurement begins and ends use the Intermediate VIs instead of the Easy VIs Figure 24 8 shows you how to measure the period and frequency for high frequency signals The Intermediate VIs described in Figure 24 8 include the Delayed Pulse Generator Config Event or Time Counter Config Counter Start CTR Control Counter Read and the Counter Stop VIs The Delayed Pulse Generator Config VI configures counter 1 to generate the gate signal The Event or Time Counter Config VI configures the counter to count the number of pulses while it is gated The Counter Start VI begins the counting operation for counter first then counter 1 The Counter Read VI returns the count value from counter which is used to determine the frequency and period measurement The Counter Stop VI stops the counter operation PULSE Counter Counter D Control Counter al Start Start Read ME aes SESE e E eee read output state Figure 24 8 Measuring High Frequency Signals Using Intermediate VIs LabVIEW Data Acquisition Basics Manual 24 6 National Instruments Corporation Chapter 24 Measuring Frequency and Period A third method to determine frequency involves timing how long it takes a number of cycles of the TTL signal connecte
282. sections below describe methods to find problems with VI construction All the techniques discussed can be used by themselves or in conjunction with one another The best way to determine if your application executed without an error is to use one of the error handler VIs in your application The Error Handler VIs are located in Functions Time amp Dialog You can only use these VIs with Intermediate and Advanced VIs Easy I O VIs already include error handling capabilities within each VI Each Intermediate and Advanced VI has an error input and output clusters named error in and error out respectively The error clusters contain a Boolean that indicates whether an error occurred the error code for the error and the name of the VI that returned the error If error in indicates an error the VI returns the same error information in error out and does not perform any DAQ operations error in no error error out When you use any of the Intermediate or Advanced VIs in a While Loop you should stop the loop if the status in the error out cluster reads TRUE If you wire the error cluster to the General Error Handler VI or the Simple Error Handler VI the VI deciphers the error LabVIEW Data Acquisition Basics Manual 27 2 National Instruments Corporation Chapter 27 Debugging Techniques information and describes the error to you The following diagrams show how to wire a typical DAQ VI to an error handler Figure 27 2 Error Check
283. seeeneeseees 8 3 National Instruments Corporation vil LabVIEW Data Acquisition Basics Manual Table of Contents Digital Triggering Examples 0 0 eee eeceeseeeeeneeeseesenseeseenaes 8 6 Analog TAS Pern Goss ai eoa ai cek crests de ahees ina makes ee 8 6 Analog Triggering Examples 0 0 0 0 cceeeseesesseeseceeeseeeseeseenseeseenaes 8 7 SoftWare Trip Seri o oninia ner nA cosas Mosves sche EE dees E dee tvact O E edie 8 10 Conditional Retrieval Examples cece eeeeceeseeseeseeeseeseenseeneenees 8 12 Part 3 Making Waves with Analog Output Chapter 9 Letting an Outside Source Control Your Acquisition Rate Externally Controlling your Channel Clock 0 eee ee ceseeeeeeeeseeseeeseeseeeseeseeeaeeseeens 9 3 Externally Controlling your Scan Clock oo eee eee eseeeeseceeeceeeseeseeeseceesseeseeeseesseeas 9 5 Externally Controlling the Scan and Channel Clocks 00 eee ee eeeeseeseeeeeseeeeeeeeens 9 8 Chapter 10 Things You Should Know about Analog Output Sinpsle Pomt Qutput ie a steedecesh seri vend ease EE a a AE eens se 10 1 Buffered Analog Output sz restao n ea ctedesteessdacsgeveabiacetee bebectctussevcenes odie 10 1 Chapter 11 One Stop Single Point Generation single Immediate Updates ns sos irronneita e EEE EE E EEEE 11 1 Multiple Immediate Updates s nssesesesessseeseeseesresrsesrestsresresrsrestesestrstssrntesrerenresresenet 11 2 Chapter 12 Buffering Your Way through Waveform Generation Buffered Analog Output isic c ccsss
284. signals 21 2 EEPROM for storing calibration constants 20 1 to 20 3 default load area 20 2 factory area 20 2 user area 20 2 to 20 3 elapsed time counting See events or elapsed time counting electronic support services B 1 to B 2 Error Handler VIs 27 2 error handling debugging VIs 27 2 to 27 3 VIs 3 8 to 3 9 Event or Time Counter Config VI LabVIEW Data Acquisition Basics Manual counting external events 25 6 to 25 7 measuring frequency and period 24 6 events or elapsed time counting 25 1 to 25 5 adjacent counters for counter chips table 25 2 to 25 3 cascading counters 25 2 connecting counters to device figure 25 1 counting events or elapsed time 25 3 to 25 5 gaining more control over counting operations 25 6 to 25 7 overview 25 1 to 25 3 execution highlighting 27 3 to 27 4 external control of acquisition rate 9 1 to 9 8 channel and scan intervals using channel clock figure 9 2 channel clock control 9 3 to 9 5 choosing between triggering and external clock control 4 4 description 9 1 to 9 3 round robin scanning figure 9 2 scan clock control 9 5 to 9 8 simultaneous control of scan and channel clocks 9 8 external conversion pulses 9 4 to 9 5 F faxback support B 2 filtering 16 5 floating signal sources 5 3 FOUT output 21 5 23 4 FREQ OUT output 21 5 23 4 frequency and period measurement 24 1 to 24 7 cascading counters 24 3 connecting counters for measuring 24 2 to 24 3 equation
285. simple buffered examples 15 7 to 15 9 bulletin board support B 1 C calibration See SCXI calibration cascading counters 24 3 25 2 channel addressing AMUX 64T devices 5 12 to 5 13 SCXI modules 18 1 to 18 2 National Instruments Corporation VI channel port and counter addressing 3 9 to 3 11 channel clock 9 3 to 9 5 channel and scan intervals using channel clock figure 9 2 considerations for specific boards notes 9 5 controlling externally 9 3 to 9 5 rate parameter 5 17 setting channel clock rate 9 3 simultaneous control of scan and channel clocks 9 8 TTL signal example 9 3 circular buffered analog input continuous acquisition from multiple channels 7 11 to 7 13 examples basic circular buffered analog input 7 13 to 7 14 Cont Acq to File scaled vi 7 15 Cont Acq to Spreadsheet File vi 7 15 Cont Acq amp Chart buffered vi 7 14 Cont Acq amp Graph buffered vi 7 15 how circular buffers work figure 7 10 overview 7 10 to 7 11 circular buffered analog output changing waveform during generation 12 3 to 12 5 eliminating errors 12 5 circular buffered digital I O examples 15 9 to 15 10 code width calculating 5 6 to 5 7 cold junction compensation 19 3 to 19 4 column major order 3 14 to 3 16 common mode voltage definition 5 10 illustration 5 10 common questions about LabVIEW data acquisition A 1 to A 5 conditional retrieval 8 10 See also software triggering configuration See install
286. sition or edge on the SOURCE input then the counter does not begin counting until the next SOURCE transition or edge You can also use a counter with no gating allowing the software to initiate the counting operation National Instruments Corporation 21 3 LabVIEW Data Acquisition Basics Manual Chapter 21 Things You Should Know about Counters Knowing Your Use the OUT signal of a counter to generate various TTL pulse waveforms If you are incrementing the count register value you can configure the OUT signal to either toggle signal states or pulse when the counter register reaches a certain value The highest value of a counter is called the terminal count TC If you are decrementing the counter register value will be 0 If you chose to have pulsed output then the counter outputs a high pulse that is equal in time to one cycle of the counter s SOURCE signal which can be either an internal or external signal If you chose to have a toggled output you just change the state of the output signal from high to low or low to high If you want more control over the length of high and low outputs then you should use a toggled output Refer to Chapter 22 Generating A Square Pulse or Pulse Trains for more information Multiple counters can be concatenated for a greater counting range on most devices For more information on how to concatenate counters refer to Chapter 25 Counting Signal Highs and Lows Counter Chip Most Nati
287. so you can send more digital values out at a time The order of grouped ports affects which handshaking lines you use If you want to group ports 0 and 1 and you list the ports in the order of 0 1 then you should use the handshaking lines associated with port 1 In other words always use the handshaking lines associated with the last port in the list So if the LabVIEW Data Acquisition Basics Manual 15 2 National Instruments Corporation Chapter 15 Shaking Hands with a Digital Partner ports are listed 1 0 then you should use the handshaking lines associated with port 0 For DAQ devices other than the DIO 32F devices you must connect all the STB lines together if you are using more than one port or grouping ports for digital input as shown in Figure 15 1 You should connect only the IBF line of the last port in the port list to the other device No connection is needed for the IBF signals for the other ports in the port list External Device last port in portList Figure 15 1 Connecting Signal Lines for Digital Input If you are using more than one port or grouping ports for digital output on DAQ devices other than the DIO 32F devices you should connect National Instruments Corporation 15 3 LabVIEW Data Acquisition Basics Manual Chapter 15 CF Note Shaking Hands with a Digital Partner only the handshaking signals of the last port in the port list as shown in the Figure 15 2 External Device last por
288. sresrrsrrsreresrsresreseseeses 8 6 National Instruments Corporation xiii LabVIEW Data Acquisition Basics Manual Table of Contents Figure 8 5 Figure 8 6 Figure 8 7 Figure 8 8 Figure 8 9 Figure 9 1 Figure 9 2 Figure 9 3 Figure 9 4 Figure 9 5 Figure 9 6 Figure 9 7 Figure 11 1 Figure 11 2 Figure 11 3 Figure 12 1 Figure 12 2 Figure 12 3 Figure 12 4 Figure 12 5 Figure 13 1 Figure 14 1 Figure 15 1 Figure 15 2 Figure 15 3 Figure 15 4 Figure 15 5 Figure 15 6 Figure 15 7 Figure 15 8 Figure 15 9 Analog Triggering with Your DAQ Device 0 eee eeeeeeseeeeeeees 8 7 Block Diagram of the Acquire N Scans ATrig VI eee 8 8 Timeline of Conditional Retrieval ieeeeeeeeeceeeeeteeeeeeeeeenees 8 11 The AI Read VI Conditional Retrieval Cluster 0 0 eee 8 12 Block Diagram of the Acquire N Scans ATrig VI eee 8 13 Channel and Scan Intervals Using the Channel Clock 9 2 Round Robin Scanning Using the Channel Clock oe 9 2 Example ota TTL Sonal senie np ra E EEEE 9 3 Getting Started Analog Input Example VI oo eee cece eeeeee 9 4 Setting the Clock Source Code for External Conversion Pulses for E Seties Devices chk ite dies taste Me gna edna 9 5 Externally Controlling Your Scan Clock with the Getting Started Analog Input Example VI ou eee ee eeeceseceeeseeeseceeeeseseeenaeeeeeeseeneees 9 7 Controlling the Scan and Channel Clock Simultaneously 9 8 Singl
289. ss an empty channel array and the group number to the group configuration VI You do not need to erase a group to change its membership If you reconfigure a group whose task is active LabVIEW clears the task and returns a warning LabVIEW does not restart the task after you reconfigure the group Pointer to a pointer to a block of memory handles reference arrays and strings An array of strings is a handle to a block of memory containing handles to strings A type of digital acquisition generation where a device or module accepts or transfers data after a digital pulse has been received Also called latched digital I O A form of triggering where you set the start time of an acquisition and gather data at a known position in time relative to a trigger signal Hexadecimal Hertz The number of scans read or updates written per second G 7 LabVIEW Data Acquisition Basics Manual Glossary IEEE immediate digital I O input limits input range interrupt interval scanning I O LabVIEW Data Acquisition Basics Manual Institute of Electrical and Electronic Engineers A type of digital acquisition generation where LabVIEW updates the digital lines or port states immediately or returns the digital value of an input line Also called nonlatched digital I O The upper and lower voltage inputs for a channel You must use a pair of numbers to express the input limits The VIs can infer the input limits from the input range
290. ssion below the use of the Easy and Intermediate VIs will be discussed You can refer to the Getting Started Counters VI as well as the How To Count VI for examples on how to use Easy I O and Intermediate VIs to count events or elapsed time You can find the Getting Started Counters VI in examples daq run_me 11b The Easy VI that counts events or time the Count Events or Time VI is located in Functions Data Acquisition Counter Figure 25 2 shows how you would use the VI to count external events This VI displays a dialog box if an error occurs use counters SOURCE Figure 25 2 Using the Count Events or Time VI to Count External Events National Instruments Corporation 25 3 LabVIEW Data Acquisition Basics Manual Chapter 25 Counting Signal Highs and Lows In Figure 25 2 the counter begins counting the rising edges at the SOURCE input on the first iteration of the while loop Pressing the stop button will stop the counter and output the present count to the front panel of the VI The counter size input is a menu ring where you have the choice to use a single 16 bit Am9513 counter or a 24 bit DAQ STC counter or cascade two Am9513 counters as a 32 bit counter By default this VI counts the rising edges of the SOURCE signal You can change the value of the source edge input so it will count the falling edges of the SOURCE signal In order to figure out where the inputs and outputs are located on this VI remember to use the Help win
291. t values If you want to use the same digital values from one loop LabVIEW Data Acquisition Basics Manual 14 2 National Instruments Corporation Chapter 14 When You Need It Now mmediate Digital 1 0 iteration to another only set iteration to zero for the first iteration of the loop then change it to a value greater than zero If you are using an SCXI module for nonlatched digital I O refer to the SCXI Channel Addressing section in Chapter 18 Special Programming Considerations for SCXI of this manual for instructions on how to specify port numbers National Instruments Corporation 14 3 LabVIEW Data Acquisition Basics Manual Shaking Hands with a Digital Partner You have just learned that in LabVIEW using non latched immediate digital I O you can use digital lines to acquire and generate data But what if you want to pass a digital pattern after receiving a digital pulse In this case you should use latched digital I O also called handshaking For example you want to acquire an image from a scanner The scanner sends a pulse to your DAQ device after the image has been scanned and it is ready to transfer the data Then your DAQ device reads a digital pattern which can be 8 16 or 32 bits in length The scanner sends out another pulse when it is ready to send another digital pattern After your DAQ device receives this digital pulse it reads the data This process repeats until all the data is transferred
292. t accompanies the device Windows The NI DAQ Driver called NIDAQ DLL is installed in your Windows system directory Note Windows NT The NI DAQ driver consists of two files NIDAQ DLL and NIDAQNT SYS During installation LabVIEW copies the NIDAQ DLL file to your Windows system32 directory and the NIDAQNT SYS file to your Windows driver directory National Instruments Corporation 2 3 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Hardware Support National Instruments periodically upgrades LabVIEW to add support for new DAQ hardware To make sure that this version of LabVIEW supports the hardware you are going to use refer to the following tables Table 2 1 LabVIEW DAQ Hardware Support for Windows AT Series PC Series EISA NEC External PCMCIA SCXI Devices Devices Devices Devices Devices Cards Modules AT A2150 Lab PC EISA NEC AI AMUX 64T DAQCard SCXI 1000 AT AO 6 10 PC AO 2DC A2000 16E 4 SC 2040 500 SCXI 1001 AT DIO 32F PC DIO 24 NEC AI SC 2042 RTD DAQCard SCXI 1100 AT DSP2200 PC DIO 96 16XE 50 SC 2043 SG 700 SCXI 1102 AT MIO 16 16D PC LPM 16 NEC MIO DAQPad 12002 DAQCard SCXI 1120 AT MIO 16DE 10 PC OPDIO 16 16E 4 DAQPad MIO 1200 SCXI 1121 AT MIO 16E 1 PC TIO 10 NEC MIO 16XE 502 DAQCard SCXI 1122 AT MIO 16E 2 16XE 50 AO 2DC SCXI 1124 AT MIO 16E 10 DAQCard SC
293. t in portList Figure 15 2 Connecting Digital Signal Lines for Digital Output There are two types of digital handshaking non buffered and buffered Non buffered handshaking is similar to nonlatched digital I O because LabVIEW updates the digital lines immediately after every digital or handshaked pulse With buffered handshaking LabVIEW stores digital values in memory to be transferred after every handshaked pulse Both non buffered and buffered handshaking transfer only one digital value after each handshaked pulse For basic digital applications use non buffered handshaking Use buffered handshaking when your application requires multiple handshaking pulses to be created By using a buffer with multiple handshaking pulses the software spends less time reading or writing data leaving more time for other operations On the DIO 32F devices with non buffered handshaking you can group 1 2 or 4 ports together For buffered handshaking on the DIO 32F devices you can group only 2 or 4 ports together You can use only Intermediate or Advanced Digital VIs for digital handshaking in LabVIEW The Intermediate VIs work for most all LabVIEW Data Acquisition Basics Manual 15 4 National Instruments Corporation Chapter 15 Shaking Hands with a Digital Partner non buffered and buffered digital handshaking applications However for some DAQ devices you may need to use a combination of Intermediate and Advanced VIs Non Buffered Handshaking
294. t on ADC precision figure 5 6 measurement precision for various device ranges and limit settings table 5 8 SCX gains 18 2 to 18 4 VI limit settings 3 11 to 3 13 linearizing voltage levels 16 5 National Instruments Corporation Index Macintosh systems configuring DAQ devices 2 16 to 2 18 NI DAQ drivers 2 3 questions and answers A 5 SCXI chassis hardware configuration 2 20 to 2 21 software configuration 2 25 to 2 27 manual See documentation maximum sampling rate per channel 7 5 Measure Frequency VI 24 5 to 24 6 Measure Pulse Width or Period VI determining pulse width 23 2 to 23 3 measuring frequency and period 24 4 measurement system choosing 5 3 to 5 6 differential measurement system 5 9 to 5 10 nonreferenced single ended measurement system 5 11 to 5 12 referenced single ended measurement system 5 10 to 5 11 memory allocation errors Windows A 3 to A 4 Microsoft Windows See Windows environment multiple channel single point analog input 6 2 to 6 5 multiple immediate updates 11 2 to 11 3 multiple waveform acquisition choosing between single point and multi point acquisition 4 4 procedure for acquiring 7 3 to 7 5 multiplexed mode SCXI analog input modules 17 4 analog output modules 17 4 channel addressing 18 1 to 18 2 digital and relay modules 17 5 SCXI 1200 Windows 17 4 My Single Scan Processing VI 6 5 LabVIEW Data Acquisition Basics Manual Index NI DAQ file for Macintosh
295. t system Root mean square A way to organize the data in a 2D array by rows Referenced single ended Resistance temperature detector A temperature sensing device whose resistance increases with increases in temperature Real Time System Integration bus The National Instruments timing bus that interconnects data acquisition boards directly by means of connectors on top of the boards for precise synchronization of functions A LabVIEW DAQ VI library containing VIs that perform basic operations concerning analog I O digital I O and counters G 12 National Instruments Corporation S sample sample counter scan scan clock scan rate scan width SCXI sec settling time signal conditioning signal divider National Instruments Corporation Glossary A single one and only one analog or digital input or output data point The clock that counts the output of the channel clock in other words the number of samples taken On boards with simultaneous sampling this counter counts the output of the scan clock and hence the number of scans One or more analog or digital input samples Typically the number of input samples in a scan is equal to the number of channels n the input group For example one pulse from the scan clock produces one scan which acquires one new sample from every analog input channel in the group The clock controlling the time interval between scans On boards with interval sc
296. takes the data and the trigger settings In the AI Read VI you specify parameters to retrieve the data from the data acquisition buffer Then your application calls the AI Clear VI which deallocates all buffers and other resources used for the acquisition by invalidating the taskID If an error occurs in any of these VIs your program passes the error through the remaining VIs to the Simple Error Handler VI which notifies you of the error For many DAQ devices the same ADC samples many channels instead of only one The maximum sampling rate per channel is maximum sampling rate number of channels above is the same as the sampling rate per channel To figure out your maximum scan rate you must divide the maximum sampling rate by the number of channels In Appendix B Hardware Capabilities in the LabVIEW Data Acquisition VI Reference Manual maximum sampling rates are listed for each DAQ device The scan rate input in all the VIs discussed National Instruments Corporation 7 5 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition Simple Buffered Analog Input Examples Simple Buffered Analog Input with Graphing Figure 7 6 demonstrates how you can use the AI Acquire Waveforms VI to acquire two waveforms from channels 0 and 1 and then display the waveforms on separate graphs This type of VI is useful in comparing two or more waveforms or in analyzing how a signal looks before and after
297. ter llb DAQ example file 3 2 counters accuracy of counters 22 8 to 22 9 basic functions 21 1 to 21 4 capabilities 21 1 choosing between counting methods 4 5 choosing between digital or counter interfacing 4 3 to 4 4 counter chips used in National Instruments devices 21 4 counting signal highs and lows 25 1 to 25 3 dividing frequencies 26 2 to 26 3 events or elapsed time counting 25 1 to 25 5 frequency and period measurement 24 1 to 24 7 connecting counters for measuring 24 2 to 24 3 high frequency signals 24 5 to 24 7 how and when to measure 24 1 to 24 2 low frequency signals 24 4 to 24 5 gaining more control over counting operations 25 6 to 25 7 gating levels figure 21 3 pulse train generation 22 5 to 22 8 continuous pulse train 22 5 to 22 7 finite pulse train 22 7 to 22 8 pulse width measurement 23 1 to 23 4 controlling pulse width measurement 23 3 determining pulse width 23 2 to 23 3 increasing measurable width range 23 4 square pulse generation 22 1 to 22 5 single square pulse generation 22 3 to 22 5 square wave generation with no counters available 21 5 stopping counter generations 22 9 to 22 30 LabVIEW Data Acquisition Basics Manual timebase uncertainty 22 8 to 22 9 CTR Control VI enabling and disabling FOUT signal 21 5 measuring frequency and period 24 6 CTR Mode Config VI 21 3 current setting for VIs 3 7 current value conventions for VIs 3 7 customer communication xxi B 1 t
298. termediate VIs in LabVIEW Figures 12 4 shows the AO Continuous Gen VI which is more efficient than the Easy Analog Output VIs in that it configures National Instruments Corporation 12 3 LabVIEW Data Acquisition Basics Manual Chapter 12 Buffering Your Way through Waveform Generation and allocates a buffer when its iteration input is 0 and deallocates the buffer when the clear generation input is TRUE device 40 Continuous Genwi channels update rate new voltages Figure 12 4 Circular Buffered Waveform Generation Using the AO Continuous Gen VI With the AO Continuous Gen VI you can configure the size of the data buffer and the limit settings of each channel For more information on how to set limit settings refer to Chapter 3 Basic LabVIEW Data Acquisition Concepts The Continuous Generation example VI located in examples daq anlogout 11b uses the AO Continuous Gen VI In this example the data completely fills the buffer on the first iteration On subsequent iterations new data is written into one half of the buffer while the other half continues to output data To gain more control over your analog output application use the Intermediate VIs shown in Figure 12 5 With these VIs you can set up an alternate update clock source and you can monitor the update rate the VI actually uses The AO Config VI sets up the channels you specify for analog output The AO Write VI places the data in a buffer The AO Start VI
299. the specified device does not support your requested action If you need to use a frequency that is not listed above then refer to Chapter 26 Dividing Frequencies for more information Gaining More Control over Your Counting Operations If you want more control over counting events or time use the Intermediate VIs These VIs allow you to trigger or gate the counting operation Figure 25 4 shows how to count external events using Intermediate Counter VIs Event or Time Counter Config Counter Start Counter Read and Counter Stop count Continuous court Counter Stop ey counter size Figure 25 4 Using the Intermediate Vis to Count External Events This VI tells the counter to count the number of rising edges on the SOURCE input until the stop button is pressed The Event or Time Counter Config VI configures one or two counters to count the edges of the signal at the SOURCE input The counter size input is a menu ring similar to the Easy I O examples You have the choice to use a single 16 bit Am9513 counter or a 24 bit DAQ STC counter or cascade two Am9513 counters as a 32 bit counter The National Instruments Corporation 25 5 LabVIEW Data Acquisition Basics Manual Chapter 25 Counting Signal Highs and Lows event source timebase input is set to count the edges of the SOURCE signal by default a 0 0 default value The source edge input is set to count on a rising edge by default In order to figure out the locatio
300. the DAQ device gain and the actual limit settings The group channel settings cluster array also shows the input limits for each channel LabVIEW always scales the input data as you specified unless you select binary data only Therefore the gains are transparent to the application You can specify the input signal limits and let LabVIEW do the rest 18 4 National Instruments Corporation Chapter 18 Special Programming Considerations for SCX SCXI Settling Time The filter and gain settings of your SCXI modules affect the settling time of the SCXI amplifiers and multiplexers You should always enter your jumpered filter settings and your jumpered gain settings if applicable in the configuration utility LabVIEW uses the gain and filter settings to determine a safe interchannel delay that allows the SCXI amplifiers and multiplexers to settle between channel switching before sampling the next channel With previous releases of LabVIEW you had to determine the safe interchannel delay or channel clock rate Beginning with LabVIEW 3 0 LabVIEW calculates the delay for you If you set a scan rate that is too fast to allow for the default interchannel delay LabVIEW shrinks the interchannel delay and returns a warning from the AI Start or AI Control VIs You can refer to your hardware manuals for SCX settling times You can open the advanced level AI Clock Config VI to retrieve the channel clock selection Set the which cloc
301. tion National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware Leave the Chassis set to 1 if you have only one chassis You will use this number to access the SCXI chassis from your application If you have multiple chassis advance the Chassis to configure the next chassis after you finish configuring the first chassis Select the appropriate chassis type for your chassis This enables the remaining fields on the panel If you have only one chassis leave the Address field and the address jumpers on your SCXI chassis set to 0 If you have additional chassis you need to select a unique hardware jumpered address for each chassis and enter it in the Address field Leave the Method set to Serial which means that LabVIEW communicates with the chassis serially using a DIO port of the plug in DAQ device The Path sets itself automatically to the device number of the appropriate DAQ device when you enter the Cabled Device information in step 5b Enter the configuration for each slot in the chassis The fields in the bottom two sections of the window reflect the settings for the selected Module number Refer to your SCXI chassis hardware manual to determine how the slots in a chassis are numbered You must set the following fields for each SCXI module you install a Module type Select the correct module type for the module installed in the current slot If the current slot does not have a modul
302. tion of this chapter for more information on WDAQCONF Configuring Your DAQ Device for EISA Bus Computers The SETUP program shipped with the EISA bus DAQ devices copies the EISA configuration files The names of these files follow the format NICxxxx CFG where xxxx is the number in your system that identifies each device You must copy these files into the directory that contains your EISA system configuration utility If your utility is on a disk copy the files to that disk The name of this utility varies with different devices Consult your software user manual that came with your software for the correct utility name for your device g gt Note If you are using an EISA A2000 use a separate utility to installa CFG file from a disk that accompanies the device Follow these steps after you have installed your device 1 If your system configuration utility resides on a disk insert that disk into drive A 2 Turn on your computer 3 Use the system configuration utility to record the base address DMA and interrupt settings 4 Restart your computer Start the WDAQCONF utility by double clicking on its icon and continue with the Configuring and Testing Your DAQ Devices with WDAQCONF in Windows section of this chapter If you are installing any of the following devices you must bypass running the EISA system configuration utility and directly install the devices in WOAQCONF from the Devices menu e All DAQCard
303. tioning Amplification Isolation Filtering Transducer excitation Linearization LabVIEW Data Acquisition Basics Manual 16 2 National Instruments Corporation Chapter 16 Things You Should Know about SCX Figure 16 1 shows some common types of transducers signals and the required signal conditioning for each Transducers Signals Signal Conditioning Thermocouples Amplification Linearization and Cold Junction Compensation Current Excitation Four Wire and Three Wire Configuration Linearization Strain Gauges Voltage Excitation Bridge aS Se poom Configuration and Linearization amm UUSA DAQ Device or High Voltages Common Mode Voltages Isolation Amplifiers Optical Isolation Loads Requiring AC Switching Electromechanical Relays or Large Current Flow or Solid State Relays Signals with High Frequency Noise Lowpass Filters Figure 16 1 Common Types of Transducers Signals and Signal Conditioning Amplification The most common type of signal conditioning is amplification The two advantages to amplifying electrical signals are that it improves the accuracy of the resulting digitized signal and that it reduces noise For the highest possible accuracy the signal should be amplified so that the maximum voltage swing equals the maximum input range of the analog to di
304. tions install the NI DAQ for Windows drivers from those disks In any case make sure you install and use the latest version of the NI DAQ drivers Macintosh My analog input Vis returns error 10845 buffer overflow What is the problem If you do not have an NB DMA 2800 or NB DMA8G board in your Macintosh and are trying to acquire at sampling rates not scan rates greater than 8 kHz you may get this error Even at sampling rates under 8 kHz depending on the type of machine you may run into overflow error problems if there is a lot of other interrupts that need to be serviced This is all due to the long interrupt latencies If you do have either DMA board in your Macintosh make sure that you have a RTSI cable connecting your DAQ device and the DMA board Even after you connect a RTSI cable restarting LabVIEW may help Also if you have a Quadra your errors may be caused by prolonged network interrupt latencies which prevents the NI DAQ driver from copying the data in the DAQ device resident memory to the memory on your computer In this case you can either disable AppleTalk in the Chooser and disconnect your AppleTalk cable or contact National Instruments and ask for the newest revision of the NB MIO 16X which has a larger device resident memory if you are using either of those DAQ devices National Instruments Corporation A 5 LabVIEW Data Acquisition Basics Manual Customer Communication For your convenience
305. to Measure Elapsed Time LabVIEW Data Acquisition Basics Manual 25 6 National Instruments Corporation Chapter 25 Counting Signal Highs and Lows Counters enable you to count the edges of TTL signals whether the signals are external or internal to the DAQ device Counting external signals is called counting events whereas counting internal signals is called elapsed time Since counters count events or time you can combine these two capabilities in order to count events for a certain period of time The basic capability of counting TTL signals allows you to perform many complex functions National Instruments Corporation 25 7 LabVIEW Data Acquisition Basics Manual Dividing Frequencies When would you need to divide the frequency of a TTL signal Sometimes you may need to use an internal signal at a certain frequency but this frequency is not available on your data acquisition DAQ device In order to get the frequency you need you can divide the available device frequencies You can also divide the frequency of an external signal Frequency division is outputting a pulse or pulse train from a counter every N cycles of an internal or external source Counters can only decrease or divide down the frequency of the source signal The resulting divided down frequency is equal to the input frequency N timebase divisor N timebase divisor can only be an integer number not a real number and must also be greater than 1 Pe
306. tomatically configures any Plug and Play devices you have put in your computer from the last time you configured the system This utility also deconfigures any Plug and Play device you have removed from your computer since the last configuration You must run the appropriate DAQ configuration utility for your system after installing a new Plug and Play device to obtain a mapping for the newly installed device to an NI DAQ device number When your DAQ configuration utility detects a new Plug and Play device in your computer it assigns the first available device number to the new device Then the utility assigns the default resources to the new device e g I O address DMA channels or IRQ levels When you remove your device from your computer the configuration utility deallocates these resources and puts an Empty string in the Select a Device Number box LabVIEW Data Acquisition Basics Manual 2 10 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware You must run your DAQ configuration utility after you install or remove any National Instruments Plug and Play devices Configuring Devices with Plug and Play Software If you already have Plug and Play software in your system the DAQ configuration utility operates significantly differently If the Plug and Play software in your system has its own separate configuration utility you must use the system configuratio
307. type in the Channel Configuration section If your terminal block applies gain to your SCXI input channels enter those gain settings in this section as well Press the save button to save this module configuration To go back to the SCXI Configuration window to configure the next module press the return button The SCXI Configuration window has a Help window with entries for each input field that you can refer to if you have other questions Software Configuration on the Macintosh To use SCXI with LabVIEW you must enter the configuration for each SCXI chassis using NI DAQ Select SCXI Configuration in the NI DAQ menu bar to bring up the SCXI Configuration window as shown in Figure 2 13 National Instruments Corporation 2 25 LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware Devices Device Configuration SCHI Configuration SIN Errors 1 0 pe Eda me sd Gair Figure 2 13 Accessing the NI DAQ SCXI Configuration Window on the Macintosh Figure 2 14 shows NI DAQ with the SCXI Configuration window selected 4 8 0 SCHI a Chassis lt 1 J ScHI 1001 ee ae Method Serial AUTE modulefe 1 e Cabled Tove T Operating Mode Multiplexed Channell 0 Filter 4Hz _i Gain 1000 input Mode Figure 2 14 SCX Configuration Window in NI DAQ LabVIEW Data Acquisition Basics Manual 2 26 National Instruments Corpora
308. ual Chapter 19 Common SCX Applications input to an iteration terminal of a loop Every time you call the DIO Port Config VI the digital line values are reset to default values If you want to maintain the integrity of the digital values from one loop iteration to another do not set iteration to 0 except for the first iteration of the loop For an example on SCXI digital output refer to SCXI 116x Digital Output VI located in examples dagq digital digio 11b Even though this VI uses Advanced VIs it is functionally equivalent to the Easy Digital VI Write to Digital Port we Note If you are also using SCXI analog input modules make sure your cabling DAQ device is cabled to one of them Multi Chassis Applications Multiple SCXI 1001 chasses can be daisy chained together using the SCXI 1350 or SCXI 1346 multichassis cable adapters and an MIO Series DAQ device other than the DAQPad MIO 16XE 50 Every module in each of the chassis must be in multiplexed mode Only one of the chassis will be connected directly to the DAQ device When you daisy chain multiple chasses to a single DAQ device each chassis multiplexes all of its analog input channels into a separate onboard analog input channel The first chassis in the chain uses onboard channel 0 the second chassis in the chain uses onboard channel 1 and so on Therefore to access channels in the second chassis you must select the correct onboard channel as well as the correct chass
309. uffer fast enough before LabVIEW overwrites the data into the buffer When your VI tries to read data from the buffer that has not yet been collected LabVIEW waits for the data your VI requested to be acquired and then returns the data If your VI does not read the data from the circular buffer fast enough the VI sends back an error telling you that the data that you retrieved from the buffer is overwritten data Continuously Acquiring Data from Multiple Channels You can continuously acquire time sampled data from one or more channels with the Intermediate Analog Input VI AI Continuous Scan An example using this VI is the Acquire amp Process N Scans VI found in examples daq anlogin anlogin 11b This example is shown in Figure 7 12 There are inputs for setting the channels size of the National Instruments Corporation 7 11 LabVIEW Data Acquisition Basics Manual Chapter 7 Buffering Your Way through Waveform Acquisition CF input limits no change number of scans to aoquire 1000 buffer sie 4000 scans LabVIEW Data Acquisition Basics Manual 7 12 Note channels 0f abe 1000 sears sec circular buffer scan rate and the number of samples to retrieve from the circular buffer each time This VI defaults to a buffer size of 1000 samples and 500 scans to read which means the VI reads in half of the buffer s data while the VI fills the second half of the buffer with new data The number of scans to read
310. uisition VI Reference Manual for more information on the use of digital triggers on your DAQ device LabVIEW Data Acquisition Basics Manual A 2 National Instruments Corporation Appendix A LabVIEW Data Acquisition Common Questions Note The NB MIO 16 has an EXTTRIG pin but cannot support start and stop triggering When are the data acquisition boards initialized All data acquisition boards are initialized automatically when the first DAQ VI is loaded in on a diagram when you start LabVIEW You can also initialize a particular board by calling the Device Reset VI Windows open a VI that calls a DAQ VI or drop a DAQ subVI on a block diagram and crash The first time a DAQ VI is loaded into memory in LabVIEW LabVIEW opens the library d11 that controls data acquisition A crash at this time indicates a problem in communicating with the driver This may indicate that there is a conflict with another device in the machine To determine the source of the problem quit LabVIEW and Windows re launch Windows and run wdaqconf exe Run a simple configuration test with the NI boards in the machine If this results in acrash there is probably a conflict with another device in the machine or the driver s file versions do not correspond for some reason If not you need to obtain the latest version of the DAQ driver from NI BBS World Wide Web or FTP site We have also seen cases where the video driver conflicts with both WDAQCO
311. uisition rate is not as consistent as that which can be achieved through hardware timed control loops Generally if you do not need a precise acquisition rate for your control loop use software timed control loops Besides user interaction a large number or large sized front panel indicators like charts and graphs affect control loop rates Refreshing the monitor screen interrupts the system clock which controls loop rates Therefore you should keep the number of charts and graphs to a minimum when you are using software timed control loops An example of software timed control loops is the Analog IO Control Loop immed VI located in examples daq anlog_io 11b LabVIEW Data Acquisition Basics Manual 6 6 National Instruments Corporation Chapter6 One Stop Single Point Acquisition The following diagram shows how to perform software timed analog T O using the AI Read One Scan and AO Write One Update VIs transposed waveform chart petits seu 40 Channels O81 a SESSE e Lias loop rate scan rate 5 loops sec Figure 6 7 Software Timed Analog 1 0 The AI Read One Scan VI configures your DAQ device to acquire data from analog channels 0 and 1 Once your program acquires a data point from channels 0 and 1 it performs calculations on the data and outputs the results through the same channels 0 and 1 Because the iteration count is connected to the AI Read One Scan and AO Write One Update VIs the application configures t
312. ules with digital components support this mode When your program calls a function in nonlatched digital I O mode LabVIEW immediately updates the digital line or port output state or returns the current digital value of an input line depending on the digital line direction LabVIEW inputs or outputs only one value on a digital line in this mode You can completely configure port and sometimes line direction in software and you can switch directions repeatedly in a program if necessary A typical example of when you might use nonlatched immediate digital I O is in controlling or monitoring relays You can also use multiple ports or groups of ports to perform digital I O functions especially if you only have four lines in a port and need to transfer a byte at a time In order to group digital ports you must use Intermediate or Advanced VIs in LabVIEW You can read more about grouping multiple digital ports in the next chapter Chapter 15 Shaking Hands with a Digital Partner This chapter focuses on transferring data across a single port You only use the Easy Digital VIs for nonlatched digital I O Figure 14 1 shows the Easy VIs and their various inputs and outputs The four Easy VIs can read data from or write data to a single digital line or to an entire port immediately For an example of how to use the Easy Digital VIs refer to the Getting Started Digital I O VI in examples daq run_me 11b Use the Easy Digital VIs for most Nati
313. uments Device Note National Instruments Corporation 2 5 Some DAQ devices have jumpers to set analog input polarity input mode analog output reference and so on Before you install your device check your hardware user manuals to see if your device has jumpers and how to change its settings Then you can determine whether you need to change any jumper settings Be sure to record any jumper settings that you change so that you can enter the information correctly in the configuration utility Windows If you are using multiple DAQ devices you might have to change the base address switches so that the address ranges of the devices do not overlap You might also need to change the DMA and IRQ level jumpers to avoid conflicts For devices that do not have base address switches or DMA and IRQ jumpers these settings can be assigned in the configuration utility or through the operating system if you are using Windows 95 After you have checked and recorded your jumper settings turn off your computer and insert your National Instruments devices Windows You may insert PCMCIA cards without turning off your computer The next step depends on what type of computer you have Go to the appropriate section below to continue the configuration of your devices LabVIEW Data Acquisition Basics Manual Chapter 2 Installing and Configuring Your Data Acquisition Hardware Configuring Your DAQ Device in Windows WDAOCONF Configurin
314. unction to determine the larger of the two values You do not have to use the Max amp Min function in this way for the application to work but the function helps control the size of the scan backlog which is how many samples that are left over in the buffer This VI will continuously read and display the data from channel 0 until an error occurs or until you press the stop button Read amp chart data until an error occurs or the stop button pressed Transposed antinucus Scan Backlog Waverorm Acquisition co at a time 1000 stop o Figure 7 14 Basic Circular Buffered Analog Input Using the Intermediate VIs Other Circular Buffered Analog Input Examples There are many other circular buffered analog input VIs that are included with your LabVIEW application The following sections briefly explain some of these VIs You can find the first two VIs in LabVIEW Data Acquisition Basics Manual 7 14 National Instruments Corporation Chapter 7 Buffering Your Way through Waveform Acquisition examples daq anlogin anlogin 11b and the rest of the example VIs in examples daq anlogin strmdisk 11b For information on how these examples work and how to modify them open Windows Show VI Information or open the Help window by choosing Help Show Help Cont Acq amp Chart buffered vi The Cont Acg amp Chart buffered vi demonstrates circular buffered analog input similarly to the previous example but this VI includes other front pan
315. up Contia vi AO Hardware Config vi AQ Single Update vi Simple Error Handler channels sc md chO 5 Woltage current array 0 0 Digital Input Application Example To input digital signals through an SCXI chassis you can use the SCXI 1162 and SCXI 1162HV modules and the Easy Digital VI Read from Digital Port as shown below Number to array to cluster conversion The port number is a string expressed in the SCX MDY 0 format where you are trying to input from the digital input module on slot y of National Instruments Corporation 19 15 LabVIEW Data Acquisition Basics Manual Chapter 19 Common SCX Applications cr LabVIEW Data Acquisition Basics Manual 19 16 Note Note chassis x The last identifier is always port 0 because the whole module is considered one port The port width should be the number of lines in a port on your SCXI module if you are operating in multiplexed mode For the SCXI 1162 and SCXI 1162HV the port width is 32 lines If you are operating in parallel mode the port width should be the number of lines on your DAQ device The DIO 32F device can access all 32 lines of the SCXI modules at once by using the SCXI 1348 cable assembly The DIO 24 and the DIO 96 devices can only access the first 24 lines of these modules when configured in parallel mode For the fastest performance in parallel mode you can use the appropriate onboard port numbers instead of the SCXI channel string
316. up can be active at any given time That is once a control VI starts a timed acquisition with group n subsequent control and read calls must also refer to group n You use the task ID to refer to the group Devices that increase the number of measurement channels while still using an single instrumentation amplifier Also called AMUX devices A LabVIEW DAQ library containing VIs that generate single values or multiple values waveforms to output through analog channels A collection of analog output channels You can associate each group with its own clock rates buffer configurations and so on A channel cannot belong to more than one group A trigger that occurs at a user selected point on an incoming analog signal Triggering can be set to occur at a specified level on either an increasing or a decreasing signal positive or negative slope G 2 National Instruments Corporation AO array BCD bipolar buffer C cascading channel channel clock circular buffered I O clock cluster code width column major order National Instruments Corporation Glossary Analog output Ordered indexed set of data elements of the same type Binary coded decimal A signal range that includes both positive and negative values for example 5 to 5 V Temporary storage for acquired or generated data Process of extending the counting range of a counter chip by connecting to the next higher counter
317. ur Configuration Utility to Configure Devices Install and Configure SCXI Read Chapter 3 Basic Data Acquisition Concepts and Chapter 4 Where You Should Go Now Figure 2 1 Installing and Configuring DAQ Devices NI DAQ driver software provides LabVIEW with a high level interface to DAQ devices and signal conditioning hardware LabVIEW Data Acquisition Basics Manual 2 2 National Instruments Corporation Chapter 2 Installing and Configuring Your Data Acquisition Hardware Figure 2 2 shows the relationship between LabVIEW NI DAQ and DAQ hardware LabVIEW VIs NI DAQ Drivers Data Acquisition Devices Figure 2 2 How NI DAQ Relates to Your System and DAQ Devices Macintosh NI DAQ for the Macintosh device drivers are bundled in a single file that determines which drivers to load When you restart your computer this file called NI DAQ determines which devices are installed in the system and loads their corresponding drivers NI DAQ uses its control panel settings to determine what SCXI hardware is configured and what the default device settings are for devices in the computer If you are using DMA NI DAQ also communicates with NI DMA DSP for DMA services When you install LabVIEW the installer places both of these files on your hard drive Note Windows If you are using an EISA A2000 you use a separate utility to install a CFG file from a diskette tha
318. ur digital I O operation you should connect the outside signal to the I O connector or the RTSI connector For more information on these connectors refer to your hardware manual for your device The names and functions of handshaking signals vary For the DIO 32F devices there are two handshaking lines the REQ request line and the ACK acknowledge line Use the REQ line as the handshaking line to trigger digital input You can use the ACK line as the handshaking line to trigger digital output For all other DAQ devices that perform handshaking there are four handshaking signals Strobe Input STB Input Buffer Full IBF Output Buffer Full OBF and Acknowledge Input ACK You use the STB and IBF signals for digital input operations and the OBF and ACK signals for digital output operations When the STB line is low LabVIEW loads data into the DAQ device After the data has been loaded IBF is high which tells the external device that the data has been read For digital output OBF is low while LabVIEW sends the data to an external device After the external device receives the data it sends a low pulse back on the ACK line Check your DAQ device hardware manual for information on which digital port s can be configured for handshaking signals For all the DAQ devices that support handshaking there are separate handshaking lines for each digital port Sending Out Multiple Digital Values You can group multiple ports together
319. uts you cannot implement some of the more detailed features of DAQ devices such as triggering interval scanning or coupling In addition these VIs always reconfigure at start up When you need a hi speed or efficiently run program these configurations can slow down processing time When you need speed and more efficiency use the Intermediate VIs which configure an acquisition only once and then continually acquire data without ever re configuring The Intermediate VIs also offer more error handling control more hardware functionality and efficiency in developing your application than the Easy VIs You typically use the Intermediate VIs to perform buffered acquisitions You can read more National Instruments Corporation 6 3 LabVIEW Data Acquisition Basics Manual Chapter 6 One Stop Single Point Acquisition about buffered acquisitions in Chapter 7 Buffering Your Way through Waveform Acquisition The Intermediate Analog Input VI AI Single Scan VI does multiple channel single point acquisitions as shown in Figure 6 4 data remaining taskID out voltage data binary data acquisition state error out taskID in opcode 2 read newest time limit in sec compute 1 output units volts 1 error in no error Figure 6 4 The Al Single Scan VI Help Diagram The AI Single Scan VI returns one scan of data You can also use this VI to read only one point if you specify one channel Use this VI only in conjunction with th
320. vice If more than one scan was stored in the DAQ device FIFO when the AI Single Scan VI was called the LabVIEW diagram was not able to keep up with the acquisition rate This is detected by monitoring the data remaining output of the AI Single Scan VI In other words you have missed at least one control loop interval This indicates that your software overhead is preventing you from keeping up with your hardware timed loop rate In Figure 6 8 the loop too slow boolean indicator is set to TRUE whenever this occurs loop too stow AQ Channels 0 amp 1 transposed waveform char eH saul Hl Cea Be continuous input limits no chan acquisition Compute 14 loop interval in msec E my al o Leentral a cale 1000 ist al cnan my z o Hcntrol i cal o atinne timid r 2nd al eharlf He lc channels O no buffer SOL Toop rate sean ratel 650 loops sec read newest read oldest Figure 6 8 Analog 10 Control Loop hw timed VI Block Diagram In this diagram the AI Config VI configures the device to acquire data on channels 0 and 1 The applicat
321. voltage at this reference can vary with respect to the measurement system ground G 10 National Instruments Corporation 0 onboard channels OUT output pin output limits P parallel mode pattern generation PGIA Plug and Play devices postriggering pretriggering pulse trains pulsed output National Instruments Corporation Glossary Channels provided by the plug in data acquisition board A counter output pin where the counter can generate various TTL pulse waveforms The upper and lower voltage or current outputs for an analog output channel The output limits determine the polarity and voltage reference settings for a board A type of SCXI operating mode in which the module sends each of its input channels directly to a separate analog input channel of the device to the module A type of handshaked latched digital I O in which internal counters generate the handshaked signal which in turn initiates a digital transfer Because counters output digital pulses at a constant rate this means you can generate and retrieve patterns at a constant rate because the handshaked signal is produced at a constant rate Programmable gain instrumentation amplifier Devices that do not require dip switches or jumpers to configure resources on the devices also called switchless devices The technique you use on a data acquisition board to acquire a programmed number of samples after trigger conditions are
322. wn clock rates handshaking modes buffer configurations and so on A port cannot belong to more than one group A collection of digital output ports You can associate each group with its own clock rates handshaking modes buffer configurations and so forth A port cannot belong to more than one group A TTL level signal having two discrete levels a high and a low level Dual inline package G 5 LabVIEW Data Acquisition Basics Manual Glossary dithering DLL DMA down counter driver DSP E EEPROM EISA event external trigger F FIFO filtering floating signal sources LabVIEW Data Acquisition Basics Manual The addition of Gaussian noise to an analog input signal Dynamic link library Direct memory access A method by which data you can transfer data to computer memory from a device or memory on the bus or from computer memory to a device while the processor does something else DMA is the fastest method of transferring data to or from computer memory Performing frequency division on an internal signal Software that controls a specific hardware device such as a data acquisition board Digital signal processing Electrically erased programmable read only memory Read only memory that you can erase with an electrical signal and reprogram Extended Industry Standard Architecture The condition or state of an analog or digital signal A voltage pulse from an external source that
323. x in your channel list when you sample a single AMUX 64T channel LabVIEW then scans four eight or 16 channels for every device channel for one two or four AMUX 64T devices respectively However the AMUX 64T has a LabVIEW Data Acquisition Basics Manual 5 14 National Instruments Corporation Chapter 5 Things You Should Know about Analog Input fixed scanning order Table 5 4 shows the order in which LabVIEW scans the AMUX 64T channels for every DAQ device input channel when you use one or two AMUX 64T devices Table 5 4 shows the order in which LabVIEW scans the AMUX 64T channels for every DAQ device input channel when you use four AMUX 64T devices If you want to scan more than one AMUX 64T channel you must enter the device channels in your scan list Table 5 3 Scanning Order for Each DAQ Device Input Channel with Four AMUX 64Ts AMUX 64T Channels DAQ Device One Device Two Devices Channel Device 1 Device 1 Device 2 0 0 1 2 3 0 1 2 3 0 1 2 3 1 pee ne es 2 8 9 10 1 8 9 10 1 8 9 10 1 3 hat ne ae 4 16 17 18 19 16 17 18 19 16 17 18 19 5 20 21 22 23 20 21 22 23 20 21 22 23 6 24 25 26 27 24 25 26 27 24 25 26 27 7 28 29 30 31 28 29 30 31 28 29 30 31 8 32 33 34 35 32 33 34 35 32 33 34 35 9 36 37 38 39 36 37 38 39 36 37 38 39 10 40 41 42 43 40 41 42 43 40 41 42 43 11 44 45 46 47 44 45 46 47 44 45 46 47 12 48 49 50
324. xample 7 9 square pulse generation 22 1 to 22 5 overview 22 1 to 22 3 single square pulse generation 22 3 to 22 5 Generate Delayed Pulse VI 22 4 physical connections figure 22 4 using Intermediate VIs 22 4 to 22 5 STB Strobe Input line 15 2 strain gauges for measuring pressure example 19 11 to 19 14 Strobe Input STB line 15 2 T technical support B 1 to B 2 telephone and fax support B 2 temperature measurement applications SCXI amplifier offset 19 4 to 19 5 sensors for cold junction compensation 19 3 to 19 4 using RTDs 19 9 to 19 11 using thermocouples 19 2 to 19 5 VI examples 19 5 to 19 9 terminal count TC 21 4 thermocouples for measuring temperature example 19 2 to 19 5 timebase period uncertainty 22 8 to 22 9 toggled counter signal generation 22 1 LabVIEW Data Acquisition Basics Manual Index transducers common transducers table 16 1 to 16 2 excitation 16 5 linearization 16 5 signal conditioning for common types of transducers signals figure 16 3 transposing arrays 7 7 triggered data acquisition 8 1 to 8 14 analog triggering description 8 6 to 8 7 examples 8 7 to 8 10 choosing between triggering and external clock control 4 4 deciding which digital trigger setting to use A 2 digital triggering description 8 2 to 8 3 examples 8 3 to 8 6 hardware triggering 8 1 to 8 10 overview 8 1 software triggering description 8 10 to 8 12 examples 8 12 to 8 14 triggering d
325. y and period measurement Counter Stop stops the counter operation Figure 24 6 Measuring Low Frequency Signals Using Intermediate VIs A third method to determine frequency involves timing how long it takes a number of cycles of the TTL signal connected to the SOURCE input to occur Refer to the How to Measure Frequency and Period VI Case 4 for a detailed description of the block diagram It is a good idea to know what type of signal you are measuring so you can use the best approach for measuring the frequency signal Measuring the Frequency and Period of High Frequency Signals For high frequency signals you can use the Easy VI Measure Frequency to determine the frequency as shown in Figure 24 7 You can find the Measure Frequency VI in Functions Data Acquisition Counter This VI initiates the counter to count the number of rising edges of a TTL signal at the counter s SOURCE input during a gate period of a specific duration T seconds Set the gate width T to the pulse width of the gated signal The measured frequency equals count gate width The valid parameter indicates if the frequency was measured without overflow Overflow occurs when the counter reaches its highest value or terminal count TC You only need to check the valid parameter if you are using an Am9513 chip The DAQ STC National Instruments Corporation 24 5 LabVIEW Data Acquisition Basics Manual Chapter 24 Measuring Frequency and Period doe
326. y ground loop induced errors but also the noise picked up in the environment to a certain degree However the single ended configuration allows for twice as many measurement channels and is acceptable when the magnitude of the induced errors is smaller than the required accuracy of the data You should use differential measurement systems when all input signals meet the following criteria e Low Level Signals less than 1 V e Long or Non Shielded Cabling Wiring Traveling through a Noisy Environment e Any of the Input Signals Require a Separate Ground Reference Point or Return Signal If you have the following criteria read the following sections on single ended measurements An ideal differential measurement system reads only the potential difference between its two terminals the and inputs Any voltage present at the instrumentation amplifier inputs with respect to the amplifier ground is called a common mode voltage An ideal differential measurement system completely rejects does not measure common mode voltage as shown in Figure 5 8 Instrumentation Amplifier Grounded Signal Source V _ Measured Voltage Common Mode Voltage Ground Potential Noise etc Figure 5 8 Common Mode Voltage Referenced Single Ended Measurement System A referenced single ended RSE measurement system is used to measure a floating signal because it grounds the signal with respect to LabVIEW Data Acquis
327. y removing this graph indicator You can easily add other processing to your analog I O control loop by putting the analog input control loop calculations and analog output in the first frame of a sequence inside the loop and additional processing in subsequent frames of the sequence Keep in mind that this additional processing must be less than your control loop interval otherwise you will not be able to keep up with your control loop rate Improving Control Loop Performance There are some performance issues you should take into account if you plan to have other VIs or loops execute in parallel with your hardware timed control loop When you call the AI Single Scan VI in a hardware timed control loop the VI waits until the next scan is acquired before returning which means that the CPU is waiting inside the NI DAQ driver until the scan is acquired Consequently if you try to run other LabVIEW VIs or while loops in the same diagram in parallel with your hardware timed control loop they may run more slowly or intermittently You can reduce this problem by putting a software delay with the Wait ms VT at the end of your loop after you write your analog output values Your other LabVIEW VIs and loops will then be able execute during this time National Instruments Corporation 6 9 LabVIEW Data Acquisition Basics Manual Chapter 6 One Stop Single Point Acquisition Another good technique is to poll for your analog input without waitin
328. y trig A amp BT rr forgat pretrigger w 0 rig edge rising LO z E ET i eth on no Eo real peace device HE channels O l Tan lt to acquire 1000 1000 scans sec Figure 8 3 Block Diagram of the Acquire N Scans DTrig VI For more information on buffered acquisitions refer to Chapter 7 Buffering Your Way through Waveform Acquisition You must tell your device the conditions on which it will start acquiring data The following figure shows the trigger and clock LabVIEW Data Acquisition Basics Manual 8 4 National Instruments Corporation Chapter 8 Controlling Your Acquisition with Triggers cluster input where you specify the triggering conditions on the AI Waveform Scan VI trigger and clock no trig int clk trigger type no trig 0 La Fr no trigger p pretrigger edge or slope scans 0 Cno change analog chan amp level 0 W trigger channel fempty level LO Y acan clock source no change 0 no change o For this example trigger type should be set to Digital Trigger A You should only use the Digital Trigger A amp B when you have two triggers start and stop This chapter only discusses applications that use one digital trigger For more information on two triggered applications look at the description for the AI Trigger Config VI found in Chapter 6 Advanced Analog Input VIs in the LabVIEW Data Acquisition VI Reference Manual In LabVIEW y
329. you calculate using the SCXI Cal Constants VI You can also put a copy of your own constants in the default load area if you want LabVIEW to automatically load your constants for subsequent operations You can read and write to the user area LabVIEW Data Acquisition Basics Manual 20 2 National Instruments Corporation Chapter 20 SCX Calibration Increasing Signal Measurement Precision gt Note You should use the user area in EEPROM to store any calibration constants that you may need to use later This safeguards you from accidentally overwriting your constants in the default load area because you will have two copies of your new constants and you can revert to the factory constants by copying the factory area to the default load area without wiping out your new constants entirely The following sections explain how to calibrate your SCXI modules to achieve the levels of accuracy that you desire Calibrating SCXI Modules The SCXI Cal Constants VI in LabVIEW automatically calculates the SEx A Ga cal calibration constants for your module with the precision you need for const your particular application You can find this VI in Functions DAQ Calibration and Config Refer to Chapter 20 Calibration and Configuration VIs in the LabVIEW Data Acquisition VI Reference Manual for more specifics on the SCXI Cal Constants VI and each of its parameters By default calibration constants for the SCXI 1102 SCXI 1122 and SCXI 1141 are
330. zation of Ehis Manual 3 ccs seserdeceesc cote ceusecevsveven ceanes pne i i E E aia xvii Conventions Used in This Manual 0 ccccccccccssssecccessssscecceeesssseeeceessnseeeeessssseeeeeeeees xviii Related Documentation ses meneere a ee aaea aree ee AE E Ea E ago EP au EET eas xxi Customer COMMUNICATION 0 0 ccccesccccceesssscceccesesssececeeesessceceecesesseeeceeeesseeececeseaeeeeeeeses xxi Part 1 Before You Get Started Chapter 1 How To Use This Book Chapter 2 Installing and Configuring Your Data Acquisition Hardware LabVIEW Data Acquisition Hardware Support esessessssesssresssrsresresesreseseensesrssesresreee 2 4 Installing Your National Instruments Device sssessssesseseseessreesrsresresrsresreersresresesresreee 2 5 Configuring Your DAQ Device in Windows 0 sees eeeeeeeseeeeeteeeseeneeeeeens 2 6 Configuring Your DAQ Device for ISA and PCMCIA Bus COMPUTE S sie lee ses erea dessus RE aaa e EN eer peen ey Ses 2 6 Configuring Your DAQ Device for EISA Bus Computers 2 9 Configuring Plug and Play Switchless DAQ Devices in WINdOWS sce hos Se wie RA Nab pS ee A 2 10 Configuring and Testing Your DAQ Devices with WOAQCONF IN WINdOWS ennan E ean icen E balaea 2 11 Special Considerations for LabVIEW for Windows NT eseese 2 14 Changing I O Page Lock Limit 20 eee eeeesecseeereeeseeseeeeeens 2 14 User Privilege Level When Using NI DAQ ou eee eee eeeeeees 2 15 Configuring Your DAQ Device Using NI DAQ on the M

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