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SER1CH-UA User Manual

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1. SERICH UA VIN 0 5 Vbias 5 gt SERICH UA VREF Figure 9 2 Three resistor scaling and biasing 10 10 into 0 5 As with the two resistor circuit if the input of the three resistor circuit is allowed to float its output will drift to a non zero voltage With the values above it will drift to 3 3 volts Connect the Vsensor input to ground if you wish to temporarily drive the input low for a test For other input ranges the this circuit can be modified with different resistor values and still use the SERICH UA VREF as the bias source The following table lists some possible values Bipolar input A Vin Vout A Kohm B Kohm C Kohm 06 0 12 0 0 5 10 000 8 333 50 000 07 0 14 0 0 5 10 000 7 143 25 000 08 0 16 0 0 5 10 000 6 250 16 667 09 0 18 0 0 5 10 000 5 556 12 500 x 10 0 20 0 0 5 10 000 5 000 10 000 11 0 22 0 0 5 10 000 4 545 8 333 12 0 24 0 0 5 10 000 4 167 7 143 14 0 23 0 0 5 10 000 3 571 5 556 16 0 32 0 0 5 10 000 3 125 4 545 18 0 36 0 0 5 10 000 2 778 3 846 20 0 40 0 0 5 10 000 2 500 3 333 Figure 9 3 Three resistor values for various input ranges with Vias VREF 53 9 2 Op Amp scaling and biasing Adding op amps to the resistive circuits in the previous section provides further possibilities for scaling and biasing Besides increasing the input impedance of a resistive divider op amps can perform sign
2. 3 2 CAL To get the most accuracy from the DVM program described in section it is important to calibrate the A D The CAL program makes this calibration easy Like DVM there are two versions of CAL CalCmd exe is a console program that runs from the command line while CalGui exe is a Windows Graphical User Interface GUI program that uses the Microsoft Foundation Classes MFC libraries Both versions of CAL read a preliminary set of control settings from a DVM initialization file such as DvmSetup ini in the Calibrate directory and output the calibrated version of these settings into DvmSetupCal ini Don t forget to copy DvmSetupCal ini to the DVM directory and rename it before running DVM again Running either version of CAL is simple From Windows Explorer double click on the RunCalCmd or RunCalGui shortcut to start CalCmd exe or CalGui exe respectively The RunCalCmd shortcut first starts a command prompt and then runs CalCmd exe You may also type in at a command prompt either program name followed by the name of the ini file you wish to use If no ini file is specified CAL will output a ini file named DvmSetupDefault ini containing the default settings You should copy this file to a new name modify it to have the settings you prefer and run CAL again with the new ini file name as a command line or shortcut argument Both versions of CAL require that certain information is entered and that two known input signals are presented to
3. Maybe include a JPG for this too 81 14 5 Measuring temperature Reasonable temperature measurements can be made using inexpensive silicon diodes as the sensor This example shows how to use a small signal 1N4148 diode to build a temperature sensor All silicon pn junctions have a change in their forward voltage of 2 mV millivolts C with changes in temperature This thermal parameter is governed by the quantum mechanics of a pn junction and is remarkably constant across diode lots The total forward diode voltage depends on the amount of current flowing though the diode and will generally be around 600 to 700 mV For any given diode if the current through it is held constant then its forward voltage will stay the same with only the TC variation remaining When used in this way it becomes a reasonable temperature sensor The SER1CH UA can easily measure changes of 2 mV out of voltages of 600 to 700 mV and the DVM program can be calibrated to display the result as a temperature The key is to maintain a constant steady current through the diode A rudimentary circuit can be as simple as lt VREF 5 0 10K VIN VOCHIITYAS 1N4148 GND Figure 14 12 Temp diode with simple resistive current source In Figure 14 12 the SERICH UA VREF is used as a 5 volt source for the diode To a crude approximation if the voltage across the 10K resistor is taken to be 5 volts then an approximately constant current of 0 5 mil
4. you can still get reasonably good results for voltage calibration by using the approximate slope and offset numbers Slope 2 96e 7 volts count Offset 0 0 volts 34 4 4 Get error message string C usage include Serich h char SerichErrorMsg int Error The ErrorMsg function takes an error number as input and returns a pointer to a null terminated string containing the corresponding message text Also see the C include file Serlch h and source file Serlch c for a listing of the error numbers and corresponding strings 35 4 5 Close device C usage include Serich h int SerichClose DEVHANDLE SerichHandle int Error The Close function closes the COM serial port It should be the last library function called Close returns 1 for success and 0 for failure The first argument to Close is the DEVHANDLE returned from the Open function This is a 32 bit value representing a file handle to the open serial port Under Windows it is equivalent to the Windows HANDLE type The second argument is a pointer to an integer that will be filled with an error code giving more detail than the simple 0 1 function return value This argument is optional and will be ignored if you pass a NULL pointer See Serlch h for a list of the possible error codes Or use the ErrorMsg function to get the message string associated with the integer error number 36 4 6 Code example The following C program is a simple example of c
5. 5 Vbias 5 SERICH UA VREF gt Figure 9 1 Two resistor scaling and biasing 5 5 into 0 5 This design uses two resistors and the SERICH UA VREF as its bias source For easy construction use 1 4 watt metal film resistors with leads Carbon film resistors are not recommended because they have poor noise and TC characteristics with only a small savings in cost For vendors carrying 1 metal film resistors see the Extra supplies chapter See the SR paper Scaling and Biasing Analog Signals for the theory behind this circuit When using this circuit note that if the Vsensor input is allowed to float it will drift to 5 volts and not ground If you measure the floating input with a Fluke or other voltmeter it will read 5 volts The SER1CH UA itself will also return 5 volts if the Vsensor input is allowed to float To work correctly the input must be driven by a low impedance source such as an active sensor output If you want to temporarily hardwire the input low connect it to ground with a wire The next circuit is suitable for mapping 10 10 volts into 0 5 This design uses three resistors and the SERICH UA VREF as its bias source As with the previous circuit use 1 4 watt metal film resistors for best performance If you don t have a 5K ohm resistor on hand build one from two 10K resistors in parallel For a hands on demo of this circuit see the Examples and Experiments chapter 52 Vsensor 10 10 y
6. Comment Min Typ Max Units Analog input VIN input voltage range 0 5 0 Volts VIN input impedance 10M Q Resolution 24 bits Noise Floor 1 10 LV Reference VREF voltage 4 8 V VREF current 10 mA VREF capacitive load 10 HE Power supply Supply Voltage 8 9 16 Vdc Supply Current 2 converting 600 pA Supply Current 3 sleeping 200 pA General RS232 cable length 4 6 100 feet Operating Temperature 0 70 C Dimensions 2 13 x 3 inches Figure 12 1 SERICH UA specifications table 1 Peak to peak noise floor 2 Continuous current when performing conversions with LED off and no VREF load 3 Sleep mode occurs when the LTC2400 CS pin is held high 4 Longer cables may be possible 100 ft is the tested limit 62 12 2 Noise floor Work underway noise floor plot Figure 12 2 SERICH UA noise floor 63 12 3 Thermal response Work underway thermal response plot Figure 12 3 SERICH UA thermal response 64 Chapter 13 Circuit diagrams FREE WEB VERSION PARTIAL CIRCUIT DIAGRAMS This free web copy of the User Manual includes only partial diagrams with the circuit Overview and the VIN analog input amplifier Complete circuit diagrams are provided only with purchase of the product Install the CDROM software included in the product shipment box for the full User Manual and complete diagrams Customers who need an update or have lost their original CDROM may obtain copies of the full User Manua
7. MFG part number ST Micro LM324N MO part number 511 LM324N The selection of op amps is large each device optimizing some particular parameter Probably the most generic part available is the LM324 The LM324 has four op amps a quad in a 14 pin ic package Its close cousin the LM358 is the same op amp but with with two op amps a dual in an 8 pin ic package These traditional bipolar devices were originally developed by National Semiconductor but are now second sourced by many They offer good performance at very low cost for general applications and may be used with either single or split power supplies from as low as 5v to as high as 32v Batteries 12 volt lead acid MFG part number BB Battery BP1 2 12 T1 12v 1 2Ah DK part number 522 1007 ND MFG part number Power Sonic 12v 1 4Ah MO part number 547 PS 1212 The batteries above are small lead acid batteries A good point about lead acid is they are rechargeable A 1 2Ah battery would have enough power to run the SER1CH UA continuously for 1 2 0 0006 2000 hours 83 days 95 Copper Tailings Ruth Nevada 2007 SERICH UA User Manual Copyright Symmetric Research 2007 11 25 This material can only be reproduced in whole or part with the written permission of Symmetric Research No guarantee of suitability for any application is made with this document All liabilities are the responsibility of the user Email info symres com Web www symres com 9
8. another conversion is performed the previous digital result is lost Other Symmetric Research A D products feature sizeable FIFO buffers so the PC does not have to read the results immediately However at the 1Hz ac quisition rates of the SER1CH UA it is assumed the PC can keep up with the required digital bandwidth What kind of RS232 cable is required Use a standard straight through DB9 male to female cable Sometimes this is called a DB9MF extension cable Do not use null modem cables They swap signal wires and will not work correctly If you are using multiwire jacketed cable to make a custom cable you will need 5 conductors One each for ground power CTS RTS and DTR We also recommend shielded cable for this connection with the shield connected to the outer housing on the Dshell connectors on each end The shield will conduct away any static discharges to the enclosures on each end Split out the power conductor and route it to the 2 1mm power connector The other signals can go to the DB9 connector If you are making a perma nent installation consider using the SERICH UA DSUB model which has all connections on Dshell connectors What length RS232 serial cable can I use We have tried 100 feet of RS232 serial port cable Signal quality of the digital signals was good and the system ran without trouble Longer cables may work but have not been tested 88 Is the system opto isolated No The SER1CH UA is connect
9. boards for a total of 40 channels at 25 C 42 include graph here Figure 6 2 Production input offset spreads 43 Chapter 7 Analog Resolution This chapter covers the analog resolution of the SERICH UA The term resolution has many meanings and can cause a great deal of debate Superficially one could say the LTC2400 A D converter used in the system is a 24 bit converter and since it returns 24 bit integers it has 24 bit resolution Furthermore if you know the input voltage span you can compute the number of A D counts per volt and have one measure of the resolution See the Analog DC calibration chapter for a discussion of the counts per volt for the SERICH UA However simply knowing the number of counts per volt does not give a complete picture of the system performance The noise floor and stability of the conversions are equally important measures of the accuracy which will occur in real life applications The graphs and statistics given in the following sections should give an idea of the actual results possible with the SER1CH UA 44 7 1 Noise floor The following graphs show the short term noise floor of the SERICH UA The graphs present a variety of measurements Work underway Full Day Measuring Constant Voltage 4 94940 SER1CH UA as ref voltage VREF 399 as ref voltage 4 2 98940 4 94920 2 98920 ce 4 94900 3 lt qui 4 2 98900 gt aer A VREF 399 2 T
10. making custom RS232 cables solder cup DB connectors are convenient These are avail able everywhere including DK and MO The JDR parts are generic and of good quality at a reasonable price Since the RS232 cable is MF you need one for each end 92 Wall transformers MFG part number CUI Inc DPD090020 P5P SZ DK part number T967 P5P ND 9v 200ma 2 1mm plug 110vac US MFG part number CUI Inc DPD090050E P5P SZ DK part number T973 P5P ND 9v 500ma 2 1mm plug 220vac Euro MFG part number Xicon MO part number 412 109024 9v 200ma 2 1mm plug 110vac US Don t use switching regulated wall transformers with the SER1CH UA No damage will occur but switching regulators will introduce considerable high frequency noise into the system A common unregulated linear wall transformer is generally preferable Single twisted pair shielded cable MFG part number Belden 9501 MO part number 566 9501 100 Twisted pair provides reasonable powerline noise immunity for analog inputs This Belden cable also has a foil shield and is jacketed There are a large number of cable types available This is only one example Double twisted pair shielded cable MFG part number Belden 9502 MO part number 566 9502 100 For connecting potentiometers three wires are needed This is the double pair version of single twisted pair Use one wire from each pair as ground and the other wire of each pair as signal 1 metal film resistors MFG par
11. on each side Hence the term ratiometric measurement 48 For the SERICH UA a buffered copy of the A D reference voltage is provided on the VREF banana jack The VREF jack is capable of supplying 10ma so keep the potentiometer end to end resistance greater than 500 ohms to avoid drawing too much current A 10K pot is often ideal The SER1CH UA analog input has an input impedance of 10M ohms so the potentiometer wiper will not be significantly loaded by VIN For a hands on demonstration using a 10 turn potentiometer in ratiometric fashion see the Ratiometric potentiometer in the Examples and Experiments chapter Just how good are ratiometric techniques The following graph compares a potentiometer excited by the VREF jack with the same potentiometer excited by an external precision reference the SR VREF 399 Even though the external reference has near perfect stability and precision thermal variation in the SERICH UA LM4040A cause the SERICH UA re sponse to appear to drift By simply using the VREF jack for excitation the potentiometer drifts in exactly the same way as the A D giving near perfect results If external excitation such as a battery had been used instead of the VREF 399 the comparison would have been only yet more dramatic Full Day Measuring Constant Voltage 4 94940 SER1CH UA as ref voltage VREF 399 as ref voltage 4 2 98940 4 94920 4 2 98920 GC 494900 lt 4 2 98900 VREF 399 G 4948
12. possibilities for interesting applications As an example Figure 14 3 shows using a solar cell as a light sensor The voltage generated by the solar cell is a measure of the amount of light shining on it The cell in Figure 14 3 has a voltage ranging from 0 volts at total darkness to approximately 3 volts at full brightness Figure 14 3 Using a solar cell as a light level meter Not only can you measure the solar cell voltage with DVM you can also calibrate the second DVM readout to display the value in light level units Having a second readout calibrated into physical units makes it easy to determine the current condition of a sensor Besides its real time GUI readout display DVM also saves its data values to a disk file This makes it easy to review results after a long data run The next chapter section shows how to take a DVM output file and plot the results with GnuPlot on the computer screen or printer 73 14 2 Plotting results with GnuPlot After acquiring data with the SERICH UA you may want to plot the values GnuPlot is a useful public domain program for displaying results on the computer screen or printer in a variety of formats Copies can be downloaded for free from the web at www sourceforge net or found by searching the web on the keywords GnuPlot PDF documentation is included with GnuPlot when it is unpacked Programs such as Xcel and MatLab may also provide useful plotting tools for users already having those pro
13. to your PC with the supplied 6 ft cable Make a note of which COM port you are using on your computer You will need to know the COM number when running the application software Analog connections are made to the three banana jacks on the top panel of the SER1CH UA Reading from left to right the jacks are GND VIN VREF with the colors black red red as in Figure 2 1 The middle red banana jack is the VIN analog input All voltages are measured with respect to GND the black banana jack When you are connecting an external voltage use the VIN and GND banana jacks to connect the voltage keeping in mind the GND jack is the same as PC system ground The outer right red banana jack is the VREF output jack Don t connect the VREF jack directly to ground It is not fatal but will draw unnecessary current For initial testing connect the VIN jack to the GND or VREF to place known voltages on the analog input as in the following figures When connecting VIN to VREF you don t need to make a connection to GND because the VIN and VREF share the same ground internally Figure 2 1 VIN connected to VREF Figure 2 2 VIN connected to GND 2 2 Software installation Run the install bat file on the CD The directory SR SER1CH UA will be created on your hard disk and files will be copied there No changes will be made to the operating system registry or any other system files The SER1CH UA does not require a device driver or device dr
14. using the slope and offset formula for a straight line DataScaled Slope DataCounts Offset 4 1 It is easy to compute the slope and offset from the information generated by the CAL programs Use CAL to measure the A D counts for two known values of A D input Often the input will be specified in terms of volts but it can be in other units such as degrees or inches too This results in two DataCounts DataScaled pairs C1 51 and C2 92 These two calibration points for the straight line equation 4 1 then imply that Slope S2 S1 C2 C1 Offset S1 Slope C1 33 The CAL programs do this computation and save the resulting slope and offset values in the generated ini file DvmSetupCal ini Use these values as inputs to the ScaleData function Note that systematic offsets such as potentiometer offsets and op amp Vio errors can be removed by specifing S1 0 when calibrating Software offset correction is a powerful alternative to hardware trimming For the SERICH UA the A D counts always range from 0x00000000 to 0x00FFFFFF 0 to 16 777 215 decimal and the input voltages at which these count values occur are approximately 0 and 4 96 volts Using these values the slope in volts count should always be approximately 4 96 16777215 2 96e 7 The offset should always be approximately 0 because zero input volts maps approximately into 0 counts Even if you don t have exact calibration numbers for a specific SERICH UA
15. you don t have read permission on the selected serial port Type the command 1s 1 dev ttyS0 to see the current permissions on COMI The two easiest ways to add read permission for yourself are to join the group such as uucp or nut that owns the COM port or to type the command chmod o r dev ttyS0 as root to add world read permission to the COM port 31 4 2 Read data C usage include Serich h int SerichGetData DEVHANDLE SerichHandle long DataCounts double TimeSecSince1970 int Error Once you have successfully called Open to open and initialize the serial port you can call GetData to read in a data point as raw A D counts Get Data returns 1 for success and 0 for failure It also takes an optional Error argument for returning more detailed information when a failure occurs See Serlch h for a list of the possible error codes or use the ErrorMsg function to get the message string associated with the error number The first argument to GetData is the DEVHANDLE returned by Open containing a file handle to the open serial port GetData uses this handle when deciding which serial port to read The DataCounts argument to GetData should be a pointer to a 32 bit long integer The integer will be filled in with the A D count value The 24 bit A D count is stored as a 32 bit integer with the top 8 bits always 0 The optional TimeSecSince1970 argument returns the time when the A D conversion oc curred Pass a NULL pointer if
16. 1 di 3 3 34 3 9 3 6 4 1 4 2 6 1 6 2 7 1 1 2 8 1 8 2 9 1 9 2 9 3 9 4 9 5 12 1 13 2 12 3 14 1 SERICH UA with typical potentiometer setup 7 VIN connected to VREF o occ soe ae w woa ee e 9 VIN connected to GND cocos ma a S oe ee A EE A 9 Screen shot of GUI version of DVM program 13 Sample DVMiniinitializationfile 17 DVM ini keyword table a a 18 Sample DvmOutput asc output file in verbose mode 21 Sample DvmOutputBare asc output file in bare mode 22 Screen shot of GUI version of CAL program 25 perlch library finetion tables s s p s e dos wy a y k e 30 Sample C program calling Serichlibrary 37 A D counts with single ended input 40 Production input offset spreads sa soa pona sasra mamaga k snn w h 43 SERICH UA long term resolution plot 45 Thermal db plop ec ia s s qas s ce RI e 46 Potentiometer parameters 48 SER1CH UA ratiometric comparison 49 Two resistor scaling and biasing 5 5 into 0 5 52 Three resistor scaling and biasing 10 10 into 0 5 53 Three resistor values for various input ranges with Vbias VREF 53 Op amp unity gain buffer with scaling 54 Op amp buffer with gainof10 55 Maximum base power consump
17. 2 33 35 36 37 6 Analog DC calibration 6 1 Full Scale Voltage Span and Counts 6 2 Approximate counts per volt 6 3 Calibration slope and offset 2 e es s 7 Analog Resolution Wal NGESSA o o a u woke Blak Ya e IPN E o bao se e RA K Q a Q 8 Ratiometric measurements 9 Scaling sensor voltages 9 1 Resistivescalingandbiasing 9 2 OpAmpscalingandbiasing 10 Single ended grounding practices 11 Batteries and minimizing power 11 1 Measuring current consumption 11 2 Minimizing power wa els eek kaha a e a S Q SUS AI a AN Et i aa ee AEN e ET aaa 12 Specifications 12 1 Specificatione table 54 04 gasa adt de 12 2 Noise Mee u c s woa sa gua ee la a G S S S ERI A 12 3 Thermal response iui La 2 400 a4 be aw eR ba 13 Circuit diagrams 14 Examples and Experiments 14 1 Basic voltage measurements withprobes 14 2 Plotting results with GnuPlot 14 3 Ratiometric potentiometer 14 4 Scaling and biasing 10 volt signals into 0 5 14 5 Measuring temperature 15 Frequently Asked Questions 1541 BOT WARE o e n A OE See BR e s RUNI W 158 2 Hardware so esser e i ws a a a Oe we Aaa GW 16 Extra supplies 16 1 Small parts for cables ehe i a List of Figures 1 1 2 1 Da 3
18. 4 94880 aaa i I 4 O att LL a 2 98880 d tu WI STE e gt OD 4 94860 P fare d y wy An o LANI a WMA Z 4 2 98860 o n E O 4 94840 gt gt 2 98840 4 94820 F SER1CH UA J 2 98820 4 94800 1 I f 04 00 00 08 00 00 12 00 00 16 00 00 20 00 00 00 00 00 UTC Time Figure 7 1 SER1CH UA long term resolution plot 45 7 2 Thermal drift When making measurments over long time periods thermal drift can become a problem The graphs in this section present a number of results for the thermal drift of the system Work underway include graph here Figure 7 2 Thermal drift plot For effective ways to battle back against thermal drift see the Ratiometric measurements chapter The performance of ratiometric techniques is impressive and will greatly reduce thermal drift problems 46 Chapter 8 Ratiometric measurements When working with passive sensors one of the best ways to use the SERICH UA is to make a ratiometric measurement Such measurements are easy to set up and have the added benefit of excellent TC thermal performance The classic ratiometric sensor is a potentiometer and this section will use it as an example For applications such as active sensors where ratiometric techniques may not be possible the Scaling sensor voltages chapter has interfacing methods which may be helpful The ratiometric concept is simple All A D converters use a reference volta
19. 57 236 79 1201892236 007 2008 02 01 18 57 359 99 1201892237 169 2008 02 01 18 57 150 01 1201892238 330 2008 02 01 18 57 22 43 1201892239 492 2008 02 01 18 57 21 522 684 845 007 169 330 492 2 3 4 2 30847 0 00021 1 47836 23895 26040 95701 06543 Figure 3 5 Sample DvmOutputBare asc output file in bare mode 0 90 180 236 359 150 22 02 00 00 79 99 01 43 22 3 1 6 DVM modifying the program For those who are comfortable programming in C C and want to modify DVM this section briefly discusses the organization of the provided source code files The files DvmLib c and DvmLib h contain the major portion of DVM the part that is shared between both the GUI and CMD versions The files that start with DvmGui are used for the GUI version and the file DvmCmd c is used for the CMD version Both versions depend on the variables and functions defined in the DvmLib files Both DvmGui and DvmCmd can be built from the command prompt using the provided Makefile It accesses various settings and macros contained in the Compiler mak file in the SR SER1CH UA Lib directory and assumes that a batch file like vsvars bat has been run to set the compiler environment The sln and vcproj files can be used to build DvmGui exe and DvmCmd exe from inside the Visual Studio 2005 IDE Please refer to the comments inside the source code files themselves for more details 23
20. 6
21. 80 u r LU ce 4 2 98880 ec 4 94860 D 2 2 98860 9 4 94840 gt o 4 d gt gt giff Ka frre e J 2 98840 4 94820 F SERICH UA 4 2 98820 4 94800 e c IE i 04 00 00 08 00 00 12 00 00 16 00 00 20 00 00 00 00 00 UTC Time Figure 8 2 SER1CH UA ratiometric comparison A wide range of three terminal passive sensors have outputs proportional to the product of their settings and excitation Ratiometric techniques will work equally well for all of them However if you have only a two terminal sensor don t despair You can still gain the benefits of ratiometric measurement 49 Work underway 50 Chapter 9 Scaling sensor voltages The full scale input range of the SERICH UA is 0 to 5 volts If you have an active sensor with a different range even including negative voltages you can use scaling and biasing to map its output to be compatible with the SERICH UA 0 5 range Scaling and biasing is usually not required for passive sensors Passive sensors such as potentiometers typically have their full scale output range set by their excitation voltage If the excitation is supplied by the SERICH UA VREF a full scale sensor range of 0 5 results naturally with no scaling or biasing required Such techniques are covered in the Ratiometric measurements chapter and also have excellent TC thermal performance Active sensors on the other hand usually include op amps in their design They require a
22. A D counts 1 048 576 V V For most applications the calibration equation is actually used the other way around given the A D counts one wants to compute the corresponding voltage The DVM program is one example Given the A D counts we have V V 9 53674e 007 A D counts 9 53674e 007 1 1 048 576 and the slope and offset would be entered into the DVM ini file as 9 53674e 007 1 1 048 576 0 ChannelSlope x ChannelOffset x The ini files shipped with DVM for voltage display use these theoretically perfect values Of course physical components are never perfect and the true slope and offset will be slightly different from this ideal For an exact calibration of any particular USB4CH channel you should perform a physical calibration with the DVM Calibrate program Note that besides calibration into volts it is possible to calibrate A D counts into other physical quantities such as temperature The slope and offset can include the sensor response too The major contribution to offset error on USB4CH boards is the Vj input offset voltage of the front end op amps No op amp is ideal and the Vio parameter measures what input voltage may actually be required to zero the output For the OPA2277 amps used on the USB4CH Vio is 50 microvolts max See the TI spec sheet for this Vio specification as well as other details such as TC temperature variation The following graph shows the offset spreads measured on 10 USB4CH
23. First run DVM generating an OUT data file in bare format Then import the ASCII data file into Xcel 84 Can I use the SER1CH UA with MatLab A native MatLab format is not provided Import the DVM OUT data files in bare ASCII format Can I use the SER1CH UA with Visual Basic The User C Library supporting the system is available as a DLL It can be called from Visual Basic as well as other programming languages as long as you follow C calling conventions Please note SR does not provide Visual Basic programming advice Can I use the SER1CH UA with LabView Set up LabView VI interfaces to the SERICH UA DLL library with C call ing conventions and it will work Please note SR does not provide Lab View programming advice 15 2 Hardware What analog input voltage ranges are possible The analog input voltage may range from 0 to 5 volts This is the voltage as measured on the middle red VIN banana jack with respect to the black GND banana jack Valid count values are returned only for voltages within the specified 0 5 volt range If you wish to work with a different range then you must add circuitry such as a voltage divider or amplifier to scale the voltage into the 0 to 5 range For details see the Scaling sensor voltages chapter By using the VREF jack as a bias source bipolar ranges such as 10 10 are easily supported Many passive sensors can use the VREF jack as excitation to scale their ranges naturally into th
24. SER1CH UA User Manual Manual Revision 2007 11 25 Board Revision B Symmetric Research www symres com FREE WEB VERSION PARTIAL CIRCUIT DIAGRAMS Contents 5 1 Sampling rate 1 Introduction 2 Getting started 2 1 Hardware installation LL 22 Dot ware IMstallatid so s sess a eee ee Oe RE RR EG Rw eG 28 Des and Detta co ab ek ee eRe a Ee Hwee AR 3 Application Programs Sil DVM ee os ee s eee ee ee RA we eek Be EE G ST starting the proeram en 8244400 w RAR REE Pe ee S 3 1 2 determining the serial port o get BN or aod RA AR A A A en 3 1 4 calibrating the readouts e Q s eee ee 3 15 ASC output file format i sieci 6208408 E 6 N W daw A Rem 3 1 6 modifying the program sace saos soraa w Y os bbe hee eee 32 GAL e c s canbe g I bebe eka A a 3 2 1 starting the program 6 2645 ae Q a 8 a es 3 2 2 modifying the program cerro u s side a k s ee a aei a 3 2 3 determining the serial port o 4 User C Library IL Open dev A foes a p eS owe oe he GAR SEE DAES SE RSS 42 Read date u canoso ds oe Be Lee a SUS S Q A LS Beale data 2 64 ae KA ee SUS P S E RATA 4 4 Get error message String o as su aa aeon aa ee 4 5 Close device mopa oa a E e R RNE a e B a ER Ea AG OE EXA L uuu a e e e e a x 5 Sigma Delta A D converters 5 2 50 60Hz power line rejection 10 11 12 13 15 16 17 19 20 23 24 26 27 28 29 31 3
25. Some of the count values for other input voltages are VIN volts GND volts Counts hex Counts decimal 5 0 0x00 FFFFFF 16 777 216 5 e 0 0x00 FFFFFE 16 777 215 e 0 0x00 000001 0 000 001 0 0 0x00 000000 0 000 000 e 0 OxFF FFFFFF 0 000 001 4 0 OxFF C00000 4 194 304 0 0 0x00 000000 00 000 000 0 e 0 OxFF FFFFFF 00 000 001 Figure 6 1 A D counts with single ended input Of course in actual practice resistor tolerances and op amp offsets will prevent the system from achieving a perfect zero counts at 0 volts and likewise 274 counts at full scale 5 volts Nevertheless to a reasonable approximation the above values are good working numbers If you need to measure voltages that are negative with respect to GND please refer to the Scaling sensor voltages chapter 40 6 2 Approximate counts per volt With the total counts and the 16 volt span of the previous section in hand the theoretical counts per volt for the USB4CH is Counts per Volt 2 24 16 1 048 576 counts volt or equivalently Counts per Millivolt 1 049 counts millivolt Counts per Microvolt 1 0 count microvolt where the last two values are rounded Of course the volts per count is just the inverse Volts per Count 16 2 24 1 0 microvolts count Note that because the A D converters have noise floors greater than 24 bits the resolution implied by these numbers may not be
26. a known input signal 24 to the SERICH UA fill in the Value A text field for each display and click the MeasureA button to measure the A D counts for that signal Repeat with a second known input signal Value B and the MeasureB button The calibration results are updated each time a Measure button is pressed Click the Save button to output the calibration results to the DvmSetupCal ini file EA SER1CH UA Calibration To calibrate data from a SER1CH UA select serial port and enter title units Apply signal with value A to the SER1CH UA and click MeasureA Repeat for value B Click save to write calibration results to an ini file Serial Port COMI In ini DvmSetup ini Out ini DvmSetupCal ini Title Units Value A Value B Display 0 Voltage Volts 0 4 96 Display 1 Angle Degrees 0 360 Counts A Counts B 2505 16610430 Measure A Measure B Saved results in file DymSetupCal ini Exit Help Figure 3 6 Screen shot of GUI version of CAL program 25 3 2 1 CAL starting the program Starting CAL is similar for either the GUI or text only versions From the command line type cmd prompt gt DvmGui parameters ini cmd prompt gt DvmCmd parameters ini where the first is for the GUI display and the second for the text only display The parameters ini file is optional If not specified DVM will start up with defaults If you want to run with custom parameters they should be specified in the ini file Ther
27. a semicolon where everything from to the end of line is a comment Use text editors such as Windows Notepad or any other favorite to create and edit ini files For a listing of all the DVM ini keywords see the file SR UsbXch Dvm DvmHelpIniSyntax txt Keywords not specified in the ini file will be given default values Here is an example of a short ini file General parameters SerialPortName COM1 OutputFileName DvmOutput asc OutputFileComment Example ini showing volts and degrees OutputFileShowTimeSec ON RunMode CONTINUOUS Display 0 format and calibration parameters DisplayTitle 0 Voltage DisplayUnits 0 Volts DisplayPlaces 0 9 DisplayDigits 0 5 DisplaySlope 0 2 98511e 007 DisplayOffset 0 0 00119882 Display 1 format and calibration parameters Angular position with full range calibrated from 0 to 360 DisplayTitle 1 Angle DisplayUnits 1 Degrees DisplayPlaces 1 6 DisplayDigits 1 2 DisplaySlope 1 2 16764e 005 DisplayOffset 1 0 0536708 Figure 3 2 Sample DVM ini initialization file 17 For reference the following table describes many of the DVM ini keywords Also refer to the help file DvnHelpIniSyntax txt for the most current list DVM ini Keywords Keyword Description Values SerialPortName Name of serial port to use COMI COM2 COM3 COMA OutputFileName Name of file for saved data File name in quotes like Dv
28. al conditioning such as adding gain or filtering This section reviews two possibilities The following circuit uses a unity gain buffer to increase the input impedance of its 10K 3 3K scaling and biasing pair into the Mohm range The 3 3v bias required for this circuit is derived from the 10K 20K divider on VREF which is then op amp buffered to be stable and constant Vsensor gt 10K 10 10 SERICH UA VIN 0 5 VREF 5 0 Figure 9 4 Op amp unity gain buffer with scaling Note the input amplifier above will need a split power supply in order for its non inverting input to respond to negative signals Typically a split supply like 12 will be required By comparison the purely resistive circuits in the previous section require only VREF from the SERICH UA We assume op amp users are familiar with their power requirements You may also wish to include a small diode above to prevent accidental negative excursions from being presented to the SERICH UA 0 5 input This might happen if the 10 10 input went more negative than 10 volts No damage will occur to the SERICH UA with negative inputs but preventing it from happening is a good precaution Inexpensive bipolar op amps such as the LM358 dual or LM324 quad can offer surpris ingly good performance in such circuits With their multiple op amps per IC package such 54 devices make it easy to build circuits requiring multiple amps and buffers When using ge
29. alHs lt oorr DNIFYIAANE TETSU OL SNIddVW TYNDIS ZEZSA OL NId 690 FOLOANNOI 680 UYOLOANNOOD 684 ZEZSA 67 2002 Uoseasay JUJIWWAS 9 NSC VN HO LUIS 4 QUNN jJuawndog 83343N8 LNdNI ON SOTVNV 0 CHIVINTOd LON dN aNov aNov ANDY ANDY ANDY aNov ngani sdozz L WOL dN 34024 0229 zzzo vazi 2222 1229 gt gt NIA OV NIA Hasn gt ui sed DOL S 0 AL Ozzy ESCH ZWI42911 EEN nz 9 30010 H3N3Z dN SON dN 0024 VNVNVE LNdNI DOTVNV WOU L cH UYUALYAANOD O OL aNov N J3YA HASN ONTYSAANE ANV ONINOILIGNOD TYNDIS INANI Yasn DOTYNY 68 2002 Uoseasay JUJIWWAS 9 NSC VN HO LUIS J QUNN jJuawndog VNVvNV8 y3SN ON SOTVNV 80 TANVd INOHI LIMOVEE r q13IHS AIVIS TINA SITOA S 03 0 GNSV 34M INANI Sr OUIVNV YHSN CHONH H TONIS MOVIE NOW VNVNV8 CNNOUD SOTYNY zoer L gt N GAY Yovr VNYNVA INANI DOTYNY Loer gt gt NIA HISN a34 MOV VNVNV8 K INdLAO ONAA G V CHYTAANE over LK auA u3sn SHUOLOHNNOO MOD VNYNVE INA Jada CONV INANI SOTVNY sn 69 Chapter 14 Examples and Experiments The following are a few hands on demonstrations using the SERICH UA Several of these examples show how to implement topics covered in previous chapters These are starting points and should be modified as necessary for the work at hand Basic voltage measurements with prob
30. alling the SERICH UA function library For simplicity it does not process the error code returns include lt stdio h gt include Serich h define SLOPE 2 96e 7F lt approximate SER1CH UA volts count slope define OFFSET 0 0F lt approximate SER1CH UA offset in volts define FMT_STRING Data pt 02d is 0x 081X counts or Z1f volts at Time lf n int main void int i Success Error long Data double Scaled Time DEVHANDLE SerichHandle Open the SER1CH on COMI SerichHandle SerichOpen 1 amp Error if SerichHandle BAD_DEVHANDLE printf Failed to open the SERICH UA on COM1 n return 1 Read and scale 50 data points for i 0 i lt 50 it Success SerichGetData SerichHandle amp Data amp Time amp Error if Success 1 SerichScaleData Data SLOPE OFFSET amp Scaled NULL printf FMT_STRING i Data Scaled Time else printf Data pt Z02d failed because s n i SerichErrorMsg Error Close Success SerichClose SerichHandle amp Error return 0 Figure 4 2 Sample C program calling Serlch library 37 Chapter 5 Sigma Delta A D converters Review that sigma delta A D converters achieve their resolution by oversampling and averaging down and the boxcar averages result in a sinc response 5 1 Sampling rate Currently the sampling is set at 1Hz by a timer tick running on the PC The user has no control over the i
31. as the one marked with a x star in the Figure 9 3 table in the Scaling active sensor voltages chapter For this demo the 5K biasing resistor is built from two 10K resistors in parallel since that may be all that is on hand There are several construction techniques for building circuits of this type Here we will use vector perf board resistors with wire leads wire and solder The popular white prototype punch boards are not recommended The resistance at the punch board spring clip contacts varies considerably and is subject to corrosion Simple solder joints result in a more reliable and stable circuit Use good quality 1 4 watt metal film resistors for best performance 80 Build the three resistor 10 to 0 5 divider on vector board to demonstrate one con struction technique Review soldering resistors together Include JPEG photo Suitable resistors are listed in the extra supplies section Mention resistor values can often be built using series or parallel combinations of a single stock value So for example with the 10 three resistor divider use 4 10K resistors total with 2 in parallel to build the 5K Demonstrate the input output mapping with the scope and Gnu plots Make a point that a FLOATING input will not map to the 2 5 midpoint The input must be grounded for the output to be at 2 5 an example that the item driving the input must be low impedance Also discuss where there are pads on the RevB board for smt parts
32. at with ratiometric methods the TC spec will hardly even matter As a specific sensor example let s consider a potentiometer Many applications use potentiometers as position or angular sensors The circuit for a potentiometer hooked up to the SER1CH UA in ratiometric fashion is Potentiometer lt VREF 5 volts Ra 1 P R lt lt VINOS VA HOTYAS lt amp Figure 8 1 Potentiometer parameters The three terminals of the potentiometer are simply connected directly to the SERICH UA banana jacks With R as the total end to end potentiometer resistance R and Rp as the resistances above and below the wiper and the VREF jack providing the excitation the potentiometer voltage is given by the resistor divider equation Vin Vwiper si R R Vref PR R Vref Ke P Vref 8 2 where P denotes the physical wiper position and ranges from 0 to 1 so that R PR Substituting this Vin into 8 1 results in AD counts Vin Vref AD Full ScaleCounts P Vref Vref i AD Full ScaleCounts P AD FuliScaleCounts where the V ey factor cancels and ADcounts is a function of only the potentiometer position regardless of the value Vref In fact this is really a bridge or differential measurement The A D forms one side of the bridge while the potentiometer forms the other side As long as the voltage at the top of each leg of the bridge is the same all that matters is the the ratio of the resistors
33. banana pin will affect absolute measurement accuracy Work underway 56 Chapter 11 Batteries and minimizing power With its small current consumption the SERICH UA is a good match for many low power bit banging applications This chapter reviews the steps required for achieving the lowest power possible The steps are easy but important to be aware of for success The chapter sections review how to measure the SERICH UA current consumption then a check list of power minimizing steps and conclude with an example of using battery power 57 11 1 Measuring current consumption The physical current consumed by the SERICH UA can be measured in a various ways If the unit is out of its enclosure one way is to measure the voltage drop across the 5 1 ohm antisurge resistor R900 in the power supply area of the board Then use Ohm s law to compute the current If the unit is in its enclosure you have two options One is to include an external series resistor in the power supply line Any resistor with a few ohms to a hundred ohms resistance will suffice The voltage drop then implies the current Alternatively you can use an ammeter in series with the power supply and read the current directly It will require an accurate ammeter with better than 1 milliamp accuracy Once you have measured the current consumption you ll of course want to compare it against the quoted specs The table below computes the theoretical maximum base power r
34. d OutputFileShowTimeYmd ON which add columns containing time as seconds since 1970 and as year month day respectively The second sample DVM asc output file was created in bare mode with all the optional outputs turned off so only the data values are included This mode makes it easy for the file to be imported into analysis programs like Excel or MatLab 20 Header General File Info HeaderFormatRev DvmRev FileName FileCreationD IniFileName Ini Parameters Data ate 2 2 01 DvmOutput asc 2008 02 01 18 57 12 DvmSetup ini SerialPortName COM1 OutputFileName Dvm0utput asc OutputFileComment Example ini showing volts and degrees OutputFileShowHeader ON OutputFileShowIndex ON OutputFileShowTimeSec ON OutputFileShowTimeYmd ON RunMode DisplayTitle DisplayUnits DisplayPlaces DisplayDigits DisplaySlope DisplayOffset DisplayTitle DisplayUnits DisplayPlaces DisplayDigits DisplaySlope DisplayOffset Sample 1 2 3 4 2 0 NOn OO H r Figure 3 4 Sample DvmOutput asc output file in verbose mode B Volts 00021 23895 47836 26040 95701 06543 30847 CONTINUOUS Voltage Volts 9 5 2 98511e 007 0 00119882 Angle Degrees 6 2 2 16764e 005 0 0536708 Degrees Time Sec Time YMD HMS 0 02 1201892232 522 2008 02 01 18 57 90 00 1201892233 684 2008 02 01 18 57 180 00 1201892234 845 2008 02 01 18
35. e disabled to minimize power For more information see the Batteries and minimizing power chapter Is the SER1CH UA connected to system ground Yes The black GND banana jack on the SERICH UA top panel is connected to the RS232 DB9 ground pin on the back panel which in turn is connected to PC ground In addition the outer ring of the 2 1mm power supply connector is also connected to the black GND jack If you use a grounded power supply then the SERICH UA will also be connected to that ground Note that even though the wall transformer supplied with the system is an unregulated floating power supply or even if you use battery power the system is still connected to the PC ground via the DB9 RS232 connection Is there any antialiasing filter How The SER1CH UA does not have an op amp antialias filter in its front end signal conditioning However fow low frequency measurements 60 or 50Hz rejection is the most common requirement and the LTC2400 A D converter has excellent power line rejection internally See the 60 and 50Hz power line rejection section for more information For rejection of higher RF frequencies simple RC filters are usually recom mended and there are pads for installing a variety of RC combinations on the SER1CH UA front end signal conditioning See the Circuit diagrams do I select 50Hz rejection The internal LTC2400 A D filter can be set to either 60 or 50Hz rejection but not both The selection is made w
36. e full range of the SERICH UA See the Ratiometric chapter for a discussion Can I overdrive the VIN analog input Moderate overvoltages in the range of 20 volts are ok Input currents are limited by the signal conditioning on the SERICH UA front end However overdriving the input is hard on the system We recommend adding suitable external circuitry to deal with the particular problems at your site rather than 85 making the SERICH UA take the brunt of the overload Zener diodes TVS diodes and gas arrestor tubes are all popular overload protection techniques depending on the size and magnitude of the problem Do static shocks hurt the banana jack inputs Yes Although the input circuitry has resistors and capacitors to help guard against static shocks on the banana jack connectors static discharges are brutal to any electronics This includes small sparks generated from walking over a carpet Static dis charge events will result in a degradation of the electronics even if total failure does not occur Before touching the banana jack inputs take a moment and discharge yourself by touching a nearby metal object such a metal desk or a computer case Then touch the metal case of the SER1CH UA and then finally the banana jack inputs for any connections that must be made The moment spent consistently performing this simple routine will significantly reduce static damage Why does waving my hand change the DVM voltage The inpu
37. e is nothing special about the ini filename any filename may be used In fact having several ini files for different setups can be very handy Several program shortcuts are also included in the DVM directory Double click on them to execute Copy the shortcuts to the desktop or start menu for easy access if needed You can also make multiple copies of the shortcuts and edit their properties to run with different ini setups OLD TEXT REGARDING RUNNING If no parameters ini file is specified DVM will create an ini file named DvmSetupDefault ini containing the default settings Copy this file to a new name and modify it to have the settings you prefer Once DvmCmd exe starts it displays a prompt showing the serial port it will use If this is not correct edit the ini file and try again Also see the Selecting the serial port section for a discussion about how to choose a valid serial port Once the serial port selection is correct press the ENTER key to begin acquiring data Once DvmGui exe starts it displays a dialog box showing the default serial port specified in the ini file If this is not correct use the serial port dropdown list box to select the serial port that s connected to the SERICH UA Then click the run button to begin acquiring data 26 3 2 2 CAL modifying the program For those who want to modify CAL and are comfortable programming in C C this section reviews the organization of its source code files T
38. e linear scale and offset transformation This transformation is really nothing more than using the familiar y mz b equation for a straight line where the scale factor m and the offset b are controlled by user settable cali bration parameters located in the DVM ini initialization file The easiest way to determine the proper parameter values is to use the CAL program 19 3 1 5 DVM ASC output file format Both the GUI and command line versions of DVM save their acquired data to ASCII output files Typically it is named DvmOutput asc but you can select the filename with the ini keyword OutputFileName Including summary header data can be controlled with the ad ditional OutputFileShowHeader keyword For importing into Excel use OutputFileShow Header OFF to suppress the header text and include only the data values themselves DVM will not overwrite an existing asc output file So if you ve already run DVM once rename or delete any existing ASC output file before running DVM again Changing the ini keyword OutputFileName will also work and reloading the initializations will work Now let s see what some DVM asc output files look like The first sample output file was created in verbose mode with all the optional outputs turned on It has OutputFileShow Header ON so the header information is included and has OutputFileShowIndex ON so a extra column with the sample number is included In addition it has OutputFileShow TimeSec ON an
39. ed to the ground and signal wires of the RS232 DB9 Those signals are not opto isolated from the analog ground of the SERICH UA Users requiring a floating system should use RS232 opto iosolators that support CTS RTS and DTR and floating power supplies such as an unregulated wall transformer or a battery Will USB to RS232 dongles work Only dongles that support the RS232 signals RTS CTS DTR can be used Be careful many dongles support only RX and TX One USB to RS232 dongle we have used successfully is from Keyspan It is clearly advertised as supporting all the RS232 signals including RTS CTS DTR Various other dongles have failed so don t make assumptions Does the SER1CH UA record GPS time Not directly However the DVM application program is capable of recording the PC time along with each sample If you have a GPS receiver or NTP time setting your PC clock then that time will be recorded in the DVM files as a result See the Software chapter for more details on DVM PC time stamping Note that time stamps derived from the PC clock give at best millisecond accuracy This is perfectly adequate for many applications particularly if they are sampling at the 1Hz rate For more precise time stamping SR has other A D converter products with accuracy in the sub microsecond range 89 Chapter 16 Extra supplies A small collection of parts for getting started with the SER1CH UA is included with all new orders We will be
40. ename any filename may be used In fact having several ini files for different setups can be very handy Several program shortcuts are also included in the DVM directory for quick starts Double click on them to execute Copy the shortcuts to the desktop or start menu for easy access if needed You can also make multiple copies of the shortcuts and edit their properties to run with different ini setups If no ini file is specified DVM will create an ini file named DvmSetupDefault ini containing the default settings Copy this file to a new name and modify it to have the settings you prefer Once DvmGui exe starts its display window shows the RS232 serial port it will use If this port selection is not correct select the serial port that the SER1CH UA is connected to from the pull down list and click the Run button to begin acquiring data You will probably want to edit your ini file so the program starts up with the correct port in the future Also see the section determining the serial port for a discussion about how to choose a valid serial port In the case of the DvmCmd exe console version of the program at startup it displays a prompt showing the serial port it will use If this is not correct edit the ini file and try again Once the serial port selection is correct press the ENTER key to begin acquiring data 15 3 1 2 DVM determining the correct serial port For DVM and CAL to run correctly it is important to select the se
41. equirement Not all these individual current components are consumed at the same time and usually the typical current consumption will be approximately 600 microamps as quoted in the specification table SER1CH UA MAXIMUM BASE POWER CONSUMPTION PART DESCRIPTION CURRENT CONSUMPTION IN milliamps R112 47K 0 5v 0 10638 R115 47K 0 5v 0 10638 R122 1M 5v 0 00500 U110 74HC14 quiesent 0 04000 U200 LTC2400 A D converter while running 0 20000 R211 100K 5v 0 05000 U210 TLC27L2 quiesent 0 03400 U910 TLC27L4 quiesent 0 06800 R921 LM4040 with 24K source resistor 2 5v 24K 0 10417 R922 100K 2 5v 0 02500 R923 100K 2 5v 0 02500 Total base current consumption in milliamps 0 76393 Figure 11 1 Maximum base power consumption 58 11 2 Minimizing power If you are consuming more current than the amount listed in the table in Figure 11 1 there are four possible offenders e The green power LED is on consuming 10 milliamps e A low value resistance is connected between VREF and GND e Custom software is not handling the RS232 port correctly e The power supply is greater than 18 volts Disconnecting the green power LED can be done by removing jumper J910 on the board It may be hard to believe a simple green LED can consume over 10 times more current than the A D circuit itself but it is true Removing the LED jumper will save that current Having a visible power indicator is handy in the lab but takes its toll when running from bat
42. ered from batteries or solar cells for field applications Along with an analog input for A D conversions a buffered copy of the A D reference is also provided for the user This is useful for ratiometric applications such as measuring potentiometer positions and other sensor values By using the same reference voltage for the sensor and A D measurement variations due to temperature drift are virtually eliminated The digital interface is to a PC RS232 serial port Software access is from user space without the need for a kernel mode device driver A Windows GUI DVM application is included for displaying conversion results as well as saving acquired data to a hard disk Easy to use the system requires power from a wall transformer or battery connection to the user s sensor and a PC Among the features of the SERICH UA are e 24 bit one channel A D converter design for DC measurements e Low power consumption 600 microamperes during conversion e Power supply voltage can range from 9 to 18 volts e Buffered analog input with 10M ohm input impedance e Buffered A D reference voltage provided for ratiometric measurements e General use includes applications with potentiometers and other passive sensors e Banana input plugs test leads wall transformer and software included We hope the SERICH UA is a useful tool for your applications Typical usage One popular SER1CH UA setup is with a potentiometer for measuring angular or linear pos
43. es 71 Plotting results with GnuPlot 74 Ratiometric potentiometer 0 eee rr 78 Scaling and biasing 10 volt signals into 0 5 80 Measuring temperature 82 70 14 1 Basic voltage measurements with probes Measuring a voltage with the SERICH UA is similar to using other voltmeters with the voltage source being connected between the red VIN and black GND banana jacks Figure 14 1 shows a pair of AA batteries in series and the alligator test leads supplied with the system used to measure their voltage Figure 14 1 Two lead voltage measurement of a battery Since two AA cells in series is approximately 3 volts if you use the DVM program with the startup file DvmVoltage ini you should see the following on your computer screen Sample 5 Voltage Volts Voltage Volts In this particular DVM display both readouts have been calibrated in volts For many 71 applications it is useful to calibrate the second DVM readout into other more physical units proportional to the voltage such as potentiometer position temperature etc It is convenient to have two readouts so you can monitor the raw sensor voltage while also displaying the physically sensed quantity See the Software chapter of this User Manual and the CAL program for more details Besides
44. example if the RunMode Single radio button is selected a single data sample will be acquired each time the Run button is pressed If Continuous is selected DvmGui will acquire data at a 1Hz rate until the Stop button is pressed Many other options can be specified in the DVM ini file Both the GUI and command line versions use the same ini syntax For example one ini option is to specify an output data file That way acquired values are displayed on the screen in real time and also saved to disk See the ASC output file section for more information about the format Note that while the output filename is displayed on the GUI screen for information it is specified in the ini file Besides saving data to disk DVM can also record the time at which the each data sample was acquired The PC clock is used as a time source and the timestamps can be saved in a variety of formats See the DVM ini syntax section for the possible choices 14 3 1 1 DVM starting the program Starting DVM is similar for either the GUI or text only console mode versions From the command line type cmd prompt gt DvmGui parameters ini cmd prompt gt DvmCmd parameters ini where the first is for the GUI display and the second for the text only display The parameters ini file is optional If not specified DVM will start up with defaults If you want to run with custom parameters they should be specified in the ini file There is nothing special about the ini fil
45. fully usable For example at a sampling rate of 100 Hz the system has a noise free repeatable count value of 20 bits There are four bits or 2 4 1 0 16 microvolts of noise You may prefer to work in 20 bit counts and 16 microvolts per count for your calculations at that sampling rate The input voltage span depends on the gain setting of the front end op amps The above calculation assumes a gain of 1 on those amplifiers By changing resistors on the board it is possible to run the amplifiers with gains of 1 to 100 with no increase in the noise floor This is discussed in the Analog inputs chapter The full scale input range will be smaller with added gain but the counts per volt will be more sensitive We do not recommend using the ADS1255 PGA feature to increase the counts per volt As with most sigma delta A D converters claiming to have a PGA the ADS1255 implements this function by changing the effective oversampling When doing this the noise floor increases in direct proportion This is in contrast to changing the gain of the USB4CH op amps where the gain can be increased without corresponding noise floor increases Al 6 3 Calibration slope and offset For the general differential DC transfer function in the Analog inputs chapter A D counts slope V V offset applied to a theoretically perfect USB4CH the slope is the A D counts per volt as in the previous section and the offset is zero So the equation becomes
46. ge to set their full scale range Voltages less than full scale are compared with the reference and a proportional number of counts returned If measurements can be arranged so the A D reference is also used to excite the passive sensor then the sensor and A D response will both scale in the same way With this technique measurements become insensitive to variations in the reference voltage or sensor excitation yielding excellent results Let s use a few equations to see how ratiometric methods work A D converters accept an analog input voltage and produce a digital output count The converter determines the output by comparing the input against a reference voltage Denoting the A D reference voltage by Veg one might write AD counts Vin Vref R AD FullScaleCounts 8 1 where the AD FullScaleCounts 18 fixed by the architecture of the converter In the case of a 24 bit converter the full scale counts might be 0xFFFFFF and an input voltage that is half of the reference would return 0x7FFFFF For most systems the Mat reference voltage is generated by a component separate from the A D converter In the case of the SERICH UA the reference is a 2 5 volt LM4040A bandgap device This part has a typical 15 ppm C thermal variation and so the reference voltage may vary by 15 1078 2 5 volts 37 5 microvolts C Equation 8 1 makes 47 it clear that changes in Ver will affect the output counts as much as Vin however we will see th
47. glad to supply additional parts if you contact us The following list of mail order suppliers and part numbers may also be useful for obtaining small parts for use with the SERICH UA DigiKey www digikey com 1 800 344 4539 Mouser Electronics www mouser com 1 800 346 6873 JDR Microdevices www jdr com 1 800 538 5000 Abbreviations used below MFG Manufacturer DK DigiKey MO Mouser JDR JDR Microdevices 90 16 1 Small parts for cables etc Some of the most commonly used small parts in SER1CH UA applications are as follows This is only a small listing of the parts and suppliers available Many others are acceptable 2 1mm power plug MFG part number CUI Inc PP3 002A DK part number CP3 1000A MFG part number Kobiconn MO part number 1710 2131 These are discrete wire power plugs suitable for soldering wires to They are useful for connecting batteries and other custom power sources to the SER1CH UA Use these instead of chopping the plug off of your wall transformer Alligator clips MFG part number Mueller BU 30 DK part number 314 1010 ND MFG part number Silvertronic 501793 MO part number 835 501793 The Mueller BU 30 clip has a good spring and strong teeth The connection is wire crimp which should also be soldered for low resistance Making cables with these clips requires skill but they result in inexpensive connections of good quality that are easy to use The Silvertronic part is equi
48. grams The techniques for plotting results with GnuPlot or similar programs all follow the same pattern First run the SERICH UA DVM program to acquire values and save the results to an output disk file For this example we assume data from the solar cell in the previous section has been saved in the file DvmOutputSolar asc The DVM output files are in ASCII format with the data in columns which can be imported into plotting programs The asc output files may also be reviewed in text editors such as Notepad The following is a portion of the DVM asc output data file that might result Data Sample Volts OneToTen Time Sec Time YMD HMS 1 0 7 1 42 1202171952 468 2008 02 05 00 39 12 468 2 0 7 1 43 1202171953 629 2008 02 05 00 39 13 629 3 0 7 1 43 1202171954 791 2008 02 05 00 39 14 791 4 0 7 1 45 1202171955 953 2008 02 05 00 39 15 953 5 0 7 1 49 1202171957 114 2008 02 05 00 39 17 114 6 1 0 2 01 1202171958 276 2008 02 05 00 39 18 276 7 0 9 1 90 1202171959 438 2008 02 05 00 39 19 438 8 1 0 1 99 1202171960 599 2008 02 05 00 39 20 599 9 1 2 2 34 1202171961 761 2008 02 05 00 39 21 761 Figure 14 4 DVM output file fragment from DvmOutputSolar asc To produce an output file with these data columns DVM was run with the ini startup parameters shown in Figure 14 5 Besides the general output format this ini file also specified the second display should be formatted in light level units of 1 to 10 You may wish to calibrate into othe
49. he files CalLib c and DvmLib c are both required to build CAL The files that start with CalGui cpp and CalCmd c are the additional user interface source for the GUI and CMD versions of the programs Both versions depend on the variables and functions defined in the CalLib and DvmLib files Both CalGui exe and CalCmd exe can be built from the command prompt using the pro vided Makefile It accesses various settings and macros contained in the Compiler mak file in the SR SER1CH UA Lib directory and assumes that a batch file like vsvars bat has been run to set the compiler environment The sln and vcproj files can be used to build CalGui exe and CalCmd exe from inside the Visual Studio 2005 IDE Please refer to the comments in the source code files themselves for more details 27 3 2 3 CAL determining the correct serial port For DVM and CAL to run correctly it is important to select the serial port which is actually connected to the SERICH UA The Windows Device Manager can help narrow down the choices by showing which ports are even available The Device Manager can be accessed graphically from the Control Panel or from MyCom puter properties It can also be accessed from a command prompt by typing devmgmt msc and pressing ENTER Once the Device Manager window is showing open or expand the Ports COM amp LPT1 class The available serial ports are listed as Communications Port COMx Some addi tional COM ports may be assigned to ot
50. her devices such as modems but these will not be listed in the Ports class and can not be used with the SERICH UA Now that the possible serial ports have been identified you can run DvmGui to test them out Using the provided alligator clip cables connect VREF from the red outer banana jack to VIN on the red middle banana jack This provides a known voltage of about 4 96v to the A D inputs Select one of the possible serial ports in the DvmGui dropdown list and click the run button If you see the sample number incrementing and the voltage display showing 4 96 volts you have the right serial port If not click the stop button and repeat with the next serial port you want to try 28 Chapter 4 User C Library Besides finished applications like DVM and CAL the SERICH UA comes with a function library for users writing their own programs These functions can be statically linked to C programs or called as a Dynamic Link Library DLL under Windows and a shared library so under Linux The library is written in C but can be called from languages such as Visual Basic and LabView as long as C calling conventions are followed The methods for calling DLL functions are specific to each language and typically require declarations describing the parameters being passed Check your language documentation for details The typical sequence of calls to use the library is simple First call Open to initialize the COM serial port and A D Then cal
51. ica Bold 18 set ylabel Volts font Helvetica Bold 18 set xrange 0 120 About 2 minutes of data set yrange 0 5 Solar panel outputs 3 3v in strong sunlight PLOT THE SOLAR DATA set title SER1CH UA Solar Panel Data font Helvetica Bold 18 plot DataFile index 1 using ColSample ColVolts linestyle 1 title Solar panel voltage Figure 14 6 GnuPlot commands for plotting DvmOutputSolar asc 76 Volts SER1CH UA Solar Panel Data yee Light very close gt Light off Solar panel voltage e Figure 14 7 SER1CH UA solar cell data example plot 77 14 3 Ratiometric potentiometer Three wire ratiometric measurements are an excellent way to minimize errors due to temper ature drift The math behind such techniques is covered in the Ratiometric measurements chapter earlier in this User Manual The demo reviewed here shows the connections for a three wire measurement using a precision 10 turn wire wound potentiometer For a ratiometric measurement the A D reference voltage provided on the red VREF banana jack should be used as the excitation voltage for the potentiometer and the po tentiometer wiper should be connected to the VIN jack The photo below shows the connections For a schematic see the Ratiometric measurements chapter Here a 10K ohm potentiometer has been used This means a total of 5V 10K 0 5 milliamps is flow ing through the potentiometer This is good it is a large eno
52. ith soldered on surface mount resistors on the SERICH UA circuit board Usually customers in specific countries want only one setting or the other Please specify 50Hz rejection at the time of your order if required If not specified the system will be set for 60Hz rejection Customers wishing to change the 60 50Hz setting themselves should refer to the Circuit diagrams and the Linear Tech LTC2400 spec sheet for details Is twisted pair good for analog inputs Yes Even though the SERICH UA sigma delta A D converter has excellent 87 60 50 Hz rejection it is better to avoid power line noise in the first place Twisted pair for the input signals is one of the best ways to do so The long red and black test leads typically used with voltmeters create large open loops which easily pick up power line noise Even simple steps such as loosely twisting red and black test lead pairs together can substantially reduce power line noise pickup Jacketed twisted shielded pair round cable is even better Note that foil shielding does not do much good against 60 50Hz noise What foil shielding does help with is to protect against ESD static discharge damage and RF noise At 60 50Hz it is the twist that does the job Does the SER1CH UA have any digital buffering No the SERICH UA does not have memory for buffering accumulating con verted results After a conversion the one digital result is saved on the A D chip and the PC must read that result If
53. ition The photo below shows a ratiometric connection where the SER1CH UA provides the potentiometer excitation with its VREF jack No other equipment is required This particular potentiometer is a 10 turn device The connections are the same for other types of potentiometers See the Examples and Experiments chapter for a more detailed discussion Figure 1 1 SERICH UA with typical potentiometer setup Many other types of passive and active sensors requiring DC measurements at a 1Hz sampling rate can also be used Strain gauges photocells and pressure sensors are a few examples With an input impedance of 10M ohms the system adds only a very light load to whatever it is connected to The setup shown here is powered from a single 9 volt battery With its low power consumption the system can run for long periods from small power sources Also besides the banana jack version of the SERICH UA other models with Dshell connectors for front and back panel connections and a narrow 1 inch wide model with inline headers for borehole applications are also available Chapter 2 Getting started Installation of the SER1ICH UA is straightforward Here are the steps to follow 2 1 Hardware installation Connect the SERICH UA to the supplied wall transformer with the 2 1mm power connec tor The green power LED on the top panel should light up If not make sure the wall transformer has power Then connect the RS232 DB9 on the SERICH UA back panel
54. iver installation Application programs such as DvmGui exe may be run as soon as the SER1CH UA is connected to a serial port and the SER1CH UA is powered up To uninstall the software simply delete the SR SER1CH UA directory 10 2 3 Do s and Don ts DO use the provided 9 vdc wall transformer or a 9 volt battery to power the system DO use the system with RS232 ports that support RTS DTR and CTS DO read the FAQ chapter for general questions regarding the SERICH UA DO use the SERICH UA to measure positive voltages in the 0 5 volt range on the red VIN banana jack with respect to the black GND banana jack DON T exceed 18 volts on the power supply Excessive power supply voltages will result in high power supply current drain DON T expect to make precision measurements with floating inputs The analog input VIN must be connected to a voltage source to make an accurate measurement VREF and GND are convenient voltages for initial testing DON T short circuit the VREF A D reference output banana jack to the black GND jack The output is current limited so no damage will occur however any current sourced by VREF is ultimately provided by the SER1CH UA power supply DON T use the SERICH UA to measure 110 vac or other high voltages You will damage the system and perhaps even your computer 11 Chapter 3 Application Programs The SERICH UA comes with two finished application programs DVM and CAL With these prog
55. l GetData each time you want a new A D sample followed by ScaleData if you want to convert the A D counts to volts or other units Finally when finished call Close to free the COM port for other programs Be sure to include the header file Serlch h in any C source code using the library This file contains prototypes and defined constants that can help make your program more maintainable and readable When using dynamic linking make sure the Serlch dll library is on your Windows execution path so it can be found at runtime Under Linux the shared library libser1ch so should be on the LD_LIBRARY path The table on the following page summarizes the SER1CH UA library functions and their parameters Each function is also described in more detail in the following sections along with a code fragment to show typical calls from C 29 SER1CH UA Library Function Summary Function Parm IO Type bits Description SerlchOpen Open the serial port and initialize A D return O DEVHANDLE 32 BAD _DEVHANDLE on failure SerialPortNumber I integer 32 Serial port number 1 COM1 2 COM2 Error O pointer to integer 32 Detailed error code SerlchGetData Read a data point and the PC time return O integer 32 1 for success 0 for failure SerlchHandle I DEVHANDLE 32 Handle to SERICH UA serial port DataCounts O pointer to integer 32 Data poi
56. l by emailing SR at info symres com Use the Adobe Acrobat reader View Rotate View Clockwise command to present the diagrams horizontally on the screen EIKON OE RE EE 66 Digital RS232 EE 67 Analog A D Input Buffer 68 Analog A D User Banana scooter tota 69 65 2002 Uoseasay JUJIWWAS 9 NSC VN HO LUIS J QUNN lu uinooq MIIAHINO LO SSION MOT YO NOIIVINIAII YVANIT SYOLIANNOI UNMOd WUT UHMOd AYILIVE YO VANUOASNVEL TIVM TT 6 SHOVd DIIVNYIHOS ATddNS YAMOA 002 00T SNOIIIANNOI MOVL YNVNVE AONAUGAGY YASN AJAAAANA AG UND SLO UYLd SLY SHASINOHA THNNVHO INANI DOTUNY LIE 77 ANO VYALYHANOI G V 118 7 OOPZOLT FOVAYIINI TEZSY 8 BOVd OILVWEHOS L S SHOVd OLLVWWEHOS 9 7 SAOVd OILVWEHOS SYOLOANNOD SOTYNY UALYFANOD G V UOLOANNOD 694 ZEzTSU MIIAYIAO WWHOWId MOOTH VO HITHIS US 66 1002 u91e s ti JUJIWWAS 9 NSA YN HOLHIS 4 QUNN juaun9og YOLOANNODO 22254 IVLISIO ZO LOSNNOO ON SYAHILO TTY CASO HIV UND SLO WIqQ SIA X INO 31734 680 q13lHs lt rs4 UNO aNd ceesu 70028258 mm INId T XEFCEZS ZNid INIA y XLzezsu ENId ZNid z SLO ZEZSU HS YNId ZNId Z UNO 26258 SNId ENId E DESS SNId 8Nid g I SIE ZNId Gast ETH HLa 2ezs8 lt lt Slo eeesu 8NId Gast SICH guu zezsu lt DR22232 6NId SNid qi3
57. liamps will be flowing in the diode Of course the current is only approximately constant because as the forward diode voltage changes with temperature the voltage across the 10K resistor changes also Nevertheless for many applications this is may be ok With the addition of an op amp a better constant current source can be implemented as in Figure 14 13 For this circuit the SERICH UA VREF is divided down to 1 volt for the 82 noninverting op amp input By negative feedback the inverting terminal is also forced to be at 1 volt and this 1 volt puts a constant current down the 10K resistor connected to the inverting terminal Since no current flows into the inverting terminal of the op amp the same constant current flows though the diode The output of the amp will be at 1 volt plus the forward diode drop For this circuit an LM358 or LM324 is a good generic op amp to use These devices can even be powered in single supply fashion by VREF itself Consuming only about 1 milliamp of power their power requirements will not overload the VREF output No split op amp supply is required VREF 5 0 10K 1 0 volt VIN VOHIITYAS 1N4148 10K KZ GND Figure 14 13 Temp diode with constant current op amp source Many silicon diodes are suitable for use as temperature sensors The 1N4148 or 1N914 are among the least expensive costing as little as 0 05 even in small quantities The pn junctions of bipolar transistor
58. ly have to connect the three terminals to the SERICH UA and calibrate appropriately The above pot has a linear travel length of 120 mm 4 7 inches Sensors general DK part number Many see their sensors listings MO part number Many see their sensors listings Both DK and MO have extensive selections of sensors that are suitable for use with the SER1CH UA Pressure vibration and light sensors are just a few in their listings They can often provide an easy solution to sensor selection PDF copies of the DK and MO catalogs are available for free download from their web sites For many simple measurements like position or temperature often very simple parts like potentiometers and diodes can do a perfectly good job See the appropriate part listings here and chapters in the User Manual 94 Sensors temp diodes MFG part number Fairchild 1N4148 DK part number 1N4148FS ND MFG part number Fairchild 1N4148 MO part number 512 1N4148 Virtually any silicon pn junction may be used as a temperature diode Even the most inex pensive small signal silicon diode does a reasonable job The generic 1N4148 or 1N914 are probably the least expensive although if you have something else in your spare parts box it will probably do as well More expensive solid state temp sensors are available at many of the semiconductor companies like National Semiconductor and TI Op Amps MFG part number TI LM324N DK part number 296 1391 5 ND
59. mOutput asc OutputFileComment Arbitrary text to help identify the saved data Descriptive comment in quotes like Test 4 OutputFileShowHeader Switch controlling whether ON OFF output file includes headers OutputFileShowIndex Switch controlling whether ON OFF output file includes sample num OutputFileShowTimeSec output time as seconds since ON OFF 1970 OutputFileShowTimeYmd Output time as YMDHMS ON OFF RunMode Sampling mode SINGLE CONTINUOUS Keywords specific to display readout N 0 1 DisplayTitle N Title String like Voltage DisplayUnits N Units String like Volts DisplayPlaces N Total number of digits Integer like 9 DisplayDigits N Digits after decimal point Integer like 5 DisplaySlope N Calibration slope Float like 7 27444e 007 DisplayOffset N Calibration offset Float like 0 0000953873 Figure 3 3 DVM ini keyword table 18 3 1 4 DVM calibrating the readouts Now you should see the data acquired from the single SER1CH UA channel being displayed twice on the dialog box These two displays represent the same data scaled into different units For example the first display could show volts while the second display could show user units such as inches or degrees or ounces or etc depending on the specific type of sensor being used Both displays are generated from the raw data which comes in as A D counts by applying a simpl
60. n device C usage include Serich h DEVHANDLE SerichOpen int SerialPortNumber int Error The Open function opens and initializes the specified COM serial port and SERICH UA A D It should be the first library function called The first argument passed to Open is an integer from 1 to 9 that specifies the serial port to use A value of 1 corresponds to COMI under Windows or dev ttyS0 under Linux 2 selects COM2 etc You may want to check the Device Manager under Windows to see which COM ports are available on your machine as described in section on page The second argument is a pointer to an integer that will be filled with an error code giving some detail about the failure if one occurs An error code of 0 means the open succeeded This argument is optional and will be ignored and not filled in if you pass Error NULL See Serlch h for a list of the possible error codes Or use the ErrorMsg function to get the message string associated with the integer error number Open returns a file handle to the open serial port in the form of a specially defined data type called a DEVHANDLE Under Windows this is a void and is equivalent to the Windows HANDLE type Under Linux it is an integer In both cases the size is 32 bits and this file handle provides a shorthand way for the OS to access the selected serial port If Open fails the return value is BAD_DEVHANDLE which is defined as 1 Note that under Linux Open will fail if
61. n independent power supply and commonly have a output range of 5 5 or 10 10 volts When working with these types of sensors it is desirable to scale and bias their full range into the SERICH UA 0 5 so none of the 24 bit A D span is lost A few of the more popular circuits for mapping active sensor ranges are reviewed in this chapter In many cases precision low noise mapping can be done with a few resistors while for applications requiring gain an op amp may be required For additional information you may also find the following useful e the Examples and Experiments chapter for a hands on 10 10 demo e the SR paper Scaling and Biasing Analog Signals for theory SR papers and app notes can be found on the web at www symres com The following sections give a quick review of the techniques 51 9 1 Resistive scaling and biasing Active sensors usually have output ranges reflecting the op amps and power supplies they use The most common ranges are 5 5 and 10 10 volts and this section reviews resistive circuits for mapping these ranges into the SERICH UA 0 5 volts Besides being simple these circuits introduce very little noise to the signal Furthermore active sensor outputs can usually drive the moderate input impedance of these circuits to full accuracy while the SERICH UA 10M ohm input presents no load to them either The circuit for mapping 5 5 volts into 0 5 is Vsensor 5 5 7 SERICH UA VIN 0
62. neric parts remove amplifier input offset errors in software The next circuit adds gain to the input signal After amplifying by 10 the signal is scaled and biased into the SERICH UA 0 5 range with the 10K resistor pair When building a design like this it is ideal to place the gain amplifier out near the sensor Low voltage signals like the 500mV input are much more sensitive to noise pickup than high voltage levels Any long cable could then be placed between the output of the gain amplifier and the 10K divider pair Check to make sure the cable capacitance has not caused instability and amplifier oscillations Vsensor gt 10K 500mV SERICH UA VIN 0 5 Gain 10 IK VREF 5 0 Figure 9 5 Op amp buffer with gain of 10 With the small input range of this circuit it is easy for a signal more negative than 500mV to get hooked up to the input by accident As before a small diode may be added to protect against negative voltages at the SER1CH UA VIN input For a single ended circuit such as this do not allow ground currents from other devices to flow on the ground wire of the cable connecting the op amp to the SERICH UA GND jack Excessive common mode currents such as those from motors will bounce the ground connection and be apparent in the SER1CH UA measurements 99 Chapter 10 Single ended grounding practices The SER1CH UA has a single ended input Excessive currents flowing on the black GND
63. nt as raw A D counts TimeSecSince1970 O pointer to double 64 PC time of data point as seconds since 1970 Error O pointer to integer 32 Detailed error code SerlchScaleData Scale data point counts to other units return O integer 32 1 for success 0 for failure DataCounts I pointer to integer 32 Data point as raw A D counts Slope I floating point double 64 Slope of scaling formula Offset I floating point double 64 Offset of scaling formula ScaledData O pointer to double 64 Data point scaled to other units Error O pointer to integer 32 Detailed error code SerlchErrorMsg Get string associated with error code return O pointer to char 8 Null terminated C style string Error I integer 32 Detailed error code SerlchClose Close the serial port and A D return O integer 32 1 for success 0 for failure SerlchHandle I DEVHANDLE 32 Handle to SERICH UA serial port Error O pointer to integer 32 Detailed error code Figure 4 1 Serlch library function table In addition to standard data types like integer and pointers to integers the table also lists DEVHANDLE This special data type is defined in SrHelper h and varies depending on OS Under Windows it is a void and is equivalent to the Windows HANDLE type Under Linux it is an integer In both cases the size is 32 bits and the parameter refers to an open file handle which gives the OS a shorthand way to refer to the device 30 4 1 Ope
64. nternal oversampling rate used in the LTC2400 It is nominally 7Hz where this frequency is not crystal controlled and is set only by internal RC components inside the chip Furthermore the LTC2400 has a relatively low oversampling rate resulting in poorer res olution than other 24 bit A D converters which have higher oversampling However in return you get much lower power consumption Compare the power usage and resolution with an A D such as the LTC2440 series or ADS1255 5 2 50 60Hz power line rejection Because of their internal oversampling and digital filtering sigma delta converters such as the LTC2400 used in the SER1CH UA are capable of excellent power line noise rejection The internal sampling rate of the SERICH UA LTC2400 is automatically set to place the first notch of the sigma delta digital filter at 60Hz International users may change the oversampling rate to place the first notch at 50Hz Review that the power line noise rejection is typically greater than 120 dB 38 Chapter 6 Analog DC calibration The physical quantity measured by the SERICH UA is voltage with its A D converter returning a count proportional to the input voltage When the input voltage is low a low count value is returned and as the input voltage increases the count value increases The exact relationship between a particular input voltage and the A D counts is referred to as the DC calibration It is well approximated by a straight line wi
65. r light level units as appropriate Once the DvmOutputSolar asc file has been acquired start GnuPlot and issue the com mands in Figure 14 6 at its prompt 74 General ini parameters OutputFileName Dvm0utputSolar asc DutputFileComment Measuring solar panel response OutputFileShowHeader ON OutputFileShowIndex ON OutputFileShowTimeSec ON OutputFileShowTimeYmd ON RunMode CONTINUOUS Display 1 format and calibration parameters DisplayTitle 1 Light Level DisplayUnits 1 OneToTen DisplayPlaces 1 6 DisplayDigits 1 2 DisplaySlope 1 6 02121e 007 DisplayOffset 1 0 00147941 Figure 14 5 DVM startup file fragment from DvmSetupSolar ini You can also save the commands in Figure 14 6 to a file and then run them in GnuPlot with the load command The file Solar gp in the examples software directory has the complete set of commands required to produce the following graph The core GnuPlot command is plot With that single command you can display simple plots Additional commands should be used for features like graph titles Refer to the GnuPlot documentation for more information 75 SET FILE FORMAT PARAMETERS DataFile DvmOutputSolar asc ColSample 1 ColVolts 2 ColLight 3 ColSeconds 4 ColTime 5 SET AXIS DATA LIKE TIC MARK STYLE FORMAT LABEL AND RANGE set xtics nomirror font Helvetica Bold 14 set ytics nomirror font Helvetica Bold 14 set xlabel Sample font Helvet
66. rams you can acquire data display it on the screen save it to disk and calibrate the system Even for those planning to write their own custom software running these programs will help you quickly understand how the system works The DVM program displays its data on the screen in familiar digital voltmeter style with large green readouts that are easy to see Even though the SERICH UA has only one channel there are two readouts of the same data that can each be calibrated into different display units So for example one readout could display sensor volts while the other displays physical sensor units There is also a command line only version of DVM if you don t want the GUI display The CAL program is useful for gathering calibration coefficients for the DVM program Not only can it provide absolute calibration for the system it can also easily calibrate into physical units for the DVM readouts These programs can be found in subdirectories of SR SERICH UA If you wish to run with predefined configurations there are shortcuts that can be double clicked to run immediately Further information about configuring and running these programs is given in the following sections gt DVM enhanced dual readout digital voltmeter gt CAL DVM calibration into volts and user units 12 3 1 DVM DVM is a program with a display and function much like a digital voltmeter If instruments such as Fluke meters are familiar then you will find DVM eas
67. rial port which is actually connected to the SERICH UA The Windows Device Manager can help narrow down the choices by showing which ports are even available The Device Manager can be accessed graphically from the Control Panel or from MyCom puter properties It can also be accessed from a command prompt by typing devmgmt msc and pressing ENTER Once the Device Manager window is showing open or expand the Ports COM amp LPT1 class The available serial ports are listed as Communications Port COMx Some addi tional COM ports may be assigned to other devices such as modems but these will not be listed in the Ports class and can not be used with the SERICH UA After identifying the possible port selections in Device Manager you can run DvmGui exe to test them out Use an alligator clip to connect the SERICH UA VREF from the red outer banana jack to the red VIN banana jack in the middle This provides a known voltage of about 4 96v to the SERICH UA A D input Then select one of the possible serial ports in the DvmGui exe dropdown list and click the run button If you see the voltage display showing 4 96 volts and the acquired sample number incrementing then you have the right serial port If not click the stop button and repeat with the next serial port in the DVM list you want to try 16 3 1 3 DVM ini syntax The layout of a DVM ini file is free format ASCII with a simple syntax of the form keyword value Comments are denoted with
68. s such as the 3904 or 3906 can also be used See the Extra supplies chapter for a few vendors More sophisticated solid state sensors optimized for temperature measurement are also available Visit the web sites of National Semiconductor TI and many other semiconductor companies Calibrate DVM into C or F for a nice display on the computer screen of the temperature measured in this way 83 Chapter 15 Frequently Asked Questions The following FAQ may help if you have general questions about the SER1CH UA 15 1 Software Do you include source code Yes The source code for all the supplied software is included with the system at no extra cost The software is also available for free download from our web site www symres com Please review before purchase to make sure the SER1CH UA is a match for your applications Current customers should also download from the website to get any version updates What format are the DVM acquisition files in ASCII text with the data listed in columns The files can be read into text editors as well as imported into programs such as spreadsheets Two ASCII formats are possible verbose and bare Verbose has a header with information about the DVM acquisition parameters in addition to the data Bare format has just the data Besides the converted A D data the PC time stamp at which A D data is acquired is optionally provided as a column Can I use the SERICH UA with Xcel spreadsheets
69. t impedance of the SER1CH UA is 10M ohms Waving your hand over the input banana jacks when nothing is connected will induce a measurable charge and voltage change by capacitive coupling DVM reflects this change Connect the analog input VIN to the VREF or GND jacks and you will no tice that the effect disappears This behavior is typical of all precision high input impedance voltmeters Floating inputs tend to wander as as various charged entities are brought near their inputs Connect the input to specific low impedance voltages to make accurate measurements Can I connect a 10 ohm resistor to the VREF output No Connecting a 10 ohm resistor across the 5 volt VREF and GND would theoretically result in a current of 5 10 0 5 amp flowing Obviously this is more current than a device like the SERICH UA is designed to supply No damage will occur by connecting a 10 ohm resistor or even shorting VREF directly to ground The output is current limited and will supply an absolute maximum current of about 40ma On our spec sheet lists a max of 10ma to stay within compliance When overloaded the output will simply drop and fall out of regulation If you need more than a few milliamps of reference current then use VREF to drive an offboard buffer 86 Why is the system consuming more than 10ma You probably have the green power LED enabled which consumes considerably more than the SERICH UA base power consumption The green LED jumper must b
70. t number Yageo many values DK part number Value XBK ND MFG part number Xicon many values MO part number 271 VALUE RC Metal film resistors give good performance for scaling and biasing applications They cost very little more than carbon film parts but have better TC and noise characteristics The parts above are standard 1 4 watt types with wire leads For most applications precision greater than 1 metal film costs considerably more and may not deliver substantially improved performance Hand matching 1 metal films is a reasonable way to obtain tightly matched pairs Hand matched carbon films will not deliver the same performance 93 Potentiometers 10 turn 10K ohm MFG part number Vishay Sfernice 53411103 MO part number 594 53411103 MFG part number Bourns 3540 series DK part number 35405 1 103 ND A 10 turn pot is a simple and reasonably accurate sensor to use when testing the SER1CH UA Connect the three potentiometer connections to the three banana jacks with the wiper going to the red VIN jack and you can make accurate angular measurements There are many manufacturers of 10 turn pots A 10K ohm unit will not draw excessive current from the VREF output Potentiometers linear slider 10K ohm MFG part number Alps RSAON1159002 MO part number 688 RSAON1159002 Linear slider pots do not have the accuracy of a 10 turn pot but they are ideal for making linear position measurements As with rotary pots you on
71. ter to the three terminals of the SERICH UA and you are ready Calibrate the linear potentiometer into physical length units with the CAL program For linear measurements over greater distances there are also string potentiometers Figure 14 10 Linear slider potentiometer For other types of passive ratiometric applications there are also sensors such as strain gauges tilt meters and pressure transducers that all connect naturally to a three wire interface 79 14 4 Scaling and biasing 10 volt signals into 0 5 The SERICH UA has a full scale input range of 0 5 volts as measured with respect to its red VIN and black GND banana jacks However for many applications you may require a different full scale range In particular 10 10 is popular for many active sensors Scaling and biasing a 10 10 signal into the 0 5 range is fairly easy with a few resistors This demo shows how to preform the mapping with four 10K ohm resistors More details about scaling and biasing can be found in e the Scaling active sensor voltages chapter of this User Manual for other voltage ranges e for additional theory the SR application note Scaling and Biasing Analog Signals The demo circuit for 10 10 mapping is as in Figure 14 11 10K VREF 5 volts 10K Active Sensor 10K VIN 0 5 VO HIVES 10 10 10K Figure 14 11 Scaling and biasing 10 10 with four 10K resistors This circuit is the same
72. teries After disabling the green power LED it is also easy to forget that resistive loads connected between the VREF banana jack and GND will consume additional power For example if a 1K ohm potentiometer is connected between VREF and GND that alone will consume 5 milliamps And that 5 milliamps will have to be supplied by the SER1CH UA power supply A 10K potentiometer would a give a better tradeoff between avoiding noise and minimizing power consumption The third item handling the RS232 serial port correctly is a concern only if you are writing your own custom software The problem is with RS232 inputs on the PC end of the DB9 cable and the impedance they present typically 5K ohms If such an input is driven at 5 volts by the SERICH UA then this will consume 1 milliamp which ultimately must provided by the power supply The way to battle against the third item is to note the SERICH UA has only one input to the PC RS232 port the CTS signal Don t idle this signal high or you will sink unnec essary current on the order of 1 to 2 milliamps An easy way to avoid touble is to assert the LTC2400 chip select signal RS232 RTS only when needed When this signal is de asserted then the CTS input will automatically idle low and not burn unnecessary power Application programs like DVM supplied with the SER1CH UA do this automatically The last item using a power supply greater than 18 volts is a serious error Circuity on the SER1CH UA wo
73. th a slope and offset Performing a calibration requires measuring the slope and offset so application software can convert counts into volts As shipped the SER1CH UA software is only approximately calibrated Programs such as DVM have a typical slope and offset in their ini files These values are reasonably good but for highest accuracy each SERICH UA must be calibrated on site by the user The following sections cover the calculations involved with DC calibration For an easy to use calibration program see the DVM CAL program To perform an absolute calibration requires either a precision voltage reference or a pre cision voltmeter Reference standards such as the Symmetric Research VREF 399 are suitable calibration tools You can also use less stable voltage sources if you have an independent precision voltmeter such as an HP34401 to monitor the source with 39 6 1 Full Scale Voltage Span and Counts The SERICH UA has a 24 bit A D converter with 274 counts spread out evenly over the entire 0 to 5 volt input span of the system TOTAL 24 BIT A D COUNTS 2 24 16 777 216 decimal Counts are returned by the GetData library function as 32 bit integers For 0 input volts zero counts will be returned and as the VIN input voltage increases the count value will also increase Counting upward from 0 volts to the maximum 5 there are 224 counts The SER1CH UA is a single ended positive voltage system always returning postive counts
74. the SER1CH UA for calibration measurements to be taken The required information includes the display title eg voltage and name of the units to be used eg volts the value of one known input signal and the value of a different known input signal Because DVM displays the acquired data in two ways for example in volts and in inches appropriate calibration information is needed for both displays Once CalCmd exe starts it displays a prompt showing the serial port it will use If this is not correct please quit edit the ini file and try again Also see the section Selecting the serial port for a discussion about how to choose a valid serial port Once the serial port selection is correct and you are ready to continue CalCmd prompts you to enter the required calibration information starting with the display titles and units Then apply a known input signal to the SER1CH UA enter its value and press a key to measure it Repeat this for a second known input signal CalCmd then computes the calibration results and outputs them to the DvmSetupCal ini file Once CalGui exe starts it displays a dialog box showing the default serial port specified in the ini file If this is not correct use the serial port dropdown list box to select the serial port that is connected to the SERICH UA CalGui provides you with text boxes for entering the required calibration information like the display titles and units To perform the actual calibration apply
75. tion 58 Specificationstable 62 SERICH UA MOS HOOP os aos sak ee EN e Ra 63 SERICH UA thermal response coreo e Re eee 64 Two lead voltage measurement of a battery 71 14 2 14 3 14 4 14 5 14 6 14 7 14 8 14 9 14 10 14 11 14 12 14 13 Pomona test leads for voltage measurements 72 Using a solar cell as a light level meter 73 DVM output file fragment from DvmOutputSolar asc 74 DVM startup file fragment from DvmSetupSolar ini 75 GnuPlot commands for plotting DvmOutputSolar asc 76 SERICH UA solar cell data example plot 77 10 turn potentiometer SERICH UA connections 78 10 turn potentiometer reverse side connections 79 Linear slider potentiometer 2 6 64 By is eae be ee 79 Scaling and biasing 10 10 with four 10K resistors 80 Temp diode with simple resistive current source 82 Temp diode with constant current op amp source 2 83 Chapter 1 Introduction The Symmetric Research SER1CH UA is a precision analog to digital converter for DC applications requiring 24 bit A D conversions at a 1Hz sampling rate In addition to its high resolution the system also has very low power consumption With an active power requirement of only 600 microamperes at 9 volts it can be easily pow
76. ugh current to avoid noise problems but still small enough to avoid putting a high load on the VREF output Figure 14 8 10 turn potentiometer SER1CH UA connections The connections on the bottom side of the potentiometer are simple wires to the three potentiometer terminals as in Figure 14 9 For an application of this type you may want the second DVM readout display to be calibrarted in Turns See the ini startup file in Examples DvmPotentiometer ini for an example Generating suitable custom calibration parameters is easy with the CAL program Running CAL first turn the potentiometer all the way to its lowest setting and take a measurement Then do the same at the maximum number of turns and save the CAL results to an ini startup file 78 Figure 14 9 10 turn potentiometer reverse side connections How well do ratiometric methods work to reduce the problems of temperature drift With the above setup the relative wiper voltage from the potentiometer as read by the SER1CH UA did not vary by more than 30 microvolts in our experiments For quantitative results see the plots in the Ratiometric measurements chapter Potentiometers are useful for measuring angular position However they are only one class of sensors suitable for ratiometric use For linear measurements there are linear slider potentiometers Using a linear potentiometer is the same as a 10 turn rotational device Connect the three terminals of the linear potentiome
77. uld be damaged by power greater than 18 volts and is protected by a TVS device When the external power supply exceeds 18 volts the TVS turns on and clamps the voltage to safe levels Normally the TVS is there to protect against power supply spikes However if the power supply voltage is simply too high the TVS will equally well turn on and present a heavy load to your external supply Check your power supply equipment beforehand and don t exceed 18 volts 59 11 3 Batteries Once you have minimized the power consumption of the system you may be interested in powering the SER1CH UA from batteries 9 volt batteries are attractive temporary power supply for this system running over 100 hours For longer term power lead acid 12 volt batteries are useful Work underway 60 Chapter 12 Specifications The table on the following page lists the leading SER1CH UA operating specifications Many of the values are discussed in more detail in their respective chapters The table here lists the primary analog components used on the board Copies of the manufacturer specification sheets are also included in the directory Docs ChipSpecs A D converter LTC2400 Linear Technology A D voltage reference LM4040A National Semiconductor Front end op amp TLC27L2 Texas Instruments 61 12 1 Specifications table SER1CH UA Specs Parameter
78. using the alligator leads supplied with the system you can also use standard red black banana plug test leads In Figure 14 2 a pair of Pomona test leads are shown connected to the SERICH UA banana jacks If you need a pair of heavy gauge test leads they may be ordered as an accessory for the basic system Figure 14 2 Pomona test leads for voltage measurements When making two wire voltage measurements as in Figures 14 1 and be aware the black GND banana jack is ultimately connected to the power ground and enclosure of the PC via the DB9 RS232 serial port connector The analog inputs are not floating as they are with a hand held voltmeter Also be aware current flowing in the ground system can cause noise in your measurements Use a star layout for ground and ideally keep your sensor at one end of the star without system ground currents passing though its circuit Another difference with typical hand held voltmeters is the voltage between the VIN and GND jacks should be in the range of 0 5 volts The system will tolerate moderate voltages outside of this range but do not attempt to measure 110 vac from the wall socket with this device Doing so will void the warranty If you need to measure voltages outside the 0 5 72 range please use the techniques in the Scaling active sensor voltages chapter in this User Manual or the 10 10 section further on in these examples Simply being able to measure and record voltages provides many
79. valent to the Mueller Johnson banana plugs MFG part number Johnson Emerson 108 753 001 DK part number J149 ND MO part number 530 108 0753 1 These uninsulated banana plugs have a 6 32 screw in the end When plugged into the red and black jacks on the SER1CH UA they provide screw terminal connections 91 Solder terminal lugs for Johnson banana plugs MFG part number Keystone 7329 DK part number 7329K ND MO part number 534 7329 The Keystone solder lugs are useful for making screw terminal connections to the Johnson banana plugs It is also easy to clip alligators onto these lugs when they have no wire soldered on The lugs listed above are flat Lugs with internal tooth lock washer holes are also available for even more secure connections Pomona test leads MFG part number Pomona 5519A DK part number 501 1004 ND MO part number 565 5519A To use these test leads with the SER1CH UA you must trim or cut away the banana plug insulating sheath Do this with a utility knife or razor blade carefully cutting away the plastic sheath DB9 molded serial port cables MFG part number generic JDR part number CBL DB09 MF Finished molded 6 cable Commonly referred to as a DB9 MF male female extension cable All pins are connected straight through Null modem cables will not work DB9 solder cup Dshell connectors MFG part number generic JDR part number DBO9P male JDR part number DB09S female For
80. y to use There are two versions of DVM a GUI version with graphical display and a command line console mode version The GUI version is available only for Windows while the command line version is available for both Windows and Linux When up and running the GUI version will look like 2g SER1CH UA Digital Volt Meter This program acquires data from a SER1CH UA To run first select the serial port you are using then click the run button to acquire a new sample every second until the stop button is pressed Click exit to end the program Serial Port Run Mode C Single Ini file DymSetup ini Out file DymOutput asc COMI D e Continuous Sample 70 Voltage Degrees Figure 3 1 Screen shot of GUI version of DVM program A feature of DVM is although the SERICH UA only has one acquisition channel DVM has two separate readouts The same data can be displayed twice but scaled into different units This can be useful for example if you would like to monitor the voltage from a sensor and display physical sensor measurement units at the same time In the display above the first readout shows sensor units as volts while the second display shows the physical 13 sensor reading in this case an angle is shown as might occur with a potentiometer Both displays are generated from the raw A D counts by applying a simple linear scale and offset transformation A few DVM options can be specified on the GUI screen For
81. you wish to ignore this parameter When used the PC clock time as seconds since 1970 of when the A D conversion occurred will be returned This value can be converted into the more common year month day hour minute second format with the SrSecTimeSplit function from SrHelper c or with the standard C runtime function gmtime 32 4 3 Scale data C usage include Serich h int SerichScaleData long DataCounts double Slope double Offset double DataScaled int Error Once you have read a data sample in with GetData you can use the function ScaleData to convert its raw A D counts to other units such as volts or inches ScaleData returns 1 for success and 0 for failure It also takes an optional Error argument for returning more detailed information when a failure occurs See Serlch h for a list of the possible error codes or use the ErrorMsg function to get the message string associated with the error number The first argument to ScaleData DataCounts is a 32 bit integer containing the A D counts returned by GetData The 24 bit A D count is stored as a 32 bit integer with the top 8 bits always 0 The second and third arguments Slope and Offset are 8 byte floating point doubles that are used to linearly convert from raw A D counts to some other units such as volts The scaled result is returned in the 8 byte floating point double parameter pointed to by DataScaled Converting from A D counts to converted scaled data is done

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