DBK16 - Measurement Computing
Contents
1. 0 90 4 5V For DBK16 only Externally apply the shunt resistor and set the voltage to VD as derived above for each transducer This is done by adjusting the trimpots labeled GAIN and SCALE for the associated channel The GAIN trimpot is used for course adjustment and the SCALE trimpot for fine tuning For DBK43A only DBK43 is equipped with a physical switch that allows the shunt to be applied when directed by the software For each DBK43A to be adjusted move this physical switch from NORM to CAL 2 In LogView open the LogBook Hardware Configuration window and select the DBK43A LogBook Hardware Configuration Button and Screen 3 Select the DBK43A from the LogBook Hardware Configuration window s hardware tree 4 Set the list box to the right to CAL If the DBK43A is not displayed click the to the left of the base channel to which it is attached to expand the hardware tree Setting a DBK43A Cal Norm Switch to CAL 5 Repeat this process for each DBK43A that is to be adjusted 6 Click OK to lock in the changes 7 Open the Analog Input Channel Grid In the Param1 column see page 19 for location select all of the DBK43A channels that are to be adjusted Select Mode Shunt from the drop down list above the grid Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 8 Click the Download button to send the current configuration to the LogBook 9 Select Indictor2. All the DBK16 channels should say bridge Changing the type will allow us to set the offset and gains in the DBK16 When setting up the DBK16 gains enable only the channel you are setting up Turn all the others off in DaqView Also set DC coupling and disable the on board filter during the gain and offset settings First we want to remove all the offset adjustment from the circuit Set the type to Offset Gain Enable the input reading column from the Acquire menu or the tool bar While reading the spreadsheet set the trimpot labeled OFFSET to read a value of 0 00 Disable the input reading column Next set the type to Input Gain This allows us to set the input amplifier gain The DBK16 has a 5 mV signal on the input so the reading that we want to set the trimpot labeled GAIN to is 005 Input Gain Enable the input reading column and set the Input Gain Disable the input reading column Typical Input Gain settings Gain DaqView Reading Gain DaqView Reading 100 0 5 volts 200 1 0 volts 300 1 5 volts 400 2 0 volts 500 2 5 volts 600 3 0 volts 700 3 5 volts 750 3 75 volts 800 4 0 volts 900 4 5 volts 1000 5 0 volts 1200 6 volts requires DaqBook DaqBoard to be in unipolar mode Next set the type to Scaling Gain This allows us to set the scaling amplifier gain When setting the scaling gain the input gain is also present and must be considered when making the adjustment The scaling gain reading you w
3. Lower Channel Source Bridge BCR 2 Excitation Sensing Source Bridge Sensing Excitation Excitation Regulator 2 2 MUX MUX G1 G0 Gain Adjust P1 Address Lines Jumper Jumper Low Pass Filter Offset Adjust Scaling Amplifier Unity Gain Buffer Input Gain Amplifier Note 1 a f LPF V0Adj VRef These indicated lines connect to Source and Source lines of the Lower Channel Circuit BCR stands for Bridge Completion Resistors Gain Adjust 1 2 DC Coupling AC Bypass Filter 5 mV Address Recog S1 DBK16 Block Diagram A wide range excitation regulator is adjustable from 1 5 to 10 5 VDC with a current limit of 50 mA The DBK16 requires a 12 to 15 VDC external excitation voltage that can be supplied from the DBK30A battery module or other user supplied source Hardware Setup CAUTION Each regulator has a maximum current of 50 mA The maximum amount of excitation that can be provided by the DBK16 excitation regulator is represented by the following equation VEXC MAX 0 05 RGAGE Where RGAGE the resistance of 1 element in the bridge circuit Exceeding the maximum allowed excitation can cause the DBK16 to fail Card Connection For DBK16s the strain gage is configured as a 4 element bridge There are 4 legs in a bridge circuit the quarter half or full designation refers to how many e
4. 1 Apply the second load to each gage channel The value of this load should approximate that of the maximum expected load For the best results a gain should be selected so that the bridge s maximum output equals 90 of the A D s input range 2 Calculate the desired voltage for the second point using the following equation VD LA LM VI 90 Where VD Desired voltage for 2nd point of calibration LA Applied load used in calibrating the 2nd point LM Maximum load expected during usage VI Input voltage range Example The load standard that will be applied to the gage as the 2nd point in the 2 Point calibration is 100lbs The maximum expected load during usage is 150lbs The programmable input range of the data acquisition system is set for 5V The desired output voltage of the strain gage signal conditioning electronics is VD 100 150 5 0 90 3V In this example we should adjust the GAIN and SCALE trimpots until a value of 3V is measured If 150lbs is applied to the gage a voltage of 4 5V will be measured VD 150 150 5 0 90 4 5V 3 Apply the second calibrated load to each gage and set the voltage to VD as derived in step 2 Do this for each transducer by adjusting the trimpots labeled GAIN and SCALE for the associated channel Note that the GAIN trimpot provides most of the amplification course adjustment while the SCALE trimpot allows for fine tuning Repeating the Process Since ad
5. board adjustment for external source Gain Range 100 1250 Types of Bridges Accommodated Full Bridge Kelvin Excitation 6 wire Full Bridge 4 wire Half Bridge 3 wire Quarter Bridge 2 wire Bridge Resistors On board provisions for 4 bridge completion resistors per channel Type Input Differential DC Input Impedance 100 M in parallel with 150 pF CMRR 115 dB Excitation Voltage Source External 13 18 VDC 50 mA circuit Excitation Current Output 50 mA max current limited at 60 mA Excitation Sensing Local or Remote Excitation Regulation Line Regulation 0 025 Load Regulation 0 05 Reference Voltages 2 500 VDC Reference Accuracy 0 05 Reference Drift 3 ppm C Gain Calibration Reference 5 00 mVDC Reference Accuracy 0 2 Reference Drift 20 ppm C Committed instrumentation amplifier for each section with a gain adjust from 100 to 1250 via externally accessed 15 turn trimpot Gain Accuracy 0 5 Gain Drift 50 ppm C Input Offset 100 V max Offset Drift 4 V C Output Offset 20 V Offset Drift 200 V C Offset Adjustment 0 100 of range 0 5 00 VDC 15 Turn trimpot Full Scale Sensitivity Range 5 00 VDC Excitation 0 8 to 10 mV V 10 00 VDC Excitation 0 4 to 5 mV V Scaling Amplifier Gain Range 1 to 10 15 Turn trimpot Low Pass Filter 3 pole Butterworth User By Passable 9dB User set Corner Frequency DBK16 pg 32 8798
6. filter gain GF is 2 otherwise GF 1 Example 1 If GI 250 and the filter is disabled the GAIN trimpot would be adjusted to obtain 1 25V Example 2 If GI 250 and the filter is enable the GAIN trimpot would be adjusted to obtain 2 50V 7 Select Indictors Disable Input Reading Column from the menu bar Adjust the Scaling Amplifier Gain Adjust the Scaling Amplifier Gain as follows 1 In the Param1 column see page 19 for location select all of the DBK43A channels that are to be adjusted 2 Select Mode SetScalingGain from the drop down list above the grid This selection commands the calibration multiplexer to route a 5mV reference through all of the amplification stages as shown below Mode ScalingGain 5 milli Volt Reference Route DBK16 pg 24 879895 DBK Option Cards and Modules 3 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 4 Click the Download button to send the current configuration to the LogBook 5 Select Indictors Enable Input Reading Column from the menu bar to display the values for each channel 6 For the associated channel set the voltage to GT 0 005 for each transducer by adjusting the trimpot labeled SCALE Use the total system gain GT calculated earlier Example If GT 435 5 the SCALE trimpot would be adjusted to obtain 2 17 V 7 Select Indictors Disable Input Reading Column from the menu bar Trimming Bri
7. is the expansion channel number This number is needed when writing a program to read from that particular channel For more information on multiplexing refer to the Signal Management chapter DBK16 pg 8 879895 DBK Option Cards and Modules Calibrating DBK16 for Daq Devices Reference Note This section covers calibrating a DBK16 that is being used in a Daq device application LogBook users refer to Calibrating DBK16 and DBK43A for LogBook which begins on page 15 Bridge circuit transducers are used for many different applications and the DBK16 is flexible enough to support most of them Each DBK16 channel circuit has an excitation regulator a high gain 100 1250 input amplifier with offset adjustment a low pass filter a scaling 1 10 amplifier and a calibration multiplexer There are 4 trimpots to set up each channel circuit The trimpots are labeled to represent the following adjustments EXC for adjusting the Excitation Voltage to the transducer GAIN for setting the gain of the input amplifier OFFSET for adjusting the circuit offset for quiescent loads or bridge imbalance SCALE for setting the gain of the scaling amplifier Proper setup includes the use of software commands that control the calibration multiplexer in each circuit The calibration multiplexer is used to switch the bridge circuit out and apply reference voltages to the input for use in the DBK16 setup The calibration multiplexer also allows the Daq dev
8. of a Unit Conversion from Voltage to Pounds The trimpots provide course tuning so large quiescent offsets can be nulled and the bridge signal can be amplified to match the A D input range Once these adjustments are made the operator can periodically fine tune the calibration via software using LogView s 2 Point calibration feature LogView s scale and offset features provide a simple means to apply a transfer function that converts the voltage to user units for example pounds as in the above block diagram Bridge circuit transducers are used for many different applications and the strain gage signal conditioning modules are flexible enough to support most of them Each channel circuit has an excitation regulator a high gain x100 to x1250 input amplifier with offset adjustment a low pass filter a scaling x1 to x10 amplifier and a calibration multiplexer DBK Option Cards and Module 879895 DBK16 pg 15 By using software controlled multiplexers on board reference voltages can be read by the data acquisition system so that precise gains and offsets can be set LogView provides a means of easily controlling the calibration multiplexers so that the reference voltages can be displayed while the trimpots are being adjusted There are four trimpots to set up each channel circuit The trimpots are labeled to represent the following adjustments EXC for adjusting the excitation voltage to the transducer GAIN for setti
9. 18 R19 and the upper channel resistors are R5 R6 R7 These resistor locations are arranged to allow the use of an 8 position DIP network as a convenient means of changing all 6 resistors at once The machined pin socket allows you to insert individual resistors should the two filter sections have different corner frequencies The table to the right lists common frequencies nominal resistance values and Bourns part numbers 3 7Hz 100K 4116R 001 104 Note Due to settling time the filter should not be enabled during the DBK16 setup DBK16 s active low pass filters have an inherent gain of 2 You must factor this gain into your setup calculations To change the gain to 1 remove the following 10 K resistors R44 for the upper channel R46 for the lower channel Reference Note Methods of calibrating DBK16 are discussed in the calibration section DBK Option Cards and Module 879895 DBK16 pg 7 Channel and Card Address Selection The lower and upper channels on the DBK16 are multiplexed into one of the channels 0 to 15 The base channel that the DBK16 is multiplexed into is set by the shunt jumper on the16 2 header designated JP1 see previous figure DBK16 Board Layout Each base channel can have up to 16 expansion channels multiplexed into it Since the DBK16 represents two expansion channels eight DBK16 cards can be multiplexed into each base channel To distinguish channels there is a card address bank of
10. 895 DBK Option Cards and Modules 3 Wire Quarter Bridge Positive R EOUT for DBK16 The quarter bridge configuration makes use of one element of the strain gage The three wire quarter bridge can be configured as positive or negative The above figure represents the positive plus configuration In this setup the magnitude of voltage out is inversely proportional to the change in resistance R EOUT When using a quarter bridge external strain gage in the positive configuration the following applies Upper Channel R12 and R13 are to be installed Lower Channel R24 and R25 are to be installed An external BCR is to be placed in the EXC to R1 line see previous figure Excitation To supply excitation voltage to a single DBK16 Connect J1 terminals SRC and SRC to a source of filtered not necessarily regulated DC between 12 and 15 V To supply excitation to multiple DBK16s 1 Connect J1 terminals SRC and SRC to a source of filtered not necessarily regulated DC between 12 and 15 V 2 Connect J2 of the powered DBK16 to J1 of the next DBK16 see figure The excitation power terminals are wired in parallel to daisy chain multiple DBK16s in systems with more than 2 transducers The user supplied excitation source is attached to a voltage regulator in the DBK16 circuitry This regulator provides the excitation to the actual transducer there is a separate
11. 95 DBK Option Cards and Modules
12. C and EXC terminals on the DBK16 7 Send the DBK16SetOffset command usually through a gain setting in the software support Adjust the OFFSET trimpot for a reading of 0 00 volts This removes all offset from the DBK16 channel circuit 8 Send the DBK16SetInputGain command usually through a gain setting in the software support Adjust the GAIN trimpot for a voltage reading equal to 005 the desired input amplifier gain 9 Send the DBK16SetScalingGain command usually through a gain setting in the software Adjust the SCALE trimpot for a voltage reading equal to 005 the desired input amplifier gain the desired scaling amplifier gain 10 Send the DBK16 ReadBridge command default With the quiescent normal or inactive load or strain applied adjust the OFFSET trimpot for a reading of 0 00 volts This adds offset to the circuit to compensate for the quiescent load and allows maximum resolution for the measurement 11 Enable the low pass filter and or AC coupling if required for your application 12 From the transducer specifications and the total gain of the DBK16 channel calculate the Daq device voltage transducer units and apply it to your Daq device voltage readings through software 13 Apply a known load or strain and verify the DBK16 and software settings Set Up Notes The offset adjustment is unipolar 0 to 5 V on the input amplifier output If the offset can not be adjusted to 0 00 V at the end of the setup pr
13. DBK16 2 Channel Strain Gage Card Overview 1 Hardware Setup 2 Card Connection 2 Excitation 5 Card Configuration 6 Calibrating DBK16 for Daq Devices 9 DaqBook 100 Series amp 200 Series and DaqBoard ISA type Configuration 10 DaqBook 2000 and DaqBoard 2000 Series Configuration 10 Software Setup 11 GageCal Program 11 Example 12 Using the DBK16 with 3 Wire Strain Gages 13 Calibrating DBK16 and DBK43A for LogBooks 15 Overview 15 Calibration Methods 16 Procedures Common to All Calibration Steps Required 17 Nameplate Calibration and Manual Calibration 20 Channel Calibration Procedure 23 2 Point Calibration 26 Shunt Calibration 28 Creating a Units Conversion Transfer Function 30 Periodic Calibration Without Trimpots 31 DBK16 Specifications 31 Reference Notes o Chapter 2 includes pinouts for P1 P2 P3 and P4 Refer to pinouts applicable to your system as needed o In regard to calculating system power requirements refer to DBK Basics located near the front of this manual Overview The DBK16 will condition signals from most types of bridge circuit configuration transducers that have a signal output of less than 50 mV Strain gages and load cells are common types of these transducers For half and quarter bridge strain gages the DBK16 can accommoda
14. ant to read is 005 input gain scaling gain Enable the input reading column and set the Scaling Gain Disable the input reading column For an input gain of 200 typical scaling gains are Scaling Gain DaqView reading 2 2 0 volts 4 4 0 volts 6 6 0 volts 8 8 0 volts 10 10 0 volts requires DaqBook DaqBoard to be in unipolar mode Now all the gains are set correctly and we have to adjust the offset for any bridge circuit imbalance or quiescent loads Enable the on board filter Set the type to Bridge Make sure the quiescent load is applied Enable the input reading column and adjust the trimpot labeled OFFSET for a reading of 0 00 If you can not adjust it to 0 00 try dropping your input gain and compensate for the drop by raising your scaling gain If it still does not adjust to 0 00 swap the BRG and BRG wires to reverse the polarity of the signal The offset adjustment is unipolar and only affects the input gain After the final offset is made the gain readings will be incorrect if you want to go back and check them unless the circuit offset is removed Step 7 in typical setup procedure Using the DBK16 with 3 Wire Strain Gages Each single element 3 wire strain gage has 1 wire connected to one side of the gage element and 2 wires connected to the other Follow these steps for using the DBK16 with the 3 wire single element strain gages 1 Install bridge completion resistors R12 and R13 R24 and R25 for l
15. ct Indictors Enable Input Reading Column from the menu bar This displays the offset values for the enabled channels 6 Set the offset voltage to 0 0V for each transducer by adjusting the trimpot labeled OFFSET for the associated channel 7 Select Indictors Disable Input Reading Column from the menu bar Adjust the Input Amplifier Gain Perform the following steps to adjust the Input Amplifier Gain 1 In the Param1 column see page 17 for location select all of the DBK43A channels that are to be adjusted 2 Select Mode SetInputGain from the drop down list above the grid This selection commands the calibration multiplexer to route a 5mV reference through the Input Amplifier and bypass the Scaling amplifier see following figure Note If the filter is enabled not bypassed accommodate an additional x2 gain stage DBK Option Cards and Module 879895 DBK16 pg 23 Mode SetInputGain 5 milli Volt Reference Route 3 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 4 Click the Download button to send the current configuration to the LogBook 5 Select Indictors Enable Input Reading Column from the menu bar to display the values for each channel 6 For the associated channel set the voltage to GI GF 0 005 for each transducer by adjusting the trimpot labeled GAIN Use the Input Amplifier Gain GI calculated earlier Note If the filter is enabled the
16. d to the data acquisition system s input range Using the LogBook s 5V input range the required gain is calculated by dividing 5V by the maximum output voltage of the sensor Before performing the calculation it is typically a good idea to pad the maximum sensor voltage by about 5 so that once amplified it won t bump into the limit of the 5V range G VLB VGO VGO 5 Where G Gain VLB LogBook input range VGO Maximum gage output For the strain gage in the previous example with a maximum output of 10 5mV the required gain is G 5 0V 0 0105V 0 0105V 0 05 453 5 For the above load cell with a maximum output of 20 5mV the required gain is G 5 0V 0 0205V 0 0205V 0 05 232 3 Determining the Gain of Each Amplification Stage The system s total gain is GT GI GF GS Where GT Total gain GI Input amplifier gain GF Filter gain GS Scaling amplifier gain Note Maximum gain calibration is x1000 for 5V range DBK Option Cards and Module 879895 DBK16 pg 21 The majority of the gain should be assigned to the Input Amplifier with the Scaling Amplifier used for fine tuning If the filter is enabled a gain of x2 is automatically introduced The input amplifier has a gain range of 100 to 1250 the filter gain 1 or 2 and the scaling amplifier has a range of 1 to 10 For the strain gage example if we round off our gain to 420 any of these po
17. dge Quiescent Load Most bridges have some level of offset even if no quiescent load is present In quarter and half bridge situations use of 1 bridge completion resistors can cause up to 1mV V of offset If the bridge has 4mV of offset and the Input Amplifier is set to x100 the Offset potentiometer would need to nullify 400mV DBK16 For DBK16s the Offset Potentiometer can adjust out 0 to 5V of offset amplified by the Input Amplifier DBK43A For DBK43As the Offset Potentiometer can adjust out 1 25 to 5V of offset amplified by the Input Amplifier Trimming Bridge Quiescent Load If a significant amount of quiescent offset is present and the Input Amplifier gain is set too high the Offset Potentiometer will not have enough range to adequately nullify the offset In this case the gain of the Input Amplifier must be reduced while the gain of the Scaling Amplifier is increased proportionately Use the following steps to trim bridge quiescent load unload the bridge 1 In the Param1 column see page 19 for location select all of the DBK43A channels that are to be adjusted 2 Select Mode Bridge from the drop down list above the grid This selection commands the calibration multiplexer to route the transducer output through the analog path as shown below DBK Option Cards and Module 879895 DBK16 pg 25 Mode Bridge Reference Route 3 Turn off all the channels in the system except for those DBK43A chann
18. djusted you must 1 Reposition the DBK43A s physical calibration switch located next to the Power LED to the CAL position 2 Select CAL in LogView This is detailed in the following paragraph Open the LogBook Hardware Configuration window and select DBK43A see following figure In the Configurations settings box set the CAL NORM Switch to CAL If the DBK43A is not displayed click the to the left of the base channel to which it is attached this action expands the hardware tree in the LogBook Hardware Configuration window Repeat this process for all DBK43A units that are to be adjusted Click OK to lock in the changes Setting a DBK43A Cal Norm Switch to CAL DBK16 pg 18 879895 DBK Option Cards and Modules 3 In the Param1 column see next figure for location select all of the DBK43A channels that are to be adjusted 4 Set Mode equal to Excitation from the drop down list located above the DBK Parameters tab 5 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted Selecting Mode Excitation for DBK Parameter 1 6 Click the Download button to send the current configuration to the LogBook 7 Select Indictors Enable Input Reading Column from the menu bar to display the excitation values for each channel Download Button Selecting Enable Input Reading Column from the Indicators Pull Down Menu 8 Set the excitation voltage for each tra
19. dure is as follows 1 Disable the low pass filters JP4 and or JP5 and set DC coupling install JP2 and or JP3 for all the channels that are being setup If you plan on using the filter during your acquisition take note of the gain in the filter stage default 2 or 1 with resistor removed and allow for it in your setup 2 Determine what the excitation for the transducer will be from the transducer specifications and the current limitations of the DBK16 excitation regulator 3 Determine what the maximum voltage will be from the transducer at maximum load or strain and calculate what the DBK16 channel total gain should be based on a full scale Daq device 5 V to 5 V for DaqBook and DaqBoard ISA type in bipolar mode 0 to 10 V for DaqBook 100 amp 200 DaqBoard ISA type and DaqBoard 2000 in unipolar mode 10 to 10 V for DaqBoard 2000 in bipolar mode and Daq PC Card See examples on page 12 DBK Option Cards and Module 879895 DBK16 pg 9 4 Determine how the total gain will be distributed between input amplifier gain filter gain and scaling amplifier gain See examples on page 12 5 Hook up the transducer to the terminal strips labeled Lower or Upper according to the figures in the Card Connection section Install the appropriate bridge completion resistors if applicable 6 Set the excitation voltage for the transducer by adjusting the trimpot labeled EXC and measuring the voltage with a voltmeter across the EX
20. els that are to be adjusted 4 Click the Download button to send the current configuration to the LogBook 5 Select Indictors Enable Input Reading Column from the menu bar to display the offset values for each channel 6 For the associated channel set the offset voltage to 0 0V for each transducer by adjusting the trimpot labeled OFFSET Note If you are unable to nullify the quiescent offset of the bridge your Input Amplifier gain may be too high Information regarding gain redistribution can be found in the section entitled Determining the Gain of Each Amplification Stage 7 Select Indictors Disable Input Reading Column from the menu bar 2 Point Calibration This 2 point calibration method makes use of trimpot adjustments It should not be confused with the LogView software 2 Point Calibration discussed in the LogView chapter in the LogBook User s Manual In the 2 Point calibration method the user places two known loads on the gage one at a time then adjust the trimpots until the expected value is reached Typically the first of loads is no load In the case of a weight scale the scale would first be unloaded to adjust the offset then a known load near maximum expected would be applied to adjust the gain Shunt calibration discussed immediately after this 2 Point Calibration section is the same as the 2 Point method except the second load is applied in a simulated fashion by shunting 1 leg of the brid
21. figuration to the LogBook 5 Select Indictors Enable Input Reading Column from the menu bar to display the offset values for each channel 6 For the associated channel apply the first calibrated load to each gage typically no load and set the voltage to 0 0V for each transducer by adjusting the trimpot labeled OFFSET If the first point is an actual calibrated load you must move the load to each gage one at a time to adjust its associated offset Adjust the Input and Scale Amplifier Gain For the best results a gain should be selected so that the bridge s maximum output equals 90 of the A D s input range 1 Use the following equation to calculate the desired shunt voltage VD VD Ls LM VI 90 Where VD Desired voltage from the after amplification when the shunt is applied Ls Simulated load produced by shunt LM Maximum load expected during usage VI Input voltage range Example The simulated load produced by the shunt 100lbs The maximum expected load during usage is 150lbs The programmable input range of the data acquisition system is set for 5V The desired output voltage of the strain gage signal conditioning electronics is VD 100 150 5 0 90 3V In this example we would adjust the GAIN and SCALE trimpots until a value of 3V is measured If 150lbs is applied to the gage a voltage of 4 5V will be measured DBK16 pg 28 879895 DBK Option Cards and Modules VD 150 150 5
22. ge with a shunt resistor Shunt calibration is preferred in cases where applying a real load near the maximum expected is not practical Initialize the System 1 Download a single setup and continuously display data in LogView The continuous display can remain throughout the procedure since the calibration multiplexers do not need reset between steps 2 In the Param1 column see page 19 for location select all of the DBK43A channels that are to be adjusted 3 Select Mode Bridge from the drop down list above the grid This selection commands the calibration multiplexer to route the transducer voltage through the analog path 4 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 5 Click the Download button to send the current configuration to the LogBook 6 Select Indictors Enable Input Reading Column from the menu bar to display the offset values for each channel DBK16 pg 26 879895 DBK Option Cards and Modules Adjust the Offset For the associated channel apply the first calibrated load to each gage typically no load and set the voltage to 0 0V for each transducer This is accomplished by adjusting the trimpot labeled OFFSET If the first point is actually a calibrated load you will need to move the load to each gage one at a time to adjust its associated offset Adjust the Input and Scale Amplifier Gain Complete the following steps to adjust the channel gain
23. ice to record the individual adjustments The next table shows the setup commands their binary codes and a description of their function These commands are accessible through DaqView and the Daq device driver as gain settings and through most third party software support as well as GageCal Setup Command Code Description Dbk16ReadBridge 00 Reads bridge circuit with all gains and offsets included normal operation Dbk16SetOffset 01 Applies a grounded input and allows the user to read the circuit offset voltage multiplied by the input amplifier and the low pass filter gain Dbk16SetScalingGain 10 Applies 5 mV to the input and allows the user to read the voltage out of the circuit through the input gain amplifier the low pass filter and the scaling gain amplifier Dbk16SetInputGain 11 Applies 5 mV to the input and allows the user to read the voltage out of the circuit through the input gain amplifier and low pass filter only The following equations represent the voltage recorded by the Daq device when the calibration mux is set in 1 of 4 possible settings Code Equation 00 Vout Scaling Gain Filter Gain InputGain bridge circuit voltage offset voltage 01 Vout Filter Gain Input Gain offset voltage 10 Vout Filter Gain Scaling Gain Input Gain 5 mV offset voltage 11 Vout Filter Gain Input Gain 5 mV offset voltage Asterisk implies the filter is enabled A typical setup proce
24. ill recommend a suitable value but make sure that the maximum output current of the excitation regulator is not exceeded Initialize LogView Launch LogView and use the LogBook Hardware Configuration window hardware tree to configure all of the DBK options that are to be used in the system If needed refer to the LogView chapter LogBook Hardware Configuration Button and Screen Open the Analog Input Channel Configuration Window Click the User Scaling Tab and verify that all of the strain gage channels that are to be adjusted have scale and offset values of 1 and 0 respectively DBK Option Cards and Module 879895 DBK16 pg 17 Analog Input Channel Configuration Window Button and Screen User Scaling Tab Selected For all of the strain gage channels that are to be adjusted set their ranges to 5V Click the DBK Parameters tab to expose the strain gage signal conditioning programmable settings Click the Attach button to substantiate a connection between the PC and the LogBook Adjust the Excitation DBK16 For DBK16 set the excitation voltage for the transducer by adjusting the trimpot labeled EXC and measuring the voltage with a voltmeter across the EXC and EXC on the bridge or at the terminals of the signal conditioning module Adjust the Excitation DBK43A DBK43A is equipped with a switch that allows the excitation voltage to be read by the LogBook and displayed in LogView For all DBK43A units to be a
25. justing the gain for the first time will have an affect on the offset it is recommended that offset and gain adjustment be performed twice for each channel DBK Option Cards and Module 879895 DBK16 pg 27 Shunt Calibration Shunt calibration is virtually identical to the 2 Point method just discussed except that the second point is simulated The simulated load is achieved by shunting one leg of the bridge with a shunt resistor Shunt calibration is the preferred calibration method when applying a real load of a value approximating the maximum expected load is not practical To adjust the channel gain the shunt must be applied to the bridge Calculate and install the necessary shunt resistor before continuing DBK43A has direct support for shunt calibration accommodating the resistor in its enclosure and allowing the software to apply it when requested DBK16 does not have direct support so the shunt resistor must be applied externally and switched in manually Adjust the Offset Adjust the offset as follows 1 In the Param1 column select all of the DBK43A channels that are to be adjusted 2 Select Mode Bridge from the drop down list above the grid This selection commands the calibration multiplexer to route the transducer voltage through the analog path 3 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 4 Click the Download button to send the current con
26. l application To install the GageCal program on your computer close all other programs and run SETUP EXE on Disk 1 or CD ROM as applicable from Windows 3 1 3 11 or Windows 95 98 Me Follow the installation instructions from the setup program Execute GAGECAL EXE from a Windows environment to start the program The first screen that appears will set up the Daq device interface Input the correct Daq device interface information and click OK If the program does not detect the Daq device please check connections and try again or refer to the troubleshooting tips in the Troubleshooting Tips chapter Through GageCal DBK16 channels can be configured and calibrated as needed The typical procedure for using GageCal with a DBK16 is as follows 1 Highlight the expansion channel number you want to configure and calibrate Notice the channel numbers are listed 16 to 271 with respect to the Daq device if necessary see the section entitled Channel and Card Address Selection 2 Click on the CONFIGURE button Setup and verify your hardware setting with the diagram on the screen Please note that the coupling must be set to DC and the filter must be disabled to calibrate the DBK16 After the hardware is setup and verified click on the ACCEPT button to configure the next channel or ACCEPT CONFIGURATION AND EXIT to return the main GageCal screen 3 Highlight the first configured channel and click on the button labeled CALIBRATE The Application Pa
27. lements in the bridge are strain variable A quarter bridge has 1 strain variable element a half bridge has 2 and a full bridge has 4 Each DBK16 channel has locations for bridge completion resistors These resistors of fixed values are necessary to fill out the bridge configuration In the following diagram a 4 element bridge type strain gage is referenced to the upper and lower channel bridge completion resistor designations for the DBK16 Bridge resistors are used in either the DBK16 or the strain gage but not in both at the same time DBK16 pg 2 879895 DBK Option Cards and Modules Connections are provided for Kelvin type excitation The excitation regulators stabilize the voltage at the points connected to the on board sampling dividers Unless you run separate sense leads to the excitation terminals of the strain gage the voltage regulation is most accurate at the terminal blocks on the DBK16 In a Kelvin type connection six wires run to a 4 element strain gage and the excitation regulation is optimized at the strain gage rather than at the terminal blocks For high accuracy this can be a worthwhile connection for as little as 10 feet of 22 gauge lead wire Kelvin Excitation Leads Full Bridge Resistor Configuration for DBK16 The full bridge configuration makes use of all four elements of the strain gage When using a full bridge external strain gage all four elements the following applies to the DBK16 on board resis
28. more useful to you than volts For example you could obtain readings with pounds as the designated Units The reading in pounds will be based on the raw input value typically Volts and the indicated Scale and Offset adjustment To create the transfer function 1 Type the desired unit name in the Units column 2 Select an appropriate range e g unipolar 3 Enter the linear scale relation to Volts e g 25 pounds per Volt 4 Enter any offset from 0 for example an empty basket used in an application reads 0 1 V The reading and range columns will automatically change to the adjusted values DBK16 pg 30 879895 DBK Option Cards and Modules DBK Option Cards and Module 879895 DBK16 pg 31 Periodic Calibration Without Trimpots Once the trimpots have been adjusted during initial installation periodic trimming can be performed through LogView s 2 Point software calibration The LogView procedure does not require the use of trimmpots and should not be confused with the 2 point method discussed in this section of the manual Refer to the LogView chapter in the LogBook User s Manual for information regarding 2 point calibration via software DBK16 Specifications Name Function 2 Channel Strain Gage Input Card Input Connectors Screw terminals for signal connections Output Connector DB37 male mates with P1 using CA 37 x cable Number of Channels 2 Excitation Voltage Range 1 50 to 10 50 VDC 50 mA on
29. ng the gain of the input amplifier OFFSET for adjusting the circuit offset for quiescent loads or bridge imbalance SCALE for setting the gain of the scaling amplifier Signal FlowRelationship of Software Controlled Multiplexers and On Board Reference Voltages This calibration procedure can only be executed while LogBook is attached to a PC that is running LogView To adjust trimpots use one of the following calibration methods as appropriate Nameplate 2 Point Shunt or Manual Calibration Methods Several different calibration techniques are supported by strain gage signal conditioning modules Calibration methods include Nameplate 2 Point Shunt and Manual From the following discussion select the calibration method that is best for your application Nameplate uses the transducer s published specs Nameplate calibration is typically used with packaged load cells with millivolt per volt mV V transfer functions Using the mV V spec of the load cell or a strain gage s Gage Factor GF the necessary system gain can be calculated and applied to a channel 2 Point uses 2 known loads one of which might be no load The 2 Point calibration method requires the operator to apply two known loads to the load cell or strain gage one at a time while the data acquisition system takes measurements Typically the first point is with no load applied and the second point is close to the maximum load capaci
30. nsducer by adjusting the trimpot labeled EXC for the associated channel while reading their values in LogView 9 Select Indictors Disable Input Reading Column from the menu bar Selecting Disable Input Reading Column from the Indicators Pull Down Menu DBK Option Cards and Module 879895 DBK16 pg 19 10 Return the physical calibration switches of the applicable DBK43As to the NORM position 11 In LogView open the LogBook Hardware Configuration Window hardware tree and select NORM for each DBK43A This completes the section entitled Procedures Common to All Calibration Steps Required Nameplate Calibration and Manual Calibration To properly calibrate a strain gage channel using the Nameplate method the required gain must first be calculated If the desired gain and offset are already know as in the Manual calibration method skip to the section Determining the Gain of Each Amplification Stage The following examples outline the necessary steps for determining the required gain for Nameplate calibration Both strain gage and load cell examples are provided Calculating the Required Gain Determining a Strain Gage s Maximum Output Voltage Most strain gages come with Gage Factors GF used to calculate the approximate output of the bridge circuit with a typical strain value The formula is VBR VEXC G S B 4 See following important notice Where VBR Bridge output voltage VEXC Exci
31. nt the full scale of the sensor usually full scale Daq device input with a little space to prevent saturation divided by the full scale sensor output Example The strain gage above at 4000 microstrain will output 10 5 mV If using a DaqBook in bipolar mode full scale is 5 V Also we will allow 0 5 V space on the full scale input The DBK16 gain should be 4 5 V 10 5 mV 428 6 Now we must determine how to distribute the gain in the DBK16 typical setup procedure step 4 There is the input amplifier that has a gain range of 100 to 1250 the filter gain 1 or 2 and the scaling amplifier that has a range of 1 to 10 If we round off our gain to 420 any of these possible settings will work Input Gain 420 100 240 300 Filter Gain enabled No Yes 2 Yes 1 No Scaling Gain 1 2 1 1 75 1 4 Total DBK16 Gain 420 420 420 420 After we determine how all our gains will be distributed the sensor can be hooked up to the DBK16 the bridge completion resistors installed and the excitation voltage set Then we can proceed to set the gains We will use DaqView for this DBK16 pg 12 879895 DBK Option Cards and Modules DBK Option Cards and Module 879895 DBK16 pg 13 Launch DaqView and set it up for the DBK16 at the correct Daq device input channel determined by the setting of JP1 and S1 On return to the DaqView main spreadsheet screen notice the type column in the spreadsheet
32. ocedure try swapping the BRG and BRG wire connections or dropping the input gain and increasing the scaling gain For very high system gains the Scaling Gain might have to be set first with the Input Gain low and then set the Input Gain the Daq device can only measure up to 10 V DaqBook 100 Series amp 200 Series and DaqBoard ISA type Configuration Use of the DBK16 requires setting jumpers in DaqBooks 100 Series amp 200 Series device and DaqBoards ISA type 1 If not using auxiliary power place the JP1 jumper in the expanded analog mode Note This default position is necessary to power the interface circuitry of the DBK16 via the internal 15 VDC power supply If using auxiliary power e g a DBK32A or DBK33 you must remove both JP1 jumpers refer to Power Management in the DBK Basics section and to the DBK32A or DBK33 sections as applicable Configuration Jumpers 2 For DaqBook 100 DaqBook 112 and DaqBook 120 only place the JP4 jumper in single ended mode DaqBook 2000 and DaqBoard 2000 Series Configuration No jumper configurations are required for these 2000 series devices DBK16 pg 10 879895 DBK Option Cards and Modules Software Setup Reference Notes o DaqView users Refer to chapter 3 DBK Setup in DaqView o LogView users Refer to chapter 4 DBK Setup in LogView GageCal Program GageCal is not used for LogBook applications Note GageCal is best suited for a load cel
33. ower channel 2 Attach the 1 wire side of the gage element to the EXC and SEN terminals 3 Attach one wire on the 2 wire side of the gage to BRG terminal 4 Attach one more bridge completion resistor to the end of the other wire on the 2 wire side of the gage element 5 Attach the other side of the 3rd bridge completion resistor to the EXC terminal DBK16 pg 14 879895 DBK Option Cards and Modules Calibrating DBK16 and DBK43A for LogBooks Reference Note This section covers calibrating a DBK16 that is being used in a LogBook application Daq users Refer to Calibrating DBK16 and DBK43A for Daq Devices which begins on page 9 Overview 15 Calibration Methods 16 Procedures Common to All Calibration Steps Required 17 Nameplate Calibration and Manual Calibration 20 Channel Calibration Procedure 23 2 Point Calibration 26 Shunt Calibration 28 Creating a Units Conversion Transfer Function 30 Periodic Calibration Without Trimpots 31 Overview Calibrating a strain gage channel includes One time adjusting of the bridge excitation One time tuning of the electronic gains and offset via trimpots to maximize performance and dynamic range Applying a transfer function to the voltage output to convert it to engineering units e g pounds kilograms Executing a software scale and offset adjustment periodically to maintain accuracy Example
34. rain units Bridge circuit output voltage 4 linear estimate some strain gages are not linear refer to strain gage theory for more information If we have a 120 ohm strain gage with a gage factor of 2 1 and excitation voltage of 5 V due to the current limitation of the excitation regulator on the DBK16 it must be less than 6 V and we are measuring 4000 microstrain Bridge output voltage for 4000 microstrain 5 2 1 4000 10 4 10 5 mV 6 A load cell example Load cells come with a mV V specification which means for each volt of excitation at maximum load the load cell will output a specific millivolt level Consider a 3000 pound load cell rated at 2 05 mV V using 10 V of excitation assume it is a 350 ohm load cell When 3000 pounds are applied the voltage out of the load cell is 10 2 05 10 3 20 5 mV For 1000 pounds it would be 1000 3000 10 2 05 10 3 6 833 mV Now that we know what our full scale voltage will be from our sensor we can calculate what the voltage gain should be on the DBK16 so the full scale sensor output will correspond to the full scale Daq device input Full scale Daq device inputs are 5 to 5 V for DaqBook and DaqBoard ISA type in bipolar mode 0 to 10 V for DaqBook DaqBoard ISA type and DaqBoard 2000 in unipolar mode 10 to 10 V for DaqBoard 2000 in bipolar mode and Daq PC Card To calculate the needed DBK16 gains use the maximum voltage you want to represe
35. rameters screen appears There are 2 types of calibration that the DBK16 can accommodate Nameplate calibration allows you to enter specifications of your transducer and application Two Point calibration allows you to enter two points of millivoltage out of the transducer vs pounds or other physical units From the parameters you enter GageCal instructs you how to set up the DBK16 Note All application parameters entered will be used in the DBK16 setup Any inaccuracies will result in the DBK16 being configured incorrectly 4 Click on the CONTINUE button and follow the instructions from the GageCal program GageCal has a help file that will explain any questions on the different screens or menus If you have trouble in your setup a DIAGNOSTIC window can show a DBK16 circuit to help you troubleshoot the problem 5 After GageCal completion go to DaqView and convert 5 V to engineering units using mx b DBK Option Cards and Module 879895 DBK16 pg 11 Example The following examples perform selected steps for a typical setup There will be strain gage and load cell examples Referring to the typical setup procedure step 3 says to determine the maximum voltage from the transducer at maximum load or strain A strain gage example Most strain gages come with Gage Factors GF used to calculate the approximate output of the bridge circuit with a typical strain value The formula is Excitation Voltage Gage Factor Strain in st
36. regulator for each transducer hence two regulators per DBK16 Each regulator has a maximum current of 50 mA The maximum amount of excitation that can be provided by the DBK16 excitation regulator is represented by the following equation VEXC MAX 0 05 RGAGE Where RGAGE the resistance of 1 element in the bridge circuit DBK Option Cards and Module 879895 DBK16 pg 5 The user supplied excitation source should provide adequate current levels for all the DBK16s that are powered The minimum current required for the user supplied excitation source for each transducer 2 per DBK16 is IMIN Excitation voltage R 5 mA where R the resistance of 1 element in the bridge circuit The user supplied excitation source must be 12 to 15 VDC and connected with the proper polarity Enhanced DBK16 cards contain two additional jumpers JP6 and JP7 Their configuration determines whether the channel excitation regulator s power source is external default or internal Review the following note and CAUTION prior to selecting the internal power source JP6 Selects the upper channel s source Default is external JP7 Selects the lower channel s source Default is external It is possible to power excitation regulators from an internal 15 V on the LogBook s or Daq device s P1 if no other DBKs are being used On enhanced DBK16 cards two 3 pin headers JP6 for upper channel and JP7 for lower channel are set by default to
37. s Enable Input Reading Column from the menu bar to display the excitation values for each channel 10 Set the voltage to VD as derived above for each transducer This is accomplished by adjusting the trimpots labeled GAIN and SCALE for the associated channel The GAIN trimpot provides for course adjustment The SCALE trimpot provides for fine tuning DBK Option Cards and Module 879895 DBK16 pg 29 11 Select Indictors Disable Input Reading Column from the menu bar 12 Return the physical NORM CAL switches of the applicable DBK43As to the NORM position 13 In LogView open the LogBook Hardware Configuration window and return each DBK43A back to NORM Repeating the Process Since adjusting the gain for the first time will have an affect on the offset it is recommended that offset and gain adjustment be performed twice for each channel Creating a Units Conversion Transfer Function To make the data from your gage more useful it should be recorded in terms of units appropriate to your application such as pounds kilograms inches mm or Hg A transfer function is needed to convert volts to these more meaningful units For this purpose LogView provides a means of assigning a mathematical scale and offset to each channel Scale and offset information from that chapter has been repeated below for convenience In User Scaling you can create a transfer function The function allows LogView to display units that could be
38. ssible settings will work Option A Option B Option C Option D Input Gain 420 100 240 300 Filter Gain enabled No Yes 2 Yes 2 See Note No Scaling Gain 1 2 1 1 75 1 4 Total Gain 420 420 420 420 For Option C the LPF gain is typically x2 For gains of x1 if the filter is enabled the following apply DBK16 For a gain of x1 if the filter is enabled 10K resistors R44 and R46 must have been previously removed for the low and high channels respectively DBK43A For a gain of x1 if the channel filters are enabled removal of the following 10 K resistors applies Ch0 R144 Ch1 R244 Ch3 R444 Ch4 R544 Ch5 R644 Ch6 R744 Ch7 R844 DBK16 pg 22 879895 DBK Option Cards and Modules Channel Calibration Procedure Adjust the Offset The following steps are used to adjust the offset 1 In the Param1 column see page 19 for location select all of the DBK43A channels that are to be adjusted 2 Select Mode SetOffset from the drop down list above the grid This selection commands the calibration multiplexer to route the 0 0V reference through the entire analog path see following figure Mode Offset 0 0 Volt Reference is Routed 3 Turn off all the channels in the system except for those DBK43A channels that are to be adjusted 4 Click the Download button This sends the current configuration to the LogBook 5 Sele
39. tation Voltage G Gage Factor S Strain in user units in uStrain B Configuration factor 1 for bridge 2 for bridge 4 for full bridge The equation VBR VEXC G S B 4 produces a linear estimate If you are using a non linear strain gage you should refer to strain gage theory for additional information as needed For a 120 ohm strain gage with a gage factor of 2 1 and excitation voltage of 5 V applying 4000 microstrain would produce an bridge output of 10 5mV for a bridge configuration VBR 5 2 1 4000x10 6 4 10 5mV Determining a Load Cell s Maximum Output Voltage Load cells come with a mV V specification for each volt of excitation at maximum load the load cell will output a specific millivolt level VLC R VEXC Where VLC Load cell output voltage R Load cell spec mv V VEXC Excitation voltage DBK16 pg 20 879895 DBK Option Cards and Modules Consider a 3000 pound load cell rated at 2 05 mV V using 10 V of excitation assume a 350 load cell When 3000 pounds is applied the voltage out of the load cell is 20 5mV VLC 10 2 05 10 3 20 5 mV If 1000 pounds were applied we would see 6 833 mV This is arrived at as follows 1000 3000 10 2 05 10 3 6 833 mV Using the Calculated Maximum Voltage to Determine the Necessary Gain To maximize the resolution and dynamic performance of the system the sensor s output should be amplified to correspon
40. te user supplied bridge completion resistors that complete the bridge circuit The bridge circuit must be complete for the DBK16 to operate correctly Each channel of the DBK16 offers a selectable 3 pole low pass filter with a user set cut off frequency Up to 8 DBK16 boards can be connected to each of 16 analog LogBook or Daq device base channels for a maximum of 256 input signals Remote sense terminals are used with 6 wire Kelvin connections The DBK16 provides an amplifier gain range of 100 to 12 500 for use with strain gages having 0 4 to 10 mV V sensitivities Most strain gages are specified for a full scale value of weight force tension pressure or deflection with an output of mV V of excitation For example a strain gage with a full scale rating of 1000 lb of tension might output 2 mV V of excitation at full load With an excitation of 10 VDC 1000 pounds of load would produce an output of 20 mV The card s 0 to 5 VDC offset and output scaling permit nulling of large quiescent inactive or motionless loads and expansion of the dynamic range for maximum resolution Typically the quiescent output is non zero Prior to a force being applied a mounted strain gage can be in a state of partial deflection resulting in an output In the case of a tension gage this output may be due to the weight of a hook or empty container DBK Option Cards and Module 879895 DBK16 pg 1 Output Channel Select Header JP1 Upper Channel
41. ter frequency determining resistor network can be inserted into an IC socket The AC or DC coupling choice on each channel is set by the presence or absence of a shunt jumper on a two pin header If the shunt jumper is in place the coupling is DC If the shunt jumper is absent the coupling is AC JP3 is used to configure the upper channel s coupling JP2 is used to configure the lower channel The choice of using or bypassing the low pass filter for each channel is made by the orientation of shunt jumpers on a 2 2 pin header When the shunt jumpers are oriented in the same way as the bypass symbol horizontal parallel with labels on card the filter is bypassed When the shunt jumpers are oriented in the same way as the filter symbol vertical the filter is in the signal path JP4 is used to configure the upper channel JP5 is used to configure the lower channel Frequency Resistance Bourns Part Number 37Khz 10 4116R 001 100 19Khz 20 4116R 001 200 7Khz 50 4116R 001 500 3 7Khz 100 4116R 001 101 1 9Khz 200 4116R 001 201 700Hz 500 4116R 001 501 370Hz 1K 4116R 001 102 190Hz 2K 4116R 001 202 70Hz 5K 4116R 001 502 37Hz 10K 4116R 001 103 19Hz 20K 4116R 001 203 7Hz 50K 4116R 001 503 The corner frequency of the low pass filters is determined by three resistor values in each filter circuit Located in the center of the card the lower channel resistors are R17 R
42. three switches on each DBK16 These switches are binary weighted with eight possibilities 0 7 Base Channel First Expansion Channel Number N 0 16 1 32 2 48 3 64 4 80 5 96 6 112 7 128 8 144 9 160 10 176 11 192 12 208 13 224 14 240 15 256 DIP Switch Setting Card Channels n C B A Upper Lower Open Open Open 1 0 Open Open Closed 3 2 Open Closed Open 5 4 Open Closed Closed 7 6 Closed Open Open 9 8 Closed Open Closed 11 10 Closed Closed Open 13 12 Closed Closed Closed 15 14 The switch settings are open 0 closed 1 enabled The weights when closed are A 1 B 2 C 4 The table above shows the switch settings The table to the right lists card channels n with respect to the base channel Since the LogBook or the Daq device has sixteen base channels up to 128 DBK16s can be used providing a maximum of 256 channels To keep track of all base and expansion channels the base channels are designated 0 to 15 and the expansion channels are designated 16 to 271 Channel 16 is the first channel on the first expansion board lower channel on card address 0 with JP1 set to CH0 Channel 271 is the last channel on the last expansion board upper channel on card address 7 with JP1 set to CH15 To calculate the actual input channel use the above tables and add the applicable N and n The result
43. tor configuration Upper Channel R10 R11 R12 and R13 are not installed Lower Channel R22 R23 R24 and R25 are not installed DBK Option Cards and Module 879895 DBK16 pg 3 Half Bridge R1 and R2 EOUT Resistor Configuration for DBK16 The half bridge configuration makes use of two elements of the strain gage When using a half bridge external strain gage two of four elements the following applies to the DBK16 on board resistor configuration Upper Channel R10 and R13 are to be installed Lower Channel R22 and R25 are to be installed Note that other Half Bridge scenarios exist The one illustrated applies to the equation R1 and R2 EOUT 3 Wire Quarter Bridge Negative R EOUT for DBK16 The quarter bridge configuration makes use of one element of the strain gage The three wire quarter bridge can be configured as positive or negative The above figure represents the negative minus configuration In this setup the magnitude of voltage out is directly proportional to the change in resistance R EOUT When using a quarter bridge external strain gage in the negative configuration the following applies Upper Channel R10 and R11 are to be installed Lower Channel R22 and R23 are to be installed An external BCR is to be placed in the EXC to R1 line see previous figure DBK16 pg 4 879
44. ty of the gage While measuring the first point the offset is nulled and while measuring the second point the gain is adjusted to span the majority of the input range of the A D No gain calculations are required to perform this calibration method DBK16 pg 16 879895 DBK Option Cards and Modules Shunt applies a shunt resistor to the bridge to simulate a load Shunt calibration is identical to 2 Point calibration except that the second point is simulated so that applying a load near the gage s maximum load is unnecessary To simulate a bridge imbalance a shunt resistor is placed across one leg of the bridge Once the shunt resistor value has been calculated it is applied to the bridge to provide the desired simulated load No gain calculations are required to perform this calibration method Manual used to assign specific gains and offsets If a particular gain and offset are already known these values can be used to setup a strain gage channel Procedures Common to All Calibration Steps Required Set the Selected Channel s to DC Coupling Since the applied calibration signals are DC set DC coupling for all the channels that are being adjusted If your application requires AC coupling don t forget to remove the jumpers when the adjustment procedure has been completed Determine Channel Parameters Before adjusting the trimpots the excitation needs to be determined Typically the supplier of the gage of load cell w
45. use an external power source Moving the jumpers to the internal position connects the excitation terminals to the 15 VDC rail from P1 CAUTION Avoid overloading LogBook s DaqBook s or DaqBoard s 15 VDC power supply The power supply can be overloaded if DBK16 jumpers JP6 and or JP7 are set to Internal and one or more of the following conditions exist Additional DBKs are being used 120 bridge completion resistors are being used in the strain gage configuration Card Configuration Factory Defaults Bridge configuration Full Coupling DC Excitation source External Low pass filter Disabled by passed The cutoff frequency if enabled has a default of 3 7 Hz This is obtained using 100k resistors for R17 R18 and R19 for the lower channel and using 100k resistors for R5 R6 and R7 for the upper channel See the following board layout for resistor locations The next few sections of this document module explain the following aspects of configuring DBK16 AC Coupling and Low Pass Filter Options Channel and Card Address Selection DBK16 pg 6 879895 DBK Option Cards and Modules DBK16 Board Layout AC Coupling DC Coupling and Low Pass Filter Options Headers on the board accommodate the coupling and low pass filter options and the output channel selection see above figure Resistors can be removed to lower filter gain from 2 to 1 A fil
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