Shunt calibration CDAQ

Hi:
I’m using C-DAQ NI 9237 module with Signal Express and I have the following doubts: 1) How can I perform a shunt calibration using a ¼ Wheatstone bridge? I’m using module NI 9945 and I don’t have any way to perform the shunt.2) Concerning the half and full Wheatstone bridge the shunt calibration is possible using module NI 9949. Is the precision resistor of 100kOhm internal to the module? Can I connect an external precision resistor to pins 1 and 10 of the module? 3) If the precision resistor is internal how can I activate the resistor? I suppose that is just short-cut pin 1 to pin 10. Is that right? Regards, Diogo Ribeiro.

Hi Diogo,
Thanks for posting! To answer your questions:
The
100 kOhm shunt resistor is internal on the 9237 (connected to a switch across pins 1 and
10). The 9945 accessory performs the 1/4 bridge completion and the
circuit containing the shunt resistor is wired across R3 internally.
Running the calibration in Signal Express will automatically
connect/disconnect the shunt as necessary.
To perform the shunt
calibration on the 9949, you would use jumper cables to connect the Shunt Calibration
pins (1 and 10) across the desired resistor (you can specify the resistor used in software).
Again, the driver will automatically connect and disconnect the shunt resistor during the calibration process. You can provide
your own external shunt resistor on the 9949, but you would have to
make the measurements and scale the data yourself in software. I would recommend that you let the driver handle this.
I hope this answers your questions, if you have any others please let me know.
-John
John Passiak

Similar Messages

Gain error with shunt calibration

Hello,
I have a problem with shunt calibration of bridge based displacement transducers. The shunt calibration routine sets gain factors that give errors around 2% in the measured displacement. I have also found that the shunt calibration gain factors run out of bounds without a preceding offset null.
The hardware is a cDAQ-9188 with 9237 modules. The gauges have four wires, two input wires that I have connected to EX+ with jumper to RS+ and EX- with jumper to RS-/SC-, and two output wires that I have connected to AI+ with jumper to SC+ and AI-. LabVIEW is used with a VI shown in the attached figure.
Does anyone know why the shunt calibration behaves like that or what I do wrong?
/Emil
Attachments:
labview.png ‏19 KB

Hi Anton,
Setting the gain manually from a known displacement is not an option as some of the transducers are mounted so that they cannot be tested with gauge blocks.
Setting the DAQ Assistant Express VI or Create Channel VI to strain mode gives the same shunt factors as the general bridge mode.
I have done additional measurements to outrule any chance of coincidence with the sensing wires. With jumpers from EX+ to RS+ and from EX- to RS- on the first four of ten transducers the shunt factors are:
1.0046; 1.0246; 1.0347; 1.0246; 0.9649; 0.9811; 0.9600; 0.9720; 0.9591; 0.9793
with jumpers only on the first two transducers the shunt factors are:
1.0044; 1.0247; 0.9867; 0.9729; 0.9648; 0.9811; 0.9599; 0.9721; 0.9589; 0.9791
and finally for all transducers without jumpers the factors are:
0.9624; 0.9715; 0.9868; 0.9728; 0.9647; 0.9809; 0.9600; 0.9721; 0.9592; 0.9792
The conclusion is that the shunt factors are wrong but stable if the wiring is unchanged. Jumpers between EX and RS terminals effects the shunt factors. The shunt factors are between 0.04 and 0.06 larger with jumpers.
Should the RS terminals be connected for gauges without an extra sensing wire? Should there be a difference with and without the jumpers? Do you suggest anything special to look into regarding the EX wiring?
/Emil

Shunt Calibration Failed

Hello! I'm pretty new to LabVIEW so I apoligize if I am confusing.
I'm trying to put together a VI that will take the strain measurements from four gauges, initially based off of the example provided through the "Strain - Continuous Input.vi". I'm using a cDAQ-9147 equiped with a NI 9237 and a NI 9944. Since our system won't be changing I wanted to set the Shunt resistor value and location as constants (100,000 ohm and R3, respectively). Unfortunately when I then try to run the VI with "Enable Shunt Cal" on I get an error::
"Error -201493 occurred at DAQmx Perform Shunt Calibration (Strain).vi:5630001
Possible reason(s):
Shunt calibration failed. The calculated gain adjust is out of range. Ensure that the shunt calibration terminals are connected properly and that the shunt resistance and shunt element location settings match how the hardware is wired.
Property: AI.Bridge.ShuntCal.ShuntCalAResistance
Corresponding Value: 100.0e3
Simulated Value with Shunt: 1.750000e-3
Measured Value with Shunt: 603.757856e-6
Property: AI.Bridge.ShuntCal.GainAdjust
Requested Value: 2.898513
Possible Values: 500.0e-3 to 1.500000
Channel Name: Axial 2
Task Name: _unnamedTask<A>"
I should note that the original example works on all gauges, so I know it's a mistake I've made somewhere. I've included the VI if that will help.
Thank you!
Attachments:
Strain_HELP.vi ‏98 KB

Hi Sunkistist,
This error can be caused by one of 3 things:
Your 9237 is so far out of calibration that the gain adjustment it would take to correct it is higher than the maximum supported by shunt calibration. Since the shipping example works, and your confident with the readings, we can assume this is not the case.
Improper physical connections. Again, we can rule this out for the same reasons as #1.
Improper configuration. Check to ensure the all the bridge resistance and strain gauge information is correct.
Here are some links you might find helpful:
Shunt Calibration with NI-DAQmx
Connecting Strain Gauges and Shunt Resistors to the NI 9237
NI 9945 or NI 9944 with an NI 9237 Connection Guide
Jeff Munn
Applications Engineer
National Instruments

Does the cRIO Scan Engine Support Offset and Shunt Calibration on the 9237 module

Thanks.

Sachsm,
The documentation for the Set Shunt Calibration (Scan Interface).vi should have been in the VI help but it looks like it didn't make it so I'll make sure it gets updated. I'll double check my understanding tomorrow morning but the documentation should be the following for the inputs of this VI:
slot - Specifies the chassis slot of the strain module (9237, 9235, 9236 ). Valid values are 1 through N, where N is the number of slots in the chassis.
channel - Specifies the channel to be affected. Valid values are 0-N where N is the channel for shunt calibration.
value - Turns Shunt calibration on or off. Valid values are 0 or 1 where a value of 1 will turn shunt calibration on for the given slot and channel.
Now, for your orginal question about offsets on the AI inputs, here are my addtional thoughts:
Unlike our SCXI products, the NI 9237 does not have an internal hardware nulling circuitry because its input range is sufficiently wide so that the inputs will not saturate even with a very large initial bridge offset. Since the 9237 does not have any hardware nulling circuitry, you have to perform offset nulling with software compenstation, and save the value to use later in the application as you mentioned. For example, when an offset null is performed in DAQmx, the entire offset is stored in the Initial Bridge Voltage property and is stored in software. You should see the same offset if you used the module from DAQmx, FPGA Interface, or in the Scan Interface. With that being said, I believe what your seeing is really just the resting measurement of the module and transducer together and you should be able to zero out your measurement by performing Software Compensation.
Regarding, Offset Calibration, I think its important to make clear exactly what it is providing as the name is a little misleading. The Offset Cal feature of the 9237 is really more like an Auto Zero used for eliminating offsets generated by an amplifier stage and doesn't provide the same behavior as offset nulling. In Auto Zero Mode, the 9237 shorts the input channel to ground and subtracts the obtained measurement from all subsequent samples. Performing an auto zero is a quick calibration technique that takes place at the beginning of a scan. A typical use of the Offset calibration feature would be to set it true at the begining of acquiring data and then leaving it on indefinitely.
Personally, I do not bother enabling offset cal in my FPGA applications because the measurement of the sensor at rest takes into account all sensor and module offsets.
And finally, if your looking for some information on how to perform shunt calibration, I like to refer to the example VI located here:
C:\Program Files\National Instruments\LabVIEW 8.6\examples\CompactRIO\Module Specific\NI 9235\NI 9235 Getting Started
As it has walks through the programming steps of setting up Shunt cal and applying the Gain Factors. Its written for LabVIEW FPGA but it should be easy to use with Scan Interface.
Hope that helps a little bit,
Let me know if you have questions and I'll help where I can or bug the right engineer.
Basset Hound

Output gain adjustment factor from DAQmx Perform Shunt Calibration (strain).vi

Hi
We are using the DAQmx Perform Shunt Calibration (strain).vi to apply a gain adjustment to the output of our strain gauges. We would like to view the Gain Adjustment applied by the DAQmx Perform Shunt Calibration (strain).vi, and we have tried to do this using a property node.
I have attached screenshots of the property node we included before the DAQmx Perform Shunt Calibration (strain).vi (which seems to work fine), and the property node we have included after the DAQmx Perform Shunt Calibration (strain).vi (which doesn't output anything).
Could someone please advise of what I am doing wrong, or if ouputting the Gain Adjustment applied by the DAQmx Perform Shunt Calibration (strain).vi is even possible?
Cheers
Bart Scicchitano
(using his supervisors NI account with her permission)
Attachments:
ShuntCal_GainAdjustFactor_Before.PNG ‏29 KB
ShuntCal_GainAdjustFactor_After.PNG ‏45 KB

Hello, thank you for your response.
Sorry I wasn't clear. We get 0 from the property node when using multiple gauges in series. We have since found that the property node works when outputting the gain adjustment factor from only a single gauge, but we still cannot get it to work for multiple gauges in series.
I have posed the question in a more clear fashion (I hope) in the Labview forum (link below)
http://forums.ni.com/t5/LabVIEW/How-to-get-gain-adjust-from-multiple-strain-gauges/m-p/2304956/highl...
Thank you again for your response
Bart

Shunt calibration NI 9235

How do I wire strain gage for shunt calibration (is it different wiring than normally without shunt calibration?) and programmically set up shunt calibration at DAQmx level (not DAQ assistant)? I've got 50 feet of lead wire that's going to be added to 10 foot lead wire on 120 ohm resistance strain gages, and I need to be able to calibrate properly to take the resistance added into consideration so that we get the correct strain readings. I've looked at http://zone.ni.com/reference/en-XX/help/370466W-01/measfunds/quarter1/#GUID-F34636DC-B311-4257-BDD0-... and http://www.ni.com/pdf/manuals/374645a.pdf#page=11 strain gage and NI 9235 related manuals, but they don't completely outline how to do this.
I'd greatly appreciate any help anyone can offer.
Thanks!

Hi, here is an article that clarifies your doubt but with a different module. Now, in your case, in figure 5 from the 9235 manual states that there is a 50 kΩ internal Shunt Resistor. In summary, for the acquisition you just need to configure a strain task and input the sensor data that comes with the calibration certificate. I hope this helps
Alejandro | Academic Program Engineer | National Instruments

Expected Shunt Calibration Factors

I am trying to shunt calibrate (using a SCC-SG11) a rectangular rosette strain gage wired to an SCC-SG01 module. I'm using an SC-2345 hooked up to a laptop with a DAQCard-6036E. I am reading in an analog voltage with the SG11 engaged and subtracting the value w/o it engaged. The expected value of Vexpected=(R3*Vex*(Rshunt+R4))/(R4+Rshunt+R3*(Rshunt+R4)) is then divided by this difference to obtain the correction factor. For the Vexpected, R3=R4 correct? I am getting a correction factor value of less than 1 (~.97), which to me doesn't make sense, as the shunt calibration is supposed to correct for the wire resistance. Am I understanding this correctly that the correction factor should be >1?
Thank you in advance for your assistance
Solved!
Go to Solution.

Hi William,
If we look at what's going on internally in the SCC-SG11 by looking at pg 17-18 in the manual, it shows a diagram and a sample equation. Set all values to 120 to calculate your expected measurement and then vary it from 119 to 121 and divide by the expected value. If the resistance is higher than 120, you will get a lower measured voltage and a ratio >1. If the resistance is lower than 120, you will get a higher measured voltage and a ratio of <1.
Jake H | Applications Engineer | National Instruments

Problems performing offset null and shunt calibration in NI PXI-4220

I am using a 350 ohm strain gage for the measurements, i have already create a task in MAX, when i want to perform offset null in the task, the program shows a waiting bar and the leds in the 4220 board start to tilting, but when the waiting bar stops, MAX gets blocked. it has been impossible to me to perform the offset null, what can i try?.
which will be the correct values for the parameters beside the gage parameters for the strain measures?

Hello,
Thank you for contacting National Instruments.
Usually when this problem occurs, it is do to incorrect task configuration or incorrectly matched quarter bridge completion resistor. Ensure that you have the correct Strain Configuration chosen. The default is Full Bridge I. If you only have a single strain gauge in your configuration, you will need to change your configuration. Also ensure that if your are using a quarter bridge completion resistor make sure that it is 350Ohm not 120Ohm. If the resistor if 120Ohm you will more thank likely not be able to null your bridge.
Please see the PXI-4220 User Manual for more information about your configuration and signal connections: http://digital.ni.com/manuals.nsf/websearch/F93CCA9A0B4BA19B86256D60
0066CD03?OpenDocument&node=132100_US
Also, you can download and install the latest NI-DAQ 7.2 driver: http://digital.ni.com/softlib.nsf/websearch/50F76C287F531AA786256E7500634BE3?opendocument&node=132070_US
This 7.2 driver has a signal connections tab displayed when configuring your DAQmx Task which show you how to correctly connect your signals.
Regards,
Bill B
Applications Engineer
National Instruments

Error 200077 during Strain Gauge Calibration in Measurement and Automation Explorer V5.3.1f0

Hey Guyz!
I am experiencing a problem perfomring my shunt calibration using a 350ohm(GF 2) strain gauge connected with NI9949 and NI9237 in a NI cDAQ-9178 Hardware.
When i click on strain callibration under configuration-Device: R3 being my shunt of 100k ohm, i can measure the errors and calibration but when i hit the calibration tab, it gives me an error 200077 occured at Strain Gauge Calibration (see aatached jpeg file for the error type).
I don't know what is wrong, i have doublt-tripple checked my circuit, and have read the forums regarding the same error and have come across the "signal input range", in my case it is default kept at 1m max and -1m min. I am not sure how these values work.
Any guidance would be appreciated.
Thanks in advance.
Attachments:
error 200077.jpg ‏73 KB

Hi
This error code may be occurring due to the specified signal input range in max (-1m to 1m), being set to a value outside of the expected readings from your strain gauge.
Also the Gage Factor, Gage Resistance, Initial Voltage, Vex Source, Vex Value (V), Lead Resistance and Strain Configuration need to be configured based on your sensor specification.
This link gives more details on connecting strain gages to a DAQ device:
http://www.ni.com/gettingstarted/setuphardware/dataacquisition/straingages.htm#StrainGageCalibration
Hope this helps.
Andrew.N
Applications Engineer
National Instruments

9236 enable shunt cal property crashes crio OS with scan engine

I would like to inform users of the 9236 Quarter Bridge Strain Gauge Module of a bug. The Real-Time team is aware of this issue and I have been working with an app engineer on it for about a week and he has confirmed my findings. He says the problem is most likely a driver issue or scan engine issue and they are investigating it.
There is a bug that completely crashes the cRIO operating system with the 9236 module. Currently when a cRIO device is loaded with LV2009 SP1 or LV2010 and using scan engine interface, attempting to write the "shunt cal enable" property of a 9236 module completely crashes the VxWorks OS. If you try to access the property again, the crio crashes and enters an error state where the crio has rebooted twice without being told to. The LED indicator blinks four times to indicate this.
I have tested this with a few different hardware combinations with both the crio-9014 and crio-9012 controllers, combined with either the 8-channel 9104 back plane or the 4-channel 9102 back plane with the same results. The app engineer was able to duplicate this issue as well.
To duplicate the bug:
Load a crio device with 2009 SP1 or LV2010 and configure the device for scan engine. Locate the 9236 module in the project explorer and drag and drop it into a VI to create the IO variable. Right click the output terminal of the IO Variable and go to create > property > enable shunt calibration on a channel. Once the property is dropped, right click on it and do change to write so that you can write a boolean to the variable. It doesn't matter if you write a true or false to the property, the results are the same. Hit run, watch it crash. When it reboots, hit run again. The crio is now in a state that can only be recovered by physically resetting the device.
I love the crio stuff and I use it every day because it is very reliable and robust. This kind of thing is rare, which is why I am reporting it to the community as well as NI as it is a pretty big bug that took me a while to narrow down.
[will work for kudos]

rex1030,
Shunt calibration can be accessed using a property node. The operation will be the same, you still need to acquire two sets of data and compute the scalar.
You can obtain the necessary reference by dragging the module to the block diagram from the project. Please see http://zone.ni.com/devzone/cda/tut/p/id/9351 for more information on programmatic configuration.
Let me know if you have any other questions.
Sebastian

Shunt Calibrate Multiple Channels in One Task - Error 201398

Having created a task with multiple AI Strain Gage channels (each set with same bridge properties and quarter bridge config.), I recieve an error when passing the task to the "DAQmx Perform Shunt Calibration (Strain).vi"
My VI works fine if only a single channel is contained in the task, but more than one channel causes the error. Do I have to loop through each channel manually?
The "possible reason(s)" varies depending on my approach, but often indicates the AI.Bridge.ShuntCal.GainAdjust being requested is "-Inf"

You can start a new thread even if you have the same issue. What exactly you aregetting and show us the code for better understanding.
The best solution is the one you find it by yourself

Ni 9237 calibration -200077

I'm trying to calibrate NI 9237 + NI 9945 quarter bridge strain gage in ni max.
I get Error -200077 occurred at strain gage calibration.
Possible reasons:
Requested value is not a supported value for his property,
Property AI.Min
Requested value -1.0e-3
Valid values begin wih 18.8988984e-6
Valid values end with 103.843984e-3
Channel name: strain
I tried everything, different strain gages, different 9945's different 9237's, different cables, different computers. everything.
I changed every setting I could find in ni max.
I searched forums and inernet and what is there is not helping.
Any ideas? Please? I'm so desperate.
Solved!
Go to Solution.

I just got the same error message over and over.
What went down: When I set my min limit within the highest and lowest allowable values specified in the error dialog window, and then tried again, I got the same error all over again, but the highest and lowest allowable values shown in the window had changed to completely different numbers. This happened several times. No matter what I set my limits to, the max min allowable values would always change, so it would error out every time regardless of what I entered. Sometimes it would complain about the shunt calibration gain factor, that it couldn't set it to either "+inf" or "-inf". Looking closely at the calibration window, I noticed that NI MAX was reading the same strain value, both with, and without, the shunt resistor connected. When the calibraion subtracted Y2 - Y1, it got zero, and the inverse of zero is infinty. That's when I knew for sure it was something in my wiring and started looking into it more deeply.
Cause: Short in the lead wires running to the strain gage. When the specimen was assembled and bolted onto the fixture, the wires were obscured so that noone could see them, and they were crushed between two metal components.
Solution: Check for shorts or other issues in the strain gage wiring itself. I imagine if the strain gage circuit is open, then we would probably see the same error from NI MAX in that case as well.
Recommendation: I would request NI to add some more helpful information in the error dialog box, to suggest to the user to check wiring, etc.

Restarting Task After Performing Shunt Calibration

Hi,
I wonder if anyone can help with a problem that I am having with LabVIEW 8.5. I am using LabVIEW to measure strain gauges via SCXI 1520 signal conditioning units.
To perform a shunt calibration of the gauges I use the National Instruments example code. The problem seems to occur after the 'CalculateGainAdjust.vi' has been called. The DAQ task is passed to the calibration code, 'CalculateGainAdjust.vi' does the following:
*passes the clock configuration to the end of the VI so the original state can be restored.
*enables shunt calibration
*creates a new clock
*starts task
*reads 1000 samples
*stops task
*disables shunt calibration
*restores task state
This code executes without causing an error. If the main DAQ task is stopped and then a calibration performed the task will not restart with its original configuration and times out with the following error:
Error -200284
DAQmx Read (Analog 1D Wfm NChan NSamp).vi:11<append>
Property: RelativeTo
Corresponding Value: Current Read Position
Property: Offset
Corresponding Value: 
If a calibration is performed before the DAQ task is started then the DAQ task starts ok after calibration. It is only if the task is run then stopped to perform a calibration that the problem occurs.
Is it necessary to take into account the 1000 samples read during the calibration process? I wonder if the main DAQmx Read VI is waiting for the 1000 samples that have been already read ? Strangely enough I don't think this was an issue when the code was run on LabVIEW 8.2
Any suggestions would be appriciated
Kind Regards
Ian

Hello Ian,
Thank you for the link pointing to the downloaded examples that you have been using. More importantly, I am also glad to see that you are able to use the examples and that you found an order of operation that does not cause any error codes. You are, however, interested in continuing searching to find what causes the error in the latter case of operation, which is what I will be helping with.
Just to be sure, I have a Knowledgebase Article linked below to help avoid the error, -200284.
http://digital.ni.com/public.nsf/allkb/FEF778AD990D5BD886256DD700770103?OpenDocument
As we said, the error can occur in the latter case because something is not being setup correctly with the DAQmx task, or because the Calibration procedure is making use of the the hardware resource, and not releasing it for the DAQmx task. I will have to do more research, and reply back confirming the cause.
The examples you are using seem to be the most current, although I will take the time to compare them with those that ship with LabVIEW 8.5, which you currently have. The examples have been available since the release of the modules. As the modules have not changed, it appears that examples are at their optimum level.
Regards,
George T.
Applications Engineering Specialist
National Instruments UK and Ireland

Shunt calibration (NI 9235) when specimen not at rest.

I need to perform a shunt calibration for strain gages with 50 feet of extra lead wire. I learned from Tim Crowe at NI how to do this programmatically in LabVIEW with the NI 9235 hardware, but now I realized there's another aspect of the problem that needs to be addressed. You see, the gages will be attached to different locations on a wind tower before we have a chance to calibrate them in the program. And, unless there is no wind at the time (highly unlikely, considering Wyoming is very windy) every time we run the program and perform shunt calibration at the start of the program, there will be some initial strain being applied to the gages. Will we still be able to perform shunt calibration without messing up the data, or is there a way to perform shunt calibration just once with the lead wires before attaching the gages on site, and saving that data so it can be read into the program?
I'd really appreciate any help or suggestions you can provide.
Thanks,
Bridget

Hi Bridget,
I sent you an email on how we can go about doing a single shunt calibration for your setup, feel free to reply to it with any clarifying questions you may have.
For anyone else interested, you can create a MAX/DAQmx Task in Measurement & Automation Explorer and perform the shunt calibration in the task. The calibration coefficients are saved to that task, so if you use that specific task in LabVIEW it will use the shunt calibration done previously in the task.
-Jake B.

1520 shunt cal

Pardon the previous post, it went up prematurely.
I'm using the SCXI 1520/1314 with a quarter-bridge configuration to do a simple strain measurement with shunt calibration. I have a the standard 100K resistor installed at SCA0 and a 11,880ohm resistor installed at SCB0. When I select SCA or SCB and specify the respective installed shunt resistance, I get the error 200007 regarding shunt calibration gain adjust being out of bounds. I can only get the VI to work by selecting SCB and specifying 100Kohm shunt cal resistance (the resistance installed on SCA). With those settings, I obtain a valid gain value (around 1.003) and I can apply known strain to the gage and read reasonable values. The reverse does not work either (using SCA with 11,880ohm specified). I've checked my wiring and all seems to be correct. Is there something wrong with my VI???
Greg R.
Attachments:
strain03.vi ‏27 KB

I have found some answers… and have some more questions.
First, some of my problems with shunt cal were due to poor connections in the 1314. In particular, the SCA/SCB jumper connections are paired up with another wire (here at the QTR terminal, see Fig 2-1 on pg 2-2 of the SCXI 1520 User Manual). As noted in the manual, the method of just putting two wires into the terminal w/o joining them together can produce an unreliable connection. I soldered these wires and presto, the shunt cal began to operate w/o the error mentioned above. Then I had other problems.
Second problem is that it appears the SCA is always assumed in the DAQmx Perform Shunt Calibration (Strain).vi. To show this, I set up SCA(11,880) and SCB(no resistor), selected SCB with a DAQmx Channel property node, and specified the Shunt Resistance to be 11,880 (the resistor on SCA) using the DAQmx Shunt Cal VI. The shunt cal completed without errors, which clearly would not happen if SCB were actually used. So it seems that the AI.Bridge.ShuntCal.Select is never used by the above VI.
Third problem is that after shunt calibration, there is a large bridge offset. After some investigation, I realized that the bridge offset was the same as the shunt cal offset. It appears that the SCA switch is closed during shunt cal, but never opened afterward. I’m going to try to use the AI Parameters.VI to force the SCA to open after calibration, but my lab computer build does not currently include the “Data Acquisition” module. I’ve attached my final VI.
Greg R.
Attachments:
strain05.vi ‏33 KB

Shunt calibration CDAQ

Similar Messages

Maybe you are looking for