Shunt Calibration Failed

[Sunkistist]

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!

[robo_Jeff]

Hi Sunkistist,

This error can be caused by one of 3 things:

1. 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.
2. Improper physical connections. Again, we can rule this out for the same reasons as #1.
3. 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

[Sunkistist]

Thanks for the reply, I haven't had a chance to use the documentation you supplied until today.

Well it would appear I need to have the 9237 unit calibrated... It's now throwing the above error with the stock example. We've even checked the strain gauges through a different device. Though oddly enough I can get semi-decent strain data out of it.

[Sunkistist]

Just to check if I'm using the stock example correctly... I should:

1. Initiate signal acquisition

2. Enable "Offset Null"

3. Wait >1 second

4. Switch "Offset Null" off

5. Enable "Shunt Cal"

5. Wait >1 second

6. Turn "Shunt Cal" off

and I should now have accurate strain readings from the gauges?

[robo_Jeff]

Hi Sunkistist, 

No. You just enable offset nulling and/or shunt calibration and run the VI. As you can see from the block diagram, the nulling and/or shunt calibration occurs before the task is started. See Help>>Find Examples>>Hardware Input and Output>>DAQmx>>Analog Input>>Strain - Continuous Input.vi, for example.  Also, this forum discusses the issue.