Discrepancy between VIs with NI 9237 & DAQ Assistants

[szlats]

I have a load cell hooked up to a NI 9237 module in a cDAQ 9174. I have two separate VIs that read the raw load cell output (mV/V). Both VIs are acquiring through a DAQ Assistant. Both DAQ Assistants are configured identically, yet they output different values. One will read around 0.003 mV/V with no load while the other reads 0.03 mV/V -- an order of magnitude difference. Any thoughts on why this is? Thanks!

[Roohcifer]

Hello,

My first thought is that you may have accidentally set the sensitivity of one DAQ assistant to 10x the other, which is why you see one order of magnitude difference.  (This is easy to overlook since the decimal has just moved a place.)  If you copy one DAQ assistant over to the other VI, do you still see the same behavior?  If the behavior is identical between the two when you copy from one to the other, then the issue has to do with the configuration.  You can also try recreating each DAQ Assistant on each VI and reconfiguring from scratch.  That should remove the difference.  If you still see the discrepancy after all of these steps, then please post the two offending versions of your code so we can take a look.

Regards,

[szlats · Accepted solution]

Thanks David,

I finally tracked it down to a null-offset calibration being applied to one DAQ Assistant and not the other. Is there a way to remove this offset in DAQ Assistant? It didn't seem obvious. I only noticed after converting to DAQmx code and was able to remove it there.

[Roohcifer]

Hello,

You can configure offset nulling and shunt cal by clicking on the "Device" tab in the DAQmx configuration window.  Click on "Strain Calibration...", and there are check boxes for offset nulling and shunt cal.

Regards,