How do I read the excitation Voltage from an NI 9237

[dclancy1]

Hello everyone,

I am new to labview and have some previously set up code I am trying to work with in a research situation. We have a strain gauge connected to an NI 9237 module which in turn is connected to a cRIO-9022. 

Our issue is that during our reading there is an constant upwards trend in the data that occurs over time. We want to check the excitation voltage the 9237 is sending to the strain gauge in software so that we can (hopefully) properly account for any drifting that is occuring in the excitation voltage. In the attached project I have all our code.   

Again, any advice or guidance would be appreciated.  Right now the excitation voltage is set to 5V and we have a constant input of 5V in the VI but I would like to replace that with a reading of the excitation voltage.

Thanks in advance, 

Daniel

[dclancy1]

Can anyone please help me? I need to determine whether I can read the excitation voltage of the NI 9237 in scan engine mode or if I must switch to FPGA mode. 

If I must switch to FPGA mode can anyone assist me with that? The original code is listed in the above message as an attachement.

Thanks in advance,

Daniel

[crossrulz]

If you have a module with an Analog Input, I don't see why you couldn't wire the excitation up to an AI and log it that way.

[dclancy1]

Haha, thank you! I just came to this realization about the same time you wrote me this message. 

Thank you regardless.

Daniel

[xseadog]

Hi

Have you attached the voltage sense lines/ cables?

If disabled the supply voltage can drift.

The cables should be attached to the strain gauge supply  ( posivtive & negative)  terminals.

xseadog

[Brad_K]

Hi Daniel,

The NI 9237 performs ratiometric measurements to prevent variations in the excitation voltage from affecting measurement accuracy. This white paper talks about the NI PXIe-433x but much of what it describes is also true of the NI 9237: Measuring Bridge-Based Sensors

This might also be relevant: How Is Temperature Affecting Your Strain Measurement Accuracy?

Brad