NI 9237 Not reading correctly

[ASTDan]

Hello,

I have a NI 9237 with a Compaq DAQ Chasis.

I have hooked up a power supply to the AI+ and AI- inputs.

When I read my signal from the NI 9237 with MAX I get the attached waveform.  I don't see this waveform when I hook up my scope to the input signal.  The Peak of the waveform seems to be the correct measurement.

Any Advice?

Thanks

Dan

 

[ASTDan]

Here is the screen shot

[Wilfried_71]

I think it's not a good idea to connect directly a power supply ... except if you want to burn out your module !

A wheatstone bridge must be connected to the module, not a voltage ...

[Speedy_Badger]

Hello Dan,

From the looks of the waveform you included you are getting a current path somewhere. The 9237 is a bridge based acquisition module. There are internal completion resistors that are used depending on which bridge mode you select. The closest you can get to a DAQ device in differential mode would be to use Full Bridge. This should result in a signal close to the square wave you would like to see (I'm assuming this is the goal). You will have to take into account excitation voltage and some other factors to make the magnitudes correlate with your scope results, but the overall shape should be correct.

I have a few questions as well:

1. When you say power supply, are you referring to a signal generator?

2. What bridge mode do you currently have selected?

3. Was I right to assume you should be seeing a standard pulse (square wave) waveform?

Let me know more about your application; hopefully we can get you the results you expect!

Regards,