Different DAQ readings from Signal Express and LabVIEW VI.

[5thGen]

I am using Signal Express 3.0 and LabVIEW 8.6 to read three analog signals from a cDAQ 9172 with module 9205.  I am reading the signals single endedly using the "RSE" option in both LabVIEW and Signal Express and I have grounded the COM terminal on the 9205. In the block diagram I have tried the DAQmx boxes and the DAQ Assistant box.  A DMM reads the same values that I get in Signal Express but my VI has significantly higher voltages.  Why would Signal Express and a LabVIEW VI read different input voltages from the same signals?

Thanks,

-Stephen

[dousley]

Hi Stephen,

Some questions came to mind.

1) Could you be more specific about what the actual voltage levels are that you are reading in SE and in LV? 10mV, 250mV, 7V?

2) What happens when you vary the output voltage of the 9172, does the LabVIEW VI track that change or does it stay constant?

3) What voltage ranges do you have your channels set to in LabVIEW? and in SignalExpress?

I thought that perhaps there is some scaling or ranging error that might be causing a problem in the VI.

-Dan