My analog channel's response always get satuaraed

[ni_op]

Hello dear,

 i am facing problem while taking data from DAQ-6251 connected on my PXI system. The response obtain from channel AI0 is getting saturated means, initially it starts from some finite value and then increase/decrease (RSE/NRSE is selected) automatically.

Please suggest me.

om

[Travis G.]

Hello om,

Do you have any voltage source connected to AI 0 of your PXI-6251?  If there is no actual voltage connected to that channel, the ADC in the device will float to either the positive or negative limit of your measurement scale.  This is called railing, and is entirely expected behavior.  Since your trying to take a ground referenced measurement (RSE or NRSE), try connecting a floating signal source like a AA battery across the AI 0 and AI GND (RSE) or AI SENSE (NRSE) to see if you can acquire an actual voltage.  For more information about connecting signals to your DAQ device, take a look at the M Series Help or the following tutorial:

Tutorial: Field Wiring and Noise Considerations for Analog Signals

I hope this helps,

Travis G.
Applications Engineering
National Instruments
www.ni.com/support

[ni_op]

Dear Travis,

Thanks for your reply. The problem which i am facing is, when i connect my capacitive sensor (PVDF, or Bi-morph snesor) then also it gets saturate and this happens maximum times not always. and when i connect my sensor with BNC 1120 in grounded mode or floating source mode then alos it happens.

Thanks

om

[Ryan_V[DE]]

om,

What type of excitation do your transducers require? As they appear to be piezoelectric, I would assume that they require some form of current excitation. Are you providing this? Have you tried to measure the voltage with a DMM or a scope? If you try to measure a battery in RSE (floating source) mode, do your read the correct voltage? Please let us know.

Hope this helps,