Why SCC-AI03 keeps saturating?

[zenith]

I have three SCC-AI03 voltage input modules.

One of them keeps saturating. Both channels!

Input signal comes from a high current to voltage (within +/-10V) converter.

I am not sure if the converter has its own referenced GND.

Questions are:

1) How to check if the converter has its own referenced GND?

2) Is there any effictive cure to this saturation issue?

3) SCC needs DAQ operated in NRSE mode. Is AI-GND and AI-SENSE shorted together in SCC modules?

4) The user guide of scc AI modules suggests wire a resistor between negative input and AI-SENSE on the SC-2345 board when there a high common-mode voltage is present.

     How could I know whether there is a high common-mode voltage present or not? Can I use a DMM to measure the common-mode voltage? If yes, please tell me how?

     Is saturating caused by the present high common-mode voltage?

Thanks for your time to view this post and please give me suggestions or hints. ^_^   

[MickeyD]

Hey Zenith,

I am sure we will be able to come up with a solution to your saturation issue. Your converter is really just a resistor taking a current and making a voltage I believe, so I doubt it has a referenced ground, but if it is plugged into the wall it might.  The AI- GND and AI-SENSE are shorted together in the SCC modules. 

You said that only one of the three  SCC-AI03 modules is saturating.  What is the difference between the saturated one and the other two modules?  Are the inputs the only difference or are they all the same?

Have you tried switching the modules around to see if you can get expected behavior for this measurement with one of the other modules?

Without some more information it is very difficult to say whether a common mode voltage is causing your problem, and I would say the best way to check is to use a DMM to measure the voltage difference between the ground on the SCC-AI03 and your input signal, and see what that value is.  Please get back to me with that information and we can figure out what is causing this difficulty.

Have a great week,

Michael