any idea how to monitor multiple floating singal sources with one DAQ?

[mchips]

I need to measure voltages from twenty sensor outputs which are powered by separate batteries. The sensors should be electrically isolated each other. If I use differential mode without connecting battery returns to AI GND, the common mode of sensor outputs will create errors in measurement. Is there a way to do this?

[Jason_D]

Hi mchips,

Do you already have hardware or are you looking to purchase something that can accomplish this for you? 

What kind of voltages are we talking about?  We have boards that can do ch/ch isolation, are you sure you need this or do you just need better grounding of each signal?  What kind of CMRR (common mode rejection ratio) are you looking for?  Lastly, how fast are we looking to take these measurements?

Simply addressing your question about the differential mode connection I think you would want to make sure that you are using bias resistors.  Please see:

 https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

More Specifically the picture attached.

Sincerely,

Jason Daming

[mchips]

I am looking for ch/ch isolation data acquisition for at least 20ch and signal range is 1mV to 1V. I am taking one data every 5 seconds or so.

[Jason_D]

Hi mchips,

For as many channels as you have and at this comparatively slow rate I think that getting a switch to multiplex through your lines and then use DAQ to take your readings is ideal.  You would want a switch like the 1163R (https://www.ni.com/en-us/support/model.scxi-1163r.html) and a DAQ device that corresponds to the type of sensors you have. 

If you would like more detailed assistance, I can arrange for a Field Sales Engineer to contact you and possibly even give you a visit.  Otherwise you are more than welcome to call in to me at 1-866-275(ASK)-6964(MYNI) and reference your service request # which is 1243695.

Sincerely,

Jason Daming

[mchips]

thanks for info. I was thinking about multiplexing also. I am not sure though the outputs do not spike when they are switched in. Hopefully they don't since they are measured in differentially.