How to set the commond-mode voltage for PXI-6229

[doca_walka]

So I am using the PXI-6229 to capture 3 different signals, and then analyze them in LabView; one signal is an AC voltage output, and the other 2 are sensor voltages (~5.7V). I have noticed that when the AC voltage exceeds the Maximum Working Voltage the voltages of the 2 sensors become unreliable. Through some reading and poking around on Google, it appears that if I can apply a voltage to the Common pin of the board then I will be able to measure the larger voltages - but I am not sure if this will fix the issue I am having.

When the AC voltage signal hits ~10.6V both of the sensor signals go to that same value, despite being wired to a 5.7V power source. Any help and/or clarification on this issue would be greatly appreciated. 

Thank you

[cstorey · Accepted solution]

What you really want to do is attenuate that AC signal by a known amount before it get to the card. Say divide by 2, then multiply your measurement value by 2 in software to account for the attenuation.

Have a look here for how to setup a voltage attenuator.. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/vdivac.html

Craig

[doca_walka]

Yeah, I ended up rectifying the signal and then running it through a voltage divider, and then multiplying that amount back in the software.