DC offset on AC signals

[kasula]

Hello,

    I am using NI PXI 6289 DAQ card with NI PXI 8106 microcontroller on PXI 1042Q chasis. I have a question regarding the DC offset that I observe on the AC signal. I have 2 dc volatges and 1 ac voltage signals to measure. When I connect only the ac signal I do not see any offset on the signal. But when I connect the dc voltages on other channels I see DC offset on the AC signal. Is there any way to get rid of this offset?

T hanks,

kartik 

[John_P1]

Hi Kartik,

Like all multiplexed boards, the 6289 is susceptible to what we call "ghosting" under certain circumstances (high source impedance, large voltage difference between channels, fast convert rate... etc.).  I suspect this is what you are experiencing.  If this is indeed the case, you can refer to the following link for advice how to correct the issue:

How Do I Eliminate Ghosting From My Measurements?

Be sure to post back if you have any follow up questions.  If the problem is not actually ghosting, you might want to double-check how you have everything grounded in your system (although I believe the issue is in fact ghosting).  Let us know how it goes!

Best Regards,

John