4204 measurement device (grounding question)

[MatthieuD]

Hi Guys,

I have a PXI 4204 installed in my system. I would like to use this board to read some signals from a synchro resolver...

The property of a synchro is that you get 3 different amplitude voltages in phase, or out of phase compared to an excitation voltage (for the synchro). (the synchro acts as a rotating transformer). these voltages are referenced as V1, V2 and V3.

The voltage level is around 30V Peak. I would like to measure those 4 signals (excitation and synchro signals) with that board, but I m a bit worried of common mode voltages (These measurement should be taken between outputs V1 to V2, V2 to V3 and V3 to V1), and don't have a real common gnd line...

Would this be safe for both my card and my syncho?

Thx a lot

Matthieu

[NI-Bongo · Accepted solution]

Hi Matthieu,

The PXI-4204 is has overvoltage protection to handle up to +/-110 Volt transients.  It can measure between +/- 100 volts.  From my understanding of your setup, the largest swing you might see with your setup is 60 volts if measuring differentially (if V1 were at -30 Volts and V2 were at 30 Volts, say).  If your synchro resolver is riding 40 VDC above the DAQ system ground, then common mode voltages may be a problem.  Otherwise, I don't think you should have a problem.  The DAQ device has a fairly high input impedance (2 MOhms differentially) and should in no way damage the synchro resolver.

PXI-4204 Product Manual and Specifications
http://www.ni.com/pdf/manuals/373529c.pdf

Let me know if you have more questions about this or if this response wasn't clear.