High Voltage Acquisition

[leachdor]

Hi all, Need some help finding some hardware.  We're looking to monitor phase balance between 3 phases.  The source will be 480VAC, that we would like to perform an FFT on each leg to leg (3 total) and make sure the peak at the fundamental is correct on each. (And a few other things)Simply from hardware does NI make hardware capable of taking in such a high voltage signal? (3 channels would be ideal)Thanks

[Roberto Bozzolo]

I don't know if there's a suitable hardware for these potentials but for security reasons you should consider to isolate the acquisition system (and the operator that is using it) from the field by means of transformers that both isolate the signal and can reduce the voltage level to a resonable value. According to regulations (at least european ones) the transformers should have a grounded shield between primary and secundary winding, otherwise the last one must be grounded to guarantee that the instrument connected is not raised to an unsafe potential.
We normally use such transformers but we only are interested in voltage value and we do not perform FFT and other signal analisys: in your case you should possibly consider if the slight phase shift introduced by the transformers influences your measures.

[leachdor]

Hi Roberto, Your right on that last part, we can't step it down as it would change the harmonics a bit on the FFT.  Thought about that idea, and "management" made it a requirement to perform the analysis on  raw data.  (Which for this application  I would agree.)Just to say it in a different way, basically we need a waveform of the voltage across two legs.  I think I said we need 3 i/o, thats actually 6. (Two per pair)  So we would plug phase A in, Phase B in which would give us a voltage waveform between the two...then we need to view the harmonics on that signal.  Software end won't be an issue, but you know 480V is standard in an industrial environment, it would be hard to believe NI doesn't have hardware for it?I saw on another post there was an SCXI card that could support up to 1000V, but the p/n he listed brings up a card that supports only 300V....must have changed since then....Appreciate any further help!Don

[Chris R.]

There's the <a href="http://sine.ni.com/nips/cds/view/p/lang/en/nid/14857" target="_blank">PXI-4071 DMM</a> that can measure up to 1000V peak. It's a single-channel device. You might also have some luck using a <a href="http://www.ni.com/digitizers/" target="_blank">digitizer product</a> with some sort of <a href="http://www.tequipment.net/LinkInstrumentsADF25A.html" target="_blank">attenuating probe</a>. ChrisMessage Edited by Chris R. on 07-31-2008 11:29 AM