measuring high level signals

[TommyHelter]

Hello all,

I need to measure high voltages (120, 277 and 480) harmonics (up to 64th harmonic of 60 Hz signal).  What would be the best (lowest distortion) method of stepping these signals down so as to sample these voltage waveforms for harmonic analysis.

Tom Held
(TommyHelter)

[Ryan_V[DE]]

Tom,

As far as I know, we don't offer any solutions that will work directly with your specifications. This is an interesting application as you require both high voltage and bandwidth. I would recommend creating a custom high-impedance voltage divider in order to bring your signals within range of your DAQ card. In order to be safe and prevent damage of the DAQ card, I would also implement some form of external clamping circuitry to supress any voltage spikes you may see on your inputs.

Hope this helps,

[TommyHelter]

Makes good sense.  Thank you.

Tom H.

[Logan_K]

Just to clarify your application - the maximum limits of your signal are going to be 480V at 3,840Hz (64 x 60). We provide two solutions for measuring up to 480V:
1) SCXI-1125 with the TBX-1316 attentuator. This only provides a bandwidth of 500Hz.
2) PXI-4071 DMM/Digitizer - in the isolated digitizer mode, this board has a bandwidth of 500kHz at up to 700V.

So, given these two high voltage options, the only one that provides the bandwidth that you will need is the PXI-4071 isolated DMM.

Regards,
Logan K

[AnalogKid2DigitalMan]

I would advise electrical isolation between the divider and the DAQ card too; either optical or galvanic, if possible in case of a component failure. Mainly to protect humans, but will also protect PC and devices connected to it.

Is there off-the-shelf test equipment available to do these tests? If so then maybe interface via USB, GPIB, or serial to transfer data to PC for further analysis?

[TommyHelter]

As you can see, nad as stated, it is hard to find both high freq and high voltage "off-the-shelf" without them being part of a full (proprietary) test system (which is not hwta I want to do).

I thank you all for your further comments.  Optical iso sounds like the best approach.  I will also take another look at the NI products you have suggested.  I would be doing waveform capture so I think the DMM will not really suit me here.

Thanks again.   This is such a great forum with real knowledgeable people.

Tom H.

[Ryan_V[DE]]

Tom,

Actually, the 4071 has a waveform mode where it can acquire 10 bits of resolution at 1.8MS/s, up to 700VAC. I was thinking that you already had a DAQ card and were looking for external signal conditioning - my apologies. Please give us a call at 1-800-433-3488 if you would like more information on this device.

Hope this helps,

[TommyHelter]

Excellent!  Thank you.
Tom H