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# Digital Multimeters (DMMs) and Precision DC Sources

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## PXI-4065 AC Measurement Speed

Hi,

I am looking to configure a PXI system that will consist of 4 PXI-4065 DMMs.

For my application, I would like to measure input voltage/current (DMMs 1&2) and output voltage/current (DMMs 3&4) of a variable transformer.
I would like to capture the AC voltage and current output as I sweep the transformer from 0-100% across a resistive load.

My question is how fast can the 4065 read a 50/60Hz AC signal?

From the specsheet I see that AC measurements at 10-100KHz bandwidth is 1S/s @6.5 digits of resolution. I’ve also read in other post about getting 50-100S/s by changing resolution and aperture, but these values seem to come from the DC specifications table. So as you can see, I’m a little confused on the measurement speed and 1S/s is too slow for my application.

Ideally I would like to read peak rms values anywhere from 0.1-0.25 seconds to obtain a smooth looking voltage and current curve on an xy graph.

Any help/explanations is greatly appreciated.

best regards,

Jeremy

Message 1 of 6
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## Re: PXI-4065 AC Measurement Speed

I would say wrong device .. you don't want the settle time of the AC to DC converter that is used to measure AC

You need 8 fast synchronious channels  like the 4300 or 4310 (not shure if they fit to the following..)

and a RM-26999

to measure the high voltages and currents in the needed bandwidth

yepp another price tag

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Message 2 of 6
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## Re: PXI-4065 AC Measurement Speed

Thank you for your response Henrik_Volkers. Yes I figured it would be too slow but figured it was worth asking.

In previous applications I just used digital power meters, but for this design, I was trying to get away from external instruments and have everything built into 1 system and write a calibration routine myself (avoid my quality department)

Another solution might be to use a CT with a dc volt or current output and an RMS voltage converter (AC in, DC signal out) but I haven’t been able to find converters that are fully linear from 0-100% full range.

Best regards,

Jeremy Hall

Message 3 of 6
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Solution
Accepted by topic author JHall92

## Re: PXI-4065 AC Measurement Speed

Try adjusting the resolution and the settling time to achieve faster measurement speeds.

A 5.5 digit resolution looks like it may give you the measurement speed you desire.

The links below describe the 4065 AC measurement, measurement cycle, and default settings. You can change default settings in your program.

NI 4065 DMM Measurement Cycle - NI

AC Voltage - NI

DMM Measurement Defaults - NI

Message 4 of 6
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## Re: PXI-4065 AC Measurement Speed

AC measurements are pretty slow on 4065. If your application can afford it, then select a lower Digits Resolution value.

FWIW, PXIe-408x series are a lot faster at this. They also have better specs 🙂

Marcos Kirsch
Chief Software Engineer
NI Driver Software
Message 5 of 6
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## Re: PXI-4065 AC Measurement Speed

Thanks guys for the responses.
After digging a little deeper into the NI-DMM documentation provided above, I found that changing the resolution could give measurement speed I desire.
Fortunately my application only requires measurements between 0-280VAC with 1 decimal place. So I believe 4.5 digits will work.

Message 6 of 6
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