Fluke DMMs and VFD motor drives

Nov 10, 2009 4 Replies
D

I'm considering the purchase of a new Fluke DMM. I like the low-impedance feature of the 117, but the low-pass filter feature of the 87 is also attractive.



I had a conversation with a support engineer at Fluke today to try to help me decide between these two meters.



It came down to the question of whether the variable-frequency drives I come across will have noisy outputs which the low-pass filter will be helpful in dealing with.



Among other services, I install some (3-phase, mostly) VFDs for 230v motors on old printing equipment to give them a 2nd life.



I have no idea how many (ie, percentage) of VFDs are "noisy" that will make measurement difficult with a DMM w/o low-pass filtering. Is this a common problem?



If you've got some experience in this area I'd like to hear your comments.



Thanks, Dave



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D

The Fluke 289 has both a low pass filter and LowZ input impedance. But you get the annoyance of the short battery life and graphical display.

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Check out the new Fluke 28-II rugged meter, it also has the filter, but no lowZ:

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Quote: "Unique function for accurate voltage and frequency measurements on adjustable speed motor drives and other electrically noisy equipment (28 II)" but that is just the normal low pass filter feature.

Dave.

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D

Modding a meter can potentially make it unsafe, so not a good idea to recommend. The Fluke 289 has both features, so no need to bodge it.

Dave.

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J

I use my 289 as a clock since I don't have a clock in most places I am at, except my desk or bench. I can't wear watches.

P.S. I wish it was a little faster in response.

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T

FYI, the Fluke 43 PQAs on campus show the whole mess of PWM up at

15kHz or whatever they run them at. I forget the VFD type in the lab, but obviously it produces a PWM ("noisy"?) output. It still reads correctly, as far as I know (RMS, power factor, ...).

Tim

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