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 hel=
p me
decide between these two meters.
>
> It came down to the question of whether the variable-frequency drives I c=
ome
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 moto=
rs
on old printing equipment to give them a 2nd life.
>
> I have no idea how many (ie, percentage) of VFDs are "noisy" that will ma=
ke
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
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