Measuring output of a VFD
Measuring output of a VFD
(OP)
Greetings, I'm trying to measure the output voltage of a vfd (yaksawa pc606) thats programmed for a max voltage of 200 v.
Using 2 different t-rms dmm's i am measuring appx. 250v.
Are the dmm's leading me "astray" because of the high switching freq??
Thanks in advance
Using 2 different t-rms dmm's i am measuring appx. 250v.
Are the dmm's leading me "astray" because of the high switching freq??
Thanks in advance





RE: Measuring output of a VFD
Unless your DMM specifically says it reads true RMS voltage, it does not. If so, you are reading peak voltages of the pulses. Either get a DMM with true RMS sensing, or believe it or not, a cheap little analog VOM works well for that. I carry one around specifically for that purpose. It's not good for much else, but the old iron vane meter has no choice but to show you RMS voltage on a PWM output.
Quando Omni Flunkus Moritati
RE: Measuring output of a VFD
and an Amprobe (can't remember the model). Both are true-rms
DMM's. I'll try using my simpson 860.
RE: Measuring output of a VFD
your meters are showing the true rms value correctly, which is always approximately the DC-link voltage.
The reason is that they take into consideration all frequencies involved up to several kHz.
If you want to measure the RMS-Value of the fundamental you can use a low pass filter consisting of a suitable RC-combination to remove the switching frequency.
RE: Measuring output of a VFD
Using a Simpson and a 1940's vintage Weston I measured 200-202 vac.
I understand now,Question answered.
Till next time,
Underling99
RE: Measuring output of a VFD
Several million years ago when transistor PWM drives first started coming out most manufactures recommended that you do not use a true RMS DMM to check output voltage. The originally recommended was that you use an analog meter (Simpson, Triplet, etc.) to check output voltage. In house we built a capacitor filter that gives us a sinusoidal wave shape for DMM's. You may want to contact yaksawa or a company that packages yaksawa drivers and get their recommendation.
Good Luck
RE: Measuring output of a VFD
RE: Measuring output of a VFD
RE: Measuring output of a VFD
http://www.ece.uwaterloo.ca/~ece100/lab/il1notes.pdf
See section 1.3 ... on page 5 ...for discussion on Crest Factor influence on digital meters.