TYPE OF VOLTMETER FOR VFD

[bure961]

I use a fluke t pro voltmeter as a voltage tester most days . Does anyone have a voltmeter that can be used on the out put of vfd's to get a volt reading that does not come up scrambled ? Is there a particular type of meter to use and can someone make a recommendation on one from experience? Thank you.

 

[Jraef]

Good old fashioned Simpson 260 analog iron vane volt meter. Because it is an inductive circuit just like the motor, it reacts to the PWM output in pretty much the same way a motor does, which is what you are after I suppose. Digital multimeters are not going to get there until there are at least 4 digits to the left of the decimal point on the price tag. it takes a lot of extra filtering to get a DMM to act like that old piece of iron.

Just out of curiosity though, why is this important to you? Do you not trust what the VFD is telling you?

 

[bure961]

Troubleshooting a motor/ vfd, can not tell what the motor is getting as far as voltage from the vfd when the readings are all over the place. Megged motor and that was good. Vfd tripping out in 15-20 seconds .Vfd and motor are 200' plus away from each other. Finally found a bad gear box. What kind of cost would a meter like that be ? Thank you.

 

[PetrosA]

Triplett Model 630-NA is a good one. Just saw one go on eBay for under $20. You can get new analog meters, but anything decent will cost at least a few hundred bucks.

 

[milldrone]

Is there a particular type of meter to use and can someone make a recommendation on one from experience? Thank you.

Good old fashioned Simpson 260 analog iron vane volt meter.

Just out of curiosity though, why is this important to you? Do you not trust what the VFD is telling you?

Troubleshooting a motor/ vfd, can not tell what the motor is getting as far as voltage from the vfd when the readings are all over the place. Megged motor and that was good. Vfd tripping out in 15-20 seconds .Vfd and motor are 200' plus away from each other. Finally found a bad gear box. What kind of cost would a meter like that be ? Thank you.

If you intend to do voltage measuring tests at this distance from the VFD, keep this in mind. There is a phenomenon That happens with VFD's and distance it is sometimes referred as reflected wave. It makes voltage spikes at the motor that have the ability to puncture the motor insulation. This can also happen to the meter (and you). Personally, I would not trust a CAT4 @ 1000 volt meter to be safe at that distance. Just food for thought.

 

[__dan]

The Fluke 87V has a low pass filter that can be switched in and is designed to compensate for vfd voltage output reading. Put the leads on the terminals, switch on the low pass filter, and the vfd voltage reading drops by 80 to 90 volts. Have not seen a problem with the steadiness of the reading and not sure if my earlier version 87 has that feature.

 

[__dan]

And at 200 ft from the vfd to the motor, I would be thinking about checking the manufacturer's spec for allowed distance and adding a line reactor or output filter if called for by the manufacturer.

 

[junkhound]

Scopemeter.

We always use a Fluke scopemeter or TEK scope for anything other than clean 60 Hz.

You can get a used first gen Fluke 123 off various online sellers for under $250.

 

[iwire]

I would follow Jraef's suggestions without hesitation.

I also have a Simpson 260 that could be for sale if the price is right.

 

[gar]

140626-0946 EDT

Jraef and others:

A Simpson 260 is not an iron vane instrument. It is a moving coil instrument, described as a Weston-d'Arsonval type movement.

Older 260s used a pivot and jewel suspension. Newer units have a taut-band suspension that virtually eliminates hysteresis.

Mechanical inertia of the Simpson determines its mechanical bandwidth. In AC mode with a sine wave at 10 Hz there is very little needle oscillation. At 8 Hz there is about 1 to 2% flutter. This was measured on a taut-band 260. AC rectification occurs at the input, and the integrating (averaging) function occurs after rectification. The average function cannot be applied before rectification because that would simply reduce the amplitude of the AC signal.

You can use the Simpson 260 as a ballistic galvanometer in the 10 to 100 ms range to measure pulse duration. Basically for short time intervals the 260 looks like a mathematical integrator.

An RC filter at the input to a digital voltmeter can smooth out variations in the DC mode, but will create problems in the AC mode.

.

 

[mike_kilroy]

I think it may be worth reiterting some previous comments as to WHY BOTHER?

Like many others, I have been diagnosing all kinds of vfd - and like your typical example case here - vfd blamed - issues since about 1975. If I had to guess, I would say I have diagnosed similar cases to yours around 2500 times. Of those, I used an ld mechanial analog meter to measure actual motor voltage as part of the diagnosis maybe

 

[mike_kilroy]

I think it may be worth reiterting some previous comments as to WHY BOTHER?

Like many others, I have been diagnosing all kinds of vfd - and like your typical example case here - vfd blamed - issues since about 1975. If I had to guess, I would say I have diagnosed similar cases to yours around 2500 times. Of those, I used an ld mechanial analog meter to measure actual motor voltage as part of the diagnosis maybe

- no edit button and it posted while writing - Grrrr!

THREE TIMES! And none helped solve the issue.

I think you do not need to measure output voltage, especially today since all those vfds will tell you outpu voltage and current anyway. My suggestion is save your $20 ebay money and buy a case of beer instead.

 

[Besoeker]

I use a fluke t pro voltmeter as a voltage tester most days . Does anyone have a voltmeter that can be used on the out put of vfd's to get a volt reading that does not come up scrambled ? Is there a particular type of meter to use and can someone make a recommendation on one from experience? Thank you.

Most VFDs that I've dealt in at least the last decade have output voltage as a parameter that can be displayed on the MMI keypad.
Why would you want to put yourself at personal risk sticking a meter on the output terminals?

 

[John Valdes]

Digital and analog meters can read low voltage (0-600volts) VFD outputs accurately and safely.

It does not matter if you have a Simpson or a Fluke. They both work. And both will be very accurate.
Using the VFD panel display readout is not very accurate. Good for reference, not troubleshooting.

 

[mike_kilroy]

Digital and analog meters can read low voltage (0-600volts) VFD outputs accurately and safely.

Hate to disagree, but most digital meters I have tried fail miserably on this PWM output. You DO realize this output (assuming a 460v drive) is either 0vdc, 650vdc, or 1300vdc, irregardless of speed, depending on when the digital meter samples it, right? But that is just my experience over many years.

Using the VFD panel display readout is not very accurate. Good for reference, not troubleshooting.

Hate to disagree, but if the vfd generating the output volts and current cannot tell you EXACTLY what it is putting out, sounds like you have a really really cheap poorly designed vfd from China made in the moonlight hours by pirates in someone else's vfd plant, maybe named Pofoong or something, although they often don't even put ANY name on them. But that is just my experience over many years.

 

[Besoeker]

Using the VFD panel display readout is not very accurate.

How exactly have you validated their accuracy?