What kind of reading would you get w/ Simpson 260 on VSD output?

[Electric-Light]

Some Fluke meters have a digital filter they call "Lo-Pass" which ignores high frequency component of VSD output that motors ignore. Without using it, it will read high frequency components and read a higher value.

http://support.fluke.com/find-sales/download/asset/2155848_a_w.pdf

In another article on Fluke, it said that techs prefer to use analog meter on VFD, because "they display voltage as the motor sees it", but when I checked the specs on Simpson 260, the AC bandwidth is something like 100KHz.

So... when you hookup a Simpson 260 to a VSD, would it read just like a common DMM because of its 100KHz bandwidth, or would it see the voltage as seen with Lo-Pass enabled Fluke?

 

[gar]

100922-1348 EST

ElectricLight:

A Simpson 260, at least mine, do quite well above 100 kHz. Works to several hundred.

My 40 year old Simpson 270 is down 3 DB (.707) at 900 kHz.

My Fluke 27 starts to rise about 40 kHz, then falls off of a cliff about 300 kHz.

,

 

[Electric-Light]

100922-1348 EST

ElectricLight:

A Simpson 260, at least mine, do quite well above 100 kHz. Works to several hundred.

My 40 year old Simpson 270 is down 3 DB (.707) at 900 kHz.

My Fluke 27 starts to rise about 40 kHz, then falls off of a cliff about 300 kHz.

,

So, in other words, the 260 will have the same problem of including high frequency component that motor does not respond to? Fluke 87 offers a 3dB @ 1KHz Lo-pass filter option to ignore high frequency motors do not respond to.

 

[steve66]

A VFD output would have a Pulse width modulated signal. So a 100 KHZ PWM is going to have a square wave that has components at higher frequencies. The "corners" of a square wave have components at harmonics up to infinity.

So just because a meter has good response up to 100KHZ doesn't mean its going to accurately read a square wave at 100KHZ.

But if it measures up to several hundred KHZ, like Gar said, it should read pretty close to a good DMM, even for a 100KHZ square wave. So it wouldn't work like the meter that has a low pass filter.

Unless the meter doesn't read true RMS. If it doesn't read true RMS, it may read a voltage more like the motor sees it. (I.E - it wouldn't see the square corners on the PWM signal.)

 

[steve66]

Lots of 260 manuals here:

http://simpson260.com/downloads/downloads.htm

I pulled up the series 8 owners manual. It doesn't look like it is true RMS. THere is a note about being calibrated to show the RMS value of a sine wave.

So that leaves the question - How will a meter like this respond to a PWM VFD output??

 

[Electric-Light]

I don't understand why you bring up true RMS as anything remotely relevant.

We could have 120v 75kHz power that a heating strip may respond like 60Hz power, but motor would not run at all because the impedance is so high at 75KHz it basically hinders conduction.

 

[gadfly56]

Gar, steve66:

The OP is interested in NOT having his meter respond at the high kHz range.

 

[steve66]

Gar, steve66:

The OP is interested in NOT having his meter respond at the high kHz range.

Yes, understood.

I don't understand why you bring up true RMS as anything remotely relevant.

We could have 120v 75kHz power that a heating strip may respond like 60Hz power, but motor would not run at all because the impedance is so high at 75KHz it basically hinders conduction.

Your VFD output will probably be something like a 20 KHZ pulse width modulated voltage. So your Simpson 260 meter will measure the 20 KHZ output voltage, not the 60 Hz filtered voltage that you want to see.

But your 260 meter won't even measure the 20 KHZ signal right, because it will be assuming it is a 20 KHZ sine wave.

So I think I'm just confirming what you already knew: If you want to measure the VFD output, either find a meter with a very low frequency range, or get the one with a filter.