# Fluke 87V - Low-Pass-Filter



## HARRY304E (Sep 15, 2010)

Hans Gebert said:


> Hey all,
> I'm new but nevertheless have a question which is quite important for me.
> I'm considering to buy a new Multimeter but I'm not sure if I want a Fluke 83-V or an 87-V.
> The feature whitch makes the difference is the Low-Pass-Filter the 87-V has. Fluke states it is for measuring VFDs to get the correct voltage readings (without noise...)
> ...


Welcome Hans..:thumbup:


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## fanelle (Nov 27, 2011)

The other thing separating those meters is the 87v is true rms and the 83v is average responding. If you are going to do and industrial work or work with vfds plcs or any other instrumentation or controls go for the 87v


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## Hans Gebert (Jan 28, 2013)

Ok that point i didn't see...so it'll be the 87-V..nevertheless..any comments on that low-pass-filter?

Anyone who can explain this topic profoundly will get a big hug from me :E


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## Big John (May 23, 2010)

A VFD has what's called a carrier frequency: It's the number of times per second the transistors fire to create the waveform that's going to the motor. For example, even though the motor might be running at 45Hz, the VFD might very well be adjusting the voltage at 2kHz to create that 45Hz wave form.

If you take a meter without a low-band pass and connect it to a VFD to determine the frequency driving the motor, more than likely the meter is going to be overwhelmed by that carrier frequency and will read 2kHz no matter what the motor is running at.

Low-band pass ignores everything above the low-frequency band, and allows you to monitor the power instead of the carrier signal. If you plan on doing any drive work, it's a must-have.


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## stuiec (Sep 25, 2010)

Big John said:


> A VFD has what's called a carrier frequency: It's the number of times per second the transistors fire to create the waveform that's going the motor. For example, even though the motor might be running at 45Hz, the VFD is might very well be adjusting the voltage at 2kHz to create that 45Hz wave form.
> 
> If you take a meter without a low-band pass and connect it to a VFD to determine the frequency driving the motor, more than likely the meter is going to be overwhelmed by the carrier frequency and will read 2kHz no matter what the motor is running at.
> 
> Low-band pass ignores everything above the low-frequency band, and allows you to monitor power instead of carrier signal. If you plan on doing any drive work, it's a must-have.


 
Its all about the hugs with you isn't it :no:


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## Big John (May 23, 2010)

stuiec said:


> Its all about the hugs with you isn't it :no:


 I wasn't gonna reply at all until I saw the part about the hug. Then I put some effort into it.


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