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From: DaveC on 10 Nov 2009 15:12
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 help me
decide between these two meters.

It came down to the question of whether the variable-frequency drives I come
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 motors
on old printing equipment to give them a 2nd life.

I have no idea how many (ie, percentage) of VFDs are "noisy" that will make
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

From: Jon Slaughter on 10 Nov 2009 15:34
DaveC wrote:
> 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
> help me decide between these two meters.
>
> It came down to the question of whether the variable-frequency drives
> I come 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
> motors on old printing equipment to give them a 2nd life.
>
> I have no idea how many (ie, percentage) of VFDs are "noisy" that
> will make 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

I would go with the 87 as it seems to be better in just about every way
looking at the specs. It has better accuracy and resolution in almost all
categories.

From: DaveC on 10 Nov 2009 15:46
> I would go with the 87 as it seems to be better in just about every way
> looking at the specs. It has better accuracy and resolution in almost all
> categories.

Accuracy and resolution are great, but for me in my work these really come in
second to features (the low-Z and low-pass features, specifically).

If it were not for the lack of a low-Z feature I'd buy the 87 in a second.

But I need to determine if -- as pertains specifically to VFD voltage
measurement -- the 117 is deficient (ie, does noise really cripple voltage
measurement, and how often is this a problem when working in VFDs) in this
respect.

Thanks.

From: Jamie on 10 Nov 2009 18:52
DaveC wrote:
> 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 help me
> decide between these two meters.
>
> It came down to the question of whether the variable-frequency drives I come
> 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 motors
> on old printing equipment to give them a 2nd life.
>
> I have no idea how many (ie, percentage) of VFDs are "noisy" that will make
> 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
>
A scope meter is the best tool for such a job..

From: David L. Jones on 10 Nov 2009 18:42
DaveC wrote:
> 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
> help me decide between these two meters.
>
> It came down to the question of whether the variable-frequency drives
> I come 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
> motors on old printing equipment to give them a 2nd life.
>
> I have no idea how many (ie, percentage) of VFDs are "noisy" that
> will make 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

The Fluke 289 has both a low pass filter and LowZ input impedance. But you
get the annoyance of the short battery life and graphical display.
http://us.fluke.com/usen/Products/Fluke+289.htm

Check out the new Fluke 28-II rugged meter, it also has the filter, but no
lowZ:
http://us.fluke.com/usen/Products/Fluke+27+II+28+II.htm

Quote:
"Unique function for accurate voltage and frequency measurements on
adjustable speed motor drives and other electrically noisy equipment (28
II)"
but that is just the normal low pass filter feature.

Dave.

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