Fluke DMMs and VFD motor drives

[DaveC]

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

 

[Jon Slaughter]

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.

 

[DaveC]

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.

 

[David L. Jones]

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.

--
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.eevblog.com

 

[Jamie]

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..

 

[David L. Jones]

Jon Slaughter wrote:

DaveC wrote:
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.

If you really want the low-z and LP filter then why not get the 117
and create a simple LP model? You could probably even add it to the
fluke somehow. It's pretty simple to do. Either a res and cap(not for
current though).

Modding a meter can potentially make it unsafe, so not a good idea to
recommend.
The Fluke 289 has both features, so no need to bodge it.

Dave.

--
================================================
Check out my Electronics Engineering Video Blog & Podcast:
http://www.eevblog.com

 

[Jamie]

David L. Jones wrote:

Jon Slaughter wrote:

DaveC wrote:

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.

If you really want the low-z and LP filter then why not get the 117
and create a simple LP model? You could probably even add it to the
fluke somehow. It's pretty simple to do. Either a res and cap(not for
current though).


Modding a meter can potentially make it unsafe, so not a good idea to
recommend.
The Fluke 289 has both features, so no need to bodge it.

Dave.

I use my 289 as a clock since I don't have a clock in most places I am

at, except my desk or bench. I can't wear watches.

P.S.
I wish it was a little faster in response.

 

[DaveC]

A scope meter is the best tool for such a job..
[Jamie]

Why?

Also, I already have a hand-held scope (Tektronix) so I don't want to spend
$$ unnecessarily on features I already have in maybe another tool.

Dave

 

[Jamie]

DaveC wrote:

A scope meter is the best tool for such a job..

[Jamie]

Why?

Also, I already have a hand-held scope (Tektronix) so I don't want to spend
$$ unnecessarily on features I already have in maybe another tool.

Dave

Because working with VFD's, especially with Vector mode drives, You see

a lot more happening in the output over what a DMM can show you.

Even my Fluke 289 with it's low pass will give incorrect readings of
what is really happening if a Vector drive isn't tuned, incorrect
induction values, defective encoder, something etc..

If all you're looking for is a ball park figure, then I guess you could
use a low pass DMM.

It's up to you.

For every man, they have their own tool!

 

[Jon Slaughter]

DaveC wrote:

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.

If you really want the low-z and LP filter then why not get the 117 and
create a simple LP model? You could probably even add it to the fluke
somehow. It's pretty simple to do. Either a res and cap(not for current
though).

Essentially the meter probably just averages the digital samples which is
more effective IMO. don't know why they couldn't add that feature to all
there meters.

 

[Gunner Asch]

On Tue, 10 Nov 2009 14:34:22 -0600, "Jon Slaughter"
<Jon_Slaughter@Hotmail.com> wrote:

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.

I agree.

Gunner, Fluke 77 (many) user

DISCLAIMER: The content does not reflect the thoughts or opinions of either
my ISP, myself, my company or employer, my friends (if any,) my goldfish or
my neighbour's mad dog; don't quote me on that; don't quote me on anything;
all rights reserved; the post is distribution copyrighted to the extent that
you may distribute the post and all its associated parts freely but you may
not make a profit from it or include the post in commercial publications
without written permission from the Prime Minister of Hutt Province; other
copyright laws for specific posts apply wherever noted or not noted, either
deliberately, negligently, or otherwise; posts are subject to change without
notice; posts are slightly enlarged to show detail; any resemblance to
actual persons, living or dead, is unintentional and purely coincidental;
hand wash only, tumble dry on low heat; do not bend, fold, mutilate, or
spindle; do not pass go; do not collect $200; your mileage may vary; no
substitutions allowed; for a limited time only; the post is void where
prohibited, taxed, or otherwise restricted; the post is provided "as is"
without any warranties expressed or implied; user assumes full liabilities;
not liable for damages due to use or misuse; an equal opportunity abuse
employer; no shoes, no shirt; quantities are limited while supplies last; if
defects are discovered, do not attempt to fix them yourself but return to an
authorised post service centre; caveat emptor; read at your own risk;
parental advisory - explicit words; text may contain material some readers
may find objectionable, parental guidance is advised; not suitable for
children; not suitable for adults; not for human consumption; keep away from
sunlight, pets and small children; limit one-per-family; no money down; no
purchase necessary; to approved purchasers only; facsimiles are acceptable
in South Australia; you need not be present to read this post; some assembly
required; batteries not included; action figures sold separately; no
preservatives added; tools not included; safety goggles may be required
during use; sealed for your protection, do not use if the safety seal is
broken; call before you dig; for external use only; if a rash, redness,
irritation or swelling develops, discontinue use; use only with proper
ventilation; avoid extreme temperatures and store in a cool, dry place; keep
away from open flames, naked flames and old flames; avoid inhaling fumes;
avoid contact with mucous membranes; do not puncture, incinerate, or store
above 60 degrees Centigrade; do not place near flammable or magnetic source;
smoking the post may be hazardous to your health; the best safeguard, second
only to abstinence, is the use of a good laugh; text used on the post is
made from 100% recycled electrons and magnetic particles; no animals were
used to test the hilarity of this post other than Synapse Syndrome; no salt,
MSG, artificial colour or flavour added; may contain traces of replies to
peanuts; if ingested, do not induce vomiting, if symptoms persist, consult
your humourologist; post is ribbed for your pleasure; slippery when wet;
must be 18 to read; possible penalties for early withdrawal; post offer
valid only in participating newsgroups; slightly higher in South Australia;
allow four to six weeks for delivery; damage from hurricane, lightning,
tornado, tsunami, volcanic eruption, earthquake, flood, orgasm, misuse,
self-abuse, neglect, unauthorised repair, damage from improper installation,
broken antenna, marred cabinet, incorrect line voltage, missing or altered
serial numbers, sonic boom vibrations, electromagnetic radiation from
nuclear blasts or other Acts of God are not covered; incidents owing to
aeroplane crash, ship sinking, motor vehicle accidents, leaky roof, broken
glass, falling rocks, mud

 

[DaveC]

The noise issues you mention aren't particularly clear. Many VFDs will
radiate some HF/RF noise, but a well-designed instrument should be
relatively immune to radiated noise.
[...]
The peak phase-to-phase potentials should be addressed by Fluke to insure
that the DMM can safely withstand these tests.

I don't think it's a fear that the Fluke won't survive a measurement, but
whether the readings will be accurate -- maybe the noise will confuse the DMM
if not lo-pass filtered.

I would expect that having a handheld, battery powered (floating)
scope-meter instrument would be more appropriate for analysing VFD outputs,
than a DMM would be. After all, it can be determined that a motor drive has
an output with common
light bulbs (LERs - light emitting resistors).

LER -- have to remember that one...

You (and others) make a good point that maybe a DMM -- alone -- isn't the
best tool for troubleshooting a VFD. I have a nice handheld Tek scope (222PS)
that might fit the bill nicely (fully isolated; floatable to 850v/ch; rated
to 400v/ch, 800v in differential mode).

I think I'll go for the Fluke 117. It's got low-Z and cap (to 10K uF) mode
that I need. And I'll bring the Tek along when I go to look at a troubled
VFD.

Thanks for your comments. They're were helpful. You just saved me a few
hundred $$.

Dave

 

[Greg O]

"DaveC" <invalid@invalid.net> wrote in message
news:0001HW.C71F09370001469EB08A39AF@news.eternal-september.org...

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 have been working with VFD's for ~10 years and have never measured the
voltage supplied to the motor. Most VFD's have the capability to show the
output voltage, amps, frequency, so for the most part why would you need to?
Greg

 

[James Sweet]

Jon Slaughter wrote:

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.

I love my 87, although I do miss the low ohms feature and audible diode
test that my 79 had.

 

[Gunner Asch]

On Tue, 10 Nov 2009 21:30:49 -0600, "Greg O" <goo1959@hotmail.com>
wrote:

"DaveC" <invalid@invalid.net> wrote in message
news:0001HW.C71F09370001469EB08A39AF@news.eternal-september.org...
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 have been working with VFD's for ~10 years and have never measured the
voltage supplied to the motor. Most VFD's have the capability to show the
output voltage, amps, frequency, so for the most part why would you need to?
Greg

Frankly..I do the same..for longer and the old Fluke 77s do everything I
need done on both ends of a VFD. And frankly..unless one is a
Electronic (component level) tech...one simply doesnt need to diagnose
too deep into them. And diagnosing them down deep takes a significant
amount of (billable) time..so I simply check em out..find out what is
not working properly...fix it if I can easily, or simply order a new
one.

The customer cant afford a lot of diagnosis down deep at $75 an hour for
a $300 5hp vfd.

Gunner

"Aren't cats Libertarian? They just want to be left alone.
I think our dog is a Democrat, as he is always looking for a handout"
Unknown Usnet Poster

Heh, heh, I'm pretty sure my dog is a liberal - he has no balls.
Keyton

 

[Phil Hobbs]

DaveC wrote:

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.

Owning an 87 is the mark of a True Hardware Guy (tm).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

 

[Jamie]

Phil Hobbs wrote:

DaveC wrote:

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.


Owning an 87 is the mark of a True Hardware Guy (tm).

Cheers

Phil Hobbs

Well I must be half way between a hardware guy and a geek!

I use a 289 when not at the bench most of the time for
remote DMM work. I Also like the logging function in it which
seems to work well. Just wish it had a faster sampling on it.