Fluke DMMs and VFD motor drives
in [Repair]
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From: Jon Slaughter on 10 Nov 2009 19:08 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.
From: David L. Jones on 10 Nov 2009 19:27 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
From: Jamie on 10 Nov 2009 20:01 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.
From: DaveC on 10 Nov 2009 20:13 > 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 $$ unnecessarily on features I already have in maybe another tool. Dave
From: Jamie on 10 Nov 2009 20:45 DaveC wrote: >>A scope meter is the best tool for such a job.. > > [Jamie] > > Why? > > Also, I already have a hand-held scope (Tektronix) so I don't want to spend > $$ 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!
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