21 Jul
2006
21 Jul
'06
1:19 a.m.
Thanks to my sister's bf's generosity, I am now the proud owner of a
Fluke 87 "TRUE RMS MULTIMETER".
However, I am told it needs recalibration (this is why he gave it
away). It is not _grossly_ out of calibration; as a quick test, I
measured +5V and +12V from a handy (running) computer and local mains
voltage; I got 4.99V (DC), 12.17V (DC), and 122.7V (AC) - all totally
plausible. (Actually, when I first turned it on, it appeared as though
most of the segments on the display were flaky, some dim, some just not
working. I took it apart and put it back together and now the display
totally works - the connection from the pcb to the display is pure
pressure, and I conjecture something jarred it slightly loose.)
I did a bit of searching, but didn't find any manuals around (eg,
bitsavers' fluke/ directory didn't have anything relevant-looking).
Anyone know the procedure, or can point me at a manual somewhere?
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21 Jul
21 Jul
10:27 a.m.
der Mouse wrote:
Thanks to my sister's bf's generosity, I am
now the proud owner of a
Fluke 87 "TRUE RMS MULTIMETER".
Excellent! I was similarly "gifted" with my 8840A but it is
*way* too "overkill" (5-1/2 digits?) and not very portable
(mains powered).
However, I am told it needs recalibration (this is why
he gave it
away). It is not _grossly_ out of calibration; as a quick test, I
measured +5V and +12V from a handy (running) computer and local mains
voltage; I got 4.99V (DC), 12.17V (DC), and 122.7V (AC) - all totally
Biggest problem is finding a source of known accuracy. Calibrating
a 4-1/2 digit meter to a source that's only 0.5% accurate is just
a waste of time (I rarely recalibrate my 8840 for just this
reason -- going over to the lab to get access to good
NIST traceable sources is a royal PITA). For example, the 8840's
calibration "requires" sources accurate to 10ppm.
Is there any reason why you *need* to have it's rated accuracy
(besides "gee, it would be nice...")? More often than not,
I rely on an old Simpson VOM for troubleshooting -- if things
look "close enough", they often are. And, if they aren't
"close enough", it's easier (for me) to swap in a replacement
part -- I have access to a fair bit of surplus. (I'd rather
spend my time working on *new* product designs than
"playing technician").
Of course, if it is something truly irreplaceable (irreSWAPable?),
I'll figure out what's broke and repair that, but even then
the problem is usually pretty easily spotted with an out-of-cal
DMM.
Many labs will calibrate for ~$50 and *certify* the calibration in
the process.
plausible. (Actually, when I first turned it on, it
appeared as though
most of the segments on the display were flaky, some dim, some just not
working. I took it apart and put it back together and now the display
totally works - the connection from the pcb to the display is pure
pressure, and I conjecture something jarred it slightly loose.)
Yes. A consequence of being a handheld meter! Be thankful...
I can't do that with mine! :>
I did a bit of searching, but didn't find any
manuals around (eg,
bitsavers' fluke/ directory didn't have anything relevant-looking).
Anyone know the procedure, or can point me at a manual somewhere?
I'll check a few friends with similar "yellow meters" and
see if one turns up. Fluke was pretty good about providing
detailed service information in their manuals (though I
don't know if that has changed in the years since the 8840).
Enjoy your new toy! :>
11:19 a.m.
However, I am
told it needs recalibration (this is why he gave it
away). It is not _grossly_ out of calibration; as a quick test, I
measured +5V and +12V from a handy (running) computer and local
mains voltage; I got 4.99V (DC), 12.17V (DC), and 122.7V (AC) - all
totally plausible.
Biggest problem is finding a source of known accuracy.
Calibrating a
4-1/2 digit meter to a source that's only 0.5% accurate is just a
waste of time Is there any reason why you *need* to have [its] rated
accuracy
(besides "gee, it would be nice...")?
No. But I don't know how its calibration works; if it's possible that,
for example, voltage is fine but resistance is totally wonky, I'd like
to fix the latter. Or, the 1-10V and higher ranges are fine but the
sub-1V ranges are out of whack. These may not be possible - but I
don't know, and until I do, I have to consider it suspect.
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1:04 p.m.
der Mouse wrote:
Good point. No doubt it does much of this in "software"
based on observations with calibration references (I know
there's a fair bit of work calibrating the 8840 on the
various different ranges, etc.). And, as such, the
designers could have chosen lots of *different* measurement
schemes/algorithms (internally) to get the accuracy they wanted.
I sent emails to friends known to have Fluke DMMs -- if
no luck *here*, maybe one of them will come through with
the goods...
Is there any
reason why you *need* to have [its] rated accuracy
(besides "gee, it would be nice...")?
No. But I don't know how its calibration works; if it's possible that,
for example, voltage is fine but resistance is totally wonky, I'd like
to fix the latter. Or, the 1-10V and higher ranges are fine but the
sub-1V ranges are out of whack. These may not be possible - but I
don't know, and until I do, I have to consider it suspect.
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