"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:qtoe815rr9q12qlnntk9co21db4gtc0t1d@4ax.com...
Quote:
On Sun, 15 May 2005 07:50:42 -0700, the renowned "Watson A.Name -
\"Watt Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> wrote:
"Michael" <NoSpan@att.net> wrote in message
news:42874D32.71868CB0@att.net...
"Watson A.Name - \"Watt Sun, the Dark Remover\"" wrote:
I have fifty 910 ohm 1/4W carbon composition resistors, still in
the
paper tape, which is labeled:
OHMITE
910 OHM
1/4 W 5%
RC07GF911J
OC9115
Judging from the last line, they're 14 years old. They've never
been
used, AKA New Old Stock. Every resistor measures greater than
5%,
some
are over 1k. Over 14 years, would drift from aging cause them to
go
that far out of tolerance? I have carbon film resistore much
older
than
these and they still measure within 5% tolerance, usually within
2%.
Thanks.
Do you know their history? Maybe they were out of tolerence at
time
of
manufacture.
I don't know their history, only that they are still in the tape that
they were in when they came from the factory, with the factory
designation stamped on the tape, so they should be NOS. I've seen
tapes
from some place that have various components customized for a
stuffing
machine, and this is not one of those.
One would think that it would not be possible for these to be out of
tol
when they come from the mfgr, unless there was a major malfunction in
their testing equipment. However, I've heard of such things as
warehouses catching on fire, or goods being shipped in a ship hold
next
to a steam boiler, where in either case the goods were exposed to
excessive temperatures. This could have caused some change. But my
experience is that higher temperaturss cause resistors to become
lower
resistance.
I always heard that carbons change value with humidity. I have
many
unused
Allen Bradley 5% 1/2W carbons which I took from new stock in the
early
70's, and
checking a few of the BROWN-third-band ones at random show all
within
tolerence.
I checked another bag of loose carbon comp resistors, 6.8 ohm, 1/4W,
5%.
All of them are also greater than 5% out of tolerance, and that is
taking into account the 0.4 ohm resistance of the test leads.
Maybe your meter needs a new battery? ;-) Long ago I bought a Micronta
DVM for the guys to use in testing product (to replace one they
killed, and needed *now*). I was surprised to find how nonlinear it
was-- a good fraction of 1%, though still within specs-- it had some
crap ASIC that was nowhere near the virtually perfect performance of
the Intersil inspired chips.
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I rechecked a bunch of them with a bench DMM and they're all the same:
5% or more higher than marked. The 6.8 ohms measure 7.2 or more. The
910s measure close to 1k. Usually I measure a 1% precision resistor on
the same range, just to make sure things are working right.
Someone should take the initiative and include a precision resistor in
each DMM, with the two leads sticking out the front. Something similar
to the calibration source that I've seen on the front of decent
o'scopes. A 1% resistor costs only a penny or two.
Quote:
There were also problems about 20-30 years ago, well covered in the
trade rags at the time, about out-of-tolerance mil-spec resistors.
Don't recall whether they were film or composition types. It was a bit
of a scandal-- when you pay 20 or 50 times the price, you don't
necessarily expect them to be worse than the standard commercial types
(though it makes sense that problems could crop up due to low-volme
special production arrangements).
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Reminds me of the 3 foot cat5 patch cords we ordered. Came bagged 50 to
a bag. Supposed to be tested to cat5 specs. I reached in and pulled
out a half dozen with one end bare, no connector. Well, if they really
_were_ tested, they would've caught that 'minor' problem. :-P
Quote:
Best regards,
Spehro Pefhany
--
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