orgnut at yahoo.com
Fri Mar 7 08:56:00 CET 2014
>>> I spotted a device on the table of the company calibration office...
>>> As I recall, it was a 100A capable resistor... 0.10 OHM.
>>> No idea what it was meant for; big binding posts at one end, and a slab
>>> of sheet steel in a "W" shape (smooth curves, not sharp bends).
>> External shunt for an ammeter?
> More likely a dummy load for power supply testing. (Normally, ammeter shunts are sized to dissipate as little power as possible.)
Another (OT) story...
I used to work in an electronic calibration lab, but I don't recall having a resistor of that
description -- however, it reminds me of another story...
While our job was calibrating and maintaining our company's electronics, we occasionally had to
do some incoming inspection work -- checking incoming components for accuracy. This particular
time I had a batch of 0.1 ohm 1% resistors (I think those were the numbers, at least something
on that order). I found by checking them right at the body of the resistors they were
out-of-spec low, and checking at the end of the leads they were out-of-spec high. Fun! :-)
To measure them, I used the lab's Current Calibrator -- a special power supply whose voltage was
controlled to give a constant (dialed-in) current. Then with a DVM and mini-hooks I could
attach these DVM leads anyplace along the resistor's leads. At 1 amp, the voltage (read on the
DVM) was equal to the resistance. Ohm's law, of course: R = E/I, where I is a constant 1. And
1 amp was well within the power specs of these resistors.
I ended up checking them at a distance of about a quarter inch from the body, because I expected
that would be about the way they would be eventually mounted. They all passed that way. And
fortunately I never had another batch of these resistors! :-)
-=- Larry -=-
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