Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old July 13th 03, 05:40 PM
RonSonic
 
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Default Low ohms, (Dick Smith ESR meter), measurement problems

On Tue, 08 Jul 2003 05:23:26 +1000, Bob Parker wrote:

"Asimov" wrote:

"Lenny" wrote to "All" (06 Jul 03 09:02:29)
--- on the topic of "Low ohms, (Dick Smith ESR meter), measurement problems"

The ESR meter uses something like 100KHz AC signal frequency. You are
bound to fool it with the long wires's inductive reactance! The dc meter
has no such reactive problems.

Asimov
******


G'day,
My little reactance calculator says that it only takes about 40uH
of inductance to give a reactance of 26 ohms at 100kHz, which is
approximately the effective measurement frequency of the DSE ESR
meter. Long lengths of wire in a building would easily have 40uH of
inductance.
Sorry the meter led you astray, Lenny. It was only ever meant for
testing electrolytic caps and measuring low resistances which don't
have a significant amount of series inductance.


One place where that characteristic is really helpful is with some of the small
toroidal trannies in switching supplies. Shorted ones and good ones look about
the same to your average bench DC Ohmmeter. They look radically different on the
DS ESR meter.

Ron

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