Re: ESR Meter - Roll your own - ESRrev0.JPG

On Jul 11, 2:42 pm, Mike wrote:

iz7ath says the esr tester circuit came from an Italian magazine,
Nuova Elettronica N212. It would be interesting to see their
writeup, because its operation seems backwards to me. If no
capacitor is connected, the bridge is balanced, and there's no
signal to the meter, which reads 0. With a capacitor connected
the bridge becomes unbalanced. A perfect capacitor, esr = 0 ohms,
maximally unbalances the bridge, and presumably pushes the meter
to full scale. A poor capacitor reads slightly less than full
scale. For example, with esr = 1 ohm (which is not a very good
capacitor by today's standards) we still get a nearly full-scale
meter reading, because 1 ohm is so much less than 22 ohms, and
is still pretty close to zero ohms by comparison. So the meter
is hard to read, showing little change for various capacitor esr
values in the sub-1-ohm region of interest. In fact, 1-ohm and
0.1 ohm capacitors would have nearly the same reading. Not good!

The same meter was published by Marvin Smith in the July 2001 edition
of Poptronics. A quick google search found many references to the
Poptronics article, but no copy of it. I know it's the same meter
since I have a PDF copy of the Poptronics article.

We'd love to see a copy of the article. Failing that, a posting
of the relevant portion of the meter-reading interpretation and
of the circuit-operation explanation would be helpful. Be sure
to include the author's full names for credit.