"John Larkin" wrote in message

But as a practical matter, how much resolution is really
necessary?

Ed


"Resolution" in the sense of being able to resolve milliohms. We are
currently buying polymer aluminum electrolytic caps that have typical
ESRs in the 1-2 mohm range. And there's a host of various LDOs,
integrated switchers, and homebrew power supplies around that care a
great deal about output cap ESR. The inverting switcher I posted to
this group cares a lot about cap esr; it needs low esr to kill output
ripple and high esr for loop stability, with, optimistically, some
workable compromise point in the middle.

ESR over temperature is an even nastier issue. I bet there's a lot of
electronics out there that will fail below 0C, as the caps change esr
and the regulator loops start to oscillate.

If all you want to do us spot bad filter caps in TV power supplies, a
simple 2-wire scalar impedance measurement, in the 1 ohm ballpark, is
all you need. But then, checking ripple with a scope is just as good.
A true esr measurent instrument would be useful in design, and it may
as well perform some other functions while you're at it.

John

As JL points out, in designing power supplies (Power Electronics), the need
to know the Cap's ESR from 1.0mR to 150mR is very important. If the meter
petered out at 10mR then you will lose a large part of the market. Also ESL
but that is usually a small quantity in low ESR caps but if this tester did
ESZ that may be as good or better than ESR, killing two birds with one
stone.
Cheers,
Harry