The one I picked up (BK Precision 881) claims to output @ 15mV and
came out June 30, 2003, so it's fairly new. I'm wondering if it's a
bad tester because it can't seem to read ESR correctly in-circuit.

Jeremy

On Tue, 2 Sep 2003 07:57:04 -0400, "Jerry G."
wrote:

Many of the older ESR meters used too high a voltage with too high a
source resistance, and are triggering or reading other components that
are connected to the one under test. This is why you have to remove the
part to properly test it. The new meters use typically about 50 to 100
mV with a very low source resistance. At about 250 to 300 mV, they can
start to trigger other devices (especially some semiconductors), and
these would be included in the measurements.

If you have a shorted or very leaky cap, the ESR meter can be fooled,
and thus give a low reading. ESR meters are good for when caps go
opened, which is the most common type of failure with them. In the case
of the older types of ESR meters used on modern circuit boards, the
meter will read the other components wired in.

A descent ESR meter is very low in cost these days, in relation to the
savings you will get. I would suggest in investing in one if you plan on
testing a lot of caps. There are a number of good ones on the market
today. The Bob Parker one is one of the best rated ones I have been
reading and hearing about.


You can visit Bob Parker's web page:
http://www.ozemail.com.au/~bobpar/

Jeremy wrote:
The one I picked up (BK Precision 881) claims to output @ 15mV and
came out June 30, 2003, so it's fairly new. I'm wondering if it's a
bad tester because it can't seem to read ESR correctly in-circuit.

Jeremy

Typically, ESR is not a problem in a high impedance circuit.
ESR is often a problem in a low impedance circuit...like a power supply.
If you have a bunch of caps in parallel, the ESR meter can't tell which
if any are bad. Other stuff in the circuit makes it worse.
I've had zero success with ESR measurements in circuit. The only place
it works is where there's only one cap that could be removed easily for
testing. And that's happened...well...never.
mike




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