"Ross Herbert" wrote in message
...
On Wed, 31 Dec 2008 09:30:11 -0800 (PST), wrote:

:On Dec 30, 6:27 pm, "Leonard Caillouet" wrote:
: wrote in message
:
:
...
:
:
:
: I have a question about ESR measurements.
:
: I have been doing some reading about ESR and the literature indicates
: it can be a strong function of frequency. In the design a SMPS I
: assume the ESR of importance is at switching frequencies (at least
: for the line side capacitor).
:
: I have also noticed that often the measurement made in trouble
: shooting are low frequency measurements (step function - looking at
: the abrupt change in voltage).
:
: Is the above accurate and if so when a cap goes bad do the low
: frequency measurements catch the majority of the high frequency ESR
: failures. Are there significant failure modes where a low frequency
: ESR measurement would miss the higher frequency ESR failure?
:
: Thanks Much,
:
: Most of the ESR meters that I have seen test in the 50-200 kHz range.
This
: pretty much covers the switching frequencies of most power supplies, at
: least in consumer equipment that I am familiar with.
:
: Leonard
:
:Thanks everyone for your replies, you have answered my questions.


Now to throw in a curve ball...

In designing his Tan-Delta meter, Cyril Bateman used 100Hz sine. His
theory was
that using 100KHz could cause the measuring lead inductance to exceed the
self
inductance of the capacitor under test and thus complicate the accuracy of
the
result.

The thing is with a bog-standard ESR meter, it's all about relative
measurements, 'feel', experience, and intuition rather than accuracy.
Determining whether or not an electrolytic is faulty by way of its ESR, is a
bit of a black art, and is with any ordinary 'in-circuit' ESR meter. The
reading just gives you some help and 'feel good' backup. This is why I have
contended on many occasions that such an instrument is not one of absolutes,
and cannot be just picked up and used to give 'go / no go' definitive
answers about the state of a cap, by anyone who chooses to buy one. It's
just a helper that gives you one more pointer, allbeit a mostly pretty good
one, without having to remove the cap (generally) from the circuitry that
it's in.

The thing is with the inductance argument, I would have thought that given
that the self inductance of a 'standard' electrolytic is quite high due to
the way they are constructed, the inductance of the test leads would have
been pretty insignificant in comparison ??

Certainly, in practice, if it is a 'problem', it has never caused me any
trouble with using my Bob Parker to help identify bad 'uns ...

Arfa