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.