On Fri, 2 Jan 2009 11:11:21 -0000, "Arfa Daily" wrote:

:
:"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.
etermining 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
ne, 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
:


I agree entirely. With regard to everyday servicing you only really require a
"relative" indication. In some cases some intuitive interpretation on the part
of the user is required to determine whether a cap is "bad" and requires
replacing. Obviously, if the indication is way too high it doesn't take any
intuition to decide to replace.