:
::> On Wed, 31 Dec 2008 09:30:11 -0800 (PST),
[email protected] wrote:
:>
:> :>
:> :>
:>
:> :>
:> :>
:> :>
:> :> >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.