On Jan 2, 7:13*am, "Leonard Caillouet" wrote:
"Arfa Daily" wrote in message

...









"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

*Ditto Arfa's comments. *I have three ESR meters and they all read
differently, but they giv me enough info to sort out which caps are bad and
which not. *And when there is doubt, change them. *Caps are cheaper than the
time to worrry about sorting out the accurate measure, which is somewhat
meaningless anyway, as circuits vary so much. *What might be bad for one
application may be ok for another. *Regardless, if the ESR seems high I just
change them.

Leonard


Back to ESR measurements,

In the past I have had any test equipment available to me I
wanted. At this point I am trying to collect test equipment on a
very limited budget. So my interest in ESR testers.

Thanks again everyone for all the info. I have summarized
below what I think I am hearing here and other places. I would
appreciate any comments to the validity of the statements below.

Inexpensive “bog - standard”, In Circuit ESR measurements of
Caps in trouble shooting “consumer electronics” came about due to the
Common and Sever Failure Mode of Dried Out Electrolytic Capacitors.
The ESR changed by a factor of 10X to 30X so was easy to pick up with
simple inexpensive in circuit ESR testers. These meters are a great
tool to have in a persons toolbox to expedite greatly trouble shooting
of failed or troubled circuits due to this capacitor failure mode.

If used for this purpose, due of the severity of the failure mode
(10X to 30X increase in ESR), you don't necessarily need to be too
concerned with accuracy. Many different meters designs out there
which may give different readings between themselves, each do a great
job helping to finding a large majority of capacitors that are causing
circuit problems due to this failure mode.

In trouble shooting consumer electronics for this failure mode,
what is more important is that you get a feel for what your particular
meter readings mean for electrolytic capacitors with different
parameters such as Capacitance, Temperature Rating and the importance
of low ESR in the particular type of circuit you are trouble shooting
(for example some caps may measure higher ESR's because they were not
low ESR Caps to begin with).

I can imagine that good calibration between the SAME design of
meters might come into play if people want to compare results to
assess each others expertise in trouble shooting this failure mode for
different electrolytics and circuits . Even here the requirements
may be fairly low since the failures are so sever (10X to 30X)

This is an exaggeration but an INEXPENSIVE IN CIRCUIT ESR tester
could be compared to a 12 volt sensor in trouble shooting a cars
electrical system. It does not need to be a very accurate tool and
may not be the right tool to use in all situations but it is A VERY
USEFULL TOOL. Many different simple designs of the voltage sensor work
well.

For other lower failure rate capacitor problems other In or Out of
circuit testers such as capacitance meters, capacitance leakage
meters, testers that can test capacitor parameters nearer their
operating conditions such as voltage of operation, imposed voltage (or
current) waveform and magnitude and frequency, are useful tools.

For these lower failure rate capacitor failures, another low
overhead and perhaps time saving approach is to pin point the circuit
that is having problems and replace a suspected capacitor with a known
good capacitor to determine if the capacitor is part of the problem.

Thanks again for all of your responses, information and sharing your
experience,

Jeroni Paul, I really like the LM324 ESR meter