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Frequency of ESR measurements

Discussion in 'Electronic Repair' started by [email protected], Dec 30, 2008.

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  1. Guest

    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,
     
  2. 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
     
  3. Arfa Daily

    Arfa Daily Guest

    Exactly ditto.My Bob Parker meter works at around 100kHz, and I have never
    had a problem with it picking up any (several per week) faulty caps.

    Arfa
     
  4. Jim Yanik

    Jim Yanik Guest

    one thing to consider is the waveform of the usual switcher;the cap has to
    deal with a fast rise waveform rich in harmonics.2nd and 3rd harmonics will
    still have a lot of energy.

    your usual 60hz XFMR supplies dealt with a sinewave.
     
  5. Guest

    Thanks everyone for your replies, you have answered my questions.
     
  6. Franc Zabkar

    Franc Zabkar Guest

  7. Arfa Daily

    Arfa Daily Guest

    That does appear to be so. Without looking it up, I just had it fixed in my
    head that it was around 100kHz. With the fact that it is a highly asymmetric
    waveform, duty factor-wise, I guess that it's hard to quote it as an actual
    frequency. It's sort of 100+ kHz 'width' pulses, repeated at a frequency of
    2kHz ...

    Arfa
     
  8. Jamie

    Jamie Guest

    So, its a 2 Khz signal with 2000/100000 = 2 % duty cycle =

    1/2000*0.02*0.5 = 5 uS(+) pulse


    http://webpages.charter.net/jamie_5"
     
  9. Franc Zabkar

    Franc Zabkar Guest

    Remember that they're also current pulses, not voltage pulses, so the
    voltage appearing across the cap is a trapezoid. I don't know how this
    compares with a meter that generates a sinusoidal test voltage,
    assuming that's how others do it.

    - Franc Zabkar
     
  10. John Bachman

    John Bachman Guest

    The Capacitor Wizard uses a 100Khz sinusoidal signal. The Bob Parker
    design is as described - that is what is used in our Blue ESR meter.
    Bob always represented that his method is the equivalent of a 100Khz
    signal.

    Other designs are described in our comparison at
    www.anatekcorp.com/esr_compare.htm

    John
    AnaTek Corporation
     
  11. Arfa Daily

    Arfa Daily Guest

    Ah. So that's where I got it from. Direct from Bob .... Arfa
     
  12. Jeroni Paul

    Jeroni Paul Guest

    That does appear to be so. Without looking it up, I just had it fixed in my
    I have this meter:
    http://es.geocities.com/podernixie/ESR/index-en.htm
    and it outputs a 60 mVpp sine wave at 80 kHz. It works great.
     
  13. Ross Herbert

    Ross Herbert Guest

    On Wed, 31 Dec 2008 09:30:11 -0800 (PST), 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.
     
  14. Arfa Daily

    Arfa Daily Guest

    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
     
  15. 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
     
  16. Guest

    Just out of curiosity, has anyone tried using an infrared
    thermometer to try and find bad or failing caps. I did a quick search
    on the on the internet and found units you can get for as little as
    $20. The spot size is very small and I believe the top of the cap is
    an ideal target. Could use a black sharpie to make a small black spot
    for even better measurements. A SMPS cap which had a High ESR should
    read high in temp, might be more sensitive than using your finger to
    test for temperature. An open or failed cap should read low. Of
    course the unit being tested couldn't be completely dead. If it
    worked one nice feature would be being able to identify bad caps
    before even removing the PC board.

    The power dissipated in the cap should be proportional to the
    increase in ESR ,the temperature increase should be on the fist order
    equal to the power dissipated in the cap. So if the original
    temperature rise due to the new caps ERS was 1 degree C and the ESR
    increased by a factor of 10 the old caps temperature should be about
    10 deg higher, easy to measure.

    Might be able to find bad IC's as well. Perhaps the increase in
    sensitivity using this device would help find other failing or failed
    components as well. Might also be useful in identifing failing or
    failed components in very high voltage circuits. Those components you
    would not want to touch with power on.

    Don't know if the idea has any merit but thought I would mention it.

    Gordon ,
     
  17. Guest


    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
     
  18. Ross Herbert

    Ross Herbert Guest

    :
    ::> On Wed, 31 Dec 2008 09:30:11 -0800 (PST), 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.
    :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
    :eek: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.
     
  19. Arfa Daily

    Arfa Daily Guest

    A very good example of this occured on my bench last Friday. I had a Sony
    DVD / HC that was very 'iffy' at the beginning of a disc. It would freeze
    and pixellate pretty much at random, but if you left it and it managed to
    get past the intro without totally falling over, it would play ok for the
    rest of the disc. On auto setup, it would proceed ok on single layer and CD
    discs, but fail every time on a dual layer. I had a laser for the model on
    the shelf, so tried it, but it was just as bad. I then turned my attention
    to the little servo board under the deck, where there were several surface
    mount electrolytics. For no other reason than that similar caps in a similar
    location give all sorts of odd problems on many of the Sony CD players from
    a few years ago, I got out the ESR meter, and ran it over these caps. Now I
    don't know about your experience of ESR and SM electros, but I've always
    found that even with brand new ones, the ESR is significantly higher than
    you would expect for the same value and voltage of a through-hole type.

    There were two 22uF 10v ones on the board, and the first one measured 5
    ohms. Now if that was a through-hole one, you'd immediately say it was bad,
    but for a SM, that is quite possibly a satisfactory figure. When I measured
    the other one, it went 3 ohms, so I found another similar one on another
    board, and measured that. It also went about 3 ohms. So, based on the fact
    that two of them read one value, and a third read a slightly different
    amount, I applied experience, gut feeling and the measurements, and went
    ahead and replaced it. Result ? Total cure, and the ESR meter played only a
    supporting role in achieving that.

    Arfa
     
  20. John-

    I built one of your Blue ESR meter kits and am impressed with it.

    Somewhere I read that there is an industry specification or common
    practice, that requires ESR measurement to be made at 100 KHz. If it is
    in fact a "standard" method, you should petition that standards
    committee to agree that your method is equivalent.

    As others commented, approximate methods for measuring ESR may be
    adequate for detecting common failures. However, I do not think the Bob
    Parker method is approximate. As long as there is no significant
    inductance involved, it seems to be quite accurate. Try putting
    resistors in series with low-ESR capacitors. Taking the low ESR into
    account, the meter should measure close to the same value as when
    connected across the resistors alone. I expect it will agree with other
    methods of measuring the resistors. Certainly better than ten percent!

    Fred
     
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