ESR and capacitance readings different on different meters - Page 1
Forum section: electronics / testgear

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: November 20, 2019, 11:39:32 am
content: I have today received a used Peak ESR60 meter. Naturally I wanted to compare it with the DE-5000 that I already own. The reason for buying the Peak was it is designed to be used in-circuit. Can anyone help me understand why I am getting very different readings from both meters at the same test frequency?From the Peak manual I can see that the Peak tests at 100Khz:Quote from: Peak ESR60/ESR70 User ManualThe DE-5000 can be set to test at various frequencies. To compare readings, I ran the calibration procedure on both meters and set the DE-5000 to 100kHz to match the test frequency used by the Peak. I then tested two random 10μF electrolytic capacitors that I had to hand. One is a quality 105deg cap, the other a cheap 85deg part. Here are the readings I got:Peak @ 100kHz:Sample 1: 9.78μF, ESR 1.11ΩSample 2: 9.63μF, ESR 1.08ΩDE-5000 @ 100kHz:Sample 1: 6.43μF, ESR 1.10ΩSample 2: 6.47μF, ESR 1.07ΩAs can be seen, the ESR values seem to approximately agree, but the capacitance value is well under what it should be on the DE-5000. I then tested the same capacitors on the DE-5000 at 100Hz:DE-5000 @ 100Hz:Sample 1: 9.72μF, ESR 6.9ΩSample 2: 9.61μF, ESR 4.7ΩThis time the capacitance values are approximately correct, but the ESR values are completely different.I am aware that the effective capacitance measurement will vary depending on the test frequency so I am not surprised by the different readings on the DE-5000 at different frequencies, however, why do the readings not match the Peak at the same test frequency?While researching, I came across this post which also confused me:https://electronics.stackexchange.com/questions/290252/at-what-test-frequency-should-electrolytic-capacitors-be-measuredTo quote the reply that was confirmed as correct:Quote from: Stackexchange post (excerpt)The DE-5000 would seem to have a problem obtaining the "correct" (that is to say expected) capacitance reading at 100kHz which seems consistent with this statement, but how/why does the peak test at 100kHz and still manage to get the reading correct? Does it test ESR at 100kHz but capacitance at a different frequency?For all practical purposes, the Peak seems to produce an accurate (and very quick!) reading but I am trying to understand why my instruments are returning the results they are, and whether, in fact, the ability of the DE-5000 to test at various frequencies provides a more detailed insight, or whether its readings are simply wrong. Any insight would be appreciated.

author: wraper
author_rank: Unknown
timestamp: November 20, 2019, 11:49:18 am
content: Peak measures only ESR at 100 kHz. Capacitance is separate measurement, most likely done as in multimeters, not proper LCR meter. FYI capacitance and ESR depends on frequency, especially noticeable for electrolytic capacitors.

author: SilverSolder
author_rank: Super Contributor
timestamp: November 20, 2019, 12:12:07 pm
content: I get that the impedance of a capacitor changes with frequency due to inductance - but why would its resistance change so much?

author: TurboTom
author_rank: Super Contributor
timestamp: November 20, 2019, 12:42:29 pm
content: It's very unlikely that the Peak meter actaully measures capacity of electrolytics at 100kHz (as @wraper already mentioned). To be sure, you can connect a scope parallel to the capacitor to monitor what kind of voltages/frequencies the meter applies to the DUT.

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: November 20, 2019, 06:12:20 pm
content: I had a look at the signals on the scope which was an interesting exercise. The DE-5000 produces a constant sine wave at the approximate frequency of the test. At low frequencies such as 100Hz, this was a clean sine wave. At 100kHz, the wave gets noisy and the scope starts to have trouble triggering. The in-built frequency counter has trouble measuring the frequency. With the cap removed, the sine-wave is clean again. I guess the meter is measuring how the cap affects the generated sine wave at the the selected frequency.The Peak tester does not emit a continuous pulse like the DE-5000, but seems to output a single short burst and the frequency counter cannot handle this. I managed to capture it using single shot mode. It looks like its trying to do a sweep of some sort, but as for exactly what its doing, why the pulse is stepped, or what the three preceding negative pulses are, I'm not sure. Can anyone shed any light on this?