LCR meters - capacitance measurements at high frequency. - Page 1
Forum section: electronics / testgear

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 02:52:58 pm
content: Hi everyone,I was just checking someNichicon PSF series 270µF, 16Vcapacitors. The data sheet states that those caps should have a dissipation factor of < 0.1 (measured at 120 Hz) and an ESR of <= 10 mOhm (measured between 100 and 300kHz). Measuring the ESR in high frequency mode I notice that my meter only shows nonsensical capacitance values (see screenshots). Since the data sheet is not super clear if the capacitor is expected to maintain its capacitance at high frequency I wonder: Am I hitting the physical limit of electrolytic capacitors or the limit of my test gear? Or in other words can you even measure the capacitance of this kind of electrolytic capacitors using frequencies of >= 100 kHz?(Attached: measurements of a sample cap at 100 Hz, 120 Hz, 1 kHz, 10, kHz, 100 kHz and 200 kHz)

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 14, 2023, 03:03:36 pm
content: How long are your test leads? What is the loop area of the leads? Do you have a picture of the setup?

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 03:18:14 pm
content: The lead length is 60 cm (~75 cm, with clips and connectors). I also attached a picture of the setup.

author: gamalot
author_rank: Super Contributor
timestamp: May 14, 2023, 03:27:24 pm
content: 100KHz is too high for aluminum electrolytic capacitors.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 14, 2023, 03:34:31 pm
content: Run the Short and Open Compensation at the high frequency and measure again.

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2023, 03:40:26 pm
content: Quote from: Traceless on May 14, 2023, 02:52:58 pmAt some point series inductance of either your test apparatus or the capacitor itself (ESL) begin to affect and then dominate the reactance of the capacitor. If you follow the calibration procedures the inductance from the meter and leads should be largely compensated for, but nothing is perfect and moving the leads even a little bit can change things. However, most of what you are seeing is probably due to the ESL of the capacitor.

author: mawyatt
author_rank: Super Contributor
timestamp: May 14, 2023, 03:57:30 pm
content: As mentioned by bdunham7 you are seeing the impedance result after series resonance with the ESL (and maybe lead inductance) of the capacitor, this is why the display shows a negative capacitance (computed from the impedance angle with is + for inductive reactance and - for capacitive reactance).Better results might be to forgo the usual Kelvin Type test leads and use a fixture that directly attaches to your LCR meter which allows leaded device direct plug in, the Tonghui TH26048A and BK Precision TL89F-1 are examples of these fixtures.BTW what LCR meter are you using?Best,

author: Sighound36
author_rank: Frequent Contributor
timestamp: May 14, 2023, 04:00:06 pm
content: Hi MikeFor a quick test the Kelvins are fine, for stabilty accuracy & repeatability a fixture is the way to go.

author: gamalot
author_rank: Super Contributor
timestamp: May 14, 2023, 04:03:48 pm
content: Quote from: mawyatt on May 14, 2023, 03:57:30 pmIt looks like this one:https://www.twintex-china.com/digital-lcr-meter-10khz-30khz-200khz.html

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 04:05:22 pm
content: I did the compensation a couple of times, I also ran the full compensation (for all measurements modes). Doesn't really help with the capacitance - the ESR value might be accurate though. The meter is also pretty touchy at high frequency both with leads shorted and leads open. I enabled data logging and logged one dataset at 200kHz with shorted leads and one dataset with open leads. ESR with shorted leads seems stable but the other values are all over the place.Edit: first column in the csv files is Cs, second column is Rs

author: gamalot
author_rank: Super Contributor
timestamp: May 14, 2023, 04:06:47 pm
content: Quote from: Sighound36 on May 14, 2023, 04:00:06 pmThis has nothing to do with test leads or fixtures, it's a limitation of the capacitor itself.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 04:21:52 pm
content: @bdunham7 Even after compensation capacitance readings seem to be a problem with shorted leads (between -700µF and + 1mF depending on how I connect the probes), resistance is a problem with open leads (negative kOhm Readings with open leads)@mawyatt: I use theMatrix MCR5200. The leads are connected via 4 BNC connectors so the banana fixtures won't fit I'm afraid.@gamalot: I was suspecting that high frequencies might be an issue with electrolytics - still wondering though if there might be an issue with the meter at the higher frequency settings. Unfortunately this is my only LCR meter so I have little to compare it against.

author: mawyatt
author_rank: Super Contributor
timestamp: May 14, 2023, 04:45:41 pm
content: Nice LCR Meter, the mentioned fixtures should plug directly into the 4 BNCs on the meter front panel, these are positioned such that the fixtures need no additional cables and have the right type BNC ConnectorWe don't have a 270uF 16V on hand, but do have a 220uF 25V which might be similar. Attached are plots showing a frequency sweep for 10Hz to 1MHz with our IM3536 LCR meter. Plots were created by python routines we developed as a means to do these type sweeps, as well a Voltage sweeps and even some temperature sweeps. Don't want to distract from your thread, but if interested will discuss and link.Edit: Here's what the fixtures look like. Also added another plot showing how the effective capacitance steeply rises as you approach series resonance.Anyway, hope this helps and you can see the series resonance around ~45KHz, which seems typical for these type electrolytic capacitors.Best,

author: gamalot
author_rank: Super Contributor
timestamp: May 14, 2023, 04:48:33 pm
content: I finally found a 270uF capacitor. With a Keysight test fixture, after open and circuit compensation, you can still see the measured negative capacity.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 06:03:14 pm
content: Quote from: mawyatt on May 14, 2023, 04:45:41 pmThank you. Yes you are absolutely right those fixtures should fit. On the first picture I found the BNC connectors were not really visible so I assumed this would be a fixture similar to the one of the DER-EE 5000. Might be handy to get one of those.@mawyatt, @gamalot: Thank you for taking the effort and time to find and measure those caps You are awesome. In the meantime I've also been experimenting around with different caps. I found aNichicon FW series 63v, 47µFthat I was able to measure pretty accurately across all frequencies*, see results attached. A 1µF 450V cap was also at least roughly in the right ball-park. Maybe high frequency becomes more of an issue with higher capacitance?(*At high frequency I had to adjust the leads carfully a few times though before I got an accurate reading. 100kHz was quite a bit off but still within reason, unlike the negative readings with the bigger cap.)

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2023, 06:09:36 pm
content: Quote from: Traceless on May 14, 2023, 04:05:22 pmIf the overall Z is very low, the measured signal values will be very low as well and the LCR meter will have trouble giving you a stable result since it has to do the math with a low, noisy signal. Oddly, every LCR meter I've ever seen doesn't alert you to this and just tries to display the wildly varying results. So if don't get a stable reading from a simple component, it is probably because of the signal level and noise.

author: exe
author_rank: Unknown
timestamp: May 14, 2023, 06:35:02 pm
content: Well, this is not a typical electrolytic cap, it's a solid polymer cap, those are, afaik, designed for SMPS and work at higher frequencies. Those are often specified at 100kHz and, I suspect, can handle much higher frequencies. Here, for example, an alu-cap is specified for ripple at 500kHz:https://www.chemi-con.co.jp/en/products/detail-condenser.php?part_number=HHXF250ARA151MHA0G

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 06:47:52 pm
content: Quote from: mawyatt on May 14, 2023, 04:45:41 pmI think the plots are interesting, feel free to place a link for further discussion! What is the resolution/step size of the sweep?Quote from: bdunham7 on May 14, 2023, 06:09:36 pmThanks for the explanation. It's also reassuring to know that this seems to be a general problem with LCR meters and not some oddity with my particular model/unit.@exe: Well spotted I did miss that the PSF series is actually a polymer cap. You find similar caps often used in thein the input power circuitry of mainboards/graphics adapters.Edit: Actually I'm not even sure if they are (Polymer)-Electrolytics or not. I've seen similar capacitors declared asPolymer Aluminium Electrolytic Capacitor. The Nichicon PSF Datasheet I linked calls the PSF series "Conductive Polymer AluminumSolidCapacitors". However if you look at thetitle page of the Nichicon document that lists the PSF seriesit says "Aluminum Electrolytic Capacitors".

author: sonpul
author_rank: Regular Contributor
timestamp: May 14, 2023, 07:36:37 pm
content: The DE-5000 does not measure 270uFx16V Panasonic Os-Con at 10KHz and 100KHz. OL is displayed. As explained, this is because the formula for which the calculation is made perceives the capacitor as an inductance. That's why you have negative values.

author: mawyatt
author_rank: Super Contributor
timestamp: May 14, 2023, 08:37:23 pm
content: Quote from: bdunham7 on May 14, 2023, 06:09:36 pmThe Hioki IM3536 does indicate when a measurement result is questionable, it also displays the Voltage across the DUT and the DUT Current. The Tonghui TH2820 also displays the DUT Voltage and Current, and both LCRs also have selective averaging, selectable drive voltage levels and driver impedance, all helpful for acquiring accurate results with certain DUTs.These are very handy to keep an eye on when doing measurements, as it might help avoid a bogus result!!Best,

author: mawyatt
author_rank: Super Contributor
timestamp: May 14, 2023, 08:42:28 pm
content: Quote from: Traceless on May 14, 2023, 06:47:52 pmHere's the link.https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/msg4774100/#msg4774100The step size is selectable for decade or linear frequency sweeps as a bunch of other things, check on the thread above.Best,

author: Traceless
author_rank: Frequent Contributor
timestamp: May 14, 2023, 09:48:52 pm
content: @mawyatt: The MCR5200 also has voltage and current monitoring (Labeled "Vm", "Im" on the bottom). For whatever reason this is disabled by default but can simply be enabled via menu. You can also adjust the drive voltage (0.1V, 0.3V and 1V the impedance 30 Ohm/100 Ohm). It also has some other nice perks, like the binning mode for instance (seemanualp. 18). It has a red fail and a green pass indicator on the front panel and you can separately customize the audio feedback (beep off, long, short, two beeps) for pass/fail.