Products > Test Equipment

LCR meters - capacitance measurements at high frequency.

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gamalot:

--- Quote from: Sighound36 on May 14, 2023, 04:00:06 pm ---Hi Mike

For a quick test the Kelvins are fine, for stabilty accuracy & repeatability a fixture is the way to go.

--- End quote ---

This has nothing to do with test leads or fixtures, it's a limitation of the capacitor itself.

Traceless:
@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 the Matrix 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.

mawyatt:
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 Connector

We 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,

gamalot:
I finally found a 270uF capacitor. With a Keysight test fixture, after open and circuit compensation, you can still see the measured negative capacity.

Traceless:

--- Quote from: mawyatt on May 14, 2023, 04:45:41 pm ---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.

--- End quote ---

Thank 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 a Nichicon FW series 63v, 47µF that 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.)

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