Measuring capacitance with DE-5000 - readings changing

[gpdb]

When measuring capacitance with my DER DE-5000 LCR meter, I keep running into the capacitance reading slowly increasing. As I leave it connected, it will change by 0.1pf about once a second. I'm measuring at 100khz and parallel mode. Has anyone experienced this before, and should I be waiting for the reading to stop moving to record it? I've specifically been measuring humbuckers, and I've used an alligator clip to connect it in series, and then I put the bare and ground wire on one clip, and the remaining wire on the other one. It seems to measure DCR and inductance just fine.

[antigua]

I just tried it, I got something closer to 0.1pF drift every five to ten seconds. I'd just consider it to be accurate to within 1pF, because its so sensitive that just moving the lead wires around will change the reading. In fact you want to make sure that with Fender pickups that the lead wires are not touching, to exclude them from the capacitance measure. For shielded cable, like Gibson and most of the rest, you have to do your best to subtract it from the measured value, because disconnecting shielded hookup wire from a pickup can be too invasive or time consuming. If you determine the C per inch of the cable separately, it's not too much trouble to subtract it. Here's a thread where I had measured some wires and cables guitarnuts2.proboards.com/thread/7725/capacitive-coupling-various-guitar-parts

It might be drifting quickly due to interference or a charge buildup. Try touching the terminals together to discharge the buildup, if there is one. 

[gpdb]

Thanks Antigua! Appreciate the assistance. That post you linked is very fascinating too. I would think measuring the capacitance with the hookup wire would be more indicative of "real performance" as opposed to removing it, but I can see the merits of the other way too. 

[antigua]

Mar 5, 2022 18:28:59 GMT -5 gpdb said:

Thanks Antigua! Appreciate the assistance. That post you linked is very fascinating too. I would think measuring the capacitance with the hookup wire would be more indicative of "real performance" as opposed to removing it, but I can see the merits of the other way too. 

That's true but the cable can vary in length, but I also see a lot of people coil up the unused length of cable rather than cut it shorter. 

When it comes to how pickups will sound, the capacitance doesn't make a huge difference anyway. If you figure the difference is 70pF, you can touch a 70pF can across the terminals of the guitar cable while it's plugged in to hear the relative difference. It will tend to move the peak by maybe 100Hz, which you might not even be able to hear. For me, audible differences start around 1nF. I'm mostly interested in capacitance just because I want to know all there is to be known, even if it doesn't have a huge effect on the tone. Like if there was some easy way to determine the grade of steel or allows used, I'd measure that too, but that's not so easy, unfortunately. 

[JohnH]

I don't have a proper LCR meter only a multimeter that has L and C ranges. It's very useful, but not nearly as sensitive.

But I'm very impressed that variations of just 0.1pF are even indicated. I expect it wouldn't take much to cause that. Maybe a butterfly sneezed in Siberia?

[stratotarts]

The lowest capacitance range on the DER is 200pF and the specified resolution is 2%. That's 4 pF, and also it's recommended in the specs to do an open/short calibration before performing measurements on that range. It might not be practical or necessary to routinely measure pickups to such accuracy. Just take it as a close measurement, limited by the expected error.

[gpdb]

Ultimately I'm going to be creating a frequency response chart for them anyways so it doesn't make a huge difference to me. I was hoping that for most of my tests I could just use inductance and capacitance to create an easy dataset to run some clustering algorithms on so that I could group different pickups by the data. I was already able to get some mildly promising results testing out Antigua's dataset on his website, but it's still really early. I've got around 40ish pickups now I've been collecting for this purpose.

[stratotarts]

A statistical breakdown on unloaded pickups won't produce much useful insight. The inductance, yes, but the capacitance doesn't contribute enough difference to the final loaded response to be relevant in a bulk comparison.

[antigua]

When it comes to capacitance, I think most of the mystery is in Fender single coils, because they're simple enough and remove extraneous concerns. For whatever reason, capacitance varies a lot between Strat pickups, from as low as 75pF to as high as 200pF. A factor of the capacitance is the overall coil geometry, a wider coil like a Jazzmaster pickup has an inherently lower capacitance, and it can be said that the more spread out a coil is from start to the finish, the lower the capacitance. Telecaster neck pickups, being tall and narrow, demonstrate the opposite. I suspect the variability has to do with tension, neatness of the coil, and the thickness of the insulation, but I don't have enough information to be more specific than that. I made some test pickups, but the results were inconclusive, the capacitance varied too much, even when I tried to create consistent examples.