Today, I’d probably run the scenario in an EM simulator and get the capacitance that way. But there probably is some theoretical formula for this, perhaps with some experimentally-derived tweaks baked in. Even if there is vacuum or an inert gas in the can, such capacitor standards should be amenable to homebrewing with good results. ? The geometry of this design is inherently accurate and with some investigation of “how they did it”, should be quite reproducible - perhaps with even better results thanks to better modeling tools today, and all the low cost CAM for lead forming and such. If someone asked me to make a center plate, I’d just order a SMT stencil with a suitable singular circular hole in it. These are cut way more accurately than what can be done in a low-brow home workshop.?

Cheers, Kuba

15 aug. 2022 kl. 6:39 fm skrev Dr. David Kirkby, Kirkby Microwave Ltd <drkirkby@...>:

?I see a General Radio 0.01 pF 0.03% capacitor on eBay today



(image attached, as eBay links soon disappear).

These use 3 terminals, not 4. In the case of the 1 fF, 10 fF, 100 fF and 1 pF values, there are two capacitor plates with a grounded plate between them. The size of the hole in the plate determines the capacitance.

I wonder how one goes about determine the size of the hole? I'm interested if I could make something like this and put it on my Agilent 4284A and 4285A LCR meters. I have no idea what I would trust the mot - the LCR meter or my homemade capacitor. Both LCR meters are outside their calibration period, but both were calibrated within the last 5 years by Keysight, and have been in my possession since they were calibrated.

Dave