Electronics > Metrology

Binding posts/banana sockets cleaning on DMMs/metrology lab gear?

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We all know importance of clean copper-copper connection to reduce TEMFs and contact resistance, especially doing sensitive low-voltage measurements, but how you guys keep contacts clean?
I saw different methods, but rarely see anyone shared techniques they used to keep connector clean.

My main question is regarding copper non-plated terminals, as they oxidize really quick.
It's much less of a problem with gold-plated terminals, but still could be an issue there.

Here's some real data how badly this can screw measurements:

Setup : 3458A sampling on VHP101 95K 0.005% resistor with PMO, specified at 0.3ppm/K in window +20 to +40C.
Brown bold line on graph is temperature from BME280 sensor, blue stagged line is TEMP?
Green bold line - ppm deviation (scale on most left) from median
Green dots - samples.

As you can see resistance go crazy with span almost 50 ppms! So before I doubt my 3458A proper operation, let's hook same resistor, using same connection wires to gold-plated bananas on K2002:

Much less deviation, even though reading noise is way larger on Keithley 2002 (you can see sample dots all over the place). But what is more important - averaged resistance reading closely matches temperature graph, as it should be. In both cases connection done is using copper wire in 4-wire mode at DMM end and TRX connectors on resistor box end.

I cleaned connection wire and reconnected it back to 3458 posts to get 2nd set of data. Will see how it goes tomorrow.

So I'd like to hear more about ways to keep sensitive gear terminals in good order, if you have something to share. Non-destructive methods are welcome.  :popcorn:

I use Deoxit on my 34420A from time to time and nothing on my 3458As, never had an issue though. Not sure what you see is an oxid problem, we will see.

a few years ago I made this list

and found a good app note from Fluke http://support.fluke.com/find-sales/download/asset/2548277_6001_eng_a_w.pdf

and found an interesting article at a German university (unfortunately it is written in German)
In there is a nice table with "Seebeck-Koeffizienten"

Nice list indeed. The CuBe value seems high though (even higher than brass) since there is only a few percent Be included. Was this measured or is there a reference somewhere? I have not seen that with my K2002 (no binding posts, so i sometimes use selfmade CuBe cables besides Pomona cables), with brass I have seen highr values.

So you just subtract the Kupfer 6.5 from the values and you have the copper coefficients :)


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