[volt-nuts] Best way to measure micro Ohms

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Sep 17 13:42:57 EDT 2017

In message <CANX10hA5BeZYCXJORQ5r4h=CbbV2JpZedsWKFswg0hU6HNP-QA at mail.gmail.com>, "Dr. David Kirkby (Kirkby Microwave Lt
d)" writes:

>I want to measure the resistance between two bits of aluminum. Each are 40
>x 30 mm across. One is 250 mm long, the other is 8 mm long.

The dominant factor in the resistance you want to measure is the pressure
on the contacting surfaces.

If the contact pressure is high enough, making the joint "gas tight",
you can treat it as one contiguous piece of aluminium and just do
the math (= differential equations for complex geometries)

If the contact pressure is too low, trying to measure the joint
resistance is a fools errand, because it will not be stable over
any parameter (voltage, current, humidity, vibration, air composition,

The only known way to measure ohmic resistance in the micro-ohm
domain with any precision is caloriometric methods, and they are
experimentally troublesome to no end.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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