Re: Internal resistance again.

[John Denker <jsd@AV8N.COM>]

Ludwik Kowalski wrote:

> How can this be explained? I am sure that R
> is essentially constant. The impedance of the
> voltmeter is certainly much larger than 1 ohm.
> Looks like the "internal r" of my power supply
> changes a lot with the current.

I might not be able to explain it, and I would prefer
not to even try ... because I can make the question go
away by other means.

Suggestion:
              Four Point Probe.


          I+ >SSSSSSSSSSSSSSSSS< I-
                ^           ^
                V+          V-

where "SS" is the sample, and ">" "<" and "^" are contacts.

The idea is to measure the voltage in such a way that
there is no current flowing through the leads and/or
contacts in the voltage-measuring circuit.  It's better
than Excedrin ... prevents headaches.