[SI-LIST] Re: Sub .100 ohm measurements

Cody,
The traditional way to make low-resistance measurements is with a 
4-Wire "Kelvin" measurement-- see
   http://www.cirris.com/testing/resistance/fourwire.html

Quite a few of the medium- and higher-priced digital multimeters (DMM's)
have this capability.

On the GenRad 227X testers that we used to use at IBM Lexington/Lexmark
in the 1980's/1990'a, we could configure a 6-wire measurement that added
a drive wire and a sense wire for "guard" points.  This was for
in-circuit measurement of resistors in configurations like

                          Rx
   NODE1 -----o---------/\/\/\----------o------- NODE2
              !                         !
              !                         !
              !     Ry           Rz     !
              +---/\/\/\---o---/\/\/\---+
                         NODE3

where Rx, Ry, and Rz were all low resistances.  It's been over 16 years
since I last worked with the GenRads, and I no longer have the manuals,
so I don't recall the exact circuit configuration in the testers.  But
we could measure shunt resistors in power-supply circuits down to about
the 50 milli-ohm range with about 3% accuracy in mass production.

John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE
dBi Corporation
http://www.dbicorporation.com/

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