[Test-Equipment] Resistor measurement

[Richard Knoppow]

----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: "Discussion of Electronic Test Equipment" 
<test-equipment at mailman.qth.net>
Sent: Wednesday, July 06, 2011 6:29 AM
Subject: Re: [Test-Equipment] Resistor measurement


> Hi Richard:
>
> Why did they use a DC  measurement method?  Using AC gets 
> rid of the
> problem of DC offsets caused by different metals.  See:
> http://www.prc68.com/I/Kelvin.shtml
> Where the DC problems put a limit on how low a resistance 
> you can measure.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com

   Well DC is the traditional method and bi metalic problems 
can be solved by choice of the materials the terminals are 
made of.
   AC even at rather low frequencies, brings with it 
problems of stray reactances which must be accounted for in 
very precise measurements.
    The funny thing is that we had no means of measuring the 
reactance of production resistors. Perhaps that was not 
required by the specs we had or perhaps we had it done by an 
outside lab. Most of our resistors were of two types: carbon 
film made to mil specs, and established relibility metal 
film resistors mostly supplied to NASA contractors. These 
had very tough QC specs.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com