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May 2005

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brian Ellis <[log in to unmask]>
Date:
Wed, 4 May 2005 18:45:32 +0300
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As an ex-manufacturer of SIR equipment, I know some of the problems. I 
used glass-encased 1% spiralled resistors which had a horrific 
voltage-dependency at 1E10 ohms and higher. You should specify the 
measuring voltage and temperature when ordering them as the difference 
between 5 V and 100 V will be well outside the 1% tolerance. That having 
been said, they kept their values remarkably well over the 10 years I 
was using them.

As to reference to a standard, there are, to the best of my knowledge, 
no one is capable of direct reference at high values. It can be done 
only by comparison within the same range over several decades. For 
example, you take 1E6 standard resistor and calibrate and instrument to 
it. You measure a 1E7 resistor with that instrument on the same range. 
You then switch up a range to calibrate it to the real value of the 1E7 
resistor and you repeat the process 1 decade at a time until you reach 
1E14 ohms (which was the highest value I could measure at 5 V). I doubt 
very much whether you will be better than ±10% at the end, with all the 
hairiness of measuring high values, where a dirty look will change the 
measurement, but no one will be able to argue with you. In fact, I 
believe that I had my 1E14 resistors correct to ±5%, probably better, as 
I did the decade progression by three different methods, both static and 
dynamic. BUT it ain't easy and you need a Faraday cage,

Brian

Bev Christian wrote:
> TechNetters,
> Back from the dead!
> 
> Do any of you know where I can get SIR equipment calibrated?
> 
> I have six SIRometers and Cookson/Speciality Coating Systems no longer
> support them!  I also have one set of equipment built up from several
> pieces of individual Keithley equipment.  
> 
> Also, does anyone know where I can buy a set of NIST-traceable high
> value resistors (E6 - E12)?
> Thanks.
> 
> Bev Christian
> Research In Motion
> 519-888-7465 x 2468
> 
> 
> 
> 
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