Homebrew 100K Ω Resistance Standard

I’m upgrading my lab standards. Up until now, I’ve just depended on an old and long out of calibration HP 3468A as my lab standard. 

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I’m constructing a series of resistance standards. Here’s the 100K Ω standard.

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Some time ago I had collected a bunch of high-precision Vishay foil resistors at bargain prices from Electronics Goldmine. I put the two 200K Ω 0.01% resistors in parallel to make a 100K Ω standard. The variance should go down by the square-root of the number of components being averaged, so I think I can expect a 0.007% tolerance for the composite resistance. (Unless I’m unlucky.)

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I packaged them in a Hammond 1590B cast aluminum box.

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I expect to be building eight more of these, so I made a drilling jig out of some 1/2 inch maple from Lowe’s.

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I made up the front panel artwork on my Mac using Intaglio. The application is reminiscent of the old MacDraw. Unfortunately the developer has discontinued the app. I then printed the artwork, via my inkjet printer, onto adhesive label paper. I sprayed the page with two coats of Testor’s clear gloss enamel as a fixative for the ink. 

Finally, I cut out the label and attached it to the top of the cast aluminum box. I used the drilled holes in the top as a guide for placing the label.

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I used 14 gauge bare copper wire pulled from a scrap piece of 14 gauge Romex house wire to bond the pairs of terminals for the four-wire resistance measurement connection. 

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Then I soldered the Vishay resistors to the bus wires. I used a heat-sink clip between the solder joints and the bodies of the resistors.

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I used Pomona 3770 gold-plated tellurium copper binding posts for the “E” or voltage connections, where thermoelectric effects matter (if I ever get down to trying to make accurate measurements at a tens of parts per million level). 

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For the “I” or current terminals, I used Pomona 3760 tin-plated brass binding posts, as they are much cheaper than the 3770 series. Thermoelectric effects shouldn’t matter on the current-forcing side of the four wire resistance measurement connection.

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I’m happy with the finished product.

© Steve Byan 2011-2019