EEVblog® Electronics Community Forum
Electronics => Metrology => Topic started by: NWerner on November 05, 2021, 07:41:48 pm
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Hello,
I would like to calibrate a compensator (more specifically a Siemens &Halske Kaskadenkompensator).
I am mainly interested in the lower voltage range (<100uV) where my DMM - a Datron 1271 - is of little help. I cleaned contacts,
checked operation and made myself a fairly stable constant current source to operate it.
I have however no idear about how to calibrate this thing. If I remember correctly a inductive
voltage divider can be used. But how? Specifically I can't understand how to deal with phase errors and
I can't make much sense of the literature.
Thank you for advice.
Norman
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It looks similar to what was called a potentiometer in the first 1/2 of the 20th century. Not what potentiometer connotes today.They were used with gavanommeters.for accurate voltage measurements. Very similar to Kelvin Varley dividers but with extra stuff. Calibration would be similar to calibrating a KVD. And not a simple process. Yours looks very nicely made.
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You are right - at the heart of the compensator is a potentiometer. My unit is from the 60s and was in good shape.
I figure that it can be considered a 4-wire resistor with largish lead resistance. As I am mainly interested in
small output voltages I suppose that AC excitation is needed. Coincidently there is a RT-18 inductive voltage
divider sitting on the bench and it would be a shame to let it sit there unused.
After some reading about thermometry bridges I came up with the attached idea/concept
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What are you trying to do with it. Potentiometers are only meant to have zero current from the tap point. Any resistance or leakage from the tap to anything degrades the accuracy. The Ratio transformer is different and possibly more accurate at low voltage, just doesn't work for DC.