John, Try for older texts on electricity, 50 years or more back, before things got complicated.
The trick with potentiometers is to establish a precision current in a set of resistance decades, so that E = I * R gives a precise voltage. A galvanometer (or microvoltmeter) is used so the unknown doesn't change the precision current. A resistor and a millivolt trim resistor establish the standard cell voltage using the same precision current in the divider string. The pot that establishes the standard current from a working battery is adjusted until the voltage across the standard cell resistor nulls with the voltage from a primary standard cell. Fluke differential voltmeters use these principles, although they don't use standard cells. You can easily calibrate a Fluke DVM (not digital) to a standard cell. The thing is, standard cells don't like to be disturbed. Shipping would change the equilibrium of the electrolyte and invalidate the millivolt calibration. You can't ship primary standard cells. But they were used in portable devices like thermocouple potentiometers, because 1% accuracy was adequate. I have an extra Fluke DVM around here someplace, if you're interested. Free to a good home for experiments. Bill Hawkins -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of John Ackermann N8UR Sent: Saturday, March 14, 2009 8:34 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] OT: Basics of voltage calibration? I'm interested in learning some basics about precision voltage calibration (as can be realized by the hobbyist, not Josephson Junction systems!). A Google search hasn't turned up anything like a tutorial. Anyone know of any good app notes or other references on things like standard cells, zener references, precision potentiometers, etc? -- and how to use them? Thanks, John _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.