Reading a Thermocouple with Mercury and a Potentiometer

A hobbyist recently restored and tested a seventy-four-year-old potentiometer—a precision instrument for measuring voltage. The device uses a galvanometer balanced against a reference voltage, which comes from a Weston cell, a mercury-based standard that still produces its original specification of one-point-zero-eighteen volts. Connected to a thermocouple and tested against ice water and boiling water, the instrument proved accurate. It even measured the temperature difference between the base and tip of an alcohol flame. According to Hackaday, the story is a reminder of how precisely these analog measurement standards were engineered.

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