Null Voltmeter

A 1.0186V standard cell is on the left side. With switches in SC calibration position the upper fine and course potentiometers balance the galvanometer (about 10ma current from supply battery). At each side of 200mohm resistors the switchs select range of 9mV from left to 0mV at right. The wiper full ccw adds 0.0 mV and full cw adds 0.9 mV approximately. When the unknown battery taps into voltage divider at the location that gives within about 10 uA or less of 0A the galvanonometer is as close as I could get to balanced and the 0 mV to 9 mV value is found. I saved it as calibrated and balanced to 1.0186 standard cell with unknown voltage as 3mV and 3mV switch closed. Make sure only one switch closed at a time. Let me know if you see mistakes, have fun with it.

published 5 years ago