A simple furnace temperature controller
M Shepherdson · Journal of Scientific Instruments · 1952
A two-position controller is described for use with a thermocouple or d.c. resistance bridge as sensing element. The error signal operates a mirror galvanometer which controls the position of a spot of light on a photocell. This, through a single valve amplifier, controls a thermal relay which switches the power. The circuit is very simple and is arranged to prevent overheating of the furnace whatever probable fault develops.