Continuous Control Thermoregulator

Conditions determining constancy of furnace temperature are discussed, and it is pointed out that the effectiveness of a thermostat should be assessed by comparing the temperature fluctuations of the uncontrolled furnace with those of the controlled furnace. A continuous control thermoregulator of the photocell-thyratron type in which the controlling influence is applied through a saturated choke is described. Records obtained with different furnaces show that variations in supply voltage are mainly responsible for furnace temperature fluctuations, and that the thermoregulator reduces these fluctuations by a factor of 1/100. The use of a photocell in conjunction with a phase-controlled thyratron for producing in the latter an anode current which would follow progressive changes in the illumination of the photocell was described by Hull(1) in 1929. The device has been employed by Zabel and Hancox(2) for maintaining a constant temperature in a furnace. The temperature is measured by thermocouple or resistance thermometer, the out-of-balance potential being applied to a galvanometer the mirror of which reflects light on to a V-slit in front of the photocell. The amount of light falling on the cell determines the thyratron current, a portion of which passes through the furnace windings. This method of applying the thyratron current would appear to require, in order to correct for mains voltage fluctuations of the magnitude generally experienced, a greater anode current than may be safely passed by the