Thermostat suitable for controlling air temperature, particularly in biological research

Abstract

Some of the features essential to the control of air temperature in small and unlagged containers are outlined, and apparatus is described which will control the temperature in such a container to [plus or minus] 1/50[degree] C. A system of continuous proportional control is used, based on a two-stage directly coupled amplifer whose input is dependent on the resistance of a thermistor, and whose output is fed directly to the heating element. Incorporation of variable positive feedback makes it possible to attain high sensitivity, or alternatively to use the equipment without modification as a switching thermostat and electronic relay for large power loads. A description is also included of a temperature-measuring system based on a thermistor, which will display the air temperature to [plus or minus] l/50[degree]C.