Precision temperature control

The problems associated with accurate control of temperature are discussed, and the various types of temperature-sensitive elements considered. It is shown that the thermistor offers greatest sensitivity and stability. The criteria underlying the design of a temperature-sensitive bridge using a thermistor are analysed. Details of the mechanical arrangements necessary for the close control of temperature of a volume of liquid are given, together with the design of the associated control equipment. The results of tests using the complete controller are presented, and they show that stabilities considerably better than ±0.0005°C. over a period of several hours are attainable for a volume of approximately 0.5 ft3, without recourse to excessive stabilisation of the ambient temperature. These results are reproducible over a temperature range of 20¿50°C.