PROPERTIES AND USES OF THERMISTORS 



197 



be dissipated in the element by the control circuit to permit the arrange- 

 ment to operate relays, motors or valves. 



Because of their high temperature sensitivity, thermistors have shown 

 much promise as control elements. Their adaptability and their stability 

 at relatively high temperatures led, for instance, to an aircraft engine con- 

 trol system using a rod-shaped thermistor as the control element.^ The 



thermistor, mounted in a standard one-quarter inch diameter temperature 

 bulb assembly, operated at approximately 275 degrees centigrade. It was 

 associated with a differential relay and control motor on the aircraft 28 

 volt d-c system. The power dissipation in the thermistor was two watts. 

 The resistance of a typical thermistor under these high temperature con- 

 ditions remained within ±1.5 per cent over a period of months. This 

 corresponds to about ± one centigrade degree variation in calibration. 

 Several other related designs were developed using the same control system 



