A Thermostat with Short‐ and Long‐Term Stability of ± 1.5×10−4°C

The design of a thermostat which gives a temperature stability of ± 1.5 × 10−4°C over a period of weeks is described. The temperature sensors are thermistors stabilized by heat treatment. Heat input derives mainly from stirring and heat output mainly from losses to the surroundings. Residual heat input is removed by stabilized circulating thermostats. Temperature balance is due to spread out bare wire heaters which carry a current proportional to the state of the control DC Wheatstone bridge. The controlling thermistors are maintained in two oil baths and the state of the current in the control heaters is transmitted to the thermistors by a thermal feedback system involving small heating coils which are placed in the oil baths around the thermistors and which carry a current proportional to the heating current.