Thermostat with a stability of ±3.5μK

The design of a thermostat which gives a temperature stability of +or-3.5 mu K over long periods of time is described. Heat input to the thermostat is derived by stirring only. The temperature balance is maintained by changes in the speed of stirring in accordance with the state of a thermistor-based AC Wheatstone bridge. Since the heat input source is so directly coupled to the thermostat water, the thermostat responds very rapidly. Therefore, the thermostat can adjust itself easily to the surrounding temperature without noticeable fluctuations. This method obviates hot spots inside the thermostat and therefore decreases the temperature gradients. It also eliminates the electric and magnetic fields usually created by heating elements. The thermostat has a stabilisation factor of the order of 10 6 with respect to room-temperature fluctuations.