Abstract: A temperature control system for maintaining a selected location at a preselected temperature comprises a supply of heat transfer fluid, a first control for controlling the temperature of the heat transfer fluid, a heat exchanger for receiving the heat transfer fluid and establishing a heat exchange relationship between the heat transfer fluid and the material at the selected location, a second control for controlling the supply of heat transfer fluid to the heat exchanger, and a thermostat. The thermostat is a differential thermostat having a first sensor to sense the temperature at the selected location and a second sensor to sense the temperature of the heat transfer fluid, and is connected to the second control and is operative to actuate the second control to maintain the difference between the temperatures sensed by the first and second sensors at a selected value. Therefore, adjustment of the first control cause the preselected temperature to be adjusted accordingly.

Abstract: Expansion of a fluid on increase in temperature is used to control a switch or other control output device. In one construction, two fixed quantities of fluid, separated by a flexible diaphragm, are in thermally-conductive contact with different respective regions, and change in the temperature relationship between the regions manifests itself as a change in the pressure across the diaphragm, thus displacing the diaphragm. Displacement of the diaphragm actuates a switch or a modulating control or indicating device. In other constructions, convective flow is used to influence a flow-sensitive device including a switch or a modulating control or indicating device.