Device that detects temperature changes for the purpose of maintaining the temperature of an enclosed area essentially constant. The thermostat generates signals, usually electrical, to activate relays, valves, switches, and so on when the temperature rises above or falls below the desired value. Thermostats are used to control the flow of fuel to a burner, of electric current to a heating or cooling unit, or of a heated or cooled gas or liquid into the area it serves. They are also used in fire-detection warning systems.
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