A Thermostat is a device which maintains the process temperature at a specified set point. Thermostats are used in room heating, in refrigeration, in almost all process industries and in heating systems.
A thermostat can be a simple mechanical set-up which contains a sensing elements which opens or closes a valve.
Other thermostats receive the temperature from a sensor and give a command to an actuator or a valve to open or close depending on the input signal.
These thermostats receive the temperature input from a thermocouple, thermistor or an RTD.
Modern digital thermostats can be programmed and have the temperature values and the set points on touchscreen. The set points and the response of the thermostats can be programmed.
The thermostat is different from a temperature switch in that the temperature switch does not control the temperature. Two temperature switches can be made to function like a thermostat and control a heater. One controlling the upper limit to switch off the heater and other the lower limit to switch on the heater. This, however, may not be accurate.