Temperature controllers are devices used to adjust the temperature of the controlled device to the set target temperature. The types available include digital controllers that can display temperature along with properties such as humidity, pressure or flow rate. Temperature controllers compare the temperature measured by the sensor (thermocouple or resistance temperature detector) to the target temperature, and send out a control signal used to control the output of an electric heater. The control methods used include ON/OFF control and PID control, so the right control method should be selected. The controlled device will be affected by the heat capacity and operating environment, creating different responses to temperature control. To properly control temperature, the right temperature controller should be selected for the properties of the controlled device.