Temperature controllers are needed in any situation requiring a given temperature be kept stable. This can be in a situation where an object is required to be heated, cooled or both and to remain at the target temperature (setpoint), regardless of the changing environment around it. There are two fundamental types of temperature control; open loop and closed loop control. Open loop is the most basic form and applies continuous heating/cooling with no regard for the actual temperature output. It is analogous to the internal heating system in a car. On a cold day, you may need to turn the heat on to full to warm the car to 75°. However, during warmer weather, the same setting would leave the inside of the car much warmer than the desired 75°.

For example, in a temperature control system, a high fixed alarm prevents a heat source from damaging equipment by de-energizing the source if the temperature exceeds some setpoint value. A low fixed alarm, on the other hand, may be set if a low temperature could damage equipment by freezing.

Temperature controllers are measurement devices used for temperature control. Dividing into thermocouple-type and resistor-type, the electronic temperature controllers obtain the temperature change from the sensor and send the measured data to the electronic processor. The output device will then control the temperature variation within a specific range.

Due to the fact that water is environmentally safe, abundant, easy to handle, and provides much better heat transfer than air, it is the most practical and commonly used medium for cooling of industrial processes. However, the effective use of water for cooling applications results in challenges in design and operation. Most components in a cooling water system are constructed from metallic materials, especially heat transfer equipment. These components can suffer failures due to many forms of corrosion, cracking, and other damage mechanisms. Nonmetallic components in the cooling water system may also experience degradation and failure. The varied types of damage are caused by differences in cooling water system design, temperature, flow, water chemistry, alloy composition, and operation.

A temperature controller is an instrument used to control temperature calculating the difference between a setpoint and a measured temperature. The controller takes an input from a temperature sensor and has an output that is connected to a control element such as a heater or fan.

To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or RTD as input. It compares the actual temperature to the desired control temperature, or setpoint, and provides an output to a control element. The temperature controller or thermostat is one part of the entire control system, and the whole system should be analyzed in selecting the proper equipment.