For accurate control of the process temperature without constant operator involvement all industrial thermal process relay upon a controller. The controller gets is inputs from contact temperature sensors like thermocouple, RTD or from a non-contact temperature sensor like an infrared temperature sensor. The controller transmits an electrical signal (current or voltage) to a power switch device which can be a simple relay, a solid state relay or a SCR (Silicone Controlled Rectifier).
Remember: The temperature controller is just one part of the entire control system, so it must be selected accordingly.
The basic types of temperature controllers are: