Industrial heating and temperature controllers are the electric heaters that raise a material to a set temperature, and the controllers that hold it there. They are used in plastics factories, in chip-making and on food lines. Industrial heaters come in several shapes: a band that wraps around a barrel, a rod that is inserted into a hole in a metal block, and an infrared lamp for drying a surface.
A heater alone only gets hot. The controller is what keeps the temperature steady. It reads a temperature sensor many times a second and switches the heater on or off, or changes its power, so that the reading stays at the set point.
The simplest controller switches the heater fully on when the temperature is below the set point and fully off when it is above. The temperature then swings above and below the target. A better controller adjusts how much power the heater gets. It is called a PID controller, after the three calculations that it combines: how far the temperature is from the set point, how long it has been away, and how fast it is changing. A PID controller reduces the power just before the target is reached, so that the temperature settles at the set point instead of overshooting it.
For instance, a plastics factory runs a machine that melts plastic granules and pushes them through a die to make pipes. The barrel of the machine has several zones, each with its own heater, and each zone has to hold a temperature of about 220 °C. If a zone is a little too cold, the plastic does not melt fully and the pipe has weak spots. If it is too hot, the plastic burns. A controller for each zone holds its temperature within a degree or two.
The controllers take their targets from the machine's PLC, which loads a different set of temperatures for each product. Heaters are fitted in machines such as injection moulding machines and many kinds of special-purpose machinery.
The same method is used in the furnaces of chip-making plants. The only difference is how exact the temperature must be. Like other loops, it reports to a SCADA screen.