What is Temperature Controller?

A temperature controller is a device that is used to control temperature.

The role of the temperature controller is to measure the temperature thru the thermocouple, compare it to the set point and to calculate the amount of time the heater should remain switched on to maintain a constant temperature.

Working

It does this by first measuring the temperature (process variable), it then compares to the desired value (set value). The difference between these values is known as the error (Deviation). Temperature controllers use this error to decide how much heating or cooling is required to bring the process temperature back to the desired value. Once this calculation is complete the controller will produce an output signal that effects the change required. This output signal is known as the (manipulated value) and is normally connected to a heater, control valve, fan or some other “final control element” which actually injects or removes heat from the process.

Temperature control applications in industry:

  1. Heat Treat/Oven. Temperature controllers are used in ovens and in heat

      Treating applications within furnaces, ceramic kilns, boilers, and heat

      Exchangers.

       2. Packaging.

       3. Plastics.

       4. Healthcare.

       5. Food & Beverage.

Types of Temperature controllers

1. On/off temperature Controller.
2. Proportional Control.

    3.    Proportional integral derivative control (PID)

On/off temperature Controller

An on-off temperature controller is the simplest form of control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the set point.

Working

For heating control, the output is on when the temperature is below the set point, and off above set point. Since the temperature crosses the set point to change the output state, the process temperature will be cycling continually, going from below set point to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an on-off differential, or “hysteresis,” is added to the controller operation.

This differential requires that the temperature exceed set point by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or making fast, continual switches if the cycling above and below the set point occurs very rapidly.

On-off control is usually used where a precise control is not necessary, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm.One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.

Proportional Control

Proportional controls are designed to eliminate the cycling associated with on-off control.

Types of Proportional Control Temperature controllers

1. Precisely control
2. sensitive control