Understanding temperature control options.

What is temperature control?

Temperature control is the process that applies to the control of transfer of energy from one source to another. For example, boiler to water for heating and hot water or radiator to air within occupied spaces.

How does a temperature controller work?

A temperature controller will take an input signal from a temperature sensor and will in turn create an output signal that is connected to the heating element.

The controller will compare actual temperature of a fluid or space to the desired control temperature, or setpoint.

What are the different types of controller?

On/Off Control

An on/off controller is the simplest method of control available. Quite simply the on/off controller will switch either when the actual temperature is above or below the desired set point setting.

During operation the actual temperature setting will fluctuate, going from above set point to below and back again. This fluctuation can result in frequent cycling. To prevent damage to system components, an on/off differential is added to the controller logic.

On/Off control is suitable where precise temperature control is not required.

Proportional Control

Proportional controls are designed to eliminate any frequent cycling that is associated with on/off controls.

A proportional controller effectively varies the amount of power supplied to a heater as the actual temperature approaches the desired set point. This will gradually slow down the application of heat energy so that the set point is not exceeded.

PID Control

Proportional, Integral & Derivative control (PID) combines proportional control with two further adjustments; which helps the heater automatically compensate for changes within the system.

These further adjustments, integral and derivative logic, must be individually adjusted to a particular system, either by trial and error or through automatic 'auto tune' controllers.

It provides the most accurate control of the three controller types and is best used in systems which have a relatively small mass, those that react quickly to changes in the energy added to the process.