PID control
16 Function Manual, 03/2017, A5E35300227-AC
Controlled system and actuators
Controlled system
Room temperature control by means of a heating system is a simple example of a controlled
system. A sensor measures the room temperature and transfers the value to a controller.
The controller compares the current room temperature with a setpoint and calculates an
output value (manipulated variable) for heating control.
A properly set PID controller reaches this setpoint as quickly as possible and then holds it a
constant value. After a change in the output value, the process value often changes only with
a time delay. The controller has to compensate for this response.
The actuator is an element of the controlled system and is influenced by the controller. Its
function modifies mass and energy flows.
The table below provides an overview of actuator applications.
Liquid and gaseous mass flow
Valve, shutter, gate valve
Solid mass flow, e.g., bulk material
Articulated baffle, conveyor, vibrator channel
Flow of electrical power
Switching contact, contactor, relay, thyristor
Variable resistor, variable transformer, transistor
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