Principles For Control; Controlled System And Actuators - Siemens SIMATIC S7-1200 Function Manual

Principles for control

2.1

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.
Actuators
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.
Application
Liquid and gaseous mass flow
Solid mass flow, e.g., bulk material
Flow of electrical power
16
Actuator
Valve, shutter, gate valve
Articulated baffle, conveyor, vibrator channel
Switching contact, contactor, relay, thyristor
Variable resistor, variable transformer, transistor
Function Manual, 03/2017, A5E35300227-AC
2
PID control