1. Introduction to
    control engineering

1.2 Control engineering terminology

The terms of control engineering are described here using the example of a level control.

The control loop consists of:

  • controlled system
    controlled systems are any system, installation or equipment whose behaviour is to be managed by closed loop control.
    In this example, the tank (1).

  • measuring element
    Measuring elements are all kinds of sensors that detect the process values in the control loop. In this example, a level sensor (2).

  • controller
    The controller (3) is the component that performs the actual control. It triggers actuators to carry out actions.

  • actuator
    Actuators are components that influence the process on behalf of the controller. In this example, a control valve with drive (4) at the tank inlet.

  • control system
    The control system consists of the controller and the comparing element. If necessary, the measuring element and actuator can also be counted as part of the control system.

Level control components:
1 tank
2 level sensor
3 controller
4 control valve

Elements and measured variables in control loop as block diagram

Measured variables in the control loop are:

  • controlled variable x
    In this example, the actual level in the tank (feedback value).

  • reference value w
    In this example, the desired level (setpoint).

  • manipulating variable y / controller output variable y
    In this case, the inflow into the tank or the control signal output by the controller to the actuator.

  • disturbance variable z
    In this example, the drainage from the tank.

  • actuating variable / control difference e
    Variation of the controlled variable x (feedback value) from the desired reference variable w (setpoint).

This video introduces you to another example to discover the components of a feedback control system and how they interact with each other.