Reference variable

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The reference variable is the control technology the size to which the controlled variable is to be brought. It is specified externally by the operator or another technical system. The control compares the controlled variable with the reference variable by calculating the control difference between the reference and controlled variable. The system to be controlled is then influenced accordingly via the actuator .

For example, the temperature is the controlled variable in heating. The temperature set on the thermostat is the reference variable. The difference between the set and actual temperature is the control difference. The heating power is increased or decreased accordingly.

The current value of the reference variable is the setpoint ; analogously, the current value of the controlled variable is the actual value . If the reference variable does not change over time, the terms "setpoint" and "reference variable" are also used synonymously.


  • Erwin Samal, Wilhelm Becker: Outline of the practical control technology . 21st edition. Oldenbourg, Munich 2004, ISBN 3-486-27583-6 , p. 21–23 ( limited preview in Google Book search).