Control loop, closed
In a closed loop, the desired value is continuously compared to the actual value.
w: Set point value or reference variable (required filling level)
x: Actual value or controlled variable (measured filling level)
xw: Control deviation (actual value - set point value), also known as xd
y: Controller out put signal (control variable)
z1: Disturbance variable 1 (outflow from the tank)
z2: Disturbance variable 2 (evaporation of liquid from the tank)
During a control operation a physical variable (e.g. temperature, pressure etc.) is constantly measured and compared to a set point of the variable. The aim is to cause a matching of these two values.
This closed sequence of actions is called closed-control loop.