Control difference

Block diagram of a simple standard control loop consisting of the functional elements of control system , measuring member , controller and actuator and the functional quantities controlled variable y (with actual value y _M , setpoint w and control difference e = w-y _M ), the control variable u , manipulated variable u _R and disturbance variable ( n) d

The control difference is in the control engineering , the difference e = w-y _M between the predetermined instantaneous value or setpoint w (of the command ) and the measured value or actual value y _M of the control variable .

If, for example, the temperature in a greenhouse is to be 20 ° C, but an actual temperature of 18 ° C is measured, the control difference is +2  K (Kelvin) .

The control deviation, on the other hand, is the difference x _W = y _M −w between actual value y _M and setpoint w, i.e. the negative control difference: x _W = −e.

The task of a control is to reduce the amount of the control difference, ideally to bring it to zero.

In NC technology , the deviation between the position setpoint and the actual position value is referred to as a following error .