Feedforward or Output Biasing (PID)

Feedforward a disturbance from the system by feeding the .BIAS value into the PID instruction’s feedforward/bias value.

The feedforward value represents a disturbance fed into the PID instruction before the disturbance has a chance to change the process variable. Feedforward is often used to control processes with a transportation lag. For example, a feedforward value representing ‘cold water poured into a warm mix’ could boost the output value faster than waiting for the process variable to change as a result of the mixing.

A bias value is typically used when no integral control is used. In this case, the bias value can be adjusted to maintain the output in the range required to keep the PV near the setpoint.