Which of the following statements are true? For the false statements, explain why you think they are false:
(a) Feedforward and feedback control require a measured variable.
(b) For feedforward control, the measured variable is the vari able to be controlled.
(c) Feedback control theoretically can provide perfect control (i.e., no deviations from set point) if the process model used to design the control system is perfect.
(d) Feedback control takes corrective action for all types of process disturbances, both known and unknown.
(e) Feedback control is superior to feedforward control.

Measured variable is required for feedback and feed forward as the corrective measures taken by the controller are based on the measured variable as the without the measured variable there won't be any error.

Since, error is the difference between the measured variable and a set standard.

In the feedback control mechanism, evaluation of error is done and then corrective measures are taken according to the error evaluated no matter known or unknown.

Thus option (a) and (d) are correct.