____ signal will become zero when the feedback signal and reference signs are equal.
Right Answer is:
In a closed-loop control system, the actuating error signal which is the difference between the input signal and the feedback signal (which may be the output signal itself or a function of the output signal and its derivatives and/or integrals)
Actuating signal is proportional to the rate of change of error. Hence if the feedback and reference signal are equal the error will become zero, therefore, the actuating signal will also become zero.