______ is the reference input minus the primary feedback.
Right Answer is:
Actuating signal is obtained from a comparison measuring device and is the reference input minus the primary feedback. This signal, usually at a low energy level, is the input to the control elements that produce the manipulated variable.
Manipulated variable is the quantity obtained from the control elements that is applied to the controlled system. The manipulated variable is generally at a higher energy level than the actuating signal and may also be modified in form.