Introduction: For many application, a more precise level of control is required than that of an open-loop
system. By adding a sensor that measures the condition of the load, the system can adjust itself. The
correction is made by sending an output signal from the measuring device to the controller. As shown
in Figure 1, the connection between the measurement device and controller is called the feedback loop.
The comparison between command signal and measured signal produces an error signal that applied to the
amplier. If either the command signal is changed or the measurement feedback signal is changed due to
load condition, the control will produce a dierent error signal. The result will be that the actuator will
automatically be controlled to make the proper adjustment to reach the desired condition.