A controller essentially is a/an

• A controller is essentially the comparator that compares the given input with the reference input and generates the error signal.
• The reference input is the actual signal input to the control system.
• The error signal is the input to the controller, and it causes the output to be the desired output.
• The controller is used in closed-loop control systems.

Closed-loop control system:

The closed-loop control system can be described by a block diagram as shown in the figure below.

r(t) is the error signal given to the input of the controller.

These are the systems in which the control action depends on the output. These systems have a tendency to oscillate.

Ex: Temperature controllers, speed control of the motor, systems having sensors, etc.

Advantages:

• More accurate
• Non-linear distortions are less
• The output is less sensitive to parameter changes within the system
• Bandwidth increases

Disadvantages:

• Design is complicated
• More expensive
• May become unstable, if there are malfunctions in the feedback.