For which type of control is feedback required?

The type of control that requires feedback is proportional control. Proportional control is a fundamental concept in process control systems where the output is adjusted in relation to the current error value, which is the difference between the desired setpoint and the measured process variable. Feedback is essential in this type of control as it continuously evaluates the performance of the system and adjusts the control output accordingly.

In proportional control, the controller generates an output that is directly proportional to the error, allowing for a more dynamic response that helps stabilize the system. This feedback mechanism ensures that the system can react to changes and maintain the desired operating conditions effectively.

On-off control, while it can be useful in certain applications, does not utilize continuous feedback in the way proportional control does; instead, it simply switches the output on or off based on a set threshold. Integral and derivative controls are also part of more advanced control strategies and rely on feedback but serve to enhance or complement the basic proportional approach rather than acting independently as a feedback-requiring control type.