12. Describe controllers and control modes.

Question

What will be an ideal response?

Answer 1

Controllers and Control Modes
The primary purpose of a controller is to receive a signal from a transmitter, compare this signal to a set point, and adjust the (final control element) process to stay within the range of the set point. Controller- a device designed to compare a signal to a set point and transmit a signal to a final control element. A controller is a complex device designed to control a process.

Controller modes- include proportional P, proportional plus integral PI, proportional plus derivative PR, and proportional-integral-derivative PID. Proportional control is primarily used to provide gain where little or no load change typically occurs in the process. Proportional plus integral is used to eliminate offset between set point and process variables. PI works best where large changes occur slowly. Proportional plus derivative is designed to correct fast changing errors and reduce overshooting the set point. PD works best when frequent small changes are required. Proportional integral derivative is applied where massive rapid load changes occur. PID reduces swinging between the process variable and set point.