TABLE OF CONTENTS Automatic control is required (1) for precise control of the process to produce more uniform and high quality product, (2) for processes which are too rapid for manual control and (3) in hazardous operations where remote control is a necessity. A control system is characterized by an output variable (e.g., temperature) that is automatically controlled through the manipulation of the inputs.
The inputs to the process are regulated independently without using the measurement of the controlled output variable to readjust the inputs.
This implies that the measurement of the controlled variable is used to manipulate one of the process variables.
The measurement of one input variable is used to manipulate another input variable.
Cascade control involves the use of the output of a primary controller to adjust the set point of a secondary controller and is commonly used in feedback control. The ratio and selector controls are two other control modes which use two or more interconnected instruments.
Servo-operation : In this mode, the control system is designed to follow the changes in the set point as closely as possible according to some prescribed function.
Regulatory Operation: In regulator operation, the control system is designed to keep output constant i.e. to maintain the controlled variable at a fixed value inspite of the changes in load. This is more common in the control of chemical processes.
In this type, when the...
