PRINCIPLES OF CONTROL SYSTEMS
Basic process control terms are summarized below.
Process Control Term Definitions Summary
A control system is a system of integrated elements whose function is to
maintain a process variable at a desired value or within a desired range of values.
Control system input is the stimulus applied to a control system from an external
source to produce a specified response from the control system.
Control system output is the actual response obtained from a control system.
An open-loop control system is one in which the control action is independent
of the output.
A closed-loop control system is one in which control action is dependent on the
Feedback is information in a closed-loop control system about the condition of
a process variable.
A controlled variable is the process variable that is maintained at a specified
value or within a specified range.
A manipulated variable is the process variable that is acted on by the control
system to maintain the controlled variable at the specified value or within the