YME Engineering Course

A. INTRODUCTION TO PROCESS CONTROL SYSTEM
Setpoint
Input
(Measured or Process Variable)
Output (Manipuated Variable)
Control Unit
I/P
Time Lag
Figure: Basic Control Loop
A.2. PROCESS CONTROL FUNCTIONS
The method to directly control process is roughly divided into two categories: the
loop control that inputs analog measured values (including feedback control and
feed forward control) and the sequential control that inputs operating sequences
and process status signals.
♦ Feedback Control
Control that acts to correct the process variable (e.g. Temperature in a
tank) to agree with the target value (setpoint) by comparing both.
♦ Feed forward Control
Control which takes a corrective action by measuring the disturbances
(e.g. Ambient temperature) and directly driving the valve before it affects
the process.
♦ Sequential Control
Control that successively advances each control step in accordance with
the pre-determined sequence.
YME Training Center
A-2
CS3KR3-ENG 1 ST Edition Jan 2002