How to choose the proper mode of control according to your process?


#1

As everyone knows different types control modes are there .It is a complex process to choose the proper mode of control to use on a particular process.

ON-OFF control - Popular because of its simplicity. In general it functions satisfactorily if
the process has a large capacitance and minimum dead time

Proportional - Proportional control reduces cycling below that of ON-OFF control. It
does a particularly good job when process capacitance is large and dead
time small

Proportional plus reset - The primary advantage of proportional-plus-reset is that it will eliminate
offset with load changes. It can be used even when process capacitance is
small and load changes are large.

Proportional plus reset and rate - Rate action can be very useful in minimizing overshooting of the process variable when the controller is trying to compensate for large or rapid load
changes. It is also useful in preventing overshoot of the process variable in
the start-up of batch processes.