Rockwell Automation T6200 Compressor Anti-Surge and Capacity Controller - Manual (Page 112)

Control Primer
7-10
Referring to Figure 7-6, the output responds to the step input immediately and then integrates to a
stable output.
Proportional-Plus-Derivative (PD) Action
The advantage of adding derivative action to other actions in the controller is that it has a lead that can be
used to compensate for lag in the process (Figure 7-7). Adding this lead will improve the loop response
time. A disadvantage is that derivative action over responds to process noises and high frequencies
and is not easy to use or tune. It's application is usually restricted to processes with large lags such as
temperature control of a large volume.
Figure 7-6
Proportional-Plus-
Integral (PI) Control
Action
Figure 7-7
Proportional-
Plus-Derivative
(PD) Control
Action