Rockwell Automation T6200 Compressor Anti-Surge and Capacity Controller - Manual (Page 108)

Control Primer
7-6
The advantages of the proportional action are: it is simple, easy to tune, and has a rapid response.
The disadvantage is that it has an offset.
Using the expression in Figure 7-2 and substituting e with expression 7-1 yields the expression for m
the manipulated output:
m = K ( r - c ) + b
(7-3)
Figure 7-3 is an example of how the offset can be shown by repeatedly solving for the manipulated
controller output (m) in expression 7-3. Let the setpoint (r) change from 0 to 0.23, gain (K) = 0.5,
bias (b) = 0, and c
n
= m
n-1
.
Figure 7-2
Proportional (P)
Control Action