Rockwell Automation T6200 Compressor Anti-Surge and Capacity Controller - Manual (Page 109)

Control Primer
7-7
0
0.05
0.1
0.15
0.2
0.25
Time
Level
Output (m)
Setpoint (r)
The offset is: r - c = 0.23 - 0.077 = 0.153
The ideal controller would work to make it's input equal to the setpoint. In this example the
controller stabilizes with a difference between the input and the setpoint of 0.153. This is called the
offset.
This offset can be eliminated by using proportional and integral action together, as described later.
Figure 7-3
Proportional (P)
Control Action
Offset Example