Rockwell Automation T6200 Compressor Anti-Surge and Capacity Controller - Manual (Page 107)

Control Primer
7-5
Proportional (P) Action
The proportional action has a linear response. The controller output response will have the same
shape as the controller error response but the amplitude may be different and it may also have an
offset. Refer to Figure 7-2.
Sometimes the proportional action is expressed in percentage and is called proportional band (PB).
The expression for proportional band is:
PB = 100/K + b
(7-2)
where:
b = output bias in %
K = controller gain