YME Engineering Course

I. REGULATORY CONTROL FUNCTION BLOCKS
♦ Non-Linear Gain
The non-linear gain function changes the proportional gain in accordance
with the deviation of the process variable (PV) from the setpoint value
(SV) in the control computation. As a result, a non-linear relationship is
formed between the manipulated output change (∆MV) and the deviation
of the process variable (PV) from setpoint value (SV). The non-linear gain
function is used for pH control, in which the process gain often becomes
too high near the target value, or for buffer tank level control, whose
purpose is to stabilize the discharge volume while maintaining the tank
level within the limits. The actions that realize the non-linear gain function
include “gap actions” and “squared deviation actions.”
The gap action moderates control effects by lowering the proportional gain
when the deviation is within the preset gap width (GW). The parameter of
the gap action:
• Gap width (GW):
Engineering unit data between 0 and the PV scale span range limit.
The default is 0.
The squared deviation action changes the proportional gain in proportion
to the degree of deviation when the deviation is within the preset gap
width (GW). The parameter of the squared deviation action:
• Gap width (GW):
Engineering unit data between 0 and the PV scale span range limit.
The default is 0.
♦ Deadband Action
The deadband action stops the manipulated output value (MV) from
changing while the deviation (DV) is within the preset deadband (DB)
range, by causing the manipulated output change (∆MV) to be “0.”
Figure: Characteristics of Deadband Action
YME Training Center I-17
CS3KR3-ENG 1 ST Edition Jan 2002