34
…2.14
Control Efficiency Monitor
2.14.1
Manual Tuning
The Control Efficiency Monitor may be used for manually tuning the PID parameters. The following
method describes how to tune the controller for
1
/
4
wave damping:
a) Set the integral and derivative action times to OFF.
b) Set the proportional band (PB) to a low setting.
c)
Apply a small set point change.
d) Use the Control Efficiency Monitor to note the decay ratio.
e) If the decay ratio > 0.25, increase the Proportional Band until decay ratio = 0.25
If the decay ratio < 0.25, decrease the Proportional Band until decay ratio = 0.25
f)
Leave the proportional band at the setting which gives 0.25 decay ratio and, using the Control
Efficiency Monitor, note the period between peaks.
g) Calculate and set the following parameters:
Integral action time = Period/1.5
Derivative action time = Period/6
Note. The manual tuning facility must not be used with boundless motorized valve control, as
an Integral Action Time is required for these applications.
…2
OPERATOR LEVEL
Set Point
x
1
x
2
y
1
y
2
95%
5%
t
period
PV
Start of
Calculation
t
+2%
–2%
t
settle
t
approach
Fig. 2.14 Control Efficiency Monitor Parameters
