Control Efficiency Monitor - ABB COMMANDER 351 User Manual

...2.9 Control Efficiency Monitor

PV
y
2
t
approach
Start of
Calculation
2.9.1 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
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.
x t
x
period
1
2
95%
y
1
5%
t
settle
Fig. 2.9 Control Efficiency Monitor Parameters
2 OPERATOR LEVEL...
1 / wave damping:
4
+2%
Set Point
–2%
t
25