ABB C505 User Manual page 37

2.14 Control Efficiency Monitor
Note. With cascade control, the Control Efficiency Monitor is applicable only to the master
controller.
The Control Efficiency Monitor can be used either to compare the relative performance with different
tuning parameters, or when fine tuning the PID settings, to give optimum control.
When the set point is changed, auto mode is selected or following a power failure, input failure or a
large load disturbance, the control monitor performs a series of measurements to indicate the
effectiveness of the current control parameters.
General guidelines are shown in Table 2.2.
Parameter Ideal
Setting
Rate of Fast
Approach
Overshoot Small
Decay Ratio Small
Settling Time Short
Error Integral Small
Actual Effect on Response
Setting
Too slow
Too large
Too large
(Oscill-
atory)
Too long
Too large
Table 2.2 Control Efficiency Monitor Settings
2 OPERATOR LEVEL...
Action
• Decrease proportional band
• Decrease integral time
• Increase derivative time
• Increase proportional band
• Increase derivative time
• Increase proportional band
• Increase integral time
• Increase proportional band
• Decrease integral time
If large overshoot and
oscillatory then:
• Increase proportional band
• Increase integral time
• Increase derivative time
If slow approach and
overdamped then:
• Decrease proportional band
• Decrease integral time
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