ABB 800xA Operation page 112

Loop Performance Diagnostics
the control error is often far away (more than 3% of loop range) from the target. A
low index value means that the deviation between process variable and target is
within acceptable limits.
Response speed
This parameter measures the response of the control loop. Some applications
require the control system to respond to set point changes within a given time.
Changes in packing friction, air supply capacity, or component corrosion all act to
change the response time, and the process variable will not follow the loop set point
well. This failure mode is simulated by changing the control variable of the control
system.
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Section 8 Control Loop Asset Monitor (CLAM)
3BUA000150-600