Loop Performance Diagnostics - ABB 800xA Operation

Section 8 Control Loop Asset Monitor (CLAM)
Loop Nonlinearity
Many problems in control loop performance are caused by significant nonlinearity
within the control loop. If the controller is in manual mode, a significant oscillation
is always externally generated. If the controller is in automatic mode, then a
significant external oscillation is identified based on the following characteristics:
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The analysis is based on nonlinearity analysis involving several indices.

Loop Performance Diagnostics

Loop Performance Diagnostics include the following:
Loop Tuning
The effectiveness of a Control loop operation depends on the tuning parameters of
the control loop. The plant personnel must tune the controllers and keep the process
operating at peak efficiency.
Over a period of time, the process may show signs of physical wear or the normal
operating point of the plant may shift. These changes degrade the performance of
the control loops requiring them to be retuned. When control loop performance
shows signs of degradation the Control loop asset monitor identifies and displays
the diagnostics on the faceplate.
Non oscillating loops should not exhibit significant nonlinearities and the tuning
indices should indicate potential improvement. Oscillating loops should not
oscillate due to nonlinearity (stiction and others). The Harris index should be low
and the oscillation amplitude should vary significantly.
The oscillation diagnosis is based on the oscillation indices. If an oscillation is
detected, then its main period and amplitude are described by different indices.
Other relevant measures like symmetry, regularity, severity etc. are important for
more detailed analysis. The oscillation diagnosis is not used if the data was
quantized.
3BUA000150-600
The oscillation is rather linear.
No stiction is detected.
The oscillation is rather symmetric.
The loop is not saturated.
Loop Performance Diagnostics
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