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System Control Using PID
PID is an operating mode that maintains a constant system output by comparing the monitored system
output (feedback) to a setpoint and compensating for the difference between the two. System
adjustments are increased or decreased as a function of the received feedback. This self-correcting
action eliminates the requirement for constant operator intervention.
The automatic adjustment may be either process-variable-, speed-, or position dependent.
The PID Control Switch parameter enables the PID function by allowing the user to select the PID
operating mode. Selecting PID Off disables the PID function.
1.
PID Off — Disables the PID feedback.
2.
Process PID — Monitors the control variable (e.g., temperature, pressure, etc.) as the measurement
that is to be compared to the setpoint in determining the ASD output adjustment. See
3.
Speed PID — Monitors the ASD output speed (e.g., Motor RPM, encoder, etc.) as the measurement
that is to be compared to the speed setpoint in determining the ASD output adjustment.
See
Figure 2.
4.
Simple Position PID — Monitors the load position (e.g., crane, sprayer, etc.) as the measurement
that is to be compared to the setpoint in determining the ASD output adjustment. See
Figures 1 – 3 show the relationship of the parameters required for Process PID, Speed PID, and Easy
Position PID.
Figure 1. Diagram for F359 = Process PID.
PID Deviation
Upper Limit
Process Upper Limit
F367
Process
Reference
Value
F368
Process Lower Limit
PID Deviation
Lower Limit
Feedback Signal
Figure 2. Diagram for F359 = Speed PID.
Process
Increase Rate -
Decrease Rate -
Process Upper Limit
F367
Speed
Process
Reference
Increase/
Value
Decrease Rate
F368
Process Lower Limit
Feedback Signal
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Upper Limit
F364
PID Control
F365
PID Output
Lower Limit
F372
PID Deviation
F373
Upper Limit
F364
F365
PID Deviation
Lower Limit
Delay
Filter
F361
PID Output
Upper Limit
F370
Jump Frequency
Processing
F371
PID Output
Upper Limit
F370
PID Control
F371
PID Output
Lower Limit
Figure 1.
Figure 3.
Acceleration Time 1 -
Deceleration Time 1 -
Frequency
F012
Increase/
Decrease Rate
F013
Lower Limit
Frequency
Upper Limit
Frequency
F012
Jump Frequency
Processing
F013
Lower Limit
Frequency
F009
F010
1
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