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...5 CONTROL OPERATION
5.7 Auto-tuning Introduction
Information.
• On demand user-activated tuning.
• Two types of auto-tuning – initial 'Start-up' and when close to Set Point.
• Tuning for P, PI or PID control can be selected.
• Tuning for 1/4 wave damped or minimum overshoot can be selected.
• Automatic entry of calculated control terms – unless an auto-tune error occurs.
• Error and Caution messages – indicate reason for tuning problems.
Calculated Trip
Point
PV
Output
Information. The noise level of the process is
monitored and then a step is applied to the control
output value. The response of the process is recorded
and these results are used to calculate the control
terms.
Fig. 5.6 'Start-up' Auto-tuning
20
Set Point
Time
Output Step
Size
Time
Self-tune High Limit
Signal Noise
Values at
Start of
Self-tune Low Limit
Execution
Controller
Output
Information. 'At Set Point' auto-tuning automatically
calculates the PID terms based on the process reaction
during an auto-tuning cycle. The controller output is
manipulated to give six process oscillations which are
used to determine the tuning parameters.
Fig. 5.7 'At Set Point' Auto-tuning
Hysteresis
Hysteresis
Value
Band
Output Step
Time
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