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37
3-7
Control Adjustments
3-7-1 Auto-tuning
Auto-tuning (AT) can be executed independently for any control point, or can be
executed for all control points simultaneously or in sequence. (If the DeviceNet
is being used, auto-tuning cannot be executed in sequence.)
•
If auto-tuning is cancelled, the auto-tuning will stop for all control points at the
same time. (If the DeviceNet is being used, auto-tuning can be stopped for
each control point separately.)
•
When auto-tuning is executed, the optimum PID constants and fuzzy scale for
the set point will be automatically set in the current memory bank. The follow-
ing set values will be changed.
Proportional band (P constant), integral time (I constant), derivative time (D
constant), fuzzy scale 1, fuzzy scale 2
•
The AT indicator will be lit while auto-tuning is being executed.
•
A method of obtaining the characteristics of the controlled object (the limit
cycle method), by causing the output value to fluctuate is used. The application
of the method, however, will vary depending on whether the deviation (the dif-
ference between the set point value and the process value) is greater or less
than 100
°
C or 180
°
F when auto-tuning is started.
Deviation
100
°
C or 180
°
F
Deviation
100
°
C or 180
°
F
Deviation:
100
°
C or 180
°
F
Deviation:
100
°
C or 180
°
F
Auto-tuning starts
Auto-tuning starts
Auto-tuning stops
Auto-tuning stops
Time
Time
Set point
Set point
Limit cycle: Small fluctuations in
output value (40%)
Limit cycle: Small fluctuations in
output value (40%)
•
If auto-tuning is executed for ON/OFF control, auto-tuning will be executed
with large fluctuations in the output value. After auto-tuning is completed,
2-PID control will be executed.
Auto-tuning starts
Auto-tuning stops
Time
Set point
Limit cycle: Large fluctuations in output value (100%)
Control Adjustments
Section 3-7