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9 PID CONTROL FUNCTION
9.7 Auto-Tuning
Auto-tuning procedure
1. Transferring the output value for auto-tuning to the output value (d)
Set the output value for auto-tuning to the maximum available output value multiplied by 0.5 to 1 for the output equipment.
2. Setting the parameter (s3), target value (SV), etc. that cannot be set in autotuning according to the system
3. Setting to ON b4 of (s3)+1 (operation setting ACT) to start auto-tuning
When the variation from the measured value at the start of auto-tuning to the target value reaches 1/3 or more, auto-tuning is
completed. And bit 4 of (s3)+1 (operation setting ACT) is automatically set to OFF.
Start auto-tuning while the system is stable.
If the system is unstable when auto-tuning is started, auto-tuning may not be executed normally.
Cautions on auto-tuning setting
Note that auto-tuning may not be executed normally if the cautions described below are not followed
• Difference between the target value (SV) and the measured value (PV)
If the difference between the target value (SV) and the measured value (PV) is less than 150 when autotuning is started, auto-
tuning is not executed normally. Accordingly, if the difference is less than 150, set the target value for auto-tuning. Set the
target value again when auto-tuning is completed.
• Sampling time (TS)
Make sure the sampling time is set for auto-tuning to 1 second (1000 ms) or more. It is recommended that the sampling time
is set to that it is considerably longer than the output change cycle.
Cautions on auto-tuning execution
■Program countermeasures when the input value (PV) does not change
When the input value (PV) does not change normally due to factors such as wire breakage in an analog input line, auto-tuning
is not finished. Detect and avoid such occurrences by introducing a sequence to monitor the input value or the elapsed time
from the start of auto-tuning.