8-4
Chapter 8. PID CONTROL TUNING
When the following ST start conditions are satisfied with the control method set at ST ([CtrL] = 2), the ST function
is started automatically to change the PID constants.
(1) ST start by SP change
If the SP is changed in the RUN mode, the ST function is started.
However, if the SP change width is small or if the difference between the SP and PV is small, the ST is not started.
(2) ST start by deviation occurrence
If the difference between the SP and PV is large during control in the RUN mode, the ST is started. If the
difference between the SP and PV is large when the READY mode is changed to the RUN mode, the ST is
started.
If the difference between the SP and PV is large when the control is started in the RUN mode after the power has
been turned ON, the ST is started.
Handling Precautions
• To start the ST, it is necessary that the integration time of the PID constant is
not “0” ([I-1] ≠ 0) and the derivative time is not “0” ([d-1] ≠ 0).
• To start the ST, it is necessary that the mode is the RUN mode and AUTO mode.
• To set the SP change width or the reference value used to judge large/
small difference between the SP and PV, it is necessary to set “High function
configuration”. However, the default settings before shipment apply to most
control subjects.
• When using the heat/cool control, the ST cannot be used.
Starting procedures
(1) Make sure that the PV input or operation end (heater power, etc.) is
controllable.
(2) Make sure that the mode indicator [rdy] is off and the operation is in the RUN
mode. If the indicator [rdy] is lit and the operation is in the READY mode,
change the mode to the RUN mode.
(3) Make sure that the mode indicator [man] is off and the operation is in the
AUTO mode. If the indicator [man] is lit and the operation is in the MANUAL
mode, change the mode to the AUTO mode.
(4) Set the control method of the parameter setting to ST ([CtrL] = 2).
(5) Set the SP.
If the ST is not started since the PV is close to the SP (PV ≈ SP), use the SP
value, which is greatly different from the PV value.
8 - 2 ST (Self-tuning) Function
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