8-3
● Operation during execution of AT
The AT function calculates the PID constants using the limit cycle.
(1) When the AT function is started, a point, where the SP and PV deviations are
split to “2:1”, is determined as ON/OFF change point of the MV (manipulated
variable).
(2) When the limit cycle is judged as stable, the PID constants are changed and the
AT function is completed.
Handling Precautions
• Before starting the AT function, put the PV input and/or operation end
(heater power, etc.) in the controllable status.
• When the control method is set at “ON/OFF control” ([CtrL] = 0), the
AT function cannot be started. To operate the AT function, set the
control method to “Fixed PID” ([CtrL] = 1) or “ST” ([CtrL] = 2).
• To start the AT, it is absolutely necessary that the operation is in the
READY mode and AUTO mode, and no PV input errors occur.
• If the mode is changed to the READY mode or MANUAL mode or if
the PV input error or power failure occurs during execution of the AT
function, the AT function is stopped without changing of the PID
constants.
• The number of limit cycles and period of time from the AT start to AT
end may vary depending on the control subject.
• The MV ON and OFF are repeated several times during execution of
the AT function to perform the limit cycle. (The OFF operation
described here means MV limited by the MV low limit at AT ([At.oL])
or MV high limit at AT ([oL]). The default setting before shipment is
“0%”. Additionally, the ON operation described here means MV
limited by the MV high limit at AT ([At.oH]) or MV high limit at AT
([oH]). The default setting before shipment is “100%”. If this AT
operation does not function correctly, take any of the following
measures:
(1) Change the MV low limit at AT ([At.oL]) or MV high limit at AT
([At.oH]) to an appropriate value, and then start the AT function.
(2) Use the ST function.
(3) Set the PID constants manually without use of AT.
• Appropriate PID constants cannot be obtained depending on the
control subject. If this happens, set the PID constants manually.
• The MV ON/OFF change point determined when the AT function is
started does not change even though the SP is changed while the AT
is running.
Chapter 8. PID CONTROL TUNING
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