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4 Basic Operation
4-9
Determining PID Constants (AT,
Manual Setup)
4-9-1
AT (Auto-tuning)
at
4 - 24
• When AT is executed, the optimum PID constants for the set point at that time
are set automatically. A method (called the limit cycle method) for forcibly
changing the manipulated variable and finding the characteristics of the
control object is employed.
• Either 40% AT or 100% AT can be selected depending on the width of MV
variation in the limit cycle. In the AT Execute/Cancel parameter, specify at-2
(100% AT) or at-1 (40% AT). To cancel AT, specify off (AT cancel).
• Only 100% AT can be executed for heating and cooling control.
• If the Heating/Cooling Tuning Method parameter is set to any value other than
0 (same as heating control), the PID constants are set automatically for both
heating control and cooling control.
• AT cannot be executed when control has stopped or during ON/OFF control.
• The results of autotuning are saved in the following parameters in the
Adjustment Level: Proportional Band (P), Integral Time (I), Derivative Time
(D), Proportional Band (Cooling) (C-P), Integral Time (Cooling) (C-I), and
Derivative Time (Cooling) (C-D). If the Adaptive Control parameter (adpt) in
the Initial Setting Level is set for automatic updating (auto) or notification
(info), the change will be reflected in set point response PID, disturbance
PID, and model parameters that give the system characteristics. (*For
information on adaptive control, refer to 5-3 Performing Adaptive Control.)
PID Constants Updated for 2-PID Control
Adjustment Level
p
Proportional
Band
8.0
i
Integral
Time
233
d
Derivative
Time
40
c-p
Proportional
Band (Cooling)
8.0
c-i
Integral Time
(Cooling)
233
c-d
Derivative Time
(Cooling)
40
E5@D Digital Temperature Controllers User's Manual (H224)
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