35 CPU MODULE BUILT-IN ANALOG FUNCTION
35.6 Function (PID Control Via Parameter)
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Auto-tuning function
The auto-tuning function automatically sets the best PID constants.
In the auto tuning, the control output is turned on and off, and PID constants are calculated depending on the cycle and
amplitude of hunting that occurs when overshoots and undershoots of the temperature process value (PV) to the target value
(SV) are repeated.
For the on/off operation during auto tuning, in the same way as during PID control, the control output is performed based on
the value for the cooling control output cycle setting (heating control output cycle setting, cooling control output cycle setting).
In addition, during auto tuning, when the upper limit/lower limit output limiters (heating upper limit limiter, cooling upper limit
limiter) are set, the output value (MV) is limited according to their settings.
■Auto-tuning method and cycle
PID control parameters are calculated by the relay feedback method.
Depending on the control mode, the auto tuning cycle is as follows.
• In standard PID control, two cycles of auto tuning are executed.
• In heating-cooling PID control, normally two cycles are executed. When the ambient temperature setting function is
enabled, 2.5 cycles are executed.
When auto tuning is executed, standard PID control and heating-cooling PID control each calculate the following by the relay
feedback method.
Standard PID control (forward operation, backward operation) Heating-cooling PID control
• Proportional gain
• Integral time
• Differential time
• Heating proportional gain
• Cooling proportional gain
• Integral time
• Differential time
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