674
35 CPU MODULE BUILT-IN ANALOG FUNCTION
35.6 Function (PID Control Via Parameter)
Precautions
PID control affected by the constant scan setting
Since PID control is executed in END processing, depending on the constant scan setting (0.2 to 2000ms), a delay may occur
in the sampling time or the control output cycle (heating control output cycle, cooling control output cycle), preventing stable
PID control. If PID control is not stable, check the constant scan time setting.
Multiple settings for PID control
For PID control, four settings can be configured at the same time. When devices are set in all parameters for which device
indirect specification is possible, the number of devices to be used becomes 28 at maximum per one setting, and 112 at
maximum for four settings. Ensure that no device duplication occurs in parameter settings.
When setting parameters
Parameters cannot be written in any of the following cases. Be careful when setting parameters.
• If a device already set elsewhere is set
• If an item required to be set is not set
Simultaneous use with another function
The scan time may become longer depending on another function. If the setting for the sampling time or control output cycle
is not large enough in relation to the scan time, stable PID control may not be possible. Either check and correct the setting for
the sampling time or control output cycle, or correct another function to be executed together.
When the operating status of the CPU module is set to PAUSE.
While the PID control execution command is set to on, if the operating status of the CPU module is set to PAUSE, a PID
control stop error occurs, and this function stops. If the CPU module is set to PAUSE, set the CPU module to STOP once, and
then set it to RUN.
For details on the devices to be cleared when a PID control stop error occurs, refer to the following.
Page 673 Error code overview
When the setting value of a parameter is changed during control execution
Even if the setting value of a parameter is changed during control execution, the change is not applied to the control
immediately. The change will be applied to the control in the sampling time cycle. Also, if the setting value of the sampling time
is changed, the change will be applied at the timing of the sampling cycle before the change.
■When a setting value is changed during auto tuning execution
If a setting value of the parameter corresponding to the auto tuning stop conditions
*1
is changed during auto tuning execution,
a PID control stop error will occur, causing auto tuning to stop (the other setting values will not be changed even if a change is
attempted).
*1 For the auto tuning stop conditions, refer to the following.
Page 652 Execution and stop conditions for auto tuning
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