Using PID_3Step
5.3 PID_3Step V1
PID control
Function Manual, 03/2017, A5E35300227-AC
151
The pretuning determines the process response to a pulse of the output value and searches
for the point of inflection. The tuned PID parameters are calculated as a function of the
maximum slope and dead time of the controlled system.
The more stable the process value is, the easier it is to calculate the PID parameters and the
more precise the result will be. Noise on the process value can be tolerated as long as the
rate of rise of the process value is significantly higher compared to the noise. The PID
parameters are backed up before being recalculated.
The setpoint is frozen during pretuning.
● The PID_3Step instruction is called in a cyclic interrupt OB.
● ManualEnable = FALSE
● PID_3Step is in "inactive" or "manual" mode.
● The setpoint and the process value lie within the configured limits (see "Process value
settings" configuration).
To perform pretuning, follow these steps:
1. Double-click the "PID_3Step > Commissioning" entry in the project tree.
2. Select the entry "Pretuning" in the "Tuning mode" drop-down list in the working area
"Tuning".
3. Click the "Start" icon.
– An online connection will be established.
– Value recording is started.
– Pretuning is started.
– The "Status" field displays the current steps and any errors that may have occurred.
The progress bar indicates the progress of the current step.
Note
Click the "Stop" icon when the progress bar has reached 100% and it is to be
assumed the controller tuning function is blocked. Check the configuration of the
technology object
and, if necessary, restart controller tuning.
If pretuning was performed without an error message, the PID parameters have been tuned.
PID_3Step switches to automatic mode and uses the tuned parameters. The tuned PID
parameters will be retained during power OFF and a restart of the CPU.
If pretuning is not possible, PID_3Step changes to "Inactive" mode.
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