Pretuning V1 - Siemens SIMATIC S7-1200 Function Manual

4.3.2.2

Pretuning V1

The pretuning determines the process response to a jump change 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.
Requirement
● The "PID_Compact" instruction is called in a cyclic interrupt OB.
● ManualEnable = FALSE
● PID_Compact is in "inactive" or "manual" mode.
● The setpoint may not be changed during controller tuning. PID_Compact will otherwise be
deactivated.
● The setpoint and the process value lie within the configured limits (see "Process value
monitoring" configuration).
● The difference between setpoint and process value is greater than 30% of the difference
between process value high limit and process value low limit.
● The distance between the setpoint and the process value is > 50% of the setpoint.
Procedure
To perform pretuning, follow these steps:
1. Double-click the "PID_Compact > Commissioning" entry in the project tree.
2. Select the entry "Pretuning" in the "Tuning mode" drop-down list.
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.
PID control
Function Manual, 03/2017, A5E35300227-AC
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.
Using PID_Compact
4.3 PID_Compact V1
109