Fine Tuning V1 - Siemens SIMATIC S7-1200 Function Manual

4.3.2.3

Fine tuning V1

Fine tuning generates a constant, limited oscillation of the process value. The PID
parameters are optimized for the operating point from the amplitude and frequency of this
oscillation. All PID parameters are recalculated on the basis of the findings. PID parameters
from fine tuning usually have better master control and disturbance behavior than PID
parameters from pretuning.
PID_Compact automatically attempts to generate an oscillation greater than the noise of the
process value. Fine tuning is only minimally influenced by the stability of the process value.
The PID parameters are backed up before being recalculated.
Requirement
● The PID_Compact instruction is called in a cyclic interrupt OB.
● ManualEnable = FALSE
● The setpoint and the process value lie within the configured limits (see "Process value
monitoring" configuration).
● The control loop has stabilized at the operating point. The operating point is reached
when the process value corresponds to the setpoint.
● No disturbances are expected.
● The setpoint may not be changed during controller tuning.
● PID_Compact is in inactive mode, automatic mode or manual mode.
Process depends on initial situation
Fine tuning can be started in "inactive", "automatic" or "manual" mode. Fine tuning proceeds
as follows when started in:
● Automatic mode
Start fine tuning in automatic mode if you wish to improve the existing PID parameters
using controller tuning.
PID_Comact will regulate using the existing PID parameters until the control loop has
stabilized and the requirements for fine tuning have been met. Only then will fine tuning
start.
● Inactive or manual mode
If the requirements for pretuning are met, pretuning is started. The PID parameters
established will be used for adjustment until the control loop has stabilized and the
requirements for fine tuning have been met. Only then will fine tuning start. If pretuning is
not possible, PID_Compact will change to "Inactive" mode.
An attempt is made to reach the setpoint with a minimum or maximum output value if the
process value for pretuning is already too near the setpoint. This can produce increased
overshoot.
PID control
Function Manual, 03/2017, A5E35300227-AC
Using PID_Compact
4.3 PID_Compact V1
111