Siemens SIMATIC S7-1200 Function Manual page 362

Instructions
9.2 PID_3Step
Meaning of values
State / Re- Description
tain.Mode
0 Inactive
The controller is switched off and no longer changes the valve position.
1 Pretuning
The pretuning determines the process response to a pulse of the output value and searches for the point of
inflection. The optimized PID parameters are calculated as a function of the maximum rate of rise and dead
time of the controlled system.
Pretuning requirements:
State = 0 or State = 4
•
ManualEnable = FALSE
•
The motor transition time has been configured or measured.
•
The setpoint and the process value lie within the configured limits.
•
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 as compared to the noise.
Before the PID parameters are recalculated, they are backed up and can be reactivated with Con-
fig.LoadBackUp. The setpoint is frozen in the CurrentSetpoint tag.
The controller switches to automatic mode following successful pretuning and to "Inactive" mode following
unsuccessful pretuning.
The pretuning phase is indicated with the SUT.State tag.
362
Function Manual, 03/2017, A5E35300227-AC
PID control