Siemens SIMATIC S7-1200 Function Manual page 313

If OutputPerOn = FALSE and FeedbackOn = FALSE, you cannot limit the output value.
Output_UP and Output_DN are then reset upon Actuator_H = TRUE or Actuator_L = TRUE.
If endstop signals are also not present, Output_UP and Output_DN are reset after a travel
time of Config.VirtualActuatorLimit × Retain.TransitTime/100. As of PID_3Step Version 2.3
the monitoring and limiting of the travel time can be deactivated with
Config.VirtualActuatorLimit = 0.0.
The output value is 27648 at 100% and -27648 at -100%. PID_3Step must be able to
completely close the valve.
Note
Use with two or more actuators
PID_3 Step is not suitable for use with two or more actuators (for example, in heating/cooling
applications), because different actuators need different PID parameters to achieve a good
control response.
Substitute output value
If an error has occurred, PID_3Step can output a substitute output value and move the
actuator to a safe position that is specified in the SavePosition tag. The substitute output
value must be within the output value limits.
Monitoring signal validity
The values of the following parameters are monitored for validity when used:
● Setpoint
● Input
● Input_PER
● Input_PER
● Feedback
● Feedback_PER
● Disturbance
● ManualValue
● SavePosition
● Output_PER
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.2 PID_3Step
313