Siemens SIMATIC S7-1200 Function Manual page 205

The temperature at the additional measuring point Input2 drops. The temperature of the
main controlled variable Input1 drops as well and cannot be held at the setpoint any longer.
Once the fault has been remedied, the Input2 will continue to drop and the heating power is
further increased by the limiting controller. As soon as the main controller has calculated a
lower heating power as output value, the plant returns to normal operation so that the main
controller PID_Temp_1 once again has access to the actuator. This example can be
implemented with the following SCL program code:
"PID Temp 1"(Input := "Input1");
"PID Temp 2"(Input := "Input2");
IF "PID Temp 1".PidOutputSum <= "PID Temp 2".PidOutputSum THEN
"ActuatorInput" := "PID_Temp_1".OutputHeat_PWM;
"PID_Temp_1".PIDCtrl.PIDInit := FALSE;
"PID_Temp_2".PIDCtrl.PIDInit := TRUE;
"PID_Temp_2".OverwriteInitialOutputValue := "PID_Temp_1".PidOutputSum;
ELSE
"ActuatorInput" := "PID_Temp_2".OutputHeat_PWM;
"PID_Temp_1".PIDCtrl.PIDInit := TRUE;
"PID_Temp_2".PIDCtrl.PIDInit := FALSE;
"PID_Temp_1".OverwriteInitialOutputValue := "PID_Temp_2".PidOutputSum;
END IF;
PID control
Function Manual, 03/2017, A5E35300227-AC
Using PID_Temp
6.6 Override control with PID_Temp
205