Siemens SIMATIC S7-1200 Function Manual page 435

State / Mode Description of operating mode
2 Example for definition of an offset for fine tuning cooling:
Without offset:
•
– Setpoint = Process value (ScaledInput) = 80°C
– PID output value (PidOutputSum) = 30.0
– Output value heating (OutputHeat) = 30.0
– Output value cooling (OutputCool) = 0.0
Oscillation of the process value around the setpoint cannot be generated with the cooling output
alone.
Fine tuning would fail here.
With definition of an offset for heating output (PIDSelfTune.TIR.OutputOffsetHeat) = 80.0
•
– Setpoint = process value (ScaledInput) = 80°C
– PID output value (PidOutputSum) = -50.0
– Output value heating (OutputHeat) = 80.0
– Output value cooling (OutputCool) = -50.0
By defining an offset for the heating output, the cooling output can now create an oscillation of the
process value around the setpoint.
Fine tuning can now be carried out successfully.
General requirements for fine tuning:
The PID_Temp instruction is called in a cyclic interrupt OB.
•
No disturbances are expected.
•
The setpoint and the process value lie within the configured limits.
•
The control loop has stabilized at the operating point. The operating point is reached when the process
•
value corresponds to the setpoint.
When the dead zone is switched on, the result can be a permanent control deviation (deviation between
setpoint and actual value). This can have a negative effect on fine tuning.
ManualEnable = FALSE
•
Reset = FALSE
•
Automatic (State = 3), inactive (State = 0) or manual (State = 4) mode
•
Requirements for fine tuning heating:
Heat.EnableTuning = TRUE
•
Cool.EnableTuning = FALSE
•
If PID_Temp is configured as heating/cooling controller (Config.ActivateCooling = TRUE), the heating
•
output must be active at the operating point at which tuning is to take place (PidOutputSum > 0.0 (see
tuning offset)).
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.3 PID_Temp
435