Siemens SIMATIC S7-1200 Function Manual page 186

Using PID_Temp
6.3 Commissioning PID_Temp
Example: Specification 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
● With 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
General requirements
● The PID_Temp instruction is called in a cyclic interrupt OB.
● ManualEnable = FALSE
● Reset = FALSE
● The setpoint and the process value lie within the configured limits (see "Process value
settings" configuration).
● 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.
● No disturbances are expected.
● PID_Temp is in inactive mode, automatic mode or manual mode.
Requirements for fine tuning heating
● Heat.EnableTuning = TRUE
● Cool.EnableTuning = FALSE
● If PID_Temp is configured as a heating-and-cooling controller (Config.ActivateCooling =
TRUE), the heating output has to be active at the operating point where tuning is to be
carried out.
PidOutputSum > 0.0 (see tuning offset)
186
Oscillation of the process value around the setpoint cannot be generated with the
cooling output alone. Fine tuning would fail here.
Thanks to the specification of an offset for the heating output, the cooling output can
now generate oscillation of the process value around the setpoint. Fine tuning can
now be carried out successfully.
Function Manual, 03/2017, A5E35300227-AC
PID control