Siemens SIMATIC S7-1200 Function Manual page 384

Instructions
9.3 PID_Temp
Two methods are available to calculate the PID output value with activated cooling:
● Cooling factor (Config.AdvancedCooling = FALSE):
The output value calculation for cooling takes place with the PID parameters for heating,
taking into consideration the configurable cooling factor Config.CoolFactor. This method
is suitable if the heating and cooling actuators have a similar time response but different
gains. If this method is selected, pretuning and fine tuning for cooling as well as the PID
parameter set for cooling are not available. You can only execute the tuning for heating.
● PID parameter switching (Config.AdvancedCooling = TRUE):
The output value calculation for cooling takes place by means of a separate PID
parameter set. Based on the calculated output value and the control deviation, the PID
algorithm decides whether the PID parameter for heating or cooling is used. This method
is suitable if the heating and cooling actuator have different time responses and different
gains. Pretuning and fine tuning for cooling are only available if this method is selected.
Output value limits and scaling
Depending on the operating mode, the PID output value (PidOutputSum) is calculated
automatically by the PID algorithm or defined by the manual value (ManualValue) or the
configured substitute output value (SubstituteOutput).
The PID output value is limited according to the configuration:
● If cooling is deactivated (Config.ActivateCooling = FALSE),
Config.Output.Heat.PidUpperLimit is the high limit and Config.Output.Heat.PidLowerLimit
the low limit.
● If cooling is activated (Config.ActivateCooling = TRUE),
Config.Output.Heat.PidUpperLimit is the high limit and Config.Output.Cool.PidLowerLimit
the low limit.
The PID output value is scaled and output at the outputs for heating and cooling. Scaling can
be defined separately for each output and is specified in the structures Config.Output.Heat or
Config.Output.Cool with 2 value pairs each:
Output
OutputHeat
384
Value pair Parameter
Value pair 1 PID output value high limit (heating)
Config.Output.Heat.PidUpperLimit,
Scaled high output value (heating) Con-
fig.Output.Heat.UpperScaling
Value pair 2 PID output value low limit (heating)
Config.Output.Heat.PidLowerLimit,
Scaled low output value (heating) Con-
fig.Output.Heat.LowerScaling
Function Manual, 03/2017, A5E35300227-AC
PID control