Siemens SIMATIC S7-1200 Function Manual page 388

Instructions
9.3 PID_Temp
Sampling time of the PID algorithm
The controlled system needs a certain amount of time to respond to changes in the output
value. It is therefore not advisable to calculate the output value in every cycle. The sampling
time of the PID algorithm represents the time between two calculations of the output value. It
is calculated during tuning and rounded to a multiple of the cycle time of the cyclic interrupt
OB (sampling time PID_Temp). All other functions of the PID_Temp are executed at every
call.
If cooling and PID parameter switching are activated, PID_Temp uses a separate sampling
time of the PID algorithm for heating and cooling. In all other configurations, only the
sampling time of the PID algorithm for heating is used.
If you use OutputHeat_PWM or OutputCool_PWM, the sampling time of the PID algorithm is
used as time period of the pulse width modulation. The accuracy of the output signal is
determined by the ratio of the PID algorithm sampling time to the cycle time of the OB. The
cycle time should be no more than a tenth of the PID algorithm sampling time.
If the PID algorithm sampling time and thus the time period of the pulse width modulation is
very high when you use OutputHeat_PWM or OutputCool_PWM, you can define a deviating
shorter period duration at the Config.Output.Heat.PwmPeriode or
Config.Output.Cool.PwmPeriode parameters to improve the smoothness of the process
value.
Control logic
PID_Temp can be used for heating or heating/cooling applications and always works with
normal control logic.
An increase of the PID output value (PidOutputSum) is intended to increase the process
value. The values at the outputs for heating and cooling resulting from the PID output value
are the result of the configured output scaling.
An inverted control logic or negative proportional gain are not supported.
If you only need an output value for your application in which an increase is to reduce the
process value (for example, discharge control), you can use PID_Compact with inverted
control logic.
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Function Manual, 03/2017, A5E35300227-AC
PID control