Cascade - Siemens SIMATIC S7-1200 Function Manual

Using PID_Temp
6.2 Configuring PID_Temp
6.2.1.6

Cascade

If a PID_Temp instance receives its setpoint from a higher-level master controller and
outputs its output value in turn to a subordinate slave controller, this PID_Temp instance is
both a master controller and a slave controller simultaneously. Both configurations listed
below then have to be carried out for such a PID_Temp instance. This is the case, for
example, for the middle PID_Temp instance in a cascade control system with three
concatenated measured variables and three PID_Temp instances.
Configuring a controller as master in a cascade
A master controller defines the setpoint of a slave controller with its output.
In order to use PID_Temp as master in a cascade, you have to deactivate the cooling in the
basic settings. In order to configure this PID_Temp instance as a master controller in a
cascade, activate the "Controller is master" check box. The selection of the output value for
heating is set automatically to OutputHeat.
OutputHeat_PWM and OutputHeat_PER cannot be used at a master in a cascade.
Subsequently specify the number of directly subordinate slave controllers that receive their
setpoint from this master controller.
If no own scaling function is used when assigning the OutputHeat parameter of the master to
the Setpoint parameter of the slave, it may be necessary to adapt the output value limits and
the output scaling of the master to the setpoint/process value range of the slave. This can be
done in the output settings of the master in the "OutputHeat / OutputCool" section.
Configuring a controller as a slave in a cascade
A slave controller receives its setpoint (Setpoint parameter) from the output of its master
controller (OutputHeat parameter).
In order to configure this PID_Temp instance as a slave controller in a cascade, activate the
"Controller is slave" check box in the basic settings.
Subsequently select the PID_Temp instance that is to be used as the master controller for
this slave controller in the Inspector window of the programming editor. The Master and
Setpoint parameters of the slave controller are interconnected with the selected master
controller through this selection (the existing interconnections at these parameters are
overwritten). This interconnection allows the exchange of information and the setpoint
specification between master and slave. If required, the interconnection can be changed
subsequently at the Setpoint parameter of the slave controller in order, for example, to insert
an additional filter. The interconnection at the parameter Master may not be changed
subsequently.
The "Controller is master" check box has to be selected and the number of slaves has to be
configured correctly at the selected master controller. The master controller has to be called
before the slave controller in the same cyclic interrupt OB.
Additional information
Additional information about program creation, configuration and commissioning when
PID_Temp is used in cascade control systems is available under Cascade control with
PID_Temp (Page 191).
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Function Manual, 03/2017, A5E35300227-AC
PID control