<9. Advanced Engineering >
9.2.3 NPAS_POU Status Propagation
When creating a loop by joining NPAS POUs, it is important both to pass status
information from upstream POUs to downstream POUs, as well as read back status
information from downstream POUs to upstream POUs.
This section describes the basics of status propagation, followed by application
programming precautions.
The figure below shows an NPAS_PID cascade loop for controlling the PV value of
AI001, where NPAS_PID_1 is the primary (upstream) control and NPAS_PID_2 is
the secondary (downstream) control. This example will be used to explain status
propagation.
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