<9. Advanced Engineering >
• Output processing
Output processing of NPAS_POU processes the result of control calculation
before its output as output signal. Output processing includes output limiter,
output velocity limiter, output clamp, output tracking, CPV pushback, etc.
• Alarm processing
Alarm processing detects process failures by monitoring process values (PV)
and manipulated output values (MV), and upon detection of a failure, informs the
operation and monitoring functions by sending an alarm message.
Of these processing functions, input processing, output processing and alarm
processing are executed in each scan cycle, while calculation processing is
executed in each control cycle.
In other words, while updating of PV values and totalization, output processing to I/O
modules and alarm monitoring are performed in every scan period of a control task,
NPAS_POU control/calculation processing is performed in every control period.
Consider an example of the Moving Average POU (NPA_AVE_M) running on an
FCN/FCJ with scan cycle defined as 200 ms. As described later, the default control
cycle is 1 second, so average computation is done once per second.
● NPAS POUs with Control Cycle and NPAS POUs without Control Cycle
Some NPAS POUs have a control cycle, while others have no control cycle. The
former, such as NPAS_PID and NPAS_AVE_M, performs internal calculation
processing, while the latter, such as NPAS_TM, NPAS_CT, NPAS_SIO** and
NPAS_SW**, performs no internal calculation processing.
When using an NPAS POU with control cycle, check its control cycle setting.
For a list of POUs with control cycle and a list of POUs without control cycle, see the
above-mentioned NPAS POU online help documentation.
● Default Control Cycle
In Logic Designer, the default control cycle of each NPAS POU is determined by the
system. As described later, the default control cycle is 1 second or longer and at
times may be longer than the scan cycle.
● How to Specify Control Cycle
If there is a need to perform control/calculation processing at intervals shorter than 1
second, you can modify the control cycle of an individual NPAS POU from its default
value.
Specifically, every NPAS POU with control cycle has an engineering parameter
named “_CTL_CYCLE”, which defaults to value 0. With this default setting, its
control cycle is determined by the system.
However, the control cycle of an individual NPAS POU can be modified by assigning
a TIME-data type numerical value to its “_CTL_CYCLE” parameter.
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