Struktury automatizace průmyslového podniku

30.9.2013
Types of Scans
• Periodic task (periodická úloha)
Like the continuous task, a periodic task executes all of its
code from top to bottom. However, when a periodic task
completes its scan, it waits a preconfigured time interval
before restarting.
program scans
1. A periodic task is always required for all numeric control
algorithms, e.g. PID controller.
2. The periodic task lets you control a process that might occur
at a significantly faster rate than the normal scan of the
continuous task can attain.
3. In a periodic task, we must insert I/O instructions if we need
actual data, otherwise it uses I/O data of the continues task.
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Types of Scans
• Event task (úloha řízená událostí, přerušeni)
Lets you execute a piece of code based on the detection of
some incident that occurs in the control system.
Events
Program scans
1. The event task either immediately take control at a high priority
2. But interrupts are potentially dangerous sources of errors
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