Struktury automatizace průmyslového podniku
Struktury automatizace průmyslového podniku
Struktury automatizace průmyslového podniku
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30.9.2013<br />
Example: Digital I/O Tags<br />
Digital output module in slot 0 of local chassis:<br />
1756-OB16D Module – Slot 0<br />
Diagnostic<br />
Data<br />
Data Per Point<br />
34<br />
Types of Scans<br />
• Continues task (spojitá úloha)<br />
PLC scans the program code from top to bottom. When it<br />
completes, it goes back to the top and restarts the process.<br />
I/O scans<br />
program scans<br />
1. A continuous task is how PLC traditionally operates.<br />
2. Continues tasks are performed at irregular intervals.<br />
3. A watchdog monitors the scan time. If it exceeds predefined value, an<br />
execution fault is displayed because PLC could accidentally lose an<br />
input signal.<br />
4. First scan (or first pass) – when the PLC is first powered ON or<br />
whenever the PLC program is started – used for initializations<br />
35<br />
17
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