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Chapter One - Coggle Diagram
Chapter One
Benefits of PLCs
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Good flexibility
Since it is not hard-wired, easy to make changes
Low Cost
If 6+ relays are used, PLCs are cheaper
Communications capable
Communications with computers, other controllers, etc.
Fast response time
Real-time capabilities, relay is the main chokepoint
Ease of troubleshooting
Resident diagnostics and override functions, unlike relays
Parts of a PLC
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I/O
Fixed
Cannot be interfaced, stuck
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Power Supply
For large systems, PLC power may not supply power to field devices
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Principles of Operation
1) System is hard wired for power, usually 120VAC
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3) Device is put into run mode, described by a sequence of events
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Modifying the Operation
If a relay system is used, there is some rewiring that needs to be done
if a PLC is used, no rewiring is necessary
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