lecture14 - 14. PLC Fundamentals PLC = Programmable Logic...

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  1 PLC = Programmable Logic Controller Where are PLCs mostly used? In control systems where a sequence of events or maintaining some variable constant is needed. e.g. In an automatic drilling machine, the automatic sequence is: 1. Start lowering the drill when the work-piece is in position 2. Start drilling 3. Stop drilling when drill has reached the required depth. 4. Retract the drill. 5. Switch off and wait for the next work-piece to appear. 14. PLC Fundamentals
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  2 We use the relay ladder logic language to write the programs. Hardware: input PLC output program input processor output memory Power supply Input interface output interface program
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3 Reasons for using interfaces: because sensors or actuators usually require much higher current than those in a PLC. In order to connect the external devices to a PLC, we use electrical isolator, e.g. optoisolator. Digital signal in a microprocessor in a PLC is usually 5 v
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This note was uploaded on 11/09/2009 for the course ENG 91301 taught by Professor Lui during the Spring '08 term at Hong Kong Institute of Vocational Education.

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lecture14 - 14. PLC Fundamentals PLC = Programmable Logic...

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