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Draw a neat labelled diagram of PLC. Explain the function of each block.

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The main parts of a PLC are, 

1) Central Processing Unit consisting of a microprocessor, and memory unit. A microprocessor is essentially a logic solver. Memory unit is used to store operating system of PLC, user program and temporary data. 

2) Power supply: A switched mode power supply is used which generates the required dc levels to power the internal circuit 

3) Programmer/ Monitor: Programmer/monitor is device used to load program into PLC from a hand held terminal or a PC 

4) I/O modules: The IO modules are for connecting outside world digital/analog input/output devices to PLC. 

5) Analog I/O module: These for connecting analog input signals derived from different sensors and transducers

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