1. Programmable logic controller is a special purpose computer designed for single use or one of several controllers on a automation network for the control of a wide variety of manufacturing machines and systems using one of five programming languages.
3. Today PLC is a 6.5 billion dollar company, and growing 20% per year.
4. Similarities of PLC and PC are both have similar architecture, both have motherboards, processor, memory, and expansion cards. Differences are PLC has no removable disk drives and PLC’s do not have a monitor.
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7. The primary difference is the virtual relay used in PLC ladder logic program is only limited by size of PLC memory, physical relay used in relay ladder logic is limited to number of poles present on relay selected.
8. input contacts on a relay logic diagram represent actual components and contacts present in control system, input instructions in PLC ladder logic only represent data values stored in PLC.
10. The processor handles all logical operations and performs all the mathematical computations. Power supply provides power to processor and modules plugged into rack. The input interface provides link between processor and external devices that measures conditions in production area. Output interface is a location for termination of wiring and signal conditioner to provide proper voltage and output drive power required by output field devices.
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17. Reliability was then and continues to be a real concern in manufacturing automation, so early PLC adoptions would have been lost if they were portrayed merely as an industry computer programmed in ladder logic.