When general-purpose computers became available, they were soon applied to control logic in industrial processes. Often technicians would spend hours troubleshooting by examining the schematics and comparing them to existing wiring. If even one wire were out of place, or one relay failed, the whole system would become faulty. Changes would require rewiring and careful updating of the documentation. The hard-wired nature made it difficult for design engineers to alter the automation process. Before, control logic for manufacturing was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers. PLC originated in the late 1960s in the automotive industry in the US and were designed to replace relay logic systems.
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The widespread use of PLCs in the industrial world certainly increases job opportunities for vocational students who have expertise and skills in this field.
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The widespread use of PLC has long been applied as a standard curriculum in vocational schools (SMK). One of the automation systems used in almost all industries is the programmable logic controller (PLC). Automation systems are vital for production departments in industry.