Programmable Logic Controllers: Definition, Historical Background, and Recent Developments, Slides of Digital Logic Design and Programming

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Programmable LogicControllers

DEFINITION^ ^ Programmable logic controllers

also calledprogrammable controllers orPLCs, are^ solid-state

members of the computer family, using integratedcircuits instead of electromechanicaldevices to implement control functions.

Function^ ^ Capable ofstoring instructions, such assequencing, timing, counting,arithmetic, data manipulation, andcommunication,to control industrial machines andprocesses.

Historical Background^ ^ The first Programmable Logic Controller(PLC) was developed by a group ofengineers at General Motors in 1968^ ^ The company was looking for analternative to replace complex relaycontrol systems

Recent PLCs^ ^ Changes include both

hardware^ (physical components) and

software^ (control program) upgrades  Faster scan times are being achieved usingnew, advanced microprocessor and electronictechnology.  Small, low-cost PLCs (Figure 1), capable ofreplacing four to ten relays, now have morepower than their predecessor, the simplerelay replacer.

Figure 1 (Small PLC with built-inI/O and detachable, handheldProgramming unit)