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Old May 18th, 2009, 12:41 PM   #9
Tom Jenkins
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Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 5,857
Historically DCS developed in the process industries and were the result of adding capabilities and communications to single loop PID controllers and using mini-computers for HMI functions. Many DCS systems use proprietary communications protocols and have proprietary programming languages, although most modern systems are more open and flexible.

PLCs grew out of component and product manufacuring as relay replacement systems. Most program in Ladder Logic but modern units have a wede variety of programming languages, analog I/O capabilities, math functins, and communications.
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