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PLCs (Programmable Logic Controllers) were introduced firstly into manufacturing in 1969, and are now the most widely employed industrial process control technology used today. PLCs are typically used to collect and disseminate information, to sequence robots and other automated devices, and to control conveyor systems in the industrial environment. PLCs have evolved from awkward systems with rather limited memories and capabilities to state of the art systems that sometimes rival distributed digital control systems in both capability and flexibility.
The National Electrical Manufacturing Association (NEMA) defines a PLC as a digitally operating electronic apparatus which uses a programmable memory for internal storage and instructions by implementing specific functions, such as, logic, sequencing, counting, timing, and arithmetic to control through digital or analog I/O modules various types of machines or processes.
The PLC is a device that can manipulate, execute, and/or monitor data from a process or communication systems. A block diagram of a PLC and how it interacts with its environment is as the PLC receives input conditions, i.e. voltage or no voltage, it examines them against the programmed code within the PLC and then executes the proper outputs associated or specified within the programmed code.
PLCs are typically programmed using a language known as RLL (Relay Ladder Logic). This language is a mixed modality language which has been around since the inception of the Programmable Logic Controller (PLC). A mixed modality language is one which uses both graphics and short syntactical statements to prompt the programmer on the use of programming functions.
Almost any modern GUI (Graphical User Interface) possesses this type of language classification. RLL contained merely of their respective short syntactical descriptors, and performed tasks which only required relay operations. RLL had been modified to include more functions such as counters, timers, mathematical operands, and communication. Some typical RLL mixed modality representations which a programmer uses to select certain desired functions in a program.
The correct mixed modality representation, for any given application, depends upon the hardware to be utilized and the desired action to be enacted by another operator or device. When picking the graphic symbols during RLL programming, the programmer is confronted by menus which contain both a symbol and a respective short syntactical descriptor. RLL is considered a mixed modality language because it uses both symbols and syntactical representations to communicate a desired function to the programmer.
On alternative to RLL (Relay Ladder Logic) is known as State Logic. State Logic is differing from RLL in two ways. It is a language which forces the user to build his or her programs with finite states. State logic also utilizes a natural language, known as ECLiPS (English Control Language Programming Software) that allows the programmers to have the freedom of writing commands in his or her own natural words. The natural language technology differs from syntactical languages because syntactical languages require the programmer to memorize specific string of characters to input into programming environment. Natural languages utilize a technology known as NPLP (Natural Program Language Processing) or Natural Language Processing (NLP) to allow its users the freedom of programming a device in his or her own natural form of communication or language. NPLP is a branch of artificial intelligence that allows the user to interact with the system in his or her own natural language.
Programming this type of language contains of writing text statements, in the programmer's natural language within the software program. The programmer executes a menu choice which, in turn, initiates a check through the words used. Similar to have a way of a word processor performs a spell checks, any words that are not known to the ECLiPS software are identified and flagged to the user. The system then asks user to define any word that it does not recognize by selecting a synonym from its existing terminology bank.
