外文翻译-PLC可编程逻辑控制器.doc

Programmable logic controller A programmable logic controller (PLC) or programmable controller is used for electrical and mechanical process automation of the digital computer, such as control of machinery on factory assembly lines, amusement facilities, or lighting. Programmable controller is used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is a real time system since output results must be produced in response to input conditions within a bounded time; otherwise it will lead to wrong operation 1. Development Early PLCs were designed to replace relay logic systems. These ladder logic of the programmable controller is a very similar with the relay logic diagrams. Select representation for the purpose of this procedure is to reduce the existing technical personnels training needs. Other early programmable controller using instruction list programming, programming logic solver is based on a stack. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a very high-level programming language designed to program PLCs based on state transition diagrams. Many early PLCs did not have accompanying programming terminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more common for ladder logic to be used, for the aforementioned reasons. Update format such as logic and function block (this is a similar logic description using digital logic integrated circuit), but they are still no