外文翻可编程控制器.docVIP

电子与信息工程学院 本科毕业论文(设计) 外 文 文 献 翻 译 译文题目： Programmable logic controllers Hardware, software architecture 学生姓名： 吴凡 专 业： 电气工程及其自动化 指导教师： 李东京 2012年12月 Programmable logic controllers: Hardware, software architecture Many respects, the architecture of the programmable logic controller (PLC) resembles a general-purpose computer with specialized input/output (I/O) modules. However, some important characteristics distinguish a PLC from a general-purpose computer. Most important, a PLC is much more reliable, designed for a mean time between failures measured in years. Second, a PLC can be placed in an industrial environment with its substantial amount of electrical noise, vibration, extreme temperatures, and humidity. Third, PLCs are easily maintained by plant technicians. Basic PLC hardware architecture The basic architecture of a PLC consists of main components-the processor module, the power supply, and the I/O modules. The processor module consists of the central processing unit (CPU) and memory. In addition to a microprocessor, the CPU also contains at least an interface to a programming device and may contain interfaces to remote I/O and other communication networks. The power supply is usually a separate module, and the I/O modules are separate from the processor. The types of I/O modules include discrete (on/off), analog (continuous variable), and special modules like motion control or high-speed counters. The field devices are connected to the I/O modules. Depending on the amount of I/O and the particular PLC processor, the I/O modules may be in the same chassis as the processor and/or in one or more other chassis. Up until the late 1980s, the I/O modules in a typical PLC system were in chassis separate from the PLC processor. In the more typical present-day PLC, some of the I/O modules