可编程逻辑控制器

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可编程逻辑控制器
就象先前提到的那样，可编程逻辑控制器（PLC或PC）是迄今为止最重要的商用逻辑控制设备。它的发展开始于1968年，由通用电气公司通过加强电子工业从而完成了ELETROMECHANICAL到用于控制机器，材料加工和装配汽车的中继系统的转变。他们的中继系统已经完成了非常大而且复杂的系统，而且当要改变制造流程时，需要大量的线路更换工作或者甚至直接抛弃该系统。这变成了那个年代自动化工业的典型的模式转换中备受批评的事。一部分制造商对这样的批评作出了反应，从而基于软件的可编程控制器诞生了。它能实现中继网络的所有的逻辑控制功能，但它们就象计算机一样是在软件（程序）中实现的，这意味着生产流程转变或模式的完全转变现在不再需要抛弃系统或更换大量电线了。而在PLC的程序中的改变相应就快多了而且容易多了。

Programmable Logic Controller
As mentioned previously, the programmable logic controller (PLC or PC) is by far the most important commercially available logic control device. Its development began in 1968 when General Motors Corp. solicited the electronics industry for an alternative to the eletrome-chanical relay logic systems used to control machining, materials handling, and assembly in automobile manufacture. Their relay systems had become very large and complex and required a great amount of rewiring and even outright scrapping when changes in manufacturing processes were needed. This became particularly critical during the years model changeovers typical of the auto industry. A number of manufacturers responded and the software-based programmable controller was born. It could duplicate all the logic control functions of relay networks, but implemented them in software (a program), just like a computer. This meant that process revisions or complete model changeovers did not now require scrapping or tedious rewiring of relay systems, but instead needed only relatively quick and easy changes in the PLC’ s program.

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