IC693MDL655
IC693MDL655
传统PLC的生产被几家厂商所垄断,造成PLC的性价比增长很缓慢。这些问题都成了制约传统PLC发展的因素。近年来,随着计算机技术的迅猛发展以及PLC方面国际标准的制定,一项打破传统PLC局限性的新兴技术发展起来了,这就是软PLC技术。
软PLC的硬件体系结构不再封闭,用户可以自己选择合适的硬件组成满足要求的软PLC。
传统PLC的指令集是固定的,而实际工业应用中可能需要定义算法。软PLC指令集可以更加丰富,用户可以使用符合标准的操作指令。
PC机厂家的激烈竞争使得基于PC机的软PLC的性价比得以提高。
传统PLC限制在几家厂商生产,具有私有性,因此很难适应现有标准计算机网络,常常是PLC与计算机处在不同类型的网络中。软PLC不仅能加入到已存在的私有PLC网络中,而且可以加入到标准计算机网络中。这使得现有计算机网络的很多研究成果很容易地应用到PLC控制技术中。
软PLC的技术是基于IEC61131-3标准的,因此在掌握标准语言后开发就比较容易。
尽管软PLC技术具有很大的发展潜力,但是这项技术的实现需要解决一些重要的问题。其中主要是以PC为基础的控制引擎的实时性问题。软PLC首选的操作系统是WindowsNT,但是它并不是一个硬实时的操作系统。传统PLC具有硬实时性,正因为如此它才能提供快速、确定而且可重复的响应。而要让WindowsNT具有硬实时性,必须对它进行扩展,使得PC的控制任务具有最高的优先级,不因为NT的系统功能和用户程序的调用而被抢占。
现在,我们可以通过一些方法将实时性能加入到NT系统中去。比如,修改NT的硬件抽象层,或者NT与一种经过实用验证的硬实时操作系统组合。另外,WindowsCE等操作系统具有了NT在硬实时性方面所不具备的特性。在实际开发中也可使用其他的操作系统作为平台。
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NUM France Circuit Board Card 0224203485M 370043034 W.ref. 04-2001
NUM France Circuit Board Card 0224203897C 370148011 W.ref. 05-2002
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NUM France Circuit Board Card 0224204157G 35994806 W.ref. 06/2000
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