PLC is a computer control systems of industrial site based on software and hardware.After knowing processing technology and control requirements,the characteristics must be taken into account when designing system program to coordinate hardware,distribute PLC software and make the control system work correctly.The significance of arranging PLC program execution sequence is illustrated through elevator control program.%可编程序逻辑控制器PLC是一种基于软件和硬件控制的工业现场计算机控制系统。在了解生产工艺和控制要求的基础上,设计系统程序时必须充分考虑到硬件的特性,编制出与硬件协调配合的程序,合理分配PLC软件程序执行时序,使控制系统能精确、稳定、快速工作。反之,则会出现一些意外故障,造成控制系统误动作。通过PLC控制电梯的部分梯形图程序来说明合理安排PLC程序执行顺序的重要性。
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