PLC控制系统的简介及设计要点

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 From the sub-structure, PLC is divided into fixed and modular two. Fixed PLC including CPU boards, I / O board, display panel, memory blocks, power and so on, into a combination of these elements are not removable as a whole. Modular PLC including the CPU module, I / O modules, memory, power supply modules, backplane, or chassis, the modules can be configured according to certain rules of combination.
 In the user view, a detailed analysis of unnecessary CPU's internal circuitry, but the working mechanism of the various parts of or should have sufficient understanding. CPU control of the CPU controller, from which to read instructions, explanation of command and execution. However, the pace of work from the vibration signal control. Computing devices used in digital or logic operations, under the command of the work in the controller. Register to participate in operations, and store intermediate results of operations, it is under the command of the work in the controller. CPU speed and memory capacity is an important parameter PLC, which determines the rate of PLC work, IO number and software capacity, thereby limiting the size of the control.

 从结构上分，PLC分为固定式和组合式两种。固定式PLC包括CPU板、I/O板、显示面板、内存块、电源等，这些元素组合成一个不可拆卸的整体。模块式PLC包括CPU模块、I/O模块、内存、电源模块、底板或机架，这些模块可以按照一定规则组合配置。
 在使用者看来，不必要详细分析CPU的内部电路，但对各部分的工作机制还是应有足够的理解。CPU的控制器控制CPU工作，由它读取指令、解释指令及执行指令。但工作节奏由震荡信号控制。运算器用于进行数字或逻辑运算，在控制器指挥下工作。寄存器参与运算，并存储运算的中间结果，它也是在控制器指挥下工作。CPU速度和内存容量是PLC的重要参数，它们决定着PLC的工作速度，IO数量及软件容量等，因此限制着控制规模。
 PLC使用系统存储器（现在大部分采用闪存技术了）用于过程控制系统。除了这个操作系统之外，它还包括一个由梯形图翻译成而进制形式的用户程序。快擦型存储器（Flash Memory）的内容只有在改变用户程序的时候可以被改变。PLC控制器比快擦型存储器使用得更早，EPROM存储器比快擦型存储器也更早，快擦型存储器必须用紫外线灯擦除，并在编程器上进行编程。由于快擦型存储器技术的应用，使得这个过程大大缩短了。在应用程序开发中，通过一个串行电缆可以对程序存储器进行重新编程。

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