PLC介绍及外文翻译.doc - 可编程控制器简介
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更新于2023-11-23
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可编程控制器（PLC）是指在20世纪60年代晚期在美国首次出现的一种用于替代继电器的可编程逻辑控制器。它用于实现逻辑判断、定时、顺序控制等功能。通用汽车公司最早提出了PLC的概念。PLC的基本设计是对计算机功能的改进，具有灵活性、通用性和其他优点，并且相对于继电器控制系统而言更简单易操作，价格更便宜，控制器硬件是标准化的整体。根据用户的实际应用目标，PLC的软件可以控制用户程序的存储内容、控制器和连接控制器的记忆等。
System memory (today mostly implemented in FLASH technology) is used by a PLC
for a process control system. Aside form. this operating system it also contains a user
program translated forma ladder diagram to a binary form. FLASH memory contents can
be changed only in case where user program is being changed. PLC controllers were used
earlier instead of PLASH memory and have had EPROM memory instead of FLASH
memory which had to be erased with UV lamp and programmed on programmers. With the
use of FLASH technology this process was greatly shortened. Reprogramming a program
memory is done through a serial cable in a program for application development.
User memory is divided into blocks having special functions. Some parts of a memory
are used for storing input and output status. The real status of an input is stored either as
“1”or as “0”in a specific memory bit/ each input or output has one corresponding bit in
memory. Other parts of memory are used to store variable contents for variables used in
used program. For example, time value, or counter value would be stored in this part of the
memory.
PLC controller can be reprogrammed through a computer (usual way), but also
through manual programmers (consoles). This practically means that each PLC controller
can programmed through a computer if you have the software needed for programming.
Today’s transmission computers are ideal for reprogramming a PLC controller in factory
itself. This is of great importance to industry. Once the system is corrected, it is also
important to read the right program into a PLC again. It is also good to check from time to
time whether program in a PLC has not changed. This helps to avoid hazardous situations
in factory rooms (some automakers have established communication networks which
regularly check programs in PLC controllers to ensure execution only of good programs).
Almost every program for programming a PLC controller possesses various useful
options such as: forced switching on and off of the system input/outputs (I/O lines),
program follow up in real time as well as documenting a diagram. This documenting is
necessary to understand and define failures and malfunctions. Programmer can add
remarks, names of input or output devices, and comments that can be useful when finding
errors, or with system maintenance. Adding comments and remarks enables any technician
(and not just a person who developed the system) to understand a ladder diagram right
away. Comments and remarks can even quote precisely part numbers if replacements
would be needed. This would speed up a repair of any problems that come up due to bad
parts. The old way was such that a person who developed a system had protection on the
program, so nobody aside from this person could understand how it was done. Correctly
documented ladder diagram allows any technician to understand thoroughly how system
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