基于PLC的控制系统外文翻译资料

Controlling System Based on PLC

Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry including manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configuration time from 6 months down to 6 days [Moody and Morley, 1999].

Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh environments. Moreover, according to a study on the PLC market of Frost and Sullivan [1995], an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time.

With microelectronics and computer technology is developing rapidly, PLC (controller can be programmed) in the field of industrial control within very broad application. PLC is a digital computer-based technology, specifically for the industrial application environment designed electronic control device It uses programmable memory, and to control all types of mechanical and electrical equipment and integrated production process

With enterprises of high flexibility, high efficiency requirements, people in the face of larger and more complex production labor, not only wasting time and effort, more than it gains. Therefore, the automatic prototyping system and the emergence of widely used as a historical necessity. Molding equipment and computer technology and intelligence technology combining intelligent material molding equipment is the future development direction of the main

PLC automatic control prototyping system to replace the manual workshop. serves industrial control systems for the open and fast requirements, It can also satisfy users stability and reliability requirements. The use of automated prototyping technology to be effective for customers to lower production costs, improve production efficiency and achieve revenue growth.

• 1. CPU-Central Processing Unit

Central Processing Unit (CPU) is the brain of a PLC controller. CPU itself is usually one of the microcontrollers. Aforetime these were 8-bit microcontrollers such as 8051, and now these are 16-bit and 32-bit microcontrollers. Unspoken rule is that yoursquo;ll find mostly Hitachi and Fujicu microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care of communication, interconnectedness among other parts of PLC controller, program execution, memory operation, overseeing input and setting up of an output. PLC controllers have complex routines for memory checkup in order to ensure that PLC memory was not damaged (memory checkup is done for safety reasons). Generally speaking, CPU unit makes a great number of check-ups of the PLC controller itself so eventual errors would be discovered early. You can simply look at any PLC controller and see that there several indicators in the form of light diodes for error signalization.

1.2 Memory

System memory (today mostly implemented in FLASH technology) is used by a PLC for an process control system. Aside from this operation system it also contains a user program translated from a 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 FLASH 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. Use memory is divide 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 user program. For example, timer value, or counter value would be stored in this part of the memory.

1.3 Programming a PLC Controller

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. Todayrsquo;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 situation 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 the system inputs/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 outp

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