自动化英文文献翻译.docx

1、自动化英文文献翻译附 录Programmable logic controllerFrom Wikipedia, the free encyclopediaJump to: navigation, searchPLC & input/output arrangementsA programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machin

2、ery on factory assembly lines, control of amusement rides, or control of lighting fixtures. PLCs are used in many different industries and machines such as packaging and semiconductor machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extende

3、d temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input condit

4、ions within a bounded time, otherwise unintended operation will result.FeaturesControl panel with PLC (grey elements in the center). The unit consists of separate elements, from left to right; power supply, controller, relay units for in- and outputThe main difference from other computers is that PL

5、Cs are armored for severe conditions (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of comp

6、lex positioning systems. Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attache

7、d to a computer network that plugs into the PLC.System scale A small PLC will have a fixed number of connections built in for inputs and outputs. Typically, expansions are available if the base model does not have enough I/O.Modular PLCs have a chassis (also called a rack) into which are placed modu

8、les with different functions. The processor and selection of I/O modules is customised for the particular application. Several racks can be administered by a single processor, and may have thousands of inputs and outputs. A special high speed serial I/O link is used so that racks can be distributed

9、away from the processor, reducing the wiring costs for large plants.User interfaceSee also: List of human-computer interaction topics PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control.A Human-Machine Interface (HMI) is employed for this purpo

10、se. HMIs are also referred to as MMIs (Man Machine Interface) and GUI (Graphical User Interface).A simple system may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a programming and monitoring software instal

11、led on a computer, with the PLC connected via a communication interface.CommunicationsPLCs have built in communications ports usually 9-Pin RS232, and optionally for RS485 and Ethernet. Modbus or DF1 is usually included as one of the communications protocols. Others options include various fieldbuse

12、s such as DeviceNet or Profibus. Other communications protocols that may be used are listed in the List of automation protocols.Most modern PLCs can communicate over a network to some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system or web browser.PL

13、Cs used in larger I/O systems may have peer-to-peer (P2P) communication between processors. This allows separate parts of a complex process to have individual control while allowing the subsystems to co-ordinate over the communication link. These communication links are also often used for HMI (Huma

14、n-Machine Interface) devices such as keypads or PC-type workstations. Some of todays PLCs can communicate over a wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at network speeds up to 100 Mbit/s.PLC compared with other control systemsPLCs are well-adapted to a range

15、 of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input a

16、nd output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic (or function chart) notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods,