毕业论文外文翻-可编程控制器.docx

附 录Programmable logic controllerFrom Wikipedia, the free encyclopediaJump to: /wiki/Programmable_logic_controllernavigation, /wiki/Programmable_logic_controllersearchPLC /wiki/Input/outputinput/output arrangementsA programmable logic controller (PLC) or programmable controller is a /wiki/Digital_computerdigital computer used for /wiki/Automationautomation of /wiki/Electromechanicalelectromechanical processes, such as control of machinery on factory /wiki/Assembly_lineassembly 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, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or /wiki/Non-volatile_storagenon-volatile memory. A PLC is an example of a /wiki/Real-time_computingreal time system since output results must be produced in response to input conditions 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; /wiki/Power_supplypower supply, controller, /wiki/Relayrelay units for in- and outputThe main difference from other computers is that PLCs are armored for severe conditions (dust, moisture, heat, cold, etc) and have the facility for extensive /wiki/Input/outputinput/output (I/O) arrangements. These connect the PLC to /wiki/Sensorsensors and /wiki/Actuatoractuators. PLCs read limit /wiki/Switchswitches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use /wiki/Machine_visionmachine vision. On the actuator side, PLCs operate /wiki/Electric_motorelectric motors, /wiki/Pneumaticpneumatic or /wiki/Hydraulichydraulic cylind