【正文】 STEP 7Micro/WIN 編程軟件運行開始界面如下圖 7 所示。 輸入輸出點數(shù)對價格有直接影響。輸入模塊將電信號變換成數(shù)字信號進入 PLC 系統(tǒng)，輸出模塊相反。 （ 2）輸入輸出模塊的選擇 輸入輸出模塊的選擇應考慮與應用要求的統(tǒng)一。 (2)向超大型、超小型兩個方向發(fā)展。為了使 PLC 能處理模擬信號， PLC 廠家生產有配套的 A/D、 D/A 轉換模塊，使 PLC 可用于模擬量控制。 1987 年頒布的可編程控制器的定義如下： “可編程邏輯控制器是專為在工業(yè)環(huán)境下應用而設計的一種數(shù)字運算操作的電子裝置，是帶有存儲器、可以編制程序的控制器。因此，考慮到實際現(xiàn)場工作環(huán)境，我最終選擇了可靠性好、抗干擾能力強、通用性好等諸多優(yōu)點的 PLC 來實現(xiàn)對十字路口交通燈的控制，完成本次課程設計的任務。特別是近十幾年，隨著我國經濟的發(fā)展，城市人口與機動車輛的增多，城市交通問題越來越受到人們的關注。 關鍵詞 交通燈控制系統(tǒng)；可編程控制器（ PLC）；十字路口；科學化管理；穩(wěn)定性；可靠性 3 ABSTRACT The traditional traffic control system is mostly by digital circuit, traffic control system stability reliability and antiinterference ability is bad, With the development of society and economy, and digital circuit traffic lights to meet the growing traffic pressure, therefore, must seek a new method to replace the plex and working stability of the control system. With the development of science and technology, the programmable logic controller (PLC) function, the programmable controller has, as a kind of microputer technology as the core in automatic control equipment, has been widely used in mechanical manufacturing, metallurgy, chemical, energy, etc. It has high reliability, plete functions, strong antijamming capability, with simple structure, light weight, it is a kind of process control for industrial environment and the number of operating system. PLC control traffic lights, mainly is for use with the consideration of the characteristics of strong adaptability to environment, and its internal timer resources are very rich, but for now the widespread use of progressive light accurately control, particularly easily realize more control of the crossroads. Because of PLC work munication function, has the same path can be posed of a LAN for signal unified dispatching management, can shorten the time of waiting vehicles, scientific management. In actual application of PLC control, urban traffic lights, can according to different conditions, modified at any time to change control procedures, the signal of working time and working conditions. And relay or logic circuit control system, PLC control system has higher reliability and flexibility and economic and practical. This paper is the application of the principle of PLC to control the traffic intersection, introduced in traffic system based on PLC is introduced, and the application of PLC system of basic principle. Key words 4 Traffic control system； Programmable logic controller (PLC) ； Crossroads ； Scientific managemen； Stabilization； reliability