毕业设计-基于PLC的液位控制系统设计-精品

无 锡 职 业 技 术 学 院 毕业实践任务书课题名称 基于PLC的液位控制系统设计 指导教师 职 称 指导教师 职 称 专业名称 生产自动化 班 级 学生姓名 学 号 实习单位 课题需要完成的任务：利用信捷PLC设计液位控制系统，完成如下任务：1、 通过触摸屏、可变程序控制器变频器（PLC）、压力传感器、配电装置以及水泵实现液位控制系统的设计2、 确定控制方案，选择PLC型号，定义输入/输出，画出 PLC 端子接线图。3、 进行软件编程、完成控制梯形图并完成调试。课题计划：10年2月26日-10年3月10日 确定毕业设计课题10年3月11日- 10年3月22日 调查参观、完成调研报告10年3月22日-10年3月31日 确定方案，完成方案论证10年4月 1日- 10年4月20日 设计电路，编制程序，完成论文计划答辩时间：10年4月21日-10年4月30日 自动控制技术系 系（部、分院） 2010年 4 月 26 日无锡职业技术学院毕业设计说明书（英文翻译）PLCs -Past, Present and FutureEveryone knows there's only one constant in the technology world, and that's change. This is especially evident in the evolution of Programmable Logic Controllers (PLC) and their varied applications. From their introduction more than 30 years ago, PLCs have become the cornerstone of hundreds of thousands of control systems in a wide range of industries. At heart, the PLC is an industrialized computer programmed with highly specialized languages, and it continues to benefit from technological advances in the computer and information technology worlds. The most prominent of which is miniaturization and communications.The Shrinking PLCWhen the PLC was first introduced, its size was a major improvement - relative to the hundreds of hard-wired relays and timers it replaced. A typical unit housing a CPU and I/O was roughly the size of a 19 television set. Through the 1980s and early 1990s, modular PLCs continued to shrink in footprint while increasing in capabilities and performance (see Diagram 1 for typical modular PLC configuration). In recent years, smaller PLCs have been introduced in the nano and micro classes that offer features previously found only in larger PLCs. This has made specifying a larger PLC just for additional features or performance, and not increased I/O count, unnecessary, as even those in the nano class are capable of Ethernet communication, motion control, on-board PID with autotune, remote connectivity and more. PLCs are also now well-equipped to replace stand-alone process controllers in many applications, due to their ability to perform functions of motion control, data acquisition, RTU (remote telemetry unit) and even some integrated HMI (human machine interface) functions. Previously, these functions often required their own purpose-built controllers and software, plus a separate PLC for the discrete control and interlocking.The Great CommunicatorPossibly the most significant change in recent years lies in the communications arena. In the 1970s Modicon introduction of Modbus communications protocol allowed PLCs to communicate over standard cabling. This translates to an ability to place PLCs in closer proximity to real world devices and communicate back to other system controls in a main panel. In the past 30 years we have seen literally hundreds of proprietary and standard protocols developed, each with their own unique advantages.Today's PLCs have to be data compilers and information gateways. They have to interface with bar code scanners and printers, as well as temperature and analog sensors. They need multiple protocol support to be able to connect with other devices in the process. And furthermore, they need all these capabilities while remaining cost-effective and simple to program. Another primary development that has literally revolutionized the way PLCs are programmed, communicate with each other and interface with PCs for HMI, SCADA or DCS applications, came from the computing world. Use of Ethernet communications on the plant floor has doubled in the past five years. While serial communications remain popular and reliable, Ethernet is fast becoming the communications media of choice with advantages that simply can't be ignored, such as: * Network speed. * Ease of use when it comes to the setup and wiring. * Availability of off-the-shelf networking components. * Built-in communications setups.Integrated Motion ControlAnother responsibility the PLC has been tasked with is motion control. From simple open-loop to multi-axis applications, the trend has been to integrate this feature into PLC hardware and software. There are many applications that require accurate control at a fast pace, but not exact precision at blazing speeds. These are applications where the stand-alone PLC works well. Many nano and micro PLCs are available with high-speed counting capabilities and high-frequency pulse outputs built into the controller, making them a viable solution for open-loop control. The one caveat is that the controller does not know the position of the output device during the control sequence. On the other hand, its main advantage is cost. Even simple motion control had previously required an expe