最新毕业设计-基于PLC的液位控制系统设计.doc

电信学院毕业设计任务书

题目 基于 PLC 的污水池液位控制系统设计

学生姓名 班级 学号

题目类型 工程设计 指导教师 魏祥林 系主任

一、毕业设计（论文）的技术背景和设计依据：

与传统的人工调节液位控制系统相比，变频液位自动控制系统具有节能效果显著、人工劳动强度低，

系统工作可靠、自动化程度高等优点。

为了实现污水池液位的恒定控制，本设计要求 S7-200 PLC 作为控制器，完成对现场数据的采集、变频

器的控制、PID 控制算法的实现。

6、翻译一篇与自己所学专业或设计有关的英文资料；

三、毕业设计（论文）的主要内容、功能及技术指标：

1、系统要求用户能够直观地了解现场设备地工作状况及水位的变化；

2、要求用户能够远程控制变频器的启动和停止；

3、用户可以自行设置水位的高、低，以及控制变频器的启、停；

4、变频器及其他设备的故障信息能够及时反映在远程单片机上；

5、具有水位过高、过低报警和提示用户功能。

6、专业英文文献翻译；

PLCs --Past, Present and Future

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 PLC

When 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

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 Communicator

Possibly 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.

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.

There are many applications that require accurate control at a fast pace, but

Even simple motion control had previously required an expensive option module, and

at times was restricted to more sophisticated control platforms in order to meet

system requirements.

with servo drives. Most drives today can accept traditional commands from host (PLC

or PC) controls, or provide their own internal motion control. The trend here is to

integrate the motion control configuration into the logic controller programming

software package.

Programming Languages

This standard also defines graphical and textual sequential function chart

elements to organize programs for sequential and parallel control processing. Based

on the standard, many manufacturers offer at least two of these languages as options

for programming their PLCs. Ironically, approximately 96 percent of PLC users

recently still use ladder diagrams to construct their PLC code. It seems that ladder

and high-speed motion without giving up the rugged and reliable performance expected

from industrial control equipment.

New technology has also created a category of controllers called Programmable

Automation Controllers, or PACs. PACs differ from traditional PLCs in that they

typically utilize open, modular architectures for both hardware and software, using

de facto standards for network interfaces, languages and protocols. They could be

The Future

A 2005 PLC Product Focus Study from Reed Research Group pointed out factors

increasingly important to users, machine builders and those making the purchasing

decisions. The top picks for features of importance were.

* The ability to network, and do so easily. Ethernet communications is leading

continue to develop more sophisticated connectivity to report information to other

PLCs, system control systems, data acquisition (SCADA) systems and enterprise

resource planning (ERP) systems. Additionally, wireless communications will continue

to gain popularity.

manufacturer or a third party developer. Now these challenging locations can be

monitored with today a PC. Where industrial-grade control engines are not required,

the user can take advantage of more advanced software packages and hardware

flexibility at a lower cost.

* The ability to use universal programming software for multiple

targets/platforms. In the past it was expected that an intelligent controller would

be complex to program. That is no longer the case. Users are no longer just trained

programmers, such as design engineers or systems integrators, but end-users who

package in configuring logic, HMI, motion control and other specialized capabilities.

Possibly the ultimate wish of the end-user would be for a software package that could

seamlessly program many manufacturers PLCs and sub-systems. After all, Microsoft

Windows operating system and applications work similarly whether installed on a Dell,

HP or IBM computer, which makes it easier for the user.

Overall, PLC users are satisfied with the products currently available, while

众所周知，科技世界里只有一个永恒真理，那就是变化。这在可编程逻辑控制器（PLC）

及其各种应用的发展过程中尤为明显。自从三十多年前将 PLC 引进以来，PLC 已经在广泛的

工业领域中成为几十万控制系统的基础。

从本质上讲，PLC 是一种用高度专业化语言编程的工业计算机，并继续受益于计算机和

信息技术领域的技术进步。它的最突出之处是小型化和通信功能。

微型化的 PLC

通性等更多的功能。

现在，由于 PLC 能执行运动控制、数据采集，远程终端单元（RTU）甚至一些集成人机介

面（HMI）等功能，因此 PLC 在很多应用中也已配置齐全从而替代单一的过程控制器。以前，

这些功能通常要求他们自身内置实现这些功能的控制器和软件，此外，还需要一个用于离散

控制和互锁的独立的 PLC。

强大的通信功能

近年来，最有意义的变化也许发生在通信领域。在 20 世纪 90 年代，Modicon 推行的

Modbus 通信协议，允许 PLC 通过标准电缆进行通信。这为 PLC 更好地适用于现存的设备提供

了可能性，并且向主板上的其它控制系统通信成为可能。

在过去的 30 年里，我们真实地目睹了数百个专利化协议和标准化协议的发展，每一个协