安徽工程大学机电学院毕业设计(论文)开题报告 题 目 学生姓名 罗伟胜 单片机控制的自行车速度、里程表的设计 学号 313107010417 专业 自动化 一、本课题的研究意义、研究现状和发展趋势（文献综述） 1.1论文的研究意义 自1886年发明汽车以来,汽车走过了100多年的发展历程。但是随着科技发展和环境变化，人们越来越注重环保，自行车的使用趋势逐渐增加。因为自行车使用简易方便，环保安全，不易拥堵等诸多优点被越来越多的人们接受和喜欢。 传统的汽车转速里程表的功能有两个，一是用指针指示汽车行驶的瞬时车速，二是用机械计数器记录汽车行驶的累计里程。现代汽车正向高速化方向发展,随着车速的提高，用软轴驱动的传统车速里程表受到前所未有的挑战。这是因为软轴在高速旋转时，由于受钢丝交变应力极限的而容易断裂，同时，软轴布置过长会出现形变过大或运动迟滞等现象,而且,对于不同的车型,转速里程表的安装位置也会受到软轴长度及弯曲度的。凡此种种,使得基于非接触式转速传感器的电子式转速里程表得以迅速发展。 随着居民生活水平的不断提高，自行车不再仅仅是普通的运输、代步的工具，而是成为人们娱乐、休闲、锻炼的首选。自行车里程表能够满足人们最基本的需求，让人们能清楚地知道当前的速度、里程等物理量。主要阐述一种基于霍尔元件的自行车里程表的设计。以 ATC52 单片机为核心，A44E 霍尔传感器测转数，实现对自行车里程/速度的测量统计，采用 24C02 实现在系统掉电的时候保存里程信息，并能将自行车的里程数及速度用LED实时显示。文章详细介绍了自行车里程表的硬件电路和软件设计。硬件部分利用霍尔元件将自行车每转一圈的脉冲数传入单片机系统，然后单片机系统将信号经过处理送显示。软件部分用汇编语言进行编程，采用模块化设计思想。该系统硬件电路简单，子程序具有通用性，完全符合设计要求。 1.2单片机控制自行车速度、里程表的发展现状 传统的转速里程表的功能有两个，一是用指针指示车辆行驶的瞬时车速，二是用机械计数器记录车辆行驶的累计里程。现代车辆正向高速化方向发展,随着车速的提高，用软轴驱动的传统车速里程表受到前所未有的挑战。这是因为软轴在高速旋转时，由于受钢丝交变应力极限的而容易断裂，同时，软轴布置过长会出现形变过大或运动迟滞等现象。凡此种种,使得基于非接触式转速传感器的电子式转速里程表得以迅速发展。 在其工作原理上作出技术创新,即彻底放弃了“动磁式”或“动圈式”模拟电子式仪表，通过线包与磁钢间产生电磁转矩驱动指针工作的形式。该仪表由传感器完成各种被测物理量的采集，经过换算后直接送入单片机，再由驱动器驱动指针，在刻度盘上指示被测物理量，同时辅以被测物理量LCD数字显示。该汽车仪表在指示方式上仍然保留了第3代仪表指示直观、有动感、符合日常习惯等特点，而且批量生产的成本有望低于同等功能的模拟电子式仪表，更可贵的是在工作原理上的创新和突破，带来了技术性能质的提高。 全数字式汽车仪表后，未来汽车仪表应向何方向发展呢？虽然具体过程不清楚，但总的趋势还是比较明朗的，那就是充分应用光技术和机、电一体化技术，并突出现代信息技术和网络技术的应用，其功能将极大拓宽，指示形式将演变成计算机终端显示器。虽然人们对未来汽车仪表作出种种预测，并赋予它远远超出现在汽车仪表多得多的功能。个人认为仅从技术本身的角度出发，就目前技术条件而言，实现这些功能并没有什么问题，制约新技术在汽车仪表上应用的主要因素是制造成本。因为汽车仪表是一个量大、对成本极为敏感的产品，在其改进和创新的过程中，不仅要考虑技术的可行性、功能的拓宽、性能的改善、使用的可靠性等，更重要的是其制造成本。脱离制造成本谈汽车仪表，那只能是概念性的汽车仪表。在有关技术使用费用，特别是其依赖硬件成本进一步降低的前提下，汽车仪表未来可能发展趋势如下。 1.3直流稳压电源的发展趋势 1.从近期来看，未来车辆仪表的功能将不局限于现在的车速、里程，可能增添如下功能。 （1） 能指示安全系统运行状态，如轮胎气压、制动装置等。这些信号传输形式，将不再是简单的开关接通和断开直流信号，而是包含反映这些安全装置工作状态较多信息的调制信号，供单片机读取，以便单片机能准确地综合判断这些安全装置的工作状态，并给出故障显示提醒驾驶员，或指导维修人员排除故障，也就是说带基于单片机的仪表将有一定水平的智能化。 （2） 将防盗系统纳入仪表单片机的监管下，如车座、后行李箱等处防盗锁指纹识别开启系统，防撬振动报警装置，防盗点火起动装置等。 2.随着显示器件，如液晶显示器件的性能，特别是工作温度范围的拓宽，在价格进一步降低的前提下，仪表的功能将被极大地拓宽，形式将发生根本改变，外观上就是一个高清晰度的计算机显示器。 （1） 显示选用高效冷光源发光器件，如LCD、LED、电致发光器件等。导光系统更多体现出光学领域的新技术，如仪表面板颜色可变等满足个性化要求设计等。 3.自动导航和定位系统可能也是未来汽车仪表上不可缺少的部分，包括全球卫星定位系统和电子地图等。 4.具备完善的通讯系统，将来车辆上的计算机系统会与公共互连网相连，以便充分共享信息资源，处理通讯作业将是仪表计算机系统工作内容的一部分。 5 .仪表的计算机系统具备对路况设备进行监管的功能，可以自动控制轮胎等其他硬件对不同路面的适应。以上在基于当今成熟技术的基础上，对未来车辆仪表的发展方向做些简单设想。也许，未来车辆仪表的发展将远远超出我们今天的想象。 在当今世界范围内，车辆仪表正处于技术更新的转型期。为此，业内人士和专家对此都给予极大关注。什么样的仪表是今后车辆仪表的主流产品，什么技术是今后车辆仪表的主导技术，对于这些问题业内人士的看法可能不尽相同，但有一点是肯定的，带有基于单片机的数字技术在车辆仪表上的广泛应用，将是车辆仪表发展的必然。原因主要有4点： 1.仪表的功能由软件和硬件共同实现，而且主要是通过软件实现。这对于量大且对成本极为敏感的车辆仪表有特殊意义，因为软件的开发费用分摊到每个仪表上是非常少的。 2.与仅由电子线路硬件组成的车辆仪表相比，带有基于单片机的汽车仪表，其功能的实现手段更加灵活多样。 3.产品的“柔性”更好，即在推出新款产品时，能最大限度地利用以前产品的硬、软件设计成果，仅做少量修改便可，这在产品更新换代很快的今天和未来特别重要。 4.随着车辆电子化水平的提高，必须要求车辆仪表与车辆上其它装置交换数据。 二、主要设计（研究）内容 本课题研究的主要内容是设计一个能够实时显示速度和里程的自行车速度里程表。该里程表能够满足自行车骑行者在骑行过程中能够准确的了解自行车的行驶状态和已行驶的里程数，提高骑行者的便捷性、安全性和趣味性。 三、研究方案及工作计划（含工作重点与难点及拟采用的途径） 3.1研究方案 外部信号里程显示霍尔传感器ATC51单片机外部存储速度显示 图1 系统控制示意图 3.2工作计划 第一周：对毕业设计题目进行选题； 第二周：对选题进行分析，收集资料，填写毕业设计任务书； 第三周：对毕业设计文章排版、格式进行指导，准备开题； 第四周：认真填写开题报告将情况汇报指导老师，递交开题报告与进度表； 第五周：进行毕业设计正文部分，确定设计方案； 第六周：对常用软件进行学习，导师进行指导； 第七周：整理资料、撰写毕业设计论文（一）； 第八周：完成毕业设计（论文）初稿，指导教师审查初稿，提出修改意见； 第九周：完成毕业设计（论文）修改稿一，导师审查修改稿一； 第十周：向指导教师汇报设计完成进度，同时进行论文中期检查； 第十一周：完成毕业设计（论文）修改稿二，指导教师审查修改稿二； 第十二周：整理资料、按导师建议修改毕业设计论文（二）； 第十三周：完成设计论文（电子版）初稿； 第十四周：进行毕业设计论文修订； 第十五周：毕业设计论文（打印版）最终定稿，参加论文互评； 第十六周：提交毕业设计论文（打印版），参加毕业答辩； 四、阅读的主要参考文献（不少于10篇，期刊类文献不少于7篇，应有一定数量的外文文献） [1]陈伟.基于单片机的测速仪[J]. 电子制作，2008,10:29-30., [2]姚金明，杨俊杰.自行车转速里程表的设计[J]. 上海电力学院报，2013，03：249-252+265. [3]Krassimir T，Atanassov，Nikolai G.etal.Remark on Two Operations Over Intuitionistic Fuzzy Sets[J]. Fuzziness and Knowledge-Based Systems，2010，9(1) [4]徐丽萍.基于ATS51单片机自行车里程/速度计的设计[J]. 南京工业职业技术学院学报，2010，02：28-29. [5]贺颖，李盼，王志兰.自行车智能测速器的设计[J]. 自动化与仪器仪表 [6]李华.MCS-51系列单片机使用接口技术[M].北京航空航天大学出版社，1993 [7]文兴.自行车电子里程表的初步设计.南京工业技术职业技术学院学报，2004，6:25-28 [8]谢维成，杨加国.单片机原理与应用及C51程序设计.清华大学出版社。2006 [9]安宗权.电动电子车速里程表转速表的设计.沈阳建筑学院学报,2002,4:145-148 [10]张友德，赵志英等.单片机微机原理，应用与实验[M]上海：复旦大学出版社，2003:122-136 [11]Slotine, Weiping.Adaptive manipulator control: A case study [J]. Transactions on Automatic Control, 1995, 33(11): 995-1022 [12]谢自美.电子线路实验室侧[M].武汉：华中科技大学出版社，2000:212-230 Microcomputer Systems Electronic systems are used for handing information in the most general sense; this information may be telephone conversation, instrument read or a company‟s accounts, but in each case the same main type of operation are involved: the processing, storage and transmission of information. in conventional electronic design these operations are combined at the function level; for example a counter, whether electronic or mechanical, stores the current and increments it by one as required. A system such as an electronic clock which employs counters has its storage and processing capabilities spread throughout the system because each counter is able to store and process numbers. Present day microprocessor based systems depart from this conventional approach by separating the three functions of processing, storage, and transmission into different section of the system. This partitioning into three main functions was devised by Von Neumann during the 1940s, and was not conceived especially for microcomputers. Almost every computer ever made has been designed with this structure, and despite the enormous range in their physical forms, they have all been of essentially the same basic design. In a microprocessor based system the processing will be performed in the microprocessor itself. The storage will be by means of memory circuits and the communication of information into and out of the system will be by means of special input/output(I/O) circuits. It would be impossible to identify a particular piece of hardware which performed the counting in a microprocessor based clock because the time would be stored in the memory and incremented at regular intervals but the microprocessor. However, the software which defined the system‟s behavior would contain sections that performed as counters. The apparently rather abstract approach to the architecture of the microprocessor and its associated circuits allows it to be very flexible in use, since the system is defined almost entirely software. The design process is largely one of software engineering, and the similar problems of construction and maintenance which occur in conventional engineering are encountered when producing software. The figure1.1 illustrates how these three sections within a microcomputer are connected in terms of the communication of information within the machine. The system is controlled by the microprocessor which supervises the transfer of information betweenitself and the memory and input/output sections. The external connections relate to the rest (that is, the non-computer part) of the engineering system. Fig.1.1 Three Sections of a Typical Microcomputer Although only one storage section has been shown in the diagram, in practice two distinct types of memory RAM and ROM are used. In each case, the word „memory‟ is rather inappropriate since a computers memory is more like a filing cabinet in concept; information is stored in a set of numbered „boxes‟ and it is referenced by the serial number of the „box‟ in question. Microcomputers use RAM (Random Access Memory) into which data can be written and from which data can be read again when needed. This data can be read back from the memory in any sequence desired, and not necessarily the same order in which it was written, hence the expression „random‟ access memory. Another type of ROM (Read Only Memory) is used to hold fixed patterns of information which cannot be affected by the microprocessor; these patterns are not lost when power is removed and are normally used to hold the program which defines the behavior of a microprocessor based system. ROMs can be read like RAMs, but unlike RAMs they cannot be used to store variable information. Some ROMs have their data patterns put in during manufacture, while others are programmable by the user by means of special equipment and are called programmable ROMs. The widely used programmable ROMs are erasable by means of special ultraviolet lamps and are referred to as EPROMs, short for Erasable Programmable Read Only Memories. Other new types of device can be erased electrically without the need for ultraviolet light, which are called Electrically Erasable Programmable Read Only Memories, EEPROMs. The microprocessor processes data under the control of the program, controlling the flow of information to and from memory and input/output devices. Some input/output devices are general-purpose types while others are designed for controlling special hardware such as disc drives or controlling information transmission to other computers. Most types of I/O devices are programmable to some extent, allowing different modes of operation, while some actually contain special-purpose microprocessors to permit quite complex operations to be carried out without directly involving the main microprocessor. The microprocessor processes data under the control of the program, controlling the flow of information to and from memory and input/output devices. Some input/output devices are general-purpose types while others are designed for controlling special hardware such as disc drives or controlling information transmission to other computers. Most types of I/O devices are programmable to some extent, allowing different modes of operation, while some actually contain special-purpose microprocessors to permit quite complex operations to be carried out without directly involving the main microprocessor. The microprocessor , memory and input/output circuit may all be contained on the same integrated circuit provided that the application does not require too much program or data storage . This is usually the case in low-cost application such as the controllers used in microwave ovens and automatic washing machines . The use of single package allows considerable cost savings to e made when articles are manufactured in large quantities . As technology develops , more and more powerful processors and larger and larger amounts of memory are being incorporated into single chip microcomputers with resulting saving in assembly costs in the final products . For the foreseeable future , however , it will continue to be necessary to interconnect a number of integrated circuits to make a microcomputer whenever larger amounts of storage or input/output are required. Another major engineering application of microcomputers is in process control. Here the presence of the microcomputer is usually more apparent to the user because provision is normally made for programming the microcomputer for the particular application. In process control applications the benefits lf fitting the entire system on to single chip are usually outweighed by the high design cost involved, because this sort lf equipment is produced in smaller quantities. Moreover, process controllers are usually more complicated so that it is more difficult to make them as single integrated circuits. Two approaches are possible; the controller can be implemented as a general-purpose microcomputer rather like a more robust version lf a hobby computer, or as a „packaged‟ system, signed for replacing controllers based on older technologies such as electromagnetic relays. In the former case the system would probably be programmed in conventional programming languages such as the ones to9 be introduced later, while in the other case a special-purpose language might be used, for example one which allowed the function of the controller to be described in terms of relay interconnections, In either case programs can be stored in RAM, which allows them to be altered to suit changes in application, but this makes the overall system vulnerable to loss lf power unless batteries are used to ensure continuity of supply. Alternatively programs can be stored in ROM, in which case they virtually become part of the electronic „hardware‟ and are often referred to as firmware. More sophisticated process controllers require minicomputers for their implementation, although the use lf large scale integrated circuits „the distinction between mini and microcomputers, Products and process controllers of various kinds represent the majority of present-day microcomputer applications, the exact figures depending on one‟s interpretation of the word „product‟. Virtually all engineering and scientific uses of microcomputers can be assigned to one or other of these categories. But in the system we most study Pressure and Pressure Transmitters. Pressure arises when a force is applied over an area. Provided the force is one Newton and uniformly over the area of one square meters, the pressure has been designated one Pascal. Pressure is a universal processing condition. It is also a condition of life on the planet: we live at the bottom of an atmospheric ocean that extends upward for many miles. This mass of air has weight, and this weight pressing downward causes atmospheric pressure. Water, a fundamental necessity of life, is supplied to most of us under pressure. In the typical process plant, pressure influences boiling point temperatures, condensing point temperatures, process efficiency, costs, and other important factors. The measurement and control of pressure or lack of it-vacuum-in the typical process plant is critical. The working instruments in the plant usually include simple pressure gauges, precision recorders and indicators, and pneumatic and electronic pressure transmitters. A pressure transmitter makes a pressure measurement and generates either a pneumatic or electrical signal output that is proportional to the pressure being sensed. In the process plant, it is impractical to locate the control instruments out in the place near the process. It is also true that most measurements are not easily transmitted from some remote location. Pressure measurement is an exception, but if a high pressure of.some dangerous chemical is to be indicated or recorded several hundred feet from the point of measurement, a hazard may be from the pressure or from the chemical carried. To eliminate this problem, a signal transmission system was developed. This system is usually either pneumatic or electrical. And control instruments in one location. This makes it practical for a minimum number of operators to run the plant efficiently. When a pneumatic transmission system is employed, the measurement signal is converted into pneumatic signal by the transmitter scaled from 0 to 100 percent of the measurement value. This transmitter is mounted close to the point of measurement in the process. The transmitter output-air pressure for a pneumatic transmitter-is piped to the recording or control instrument. The standard output range for a pneumatic transmitter is 20 to 100kPa, which is almost universally used. When an electronic pressure transmitter is used, the pressure is converted to electrical signal that may be current or voltage. Its standard range is from 4 to 20mA DC for current signal or from 1 to 5V DC for voltage signal. Nowadays, another type of electrical signal, which is becoming common, is the digital or discrete signal. The use of instruments and control systems based on computer or forcing increased use of this type of signal. Sometimes it is important for analysis to obtain the parameters that describe the sensor/transmitter behavior. The gain is fairly simple to obtain once the span is known. Consider an electronic pressure transmitter with a range of 0～600kPa.The gain is defined as the change in output divided by the change in input. In this case, the output is electrical signal (4～20mA DC) and the input is process pressure (0～600kPa). Thus the gain. Beside we must measure Temperature Temperature measurement is important in industrial control, as direct indications of system or product state and as indirect indications of such factors as reaction rates, energy flow, turbine efficiency, and lubricant quality. Present temperature scales have been in use for about 200 years, the earliest instruments were based on the thermal expansion of gases and liquids. Such filled systems are still employed, although many other types of instruments are available. Representative temperature sensors include: filled thermal systems, liquid-in-glass thermometers, thermocouples, resistance temperature detectors, thermostats, bimetallic devices, optical kPamAkPamAkPakPamAmAKr027 .0600160600420and radiation pyrometers and temperature-sensitive paints. Advantages of electrical systems include high accuracy and sensitivity, practicality of switching or scanning several measurements points, larger distances possible between measuring elements and controllers, replacement of components(rather than complete system), fast response, and ability to measure higher temperature. Among the electrical temperature sensors, thermocouples and resistance temperature detectors are most widely used. 单片机系统 广义地说，微处理系统是用于处理信息的，这种信息可以是电话交谈，仪器读数或企业帐户，但是各种情况下都涉及相同的主要操作：信息处理、存储和传递。在常规的电子设计中，这些操作都是以功能平台方式组合起来的，例如计数器，无论是电子还是机械的，都要存储当前值，并按要求将该值增1。诸如采用计数器的电子钟之类的任一系统要使其存储和处理能力遍布整个系统，因为每个计数器都能存储和处理一些数字。 当前微处理化系统与上述的常规方法不同，它将处理，存储和传输三个功能分离形成不同的系统单元。这种形成三个主要单元的分离方法是冯-诺依曼在20世纪40年代所设想出来的，并且是针对微计算机的设想。从此几乎所有制成的计算机都是用这种结构设计的，尽管包含宽广的物理形式，从根本上来说他们均是具有相同的基本设计。 在微处理器系统中，处理是由微处理器本身完成的。存储是利用存储器电路，而进入和出自系统的信息传输则是利用特定的输入/输出（I/O）电路。要在一个微处理器化时钟中找出执行计数功能的一个特殊硬件是不可能的，因为时间存储在存储器中，而在固定的时间间隔下由微处理器控制增值。但是，规定系统运转过程的软件包含实现计数器功能的单元。由于系统几乎完全由软件所定义，所以对微处理器结构和其辅助电路这种看起来非常抽象的处理方法使其在应用时非常灵活。这种设计过程主要是软件工程，而且在生产软件时，就遇到产生于常规工程中相似的构造和维问题。 图1.1显示出了微型计算机中这三个单元是如何按照机器中的信息通信方式而联接起来的。该系统由微处理器控制，它管理自己与存储器和输入/输出单元的信息传输。外部的连接与工程系统的其余部分（即非计算机部分）有关。 尽管图中显示的只有一个存储单元，实际中有RAM和ROM两种不同的存储器被使用。由于概念上的计算机存储器更像一个公文柜，上述的“存储器”一词是非常不恰当的；信息存放在一系列已标号的“箱子”中，而且可按问题由“箱子”的序列号进行信息的参考定位。 微计算机常使用RAM（随机存取存储器），在RAM中数据可被写入，并且在需要时可被再次读出。这种数据能以任一所希望的次序从存储器中读出，不必按写入时的相同次序，所以有“随机” 存取存储器。另一类型ROM（只读存储器）用来保持不受微处理器影响的固定的信息标本；这些标本在电源切断后不会丢失，并通常用来保存规定微处理器化系统运转过程的程序。ROM可像RAM一样被读取，但与RAM不一样的是不能用来存储可变的信息。有些ROM在制造时将其数据标本放入，而另外的则可通过特殊的设备由用户编程，所以称为可编程ROM。被广泛使用的可编程ROM可利用特殊紫外线灯察除，并被成为E PROM，即可察除可编程只读存储器的缩写。另有新类型的期器件不必用紫外线灯而用电察除，所以称为电可察除可编程只读存储器EEPROM。 微处理器在程序控制下处理数据，并控制流向和来自存储器和输入/输出装置的信息流。有些输入/输出装置是通用型的，而另外一些则是设计来控制如磁盘驱动器的特殊硬件，或控制传给其他计算机的信息传输。大多数类型的I/O装置在某种程度下可编程，允许不同形式的操作，而有些则包含特殊用途微处理器的I/O装置不用主微处理器的直接干预，就可实施非常复杂的操作。 假如应用中不需要太多的程序和数据存储量，微处理器、存储器和输入/输出可全被包含在同一集成电路中。这通常是低成本应用情况，例如用于微波炉和自动洗衣机的控制器。当商品被大量地生产时，这种单一芯片的使用就可节省相当大的成本。当技术进一步发展，更强更强的处理器和更大更大数量的存储器被包含形成单片微型计算机，结果使最终产品的装配成本得以节省。但是在可预见的未来，当需要大量的存储器或输入/输出时，还是有必要继续将许多集成电路相互联结起来，形成微计算机。 微计算机的另一主要工程应用是在过程控制中。这是，由于装置是按特定的应用情况由微机编程实现的，对用户来说微计算机的存在通常就更加明显。在过程控制应用中，由于这种设备以较少的数量生产，将整个系统安装在单个芯片上所获取的利益常比不上所涉及的高设计成本。而且，过程控制器通常更为复杂，所以要将他们做成单独的集成电路就更为困难。可采用两种处理，将控制器做成一种通用的微计算机，正像较强版本的业余计算机那样；或者做成“包裹”式系统，按照像电磁继电器那样的较老式的技术进行设计，来取代控制器。对前一种情况，系统可以用常规的编程语言 来编程，正如以后要介绍的语言那样；而另一种情况，可采用特殊用途的语言，例如那种使控制器功能按照继电器相互连接的方法进行描述。两种情况下，序均能存于RAM，这让程序能按应用情况变化时进行相应的变化，但是这使得总系统易受掉电影响而工作不正常，除非使用电池保证供电连续性。另一种选择是将程序在ROM中，这样他们就变成电子“硬件”的一部分并常被称为“固件”。 尽管大规模集成电路的应用使小型和微型计算机的差别变得“模糊”，更复杂的过程控制器需要小型计算机实现他们的过程。各种类型的产品和过程控制器代表了当今微计算机应用的广泛性，而具体的结构取决于对“产品”一词的解释。实际上，计算机的所有工程和科学上的应用都能指定来进行这些种类的某一或某些工作。而在本设计中压力和压力变送器当某一力加到某一面积上，就形成压力，假如这力是1牛顿均匀地加在1平方米的面积上，这压力被定义为1帕斯卡。压力是一种普遍的工艺状态，它也是这个星球上的一个生活条件：我们生活在向上延伸许多英里的大气海洋的底部。空气物质是有重量的，而且这种下压的重量形成大气压。水，是生活的必需品，也是在压力之下提供给我们中的大多数人。在典型的过程工厂中，压力影响沸点温度、凝固点温度、过程效率、消耗和其他重要因数。压力的测量和控制，或者压力的不足—真空，在典型的过程控制中是极为重要的。 工厂中的工作仪器通常包括压力计、精密纪录仪、以及气动和电动的压力变送器。压力变送器实现压力测量并产生正比于所传感压力的气动或电信号输出。 在过程工厂中，将控制仪表远远放在过程的附近是不现实的，并且大多数测量是不容易从远处传来的。压力测量是一个例外，但是，如果要离测量点几百英尺外指示或记录某种危险化学品的高压，就会有来自这个压力所载的化学品所引发的危险。为了消除这一问题，开发了一种信号传输系统。这种系统常常可是气动或者电动的。使用这种系统，就可以在某一地点安装大多数的指示、记录和控制仪器。这也是最少数量的操作者有效的运行工厂成为现实。 当使用气动传送系统时，测量信号就由变送器将比例为0%～100%的测量值转换为气动信号。变送器安装在靠近过程中的测量点上。变送器输出—对气动变送器是输出压力—通过管道传给记录或控制仪表。气动变送器的标准输出范围是20～100kPa，这信号几乎在全球使用。 当使用电子压力变送器时，压力就被转换成电流或电压形式的电信号。其标准范围对电流来说是4～20mA DC，对电压信号来说是1～5V DC。当今，另一种电信号形式变的越来越常用，就是数字或离散信号。基于计算机或微处理器的仪器或控制系统的应用正推动这类信号的应用不断增加。有时，分析获取描述传感器/变送器特性的参数是很重要的。当量程已知，去获取增益就非常简单。假定电子压力传感器的量程为0～600kPa，增益定义为输出变化除以输入变化。这里，输出的电信号（4～20mA DC），而输入的过程压力（0～600kPa），这样增益就为： 此外我们在本设计中还必须对温度进行测量，温度测量在工业控制中是很重要的，因为它作为系统或产品状态的直接指标，或者作为如反应率、能量流、涡轮机效率和润滑质量等间接指标。现行的温度分度已使用了约200年，最初的仪器是基于气体和液体的热膨胀。现在尽管有许多其他类型的仪器在使用，这些填充式系统仍常用于直接的温度测量。有代表性的温度传感器包括：填充式热系统、玻璃液体温度计、热电偶、电阻温度探测器、热敏电阻、双金属器件、光学和辐射高温计和热敏涂料。 电气系统的优点包括高的精度和灵敏度，能实现开关切换或扫描多个测量点，可在测量元件和控制器之间长距离传输，出现事故时可调换元件，快速响应，以及具有测量高温的能力。其中热电偶和电阻温度探测器则被最广泛的使用。 指导教师审核意见 指导教师(签名)： 年 月 日 教研室负责人批阅意见 教研室负责人(签名)： 年 月 日
