电气及自动化专业外文翻译(13)

1、中国地质大学长城学院本科毕业论文外文资料翻译学 院工程技术学院学生姓名齐业亮专 业电气工程及其自动化学 号0431302152017年3月10日Using Linux in Embedded SystemsUNIX evokes a wide range of emotions: loved by some for its power and flexibility, despised by others for its eomplex and arcane commands. UNIX has established a checkered reputation in the world o

2、f computing.EASE OF USEUNIX is infamous for its glut of arcane , non-mnemonic, and cryptic keyboard commands, each with many command-line switches, which can be incredibly confusing to remember. Its SVR4 implementation contains more than 2,000 comands. Many of these functions can be combined, using

3、pipes and redirection. This illustrates one of UNIX 's design fundamentals: the creation of a large assortment of very specialized and modular commands that can be combined to accomplish complex tasks.While UNIX was essentially limited to use by software professionals at universities and in appl

4、ications development houses, its complex command-line syntax and resulting flexibility were considered an advantage rather than a problem.But this same flexibility also creates a major drawback for using UNIX in a business-oriented marketthe more flexible a system is, the more difficult it becomes t

5、o learn and operate.UNIX's script languages provide one form of help. Using scripts, a system administrator can tailor the system to a set of users'needs quickly.Another factor mitigating the difficulties of UNIX's arcane command language are the Graphic User Interfaces(GUIs), such as Mo

6、tif, SunView, or OpenLook. GUIs, however, place another level of incompatibility problems on what is already a complex system.Motif has been ported to the most different architectures and (because it follows the Presentation Manager style ) is perhaps closest in look and feel to a PC interface such

7、as Microsoft Windows. Sun View is also dominant because of its large installed base and the numbers of applications programmers who have become familiar with writing software to its specifications.BINARY COMPATIBILITYUNIX marketers have looked with some envy at the huge-base of shrink-wrapped applic

8、ations available in the DOS world and have promised that binary-compatible applications for systems is just around the corner. These promises have yet to be met in any significant way. While binary compatibility is not yet available, it is getting easier to share data and applications across differe

9、nt machines.PORTABILITYCompared with most operating system sources, UNIX code is quite move UNIX to different architectures. But a UNIX port to a new system is not a trivial matter, offen taking several man-years of work, and can result in glitches and malfunctions, which may create very subtle inco

10、nsistencies in performance. These bugs are often difficult to identify and correct.Having the source code available for your computer 's operating system is beneficial and detrimental: if the OS lacks certain desirable featuers, having the sources in-house greatly enhances a company's abilit

11、y to make necessary changes.On the other hand, the customized version of the operating system, with its new or modified features may later present compatibility problems with newer releases or purchased application.Why Linux?Intelligent dedicated systems and applicances used in interface, monitoring

12、 , communications, and control applications increasingly demand the services of a sophisticated, state-of-the-art operating systems. Many such systems require advanced capabilities like: high resolution and user-friendly graphical user interfaces(GUIs); TCP/IP connectivity; substitution of reliable(

13、 and low power)flash memory solid state disk for conventional disk drives; support for 32-bit ultra-high-speed CPUs; the use of large memory arrays; and seemingly infinite capacity storage devices including CD-ROMs and hard disks.This is not the stuff of yesteryear's “standalone”code, “roll-your

14、-own”kernels, or “plain old DOS”, No, those days are goneforever.Then too, consider the rapidly accelerating pace of hardware and chipset innovation accompanied by extremely rapid obsolescence of the older devices.Combine these two, and you can see why it 's become an enormous challenge for comm

15、ercial RTOS vendors to keep up with the constant churning of hardware devices . Supporting the newest devices in a timely mannereven just to stay clear of the unrelenting steamroller of chipset obsolescencetakes a large and constant resource commitment. If it' a struggle for the commercial RTOS

16、vendors to keep up, going it alone by writing standalone code or a roll-your-own kernel certainly makes no sense.With the options narrowing, embedded system developers find themselves faced with a dilemma:On the one hand, today's highly sophisticated and empowered intelligent embedded systemsbas

17、ed on the newest chips and hardware capabilitiesdemand noting less than the power, sophistication, and currency of support provided by a popular high-end operating system like windows.On the other hand, embedded systems demand extremely high reliability(for non-stop, unattended operation)plus the ab

18、ility to customize the OS to match an application's unique requirements.Linux 应用于嵌入式系统UNIX 引起了全然不同的情绪：因其能力和灵活性而受到一些人的青睐，但因其 复杂且神秘的命令而受到另一些人的藐视。在计算世界里， UNIX 已建立起一个褒义 不一的声誉。易用性UNIX 因其过于神秘、不易记忆和含义模糊的大量键盘命令而名声不佳，这些命 令每个都有很多命令行开关，这可能造成昏药而不易记忆。它的SVR4版本拥有2000多个命令，其中很多功能可通过管道和重定向进行组合。这反映了UNIX 的基本设计思想之一：

19、 生成数量很大的专用和模块化命令， 把它们结合起来就能完成各种复杂的 任务。虽然 UNIX 过去基本上限于大学和应用开发公司中的软件专业人员使用，其复杂 的命令行语法和由此而得到的灵活性被看作一个优点而不是问题。但是在面向商业的市场中使用 UNIX，却产生了一个重大的缺陷一一系统越灵活，它就变得越难学会和 操作。UNIX 的原本（或脚本）语言提供某种形式的帮助。利用原本语言，系统管理员 能很快地把系统裁剪成满足一组用户的需求。克服 UNIX 神秘命令语言之困难的另一种方法是用图形用户接口 GUI， 如 Motif,SunView 或OpenLook。然而，图形用户接口在已经很复杂的系统上增添了

20、另一 层不兼容性问题。Motif 已经移植到差别非常大的不同体系结构上（由于它仿效PresentationManager 的风格），而且在外观与感觉上也许是最接近于诸如 Microsoft Windows 一 类的PC接口。SunView由于有很大的装机数和很多应用程序员已熟悉按它的规范写 软件，所以也是一种主流图形用户接口。二进制兼容性UNIX的销售者以某种羡慕的心情关注着DOS世界中可能的大量简装应用程序，并承诺不同系统的二进制兼容的应用程序即将面世。这些承诺远未让人满足。 虽然二进制兼容性尚未获得，但现在不同机器上共享数据和应用程序正在变得更加容易。可移植性与多数操作系统源码相比，UNI

21、X程序容易移植。它用C语言编写，而不用汇编语言，使用UNIX能移植到不同的体系结构上。 但是把UNIX移植到一个新系统上也不 是一件一蹴而就的事情，常常是要几个人年的工作，还可能造成故障和失灵，从而在 性能上产生难以捉摸的不一致性。这些故障往往是难以识别与纠正的。拥有你自己的计算机操作系统的源码，既有益，也有害；如果操作系统缺少某 些所需功能，公司自己拥有源码能大大增强公司进行必要修改的能力。另一方面，具有新的或修改特性的操作系统定制版本，在日后可能出现与更新 的版本或购买的应用程序不兼容的问题。为什么用 LINUX？用于接口、监控、通信和控制应用程序的职能专用系统和设备越来越要求高级 的现代

22、操作系统的这些服务。 许多这样的系统需要如下的高级性能： 高分辨率和用户友好的图形用户界面： TCP/IP 链接；用可靠的闪存固态盘代替常规的磁盘机；支持32位的超高速 CPU使用大存储器阵列；以及似乎是无限容量的存储设备，包括CD-ROM和硬盘。这不是以前的独立代码，自己写的核，或简单的老是 DOS那些日子已永远过去。另外也考虑到硬件和芯片迅速加速的革新步伐伴随着老设备相当快地淘汰。结合这两种情况， 就能知道为什么对商用实时操作系统供应商而言， 跟上硬件设备的 不断出新已变成巨大的挑战。及时地支持最新设备，甚至不去理会不愿退让的、大力 推销的逐渐过时的芯片组， 你需要大量和不断的资材投入。

23、如果商用实时操作系统供 应商必须奋力紧跟硬件发展的话， 那么编写独立的代码或写自己的核， 这种单枪匹马 的做法一定是毫无意义的。因为选择范围很小，嵌入式系统的开发商面临这样的一种困境： 一方面，今天高度复杂的，且授权的智能嵌入式系统（基于最新的芯片和硬件性 能）所需要的正式流行的高档操作系统（如Windows）提供的那种能力、精致性，以及通用性。另一方面，嵌入式系统要求非常高的可靠性（不停机，无人照管的操作），加上有能力把操作系统改编成符合应用系统的独特的要求。其窘境是：通用桌面操作系统（如Windows）不能很好地适应于类似设备的嵌入式系统的独特需求。然而，商用实时操作系统，虽然设计成满足嵌

24、入式应用的可靠性 和配置灵活性的要求，但由于他们缺乏标准化以及没有能力跟上技术的速度发展步 伐，它们日益不合需要。开发人员做什么？幸运的是，一种新的、令人兴奋的选择系统已经出现：开放源码Linux 。 Linux提供功能强大的和高级系统管理设施。丰富的设备支持，在可靠性和鲁棒性，以及广 泛详尽的文档方面有极好的声誉。最好的（对系统开发人员而言）是Linux 不要钱有完全免费的源代码。Linux是不是像 Windows那样太大以及需要系统资源太多，以致不能满足嵌入式 系统的约束要求呢？与Windows不同，Linux本来就是模块化的，并且能够很容易缩减成紧缩配置，这种配置几乎与DOS差不多大，甚

25、至能放到一张软盘上。此外，因为Linux 源码是免费可用的，所以可以按照独特的嵌入式系统要求改编该操作系统。这样，并不令人惊奇， 开放源码 Linux 已建成了一个新的操作系统开发和支持范 例，在那里数以千计的开发人员继续贡献于不断发展的Linux 代码库。此外，几十家面向 Linux 的软件公司已经出现他们热切支持那些为建立从工厂自动化到智能 设备范围很广的应用系统的开发人员的要求。Linux对许多嵌入式系统，为了适应诸如 RAM固态盘、处理机速度，以及功耗 的约束，嵌入的 Linux 的主要任务是，使系统所需的资源最小。嵌入式操作系统可能 需要从一个芯片盘或紧凑闪存固态盘上自举；或者自举和

26、运行在没有显示器和键盘 （“无头”操作）的环境，或经有以太网连接，从远程设备装入应用程序。现成的小 Linux 有许多来源， 其中有日益增多的面向应用的 Linux 配置和分发版， 这些都被修改成适应于特定的应用。例如路由器、防火墙、互联网/ 网络设备、网络服务器、网关等。你也可能选择建立你自己喜欢的嵌入式 Linux ，从一个标准分发版开始，略去不 要的模块。虽然如此，还应该考虑从别人的工作配置基础上开始你的工作，因为他们 的版本的源仅是完全合法的，而且也是被鼓励。实时 Linux许多嵌入式系统需要对现实世界的一些事件可预测，并且受限响应。这样的实时 系统包括工厂自动化、数据采集和控制系统、

27、音频 / 视频应用，以及许多其他计算机 化的产品和设备。什么是“实时系统”？通常接受的“实时”性能的定义是，现实世 界时间必须在确定的、可预测的，以及在相对短的时间间隔内得到响应。虽然 Linux 不是一个实时操作系统 （ Linux 内核不提供所需要的事件优先级和抢 占功能），但当前有几个扩充选项可用， 这些选项把实时能力带给基于 Linux 的系统， 最通常的方法是双内核方法。用这个方法，通用（非实时） OS 运行作为实时内核的 一个任务。通用操作系统提供诸如磁盘读/写、LAN/通信、串行/并行I/O、系统初始化、内存管理等功能，而实时内核处理时限世界事件。你可以把这个看作两者兼得， 因为

28、它能够保持流行的通用操作系统好处，而增加了实时 OS的能力。就Linux来说,你能保持与标准 Linux 兼容，而以非干扰的方式增加了实时功能。当然，也可以专研并修改 Linux ，把改变成实时操作系统，因为它的源码是公开 可用的，但如果这样做，你会面临这样严重缺点，即不论特性方面，还是驱动程序方 面都不能与主流 Linux 同步前进。 简言之， 你的制定 Linux 将不能从 Linux 的不断进 展中获得好处，而这种进展是世界范围内数以千计的开发人员共同协力的结果。Linux 是一个操作系统，它担当计算机系统硬件与软件间的通信服务，Linux 内核包含了你在任何操作系统所期望的所有特性。A

29、 Low-Cost, Smart Capacitive Position Sensor Abstract：A new high-performance, low-cost, capacitive position-measuring system is described. By using a highly linear oscillator, shielding and a three-signal approach, most of the errors are eliminated. The accuracy amounts to 1卩 m ovreng. Since the outp

30、ut of the oscillatorcan directly be connected to a microcontroller, an A/D converter is not needed.I. INTRODUCTIONThis paper describes a novel high-performance, low-cost, capacitive displacement measuring system featuring:1 mm measuring range,1 卩 m accuracy,0.1 s total measuring time.Translated to t

31、he capacitive domain, the specifications correspond to:a possible range of 1 pF;only 50 fF of this range is used for the displacement transducer;50 aF absolute capacitance-measuring inaccuracy.Meijer and Schrier l and more recently Van Drecht,Meijer, and De Jong 2 have proposed a displacement-measur

32、ing system, using a PSD (Position Sensitive Detector) as sensing element. Some disadvantages of using a PSD are the higher costs and the higher power consumption of the PSD and LED (Light-Emitting Diode) as compared to the capacitive sensor elements described in this paper.The signal processor uses

33、the concepts presented in 2,but is adopted for the use of capacitive elements. By the extensive use of shielding, guarding and smart A/D conversion,the system is able to combine a high accuracy with a very low cost-price. The transducer produces three-period-modulated signals which can be selected a

34、nd directly read out by a microcontroller. The microcontroller,in return, calculates the displacement and can send this value to a host computer (Fig. 1) or a display or drive an actuator.CxFig. 1. Block diagram of the systemC refWe tai Shieldin?Fig. 2. Perspective and dime nsions of the electrode s

35、tructureII . THE ELECTRODE STRUCTUREThe basic sensing element consists of two simple electrodes with capacitanee Cx, (Fig. 2). The smaller one (E2) is surro un ded by a guard electrode. Thanks to the use of the guard electrode, the capacitanee Cx between the two electrodes is independent of movement

36、s (lateral displaceme nts as well as rotati ons) parallel to the electrode surface.The in flue nee of the parasitic capacitances Cp will be eliminated as will be discussed in Sectioffi .Accordi ng to Heere ns 3, the relative deviati on in the capacita nee Cx betwee n the two electrodes caused by the

37、 finite guard electrode size is smaller than:S <et (x/d)(1)where x is the width of the guard and d the distance between the electrodes. This deviationintroduces a nonlinearity.Therefore we require that 3 is less than 100 ppm.Also the gap betwee n the small electrode and the surro unding guard cau

38、ses a deviatio n:3 <冗(d/s)with s the width of the gap. This deviati on is n egligible compared to (l), whe n the gap width is less tha n 13 of the dista nee betwee n the electrodes.Another cause of errors originates from a possible finite skew angle a between the two electrodes (Fig. 3). Assu min

39、g the follow ing con diti ons:the potentials on the small electrode and the guard electrode are equal to 0 V,the pote ntial on the large electrode is equal to V volt,the guard electrode is large eno ugh,it can be seen that the electric field will be concentric.Fig. 3. Electrodes with angle . aTo kee

40、p the calculations simple, we will assume the electrodes to be infinitely large in one direct ion. Now the problem is a two-dime nsio nal one that can be solved by using polar-coord in ates (r, © ). In this case the electrical field can be described by:V sinV costo 0 and in tegrate over r:To ca

41、lculate the charge on the small electrode, we set with Bl the left border of the small electrode:Bl td12(5)and Br the right border:BrdlSol ving (4) results in:tan20 .2d cosl sinQ V lna2d cosl sinFor small a's this can be approximated by:(8)C右JIt appears to be desirable to choose l smaller than d

42、, so the error will depend only on theangle a .In our case, a change in Omgle of 0.6will cause an error less than 100 ppm.With a proper design the parameters£ o and l are constant,and then the capacitanee betweenthe two electrodes will depe nd only on the dista nee d betwee n the electrodes.川.E

43、LIMINATION OF PARASITIC CAPACITANCESBesides the desired sensor capacitanee C, there are also many parasitic capacitances in the actual structure (Fig.2). These capacitances can be modeled as shown in Fig.4. Here Cpl represe nts the parasitic capacita nces from the electrode E1 and Cp2 from the elect

44、rode E2 to the guard electrodes and the shielding. Parasitic capacitance Cp3 results from imperfect shieldi ng and forms an offset capacita nce. When the tran sducer capacita nce Cx is conn ected to an AC voltage source and the current through the electrode is measured,Cpl and Cp2 will be elim in at

45、ed. Cp3 can be elimi nated by perform ing an offset measureme nt.Fig. 4. Elimination of parasitic capacitancesThe current is measured by the amplifier with shunt feedback, which has a very low input impedanee. To obtain the required linearity, the unity-gain bandwidth fT of the amplifier has to sati

46、sfy the following condition:12Cf(9)CfC p2where T is the period of the in put sig nal.Since Cp2 con sists of cable capacita nces and the in put capacita nee of the op amp, it may in deed be larger tha n Cf and can not be n eglected.IV. THE CONCEPT OF THE SYSTEMThe system uses the three-sig nal con ce

47、pt prese nted in 2, which is based on the follow ing principles. When we measure a capacitor Cx with a linear system, we obtain a value:(10)M x mCx M Offwhere m is the unknown gain and Moff, the unknown offset.By perform ing the measureme nt of a refere nee qua ntity Cref, i n an ide ntical way and

48、by measuri ng the offset, Moff,by mak ing m = 0, the parameters m and Moff are eliminated.The final measurement result P is defined as:(11)(12)p M ref M off Mx M offIn our case, for the sensor capacitance C, it holds that:Adodwhere Ax is the area of the electrode, do is the in itial dista nce betwee

49、 n them,constant and d is the displacement to be measured. For the reference electrodes it holds that:C refAref d ref(13)with Aref the area and dref the distance. Substitution of (12) and (13) into (10) and then into (11) yields:Aref do dAxdrefda1 a0d ref(14)Here, P is a value representing the posit

50、ion while a1 and a0 are unknown, but stable constants. The constant a1 =Aref/Ax is a stable constant provided there is a good mechanical matching between the electrode areas. The constant ao = (Arefd0/(Axdref) will also be a stable constant provided that do and dref are constant. These constants can

51、 be determined by a one-time calibration. In many applications this calibration can be omitted; when the displacement sensor is part of a larger system, an overall calibration is required anyway. This overall calibration eliminates the requirement for a separate determination of a1 and a0.V . THE CA

52、PACITANCE-TO-PERIOD CONVERSIONThe signals which are proportional to the capacitor values are converted into a period, using a modified Martin oscillator 4 (Fig. 5j.When the voltage swing across the capacitor is equal to that across the resistor and the NAND gates are switched off, this oscillator ha

53、s a period Toff:Toff = 4RCoff. (15)Since the value of the resistor is kept constant, the period varies only with the capacitor value. Now, by switching on the right NAND port, the capacitance CX can be connected in parallel to Coff. Then the period becomes:Tx=4R(Coff+Cx)=4RCx+Toff (16)The constants

54、R and Toff are eliminated in the way described in Section IV.In 2 it is shown that the system is immune for most of the nonidealities of the op amp and the comparator, like slewing, limitations of bandwidth and gain, offset voltages,and input bias currents. These nonidealities only cause additive or

55、 multiplicative errors which are eliminated by the three-signal approach.一种低成本智能式电容位置传感器摘要：本文描述了一种新的高性能，低成本电容位置测量系统。通过使用高线性振荡器， 屏蔽和三信号通道，大部分误差被消除。其精确度在1毫米范围内达1微米。由于振荡器的输出可直接连接到微控制器，所以无需用A/D转换器。I .导言本文介绍了一种新型高性能，低成本的电容位移测量系统，特点如下：1毫米测量范围1微米精确度0.1 s总测量时间对应到电容域，规格相当于：1皮法的变化范围；只有这个范围的 50fF （fF是法拉乘以10的负1

56、5次方。f是femto 的缩写）用于位移传感器。50aF绝对电容测量误差。梅耶尔和施里尔1以及最近的范德雷赫特河，梅耶尔，和德容2提出了位移测量系统， 采用一个PSD（位置敏感探测器）作为传感元件。和本文描述的电容传感器元件相比，使 用PSD的缺点是，PSD和 LED（发光二极管）有更高的成本和功率消耗。使用2中所提概念的信号处理器，被采用到电容元件的使用中。通过广泛使用屏蔽， 智能A/ D转换，该系统能够将高精确度和低成本结合。换能器产生可以选择和直接由微 控制器读出的三段调制信号。微控制器，相应的，计算位移及发送此值到主机电脑（图 1） 或显示或驱动执行器。CxC ref图1该系统的框图金属 屏蔽图2电极结构的尺寸和透视图