光电传感器英文和译文.doc

Progress in Materials Science Volume 46 Issues 3 4 2001 Pages 461 504 The selection of sensors J Shieh J E Huber N A Fleck M F Ashby Department of Engineering Cambridge University Trumpington Street Cambridge CB2 1PZ UK Available online 14 March 2001 http dx doi org 10 1016 S0079 6425 00 00011 6 How to Cite or Link Using DOI Permissions Selection Sensing range Sensing resolution Sensing frequency 1 Introduction The Oxford English Dictionary defines a sensor as a device which detects or measures some condition or property and records indicates or otherwise responds to the information received Thus sensors have the function of converting a stimulus into a measured signal The stimulus can be mechanical thermal electromagnetic acoustic or chemical in origin and so on while the measured signal is typically electrical in nature although pneumatic hydraulic and optical signals may be employed Sensors are an essential component in the operation of engineering devices and are based upon a very wide range of underlying physical principles of operation Given the large number of sensors on the market the selection of a suitable sensor for a new application is a daunting task for the Design Engineer the purpose of this article is to provide a straightforward selection procedure The study extends that of Huber et al 1 for the complementary problem of actuator selection It will become apparent that a much wider choice of sensor than actuator is available the underlying reason appears to be that power matching is required for an efficient actuator whereas for sensors the achievable high stability and gain of modern day electronics obviates a need to convert efficiently the power of a stimulus into the power of an electrical signal The classes of sensor studied here are detailed in the Appendices 2 Sensor performance charts In this section sensor performance data are presented in the form of 2D charts with performance indices of the sensor as axes The data are based on sensing systems which are currently available on the market Therefore the limits shown on each chart are practical limits for readily available systems rather than theoretical performance limits for each technology Issues such as cost practicality such as impedance matching and reliability also need to be considered when making a final selection from a list of candidate sensors Before displaying the charts we need to introduce some definitions of sensor characteristics these are summarised in Table 1 1 Most of these characteristics are quoted in manufacturers data sheets However information on the reliability and robustness of a sensor are rarely given in a quantitative manner Table 1 Summary of the main sensor characteristics Rangemaximum minus minimum value of the measured stimulus Resolutionsmallest measurable increment in measured stimulus Sensing frequencymaximum frequency of the stimulus which can be detected Accuracyerror of measurement in full scale deflection Sizeleading dimension or mass of sensor Opt environmentoperating temperature and environmental conditions Reliabilityservice life in hours or number of cycles of operation Drift long term stability deviation of measurement over a time period Costpurchase cost of the sensor in year 2000 Full size table In the following we shall present selection charts using a sub set of sensor characteristics range resolution and frequency limits Further we shall limit our attention to sensors which can detect displacement acceleration force and temperature 2 Each performance chart maps the domain of existence of practical sensors By adding to the chart the required characteristics for a particular application a subset of potential sensors can be identified The optimal sensor is obtained by making use of several charts and by considering additional tabular information such as cost The utility of the approach is demonstrated in Section 3 by a series of case studies 2 1 Displacement sensors Consider first the performance charts for displacement sensors with axes of resolution versus range R and sensing frequency f versus range R as shown in Fig 1 and Fig 2 respectively Fig 1 Resolution versus sensing range for displacement sensors View thumbnail images Fig 2 Sensing frequency versus sensing range for displacement sensors View thumbnail images 2 1 1 Resolution sensing range chart Fig 1 The performance regime of resolution versus range R for each class of sensor is marked by a closed domain with boundaries given by heavy lines see Fig 1 The upper limit of operation is met when the coarsest achievable resolution equals the operating range R Sensors of largest sensing range lie towards the right of the figure while sensors of finest resolution lie towards the bottom It is striking that the range of displacement sensor spans 13 orders of magnitude in both range and resolution with a large number of competing technologies available On these logarithmic axes lines of slope 1 link classes of sensors with the same number of distinct measurable positions Sensors close to the single position line R are suitable as simple proximity on off switches or where few discrete positions are required Proximity sensors are marked by a single thick band in Fig 1 more detailed information on the sensing range and maximum switching frequency of proximity switches are summarised in Table 2 Sensors located towards the lower right of Fig 1 allow for continuous displacement measurement with high information content Displacement sensors other than the proximity switches are able to provide a continuous output response that is proportional to the target s position within the sensing range Fig 1 shows that the majority of sensors have a resolving power of 103 106 positions this corresponds to approximately 10 20 bits for sensors with a digital output Table 2 Specification of proximity switches Proximity switch type Maximum switching distance m Maximum switching frequency Hz Inductive 6 10 4 1 10 15 5000 Capacitive 1 10 3 6 10 21 200 Magnetic 3 10 3 8 5 10 2400 5000 Pneumatic cylinder sensors magnetic Piston diameter 8 10 3 3 2 10 1 300 5000 Ultrasonic 1 2 10 1 5 21 50 Photoelectric 3 10 3 30020 20 000 Full size table It is clear from Fig 1 that the sensing range of displacement sensors cluster in the region 10 5 101 m To the left of this cluster the displacement sensors of AFM and STM which operate on the principles of atomic forces and current tunnelling have z axis sensing ranges on the order of microns or less For sensing tasks of 10 m or above sensors based on the non contacting technologies of linear encoding ultrasonics and photoelectrics become viable Optical linear encoders adopting interferometric techniques can achieve a much higher resolution than conventional encoders however their sensing range is limited by the lithographed carrier scale A switch in technology accounts for the jump in resolution of optical linear encoders around the sensing range of 0 7 m in Fig 1 Note that radar which is capable of locating objects at distances of several thousand kilometres 3 is not included in Fig 1 Radar systems operate by transmitting high frequency radio waves and utilise the echo and Doppler shift principles to determine the position and speed of the target Generally speaking as the required sensing range increases sensors based on non contact techniques become the most practicable choice due to their flexibility fast sensing speed and small physical size in relation to the length scale detected Fig 1 shows that sensors based on optical techniques such as fibre optic photoelectric and laser triangulation cover the widest span in sensing range with reasonably high resolution For displacement sensors the sensing range is governed by factors such as technology limitation probe or sensing face size and the material properties of the target For example the sensing distance of ultrasonic sensors is inversely proportional to the operating frequency therefore a maximum sensing range cut off exists at about R 50 m Eddy current sensors of larger sensing face are able to produce longer wider and stronger electromagnetic fields which increase their sensing range Resolution is usually controlled by the speed sensitivity and accuracy of the measuring circuits or feedback loops noise level and thermal drift impose significant influences also Sensors adopting more advanced materials and manufacturing processes can achieve higher resolution for example high quality resistive film potentiometers have a resolution of better than 1 m over a range of 1 m i e 106 positions whereas typical coil potentiometers achieve only 103 positions 2 1 2 Sensing frequency sensing range chart Fig 2 When a displacement sensor is used to monitor an oscillating body a consideration of sensing frequency becomes relevant Fig 2 displays the upper limit of sensing frequency and the sensor range for each class of displacement sensor It is assumed that the smallest possible sensing range of a displacement sensor equals its resolution therefore in Fig 2 the left hand side boundary of each sensor class corresponds to its finest resolution 4 However sensors close to this boundary are only suitable as simple switches or where few discrete positions are to be measured Lines of slope 1 in Fig 2 link classes of sensors with the same sensing speed fR For contact sensors such as the LVDT and linear potentiometer the sensing speed is limited by the inertia of moving parts In contrast many non contact sensors utilise mechanical or electromagnetic waves and operate by adopting the time of flight approach therefore their maximum sensing speed is limited by the associated wave speed For example the maximum sensing speed of magnetostrictive sensors is limited by the speed of a strain pulse travelling in the waveguide alloy which is about 2 8 103 m s 1 The sensing frequency of displacement sensors is commonly dependent on the noise levels exhibited by the measuring electronic circuits Additionally some physical and mechanical limits can also impose constraints For example the dynamic response of a strain gauge is limited by the wave speed in the substrate For sensors with moving mass for example linear encoder LVDT and linear potentiometer the effects of inertial loading must be considered in cyclic operation For optical linear encoders the sensing frequency increases with range on the left hand side of the performance chart according to the following argument The resolution becomes finer i e decreases in an approximately linear manner with a reduced scan speed V of the recording head Since the sensor frequency f is proportional to the scan speed V we deduce that f increases linearly with and therefore f is linear in the minimum range of the device 2 2 Linear velocity sensors Although velocity and acceleration are the first and second derivatives of displacement with respect to time velocity and acceleration measurements are not usually achieved by time differentiation of a displacement signal due to the presence of noise in the signal The converse does not hold some accelerometers especially navigation grade servo accelerometers have sufficiently high stability and low drift that it is possible to integrate their signals to obtain accurate velocity and displacement information The most common types of velocity sensor of contacting type are electromagnetic piezoelectric and cable extension based Electromagnetic velocity sensors use the principle of magnetic induction with a permanent magnet and a fixed geometry coil such that the induced output voltage is directly proportional to the magnet s velocity relative to the coil Piezo velocity transducers PVTs are piezoelectric accelerometers with an internal integration circuit which produces a velocity signal Cable extension based transducers use a multi turn potentiometer or an incremental absolute encoder and a tachometer to measure the rotary position and rotating speed of a drum that has a cable wound onto it Since the drum radius is known the velocity and displacement of the cable head can be determined 5 Optical and microwave velocity sensors are non contacting and utilise the optical grating or Doppler frequency shift principle to calculate the velocity of the moving target Typical specifications for each class of linear velocity sensor are listed in Table 3 Table 3 Specification of linear velocity sensors Sensor class Maximum sensing range m s Resolution number of positions Maximum operating frequency Hz Magnetic induction25 360 5 104 5 105100 1500 PVT 0 25 1 31 105 5 105 7000 Sensor class Maximum sensing range m s Resolution number of positions Maximum operating frequency Hz Cable extension 0 7 151 105 1 1061 100 Optical and microwave 13 165 1 105 10 000 目录目录 1 简介简介 2 2 传感器性能图表传感器性能图表 2 2 1 位移传感器 位移传感器 3 2 1 1 分辨率 感应范围图 图 1 4 2 1 2 检测频率 检测范围图 图 2 5 2 2 线性速度传感器 线性速度传感器 6 问题 3 4 2001 年第 46 卷 页 461 504 传感器的选择 J Shieh J E Huber N A Fleck M F Ashby 剑桥大学工程系 英国剑桥 CB2 的 1PZ Trumpington 街 摘要摘要 对于一个特定的应用系统来说要选择最为合适的传感器 大量种类的传感 器存在 并且许多传感器是基于耦合的电气和机械现象 如压电 磁致伸缩和 焦电效应 传感器的性能图表是从商用设备供应商提供的数据而来 选择适当 的传感器是基于传感器的经营特色 以匹配应用程序要求 最终的选择是根据 外加的其他因素 如成本 阻抗匹配 这些案例研究说明了选拔程序 关键词关键词 传感器 选择 感应范围 检测分辨率 检测频率 1 简介简介 牛津英语大辞典 定义传感器 一个能够检测测量环境或一些变量 且 能够记录 显示 或以其他方式收到信息的设备 因此 传感器具有将刺激 转换成可测量信号的功能 这些刺激可以是力学 热学 电磁学 声学 或起 源于化学 等 的刺激 而测得的信号通一般是电信号 虽然气动 液压和光 信号也可以采用 基于广泛而最基本物理原理的传感器是工程设备中必不可少 的组成部分 考虑到市场上种类繁多的传感器 对于工程设计人员为一个新的应用程序 选择合适的传感器是一项艰巨的任务 这篇文章的目的就是提供一套简单的挑 选步骤 本研究是对胡贝尔等对执行机构选择问题的延伸和补充 传感器比执 行机构具有更为广泛的应用 根本原因 驱动器需要有效的比配功率 而传感 器是实现现性电子产品所要求的的高稳定性和增益性并能将其转换成强有效的 电信号地刺激 传感器种类的研究将在附录中详细的阐述 2 传感器性能图表传感器性能图表 在本节中 传感器性能数据以性能为横轴的二维图中进行展示 这些数据 是基于当前市场上一般可用的传感系统的 而不是具有工艺理论研究的理论知 识 如成本 实用性 如阻抗匹配 和可靠性等问题也需要从备选传感器性能 列表中进行对比 然后在做最后的选择 在阐释图表之前 我们需要介绍一些有关传感器特性的定义 在表 1 1 中 给出的性能多是厂商会给出的 然而 传感器的可靠性和鲁棒性很少以确定 的方式给出 表 1 主要传感器的特性总结 范围刺激的最大值减最小值 分辨率可测量的最小的刺激变化值 检测频率可被检测的刺激的最高频率 精度测量误差 以满课度百分比的形式给出 尺寸一般传感器的主要规格 外界环境温度和环境条件 可靠性服务时长活着运行周期 漂移长期稳定性 一段时期内的测量偏差 成本采购成本 2000 年以美元计 全尺寸表 在下面 我们将用二维的传感器特性图呈现选项 范围 分辨率和频率的限制 此外 我们应该限制我们的注意力集中于能够测量距离 加速度 力 温度的 的传感器 每个性能图展示是的实际存在的应用于各产业中的传感器 通过在图表中 添加为特定应用所需的敏感器特性 可以识分辨出传感器的子集 要想选择出 最合适的传感器是利用几个图表 并要考虑下面的表格信息如价格 该方法的 实用性表现在 2 1 位移传感器 首先考虑位移传感器的性能图表 分辨率 与范围 R 的关系 检测频率 f 与范 围 R 的关系 如图 1 和图 2 分别所示 图 1 位移传感器的分辨率与传感范围的对应系 图 2 位移传感器的检测频率与传感范围的对应关系 2 1 1 分辨率 感应范围图 图 1 对于这种传感器的分辨率对感应范围 R 的性能结构是用封闭的的加重的线标记 的 见图一 当可感应的分辨率等于感应范围即 R 是 令人吃惊的位 移传感器的范围跨越 13 个数量级 大量的竞争技术 在范围和分辨率 在这 些数轴 斜坡 1 传感器具有独特的可衡量的职位相同数量的链接类线 接近传 感器 以单一的立场是一致的是适合作为简单的接近 开 关 开关 或需要几 个分立位置 接近传感器是由一个单一的厚图带标记 1 最大开关频率接近 开关感应范围和更详细的信息汇总表 2 对位于图右下角的传感器 1 允许连 续位移测量 信息含量高 位移传感器 接近开关以外 能够提供连续的输出 响应是成正比的感应范围内目标的位置 图 1 可以看出 大多数传感器有 103 106 位置的分辨能力 这对应约 10 20 位数字输出的传感器 表 2 接近开关的规格 接近开关类型最大开关距离 m 最大开关频率 Hz 感应区6 10 4 1 10 15 5000 容量1 10 3 6 10 21 200 磁性3 10 3 8 5 10 2400 5000 气缸传感器 磁 活塞 直径超声波 8 10 3 3 2 10 1300 5000 超声波1 2 10 1 5 21 50 光电3 10 3 30020 20 000 全尺寸表 从图 1 可以很明显的看到位移传感器的感应范围集中在 10 5 101 米的区域 这 个范围左侧 AFM 和 STM 位移传感器是靠原子力来运行的 并且 Z 轴感应范 围在微米级左右 对于测量 10 米或以上的传感任务 传感器基于非接触式的 线性编码的超声波的光电技术 光学线性编码器采用干涉测量技术可以比传统 的编码