自动化专业检测翻译

1、河南理工大学河南理工大学 检测与转换技术作业姓 名： 学 号： 专业班级： 所在学院：电气工程与自动化学院 摘要 在科学技术高速发展的现代社会中，人类已经入瞬息万变的信息时代，人们在日常生活，生产过程中，主要依靠检测技术对信息经获取、筛选和传输，来实现制动控制，自动调节，目前我国已将检测技术列入优先发展的科学技术之一。 由于微电子技术，光电半导体技术，光导纤维技术以及光栅技术的发展，使得光电传感器的应用与日俱增。这种传感器具有结构简单、非接触、高可靠性、高精度、可测参数多、反应快以及结构简单,形式灵活多样等优点，在自动检测技术中得到了广泛应用，它一种是以光电效应为理论基础，由光电材料构成的器件

2、。关键字：光电传感器 光电效应光电元件传感器分类传感器应用 1 1、理论基础光电效应光电效应一般有外光电效应、光导效应、光生伏特效应。光照在照在光电材料上，材料表面的电子吸收的能量，若电子吸收的能量足够大是，电子会克服束缚脱离材料表面而进入外界空间，从而改变光电子材料的导电性，这种现象成为外光电效应根据爱因斯坦的光电子效应，光子是运动着的粒子流，每种光子的能量为hv(v为光波频率，h为普朗克常数，h6.63*10-34 J/HZ)，由此可见不同频率的光子具有不同的能量，光波频率越高，光子能量越大。假设光子的全部能量交给光子，电子能量将会增加，增加的能量一部分用于克服正离子的束缚，另一部分转换成

3、电子能量。根据能量守恒定律：式中，m为电子质量,v为电子逸出的初速度,A微电子所做的功。由上式可知，要使光电子逸出阴极表面的必要条件是h>A。由于不同材料具有不同的逸出功，因此对每一种阴极材料，入射光都有一个确定的频率限，当入射光的频率低于此频率限时，不论光强多大，都不会产生光电子发射，此频率限称为“红限”。相应的波长为 式中，c为光速，A为逸出功。 当受到光照射时，吸收电子能量，其电阻率降低的导电现象称为光导效应。它属于内光电效应。当光照在半导体上是，若电子的能量大与半导体禁带的能级宽度，则电子从价带跃迁到导带，形成电子，同时，价带留下相应的空穴。电子、空穴仍留在半导体内，并参与导电在

4、外电场作用下形成的电流。除金属外，多数绝缘体和半导体都有光电效应，半导体尤为显著，根据光导效应制造的光电元件有固有入射光频率，当光照在光电阻上，其导电性增强，电阻值下降。光强度愈强，其阻值愈小，若停止光照，其阻值恢复到原阻值。半导体受光照射产生电动势的现象称为光生伏特效应，据此效应制造的光电器件有光电池，光电二极管，管控晶闸管和光耦合器等。 2、光电元件及特性 根据外光电元件制造的光电元件有光电子，充气光电管和光电倍增管。2.1光电管 光电管的种类繁多，典型的产品有真空光电管和充气光电管，光它的外形和结构如图1所示，半圆筒形金属片制成的阴极K和位于阴极轴心的金属丝制成的阳极A封装在抽成真空的玻

5、壳内，当入射光照射在阴极上时，单个光子就把它的全部能量传递给阴极材料中的一个自由电子，从而使自由电子的能量增加h。当电子获得的能量大于阴极材料的逸出功A时，它就可以克服金属表面束缚而逸出，形成电子发射。这种电子称为光电子，光电子逸出金属表面后的初始动能为光电管正常工作时，阳极电位高于阴极，如图2所示。在人射光频率大于“红限”的前提下，从阴极表面逸出的光电子被具有正电位的阳极所吸引，在光电管内形成空间电子流，称为光电流。此时若光强增大，轰击阴极的光子数增多，单位时间内发射的光电子数也就增多，光电流变大。在图2所示的电路中，电流和电阻只上的电压降就和光强成函数关系，从而实现光电转换。当光线照射到光

6、电阴极K上时，电子从阴极表面逸出，并被光电阳极的正电厂吸收，外电路产生电流I，在负载电阻 上的电压光电管的光电特性如图3 所示，从图中可知，在光通量不太大时，光电特性基本是一条直线。图3光电管的光电特性图2光电管测量电路图1光电光结构示意图 2.2光电倍增管 由于真空光电管的灵敏度低，因此人们研制了具有放大光电流能力的光电倍增管。图4光电倍增结构示意图 从图中可以看到光电倍增管也有一个阴极K和一个阳极A，与光电管不同的是在它的阴极和阳极间设置了若干个二次发射电极，D1、D2、D3它们称为第一倍增电极、第二倍增电极、，倍增电极通常为1015级。光电倍增管工作时，相邻电极之间保持一定电位差，其中阴

7、极电位最低，各倍增电极电位逐级升高，阳极电位最高。当入射光照射阴极K时，从阴极逸出的光电子被第一倍增电极D1加速，以高速轰击D1 ，引起二次电子发射，一个入射的光电子可以产生多个二次电子， D1发射出的二次电子又被D1、D2问的电场加速，射向D2并再次产生二次电子发射，这样逐级产生的二次电子发射，使电子数量迅速增加，这些电子最后到达阳极，形成较大的阳极电流。若倍增电极有n级，各级的倍增率为 ，则光电倍增管的倍增率可以认为是N ，因此，光电倍增管有极高的灵敏度。在输出电流小于1mA的情况下，它的光电特性在很宽的范围内具有良好的线性关系。光电倍增管的这个特点，使它多用于微光测量。 2.3光敏电阻

8、光敏电阻的工作原理是基于内光电效应。在半导体光敏材料的两端装上电极引线，将其封在带有透明窗的管壳里就构成了光敏电阻。光敏电阻的特性和参数如下：2.3.1）暗电阻 光敏电阻置于室温、全暗条件下的稳定电阻值称为暗电阻，此时流过电阻的电流称为暗电流。2.3.2)亮电阻 光敏电阻置于室温和一定光照条件下测得稳定电阻值称为亮电阻，此时流过电阻的电流称为亮电流。2. .4伏安特性 光敏电阻两端所加的电压和流过光敏电阻的电流间的关系称为伏安特性，如图5所示。从图中可知，伏安特性近似直线，但使用时应限制光敏电阻两端的电压，以免超过虚线所示的功耗区。图5光敏电阻的伏安特性2.5光电特性 光敏电阻两极间电压固定不

9、变时，光照度与亮电流间的关系称为光电特性。光敏电阻的光电特性呈非线性，这是光敏电阻的主要缺点之一。2.6光谱特性 入射光波长不同时，光敏电阻的灵敏度也不同。入射光波长与光敏器件相对灵敏度间的关系称为光谱特性。使用时可根据被测光的波长范围，选择不同材料的光敏电阻。2.7响应时间 光敏电阻受光照后，光电流需要经过一段时间（上升时间）才能达到其稳定值。同样，在停止光照后，光电流也需要经过一段时间（下降时间）才能恢复到其暗电流值，这就是光敏电阻的时延特性。光敏电阻上升响应时间和下降响应时间约为10-110-3s，即频率响应为10Hz1000Hz，可见光敏电阻不能用在要求快速响应的场合，这是光敏电阻的一

10、个主要缺点。2.8温度特性 光敏电阻受温度影响甚大，温度上升，暗电流增大，灵敏度下降，这也是光敏电阻的另一缺点。2.9频率特性 频率特性是指外加电压和入射光强一定是光电流I与入射光的调制频率f之间的关系，光电二极管的频率特性较光电三极管的频率特性好，这是由于光电三极管的基射结存在电容和载流子基区需要时间的缘故。利用内光电效率原理制造的光电元件的频率特性最差，这是由于俘获载流子和释放电荷都需要一定时间的缘故。 3、光电传感器光电传感器是通过把光强度的变化转换成电信号的变化来实现控制的，它的基本结构如图6，它首先把被测量的变化转换成光信号的变化,然后借助光电元件进一步将光信号转换成电信号.光电传感

11、器一般由光源,光学通路和光电元件三部分组成.光电检测方法具有精度高,反应快,非接触等优点,而且可测参数多,传感器的结构简单,形式灵活多样,因此,光电式传感器在检测和控制中应用非常广. 光电传感器一般由三部分构成，它们分为：发送器、接收器和检测电路，如图7所示，发送器对准目标发射光束，发射的光束一般来源于半导体光源，发光二极管(LED)、激光二极管及红外发射二极管。光束不间断地发射，或者改变脉冲宽度。接收器有光电二极管、光电三极管、光电池组成。在接收器的前面，装有光学元件如透镜和光圈等。在其后面是检测电路，它能滤出有效信号和应用该信号。此外，光电开关的结构元件中还有发射板和光导纤维，三角反射板是

12、结构牢固的发射装置。它由很小的三角锥体反射材料组成，能够使光束准确地从反射板中返回，具有实用意义。它可以在与光轴0到25的范围改变发射角，使光束几乎是从一根发射线，经过反射后，还是从这根反射线返回。 图7 光电传感器是一种依靠被测物与光电元件和光源之间的关系，来达到测量目的的，因此光电传感器的光源扮演着很重要的角色，光电传感器的电源要是一个恒光源，电源稳定性的设计至关重要，电源的稳定性直接影响到测量的准确性，常用光源有以下几种： 1、发光二极管 是一种把电能转变成光能的半导体器件。它具有体积小、功耗低、寿命长、响应快、机械强度高等优点，并能和集成电路相匹配。因此，广泛地用于计算机、仪器仪表和自

13、动控制设备中。 2、丝灯泡 这是一种最常用的光源，它具有丰富的红外线。如果选用的光电元件对红外光敏感，构成传感器时可加滤色片将钨丝灯泡的可见光滤除，而仅用它的红外线做光源，这样，可有效防止其他光线的干扰。 3、激光 激光与普通光线相比具有能量高度集中，方向性好，频率单纯、相干性好等优点，是很理想的光源。由光源、光学通路和光电器件组成的光电传感器在用于光电检测时，还必须配备适当的测量电路。测量电路能够把光电效应造成的光电元件电性能的变化转换成所需要的电压或电流。不同的光电元件，所要求的测量电路也不相同。下面介绍几种半导体光电元件常用的测量电路。 半导体光敏电阻可以通过较大的电流，所以在一般情况下

14、，无需配备放大器。在要求较大的输出功率时，可用图8所示的电路。图9（a）给出带有温度补偿的光敏二极管桥式测量电路。当入射光强度缓慢变化时，光敏二极管的反向电阻也是缓慢变化的，温度的变化将造成电桥输出电压的漂移，必须进行补偿。图中一个光敏二极管做为检测元件，另一个装在暗盒里，置于相邻桥臂中，温度的变化对两只光敏二极管的影响相同，因此，可消除桥路输出随温度的漂移。 光敏三极管在低照度入射光下工作时，或者希望得到较大的输出功率时，也可以配以放大电路，如图9所示。由于光敏电池即使在强光照射下，最大输出电压也仅0.6V，还不能使下一级晶体管有较大的电流输出，故必须加正向偏压，如图9（a）所示。为了减小晶

15、体管基极电路阻抗变化，尽量降低光电池在无光照时承受的反向偏压，可在光电池两端并联一个电阻。或者象图9（b）所示的那样利用锗二极管产生的正向压降和光电池受到光照时产生的电压叠加，使硅管e、b极间电压大于0.7V，而导通工作。这种情况下也可以使用硅光电池组，如图10（c）所示。 半导体光电元件的光电转换电路也可以使用集成运算放大器。硅光敏二极管通过集成运放可得到较大输出幅度，如图11（a）所示。当光照产生的光电流为时，输出电压为了保证光敏二极管处于反向偏置，在它的正极要加一个负电压。图11（b）给出硅光电池的光电转换电路，由于光电池的短路电流和光照成线性关系，因此将它接在运放的正、反相输入端之间，

16、利用这两端电位差接近于零的 特点，可以得到较好的效果。在图中所示条件下，输出电压 由光通量对光电元件的作用原理不同所制成的光学测控系统是多种多样的,按光电元件(光学测控系统)输出量性质可分二类,即模拟式光电传感器和脉冲(开关)式光电传感器.模拟式光电传感器是将被测量转换成连续变化的光电流,它与被测量间呈单值关系.模拟式光电传感器按被测量(检测目标物体)方法可分为透射(吸收)式,漫反射式,遮光式(光束阻档)三大类.所谓透射式是指被测物体放在光路中,恒光源发出的光能量穿过被测物,部份被吸收后,透射光投射到光电元件上，如测液体、气体透明度和混浊度的光电比色计等;所谓漫反射式是指恒光源发出的光投射到被

17、测物上,再从被测物体表面反射后投射到光电元件上，如光电比色温度计和光照度计等;所谓遮光式是指当光源发出的光通量经被测物光遮其中一部份,使投射刭光电元件上的光通量改变,改变的程度与被测物体在光路位置有关，如振动测量、工件尺寸测量；而在脉冲式光电传感器中在这种传感器中，光电元件接受的光信号是断续变化的，因此光电元件处于开关工作状态，它输出的光电流通常是只有两种稳定状态的脉冲形式的信号，多用于光电计数和光电式转速测量等场合。 AbstractIn modern society, the rapid development of science and technology, mankind has

18、been into the rapidly changing information age, people in their daily lives, the production process, mainly rely on information technology by obtaining detection, screening and transport, to achieve brake control, automatic adjustment, the current detection technology has been listed as one of China

19、's science and technology priorities. As the development of microelectronics technology, optical semiconductor technology, optical fiber technology and grating technology, making increasing use of photoelectric sensors. This sensor has a simple structure, non-contact, high reliability, high prec

20、ision, multi-parameter can be measured, quick reactions and a simple structure, flexible and diverse forms, etc., has been widely used in the automatic detection technology, which is based on a photoelectric effect as the theoretical basis of the device by the optical material.Keywords: photoelectri

21、c sensor photoelectric Optoelectronics Optoelectronics Sensor Category Sensor Applications 1. Theory basis - Photoelectric effect Photoelectric effect are generally outside the photoelectric effect, photoconductive effect, photovoltaic effect. Light shone on the optical material, an electron energy

22、absorbing surface material, if the energy of the electron absorption is sufficiently large, the electrons overcome the bound material from the outside surface into the space, thereby changing the conductivity of the optoelectronic material, this phenomenon becomes outside photoelectric effect Accord

23、ing to Einstein's optoelectronic effect, the photon is moving stream of particles, the energy of each photon is hv (v is the frequency of light, h is Planck's constant, h = 6.63 * 10-34 J / HZ), thus different visible photon energy with different frequencies, the higher the frequency of ligh

24、t, the photon energy is larger. Assuming all the energy of the photon to photon, electron energy will increase, increasing the portion of the energy of positive ions bound to overcome, another part converted into electrical energy. According to the law of conservation of energy: m is the electron ma

25、ss, v is the initial velocity of the electron emitting, A microelectronic work done. From the above equation, the necessary condition to make the photoelectrons escaping the cathode surface is h> A. Since different materials have different work functions, so each of the cathode material, the inci

26、dent light has a certain limit frequency, the frequency of the incident light when the frequency falls below this limit, either how the light intensity are no photoemission this frequency limit is called the "red limit." Is the wavelength corresponding to the formula, c is the speed of lig

27、ht, A is the work function. When irradiated with light, electron energy absorption, reduces the resistivity conductive phenomenon known waveguide effect. It belongs to the photoelectric effect. When the light in the semiconductor is large and if the electron energy level width of the band gap semico

28、nductors, the electron from the valence band to the conduction band, formed in electronics, while leaving the corresponding holes in the valence band. Electrons and holes remain in the semiconductor and participate in current conductive external electric field formation. Than metal, insulator, and m

29、ost have a photovoltaic effect of semiconductor, a semiconductor is particularly significant effect of manufacturing the photovoltaic element of the light guide has the inherent frequency of the light when the light on the light resistance and enhanced conductivity, the resistance value decreases. T

30、he stronger the light intensity, the smaller the resistance, if stop light, its resistance to return to the original resistance.Semiconductor phenomenon produced by light irradiation force called the photovoltaic effect, whereby the effect of light battery manufacturing optoelectronic devices, photo

31、diodes, optocouplers, such as thyristors and control. 2. The photovoltaic elementAccording outside Optoelectronics Optoelectronics has optoelectronic manufacturing, inflatable photocell and the PMT.2.1 Photocell Many types of optical tube, the typical products and pneumatic vacuum photocell photocel

32、l, its shape and structure of the light, the semi-cylindrical sheet metal cathode and a cathode K made of metal wire as shown in the axis of a the anode a is encapsulated in an evacuated glass bulb inside, when the incident light is irradiated on the cathode, it took a single photon energy to all of

33、 the cathode material in a free electron, thereby increasing the free energy of the electron h. When the electrons acquire energy greater than the work function of the cathode material A, it can be overcome and metal surfaces bound escape form the electron emission.This e-called photoelectron.The in

34、itial kinetic energy photoelectron escape after the metal surface. When photocell normal operation, the anode potential is higher than the cathode shown in Figure 2. Under the premise of the frequency of the incident light is greater than the "red limit", the photoelectrons escaping from t

35、he cathode surface having been attracted by the positive potential of the anode, the flow of electrons formed in the inner space of the photoelectric tube, called the photocurrent. At this point, if the light intensity increases, the increase in the number of photons bombarding the cathode, the numb

36、er of photoelectrons emitted per unit time will increase, optoelectronic rheological great. In the circuit shown in Figure 2, the current and the voltage drop on the resistor, and only a function of the light intensity, in order to achieve the photoelectric conversion. When the light is irradiated t

37、o the photoelectric cathode K, the escape of electrons from the cathode surface, the positive plant was absorbed photoanode.External circuit generates a current I. The voltage on the Resistance is U.Photocell optical characteristics shown in Figure 3, seen from the figure, in the light flux is not t

38、oo large, the optical characteristics of a substantially straight line. Figure1 Figure2 Figure32.2 PMT Due to the sensitivity of the photocell low vacuum, so people have developed amplified light photomultiplier current capability。Picture4 PMTFrom the figure we can see there is a photomultiplier tub

39、e , and a cathode K of the anode A, and the photocell is different between the cathode and the anode which is provided a plurality of secondary emission electrodes , D1, D2, D3 . are referred to as a dynode , the second dynode , . , usually 10 to the dynode 15 . Photomultiplier tubes work , the adja

40、cent holding a potential difference between the electrodes , wherein the cathode potential minimum , the potentials progressively increasing the dynodes , the maximum anode potential . When the incident light cathodes K, photoelectrons escaping from the cathode of the first dynode D1 is accelerated

41、to high velocity bombardment D1, causing secondary electron emission , a plurality of the incident photoelectrons may generate secondary electrons , D1 emits two secondary electrons are accelerated and D1, D2 Q field , D2 and fired again, the secondary electron emission .produce secondary electron e

42、mission resulting stepwise such that the rapid increase in the number of electrons , the electrons reach the anode final form larger anode current . If the n -stage dynode , the multiplication rate levels , the multiplication rate of the photomultiplier tube can be considered N, therefore , the phot

43、omultiplier tube has a high sensitivity. In the case of the output current of less than 1mA , and its optical characteristics of a good linear relationship over a wide range. This feature of the photomultiplier tube , it used for measuring shimmer .2.3Photoresistor Working principle is based on the

44、photoresistor photoelectric effect. At both ends of the semiconductor light-sensitive material is mounted on the electrode leads, which was sealed in a tube with a transparent window in the shell constitutes the photosensitive resistance. Photosensitive resistance characteristics and parameters are

45、as follows: 2.3.1） Dark resistance Photosensitive resistance at room temperature, the resistance value stability under conditions of complete darkness called dark resistance, then the current flowing through the resistor is called dark current. 2.3.2) Light resistance Photosensitive resistance at ro

46、om temperature and under certain lighting conditions measured resistance value is called the current stable light resistance, then flows through the resistor is called a light current.2. .4Voltage characteristics Photosensitive the applied voltage across the resistor and the current flowing through

47、the relationship between the photoresistor called voltage characteristics shown in Figure 5. Seen from the figure, the approximate line voltage characteristics, but should be used to limit the voltage across the resistor photosensitive avoid over consumption dashed line area. Figure5 PhotoresistorVo

48、ltage characteristics2.5 Optical Characteristics Time photoresistor bipolar voltage is fixed, the relationship between light intensity and light current is called the photoelectric characteristics. Optical properties of photosensitive resistance is nonlinear, which is one of the main disadvantages o

49、f the photoresistor.2.6 Spectral characteristics Wavelength of incident light is not the same, the different sensitivity of the photosensitive resistor. The wavelength of the incident light relative to the photosensitive member and the relationship between the known spectral sensitivity characterist

50、ics. When used according to the wavelength range to be measured, and select a different material photoresistor.2.7 Response time After photoresistor by illumination, the photocurrent need to go through a period of time (rise time) to reach its stable value. Similarly, after the cessation of illumina

51、tion, the photocurrent also need to go through a period of time (fall time) to recover to its dark current value, which is the delay characteristics photoresistor. Photoresistor rise and fall response time of the response time is about 10-1 10-3s, i.e., a frequency response of 10Hz 1000Hz, can not b

52、e used in visible light sensitive resistor occasion requires a quick response, which is a major disadvantage of the photoresistor.2.8 Temperature characteristics Affected by temperature sensitive resistor is very large, the temperature rose, the dark current increases, the sensitivity decreases, whi

53、ch is another drawback of the photoresistor.2.9 Frequency Characteristics The frequency characteristic of the frequency characteristic of the photodiode phototransistor than good, since the base-emitter junction of the phototransistor the existence of capacitance and carrier base takes time's sa

54、ke. Frequency characteristics of the photovoltaic element manufactured using the principles in the worst photoelectric efficiency, which is due to the release of trapped charge carriers and requires a certain time's sake. 3、Photoelectric sensors Photoelectric sensor is the change of light intens

55、ity by converting the electrical signal into a change in control to achieve its basic structure shown in Figure 6, it is first converted into a change of the measured change in the optical signal, and further by means of an optical signal Optoelectronics converted into an electrical signal. photoele

56、ctric sensor generally consists of three parts light source, optical path and optoelectronic components. photoelectric detection method has the advantages of high precision, fast response, non-contact, etc., and can be measured many parameters, a simple structure of the sensor, in the form of flexible, Therefore, photoelectric sensors to detect and control applications in a very wide range. Photoelectric sensors are generally composed of three parts, they are divided into: a transmitter as shown, the receiver and detection circuitry shown in Figure 7, the transmitter emits a light beam