Photoelectric sensorKey word:photoeletric effect photoelectric element photoeletric sensor classification sensor application characteristics. Abstract:in the development of science and technology in the modern society,mankind has into rapidly changing information era,people in daily life,the production process,rely mainly on the detection of information technology by acquiring,screening and transmission,to achieve the brake control,automation adjustment,at present our country has put detection techniques listed in one of the priority to the development of science and technology.Because ofmicroelectronics technology,photoelectric semiconductor technology,optical fiber technology and grating technical development makes the application of the photoelectric sensor is growing .The sensor has simple structure, non-contact,high reliability,high precision,measurable parameters and quick response and more simple structure,form etc,and flexible in automatic detection technology,it has been widely applied in photoelectric effect as the theoretical basis,the device by photoelectric material composition.Text:First,theoretical foundation-photoelectric effect Photoelectric effect generally have the photoelectric effect ,optical effect,light born volts effect.The light shines in photoelectric material,according to the electronic absorption material surface energy,if absorbed energy large enough electronic will overcome bound from material and enter the outside space,which changes photoelectron materials ,this king of phenomenon become the conductivity of the photoelectric effect.According to Einstein’s photoelectron effect,photon is moving particles,each photon energy for hv(v for light frequency,h for Planck’s constant,h=6.63*10-34J/HZ),thus different frequency of photons have different energy,light,the higher the frequency,the photon energy is bigger.Assuming all the energy photons to photons,electronic energy will increase,increased energy part of the fetter,positive ions used to overcome another part of converted into electronic energy.According to the law of conservation of energy:1／2mv =hv-A2Type,m for electronic quality,v for electronic escaping the velocity,A microelectronics the work done.From the type that will make the optoelectronic cathode surface escape the necessary conditions are h>A.Due to the different materials have different escaping,so reactive to each kind ofcathode material,incident light has a certain frequency is restricted,when the frequency of incident light under this frequency limit,no matter how the light intensity,won’t produce photoelectron lauch,this frequency limit called“red limit”.The corresponding wavelength for type,c for the speed of light,A reactive for escaping.When is the sun,its electronic energy,absorb the resistivity reduce conductive phenomenon called optical effects.It belongs to the photoelectric effect within.When light is,if in semiconducter electronic energy big with semiconductor of forbidden band width,the electronic energy from the valence band jump into the conduction band,form,and at the same time,the valence band electronic left the corresponding cavities. Electronics,cavitation remained in semiconducter,and participate in electric conductive outside formed under the current role.In addition to metal outer,most insulators and semiconducter have photoelectric effect,particularly remarkable,semiconductor optical effect according to the optoelectronics manufacturing incident light inherent frequency,when light resistance in light,its conductivity increases,resistance drops.The light intensity is strong,its value,if the smaller,its resistance to stop light back to the original value.Semiconductor producted by light illuminate the phenomenon is called light emf,born volts effect on the effect of photoelectric devices have made si-based ones,photoelectric diode,control thyristor and optical couplers,etc.Second,optoelectronic components and characteristics According to the outside optoelectronics manufacturing optoelectronic devices have photoelectron,inflatable phototubes and photoelectric times once tube.1.Phototubes phototubes are various and typical products arevacuum phototubes and inflatable phototubes,light its appearance and structure as shown in figure 1 shows,made of cylindrical metal half cathodic K and is located in the wires cathodic axis of anode in A package of smoke into the vacuum,when incident light within glass shell in the cathode,illuminate A single photon took all of its energy transfer to the cathode materials A free electrons,so as to make the freedom electronic energy increase h.When electrons gain energy more than escape of cathode materials,it reactive A metal surface constraints can overcome escape,form electron emission.This kind of electronic called optoelectronics,optoelectronic escaping the metal surface for after initial kinetic energyPhototubes normal work,anode potential than the cathode, show in figure 2.In one shot more than “red light frequency is premise,escape from the optoelectronic cathode surface by positive potential attracted the anode in photoelectric tube forming space,called the current stream.Then if light intensity increases,the number of photons bombarded the cathode multiplied,unit of time to launch photoelectron number are also increasing,photo-current greatens.In figure 2 shows circuit,current so as to achieve a photoelectric conversion.When the LTT optoelectronic cathode K, electronic escape from the cathode surface,and was the photoelectric anode is an electric current,power plants absorb deoxidization device in the load resistance-I,the voltage. Phototubes photoelectric characteristics fig.03 shows,from the graph in flux knowable,not too big,photoelectric basis characteristics is a straight line.2.Photoelectric times had the sensitivity of vacuum tube duo tolow,so with people developed has magnified the photomultiplier tubes photo-current ability.Figure 4 isphotomultiplier tube structure schematic drawing.From the graph can see photomultiplier tubes also have A cathode K and an anode A,and phototubes different is in its between anode and cathode set up several secondary emission electrodes,D1,D2 and D3…Usually,double electrode for 10~15 levels.Photomultiplier tubes work between adjacent electrode,keeping a certain minimum,including the cathode potential potentials,each multiply electrode potential filtering increases, the anode potential supreme.When the incident light irradiation, cathodic K escape from the optoelectronic cathode multiplied by first accelerated,by high speed electrode D1 bombarded caused secondary electron emission,D1,an incident can generate multiple secondary electron photonics,D1 emit of secondary electron was D1,D2 asked electric field acceleration,converged on D2 and again produce secondary electron emission…So gradually produce secondary electron emission,make electronic increased rapidly,these electronic finally arrived at the anode, form a large anode current.If an level,multiply electrodes at alllevels for sigma,the multiplication of rate is the multiplication of photomultiplier tubes can be considered sigma n rate,therefore,photomultiplier tube has high sensitivity.In the output current is less than 1mA circumstances,it in a very wide photoelectric properties within the scope of the linear relationship with good.Photomultiplier tubes this characteristic, Make it more for light measurement.3.and photoconductive resistance photoconductive resistance within the working principle is based on the photoelectric effect. In semiconducter photosensitive material ends of mount electrode lead,it contains transparent window sealed in the tube and shell element photoconductive resistance.Photoconductive resistance properties and parameters are:1)dark resistance photoconductive resistance at roomtemperature,total dark conditions stable resistance called dark resistance,at the current flow resistance is called dark current.2)Light resistance photoconductive resistance at roomtemperature and certain lighting conditions stable resistance measured,right now is called light resistance of current flow resistance is called light current.4.V olt-ampere characteristics of both ends photoconductive resistance added voltage and current flows throughphotoconductive resistance of the relationship between called volt-ampere characteristics shown,as shown in figure 5.From the graph,the approximate linear volt-ampere characteristics that use should be limited,but when the voltage ends photoconductive resistance,lest than shown dotted lines of power consumption area.光敏电阻的伏安特性5.photoelectric characteristics photoconductive resistance between the poles,light when voltage fixed the relationship between with bright current photoelectric characteristics.Called photoconductive resistance photoelectric characteristics is nonlinear,this is one of the major drawback of photoconductive resistance.6.Spectral characteristics is not the same incident wavelength the sensitivity of photoconductive resistance is different also.Incidence wavelength and photodetector the relationship between relative sensitivity called spectral characteristics.When used according to the wavlength range by metering,choosedifferent material photoconductive resistance.7.Response time by photoconductive resistance after photo-current need light,over a period of time (time) rise to reach its steady value.Similarly,in stop light photo-current also need,over a period of time (down time) to restore the its dark current,this is photoconductive resistance delay characteristic . Photoconductive resistance rise response time and falling response time about 10-1~10-3s,namely the frequency response is 10Hz~1000Hz,visible photoconductive resistance cannot be used in demand quick response occasion,this is one of the main photoconductive resistance shortcoming.8、and temperature characteristic photoconductive resistance by temperature affects greatly,temperature rise,dark current increase,reduced sensitivity,which is another photoconductive resistance shortcoming.9、frequency characteristic frequency characteristics refers to an external voltage and incident light,strong must be photo-current I and incident light,modulation frequency,the relationship between the f,photoelectric diode is the freqency characteristic of the ptotoelectric triode frequency characteristics,this is because of the photoelectric triode shot “yankees there capacitance and carrier base-combed need time’s sake.By usingthe principle of the photoelectric effciency of optoelectronics manufacturing frequency characteristic of the worst,this is due to capture charge carriers and release charge need a certain time’s sake.Three,photoelectric sensorsPhotoelectric sensor is through the light intensity changes into electrical signal changes to achieve control,its basic structure,it first figure 6 by measuring the change of converting the light signal,and then using photoelectric element further will light signals into electrical signal by photoelectric sensor general. Illuminant,optical path and optoelectronics.Three components of photoelectric detection method has high precision,fast response,non-contact wait for an advantage,but measurable parameters of simple structure,sensors,form flexible,threefore, photoelectric sensor in the test and control is widely used.By photoelectric sensor generally is composed of three parts, they are divided into:transmitter and receiver and detection circuit shown,as shown in figure 7,transmitter aimed at the target launch beam,the launch of the beam from semiconductor illuminant,general light emitting diode(LED),laser diode and infrared emission diode.Beam uninterrupted lauch,or change the pulse width. Receivers have photoelectric diode,photoelectrictriode,composed si-based ones.In front of the receiver, equipped with optical components such as lens and aperture,etc.In its back is detection circuit,it can filter out effective signal and the application of the signal.In addition,the structural components in photoelectric switch and launch plate and optical fiber,triangle reflex plate is solid structure launch device.It consists of small triangle cone of reflective materials,can make a beam accurately reflected back from plate,with practical significance.It can be in with the scope of optical axis 0 to 25,make beams change launch Angle from a root almost after launch line,passes reflection or from the rotating polygon.some basic returns.Photoelectric sensor is a kind of depend on is analyte andoptoelectronics and light source,to achieve the relationship between the measured purpose,so the light source photoelectric sensor plays a very important role,photoelectric sensor power if a constant source,power is very important for design,the stability of power directly affect the accuracy of measurement,comonly used illuminant have the following kinds:1,leds is a change electric energy into light energy semiconductor devices.It has small volume,low power consumption,long life,fast response,the advantages of high mechanical strength,and can match and integrated circuits. Therefore,widely used in computer,instruments and automatic control equipment.2,Silk light bulb that is one of the most commomly used illuminant,it has rich infrare light.If chosen optoelectronics, constitutes of infrared sensor sensitive colour filter can be added to the visible tungsten lamps,but only filter with its infrared does illuminant,such,which can effectively prevent other light interference.3,compared with ordinary light laser with energy concentration, directional good,frequency pure,coherence as well as good,is very ideal light sources.The light source,optical path and photoelectric device composition photoelectric sensor used inphotoelectric detection,still must be equipped with appropriate measurement circuit.The photoelectric effect to the measurement circuit of photoelectric element of widerange caused changes needed to convert the voltage or current. Different photoelectric element,the measurement circuit required is not identical also.Several semiconductor introduces below optoelectronic devices commonly used measurement circuit.Figure 9(a)with temperature compensation given the photosensitive diode bridge type measuring circuit.When the incident light intensity slow change,the reverse resistance photosensitive diode is the slow change,the change of the temperature will cause the bridge output voltage,must compensate.Drift picture a photosensitive diode as the test components,another into windows,in neighboring bridge,the change of the temperature in the arms of the influence of two photosensitive diode,therefore,can eliminate the same output with tempereture bridge road drift.Light activated triode incident light in work under low illumination,or hope to get bigger output power,also can match with amplifying circuit,as shown in figure 9 shows.Because even in the glare photosensitive batteries,maximum output voltage also only 0.6V,still cannot make the next level 1 transistor have larger current output,so must add positive bias,as shown in figure 9(a)below.In order to reduce the transistor circuit impedance variations,base si-based ones to reduce as much as possible without light,when the reverse bias inherit in parallel a resistor si-based ones at both ends.Or like figure 9(b)as shown by the positive ge diode produces pressure drop and test the voltage produced when exposed to light,make silicon tube e stack,b the voltage between actuators than 0.7V,and conduction work.This kind of circumstance also can use silicon light batteries,as shown in figure 10(c)below.Semiconductor photoelectric element of photoelectric circuit can also use integrated operational amplifier.Silicon photosensitive diode can be obtained by integrating op-amp large output amplitude,as shown in figure 11(a)below.When light is produced,the optical output voltage in order to guarantee photosensitive diode is reverse biased,in its positive to add a load voltage.Figure 11.(b) give the photocell transform circuit,because the photoelectric si-based ones short-circuit current and illumination of a linear relationship between,so will it up in the op-amp is,inverse-phase input,using these two potential difference between the characteristics of close to zero,can get better effect.In the picture shows conditions,the output voltage U0=2IφR FThe photoelectric element by flux the role of different made from the principle of optical measurement and control system is varied,press the photoelectric element (optical measurement andcontrol system)output nature,namely,can be divided into second analog photoelectric sensor and pulse (switch)photoelectric sensor.Analog photoelectric sensors will be converted into continuous variation of the measure,it is measuered optical with a single value relations between analog photoelectric sensor. According to be measured (objects)method detection of target can be divided into transmission (absorption)type,diffuse type, shading type(beam resistance gears)three categories.So-called transmission style means the object to be tested in optical path in constant light source,the light energy through things,part of being measured by absorption,transmitted light onto photoelectric element,such as measured liquid,gas transparency and photoelectric BiSeJi etc;speed.gratifying the so-called diffuse style means the constant light by the light onto the analyte from the object to be tested,and projected onto surfaces reflect on after optoelectronic devices,such as photoelectric colorrimetric thermometer and light gauge etc;The so-called shading style means the when illuminant issued by the flux of light analyte covered by a part Jing optoelectronics,make projection on the flux change,change the object to be tested and extent of the position with the light path,such as vibration measurement,the size measurement;And in pulse photoelectricsensor in the sensors,photoelectric element in switch work of the state,the current output it is usually only two steady state of the signal,the pulse form used for photoelectric counting and photoelectric speed measurement and so on.And infrared photoelectric sensor classification and working way generally have the following kinds:1,groove photoelectric sensor put a light emitter and a receiver in a slot face-to-face outfit are on opposite sides of the photoelectric groove.Lighter emits infrared light or visible light, and in unimpeded cases light receptors can receive light.But when tested objects from slot zhongtong obsolete , light occluded ,photoelectric switches and action.Output a switch control signal,cut off or connect load current,thus completing a control movement.Groove switch is the overall of detection distance because general structure limits only a few centimeters. 2,DuiShe type optoelectronic sensor if you put lighter and receive light is separated,can make the detection distance increase.By a lighter and an inbox light sensor into a photoelectric switch is called DuiShe separate photoelectric switches,referred to DuiShe photoelectric switch.Its detection distance can reach a few meters and even a dozen meters.When using light-emitting device and recive light device are installedin test object through the path of the sides,test object by blocking light path,accept light implement action output a switch control signals.3,Reflex plate.it photoelectric switch light-emitting device type and receive light device into the same device inside,in its front pack a reflex plate.the using the reflection principle of complete photoelectric control function is called reflex plate.it reflex (or reflector reflx)photoelectric switch.Under normal circumstances, lighter the light reflected by reflex plate.it is received by accept light;Once the light path be test object to block,accept light,the light is not received photoelectric switch is action,output a switch control signals.4,Diffusion reflective photoelectric switches its detection head with a lighter and also an inbox light ware,but no reflex plate.it ahead.Normally lighter for the light collect light is not found. When test object by blocking the light,and the light reflected light,receive part implement received light signals,output a switch signals.Four,I’m the idea of photoelectric sensorWith the development of science and technology people on measuring accuracy had the higher request,this has prompted the pace with the times photoelectric sensor have updated,improvethe main means photoelectric sensor performance is the application of new materials,new technology manufacturing performance is more superior photoelectric element.For example,today the prototype of the photoelectric sensor is a small metal cylindrical equipment,with a calibration lens,transmitter into receiver focused light,the receiver out of cable to the device got to a vacuum tube amplifiers in metal cylinder on the incandescent light bulb inside a small as the light source a strong incandescent lamp sensor.Due to the sensor various defects existing in the fields,gradually faded.To appear, because of it of fiber of excellent performance,then appeared with sensors supporting the use of optical passive components, another fiber without any interference of electromagnetic signal, and can make the sensor of the electronic components and other electrical disturbance in isolation.Have a piece of plastic optical fiber core or plass light core,light outside a metallic core skins and bread this layer metal cortical density lower than light core, so low,the beam refraction in the two materials according to the border(incident Angle within a certain range,reflected),is all. Based on optical principle,all beams can be made by optical fiber to transmission.Two incident beam Angle in an Angle (along the fiber length direction within)by multiple reflectionsfrom the other end after injection,another incident angles than accept the incident light in metal skin,loss.This accept Angle within the biggest incident Angle than two times,this is because fiber slightly larger from air into density larger fiber materials hitting may have a slight refraction.In light of the optical fiber transmission from inside the influence of fiber bending(whether more than bending radius minimal bending radius).Most optical fiber is flexible,easy to install in the narrow space. Photoelectric sensor is a kind of non-contact measurement small electronic measurement equipment,rely on detect its receives the light intensity change,to achieve measurement purposes,and it’s also a vulnerable to external disturbance and lose the measurement accuracy of the device.When be being designed so besides the choice optoelectronic components,still must set GSCC signal and temperature compensating measures used to weaken or eliminate the impact of these factors.。