Photoelectric sensor
Key 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:reactive metal
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:
2
1／2mv  =hv-A
Type,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 of cathode 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 sa
me 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 are vacuum 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 energy
Phototubes 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 cath
ode 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.

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