And sensor is the important composition component in automata, it is the important part that information collects a system, the signal that suit to carry through be being measured what sensor will be experienced or answer to be changed or detects (it is telegraphic date commonly) , recycle computer or the function that the signal that circuit equipment outputs to sensor has handling achieving automata thereby, answer as a result of the noise of sensor time is compared commonly short, can pass all of computer science department to undertake to industrial production real time is controlled so.

 

 

Infra-red sensor is a kind when sensor middling sees, because infra-red sensor is to detect infra-red radiant a kind of sensor, and any objects in nature want his to stabilize prep above only absolute zero will external radiation is infra-red energy, so infra-red sensor calls a kind of very practical sensor, use infra-red sensor to be able to design a lot of practical sensor module, be like infra-red measure Wen Yi, infra-red into resemble appearance, infra-red human body explores warning apparatus, automatic door controls a system to wait.

 

 

Any objects between the universe want its temperature to exceed zero to be able to produce infra-red radiation only, like be the same as visible light in fact, its radiant energy undertakes refract and be reflexinged quite, produced infra-red technology so, use infra-red smooth detector to get because of its particular advantage attention extensively, received wide application in military affairs and civil domain. On the military affairs, infra-red explore use at control and guide, fire to accuse to dog, cautionary, target is investigated, weapon heat is aimed at implement, ship vessel navigation; In civil domain, wide application and industrial equipment monitoring, safe surveillance, provide disaster relief, diagnostic technology of remote sensing, traffic administration and medicine.

 

Infra-red sensor is defined

 

 

Infrared sensor is the sensor that the physical property that uses infrared ray will come to undertake metrical. Infrared ray weighs infra-red light again, it has reflection, reflection, scattering, interference, absorb wait for property. It is a kind of sightless light, its spectrum is located in in visible light beyond red, weigh infrared ray so.

 

The position that holds infrared ray in electromagnetic wave chart on the project (wave band) cent is: Close infra-red, medium infra-red, far extremely infra-red, far infra-red 4 wave band. Any material, the temperature with want itself to have constant only (prep above is absolutely zero) , can radiation infrared ray.

 

The measurement of infra-red sensor fundamental principle

 

Understand infra-red light above all. Infra-red light is the one part of sun’s rays chart, the biggest characteristic of infra-red light has smooth fuel factor namely, radiation quantity of heat, it is spectral in the biggest smooth fuel factor area. Infra-red light a kind of sightless light, like all electromagnetic wave, have reflection, reflection, scattering, interference, absorb wait for property. Infra-red light transmits speed to be 300000Km/s in true aerial. Infra-red light can produce attenuation in the transmission in medium, attenuation travels in the metal very big, the radiant energy outside Dan Gong is mixed through major semiconductor a few plastic, major liquid is absorbed to infra-red radiate very big.

 

 

Different gas draws rate to its each are not identical, aerosphere exists to be absorbed differently to the infra-red light of different wavelengh belt. Study the analysis makes clear, the infra-red light that is area of 1——5μm, 8——14μm to wavelengh has bigger “ diaphaneity ” . Namely the infra-red light energy of these wavelengh is better the ground is penetrable aerosphere. Any objects in nature, want its temperature to be over absolute zero only, can produce infra-red ray radiation. The smooth fuel factor of infra-red light is each are not identical to different object, heat energy intensity is different also. For example, boldface (can absorb entirely project the infra-red radiant object of its surface) , lens body (can reflex infra-red radiant object entirely) , transparent body (object of can all penetrable and infra-red radiant) with grey body (can be reflexed partly or absorb infra-red radiant object) the smooth fuel factor that differs generation.

 

Will strictly tell, nature is not put in body of boldface, lens and transparent body, and majority object attributes grey put oneself in another’s position. Afore-mentioned these character use technology of infra-red ray radiation namely Yu Weixing is remote sensing telemetering, infra-red dog the important and academic basis that waits for military affairs and scientific research project.

 

Essence of infra-red radiant physics is heat radiation. The temperature of the object is higher, the infrared ray that radiation comes out is more, infra-red radiant energy is stronger. Consider to discover, sun’s rays chart the fuel factor of all sorts of odd shade arrives from purple light red light increases gradually, and the biggest fuel factor appears inside limits of infra-red radiant frequency, because this people calls infra-red radiate heat radiation or hot ray again.

 

Infra-red radiant is basic and mensurable

 

Kirchhoff law: Below constant temperature, of the radiation flux W on area of surface features unit and absorptivity than, to any objects it is a constant, be equal to W of flux of radiate of boldface of area of this temperature similarly hereinafter. Be in given below temperature, the absorptivity of emissive rate = of the object (same wave band) ; Absorptivity is bigger, emissive rate is older also.

 

Of the heat radiation intensity of surface features and temperature just become direct ratio 4 times, so, the temperature difference with little surface features can cause the apparent change of infra-red radiate energy. This kind of feature formed the academic basis of infra-red remote sensing.

 

Bo ear thises graceful law: Namely flux of boldface global radiation follows the addition of temperature and mushroom, of it and temperature just become direct ratio 4 times. Accordingly, the little change of temperature, can cause the change with radiation flux very big density. It is infra-red device determines the theoretical foundation of temperature.

 

Dimension favour displacement is mensurable: As temperature elevatory, the peak wavelength of radiation maximum correspondence moves to shortwave direction.

 

The working principle of infra-red sensor is not complex, a typical sensor system is departmental the substance of cent is respectively:

 

1, wait for measure a target: According to waiting for the infra-red radiate that measures a target character can have the set of infra-red system.

 

2, atmosphere attenuation: When waiting for the infra-red radiate that measures a target to pass earthly aerosphere, because aeriform element is mixed,all sorts of gas and the scattering of all sorts of dissolve micelle are mixed absorb, will make what infra-red source gives out infra-red radiation happening attenuation.

 

3, optical receiver: It receives the radiate outside the ministry share out bonus of the target to transmit infra-red sensor. Be equivalent to radar antennae, commonly used it is field lens.

 

4, radiation modulator: Wait for the radiation modulation that measures a target to clinch a deal to coming from the radiation that change is optical, provide target azimuth information, and but the interference signal that filter accumulates except bedding face. Weigh modulation again dish with behead wave implement, it has a variety of structures.

 

5, infra-red detector: This is the core of infra-red system. It is to use infra-red radiate and corporeal interaction place to present the physical effect that come out to explore infra-red radiant sensor, it is to use place of this kind of interaction to present the electricity effect that come out below most circumstance. This kind of detector can be divided for photon detector and hot sensitive detector two big kinds.

 

6, detector refrigeration implement: Because certain detector must want to work below microtherm, so corresponding system must have refrigeration facility. Through refrigeration, equipment can shorten answer time, heighten exploration sensitivity.

 

7, signal processing system: Have exploration signal wave of enlarge, filter, give information from the extraction in these signal. Change this kind of message the pattern that becomes a need next, carry control equipment finally or in monitor.

 

8, indication equipment: This is the terminal unit of infra-red equipment. Commonly used monitor has oscillograph, picture tube, infra-red sensitive data, indicating instrument and recorder to wait.

 

The flow above according to, infra-red system can finish the measurement of corresponding physical quantity. The core of infra-red system is infra-red detector, according to exploration mechanism different, can divide the detector that it is heat and photon detector two kinds big.

 

The radiant energy to all sorts of incident wavelengh measures hot detector to be absorbed entirely, it is a kind of infra-red sensor that does not have a choice to infra-red light-wave. The photon effect with photon commonly used detector has outside photoemission, inside photoemission (photo-generated volt effect, photoconductive effect) with photoelectricity magnetism effect. Hot detector is to use radiation fuel factor, temperature is caused to lift after making exploration component receives radiant energy, the function that makes temperature is relied on in detector then produces change. Detect among them the change of some function, can explore a radiate. It is to pass pyroelectricity change to explore radiant below most circumstance. Receive radiation when component, when the physics that causes blame n changes, can change through corresponding n is being measured after proper commutation.

 

Heat quick detector answers time to compare photoelectricity detector to infra-red radiant answer time to want to grow more. Answer time formerly to be in commonly Ms above, and latter has Ns to measure level only. Hot detector does not need to cool, photon detector majority wants to cool.

 

The classification of infrared sensor

 

Common and infra-red sensor can divide the sensor that it is heat and photon sensor.

 

Heat up sensor

 

Hot sensor is the temperature variation that uses incident and infra-red radiate to cause sensor, make concerned physics parameter produces corresponding change then, the infra-red radiate that will decide infra-red sensor absorbs through measuring the change of concerned physics parameter.

 

The main good point of hot detector is corresponding wave band wide, can work below room temperature, use simple. But, hot sensor is corresponding time is longer, sensitivity is inferior, use at the circumstance of low frequency modulation commonly.

 

Main type has hot sensor: Heat quick sensor, thermocouple, tall Lai pneumatic release report with heat model 4 kinds.

 

1, thermal resistor sensor

 

Solution is burned after mixing by manganese, nickel, cobaltic oxide and thermal resistor is become, thermal resistor makes chip record commonly, go up in thermal resistor when infra-red radiate illuminate, its temperature is elevatory, resistance decreases. Measure thermal resistor to be worth metabolic size, can be informed incident infra-red radiant to lose by force, can judge the temperature that produces infra-red radiate object thereby.

 

2, thermocouple sensor

 

Thermocouple is by pyroelectricity power difference two kinds of older stuff are formed. Close when what infra-red radiate forms to stuff of these two kinds of metals on the contact of loop when, this contact temperature is elevatory. And another is in by the contact of infra-red radiate irradiation inferior temperature, right now, in close loop lieutenant general produces electricity of difference in temperature. Electrometric temperature difference arises in loop at the same time, the size of electrometric temperature difference, mirrorred contact to absorb infra-red radiant to lose by force. The infra-red sensor that uses phenomenon of electrometric temperature difference to be made calls thermocouple infra-red sensor, because the constant between meantime is bigger, corresponding time is longer, dynamic character is wronger, modulation frequency should be restricted it is under 10HZ.

 

3, Lai pneumatic sensor

 

Tall Lai pneumatic sensor is after using gas to absorb infra-red radiation, temperature is elevatory, what bulk increases is characteristic, the radiant outside be flushed instead loses by force. It has an air chamber, with Xiaoguan flexible and as chip as be linked together. Chip back to conduit one side it is illuminator. Before air chamber with absorb a model, it is the film of small thermal capacity. Infra-red radiate passes the window incident to absorb a model to go up, absorb a model to express absorption heat energy gas, make aeriform temperature elevatory, atmospheric pressure increases, make soft lens mobile thereby. In the across of the room, a bundle of visible light is through focusing of bar shape smooth column on soft lens, the bar state image that comes back via soft lens reflex passes bar shape smooth column to project again on photoelectric cell. When soft lens changes because of pressure and moving, bar state image and bar shape smooth column produce opposite displacement, make the smooth volume that falls to photoelectric cell produces a change, the output signal of photoelectric cell also produces change, this change quantity shoots infra-red radiant to lose by force with respect to reflective discrepancy. The characteristic of this kind of sensor is sensitivity tall, performance is steady. But answer timeliness to grow, the structure is complex, intensity is poorer, agree with only use inside the lab.

 

4, hot commentate report sensor

 

Hot commentate report sensor is a kind of heat that has polarization appearance crystal or call “ ferroelectric ” . The polarization intensity of ferroelectric (the charge on unit area) concern with temperature. Arrive when infrared radiate illuminate already the ferroelectric of polarization is chip apparently when, cause chip temperature to lift, make its polarization intensity is reduced, exterior charge decreases, this is equivalent to releasing one share charge, be called heat so commentate report sensor. If will laden resistor and ferroelectric chip are linked together, a telegraphic date arises to output on laden resistor. Output the size of signal, depend on the speed that chip temperature changes, mirror incident infra-red radiant to lose by force thereby. This shows, hot commentate the rate that the voltage of report infra-red sensor answers ratio direct ratio to change at incident radiate. Be in when constant infra-red radiate illuminate hot commentate on electric sensor when, sensor believes an output without report. In only ferroelectric temperature is in metabolic process, just telegraphic date is outputted. So, must undertake modulation to infra-red radiate (or light weighing cut) , make constant radiate becomes hand in change radiation, the constant temperature that causes sensor changes, ability brings about heat commentate report arises, output deliver the signal that change.

 

Photon sensor

 

Photon sensor is to use certain semiconductor material to be below the illuminate of incident light, produce photon effect, make material electricity property produces change. Through measuring the change of electricity property, can know infra-red radiant loses by force. Use the infra-red sensor that photon effect place makes. Sensor of photon of a general designation. The main characteristic sensitivity of photon sensor is tall, answer speed fast, have taller response frequency. But its must be commonly below microtherm the job, exploration wave band is narrower.

 

According to the working principle of photon sensor, can divide commonly for inside photoelectricity and outside photoelectricity sensor two kinds, latter is divided again for photoconductive sensor, photo-generated volt sensor and feeling of smooth magnetism telex implement wait for 3 kinds.

 

1, outside photoelectricity sensor

 

Be in when ray radiation of certain material apparently when, if the photon energy of incident light is enough big when, can make the electronic transgression surface of material, this kind of phenomenon cries outside photoemission or photoelectron launch effect. Photoelectricity diode, photoelectricity the times electronic sensor that adds a canal to wait to attribute this kind of kind. Its response rate is rapidder, need a few nanosecond only commonly. But the photon energy with electronic transgression bigger need, the radiate outside only appropriate Yu Jingong may see be used inside smooth limits.

 

2, photoconductive sensor

 

Be in when infra-red radiate illuminate certain semiconductor material apparently when, some electrons and cavity are OK in semiconductor material from before not electric manacle condition to turn into can electric free condition, make the conductivity of semiconductor increases, this kind of phenomenon makes photoconductive appearance. The sensor that phenomenon of benefit consumed conductance makes calls light to guide sensor, if vulcanization lead, Selenium changes lead, antimony,change indium, tellurium to lie between the material such as mercury to be able to make photoconductive sensor. When using photoconductive sensor, need refrigeration and the bias with be added definite, can make answer otherwise rate reduce, noise is big, answer wave band narrow, in order to cause infrared sensor damage.

 

3, photo-generated volt sensor

 

Go up in the PN knot of certain semiconductor material when infra-red radiate illuminate when, inside the knot the action of electric field falls, area of N of free electron tend, if PN writtens guarantee open circuit, written guarantee in PN two end produce an add electromotive force, call photo-generated electromotive force. Use the sensor that this effect makes or PN knot sensor. Commonly used material changes indium, antimony to change indium, tellurium to change lead of stannum of mercuric, tellurium to wait for a few kinds for arsenic.

 

4, sensor of smooth magnetism report

 

Be in when infra-red radiate illuminate certain semiconductor material apparently when, there are some of electron and cavity to diffuse inward ministry in semiconductor material, the effect that suffers strong magnetic field is like in diffuse, electron and cavity criterion each deflection one party, produce open circuit tension consequently, this kind of phenomenon calls effect of smooth magnetism report. Use the infra-red sensor that this effect makes, call smooth magnetism report sensor.

 

Sensor of smooth magnetism report does not need frigorific, answer wave band to be able to amount to 7μM left and right sides, time constant is small, answer speed fast, need not add bias voltage, internal resistance is extremely low, noise is little, have good stability and reliability. But its sensitivity is low, low noise preamplifier makes difficulty, affected consequently use.

 

Infra-red sensor structure and measure a principle

 

Infra-red radiate measures lukewarm appearance structure

 

It waits for a part to comprise by optical system, modulator, infra-red sensor, amplifier and indicator;

 

Optical system can be transmission type, also can be reflection type. The part of system of transmission type optics is made with infra-red and optical material.

 

Infra-red measure lukewarm appearance block diagram:

 

High temperature (700 ℃ above) measure an instrument, useful wave band basically is in the close red outskirt of 0.76-3μm, can choose general and optical glass or quartz to wait for material.

 

In lukewarm (100-700 ℃ ) measure an instrument, useful wave band basically is in of 3-5μm in infra-red area, use fluorine to change more magnesian, magnesian wait for material of hot pressing optics.

 

Measure microtherm (100 ℃ are the following) instrument, useful wave band basically is in of 5-14μm in the wave band outside Yuan Gong, use the data such as zinc of vulcanization of germanium, silicon, hot pressing more.

 

Modulator clinchs a deal infra-red radiate modulation namely change radiant device. It is to use electrical micro-machine to drive turntable of a tine or equidistance aperture commonly dish, through tine turntable or belt Kong Panxuan turns, cut is incident radiation and make project the radiation signal to infra-red sensor clinchs a deal change. It is easy that because the system runs to handing in,signal processing is compared, can obtain taller letter a confusion of voices to compare.

 

Structure of tall Lai pneumatic sensor

 

It has an air chamber, with Xiaoguan flexible and as chip as be linked together. Chip back to conduit one side it is illuminator. Before air chamber with recruit film, it is the film of small thermal capacity.

 

In the across of the room, a bundle of visible light is through focusing of bar shape diaphragm on soft lens, the bar state image that comes back via soft lens reflex projects through bar shape diaphragm again on photoelectric cell.

 

 

Tall Lai pneumatic sensor is after using gas to absorb infra-red radiation, temperature is elevatory, what bulk increases is characteristic, the radiant outside be flushed instead loses by force.

 

Infra-red radiate passes the window incident to absorb film to go up, absorb film to express absorption heat energy gas, make aeriform temperature lifts atmospheric pressure increases, make soft lens mobile thereby.

 

In the across of the room, a bundle of visible light is through focusing of bar shape diaphragm on soft lens, the bar state image that comes back via soft lens reflex projects through bar shape diaphragm again on photoelectric cell.

 

When soft lens changes because of pressure and moving, bar state image and bar shape smooth column produce opposite displacement, make the smooth volume that falls to photoelectric cell produces a change, the output signal of photoelectric cell also produces a change. This change quantity shoots infra-red radiant to lose by force with respect to reflective discrepancy. The depend on dot of this kind of sensor is sensitivity tall, performance is steady. But answer time to grow, structure complex, intensity is poorer, agree with only use inside the lab.

 

The performance data of infra-red sensor

 

1, voltage is answered

 

 

When (pass modulation) when infra-red radiate illuminate arrives on the sensitive face of sensor, the output voltage of sensor is compared with what input infra-red radiate power, the voltage that is called sensor is answered rate, write down RV.

 

In type:

 

US: The output voltage of infra-red sensor

 

P0: Projectile the power to area of unit of infra-red sensing element

 

A: The area of infra-red sensor sensing element

 

2, answer wavelengh limits:

 

 

Curve 1: The voltage of pyroelectricity sensor answers rate music (have nothing to do with wavelengh) .

 

Curve 2: The voltage of photon sensor answers rate curve.

 

(1) answer wavelengh limits (or say spectrum is answered) it is to state the voltage of sensor answers the concern between rate and incident infra-red radiate wavelengh, express with the curve commonly (see figure above) .

 

(2) will answer the wavelengh that leads maximum place correspondence to call peak wavelength commonly.

 

(3) answer rate drop the wavelengh of the half place correspondence of response is called end wavelengh, it is representing the wavelengh range that infra-red sensor uses.

 

3, noise equivalent power

 

The output tension that if project,the radiation power place to infra-red sensor sensing element produces, as it happens is equal to the noise voltage of sensor itself, criterion this radiate power calls “ noise equivalent power ” . Express with symbolic “NEP” normally.

 

 

Among them: Us is the output voltage of infra-red detector; P0 arrives to project the power on area of unit of infra-red sensing element; A0 is infra-red and sensitive yuan of area; UN is the integrated noise voltage of infra-red detector; RV is answered for the voltage of infra-red detector rate.

 

4, exploration rate

 

Exploration rate is the reciprocal of noise equivalent power, namely:

 

 

The exploration rate of infra-red sensor is higher, the power of the smallest radiate that shows sensor can be explored is less, sensor is more acute.

 

5, compare exploration rate

 

Compare exploration rate to make normalization exploration rate again, perhaps make explore sensitivity. Become namely essentially the sensing element area of sensor is unit area, when the bandwidth △ F of amplifier is 1Hz, of the signal voltage that the radiation place of unit power obtains and noise voltage than. Express with symbolic D* normally.

 

The physical dimension of D* : CmHz1/2W-1 (300 K)

 

6, time is invariable

 

Time constant states the output signal of infra-red sensor follows the rate that infra-red radiate changes.

 

Export time of the radiant outside signal lag Yu Gong, the time that calls sensor is invariable, it is on numerical value:

 

1 ／ of τ ＝ 2πfc

 

The Fc in type in answer to rate drop of maximum 0.707 (3dB) the modulation frequency when.

 

The heat of hot sensor is inertial with RC parameter bigger, the constant between meantime is more than photon sensor, be millisecond class commonly or longer; And the time constant of photon sensor is small second class commonly.

 

The application of infra-red sensor reachs foreground

 

The application of infra-red sensor basically reflects in the following respects:

 

1, infra-red radiometer: Use at radiation and spectral radiate to measure.

 

2, search and dog system: Use at search and dogging infra-red target, determine its space position and undertake dogging to its motion.

 

3, heat becomes like the system: The infra-red radiate that can form whole goal distributings image.

 

4, system of infra-red range finding: Realize what be apart from between the object to measure. (those who use is infrared ray when transmission do not diffuse principle, because infrared ray is passing through the refractive index when other material is very small, so the range finder of Sunday run can consider infrared ray)

 

5, communication system: Infrared communication serves as a kind of means of wireless communication.

 

6, mixture system: It is to show above is of all kinds two work in the system many combination.

 

 

Infra-red sensor application can use the temperature of Yu Fei contact to measure, aeriform composition is analysed, nondestructive flaw detection, heat resembles detecting, the scout of infra-red remote sensing and martial end, search, dog to wait with communication. The applied foreground of infra-red sensor the development as modern science and technology, will more capacious. In the development in the future, basically mix in the function of infra-red sensor sensitivity will 2 bigger rise.

 

Development trend basically has:

 

1, intelligence changes: Current infra-red sensor basically combines peripheral equipment to use, and the buy inside intelligent sensor microprocessor, can realize sensor and the two-way communication that control unit, have miniaturization, number communication, safeguard wait for an advantage simply, can work independently as a module alone.

 

2, miniature changes: Sensor miniature turns an inevitable tide. In applying now, as a result of the volume problem of infra-red sensor, bring about its to use rate far what come as pyroelectricity border is good. So infra-red sensor miniature is changed portable the effect that developed a future to its is cannot of oversight.

 

3, tall sensitivity and high-powered: On medicine, human body temperature checks an aspect, infra-red sensor received the application that comparative because of metrical fast sex, but bureau be confined to its accuracy is not tall and do not have method to replace existing temperature measurement technique. Accordingly, infra-red sensor tall sensitivity and tall sex are the inevitable trend that its did not develop.

 

 

Although show the infra-red sensor of level to still have very much inadequacy, the sensor outside Dan Gong been producinging the tremendous effect that there is it in practice modernly, of the technology as sensor and other part rise, infra-red sensor can have more function and better sensitivity, also will have wider applied range.