压力传感器的毕业设计英语论文

The Basic knowledge of Sensor and Development of SensorThe Basic knowledge of SensorA transducer is a device which converts the quantity being measured into an optical, mechanical, or-more commonly-electrical signal. The energy-conversion process that takes place is referred to as transduction.Transducers are classified according to the transduction principle involved and the form of the measured. Thus a resistance transducer for measuring displacement is classified as a resistance displacement transducer. Other classification examples are pressure bellows, force diaphragm, pressure flapper-nozzle, and so on.1、Transducer ElementsAlthough there are exception ,most transducers consist of a sensing element and a conversion or control element. For example, diaphragms,bellows,strain tubes and rings, bourdon tubes, and cantilevers are sensing elements which respond to changes in pressure or force and convert these physical quantities into a displacement. This displacement may then be used to change an electrical parameter such as voltage, resistance, capacitance, or inductance. Such combination of mechanical and electrical elements form electromechanical transducing devices or transducers. Similar combination can be made for other energy input such as thermal. Photo, magnetic and chemical,giving thermoelectric, photoelectric,electromaanetic, and electrochemical transducers respectively.2、Transducer SensitivityThe relationship between the measured and the transducer output signal is usually obtained by calibration tests and is referred to as the transducer sensitivity K1= output-signal increment / measured increment . In practice, the transducer sensitivity is usually known, and, by measuring the output signal, the input quantity is determined from input= output-signal increment / K1.3、Characteristics of an Ideal TransducerThe high transducer should exhibit the following characteristicsa) high fidelity-the transducer output waveform shape be a faithful reproduction of the measured; there should be minimum distortion.b) There should be minimum interference with the quantity being measured; the presence of the transducer should not alter the measured in any way.c) Size. The transducer must be capable of being placed exactly where it is needed.d) There should be a linear relationship between the measured and the transducer signal.e) The transducer should have minimum sensitivity to external effects, pressure transducers,for example,are often subjected to external effects such vibration and temperature.f) The natural frequency of the transducer should be well separated from the frequency and harmonics of the measurand.4、Electrical TransducersElectrical transducers exhibit many of the ideal characteristics. In addition they offer high sensitivity as well as promoting the possible of remote indication or mesdurement.Electrical transducers can be divided into two distinct groups:a) variable-control-parameter types,which include:i) resistanceii) capacitanceiii) inductanceiv) mutual-inductance typesThese transducers all rely on external excitation voltage for their operation.b) self-generating types,which includei) electromagneticii) thermoelectriciii) photoemissiveiv) piezo-electric typesThese all themselves produce an output voltage in response to the measurand input and their effects are reversible. For example, a piezo-electric transducer normally produces an output voltage in response to the deformation of a crystalline material; however, if an alternating voltage is applied across the material, the transducer exhibits the reversible effect by deforming or vibrating at the frequency of the alternating voltage.5、Resistance TransducersResistance transducers may be divided into two groups, as follows:i) Those which experience a large resistance change, measured by using potential-divider methods. Potentiometers are in this group.ii) Those which experience a small resistance change, measured bybridge-circuit methods. Examples of this group include strain gauges and resistance thermometers.5.1 PotentiometersA linear wire-wound potentiometer consists of a number of turns resistance wire wound around a non-conducting former, together with a wiping contact which travels over the barwires. The construction principles are shown in figure which indicate that the wiper displacement can be rotary, translational, or a combination of both to give a helical-type motion. The excitation voltage may be either a.c. or d.c. and the output voltage is proportional to the input motion, provided the measuring device has a resistance which is much greater than the potentiometer resistance.Such potentiometers suffer from the linked problem of resolution and electrical noise. Resolution is defined as the smallest detectable change in input and is dependent on the cross-sectional area of the windings and the area of the sliding contact. The output voltage is thus a serials of steps as the contact moves from one wire to next. Electrical noise may be generated by variation in contact resistance, by mechanical wear due to contact friction, and by contact vibration transmitted from the sensing element. In addition, the motion being measured may experience significant mechanical loading by the inertia and friction of the moving parts of the potentiometer. The wear on the contacting surface limits the life of a potentiometer to a finite number of full strokes or rotations usually referred to in the m anufacture’s specification as the ‘number of cycles of life expectancy’, a typical value being 20*1000000 cycles.The output voltage V0 of the unload potentiometer circuit is determined as follows. Let resistance R1= xi/xt *Rt where xi = input displacement, xt= maximum possible displacement, Rt total resistance of the potentiometer. Then output voltage V0= V*R1/(R1+( Rt-R1))=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt. This shows that there is a straight-line relationship between output voltage and input displacement for the unloaded potentiometer.It would seen that high sensitivity could be achieved simply by increasing the excitation voltage V. however, the maximum value of V is determined by the maximum power dissipation P of the fine wires of the potentiometer winding and is given by V=(PRt)1/2 .5.2 Resistance Strain GaugesResistance strain gauges are transducers which exhibit a change in electrical resistance in response to mechanical strain. They may be of the bonded or unbondedvariety .a) bonded strain gaugesUsing an adhesive, these gauges are bonded, or cemented, directly on to the surface of the body or structure which is being examined.Examples of bonded gauges arei) fine wire gauges cemented to paper backingii) photo-etched grids of conducting foil on an epoxy-resin backingiii) a single semiconductor filament mounted on an epoxy-resin backing with copper or nickel leads.Resistance gauges can be made up as single elements to measuring strain in one direction only, or a combination of elements such as rosettes will permit simultaneous measurements in more than one direction.b) unbonded strain gaugesA typical unbonded-strain-gauge arrangement shows fine resistance wires stretched around supports in such a way that the deflection of the cantilever spring system changes the tension in the wires and thus alters the resistance of wire. Such an arrangement may be found in commercially available force, load, or pressure transducers.5.3 Resistance Temperature TransducersThe materials for these can be divided into two main groups:a) metals such as platinum, copper, tungsten, and nickel which exhibit and increase in resistance as the temperature rises; they have a positive temperature coefficient of resistance.b) semiconductors, such as thermistors which use oxides of manganese, cobalt, chromium, or nickel. These exhibit large non-linear resistance changes with temperature variation and normally have a negative temperature coefficient of resistance.a) metal resistance temperature transducersThese depend, for many practical purpose and within a narrow temperature range, upon the relationship R1=R0*[1+a*(b1-b2)] where a coefficient of resistancein ℃-1,and R0 resistance in ohms at the reference temperature b0=0℃ at the reference temperature range ℃.The international practical temperature scale is based on the platinum resistance thermometer, which covers the temperature range -259.35℃ to 630.5℃.b) thermistor resistance temperature transducersThermistors are temperature-sensitive resistors which exhibit large non-liner resistance changes with temperature variation. In general, they have a negative temperature coefficient.For small temperature increments the variation in resistance is reasonably linear; but, if large temperature changes are experienced, special linearizing techniques are used in the measuring circuits to produce a linear relationship of resistance against temperature.Thermistors are normally made in the form of semiconductor discs enclosed in glass vitreous enamel. Since they can be made as small as 1mm,quite rapid response times are possible.5.4 Photoconductive CellsThe photoconductive cell , uses a light-sensitive semiconductor material. The resistance between the metal electrodes decrease as the intensity of the light striking the semiconductor increases. Common semiconductor materials used forphoto-conductive cells are cadmium sulphide, lead sulphide, and copper-doped germanium.The useful range of frequencies is determined by material used. Cadmium sulphide is mainly suitable for visible light, whereas lead sulphide has its peak response in the infra-red region and is, therefore , most suitable for flame-failure detection and temperature measurement.5.5 Photoemissive CellsWhen light strikes the cathode of the photoemissive cell are given sufficient energy to arrive the cathode. The positive anode attracts these electrons, producing a current which flows through resistor R and resulting in an output voltage V. Photoelectrically generated voltage V=Ip.RlWhere Ip=photoelectric current(A),and photoelectric current Ip=Kt.BWhere Kt=sensitivity (A/im),and B=illumination input (lumen)Although the output voltage does give a good indication of the magnitude of illumination, the cells are more often used for counting or control purpose, where the light striking the cathode can be interrupted.6、Capacitive TransducersThe capacitance can thus made to vary by changing either the relative permittivity, the effective area, or the distance separating the plates. The characteristic curves indicatethat variations of area and relative permittivity give a linear relationship only over a small range of spacings. Thus the sensitivity is high for small values of d. Unlike the potentionmeter, the variable-distance capacitive transducer has an infinite resolution making it most suitable for measuring small increments of displacement or quantities which may be changed to produce a displacement.7、Inductive TransducersThe inductance can thus be made to vary by changing the reluctance of the inductive circuit.Measuring techniques used with capacitive and inductive transducers:a) A.C. excited bridges using differential capacitors inductors.b) A.C. potentiometer circuits for dynamic measurements.c) D.C. circuits to give a voltage proportional to velocity for a capacitor.d) Frequency-modulation methods, where the change of C or L varies the frequency of an oscillation circuit.Important features of capacitive and inductive transducers are as follows:i) resolution infiniteii) accuracy+- 0.1% of full scale is quotediii) displacement ranges 25*10-6 m to 10-3miv) rise time less than 50us possibleTypical measurands are displacement, pressure, vibration, sound, and liquid level.8、Linear Variable-differential Ttransformer9、Piezo-electric Transducers10、Electromagnetic Transducers11、Thermoelectric Transducers12、Photoelectric Cells13、Mechanical Transducers and Sensing ElementsThe Devolepment of SensorSensor is one kind component which can transform the physical quantity, chemistry q uantity and the biomass into electrical signal. The output signal has the different form s like the voltage, the electric current, the frequency, the pulse and so on, which can sa tisfy the signal transmission, processing, recording, and demonstration and control de mands. So it is the automatic detection system and in the automatic control industry .I f automatic Technology is used wider, then sensor is more important. In information a ge, the information industry includes information gathering, transmission, process thre e parts, namely sensor technology, communication, computer technology. Because of ultra large scale integrated circuit’s rapid development after having been developed Modern computer technology and c ommunication, not only requests sensor precision reliability, speed of response and ga in information content request more and more high but also requests its cost to be inex pensive. The obvious traditional sensor is eliminated gradually because of the functio n, the characteristic, the volume, the cost and so on. As world develop many countries are speeding up to the sensor new technology’s research and the development, and all has obtained the enormous breakthrough. No w the sensor new technology development mainly has following several aspects: Using the physical phenomenon, the chemical reaction, the biological effect as the sen sor principle therefore the researches which discovered the new phenomenon and the new effect are the sensor technological improving ways .it is important studies to deve loped new sensor’s the foundation. Japanese Sharp Corporation uses the superconductivity technology t o develop successfully the high temperature superconductivity magnetic sensor and ge t the sensor technology significant breakthrough. Its sensitivity is so high and only inf erior in the superconductivity quantum interference component. Its manufacture craft is far simpler than the superconductivity quantum interference component. May use in magnetism image formation technology. So it has the widespread promoted value. Using the immune body and the antigen meets one another compound when the electr ode surface. It can cause the electrode potential change and use this phenomenon to b e possible to generate the immunity sensor. The immunity sensor makes with this kind of immune body may to some organism in whether has this kind of ant original work inspection. Like may inspect somebody with the hepatitis virus immune body whether contracts the hepatitis, plays to is fast, the accurate role. The US UC sixth branch has developed this kind of sensor.The sensor material is the important foundation for sensor technology, because the ma terials science is progressive and the people may make eachkind of new sensor For example making the temperature sensor with the high polymerthin film; The optical fiber can make the pressure, the current capacity, the temperatu re, the displacement and so on the many kinds of sensors; Making the pressure transm itter with the ceramics. The high polymer can become the proportion adsorption and t he release hydrogen along with the environment relative humidity size. The high poly mer electricity lies between the constant to be small, the hydrogen can enhance the po lymer the coefficient of dialectical loss. Making the capacitor the high polymer dielect ric medium, determines the electric capacity cape city the change, then obtains the rel ative humidity. Making the plasma using this principle to gather the legitimate polysty rene film temperature sensor below, it has the characteristic.Measured the wet scope is wide; The temperature range is wide, may reach -400 ℃ ~ +1,500 ℃; The speed of response is quick, is smaller than 1S; The size is small, may use in the small space measuring wet; The temperature coefficient is small.The ceramic electric capacity type pressure transmitter is one kind does not have the i ntermediary fluid the dry type pressure transmitter. Uses the advanced ceramic techno logy, the heavy film electronic technology, its technical performance is stable, the year drifting quantity is smaller than 0.1%F.S, warm floats is smaller than ±0.15%/10K, anti- overloads strongly, may reach the measuring range several hundred times. The survey scope may from 0 to 60mpa.German E+H Corporation and the Ame rican Kahlo Corporation product is at the leading position.The optical fiber application is send the material significant breakthrough, its uses in most early the optical communication techniques. In the optical communication use di scovered works as environmental condition change and so on the temperature, pres-su re, electric field, magnetic field, causes the fiber optic transmission light wave intensit y, the phase, the frequency, change and so on the polarization condition, the survey lig ht wave quantity change, may know causes these light wave physical quantity the and so on quantitative change temperature, pressure ,electric field, magnetic field size, use s these principles to be possible to develop the optical fiber sensor. The optical fiber s ensor and the traditional sensor compare has many characteristics: Sensitivity high, th e structure simple, the volume small, anti-corrosive, the electric insulation good, the p ath of rays may be curving, be advantageous for the realization telemeter and so on. O ptical fiber sensor Japan is in the advanced level. Like Idec Izumi Corporation and Su n x Corporation. The optical fiber send receiver and the integrated path of rays technol ogy unify, accelerates the optical fiber sensor technology development. Will integrate the path of ray’s component to replace the original optics part and the passive light component; enabl e the optical fiber sensor to have the high band width, the low signal processing voltag e, the reliability high, the cost will be low.In semiconductor technology processing method oxygenation, the photo etc hang, the proliferation, the deposition, the plane electron craft, variousguides corrosion and stea ms plates, the sputtering thin film and so on, these have all introduced to the sensor m anufacture. Thus has produced each kind of new sensor, like makes the silicon micro s ensor using the semiconductor technology, makes the fast response using the thin film craft the gas to be sensitive, the wet sensitive sensor, the use sputtering thin film craft system pressure transmitter and so on..The Japanese horizontal river company uses various guides’ corrosion technology to carry on the high accuracy three dimensional processing; the system helps the silicon resonance type pressure transmitter. The core partially presses two resonant Liang by t he feeling which above the silicon diaphragm and the silicon diaphragm manufactures to form, two resonant Liang's frequency difference correspondence different pressure, measures the pressure with the frequency difference method, may eliminate the error which factor and so on ambient temperature brings. When ambient temperature chang e, two resonant Liang frequencies and the amplitude variation are same, after two freq uency differences, its same change quantity can counterbalance mutually. It’s survey most high accuracy may reach 0.01%FS.American Silicon Microstructure Inc.(SMI) the company develops a series of low end s, linear in 0.1% to 0.In 65% scope silicon micro pressure transmitter, the lowest full measuring range is 0.15psi (1KPa), it makes take the silicon as the material, has the u nique three dimensional structure, the light slight machine-finishing, makes the wheat stone bridge many times with the etching on the silicon diaphragm, when above silico n chip stress, it has the distortion, the resistance produces presses the anti- effect but t o lose the bridge balance, the output and the pressure becomes the proportion the elect rical signal.Such silicon micro sensor is the front technology which now the sensor develops, Its e ssential feature is the sensitive unit volume is a micron magnitude, Is the traditional se nsor several dozens, several 1%. In aspect and so on industry control, aerospace doma in, biomedicine has the vital role, like on the airplane the use may reduce the airplane weight, reduces the energy. Another characteristic is can be sensitive is small surveye d, may make the blood pressure pressure transmitter.The Chinese aviation main corporation Beijing observation and control technical rese arch institute, the development CYJ series splashes thanks the membrane pressure tra nsmitter is uses the ion sputtering craft to process the metal strain gauge, it has over c ome the nonmetallic strain gauge easily the temperature influence insufficiency, has th e high stability, is suitable in each kind of situation, is measured the medium scope wi dely, but also overcame the tradition lowly to glue the precision which the type broug ht, sluggish big, shortcoming and so on slow change, had the precision high, the re-lia bility is high, the volume small characteristic, widely used in domain and so on aviati on, petroleum, chemical industry, medical service.Integrates the sensor the superiority is the traditional sensor is unable toachieve, it is a simple sensor not merely, it in at the same time the auxiliary circuit par t and send the part will integrate on together the chip, will cause it to have the calibrati on, to compensate, from the diagnosis and the network correspondence function, it mi ght reduce the cost, the gain in yield, this kind of blood pressure sensor which Americ an LUCAS, NOV ASENSOR Corporation will develop, each week will be able to prod uce 10,000.The intellectualized sensor is one kind of belt microprocessor sensor, is achievement which the microcomputer and the sensor unifies, it has at the same time the examinati on, the judgment and the information processing function, compares with the tradition al sensor has very many characteristics:Has the judgment and the information processing function, can carry on the revision, t he error to the observed value compensates, thus enhancement measuring accuracy; M ay realize the multi-sensor multi parameters survey; Has from the diagnosis and from the calibration function, enhances the reliability; The survey data may deposit and wit hdraw, easy to operate; Has the data communication interface, can and the microcomp uter direct communication.The sensor, the signal adjustment electric circuit, the monolithic integrated circuit inte gration forms ultra large-scale integrated on a chip the senior intelligence sensor. Ame rican HONY WELL Corporation ST-3000 intelligence sensor, the chip size only then has 3×4×2mm3, uses the semiconductor craft, makes CPU, EPROM, the static pressure, the dif ferential pressure, the temperature on the identical chip and so on three kind of sensiti ve units.The intellectualized sensor research and the development, US is at the leading positio n. American Space Agency when development spaceship called this kind of sensor for the clever sensor (Smart Sensor), on the spaceship this kind of sensor is extremely im portant. Our country in this aspect research and development also very backward mai nly is because our country semiconductor integrated circuit technological level is limit ed.The sensor’s development is changing day after day since especially the 80's humanities have ent ered into the high industrialization the information age, sensor techno-logy to renewal , higher technological development. US, Japan and so on developed country sensor te chnological development quickest, our country because the foundation is weak, the se nsor technology compares with these developed countries has the big disparity. Theref ore, we should enlarge to the sensor engineering research, the development investmen t, causes our country sensor technology and the foreign disparity reduces, promotes ou r country instrument measuring appliance industry and from the technical developmen t.。