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1、实用标准文案浙江师范大学行知学院本科毕业设计论文外文译译文：传感器的根底知识传感器是一种把被测量转换为光的、机械的或者更平常的电信号的装置.能量转换 的过程称之为换能.根据转换原理和测量形式对传感器进行分类.用来测量位移的电阻式传感器被归为 电阻式位移传感器.分类如压力波纹管、压力膜和压力阀等.1、传感器元件除特例外,大多数的传感器都由敏感元件、转换元件或限制元件组成.如振动膜、 波纹管、应力管和应力环、低音管和悬臂都是敏感元件,它们对压力和力作出响应把物 理量转变成位移.然后位移可以改变电参数,如电压、电阻、电容或者感应系数.机械 式和电子式元件合并形成机电式传感设备或传感器.这样的组合可用
2、来输入能量信号. 热的,光的,磁的和化学的相互结合产生的热电式、光电式、电磁式和电化学式传感器. 2、传感器灵敏度通过校正测量系统获得的被测物理量和传感器输出信号的关系叫做传感器灵敏度 K1,也就是Kk输出信号增量/测量增量.实际中,传感器的灵敏度是的,并且通过 测量输出信号,输入量由下式决定,输入量二输出信号增量/K1.3、理想传感器的特性a高保真性：传感器输出波形应该真实可靠地再现被测量,并且失真很小.b可测量最小的干扰,任何时候传感器的出现不能改变被测量.c尺寸：传感器必须能正确地放在所需的地方.d被测量和传感器信号之间应该有一个线性关系.e传感器对外部影响的灵敏度应该小,例如压力传感器
3、经常受到外部振动和温度的 响.f传感器的固有频率应该避开被测量的频率和谐波.4、电传感器电传感器具有许多理想特性.它们不仅实现远程测量和显示,还能提供高灵敏度. 电传感器可分为两大类.a变参数型,包括：i电阻式；ii电容式；文档实用标准文案iii自感应式；iv互感应式；这些传感器的工作依靠外部电压.b自激型,包括：i 电磁式；ii热电式；iii光栅式；iv压电式.这些传感器根据测量输入值产生输出电压,而且这一过程是可逆的.比方,在一般情况 下,压电式传感器可根据晶体材料的变形产生一个输出电压；但是,如果在材料上施加 一个可变电压,传感器可以通过变形或与变电压同频率的振动来表达可逆效应.5、电阻
4、式传感器电阻式传感器可以分为两大类：i那些表现为大电阻变化的物理量可通过分压方式进行测量,电位器就属于此类.ii那些表现为小电阻变化的物理量可通过桥电路方式进行测量,这一类包括应变仪和 电阻温度计.5.1 电位器绕线式电位器由许多绕在非导体骨架的电阻丝以及滑行在线圈上的触头组成.结构 原理如图,触头能够转动、直线式运动或者两运动合成的螺旋式运动.如果测量设备的电阻比电位器的电阻大,那么电压既可以是交流也可以是直流,且输出 电压与输入运动成正比.这样的电位器存在着分辨率和电子噪声的问题.分辨率是指传感器能检测到的最小 的输入增量,分辨率大小取决于线圈与滑动触头围成的面积.因此,输出电压为触头从
5、一端移到另一端时一系列阶跃.电子噪声可以通过接触电阻的振动、触头摩擦形成的机械磨损以及从敏感元件传出 的触头振动产生.另外,测得的运动量可以通过惯性和电位器中移动元件的摩擦获得较 大的机械载荷.触头外表的磨损将电位器的寿命限制为多少转.通常指的是生产商在说 明书中提及的“寿命转数,一个典型值为20*1000000转.空载电位器电路的输出电压V0由下式决定：设电阻R1=xi/xt *Rt,其中xi为输入位 移,xt为最大可能位移,Rt为电位器的电阻.那么输入电压V0= V* R1/R1 + Rt-R1 =V*R1 /Rt=V*xi/xt*Rt/Rt=V*xi/xt 上式说明,对于空载电位器输出
6、电压和输入位移呈直线关系.通过提升鼓励电压V可以获得高的灵敏度.但是,V的最大值由电位器线圈金属丝 的功率损耗P决定,即V=PRt1/2.5.2 电阻应变仪文档实用标准文案电阻应变仪是由机械应变产生电阻变化的传感器.它们可以是耦合的或者非耦合的 a耦合应变仪运用黏合剂可将应变仪与被检测的结构或部件的外表粘合或粘牢.耦合应变仪分为：i粘合在绝缘纸背后的金属细丝仪i i在环氧树脂上粘贴导电箔片的光栅iii在环氧树脂上粘贴铜或锲的半导体丝电阻应变仪可作为单个元件仅在一个方向测量应力,或者几个元件的组合体可在几 个方向同时进行测量.b非耦合应变仪一典型应变仪说明细电阻丝在悬臂弹簧偏差作用下改变电阻丝张
7、力进而改变电阻丝 的阻值.商业上通常在力、负载、压力传感器上运用此方法.5. 3电阻温度传感器此传感器的材料有以下两大类a金属如粕、铜、铐、锲的阻值会随着温度的升高而增大,即有一个正温度电阻系 数.b半导体,如用镒、钻、铭或镶的氧化物制成的电热调节器,其阻值变化与温度变化存 在一个非线性关系,即通常有一个负温度电阻系数.a金属电阻温度传感器在窄温度变化范围内,此类传感器取决于以下关系：R1=RO1+ab1-bO式中,a阻抗系数,R0为bO=O0时C的电阻b电热调节器半导体电阻温度传感器电热调节器为感温电阻器,其阻值变化与温度变化呈非线性关系.通常此类传感器 有一负温度系数.对于小的温度增量,阻
8、值的变化大体呈线性,但是如果存在大的温差, 测量电路需运用特定线性化技术生成电阻随温度变化的线性关系.电热调节器通常被制成附有玻璃质釉的半导体圆盘形状.由于电热调节器可以小到 1mn,所以响应的时间非常快.5. 4光敏元件光敏元件采用光敏半导体材料做成.当照射在半导体上的光强度增大,金属电极间 的阻抗就会降低.光敏元件常用的半导体材料有硫化镉、硫化铅和铜铸化合物.频率的有效范围由所用材料决定.硫化镉主要适用于可见光,硫化铅在红外线区有 峰值响应,所以最适合于光故障检测以及温度测量.5. 5放射性光元件当光照射到放射性光元件的阴极时,电子就会获取足够能量到达阴极.阴极就会吸 收这些电子产生一个通
9、过电阻R的电流,从而形成一输出电压V.文档实用标准文案产生的光电压V=I.R式中,I为光发射电流,I=K.B且为灵敏度,B输入照度Im 尽管输出电压能够表示照明的强度,这类元件却更多的应用于计算或调节,这里照射到 阴极的光可被中断.6、电容式传感器电容量随着相对介电常数、截面面积、或者极板间的距离的变化而变化.电容的特 征曲线说明,在空间的一段范围内,截面面积和相对介电常数的变化与电容量变化成线 性关系.不象电位器,变极距型电容传感器有无限的分辨率,这最适合测量微小的位移 增量的位移.7、电感式传感器电感可以通过改变电感电路的阻抗来调节.电容式和电感式传感器的测量技术：a用差分式电容或电感作为
10、交流电桥b用交流电位计电路做动态测量c用直流电路为电容器提供正比于容值变化的电压d采用调频法,C或者L随着振荡电路频率的变化而改变电容式和电感式传感器的一些重要特性如下：i分辨率无限ii精确到满量程的+-0. 1%i i i位移范围从25*10-6m到10-3mi v 上升时间小于50us典型的被测量是位移、压力、振动量、声音和液位.8、线性调压器9、压电式传感器10、电磁式传感器11、热电式传感器12、光电管13、机械式传感器及敏感元件文档实用标准文案原文：Basic knowledge of transducersA transducer is a device which convert
11、s the quantity being measured into an opt ical9 mechan ical. or-more common Iy-eIectrical si gna L The energy-convers i on process that takes pI ace i s referred to as transduction.Transducers are classified according to the transduction principle involved and the form of the measured. Thus a resi s
12、tance transducer for measur i ng displacement i s classified as a resistance d i spIacement transducer. Other classification examples are pressure be I lows, force diaphragm, pressure flapper-nozzle, and so on. 1、 Transducer ElementsAlthough there are exception t most transducers cons i st of a sens
13、ing e I ement and a conversion or control element. For example, d i aphragms. be I Iowsf strain tubes and rings, bourdon tubes, and cantilevers are sensing eIements which respond to changes in pressure or force and convert these physical quantities into a di spIacement. Thi s di spIacement may then
14、be used to change an eIectr icaI parameter such as voltage, resistance, capacitance, or inductance. Such combinat ion of mechanicaI and electr icaI elements form eIectromechanicaI transducing devices or transducers. Simi lar combination can be made for other energy i nput such as therma I. Photo, ma
15、gnet i c and chemica I. giving thermoelectr ic. photoe Iectr i cf eIectromaanet i cf and electrochemical transducers respectively. 2、 Transducer SensitivityThe relationship between the measured and the transducer output signal is usual ly obta i ned by caIibrat ion tests and i s referred to as the t
16、ransducer sensitivity K1= output-signal increment / measured increment . In practice, the transducer sensitivity is usually known, and, by measur ing the output signal, the input quantity i s determined from i nput= output-signa I i ncrement / K1.3、Character i st ics of an Idea I TransducerThe high
17、transducer should exhibit the fol lowing character i stics a) high fide Iity-the transducer output waveform shape be a faithful reproduction of the measured; there should be mini mum di stortion.文档实用标准文案b) There should be mini mum interference with the quantity being measured; the presence of the tr
18、ansducer 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 shou Id be a I i near re I at i onsh i p between the measured and the transducer s i gna I.e) The transducer should have minimum sensitivity to external effec
19、ts, pressure transducers, for examp I e, are often sub jected to externa I effects such vibration and temperature.f) The natural frequency of the transducer should be we I I separated from the frequency and harmonics of the measurand.4、Electr icaI TransducersElectr ical transducers exhibit many of t
20、he idea I character i sties. In addition they offer high sensitivity as we I I as promoting the possible of remote indication or mesdurement.Electrical transducers can be divided into two distinct groups: a) var iabIe-controI-parameter types, which include: i)resistance i i) capacitance i i i) induc
21、tancei v) mutuaI-i nductance typesThese transducers a I I rely on external excitation voltage for their operation, b) self-generating types,which incIude i) electromagnetic i i)thermoelectr ic i i i)photoemi ss i ve iv)pi ezo-electr ic typesThese al I themselves produce an output voltage in response
22、 to the measurand input and thei r effects are reversible. For example, a piezo-electr ic transducer norma Ily produces an output voltage in response to the deformation of a crystaI I ine mater iaI ; however, if an alternating voltage is appI ied across the material, the transducer exhibits the reve
23、rsible effect by deforming or vibrating at the frequency of the alternating voltage.5、Resistance TransducersResistance transducers may be divided into two groups, as foI Iows:文档实用标准文案i) Those which exper ience a large resistance change, measured by using potential-divider methods. Potentiometers are
24、 in this group.i i) Those which exper ience a sma I I resi stance change, measured by br idge-ci rcui t methods. Examp Ies of th i s group i ncIude stra i n gauges and resistance thermometers.5.1 Potent i ometersA I i near wi re-wound potentiometer consists of a number of turns res i stance wi re wo
25、und around a non-conducting former, together with a wiping contact which trave I s over the barwi res. The construct i on principles are shown in figure which indicate that the wiper di splacement can be rotary, translations I, or a comb i nat i on of both to give a he Iical-type motion. The excitat
26、ion voltage may be either a. c. or d. c. and the output voltage i s proportions I to the i nput motion, prov i ded the measur i ng device has a res i stance which i s much greater than the potentiometer resistance.Such potentiometers suffer from the I inked problem of resolution and electr ical nois
27、e. Resolution is defined as the smaI lest detectable change in input and is dependent on the cross-sectionaI area of the windings and the area of the sI iding contact. The output voltage is thus a serials of steps as the contact moves from one wi re to next.Electrical noise may be generated by varia
28、tion in contact resistance, by mechanicaI wear due to contact friction, and by contact vibration transmitted from the sens ing e I ement. I n add it ion, the mot ion be i ng measured may exper i ence significant mechanical loading by the inertia and fr iction of the mov i ng parts of the potentiomet
29、er. The wear on the contacting surface Iimits the I i fe of a potentiometer to a finite number of fuI I strokes or rotations usuaI Iy referred to in the manufacture1 s specification as the number of cycles of I ife expectancy1 , a typical value being 20*1000000 cycles.The output voltage V0 of the un
30、load potentiometer circuit i s determined as fol lows. Let resistance R1= xi/xt *Rt where xi = input displacement, xt= maximum possible displacement. Rt totaI 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 str
31、aight-1ine relationship between output voltage and input dispIacement for the unloaded potentiometer.It would seen that high sensitivity could be achieved simply by increasing the exc itat i on vo Itage V. however, the max imum va I ue of V i s determi ned by the max imum文档实用标准文案power dissipation P
32、of the fine wi res of the potentiometer winding and i s given by V= (PRt)1/2 .5. 2 Resistance Strain GaugesResistance strain gauges are transducers which exhibit a change in electr ical resistance in response to mechanical strain. They may be of the bonded or unbonded var iety .a) bonded strain gaug
33、esUsing an adhesive, these gauges are bonded, or cemented, di rectly on to the surface of the body or structure which is being examined.Examples of bonded gauges are1) fine wi re gauges cemented to paper backingi i) photo-etched gr ids of conducting foi I on an epoxy-resin backingi i i)a single semi
34、conductor f i I ament mounted on an epoxy-res i n back i ng with copper or nickel leads.Resistance gauges can be made up as single elements to measur ing strain in one di rection only, or a comb i nat i on of elements such as rosettes will permit simultaneous measurements in more than one di rection
35、.b) unbonded strain gaugesA typical unbonded-strain-gauge arrangement shows f ine resistance wi res stretched around supports in such a way that the deflection of the canti lever spr ing system changes the tens ion in the wi res and thus a Iters the resi stance of wi re. Such an arrangement may be f
36、ound in commercial ly avai I able force, load, or pressure transducers.2.3 Resistance Temperature TransducersThe mater iaIs for these can be divided into two main groups:a) meta Is such as platinum, copper, tungsten, and nickel which exhibit and increase in resi stance as the temperature r i ses; th
37、ey have a posit i ve temperature coefficient of resistance.b) semiconductors, such as thermistors which use oxides of manganese, cobalt, chromium, or nickel. These exhibit Iarge non-1 inear resistance changes with temperature variation and normally have a negative temperature coefficient of res i st
38、ance.c) meta I res i stance temperature transducersThese depend, for many practicaI purpose and v/ithin a narrow temperature range, upon the relationship R1=R0*1+a*(b1-b2) where a coefficient of resistance文档实用标准文案in CT, and RO resistance in ohms at the reference temperature b0=0 C at the reference t
39、emperature range .The international practicaI temperature scale is based on the platinum resistance thermometer, which covers the temperature range -259. 35 C to 630. 5 C. b) thermistor resistance temperature transducersThermistors are temperature-sensitive resistors which exhibit large non-1iner re
40、si stance changes wi th temperature var i at ion. In genera I, they have a negat i ve temperature coefficient.For smaI I temperature increments the var iation in resi stance i s reasonably Ii near; but, i f large temperature changes are experienced, special Ii near i z i ng techniques are used in th
41、e measuring circuits to produce a I inear relationship of resistance against temperature.Thermistors are norma I Iy made in the form of semiconductor di scs enclosed i n glass vitreous enamel. Since they can be made as smaI I as 1mm, quite rapid response times are possibIe.2.4 Photoconductive CellsT
42、he photoconduct i ve cell, uses a I i ght-sensit i ve semiconductor mater i a I. The resistance between the meta I electrodes decrease as the intensity of the I ight str iking the semiconductor increases. Common semiconductor mater iaIs used for photo-conductive cells are cadmium sulphide, lead sulp
43、hide, and copper-doped germanium.The useful range of frequencies is determined by mater ial used. Cadmium sulphide is mainIy suitable for visible I ight, whereas lead sulphide has its peak response in the infra-red region and is, therefore , most suitable for flame-failure detection and temperature
44、measurement.2.5 Photoemissive CellsWhen I ight str ikes the cathode of the photoemissive cel I are given sufficient energy to arr i ve the cathode. The positive anode attracts these electrons, producing a current which fIows through resistor R and resulting in an output voltage V.Photoe Iectr icaIly
45、 generated voltage V=lp.RIWhere lp=photoelectr ic current (A)t and photoelectric current lp=Kt. BWhere Kt:sensitivity (A/im)F and B=i I Iumination input (Iumen)Although the output voltage does give a good indication of the magnitude of iI Iumination, the cells are more often used for counting or con
46、trol purpose.文档实用标准文案where the Iight striking the cathode can be interrupted.6、Capaciti ve 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 indicate that variations of a
47、rea and relative permittivity give a I i near relationship on Iy over a sma11 range of spacings. Thus the sensitivity i s high for smaI I vaIues of d. Uni ike the potent ionmeter, the var iable-di stance capac it i ve transducer has an infinite resolution making it most suitable for measur i ng sma
48、I I i ncrements of di splacement or quant it i es which may be changed to produce a d i spIacement.7、Inductive TransducersThe inductance can thus be made to vary by changing the reluctance of the inductive ci rcuit.Measuring techniques used with capacitive and inductive transducers: a)A.C. excited br idges using differential capacitors inductors. b)A.C. potentiometer ci rcuits for dynamic measurements.c) D. C. ci rcuits to give a voltage proportional to velocity for a capacitor, d) Frequency-