Chapter8Measurementofforce,momentandpressureSchoolofmechanicalandpowerengineering/HenanpolytechnicuniversityContents8.1

Overview8.2Measurementofforce8.3Measurementofmoment8.4MeasurementofpressureChapterSeven

Measurementofvelocity,accelerationandvibration8.1

OverviewForce：anyinteractionthat,whenunopposed,willchangethe

motion

ofan

object.Unit“Newton”Buildingofmassstandard：InternationalPrototypeKilogramItisofcylindricalform,withdiameterandheightofabout39mm,andismadeofanalloyof

90%platinum

and

10%iridium.8.1

OverviewBuildingofforcestandard：gravityReproductionofforcestandardusingprimaryforcestandardmachineNaturalweighttypestandardmeasuringmachineHydraulicstandardmeasuringmachineLever-typestandardmeasuringmachine8.1

OverviewMoment：a

moment

isanexpressioninvolvingtheproductofadistanceandaphysicalquantity.

Itistheproductofaforceanditsarm.力對(duì)物體產(chǎn)生轉(zhuǎn)動(dòng)作用的物理量，Unit:“N·m"Momentmakesobjectsrotate，calledalsotorque(轉(zhuǎn)矩).Distortionaldeformationofshaftundertheactionoftorque，generates

shear

stressandstraininnerthematerial,calledalsotorque(扭矩).。8.1

OverviewPressure：AforceFisappliedperpendiculartoanareaA,thenthepressurePisP=F/A.垂直作用在單位面積上的力，或流體中單位面積上承受的力。也稱(chēng)為“壓強(qiáng)”，Unit:Pascal(Pa)Contents8.1

Overview8.2Measurementofforce8.3Measurementofmoment8.4MeasurementofpressureChapterSeven

Measurementofvelocity,accelerationandvibration8.2

MeasurementofforceForcemeasuringmethodMeasurementusingDynamicEffect：測(cè)量物體的質(zhì)量及其所獲得的加速度，計(jì)算測(cè)定力值。F=ma。MeasurementusingStaticEffect：通過(guò)測(cè)量物體的變形量，或與應(yīng)力相關(guān)的物理效應(yīng)來(lái)測(cè)量力值。DynamometerResistance-straingaugeMagnetostrictiongaugePiezoelectricgaugeDisplacementdynamometerResistance-straingauge

Workingprinciple結(jié)構(gòu)簡(jiǎn)單、制造方便、精度高、應(yīng)用廣泛；測(cè)量范圍：5N~20MN；測(cè)量精度：0.03%~2%Resistance-straingaugeStructuralformofelasticbody柱狀變形體5kN~5MN管狀變形體1MN~20MN徑向受載變形體<5NResistance-straingaugeStructuralformofelasticbody雙鉸鏈彎曲桿變形體<5N剪切桿式變形體外形很扁的力傳感器Resistance-straingauge在負(fù)荷作用下，彈性體的應(yīng)變是：電阻應(yīng)變片的靈敏度系數(shù)k為：μ為彈性體材料的泊松比Resistance-straingauge測(cè)力電橋

Outputvoltageofbridgecircuit：傳感器的電壓靈敏度，通常取0.5~2.5mV/VResistance-straingauge應(yīng)變式測(cè)力儀一般采用電橋電路。電橋電路的輸出信號(hào)小，精度要求高，因而測(cè)量電路要求具有高的增益、高的輸入阻抗。傳感器測(cè)量電路的集成模塊稱(chēng)作信號(hào)調(diào)理器，一般包括緩沖、放大、濾波、電壓－頻率轉(zhuǎn)換等為提高測(cè)力傳感器的精度，必須在電橋電路中采取相應(yīng)的補(bǔ)償措施，消除誤差的影響。包括初始不平衡補(bǔ)償、零點(diǎn)漂移補(bǔ)償、靈敏度補(bǔ)償、非線性補(bǔ)償、傳感器靈敏度調(diào)整等MagnetostrictiongaugeMagnetostriction

effect：鐵磁體受機(jī)械力(壓力、張力、扭力等)作用后，而引起導(dǎo)磁系數(shù)發(fā)生變化的物理現(xiàn)象。Magneticelastomerwithmagnetostriction

effectiscalledmagnetostrictionelement.PiezoelectricgaugePiezoelectriceffect：某些電介質(zhì)在沿一定方向上受到外力的作用而變形時(shí)，其內(nèi)部會(huì)產(chǎn)生極化現(xiàn)象，同時(shí)在它的兩個(gè)相對(duì)表面上出現(xiàn)正負(fù)相反的電荷。當(dāng)外力去掉后，它又會(huì)恢復(fù)到不帶電的狀態(tài)Displacementdynamometer材料受力后產(chǎn)生變形或者位移電容式電感式WeighingConceptandmeaningofweighing重量(Weight)：有些場(chǎng)合用于指重力(Weight)。而另一些場(chǎng)合又用于指物體的質(zhì)量(Mass)。二者的物理概念不同，但在工程測(cè)量中屬于同一個(gè)技術(shù)范疇。稱(chēng)重的衡器用準(zhǔn)確度級(jí)別來(lái)表征特性，它包括了非線性、重復(fù)性、滯后、溫度特性等指標(biāo)，對(duì)各單項(xiàng)不進(jìn)行控制。稱(chēng)重按工作條件分為靜態(tài)稱(chēng)重和動(dòng)態(tài)稱(chēng)重。Composition,classificationandcharacteristicsComposition機(jī)械傳遞、稱(chēng)重傳感器、測(cè)量電路和顯示儀表Classification電子皮帶秤(ElectronicBeltWeighingScale)、容器秤(ContainerWeighingScale)、吊車(chē)秤(CraneWeighingScale)、平臺(tái)秤(PlatformWeighingScale)、電子軌道衡(ElectronicRailroadTrackScale)Characteristics結(jié)構(gòu)簡(jiǎn)單、精度高、速度快、數(shù)據(jù)記錄處理方便Weight

sensorResistor-strainSensorWeight

sensorPiezomagneticSensorWeight

sensorCapacitanceSensorElectronicBeltWeighingScaleWorkingprincipleWeighingsensor：Velocitysensor：變換常數(shù)：ElectronicBeltWeighingScaleElectronicBeltWeighingScale變換常數(shù)：Contents8.1

Overview8.2Measurementofforce8.3Measurementofmoment8.4MeasurementofpressureChapterSeven

Measurementofvelocity,accelerationandvibration8.3

MeasurementofforcemomentForceMoment:力和力臂的乘積。轉(zhuǎn)矩(Torque):力矩可以使機(jī)械零部件轉(zhuǎn)動(dòng)，也稱(chēng)為轉(zhuǎn)矩。扭矩(Torque):在轉(zhuǎn)矩的作用下，機(jī)械零部件將會(huì)產(chǎn)生一定的扭曲變形，故又稱(chēng)為扭轉(zhuǎn)矩，簡(jiǎn)稱(chēng)扭矩。力矩的法定計(jì)量單位:“牛頓米”，一般用“Nm”表示。8.3

Measurementofforcemoment工程中轉(zhuǎn)矩的測(cè)量常與功率、轉(zhuǎn)速的測(cè)量聯(lián)系在一起。旋轉(zhuǎn)軸的扭矩、轉(zhuǎn)速和功率的測(cè)量，是進(jìn)行旋轉(zhuǎn)件功率控制的重要基礎(chǔ)。

電動(dòng)機(jī)內(nèi)燃機(jī)發(fā)電機(jī)泵攪拌機(jī)鉆探機(jī)加工中心車(chē)床變速器8.3

MeasurementofforcemomentMomenttransmissionmethod：利用轉(zhuǎn)矩使彈性軸產(chǎn)生扭轉(zhuǎn)變形Forcebalancemethod：利用平衡轉(zhuǎn)矩M0與被測(cè)轉(zhuǎn)矩平衡Energyconversionmethod8.3

MeasurementofforcemomentMomenttransmissionmethodUsethetorsion

deformationofelasticshaftformedbytorque.即根據(jù)彈性元件在傳遞扭矩時(shí)所產(chǎn)生物理參數(shù)的變化（變形、應(yīng)力或應(yīng)變）來(lái)測(cè)量其轉(zhuǎn)矩。listhelengthofelasticshaftφistorsionangleofelasticshaftGissheer

modulus(切變模量)IPispolarsecondmoment(極慣性矩)，F(xiàn)orthediameterdofshaft，IP=πd4/32Whenthetorsionanglemeasured:Whentheshearstressofshaftmeasured:Whenthestrainofshaftmeasured:45、135:thestrainsalongthedirectionof45o、135orelatedtoaxisoftheshaft.MeasurementofforcemomentMeasurementofforcemomentMomenttransmissionmethod電阻應(yīng)變式轉(zhuǎn)矩儀將應(yīng)變片粘在沿轉(zhuǎn)軸450、1350軸線上，轉(zhuǎn)軸在轉(zhuǎn)矩M作用下產(chǎn)生應(yīng)變?chǔ)排cM成正比。空心圓柱形軸：方形截面軸：MeasurementofforcemomentMomenttransmissionmethod電阻應(yīng)變式轉(zhuǎn)矩儀軸截面的選擇依據(jù)：工藝加工、測(cè)量值大小、抗彎曲強(qiáng)度、臨界轉(zhuǎn)速、應(yīng)變片尺寸、粘貼工藝應(yīng)變電橋電路：采用集流環(huán)從旋轉(zhuǎn)件上將轉(zhuǎn)矩測(cè)量信號(hào)傳輸?shù)届o止的儀器上MeasurementofforcemomentMomenttransmissionmethod磁電式轉(zhuǎn)矩測(cè)量?jī)xMeasurementofforcemomentMagnetizationmethod磁場(chǎng)嵌入技術(shù)（EMD,EmbeddedMagneticDomain）MeasurementofforcemomentForcebalancemethod利用平衡轉(zhuǎn)矩M0去平衡被測(cè)轉(zhuǎn)矩M，從而求得M的方法。MeasurementofforcemomentForcebalancemethod反饋式小力矩測(cè)量系統(tǒng)Contents8.1

Overview8.2Measurementofforce8.3Measurementofmoment8.4MeasurementofpressureChapterSeven

Measurementofvelocity,accelerationandvibration8.4Measurementofpressure

BasicconceptsMeasuringmethodandsensorforpressureVacuummeasurementUltrahighpressure(UHP)measurement基本概念垂直作用在單位面積上的力稱(chēng)為壓力。壓力測(cè)量一般用于液體、蒸汽或氣體等流體，也稱(chēng)為“壓強(qiáng)”。單位:“帕斯卡”，或簡(jiǎn)稱(chēng)“帕”，用“Pa”表示，1Pa=1N/m2標(biāo)準(zhǔn)大氣壓：定義為在溫度為0℃，緯度為45°的海平面上，重力加速度為9.80665m/s2

時(shí)的壓力。1atm=760mmHg=101.325kPa基本概念大氣壓力：大氣層對(duì)地球表面單位面積上所產(chǎn)生的壓力，即大氣的自重對(duì)地球表面產(chǎn)生的壓力。表壓力（正壓）：超過(guò)大氣壓以上的壓力數(shù)值，即測(cè)壓儀表顯示的壓力值絕對(duì)壓力：相對(duì)絕對(duì)真空所測(cè)得的壓力（表壓力與大氣壓力之和），又稱(chēng)總壓力或全壓力負(fù)壓力（疏空）：絕對(duì)壓力小于大氣壓力時(shí)，大氣壓力與絕對(duì)壓力之差真空度：小于大氣壓力的絕對(duì)壓力基本概念壓力量值的溯源和傳遞壓力不是基準(zhǔn)量，是力和面積的導(dǎo)出量壓力標(biāo)準(zhǔn)是由準(zhǔn)確度很高的標(biāo)準(zhǔn)儀器提供的壓力測(cè)量方法和傳感器

液體式壓力計(jì)電氣式壓力計(jì)負(fù)荷式（力平衡式）壓力計(jì)彈性式壓力計(jì)液體式壓力計(jì)U型管壓力計(jì)液體可以用水、酒精、水銀液體式壓力計(jì)槽式壓力計(jì)只需測(cè)量一側(cè)管中的液面相對(duì)于固定點(diǎn)的高度HhdP1P2A2A1液體式壓力計(jì)斜管微壓計(jì)用于測(cè)量微小壓力，精度高于一般的U型管壓力計(jì)HdhxP1P2A2<<A1彈性式壓力計(jì)特點(diǎn)價(jià)格低、簡(jiǎn)單、牢固、應(yīng)用廣泛，耐惡劣環(huán)境。頻響低、不宜動(dòng)態(tài)測(cè)量；由于彈性元件的固有遲滯，精度低彈性元件結(jié)構(gòu)簧管、膜盒、膜片、波紋管彈性式壓力計(jì)結(jié)構(gòu)特點(diǎn)：價(jià)格低，結(jié)構(gòu)簡(jiǎn)單，堅(jiān)實(shí)牢固頻率響應(yīng)低，不適于動(dòng)態(tài)測(cè)量負(fù)荷式壓力計(jì)根據(jù)靜力平衡原理和帕斯卡定律工作電氣式壓力計(jì)壓阻式電氣式壓力計(jì)應(yīng)變式平膜片電氣式壓力計(jì)電容式彈性膜片固定極板R：半徑t：厚度d：起始距離C0：起始電容量E：材料的彈性模量μ：材料的泊松比真空的測(cè)量

真空度的劃分粗真空：＞105～103Pa低真空：