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类型:k在线频道网址入口 地区: 欧美 年份:2020-07-10

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加速计简介什么是加速计?WhatareAccelerometers?加速计是测量一种装置的振动或运动加速度的设备。由振动或运动变化(加速度)产生的力会使物体“挤压”压电材料,产生与所施加力成正比的电荷。由于电荷与力成正比且质量为常量,因此电荷同样与加速度成正比。Anaccelerometerisadevicethatmeasuresthevibration,oraccelerationofmotionofastructure.Theforcecausedbyvibrationorachangeinmotion(acceleration)causesthemassto"squeeze"thepiezoelectricmaterialwhichproducesanelectricalchargethatisproportionaltotheforceexerteduponit.Sincethechargeisproportionaltotheforce,andthemassisaconstant,thenthechargeisalsoproportionaltotheacceleration.T压电加速计(振动传感器)有两种类型。第一种类型是“高阻抗”电荷输出加速计。在这种类型的加速计中,压电晶体会产生直接连接到测量仪器的电荷。电荷输出需要特殊的容纳空间以及通常会在研究机构中找到的检测仪表。这种加速计还用于不能使用低阻抗加速计的高温应用(>120C)中。Therearetwotypesofpiezoelectricaccelerometers(vibrationsensors).Thefirsttypeisa"highimpedance"chargeoutputaccelerometer.Inthistypeofaccelerometerthepiezoelectriccrystalproducesanelectricalchargewhichisconnecteddirectlytothemeasurementinstruments.Thechargeoutputrequiresspecialaccommodationsandinstrumentationmostcommonlyfoundinresearchfacilities.Thistypeofaccelerometerisalsousedinhightemperatureapplications(>120C)wherelowimpedancemodelscannotbeused.第二种加速计是低阻抗输出加速计。低阻抗加速计使用电荷加速计作为前端,但它具有一个微小的内置微电路和场效应晶体管,可以将电荷转换为低阻抗电压,从而轻松地实现与标准仪表的对接。这种加速计通常用于工业领域。加速计电源(如ACC-PS1)可为微电路提供适当的能量(18至24V@2mA恒定电流)并消除直流偏置电平,通常产生0到+/-5V的输出信号,具体取决于加速计的mV/g额定值。所有的OMEGA(R)加速计都是这种低阻抗类型。Thesecondtypeofaccelerometerisalowimpedanceoutputaccelerometer.Alowimpedanceaccelerometerhasachargeaccelerometerasitsfrontendbuthasatinybuilt-inmicro-circuitandFETtransistorthatconvertsthatchargeintoalowimpedancevoltagethatcaneasilyinterfacewithstandardinstrumentation.Thistypeofaccelerometeriscommonlyusedinindustry.AnaccelerometerpowersupplyliketheACC-PS1,providestheproperpowertothemicrocircuit18to24V@2mAconstantcurrentandremovestheDCbiaslevel,theytypicallyproducesazerobasedoutputsignalupto+/-5VdependinguponthemV/gratingoftheaccelerometer.AllOMEGA(R)accelerometersarethislowimpedancetype.加速计技术参数AccelerometerSpecifications动态范围是在输出信号失真或削减之前加速计可测量的+/-最大振幅。通常以g's表示。频率响应取决于质量、晶体压电性能和外壳共振频率。它是加速计输出在指定偏差范围内(通常为+/-5%)时对应的频率范围。g1g是因地球引力产生的加速度,相当于32.2ft/sec2、386in/sec2或9.8m/sec2。接地-加速计中有两种信号接地类型。外壳接地加速计使信号的低端连接到外壳。由于外壳是信号行进路径的一部分,且外壳可以连接至导电材料,因此在使用这种加速计时必须注意避免地平面产生的噪声。对地绝缘的加速计使电气元件与外壳隔离,不易受到地噪声的影响。高频限制是输出超出标定输出偏差时的频率。它通常取决于加速计的机械共振。低频截止是输出开始降至标定精度以下时的频率。频率更低时,输出不会“截止”,但灵敏度会迅速下降。噪声-电子噪声由放大电路产生。噪声可以使用宽带(基于频谱指定)或频谱(在特定频率指定)表示。噪声等级以g's表示,如0.0025g2-25,000Hz。噪声通常会随着频率的增加而降低,因此低频时的噪声问题比高频时的噪声问题更严重。共振频率是传感器共振或共鸣时的频率。频率测量值最好远低于加速计的共振频率。灵敏度是由以g's为单位的力产生的输出电压。加速计通常分为两个类别-产生10mV/g或100mV/g。交流输出电压的频率将与振动频率相匹配。输出电平与振幅成正比。低输出加速计用于测量高等级振动,而高输出加速计用于测量低等级振动。温度灵敏度是所测温度的每一度的电压输出。为了使温度发生变化时输出变化保持在指定的限制内,传感器会有一定的温度补偿。温度范围受到将电荷转换为低阻抗输出的电子微电路的限制。通常的范围为-50到120C。DynamicRangeisthe+/-maximumamplitudethattheaccelerometercanmeasurebeforedistortingorclippingtheoutputsignal.Typicallyspecifieding's.FrequencyResponseisdeterminedbythemass,thepiezoelectricpropertiesofthecrystal,andtheresonancefrequencyofthecase.Itisthefrequencyrangewheretheoutputoftheaccelerometeriswithinaspecifieddeviation,typically+/-5%.g1gistheaccelerationduetotheearth'sgravitywhichis32.2ft/sec2,386in/sec2or9.8m/sec2.Grounding-Therearetwotypesofsignalgroundinginaccelerometers.CaseGroundedaccelerometershavethelowsideofthesignalconnectedtotheircase.Asthecaseispartofthesignalpathandmaybeattachedtoaconductivematerial,caremustbeusedwhenusingthistypeofaccelerometertoavoidnoisefromthegroundplain.GroundIsolatedaccelerometershavetheelectricalcomponentsisolatedfromthecaseandaremuchlesssusceptibletogroundinducednoise.HighFrequencyLimitisthefrequencywheretheoutputexceedsthestatedoutputdeviation.Itistypicallygovernedbythemechanicalresonanceoftheaccelerometer.LowFrequencyCut-offisthefrequencywheretheoutputstartstofalloffbelowthestatedaccuracy.Theoutputdoesnot"cut-off"butthesensitivitydecreasesrapidlywithlowerfrequencies.Noise-Electronicnoiseisgeneratedbytheamplifyingcircuit.Noisecanbespecifiedeitherbroadband(specifiedovertheafrequencyspectrum)orspectral-designatedatspecificfrequencies.Noiselevelsarespecifieding's,i.e.0.0025g2-25,000Hz.Noisetypicallydecreasesasfrequencyincreasessonoiseatlowfrequenciesismoreofaproblemthanathighfrequencies.ResonanceFrequencyisthefrequencyatwhichthesensorresonatesorrings.Frequencymeasurementswanttobewellbelowtheresonancefrequencyoftheaccelerometer.Sensitivityistheoutputvoltageproducedbyacertainforcemeasureding's.Accelerometerstypicallyfallintotwocategories-producingeither10mV/gor100mV/g.ThefrequencyoftheACoutputvoltagewillmatchthefrequencyofthevibrations.Theoutputlevelwillbeproportionaltotheamplitudeofthevibrations.Lowoutputaccelerometersareusedtomeasurehighvibrationallevelswhilehighoutputaccelerometersareusedtomeasurelowlevelvibrations.TemperatureSensitivityisthevoltageoutputperdegreeofmeasuredtemperature.Thesensorsaretemperaturecompensatedtokeepthechangeinoutputtowithinthespecifiedlimitsforachangeintemperature.TemperatureRangeislimitedbytheelectronicmicrocircuitthatconvertsthechargetoalowimpedanceoutput.Typicallytherangeis-50to120C.加速计选型选择适合您应用的加速计时,必须考虑多种参数。∙要监视的振幅是多少?∙要监视的频率范围是多少?∙安装的温度范围是多少?∙要监视的样本尺寸和外形如何?∙是否有电磁场?∙周围是否有高强度的电噪声?∙要安装加速计的表面是否接地?∙是否处于腐蚀性环境中?∙需要本质安全型仪器还是防爆型仪器?∙是否处于潮湿环境或冲落区域?其它考虑因素:加速计的质量应明显小于待监视系统的质量。加速计的动态范围应比预期的样本振幅范围大。加速计的频率范围应与预期频率范围匹配。加速计的灵敏度应产生与现有仪表兼容的电输出。使用低灵敏度加速计测量高幅振动,反过来,使用高灵敏度加速计测量低幅振动。安装为了正确测量振动,传感器必须直接安装到机器表面。这可以通过多种安装方法实现:∙平面磁铁安装∙2极磁铁安装∙粘合剂(环氧树脂/氰基丙烯酸酯)∙安装螺柱∙隔离螺柱磁铁安装通常用于暂时性安装。磁铁安装用于将加速计安装到磁性材料上,这些材料一般可以在机床、各种装置和电机中找到。这种方式可以使传感器方便地更换位置,读取多个位置的测量值。双极磁铁安装用于将加速计安装到弯曲的磁性表面上。粘合剂和螺柱在永久安装时采用。环氧树脂和氰基丙烯酸酯等粘合剂已被证明在大多数应用中都能得到满意的粘合效果。为了避免因粘合层的弹性对振动产生任何不必要的缓冲,粘合层应尽可能薄。要卸除使用粘合剂安装的加速计,可将扳手放在扳手槽上,然后转动扳手掀开粘合层。不要使用锤子。敲击加速计会对其造成损害。安装螺柱是首选的安装方法。这种安装方式虽然需要对装置钻洞攻螺,但却坚实可靠。请确保使用指定的转矩,避免损坏传感器或使螺纹脱扣。AccelerometerSelectionWhenselectinganaccelerometerforyourapplicationmanyparametersmustbeconsidered.∙Whatisthevibrationamplitudetobemonitored?∙Whatisthefrequencyrangetobemonitored?∙Whatisthetemperaturerangeoftheinstallation?∙Whatisthesizeandshapeofthesampletobemonitored?∙Arethereelectromagneticfields?∙Isthereahighlevelofelectricalnoiseinthearea?∙Isthesurfacewheretheaccelerometeristobemountedgrounded?∙Istheenvironmentcorrosive?∙DoesthearearequireIntrinsicallysafeorexplosionproofinstruments?∙Istheareaawetorawashdownarea?OtherConsiderations:Themassoftheaccelerometersshouldbesignificantlysmallerthanthemassofthesystemtobemonitored.Theaccelerometerdynamicrangeshouldbebroaderthantheexpectedvibrationamplituderangeofthesample.Thefrequencyrangeoftheaccelerometershouldfittheexpectedfrequencyrange.TheSensitivityoftheaccelerometershouldproduceanelectricaloutputcompatiblewithexistinginstrumentation.Usealowsensitivityaccelerometertomeasurehighamplitudevibrationsandconverselyuseahighsensitivityaccelerometertomeasurelowamplitudevibrations.MountingThesensormustbemounteddirectlytothemachinesurfacetocorrectlymeasurethevibrations.Thiscanbeaccomplishedbyseveraltypesofmounts:∙FlatMagnetMount∙2-poleMagnetMount∙Adhesives(Epoxy/Cyanoacrylate)∙MountingStud∙IsolatingStudMagnetMountsaregenerallytemporarymountings.Magneticmountsareusedtomountaccelerometerstoferromagneticmaterialscommonlyfoundinmachinetools,structuresandmotors.Theyallowthesensortobeeasilyrelocatedfromsitetositeformultiplelocationreadings.Two-polemagneticmountsareusedtomountanaccelerometertoacurvedferromagneticsurface.Adhesives,andthreadedstudsareconsideredpermanentmountings.Adhesivessuchasepoxyorcyanoacrylatehaveproventoprovidesatisfactorybondingformostapplications.Keepthefilmasthinaspossibletoavoidanyunwanteddampeningofthevibrationsduetotheflexibilityofthefilm.Toremoveanadhesivemountedaccelerometer,useawrenchonthecase'swrenchflatsandtwisttobreaktheadhesivebond.DONOTUSEAHAMMER.Strikingtheaccelerometerwilldamageit.Mountingstudsarethepreferredmountingtechnique.Theyrequirethestructuretobedrilledandtappedbutprovidesolidreliablemountings.Besuretofollowthespecifiedtorquesettingstoavoiddamagingthesensororstrippingthethreads.加速计类型TypesofAccelerometers特级这些加速计甄选优质晶体并使用低噪声电路,构成了特级低噪声产品。采用316L不锈钢外壳的产品具有完全密封的结构,可以在恶劣的工业环境中工作。同时还提供FM和CSA本质安全型产品。ACC793采用标准的顶部电缆结构,而ACC797采用低矮型侧面电缆结构。PremiumGradeTheseaccelerometersaremadefrompremiumselectedcrystalsanduselownoisecircuitrytoproductapremium,lownoise,accelerometer.Their316LStainlesssteelcaseishermeticallysealedagainsttheenvironmentsotheycansurviveharshindustrialenvironments.TheyalsohaveFMandCSAIntrinsicallysafeoptionsavailable.TheACC793isastandardtopcableconfigurationandtheACC797isalow-profilesidecableconfiguration.工业级工业级加速计是工业领域中的主流产品。它们适用于从机床到油漆搅拌机的各种应用。OMEGA有四种型号可供选择。ACC101(左图)是通用型高品质低成本加速计。ACC102A具有完全密封的结构,适用于恶劣环境,它采用固定电缆,重量只有50克。采用顶部电缆的ACC786A和采用侧面电缆的ACC787A同样具有完全密封的结构,此外还具有适应各种天气的可拆卸型密封电缆。IndustrialGradeIndustrialgradeaccelerometersaretheworkhorsesofindustry.Theareusedoneverythingfrommachinetoolstopaintshakers.OMEGAhasfourmodelstochoosefrom.ACC101(shown)isahighqualitylowcostaccelerometerforgeneralpurposeapplications.ACC102Aishermeticallysealedforharshenvironments,hasafixedcableandweighsonly50grams.TheACC786A,topcable,andACC787A,sidecable,arehermeticallysealedandhavedetachablecablessealedagainsttheweather.高振动等级这种加速计用于对较高的振动等级进行监视,相对于工业级加速计而言,它的输出更低(10mV/g),质量更轻。ACC103的重量为15gms,最高可监视500g's的振动等级。它采用螺柱式安装结构,适用于振动台、振动实验室和重工业机床等领域。ACC104重量只有1.5gms,采用粘合剂式安装结构。以上两种型号的频率范围均为3到10kHz,动态范围为+/-500g's。HighVibrationAccelerometersusedtomonitorhighvibrationlevelshavealoweroutput(10mV/g)andlowermassthanindustrialaccelerometers.TheACC103weighs15gmsandcanmonitorvibrationlevelsupto500g's.Itisastudmountdesignandisdesignedforuseonshakertables,vibrationlabsandheavyindustrialmachinetools.TheACC104weighsonly1.5gmsandisdesignedforadhesivemounting.BothmodelshaveaFrequencyrangeof3to10kHzandadynamicrangeof+/-500g's.三轴型三轴加速计可测量X、Y和Z轴上的振动。它具有三个晶体,每个晶体都会对一个不同轴上的振动作出反应。输出有三个信号,每个信号表示三个轴中一个轴的振动。ACC301采用重量很轻的钛金属结构,具有10mV/g的输出和+/-500g's的动态范围,频率范围为3到10kHz。TriaxialtriaxialaccelerometersmeasurethevibrationinthreeaxesX,YandZ.Theyhavethreecrystalspositionedsothateachonereactstovibrationinadifferentaxis.Theoutputhasthreesignals,eachrepresentingthevibrationforoneofthethreeaxes.TheACC301haslightweighttitaniumconstructionand10mV/goutputwithadynamicrangeof+/-500g'soverarangeof3to10kHz.

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