建筑环境与能源应用工程专业英语课件.ppt

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1、UnitThirteenMeasurementErrorsandAccuracyBasicConceptsandTermsAmeasurablequantityisapropertyofphenomena,bodies,orsubstancesthatcanbedefinedqualitativelyandexpressedquantitatively.Measurablequantitiesarealsocalledphysicalquantities.Measurementistheprocessofdeterminatingthevalueofaphysi

2、calquantityexperimentallywiththehelpofspecialtechnicalmeanscalledmeasuringinstruments.Thevalueofaphysicalquantityistheproductofanumberandaunitadaptedforthesequantities.Thetruevalueofameasurandisthevalueofthemeasuredphysicalquantity,which,beingknown,wouldideallyreflect,bothqualitative

3、lyandquantitatively,thecorrespondingpropertyoftheobject.Weshallusethetermuncertaintytocharacterizetheinaccuracyofameasurementresult,whereasthetermerrorisusedtocharacterizethecomponentsoftheuncertainty.BasicConceptsandTermsThemeasurementerroristhedeviationoftheresultofmeasurementfromt

4、hetruevalueofthemeasurablequantity,expressedinabsoluteorrelativeform.IfAisthetruevalueofthemeasurablequantityand˜Aistheresultofmeasurement,thentheabsoluteerrorofmeasurementisζ=˜A−A.Theabsoluteerrorisusuallyidentifiedbythefactthatitisexpressedinthesameunitsasthemeasurablequantity.Abso

5、luteerrorisaphysicalquantity,anditsvaluemaybepositive,negative,orevengivenbyanintervalthatcontainsthatvalue.Oneshouldnotconfusetheabsoluteerrorwiththeabsolutevalueofthaterror.Forexample,theabsoluteerror−0.3mmhastheabsolutevalue0.3.Therelativeerroristheerrorexpressedasafractionofthetr

6、uevalueofthemeasurablequantityε=(˜A−A)/A.Relativeerrorsarenormallygivenaspercentandsometimesperthousand(denotedby‰).MeasurementError测量误差Measurementerrormaybedefinedasthedifferencebetweenthetruevalueandthemeasuredvalueofthequantity.Systematicerrors系统误差Randomerrors随机误差WhatCausesMeasure

7、mentErrors?Nowthatweknowthetypesofmeasurementerrorsthatcanoccur,whatfactorsleadtoerrorswhenwetakemeasurements?Wecanseparatethiscategoryinto2basiccategories:instrumentandoperatorerrors.instrumenterrors仪器误差operatorerrors操作误差InstrumentErrorsSomebasicinformationthatusuallycomeswithaninst

8、rumentis:acc