1、Designation: E 2428 08An American National StandardStandard Practice forCalibration of Torque-Measuring Instruments for Verifyingthe Torque Indication of Torque Testing Machines1This standard is issued under the fixed designation E 2428; the number immediately following the designation indicates the
2、 year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is to specify procedure for the cali
3、brationof elastic torque-measuring instruments.NOTE 1Verification by deadweight and a lever arm is an acceptablemethod of verifying the torque indication of a torque testing machine.Tolerances for weights used are tabulated in Practice WK6364; methodsfor calibration of the weights are given in NIST
4、Technical Note 577,Methods of Calibrating Weights for Piston Gages.21.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Com
5、biningvalues from the two systems may result in non-conformancewith the standard.1.3 This practice is intended for the calibration of static orquasi-static torque measuring instruments. The practice is notapplicable for high speed torque calibrations or measurements.1.4 This standard does not purpor
6、t to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E29 P
7、ractice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsWK6364 Practice for Torque Verification of Torque TestingMachines2.2 American National Standard:B46.1 Surface Texture4ELASTIC TORQUE-MEASURING INSTRUMENTS3. Terminology3.1 Definitions:3.1.1 elastic torque-me
8、asuring devicea device or systemconsisting of an elastic member combined with a device forindicating the measured values (or a quantity proportional tothe measured value) of deformation of the member under anapplied torque.3.1.2 primary torque standardsa deadweight force ap-plied through a lever arm
9、 or wheel, with a calibrated length orradius of a known uncertainty, that is traceable to nationalstandards.3.1.3 secondary torque standardan instrument or mecha-nism, that has been calibrated by a comparison with a primarytorque standard(s).3.1.4 torquea vector product of force and length, ex-press
10、ed in terms of N-m, lbf-in., etc.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration equationa mathematical relationship be-tween output of the unit under test and the applied standardtorque, sometimes referred to as the calibration curve.3.2.2 continuous-reading devicea class of in
11、strumentswhose characteristics permit interpolation of torque valuesbetween calibrated torque values.3.2.2.1 DiscussionSuch instruments usually have torque-to-deflection relationships that can be fitted to polynomialequations. Departures from the fitted curve are reflected in theuncertainty (see 8.4
12、).3.2.3 deflectionthe difference between the readings of aninstrument under applied torque and the reading with noapplied torque. The definition of deflection applies to outputreadings in electrical units as well as readings in units oftorque.1This practice is under the jurisdiction of ASTM Committe
13、e E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved Feb. 15, 2008. Published March 2008.2Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070,
14、Gaithersburg, MD 20899-1070, http:/www.nist.gov.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available fr
15、om American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 torque rangea range of torque values within whichthe uncertainty
16、is less than the limits of error specified for theinstrument application.3.2.5 readinga numerical value indicated on the scale,dial, electrical output or digital display of a torque- measuringinstrument for a given torque.3.2.6 resolutionthe smallest change in reading or indica-tion appropriate to t
17、he scale, dial, or display of the torquemeasuring instrument.3.2.7 specific torque devicean alternative class of instru-ments not amenable to the use of a calibration equation.3.2.7.1 DiscussionSuch instruments, usually those inwhich the reading is taken from a dial indicator, are used onlyat the ca
18、librated torque values.3.2.8 uncertaintya statistical estimate of the limits oferror in torque values computed from the calibration equationof a torque-measuring instrument when the instrument iscalibrated in accordance with this practice.4. Significance and Use4.1 Testing machines that apply and in
19、dicate torque are ingeneral use in many industries. Practice WK6364 has beenwritten to provide a practice for the torque verification of thesemachines. A necessary element in Practice WK6364 is the useof devices whose torque characteristics are known to betraceable to national standards. Practice E
20、2428 describes howthese devices are to be calibrated. The procedures are useful tousers of torque testing machines, manufacturers and providersof torque measuring instruments, calibration laboratories thatprovide calibration services and documents, and service orga-nizations using devices to verify
21、torque testing machines.5. Reference Standards5.1 Torque-measuring instruments . used for the verificationof the torque indication systems of torque testing machinesmay be calibrated by either primary or secondary standards.5.2 Torque-measuring instruments used as secondary stan-dards for the calibr
22、ation of other torque-measuring instrumentsshall be calibrated by primary standards.6. Requirements for Torque Standards6.1 Primary StandardTorque, with traceability derivedfrom national standards of length and mass, and of specificmeasurement uncertainty, that can be applied to torque mea-suring de
23、vices. Weights used as primary mass standards shallbe made of rolled, forged, or cast metal. Adjustment cavitiesshall be closed by threaded plugs or suitable seals. Externalsurfaces of weights shall have a finish of 3.2m (Ra) or less asspecified in ANSI B46.1.6.1.1 The force exerted by a weight in a
24、ir is calculated asfollows:Force 5 Mg / 9.80665! 1d / D! (1)where:M = mass of the weight,g = local acceleration due to gravity, m/s2,d = air density (approximately 1.2 kg/m3),D = density of the weight in the same units as d, and9.80665 = the factor converting SI units of force into thecustomary unit
25、s of force. For SI units, this factoris not used.6.1.2 The masses of the weights shall be determined bycomparison with reference standards traceable to the nationalstandards of mass. The local value of the acceleration due togravity, calculated within 0.0001 m/s2(10 milligals), may beobtained from t
26、he National Geodetic Information Center,National Oceanic and Atmospheric Administration.5NOTE 2If M, the mass of the weight, is in pounds, the force will bein pound-force units (lbf). If M is in kilograms, the force will be in kilogram-force units (kgf). These customary force units are related to th
27、enewton (N), the SI unit of force, by the following relationships:1 kgf = 9.80665 N (exact)1 lbf = 4.44822 NThe pound-force (lbf) is defined as that force which, applied to a 1-lbmass, would produce an acceleration of 32.1747 f/s/s.6.1.3 The lever arm or wheel shall be calibrated to deter-mine the l
28、ength or radius with a known uncertainty, that istraceable to national standards of length. The expanded uncer-tainty with a confidence factor of 95 % (K=2) for the torquecalibrator shall not exceed 0.012 % .6.2 Secondary StandardsSecondary torque standards maybe either elastic torque-measuring inst
29、ruments used with amachine for applying torque, or a mechanical or hydraulicmechanism to apply or multiply a deadweight force.6.2.1 The multiplying ratio of a force multiplying systemused as a secondary torque standard shall be measured at notless than ten points over its range with an accuracy of 0
30、.06 %of ratio or better. Some systems may show a systematic changein ratio with increasing force. For these cases the ratio atintermediate points may be obtained by linear interpolationbetween measured values. Deadweights used with multiplying-type secondary standards shall meet the requirements of
31、6.1and 6.1.2. The force exerted on the system shall be calculatedfrom the relationships given in 6.1.1. The force multiplyingsystem shall be checked annually by elastic force measuringinstruments used within their class AA loading ranges to verifythe forces applied by the system are within acceptabl
32、e rangesdefined by this standard. Changes exceeding 0.06 % of appliedforce shall be cause for re-verification of the force multiplyingsystem.6.2.2 Elastic torque-measuring instruments used as second-ary standards shall be calibrated by primary standards and usedonly over the Class AA loading range (
33、see 8.5.2.1).6.2.3 Other types of torque standards may be used and shallbe calibrated. The expanded uncertainty with a confidencefactor of 95% (K=2) shall not exceed 0.06% of the appliedtorque.7. Calibration7.1 Basic PrinciplesThe relationship between the appliedtorque and the deflection of an elast
34、ic torque-measuringinstrument is, in general, not linear. As the torque is applied,5Available from National Oceanic and Atmospheric Administration (NOAA),14th St. and Constitution Ave., NW, Room 6217, Washington, DC 20230, http:/www.noaa.gov.E2428082the shape of the elastic element changes, progress
35、ively alteringits resistance to deformation. The result is that the slope of thetorque-deflection curve changes gradually and uniformly overthe entire range of the instrument. This characteristic offull-scale non-linearity is a stable property of the instrumentthat is changed only by a severe overlo
36、ad or other similarcause.7.1.1 Localized Non-linearitiesSuperimposed on thiscurve are localized non-linearities introduced by the imperfec-tions in the torque indicating system of the instrument. Ex-amples of these imperfections include voltage and sensinginstabilities. Some of these imperfections a
37、re less stable thanthe full-scale non-linearity and may change from one calibra-tion to another.7.1.2 Curve FittingA second degree polynomial fitted tothe observed calibration data using the method of least squares,predicts the deflection values for applied torque throughout theloading range of the
38、elastic torque measuring instrument (see8.4). Such an equation compensates effectively for the full-scale non-linearity, allowing the localized non-linearities toappear as deviations. A statistical estimate, called the uncer-tainty, is made of the width of the band of these deviationsabout the basic
39、 curve. The uncertainty is an estimate of thelimits of error contributed by the instrument when torquevalues measured in service are calculated using the calibrationequation. Actual errors in service will vary for torque valuesapplied under loading and environmental conditions differingfrom those of
40、 the calibration.7.1.3 Curve Fitting for High Resolution DevicesAnnexA1 recommends a procedure for obtaining the degree of thebest-fit calibration curve for these devices.NOTE 3Experimental work by several calibration laboratories infitting higher than second degree polynomials to the observed datai
41、ndicated that, for some devices, use of a higher degree equation mayresult in a lower uncertainty than derived from the second degree fit(ASTM RR: E28-1009). Over-fitting should be avoided. Equations ofgreater than 5th degree should not be used due to the limited number oftorque increments in the ca
42、libration protocol. Numerical errors may occurif calculations are performed with insufficient precision. A device used tomeasure torque not subjected to repair, overloading, modifications, orother significant influence factors which alter its elastic properties, or itssensing characteristics, will l
43、ikely exhibit the same degree of best fit oneach succeeding calibration using this procedure. A device not subjectedto the influence factors outlined above which exhibits continued change ofdegree of best fit with several successive calibrations may not havesufficient performance stability to allow
44、application of the curve fittingprocedure of Annex A1.7.2 Selection of Calibration Torque ValuesA careful se-lection of the different torque values to be applied in acalibration is essential to provide an adequate and unbiasedsample of the full range of the deviations discussed in 7.1 and7.1.1. For
45、this reason, the selection of the calibration torquevalues is made by the standardizing laboratory.An exception tothis, and to the recommendations of 7.2.1 and 7.2.4, is made forspecific torque measurement devices, where the selection ofthe torque values is dictated by the needs of the user.7.2.1 Di
46、stribution of Calibration Torque ValuesDistributethe calibration torque values over the full range of theinstrument, providing, if possible, at least one calibrationtorque for every 10 % interval throughout the range. It is notnecessary, however that these torque values be equally spaced.Calibration
47、 torque values at less than one tenth of capacity arepermissible and tend to give added assurance to the fitting ofthe calibration equation. If the lower limit of the loading rangeof the device (see 8.5.1) is anticipated to be less than one tenthof the maximum torque applied during calibration, then
48、 thetorque values should be applied at or below this lower limit. Inno case should the smallest torque applied be below thetheoretical lower limit of the instrument as defined by thevalues: 400 3 resolution for ClassAloading range and 2000 3resolution for Class AA loading range.7.2.2 Resolution Dete
49、rminationThe resolution of a digitalinstrument is considered to be one increment of the last activenumber on the numerical indicator, provided that the readingdoes not fluctuate by more than plus or minus one incrementwhen no torque is applied to the instrument. If the readingsfluctuate by more than plus or minus one increment, theresolution will be equal to half the range of fluctuation.7.2.3 Number of Calibration Torque ValuesA total of atleast 30 torque applications per mode, clockwise or counterclockwise, is required for a calibration and, of these
