1、Designation: E2428 14Standard Practice forCalibration of Torque-Measuring Instruments for Verifyingthe Torque Indication of Torque Testing Machines1This standard is issued under the fixed designation E2428; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is to specify procedure for the calibrationof elastic torque-measuri
3、ng 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 E2624; methods forcalibration of the weights are given in NIST Technical Note 577, Methodsof Cal
4、ibrating 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. Combiningvalues from the two systems
5、 may result in non-conformancewith the standard.1.3 This practice is intended for the calibration of statictorque measuring instruments. The practice is not applicablefor dynamic or high-speed torque calibrations ormeasurements, nor can the results of calibrations performed inaccordance with this pr
6、actice be assumed valid for dynamic orhigh speed torque measurements.1.4 This standard does not purport 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
7、applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE2624 Practice for Torque Calibration of Testing Machinesand Devices2.2 American National Standard:B46.1
8、Surface Texture4ELASTIC TORQUE-MEASURING INSTRUMENTS3. Terminology3.1 Definitions:3.1.1 elastic torque-measuring 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 me
9、mber under anapplied torque.3.1.2 primary torque standardsa deadweight force appliedthrough a lever arm or wheel, with a calibrated length or radiusof a known uncertainty, that is traceable to national standards.3.1.3 secondary torque standardan instrument ormechanism, that has been calibrated by a
10、comparison with aprimary torque standard(s).3.1.4 torquea vector product of force and length, ex-pressed 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 deflection and torque established from the calibrat
11、iondata for use with the torque transducer in service, sometimescalled the calibration curve.3.2.1.1 DiscussionTorque transducers have torque-to-deflection relationships that can be fitted to polynomial equa-tions.3.2.2 continuous-reading devicea class of instrumentswhose characteristics permit inte
12、rpolation 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 8.5).3.2.3 creepThe change in deflection of t
13、he torque trans-ducer under constant applied torque.1This practice is under the jurisdiction ofASTM Committee E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved Oct. 15, 2014. Published
14、May 2015. Originallyapproved in 2008. Last previous edition approved in 2008 as E242808. DOI:10.1520/E2428-14.2Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.3For referenced ASTM standards, visit the AST
15、M 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 from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036
16、, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.3.1 DiscussionCreep is expressed as a percentage ofthe output change at a constant applied torque from an initialtime following the achievement of mechanical and
17、 electricalstability and the time at which the test is concluded.Valid creeptests may require the use of primary torque standards tomaintain adequate stability of the applied torque during the testtime interval. Creep results from a time dependent, elasticdeformation of the instrument mechanical ele
18、ment. In the caseof torque transducers, creep is adjusted by strain gage designand process modifications to reduce the strain gage response tothe inherent time-dependent elastic deflection.3.2.4 creep recoveryThe non-return to zero following acreep test.3.2.4.1 DiscussionCreep Recovery is expressed
19、as a per-centage difference of the output change at zero torque follow-ing a creep test and the initial zero torque output at theinitiation of the creep test divided by the output during thecreep test. The zero-torque measurement is taken at a timefollowing the achievement of mechanical and electric
20、al stabil-ity and a time equal to the creep test time. For many torquetransducers, the creep characteristic and the creep recoverycharacteristic are approximate mirror images.3.2.5 deflectionthe difference between the readings of aninstrument under applied torque and the reading with noapplied torqu
21、e. The definition of deflection applies to outputreadings in electrical units as well as readings in units oftorque.3.2.6 lower limit factor, LLFA statistical estimate of thelimits of error of torque values computed from the calibrationequation of the torque transducer when the torque transducer isc
22、alibrated in accordance with this practice.3.2.6.1 DiscussionThe lower limit factor is used as onefactor that may establish the lower limit of the range of torquevalues over which the torque transducer can be used. Otherfactors evaluated in the establishment of the lower limit of therange of torque
23、values are the resolution of the torquetransducer and the lowest nonzero torque applied in thecalibration load sequence.3.2.6.2 DiscussionThe lower limit factor was termed un-certainty in previous editions of E2428. While the lower limitfactor is a component of uncertainty, other appropriate errorso
24、urces should be considered in determining the measurementuncertainty of the torque transducer in service.3.2.7 readinga numerical value indicated on the scale,dial, electrical output or digital display of a torque- measuringinstrument for a given torque.3.2.8 resolutionthe smallest change in reading
25、 or indica-tion appropriate to the scale, dial, or display of the torquemeasuring instrument.3.2.9 specific torque devicean alternative class of instru-ments not amenable to the use of a calibration equation.3.2.9.1 DiscussionSuch instruments, usually those inwhich the reading is taken from a dial i
26、ndicator, are used onlyat the calibrated torque values.3.2.10 torque rangea range of torque values within whichthe uncertainty is less than the limits of error specified for theinstrument application.4. Significance and Use4.1 Testing machines that apply and indicate torque are ingeneral use in many
27、 industries. Practice E2624 has beenwritten to provide a practice for the torque verification of thesemachines. A necessary element in Practice E2624 is the use ofdevices whose torque characteristics are known to be traceableto national standards. Practice E2428 describes how thesedevices are to be
28、calibrated. The procedures are useful to usersof torque testing machines, manufacturers and providers oftorque measuring instruments, calibration laboratories thatprovide calibration services and documents, and service orga-nizations using devices to verify torque testing machines.5. Reference Stand
29、ards5.1 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 calibration of other torque-measuring instrumentss
30、hall 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 devices. Weights used as primary mass standard
31、s 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 air is calculated asfollows:Force 5 Mg/9.8066
32、5!1 2 d/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 units of force. For SI units, this factoris not us
33、ed.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 the National Geodetic Information Center,Nation
34、al 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 thenewton (N), the SI unit of force, by the foll
35、owing relationships:1 kgf = 9.80665 N (exact)1 lbf = 4.44822 N5Available from National Oceanic and Atmospheric Administration (NOAA),14th St. and Constitution Ave., NW, Room 6217, Washington, DC 20230, http:/www.noaa.gov.E2428 142The pound-force (lbf) is defined as that force which, applied to a 1-l
36、bmass, 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 length 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 torquecalibra
37、tor shall not exceed 0.012 % .6.2 Secondary StandardsSecondary torque standards maybe either elastic torque-measuring instruments 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 s
38、ystemused as a secondary torque standard shall be measured at notless than ten points over its range with an accuracy of 0.06 %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 interp
39、olationbetween measured values. Deadweights used with multiplying-type secondary standards shall meet the requirements of 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 mea
40、suringinstruments used within their classAAloading ranges to verifythe forces applied by the system are within acceptable rangesdefined by this standard. Changes exceeding 0.06 % of appliedforce shall be cause for re-verification of the force multiplyingsystem.LLFc5 =LLF121LLF221.1LLFn2(2)where:LLFC
41、= Lower limit factor of the combination, andLLF1, 2, . n= Lower limit factor of the individualinstruments6.2.2 Elastic torque-measuring instruments used as second-ary standards shall be calibrated by primary standards and usedonly over the Class AA loading range (see 8.6.2.1).6.2.3 Other types of to
42、rque 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 a torque transducer is, in general,not linea
43、r. As the torque is applied, the shape of the elasticelement changes, progressively altering its resistance to defor-mation. The result is that the slope of the torque-deflectioncurve changes gradually and continuously over the entire rangeof the instrument. This characteristic of curve is a stablep
44、roperty of the instrument that is changed only by a severeoverload or other similar cause.7.1.1 Superposed on this curve are local variations ofinstrument readings introduced by imperfections in the torquetransducer. Examples of imperfections include instabilities inexcitation voltage, voltage measu
45、rement, or ratio-metric volt-age measurement in a torque transducer. Some of theseimperfections are less stable than the characteristic curve andmay change significantly from one calibration to another.7.1.2 Curve FittingTo determine the torque-deflectioncurve of the torque transducer, known torque
46、values are appliedand the resulting deflections are measured throughout the rangeof the torque transducer. A polynomial equation is fitted to thecalibration data by the least squares method to predict deflec-tion values throughout the loading range. Such an equationcompensates effectively for the no
47、nlinearity of the calibrationcurve. The standard deviation determined from the differenceof each measured deflection value from the value derived fromthe polynomial curve at that torque provides a measure of theerror of the data to the curve fit equation.Astatistical estimate,called the Lower Limit
48、Factor, LLF, is derived from thecalculated standard deviation and represents the width of theband of these deviations about the basic curve with a probabil-ity of 95%. The LLF is, therefore, an estimate of one source ofuncertainty contributed by the torque transducer when torquevalues measured in se
49、rvice are calculated by means of thecalibration equation. Actual errors in service are likely to bedifferent if torque values are applied under mechanical andenvironmental conditions differing from those of calibration.Other sources of uncertainty could increase the uncertainty ofmeasurement of the torque transducer in service.NOTE 3While it is the responsibility of the calibration laboratory tocalibrate the torque transducer in accordance with the requirements of thispractice it is the responsibility of the user to determine the uncertainty ofthe t
