1、Designation: E2428 15aStandard Practice forCalibration and Verification of Torque Transducers1This standard is issued under the fixed designation E2428; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 The purpose of this practice is to specify the procedurefor the calibration of torque transducers.NOTE 1Verification by deadweight and a
3、 lever arm is an acceptablemethod of verifying the torque indication of a testing machine. Tolerancesfor weights used are tabulated in Practice E2624; methods for calibrationof the weights are given in NIST Technical Note 577, Methods ofCalibrating Weights for Piston Gages.21.2 The values stated in
4、SI units are to be regarded asstandard. Other metric and inch-pound values are regarded asequivalent when required.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
5、can the results of calibrations performed inaccordance with this practice 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 es
6、tablish appro-priate safety and health practices and determine the 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
7、of Testing Machinesand Devices2.2 ASME Standard:B46.1 Surface Texture42.3 BIPM Standard5JCGM 200 International vocabulary of metrologyBasic andgeneral concepts and associated terms (VIM)3. Terminology3.1 Definitions:3.1.1 primary torque standarda deadweight force appliedthrough a lever arm or wheel,
8、 all displaying metrologicaltraceability to the International System of Units (SI).3.1.1.1 Discussionfor further definition of the term met-rological traceability, refer to the latest revision of JCGM:200.3.1.2 secondary torque standardan instrument ormechanism, the calibration of which has been est
9、ablished by acomparison with a primary torque standard(s).3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration equationa mathematical relationship be-tween deflection and torque established from the calibrationdata for use with the torque transducer in service, sometimescalled the ca
10、libration 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 interpolation of torque valuesbetween calibrated torque values.3.2.2.1 Discussion
11、Such 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 the torque trans-ducer under constant applied torque.3.2.3.1 DiscussionCreep i
12、s expressed as a percentage ofthe output change at a constant applied torque from an initial1This 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 ed
13、ition approved May 15, 2015. Published May 2015. Originallyapproved in 2008. Last previous edition approved in 2015 as E242815. DOI:10.1520/E2428-15A.2Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.3For
14、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 from American Society of Mechanical Engineers (ASME), A
15、SMEInternational Headquarters, Two Park Ave., New York, NY 10016-5990, http:/www.asme.org.5BIPM, Pavillon de Breteuil, F-92312 Svres Cedex. http:/www.bipm.orgCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1time following the achieveme
16、nt of mechanical and 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 instr
17、ument mechanical element. 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 Re
18、covery is expressed 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 mec
19、hanical and electrical 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
20、with noapplied torque.3.2.5.1 DiscussionThe definition of deflection applies tooutput readings 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 tran
21、sducer when the torque transducer iscalibrated 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 t
22、he lower limit of therange of torque 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 u
23、ncertainty, other appropriate errorsources should be considered in determining the measurementuncertainty of the torque transducer in service.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
24、 those inwhich the reading is taken from a dial indicator, are used onlyat the calibrated torque values. These instruments are alsocalled limited-torque devices.3.2.8 loading rangea range of torque values within whichthe lower limit factor is less than the limits of error specifiedfor the instrument
25、 application.3.2.9 torque transducera device or system consisting ofan elastic member combined with a sensing device for mea-suring the strain or deflection of the elastic member under anapplied torque.4. Significance and Use4.1 Testing machines that apply and indicate torque are ingeneral use in ma
26、ny 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 metro-logically traceable to the International System of Units (SI).Practice E2428
27、 describes how these devices are to be cali-brated. The procedures are useful to users of testing machines,manufacturers and providers of torque measuring instruments,calibration laboratories that provide calibration services anddocuments of metrological traceability, and service organiza-tions usin
28、g devices to verify testing machines.5. Reference Standards5.1 Torque-measuring instruments used for the verificationof the torque indication systems of testing machines may becalibrated by either primary or secondary torque standards.5.2 Torque-measuring instruments used as secondary torquestandard
29、s for the calibration of other torque-measuring instru-ments shall be calibrated by primary torque standards.6. Requirements for Torque Standards6.1 Primary Torque StandardTorque, displaying metro-logical traceability to the International System of Units (SI) oflength and mass, and of specific measu
30、rement uncertainty, thatcan be applied to torque measuring devices. Weights used asprimary mass standards shall be made of rolled, forged, or castmetal.Adjustment cavities shall be closed by threaded plugs orsuitable seals. External surfaces of weights shall have a surface(Roughness Average or Ra) o
31、f 3.2m or less as specified inASME B46.1.6.1.1 The force exerted by a weight in air is calculated asfollows:Force 5 Mg/9.80665!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
32、 d, and9.80665 = the factor converting SI units of force into thecustomary units of force. For SI units, this factoris not used.6.1.2 The masses of the weights shall be determined bycomparison with reference standards metrologically traceableto the International System of Units (SI) for mass. The lo
33、calvalue of the acceleration due to gravity, calculated within0.0001 m/s2(10 milligals), may be obtained from the NationalGeodetic Information Center, National Oceanic and Atmo-spheric Administration.6NOTE 2If M, the mass of the weight, is in pounds, the force will bein pound-force units (lbf). If M
34、 is in kilograms, the force will be in6Available from National Oceanic and Atmospheric Administration (NOAA),14th St. and Constitution Ave., NW, Room 6217, Washington, DC 20230, http:/www.noaa.gov.E2428 15a2kilogram-force units (kgf). These customary force units are related to thenewton (N), the SI
35、unit of force, by the following relationships:1 lbf = 4.44822 N1 kgf = 9.80665 N (exact)The newton (N) is defined as the force applied to a 1-kg mass thatproduces an acceleration of 1 m/s/s.The pound-force (lbf) is defined as the force applied to a 1-lb mass thatproduces an acceleration of 9.80665 m
36、/s/s.The kilogram-force (kgf) is defined as the force applied to a 1-kg mass thatproduces an acceleration of 9.80665 m/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 ismetrologically traceable to the International System of Unit
37、s(SI) for length. The expanded uncertainty with a confidencefactor of 95 % (K=2) for the torque calibrator shall not exceed0.012 % .6.2 Secondary Torque StandardsSecondary torque stan-dard is typically a torque transducer used with a machine forapplying torque, or a mechanical or hydraulic mechanism
38、 toapply or multiply a 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 0.06 %of ratio or better. Some systems may show a systematic changein ratio with increasing force.
39、 For these cases the ratio atintermediate points may be obtained by linear interpolationbetween measured values. Deadweights used with multiplying-type secondary torque standards shall meet the requirements of6.1 and 6.1.2. The force exerted on the system shall becalculated from the relationships gi
40、ven in 6.1.1. The forcemultiplying system shall be checked annually by elastic forcemeasuring instruments used within their class AA loadingranges to verify the forces applied by the system are withinacceptable ranges defined by this standard. Changes exceeding0.06 % of applied force shall be cause
41、for re-verification of theforce multiplying system.LLFc5 =LLF121LLF221.1LLFn2(2)where:LLFC= Lower limit factor of the combination, andLLF1, 2, . n= Lower limit factor of the individualinstruments6.2.2 Torque transducers used as secondary torque standardsshall be calibrated by primary torque standard
42、s and used onlyover the Class AA loading range (see 8.6.2.1).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
43、the appliedtorque and the deflection of a torque transducer is, in general,not linear. 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 continuous
44、ly over the entire rangeof the instrument. This characteristic curve is a stable propertyof the instrument that is changed only by a severe overload orother similar cause.7.1.1 Superposed on this curve are local variations ofinstrument readings introduced by imperfections in the torquetransducer. Ex
45、amples of imperfections include instabilities inexcitation voltage, voltage measurement, 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 Fitti
46、ngTo determine the torque-deflectioncurve of the torque transducer, known torque 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
47、 throughout the loading range. Such an equationcompensates effectively for the nonlinearity 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
48、 the data to the curve fit equation.Astatistical estimate,called the Lower Limit 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 of
49、uncertainty contributed by the torque transducer when torquevalues measured in service 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 th
