1、Designation: E2428 14E2428 15Standard 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 adopti
2、on or, in 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 calibration of elastic torqu
3、e-measuring instruments.NOTE 1Verification by deadweight and a lever arm is an acceptable method of verifying the torque indication of a torque testing machine. Tolerancesfor weights used are tabulated in Practice E2624; methods for calibration of the weights are given in NIST Technical Note 577, Me
4、thods of CalibratingWeights for Piston Gages.21.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from t
5、hetwo systems may result in non-conformance with the standard.Other metric and inch-pound values are regarded as equivalent whenrequired.1.3 This practice is intended for the calibration of static torque measuring instruments. The practice is not applicable fordynamic or high-speed torque calibratio
6、ns or measurements, nor can the results of calibrations performed in accordance with thispractice be assumed valid for dynamic or high speed torque measurements.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the u
7、ser of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E29 Practice for Using Significant Digits in Test Data to Determine Conformance with SpecificationsE2624 Practice
8、 for Torque Calibration of Testing Machines and Devices2.2 American National Standard:B46.1 Surface Texture42.3 BIPM Standard5JCGM 200 International vocabulary of meterologyBasic and general concepts and associated terms (VIM)ELASTIC TORQUE-MEASURING INSTRUMENTS3. Terminology3.1 Definitions:3.1.1 el
9、astic torque-measuring devicea device or system consisting of an elastic member combined with a device forindicating the measured values (or a quantity proportional to the measured value) of deformation of the member under an appliedtorque.1 This practice is under the jurisdiction of ASTM Committee
10、E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.01 on Calibration ofMechanical Testing Machines and Apparatus.Current edition approved Oct. 15, 2014Feb. 1, 2015. Published May 2015. Originally approved in 2008. Last previous edition approved in 20082014 as E242808.14.D
11、OI: 10.1520/E2428-14.10.1520/E2428-15.2 Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm
12、.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.5 BIPM, Pavillon de Breteuil, F-92312 Svres Ced
13、ex. http:/www.bipm.orgThis document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that u
14、sers consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 primary torque stand
15、ardsstandarda deadweight force applied through a lever arm or wheel, with a calibrated lengthor radius of a known uncertainty, that is traceable to national standards.all displaying metrological traceability to the InternationalSystem of Units (SI).3.1.2.1 Discussionfor further definition of the ter
16、m metrological traceability, refer to the latest revision of JCGM:200.3.1.3 secondary torque standardan instrument or mechanism, that has been calibrated by a comparison with a primary torquestandard(s).3.1.4 torquea vector product of force and length, expressed in terms of N-m, lbf-in., etc.3.2 Def
17、initions of Terms Specific to This Standard:3.2.1 calibration equationa mathematical relationship between deflection and torque established from the calibration data foruse with the torque transducer in service, sometimes called the calibration curve.3.2.1.1 DiscussionTorque transducers have torque-
18、to-deflection relationships that can be fitted to polynomial equations.3.2.2 continuous-reading devicea class of instruments whose characteristics permit interpolation of torque values betweencalibrated torque values.3.2.2.1 DiscussionSuch instruments usually have torque-to-deflection relationships
19、that can be fitted to polynomial equations. Departures from thefitted curve are reflected in the uncertainty (see 8.5).3.2.3 creepThe change in deflection of the torque transducer under constant applied torque.3.2.3.1 DiscussionCreep is expressed as a percentage of the output change at a constant ap
20、plied torque from an initial time following the achievementof mechanical and electrical stability and the time at which the test is concluded. Valid creep tests may require the use of primarytorque standards to maintain adequate stability of the applied torque during the test time interval. Creep re
21、sults from a timedependent, elastic deformation of the instrument mechanical element. In the case of torque transducers, creep is adjusted by straingage design and process modifications to reduce the strain gage response to the inherent time-dependent elastic deflection.3.2.4 creep recoveryThe non-r
22、eturn to zero following a creep test.3.2.4.1 DiscussionCreep Recovery is expressed as a percentage difference of the output change at zero torque following a creep test and the initialzero torque output at the initiation of the creep test divided by the output during the creep test. The zero-torque
23、measurement istaken at a time following the achievement of mechanical and electrical stability and a time equal to the creep test time. For manytorque transducers, the creep characteristic and the creep recovery characteristic are approximate mirror images.3.2.5 deflectionthe difference between the
24、readings of an instrument under applied torque and the reading with no appliedtorque. The definition of deflection applies to output readings in electrical units as well as readings in units of torque.3.2.6 lower limit factor, LLFA statistical estimate of the limits of error of torque values compute
25、d from the calibrationequation of the torque transducer when the torque transducer is calibrated in accordance with this practice.3.2.6.1 DiscussionThe lower limit factor is used as one factor that may establish the lower limit of the range of torque values over which the torquetransducer can be use
26、d. Other factors evaluated in the establishment of the lower limit of the range of torque values are theresolution of the torque transducer and the lowest nonzero torque applied in the calibration load sequence.3.2.6.2 DiscussionE2428 152The lower limit factor was termed uncertainty in previous edit
27、ions of E2428. While the lower limit factor is a component ofuncertainty, other appropriate error sources should be considered in determining the measurement uncertainty of the torquetransducer in service.3.2.7 readinga numerical value indicated on the scale, dial, electrical output or digital displ
28、ay of a torque- measuringinstrument for a given torque.3.2.8 resolutionthe smallest change in reading or indication appropriate to the scale, dial, or display of the torque measuringinstrument.3.2.9 specific torque devicean alternative class of instruments not amenable to the use of a calibration eq
29、uation.3.2.9.1 DiscussionSuch instruments, usually those in which the reading is taken from a dial indicator, are used only at the calibrated torque values.3.2.10 torque rangea range of torque values within which the uncertainty is less than the limits of error specified for theinstrument applicatio
30、n.4. Significance and Use4.1 Testing machines that apply and indicate torque are in general use in many industries. Practice E2624 has been written toprovide a practice for the torque verification of these machines.Anecessary element in Practice E2624 is the use of devices whosetorque characteristic
31、s are known to be traceable to national standards. the International System of Units (SI). Practice E2428describes how these devices are to be calibrated. The procedures are useful to users of torque testing machines, manufacturers andproviders of torque measuring instruments, calibration laboratori
32、es that provide calibration services and documents, documents ofmetrological traceability, and service organizations using devices to verify torque testing machines.5. Reference Standards5.1 Torque-measuring instruments used for the verification of the torque indication systems of torque testing mac
33、hines may becalibrated by either primary or secondary standards.5.2 Torque-measuring instruments used as secondary standards for the calibration of other torque-measuring instruments shallbe calibrated by primary standards.6. Requirements for Torque Standards6.1 Primary StandardTorque, with traceabi
34、lity derived from national standards of length and mass, and of specificmeasurement uncertainty, that can be applied to torque measuring devices. Weights used as primary mass standards shall be madeof rolled, forged, or cast metal.Adjustment cavities shall be closed by threaded plugs or suitable sea
35、ls. External surfaces of weightsshall have a finish of 3.2m (Ra) or less as specified in ANSI B46.1.6.1.1 The force exerted by a weight in air is calculated as follows:Force5Mg/9.80665!12d/D! (1)where:M = mass of the weight,g = local acceleration due to gravity, m/s2,d = air density (approximately 1
36、.2 kg/m3),D = density of the weight in the same units as d, and9.80665 = the factor converting SI units of force into the customary units of force. For SI units, this factor is not used.6.1.2 The masses of the weights shall be determined by comparison with reference standards traceable to the nation
37、al standardsof International System of Units (SI) for mass. The local value of the acceleration due to gravity, calculated within 0.0001 m/s2 (10milligals), may be obtained from the National Geodetic Information Center, National Oceanic and Atmospheric Administration.6NOTE 2If M, the mass of the wei
38、ght, is in pounds, the force will be in pound-force units (lbf). If M is in kilograms, the force will be in kilo gram-forcekilogram-force units (kgf). These customary force units are related to the newton (N), the SI unit of force, by the following relationships:1 kgf = 9.80665 N (exact)1 lbf = 4.44
39、822 N1 lbf = 4.44822 N1 kgf = 9.80665 N (exact)The newton (N) is defined as the force applied to a 1-kg mass that produces an acceleration of 1 m/s/s.6 Available from National Oceanic and Atmospheric Administration (NOAA), 14th St. and Constitution Ave., NW, Room 6217, Washington, DC 20230,http:/www
40、.noaa.gov.E2428 153The pound-force (lbf) is defined as thatthe force which, applied to a 1-lb mass, would producemass that produces an acceleration of 32.1747 f/s/s.9.80665m/s/s.The kilogram-force (kgf) is defined as the force applied to a 1-kg mass that produces an acceleration of 9.80665 m/s/s.6.1
41、.3 The lever arm or wheel shall be calibrated to determine the length or radius with a known uncertainty, that is traceableto national standards of length. The expanded uncertainty with a confidence factor of 95 % (K=2) for the torque calibrator shallnot exceed 0.012 % .6.2 Secondary StandardsSecond
42、ary torque standards may be either elastic torque-measuring instruments used with a machinefor applying torque, or a mechanical or hydraulic mechanism to apply or multiply a deadweight force.6.2.1 The multiplying ratio of a force multiplying system used as a secondary torque standard shall be measur
43、ed at not less thanten points over its range with an accuracy of 0.06 % of ratio or better. Some systems may show a systematic change in ratio withincreasing force. For these cases the ratio at intermediate points may be obtained by linear interpolation between measured values.Deadweights used with
44、multiplying-type secondary standards shall meet the requirements of 6.1 and 6.1.2. The force exerted onthe system shall be calculated from the relationships given in 6.1.1. The force multiplying system shall be checked annually byelastic force measuring instruments used within their classAAloading r
45、anges to verify the forces applied by the system are withinacceptable ranges defined by this standard. Changes exceeding 0.06 % of applied force shall be cause for re-verification of the forcemultiplying system.LLFc 5=LLF121LLF221.1LLFn2 (2)where:LLFC = Lower limit factor of the combination, andLLF1
46、, 2, . n = Lower limit factor of the individual instruments6.2.2 Elastic torque-measuring instruments used as secondary standards shall be calibrated by primary standards 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 shall be calibra
47、ted. The expanded uncertainty with a confidence factorof 95% (K=2) shall not exceed 0.06% of the applied torque.7. Calibration7.1 Basic PrinciplesThe relationship between the applied torque and the deflection of a torque transducer is, in general, notlinear. As the torque is applied, the shape of th
48、e elastic element changes, progressively altering its resistance to deformation. Theresult is that the slope of the torque-deflection curve changes gradually and continuously over the entire range of the instrument.This characteristic of curve is a stable property of the instrument that is changed o
49、nly by a severe overload or other similar cause.7.1.1 Superposed on this curve are local variations of instrument readings introduced by imperfections in the torque transducer.Examples of imperfections include instabilities in excitation voltage, voltage measurement, or ratio-metric voltage measurementin a torque transducer. Some of these imperfections are less stable than the characteristic curve and may change significantly fromone calibration to another.7.1.2 Curve FittingTo determine the torque-deflection curve of the torque transducer,
