1、Designation: E74 18Standard Practices forCalibration and Verification for Force-MeasuringInstruments1This standard is issued under the fixed designation E74; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision
2、.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 The purpose of these practices is to specify proc
3、eduresfor the calibration of force-measuring instruments. Proceduresare included for the following types of instruments:1.1.1 Elastic force-measuring instruments, and1.1.2 Force-multiplying systems, such as balances and smallplatform scales.NOTE 1Verification by deadweight loading is also an accepta
4、blemethod of verifying the force indication of a testing machine. Tolerancesfor weights for this purpose are given in Practices E4; methods forcalibration of the weights are given in NIST Technical Note 577(1)2,Methods of Calibrating Weights for Piston Gages.1.2 The values stated in SI units are to
5、be regarded as thestandard. Other metric and inch-pound values are regarded asequivalent when required.1.3 These practices are intended for the calibration of staticforce measuring instruments. It is not applicable for dynamicor high speed force calibrations, nor can the results ofcalibrations perfo
6、rmed in accordance with these practices beassumed valid for dynamic or high speed force 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, health
7、, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of Internatio
8、nal Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3E4 Practices for Force Verification of Testing MachinesE29 Practice for Using Significant Digits in Test Data toDetermine Conformanc
9、e with SpecificationsE1012 Practice for Verification of Testing Frame and Speci-men Alignment Under Tensile and Compressive AxialForce Application2.2 ASME Standard:B46.1 Surface Texture, Surface Roughness, Waviness andLay4FORCE-MEASURING INSTRUMENTS3. Terminology3.1 Definitions:3.1.1 force-measuring
10、 instrumenta system consisting ofan elastic member combined with an appropriate instrument forindicating the magnitude (or a quantity proportional to themagnitude) of deformation of the member under an appliedforce.3.1.2 primary force standarda deadweight force applieddirectly without intervening me
11、chanisms such as levers, hy-draulic multipliers, or the like, whose mass has been deter-mined by comparison with reference standards traceable to theInternational System of Units (SI) (2) of mass.3.1.3 secondary force standardan instrument ormechanism, the calibration of which has been established b
12、ycomparison with primary force standards.3.2 Definitions of Terms Specific to This Standard:3.2.1 calibration equationa mathematical relationship be-tween deflection and force established from the calibration datafor use with the instrument in service, sometimes called thecalibration curve.1These pr
13、actices are under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.01 onCalibration of Mechanical Testing Machines and Apparatus.Current edition approved Feb. 1, 2018. Published April 2018. Originallyapproved in 1947. Last previous edit
14、ion approved in 2013 as E74 13a. DOI:10.1520/E0074-18.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandar
15、ds volume information, refer to the standards Document Summary page onthe ASTM website.4Available from American Society of Mechanical Engineers (ASME), ASMEInternational Headquarters, Two Park Ave., New York, NY 10016-5990, http:/www.asme.org.Copyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by
17、the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.2 continuous-reading instumenta class of instrumentswhose characteristics permit interpolation of forces betweencalibrated forces.3.2.2.1 DiscussionSuch instruments usually have force-to-deflection relationships that can b
18、e fitted to polynominalequations.3.2.3 creepThe change in deflection of the force-measuring instrument under constant applied force.3.2.3.1 DiscussionCreep is expressed as a percentage ofthe output change at a constant applied force from an initialtime following the achievement of mechanical and ele
19、ctricalstability and the time at which the test is concluded.Valid creeptests may require the use of primary force standards to maintainadequate stability of the applied force during the test timeinterval. Creep results from a time dependent, elastic deforma-tion of the instrument mechanical element
20、. In the case of straingage based force-measuring instruments, creep is adjusted bystrain gage design and process modifications to reduce thestrain gage response to the inherent time-dependent elasticdeflection.3.2.4 creep recoveryThe change in deflection of the force-measuring instrument after the
21、removal of force following acreep test.3.2.4.1 DiscussionCreep Recovery is expressed as a per-centage difference of the output change at zero force followinga creep test and the initial zero force output at the initiation ofthe creep test divided by the output during the creep test. Thezero force me
22、asurement is taken at a time following theachievement of mechanical and electrical stability and a timeequal to the creep test time. For many force-measuringinstruments, the creep characteristic and the creep recoverycharacteristic are approximate mirror images.3.2.5 deflectionthe difference between
23、 the reading of aninstrument under applied force and the reading with no appliedforce.3.2.5.1 DiscussionThis definition applies to instrumentsthat have electrical outputs as well as those with mechanicaldeflections.3.2.6 verified range of forcesin the case of force-measuring instruments, the range o
24、f indicated forces for whichthe force-measuring instrument gives results within the per-missible variations specified.3.2.7 readinga numerical value indicated on the scale,dial, or digital display of a force-measuring instrument under agiven force.3.2.8 resolutionthe smallest reading or indication a
25、ppro-priate to the scale, dial, or display of the force measuringinstrument.3.2.9 specific force-measuring instrumentan alternativeclass of instruments not amenable to the use of a calibrationequation.3.2.9.1 DiscussionSuch instruments, usually those inwhich the reading is taken from a dial indicato
26、r, are used onlyat the calibrated forces. These instruments are also calledlimited force measuring instruments.3.2.10 lower limit factor, LLFa statistical estimate of theerror in forces computed from the calibration equation of aforcemeasuring instrument when the instrument is calibratedin accordanc
27、e with these practices.3.2.10.1 DiscussionThe lower limit factor was termed“Uncertainty” in previous editions of E74. The lower limitfactor is used to calculate the lower end of the verified range offorces, see 8.5. Other factors evaluated in establishing thelower limit of the verified range of forc
28、es are the resolution ofthe instrument and the lowest non-zero force applied in thecalibration force sequence, The lower limit factor is onecomponent of the measurement uncertainty. Other uncertaintycomponents should be included in a comprehensive measure-ment uncertainty analysis. See Appendix X1 f
29、or an example ofmeasurement uncertainty analysis.4. Significance and Use4.1 Testing machines that apply and indicate force are ingeneral use in many industries. Practices E4 has been written toprovide a practice for the force verification of these machines.A necessary element in Practices E4 is the
30、use of force-measuring instruments whose force characteristics are knownto be traceable to the SI. Practices E74 describes how theseforce-measuring instruments are to be calibrated. The proce-dures are useful to users of testing machines, manufacturersand providers of force-measuring instruments, ca
31、libration labo-ratories that provide the calibration of the instruments and thedocuments of traceability, service organizations that use theforce-measuring instruments to verify testing machines, andtesting laboratories performing general structural test measure-ments.5. Reference Standards5.1 Force
32、-measuring instruments used for the verification ofthe force indication systems of testing machines may becalibrated by either primary or secondary force standards.5.2 Force-measuring instruments used as secondary forcestandards for the calibration of other force-measuring instru-ments shall be cali
33、brated by primary force standards. Anexception to this rule is made for instruments having capacitiesexceeding the range of available primary force standards.Currently the maximum primary force-standard facility in theUnited States is 1 000 000-lbf (4.4-MN) deadweight calibra-tion machine at the Nat
34、ional Institute of Standards and Tech-nology.6. Requirements for Force Standards6.1 Primary Force StandardsWeights used as primaryforce standards shall be made of rolled, forged, or cast metal.Adjustment cavities shall be closed by threaded plugs orsuitable seals. External surfaces of weights shall
35、have a finish(Roughness Average or Ra) of 3.2 m (125 in.) or less asspecified in ASME B46.1.6.1.1 The force exerted by a weight in air is calculated asfollows:Force 5Mg9.80665S1 2dDD(1)E74182where:M = mass of the weight,g = local acceleration due to gravity, m/s2,d = air density (approximately 0.001
36、2 Mg/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 used.6.1.2 The masses of the weights shall be determined within0.005 % of their values by comparison with reference stan-d
37、ards traceable to the International System of Units (SI) (2) formass. The local value of the acceleration due to gravity,calculated within 0.0001 m/s2(10 milligals), may be obtainedfrom the National Geodetic Information Center, NationalOceanic and Atmospheric Administration.5NOTE 2If M, the mass of
38、the weight, is in pounds, the force will bein pound-force units (lbf). If M is in kilograms, the force will be inkilogram-force units (kgf). These customary force units are related to thenewton (N), the SI unit of force, by the following relationships:1 kgf 5 9.80665N exact! (2)1 lbf 5 4.44822NThe N
39、ewton is defined as that force which, applied to a 1-kg mass,would produce an acceleration of 1 m/s/s.The pound-force (lbf) is defined as that force which, applied to a 1-lbmass, would produce an acceleration of 9.80665 m/s/s.The kilogram-force (kgf) is defined as that force which, applied to a1-kg
40、mass, would produce an acceleration of 9.80665 m/s/s.6.2 Secondary Force StandardsSecondary force standardsmay be either force-measuring instruments used in conjunctionwith a machine or mechanism for applying force, or some formof mechanical or hydraulic mechanism to multiply a relativelysmall deadw
41、eight force. Examples of the latter form includesingle- and multiple-lever systems or systems in which a forceacting on a small piston transmits hydraulic pressure to a largerpiston.6.2.1 Force-measuring instruments used as secondary forcestandards shall be calibrated by primary force standards andu
42、sed only over the Class AA verified range of forces (see8.6.3.1). Secondary force standards having capacities exceed-ing 1 000 000 lbf (4.4 MN) are not required to be calibrated byprimary force standards. Several secondary force standards ofequal compliance may be combined and loaded in parallel tom
43、eet special needs for higher capacities. The lower limit factor(see 8.5) of such a combination shall be calculated by addingin quadrature using the following equation:LLFc5 = LLF021LLF121LLF221.LLFn2(3)where:LLFc= lower limit factor of the combination, andLLF0, 1,2.n= lower limit factor of the indiv
44、idual instru-ments.6.2.2 The multiplying ratio of a force-multiplying systemused as a secondary force standard shall be measured at not lessthan three points over its range with an accuracy of 0.05 % ofratio or better. Some systems may show a systematic change inratio with increasing force. In such
45、cases the ratio at interme-diate points may be obtained by linear interpolation betweenmeasured values. Deadweights used with multiplying-typesecondary force 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.
46、1. The force-multiplyingsystem shall be checked annually by elastic force-measuringinstruments used within their class AA verified range of forcesto ascertain whether the forces applied by the system are withinacceptable ranges as defined by this standard. Changes exceed-ing 0.05 % of applied force
47、shall be cause for reverification ofthe force multiplying system.7. Calibration7.1 Basic PrinciplesThe relationship between the appliedforce and the deflection of an elastic force-measuring instru-ment is, in general, not linear. As force is applied, the shape ofthe elastic element changes, progress
48、ively altering its resis-tance to deformation. The result is that the slope of theforce-deflection curve changes gradually and continuouslyover the entire range of the instrument. This characteristiccurve is a stable property of the instrument that is changed onlyby a severe overload or other simila
49、r cause.7.1.1 Superposed on this curve are local variations ofinstrument readings introduced by imperfections in the force-indicating system of the instrument. Examples of imperfectionsinclude: non-uniform scale or dial graduations, irregular wearbetween the contacting surfaces of the vibrating reed andbutton in a proving ring, and instabilities in excitation voltage,voltage measurement, or ratio-metric voltage measurement in aload cell system. Some of these imperfections are less stablethan the characteristic curve and may change significantly fromone ca
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