ASTM_E_1270_-_88_2014.pdf

Designation:E127088(Reapproved 2014)Standard Test Method forEqual Arm Balances1This standard is issued under the fixed designation E1270;the number immediately following the designation indicates the 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()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method is designed to test balances whose lever-arm ratio is substantially equal to unity.Although largely superseded by new technologies,equal-arm balances retain a special niche for veryhigh precision weighing of larger samples(usually greater than 1 kg)as well as objects with largebuoyancy(such as gas bottles).Balances of this type can range from simple instruments of moderateprecision(1:10 000)to extremely high precision devices with precision of 1:10 000 000 or better.Anumber of accessory devices may be included for assisting in the weighing process.These devicesmay contribute to errors as well as can the basic lever mechanism.This method is designed to test theentire instrument including the accessories.1.Scope1.1 This test method can be used for testing equal-armbalances of any capacity and sensitivity.The testing procedureshould enable the user to characterize his instrument suffi-ciently to determine whether or not it is suitable for the purposefor which it is to be used.1.2 The characteristics to be examined include:1.2.1 Sensitivity at all loads,1.2.2 Lever arm ratio,1.2.3 Damping ratio(for instruments without accessorydampers),1.2.4 Period of oscillation,1.2.5 Precision,and1.2.6 Linearity and calibration of accessory devices thatprovide on-scale indication of weight.1.3 This standard does not purport to address all of thesafety concerns associated with its use.It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E617 Specification for Laboratory Weights and PrecisionMass Standards3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 capacitymaximum load recommended by the manu-facturer.Usually,the capacity refers to the maximum load oneach pan simultaneously.3.1.2 readabilityvalue of the smallest unit of weightwhich can be read.This may include the estimation of somefraction of a scale division or,in the case of a digital display,will represent the minimum value of the least significant digit.3.1.3 sensitivitysmallest value of weight which will causea change of indication which can be determined by the user.This may be independent of the readability because of thechoice of the reading device used.For example,a magnifyingglass may be used in conjunction with a reading scale toobserve a sensitivity not readily determined without the mag-nifying glass.3.1.4 precisionrepeatability of the balance indication withthe same load under essentially the same conditions.The moreclosely the measurements are grouped,the smaller the index ofprecision will be.The precision should be measured underenvironmental conditions that represent the conditions underwhich the balance is normally used.3.1.5 accuracydegree of agreement of the measurementwith the true value of the magnitude of the quantity measured.3.1.6 linearitycharacteristic of a direct reading device.If adevice is linear,calibration at 2 points(for example,0 andfull-scale)calibrates the device(for example,2 points deter-mine a straight line);if a device is nonlinear,additional pointsare needed(perhaps a great many).1This test method is under the jurisdiction of ASTM Committee E41 onLaboratory Apparatus and is the direct responsibility of Subcommittee E41.06 onWeighing Devices.Current edition approved Nov.1,2014.Published November 2014.Originallyapproved in 1988.Last previous edition approved in 2008 as E127088(2008).DOI:10.1520/E1270-88R14.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.7 standard weightany weight whose mass is given.Since weights are not always available with documentedcorrections,weights defined by class(see Specification E617)may be used if the class has sufficiently small tolerance limitsand there is an understanding that errors perceived as beinginstrumental could be attributed to incorrectly adjustedweights.3.1.8 off-center errorsdifferences in indicated weightwhen a sample is shifted to various positions on the weighingarea of the weighing pan.No separate test is described.3.1.9 full-scale calibration of an accessory deviceindicated reading at equilibrium of an accessory device when astandard weight equal to the full-