1、ASTM D5595 94=0759530 0553727 T5T(#/b Designation:D 5595-94 AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race St.Philadelphia,Pa 19103 Reprinted Irom the Annual Book of ASTM Standards.Copyright ASTM li not listed in the current combined index.will appear in the neai edtion Standard Practice for D
2、etermining Buoyancy Corrections During Precision Weighing of Low-Density Samples This standard is issued under the fixed designation D 5595;the number immediately following the designation indicates the year of original adoption or.in the case of revision,the year of last revision.A number in parent
3、heses indicates the year of last reapproval.A superscript epsilon(c)indicates an editorial change since the last revision or reapproval.1.Scope 1.I This practice covers the procedures used to determine true sample mass from scale readings,by determining the effective volume of the sample and applyin
4、g a correction for the effects of the buoyancy of the air in which samples are weighed.I.2 This practice provides the information required to determine when buoyancy corrections are warranted,and when they can be safely ignored.1.3 This practice is used whenever a small difference in mass between tw
5、o low-density samples(or the same sample on reweighing)must be determined with a high level of accuracy,to achieve the desired test method accuracy.1.4 Refer to Practice E 380 in using this practice.NOTE I-M a s s difference errors may be a major source of inaccuracy in methods that do not produce p
6、recision results even after careful weighing.The use of this procedure may be warranted,therefore,in test methods that presently display a precision of only I20%,and may subsequently display better precision and repeatability,as well as lower thresholds.1.5 This standard does not purport to address
7、all o f the safety concerns,if any,associated with its use.It is the responsibility o f the user o f this standard to establish appro-priate safity and health practices and determine the applica-bility o f regulatory limitations prior to use.2.Referenced Documents 2.I ASTM Standards:E 380 Practice f
8、or Use of the International System of Units(SI)(the Modem Metric System)2 D 1356 Terminology Relating to Sampling and Analysis of Atmospheres3 D 363 I Test Methods for Measuring Surface Atmospheric Pressure D 4230 Test Method for Measuring Humidity with Cooled-Surface Condensation(Dew-Point)Hygromet
9、er D 3670 Practice for Determination of Precision and Accu-racy of Methods of Committee D-22 3.Terminology terms used in this practice.3.1 Refer to Terminology D 1356,for definitions of other I This practice is under the jurisdiction of ASTM Committee D22 on Sampling and Analysis of Atmospheres and
10、is the direct responsibility of Subcommittee D22.01 on Quality Control.Current edition approved Aug.IS,1994.Published December 1994.2 Annual Book oIASTM Standards,Vol 14.02.Annual Book o f ASTM Siandards,Vol 1 1.03.3.2 Description o f Terms Specijk to his Standard:3.2.1 balance-precision device that
11、 is used to determine the weight or pass of a sample.Such a device usually requires ongoing calibration,but users seldom employ a correction for buoyancy effects,as presented in this proce-dure.It may be a one-pan or two-pan balance,or a device that uses an electronic force measuring system to provi
12、de a reading of weight(sometimes displayed us mass).DrscussioN-The term balance is usually reserved for devices used for precision weighing and the term scale for conventional weighing.3.2.2 balance,one-pan-balance that employs one pan for the sample,plus a balancing system that does not have a volu
13、me similar to the sample pan.3.2.3 balance,two-pan-balance that employs two pans and precision weights to determine sample weight or mass.DrscussroN-This type of balance is usually less sensitive to buoy-ancy-effect tare problems than a one-pan balance or electronic scales,which do not have similar
14、volumes on each side of the fulcrum.3.2.4 effective volume-volume that is effective in dis-placing laboratory air,and thus governs the buoyancy force for that sample or component.This buoyancy force is modified by any tare buoyancy of the balance,and is thus a function of both the sample and the bal
15、ance.3.2.5 sample-component(for example;tracer-gas sam-pler,tracer-gas source,etc.),piece of material(for example;filter paper,insulation sample,etc.)or container being weighed to a high degree of precision.3.2.6 sample,constant volume-sample that does not significantly change its ability to displac
16、e air between read-ings,even when its mass does change(for example;a sealed,hollow,metal container).3.2.7 sample density-sample mass divided by its effec-tive volume.3.2.8 sample,variable volume-sample that changes the amount of air that it displaces,as it changes mass(for example;particulate-loaded filter paper).4.Summary of Practice 4.1 Determine the effective volume of the air displaced by a sample which is being weighed or reweighed,by measuring the change in indicated weight of a typical sa