1、Designation:D423020Standard Test Method forMeasuring Humidity with Cooled-Surface Condensation(Dew-Point)Hygrometer1This standard is issued under the fixed designation D4230;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of
2、 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 test method covers the determination of the ther-modynamic dew-or frost-point temperature of ambient air bythe conden
3、sation of water vapor on a cooled surface.Forbrevity,this is referred to in this test method as the condensa-tion temperature.1.2 This test method is applicable for the range of conden-sation temperatures from 60C to 70C.1.3 This test method includes a general description of theinstrumentation and o
4、perational procedures,including siteselection,to be used for obtaining the measurements and adescription of the procedures to be used for calculating theresults.1.4 This test method is applicable for the continuous mea-surement of ambient humidity in the natural atmosphere on astationary platform.1.
5、5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 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-pria
6、te safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.For specific precautionary statements,see Section 8.1.7 This international standard was developed in accor-dance with internationally recognized principles on standard-ization establi
7、shed in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheresD363
8、1 Test Methods for Measuring Surface AtmosphericPressure3.Terminology3.1 Definitions:3.1.1 For definitions of other terms in this test method,referto Terminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 nonhygroscopic material,nmaterial that neither ab-sorbs nor retains water v
9、apor.3.2.2 mirror(front surface),na polished surface,usually ametallic surface,on which condensates are deposited.3.3 Symbols:e=vapor pressure of water vapor in moist air.ei=saturation pressure of water vapor in equilibriumwith the plane surface of ice.ew=saturation pressure of water vapor in equili
10、briumwith the plane surface of water.P=ambient pressure.r=mixing ratio.T=ambient air temperature.Td=thermodynamic dew-or frost-point temperature.RHi=relative humidity with respect to ice.RHw=relative humidity with respect to water.4.Summary of Test Method4.1 The ambient humidity is measured with a d
11、ew-andfrost-point hygrometer.1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved March 1,2020.Published April 2020.Originallyapproved in 1983.Last previous edition approved in
12、2012 as D4230 02(2012).DOI:10.1520/D4230-20.2For 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 Interna
13、tional,100 Barr Harbor Drive,PO Box 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 a
14、nd Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.4.2 The mirror or some other surface on which the conden-sate is deposited is provided with the means for cooling andheating,detection of condensate,and the measurement of thetemperature of the mirror
15、 surface.4.3 Calculations of saturation vapor pressure over water andice as functions of temperature are provided.5.Significance and Use5.1 Humidity information is important for the understandingof atmospheric phenomena and industrial processes.Measure-ments of the dew-point and calculations of rela
16、ted vaporpressures are important to quantify the humidity information.6.Interferences6.1 This test method is not applicable if other constituents inthe atmosphere condense before water vapor.7.Apparatus7.1 Dew-point hygrometers,specifically designed for me-teorological observations are available commercially.A sche-matic arrangement of a typical optical dew-point hygrometer isshown in Fig.1.7.1.1 The sample air flows through a small chamber.7.1.2 Within the chamber is a mirror or surface on whic
