ASTM_D_8446_-_22.pdf

Designation:D844622Standard Test Method forWater Vapor Content in Compressed Air Using ElectronicMoisture Analyzers1This standard is issued under the fixed designation D8446;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.1.Scope1.1 This test method covers the determination of the watervapor content in compressed air using portable or in-situelectronic moisture analyzers.Such analyzers commonly usesensing cells based on phosphorus pentoxide,P2O5,aluminumoxide,Al2O3,or silicon piezoelectric-type cells or laser-basedtechnologies.1.2 This test method is applicable for the range of conden-sation temperatures from 80 C to 60 C.1.3 Testing is often performed at reduced pressure from thefull pressure of the system or source of compressed airdepending on the capability of the specific analyzer.Testingabove 2000 kPa may introduce additional uncertainty becauseof changes in the relationship between water vapor pressureand actual moisture content at elevated pressures.1.4 UnitsThe values stated in SI units are to be regardedas the standard.No other units of measurement are included inthis standard.1.5 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,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established 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 ofAtmospheresD4178 Practice for Calibrating Moisture AnalyzersD4230 Test Method for Measuring Humidity with Cooled-Surface Condensation(Dew-Point)HygrometerD5454 Test Method for Water Vapor Content of GaseousFuels Using Electronic Moisture AnalyzersD7904 Test Method for Determination of Water Vapor(Moisture Concentration)in Natural Gas by TunableDiode Laser Spectroscopy(TDLAS)3.Terminology3.1 DefinitionsFor definitions of other terms used in thistest method,refer to Terminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 capacitance-type cell,nthis cell typically uses alu-minum coated with aluminum oxide,Al2O3,as part of acapacitor.3.2.1.1 DiscussionThe dielectric Al2O3film changes thecapacity of the capacitor in relation to the water vapor present.Silicone cells also operate on this principal by reporting acapacitance change when adsorbing or desorbing water vapor.3.2.2 dew point,ntemperature(at a specified pressure)atwhich liquid water will start to condense from the water vaporpresent as measured over water.3.2.2.1 DiscussionThe term“dew point”is often used toinclude“frost point”(see 3.2.4)when generally referring to thewater content based upon this principle,but there are uniquevalues for each for temperatures below 0 C.3.2.3 electrolytic-type cell,nthis cell is composed of twonoble metal electrode wires coated with phosphorus pentoxide,P2O5.3.2.3.1 DiscussionA bias voltage is applied to the elec-trodes and water vapor chemically reacts generating a currentbetween the electrodes proportional to the reaction with thewater vapor present.3.2.4 frost point,ntemperature(at a specified pressure)atwhich liquid water will start to condense from the water vaporpresent as measured over ice.3.2.5 laser-type cell,nconsists of a sample cell with anoptical head mounted on one end and a mirror mounted on the1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.13 on CompressedAirQuality.Current edition approved June 1,2022.Published August 2022.DOI:10.1520/D8446-22.2For 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 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 the World Trade Organization Technical Barriers to Trade(TBT)Committee.1other;however,some models will not need a mirror to reflectthe light wavelength emitted from the laser.3.2.5.1 DiscussionThe optical head contains a near infra-red(NIR)laser that emits light at a w