ASTM_D_6011_-_96_2015.pdf

Designation:D601196(Reapproved 2015)Standard Test Method forDetermining the Performance of a Sonic Anemometer/Thermometer1This standard is issued under the fixed designation D6011;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 dy-namic performance of a sonic anemometer/thermometer whichemploys the inverse time measurement technique for velocityor speed of sound,or both.Performance criteria include:(a)acceptance angle,(b)acoustic pathlength,(c)system delay,(d)system delay mismatch,(e)thermal stability range,(f)shadowcorrection,(g)velocity calibration range,and(h)velocityresolution.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2C384 Test Method for Impedance and Absorption of Acous-tical Materials by Impedance Tube MethodD1356 Terminology Relating to Sampling and Analysis ofAtmospheresD5527 Practices for Measuring Surface Wind and Tempera-ture by Acoustic MeansIEEE/ASTM SI 10 American National Standard for MetricPractice3.Terminology3.1 DefinitionsFor definitions of terms related to this testmethod,refer to Terminology D1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 axial attenuation coeffcienta ratio of the free streamwind velocity(as defined in a wind tunnel)to velocity along anacoustic propagation path(vt/vd)(1).33.2.2 critical Reynolds number(Rc)the Reynolds numberat which an abrupt decrease in an objects drag coefficientoccurs(2).3.2.2.1 DiscussionThe transducer shadow corrections areno longer valid above the critical Reynolds number due to adiscontinuity in the axial attenuation coefficient.3.2.3 Reynolds number(Re)the ratio of inertial to viscousforces on an object immersed in a flowing fluid based on theobjects characteristic dimension,the fluid velocity,and vis-cosity.3.2.4 shadow correction(vdm/vd)the ratio of the truealong-axis velocity vdm,as measured in a wind tunnel or byanother accepted method,to the instrument along-axis windmeasurement vd.3.2.4.1 DiscussionThis correction compensates for flowshadowing effects of transducers and their supporting struc-tures.The correction can take the form of an equation(3)or alookup table(4).3.2.5 speed of sound(c,(m/s)the propagation rate of anadiabatic compression wave:c 5P/!s0.5(1)where:P=pressure=density,=specific heat ratio,ands=isentropic(adiabatic)process(5).3.2.5.1 DiscussionThe velocity of the compression wavedefined along each axis of a Cartesian coordinate system is thesum of propagation speed c plus the motion of the gas alongthat axis.In a perfect gas(6):c 5R*T/M!0.5(2)The approximation for propagation in air is:cair5403 T110.32 e/P!#0.55403 Ts!0.5(3)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 April 1,2015.Published April 2015.Originallyapproved in 1996.Last previous edition approved in 2008 as D6011 96(2008).DOI:10.1520/D6011-96R15.2For 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.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.2.6 system clockthe clock used for timing acousticwavefront travel between a transducer pair.3.2.7 system delay(t,s)the time delay through thetransducer and electronic circuitry(7).3.2.7.1 DiscussionEach path through every sonic arrayaxis can have unique delay characteristics.Delay(on the orderof 10 to 20 s)can vary as a function of temperature anddirection of signal travel through the transducers and electroniccircuitry.The average system delay for each axis in an acousticarray is the average of the delays measured in each directionalong the axis:t 5t11t2!/2(4)3.2.8 system delay mismatch(tt,s)the absolute differ-ence in microseconds between total transit times ttin eachdirection(tt1,tt2)through the system electronics and transduc-ers.3.2.8.1 DiscussionDue principally to slight differences intransducer performance,the total transit time obtained with thesignal originating at one transducer can differ from the totaltransit time obtained with the sig