ASTM_E_1781_-_E_1781M_-_13.pdf

Designation:E1781/E1781M13Standard Practice forSecondary Calibration of Acoustic Emission Sensors1This standard is issued under the fixed designation E1781/E1781M;the number immediately following the designation indicates the yearof original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice covers requirements for the secondarycalibration of acoustic emission(AE)sensors.The secondarycalibration yields the frequency response of a sensor to wavesof the type normally encountered in acoustic emission work.The source producing the signal used for the calibration ismounted on the same surface of the test block as the sensorunder testing(SUT).Rayleigh waves are dominant under theseconditions;the calibration results represent primarily the sen-sors sensitivity to Rayleigh waves.The sensitivity of thesensor is determined for excitation within the range of 100 kHzto 1 MHz.Sensitivity values are usually determined at frequen-cies approximately 10 kHz apart.The units of the calibrationare volts per unit of mechanical input(displacement,velocity,or acceleration).1.2 UnitsThe values stated in either SI units or inch-pound units are to be regarded as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-conformancewith the standards.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:2E114 Practice for Ultrasonic Pulse-Echo Straight-BeamContact TestingE494 Practice for Measuring Ultrasonic Velocity in Materi-alsE1106 Test Method for Primary Calibration of AcousticEmission SensorsE1316 Terminology for Nondestructive Examinations3.Terminology3.1 DefinitionsRefer to Terminology E1316,Section B,for terms used in this practice.3.2 Definitions of Terms Specific to This Standard:3.2.1 reference sensor(RS)a sensor that has had itsresponse established by primary calibration(also called sec-ondary standard transducer)(see Method E1106).3.2.2 secondary calibrationa procedure for measuring thefrequency or transient response of anAE sensor by comparisonwith an RS.3.2.3 test blocka block of homogeneous,isotropic,elasticmaterial on which a source,an RS,and a SUT are placed forconducting secondary calibration.4.Significance and Use4.1 The purpose of this practice is to enable the transfer ofcalibration from sensors that have been calibrated by primarycalibration to other sensors.5.General Requirements5.1 Units for CalibrationSecondary calibration producesthe same type of information regarding a sensor as doesprimary calibration(Method E1106).AnAE sensor responds tomotion at its front face.The actual stress and strain at the frontface of a mounted sensor depends on the interaction betweenthe mechanical impedance of the sensor(load)and that of themounting block(driver);neither the stress nor the strain isamenable to direct measurement at this location.However,thefree displacement that would occur at the surface of the blockin the absence of the sensor can be inferred from measurementsmade elsewhere on the surface.Since AE sensors are used tomonitor motion at a free surface of a structure and interactiveeffects between the sensor and the structure are generally of nointerest,the free motion is the appropriate input variable.It istherefore required that the units of calibration shall be volts perunit of free displacement or free velocity,that is,volts per unitor volt seconds per unit.5.2 The calibration results may be expressed,in the fre-quency domain,as the steady-state magnitude and phase1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved June 1,2013.Published June 2013.Originallyapproved in 1996.Last previous edition approved in 2008 as E1781-08.DOI:10.1520/E1781_E1781M-13.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 response of the sensor to steady-state sinusoidal excitation or,in the time domain,as the transient response of the sensor to adelta function of displacement.5.3 Importance of the Test Block MaterialThe specificacoustical impedance(c)of the