1、Designation: E 2374 04Standard Guide forAcoustic Emission System Performance Verification1This standard is issued under the fixed designation E 2374; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 System performance verification methods stimulate theexamination article on which the sensor is mounted. Theresulting stress wave travels
3、in the examination article and isdetected by the sensor(s) in a manner similar to acousticemission.1.2 This guide describes methods which can be used toverify the response of an Acoustic Emission system includingsensors, couplant, sensor mounting devices, cables and systemelectronic components.1.3 A
4、coustic emission system performance characteristics,which may be evaluated using this document, include somewaveform parameters, and source location accuracy.1.4 Performance verification is usually conducted prior tobeginning the examination.1.5 Performance verification can be conducted during theex
5、amination if there is any suspicion that the system perfor-mance may have changed.1.6 Performance verification may be conducted after theexamination has been completed.2. Referenced Documents2.1 ASTM Standards:2E 750 Practice for Characterizing Acoustic Emission Instru-mentationE 976 Guide for Deter
6、mining the Reproducibility of Acous-tic Emission Sensor ResponseE 1316 Terminology for Nondestructive ExaminationsE 1419 Test Method for Examination of Seamless, Gas-Filled, Pressure Vessels Using Acoustic EmissionE 1781 Practice for Secondary Calibration of AcousticEmission Sensors3. Terminology3.1
7、 examination articlethe item which is being examinedwith AE and to which AE sensors are attached.3.2 velocitythe measured velocity of a stress wave, trav-eling in the examination article, using specified AE systemparameters and components. Velocity is often used in triangu-lation calculations to det
8、ermine the position of the AE source.3.3 auto sensor test (AST)an electronic means by which asensor can be fed an electronic pulse to excite the examinationarticle. The resulting stress wave in the examination article canbe measured by the same sensor or by other sensors that are onthe same examinat
9、ion article. See 3.4 and 3.5.3.4 auto sensor test-self test modea means by which anAST sensor may be used to check its own performance.3.5 auto sensor test-near neighbor modea means bywhich an AST sensor may be used to determine the sensitivityof one or more neighboring sensors on the same examinati
10、onarticle.4. Significance and Use4.1 Acoustic Emission data acquisition can be affected bynumerous factors associated with the electronic instrumenta-tion, cables, sensors, sensor holders, couplant, the examinationarticle on which the sensor is mounted, background noise, andthe users settings of the
11、 acquisition parameters (for example,threshold).4.2 This guide is not intended to replace annual (or semi-annual) instrumentation calibration (see Practice E 750) orsensor recertification (see Practice E 1781).4.3 This guide is not intended to replace routine electronicevaluation of AE instrumentati
12、on or routine sensitivity verifi-cation of AE sensors (see Guide E 976).4.4 This guide is not intended to verify the maximumprocessing capacity or speed of an AE system.4.5 This guide does not purport to address all of the safetyconcerns, if any associated with its use. It is the responsibilityof th
13、e user of this guide to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.5. Apparatus5.1 To determine system performance a sensor must besubjected to a stress wave traveling in the examination article.Transient stress waves are la
14、unched by mechanical or electro-mechanical devices that produce a waveform with fast rise-time, short duration and repeatable peak amplitude. Steadystate (continuous) stress waves are launched by mechanical or1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and
15、is the direct responsibility of Subcommittee E07.04 on AcousticEmission Method.Current edition approved May 1, 2004. Published June 2004.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume i
16、nformation, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.electromechanical devices that produce a waveform with longduration constant amplitude.5.1.1 Pencil Lead Brea
17、k (PLB)A mechanical pencil tech-nique whereby lead is pushed against the examination articlessurface with sufficient force to break the lead. When the leadbreaks, there is a sudden release of stress on the surface. (SeeGuide E 976, paragraph 4.3.3 and Fig. 4.)5.1.1.1 The distance between the PLB and
18、 the sensor mustbe specified.5.1.1.2 The “Hsu pencil source” uses a mechanical pencilwith a 2.5 mm lead extension, 2H hardness and 0.3 mm or 0.5mm diameter (0.3 mm is preferred).5.1.1.3 The “Nielsen shoe” can aid in breaking the leadconsistently.5.1.1.4 The pencil should be held at an angle of 30 de
19、greesto the surface.5.1.1.5 Three to five lead breaks are generally conducted toshow a consistent result.5.1.1.6 Application standards (for example, Test MethodE 1419) specify the minimum signal amplitude that must bemeasured by the AE instrumentation.5.1.1.7 Channels which are found to have unaccep
20、tably lowor high sensitivity can be recoupled (that is, replace couplant),repaired (that is, replace sensor, or cable, or both), or replaced(that is, exchanged for another channel), or both.5.1.1.8 PLB can be used to determine the apparent velocityin the examination article (apparent velocity = sens
21、or spacing/time-of-flight). “Time-of-flight” is the time required for a stresswave to travel the sensor-spacing distance5.1.2 Independent Piezoelectric PulserAn electrome-chanical device held against the examination article and used inconjunction with an electronic signal or pulse generator. Theelec
22、trical signal from the signal/pulse generator is convertedinto a mechanical displacement by the transducers crystal.(See Guide E 976, paragraph 4.3.1.) One significant advantageof this technique is that the output of the electronic signal/pulsegenerator can be adjusted in numerous ways (for example,
23、amplitude and repetition rate).5.1.2.1 The independent pulser can be used to excite thereceiving AE sensor before, during and after an examination asverification that there were no changes in coupling or sensorresponse. The independent pulser technique is particularlyuseful when there is limited acc
24、ess to the examination articlethat would preclude the use of manual techniques (for example,PLB).5.1.2.2 The independent pulser technique is particularlyuseful in continuous monitoring situations where sensors willbe on the examination article for a long period of time. In thissituation the independ
25、ent pulser is left in place and usedperiodically to assure system performance.5.1.3 AST Capable Integrated Pulser/SensorAn AE sen-sor that has been designed to accept an electronic signal/pulseinto its crystal. The mechanical displacement of the crystalexcites the examination article. The stress wav
26、e generated inthe examination article can be detected by other sensors on thesame examination article. With certain realizations of the ASTfunction (self test mode), it can also be detected by the excitingsensor.5.1.3.1 Auto Sensor Test: Near Neighbor ModeAn inte-grated pulser/sensor can be used to
27、measure sensitivity andtime-of-flight (that is, the time required for a stress wave totravel the sensor-spacing distance) for neighboring sensors onthe same examination article. The time-of-flight can be used tocalculate the apparent velocity of the stress wave (apparentvelocity = sensor spacing/tim
28、e-of-flight).5.1.3.2 Auto Sensor Test: Self Test ModeAn integratedpulser/sensor can be used to verify the performance of thesensor coupling and the sensor and channel electronics towhich it is attached by establishing a baseline duration (orenergy) measured from the AST pulse using a sensor that isk
29、nown to be operating properly and mounted optimally on theexamination article. The baseline duration number (for ex-ample, 10 000 s) can then be compared with the AST durationmeasurements from each channel on the examination article.Channels, which produce AST duration measurements that arelow compa
30、red to the baseline, should be recoupled, repaired orreplaced as necessary.5.1.4 Spring Loaded Center PunchA spring loaded devicethat imparts a mechanical impact force, creating a very largestress wave on the examination article. The spring assures aconsistent and repeatable force.5.1.4.1 The spring
31、-loaded center punch is of particularadvantage when AE sensors are distributed over large distanceson an examination article, as the imparted force is so strong itcan be detected easily.5.1.4.2 The spring-loaded center punch is readily availableand easy to apply anywhere on the examination article,
32、at anytime.5.1.4.3 To avoid damage to the surface, it is desirable toapply the center punch through an intermediate interface suchas a thin sheet of metal or coin.5.1.5 ProjectileAn object which is launched or projectedto impact the surface of the examination article. Examplesinclude a steel ball dr
33、opped onto the surface, a BB gun fired atthe surface or a mass at the end of a pendulum. In most casesthe energy being imparted onto the surface can be determined.5.1.6 Gas JetA gas jet forces a gas through a nozzle athigh pressure onto the surface of the examination article beinginstrumented. The g
34、as jet is controlled by an electronic valvewith the ability of being turned on momentarily to create atransient surface wave or kept on to create a continuous surfacewave.5.1.6.1 The gas jet is usually used in an industrial environ-ment where compressed air or gas is readily available.5.1.6.2 The ga
35、s jet is usually used in places that areinaccessible so that system verification can be carried outremotely from the sensor.5.1.6.3 The gas jet is a good device for creating a simulated,continuous leak-type, AE signal.5.1.7 Electrical Spark DischargeA spark struck betweentwo electrodes near the surf
36、ace of the examination articlegenerates stress waves that propagate in a manner similar toacoustic emission. The technique can be used in a similarmanner to a pencil lead break or independent piezoelectricpulser. The advantage of an electrical spark discharge is itsE2374042short duration and impulse
37、 type response, providing a wide-band frequency response.5.1.8 Mechanical CrackerA mechanically loaded devicewhich is embrittled or subjected to chemical attack (whichcauses it to crack at a rate controlled by the applied mechanicalload). When coupled to the surface of the examination article,the de
38、vice produces true AE signals of varying amplitude. Thismethod truly generates acoustic emission and is useful incharacterizing the AE system response to a brittle crack.6. Procedure6.1 The procedure for accomplishing system performanceverification utilizes one of the devices listed in Section 5 top
39、roduce a stress wave on the examination article. The sen-sor(s), mounted a specified distance from the verificationdevice detects the stress wave and the acoustic emission systemprocesses the information for display and storage. The operatorof the acoustic emission system examines the data to determ
40、ineif they are within the limits specified in the written testprocedure. Note that two operators may be required: one tooperate the verification device (for example, PLB) and asecond to read the data and record the results.6.1.1 Verification of Acoustic Emission transient signalparameters (or AE fea
41、tures)Waveform parameters/featuresthat are necessary for achieving the desired examination resultsare typically required to be measured, within a specified degreeof accuracy, during system performance verification. Theseparameters and the required degree of accuracy are specified inthe written test
42、procedure.6.1.1.1 An example of this process is provided in Table 1and Fig. 1 where peak amplitude from each sensor is used toverify system performance. The accuracy requirements used inthis example are found in Test Method E 1419, Table X1.2.6.1.2 Verification of Source Location AccuracySourcelocat
43、ion accuracy that is necessary for achieving the desiredexamination results are typically required to be measured,within a specified degree of accuracy, during system perfor-mance verification. The means of determining source locationand the required degree of accuracy are specified in the writtente
44、st procedure.6.1.2.1 An example of this process is provided in Table 2and Fig. 2 where linear source location accuracy is measured toverify system performance. The accuracy requirements used inthis example are found in Test Method E 1419, Table X1.2.6.1.3 Verification of System Data Acquisition Rate
45、Systemdata acquisition rate performance is influenced by systemsettings such as threshold and dead time. Generally, theoperator would like the threshold and dead-time to be as low asthe systems data acquisition rate will allow in order to optimizethe test results. To determine if a system has suffic
46、ient data rateperformance to carry out a particular test procedure theoperator attaches sensors to the examination article and usesthe verification device at various positions. During this processthe dead time setting is lowered until multiple events areobserved for a single use of the verification
47、device. In theexample which follows Test Method E 1419, Table X1.2, thisdead-time value is 10 ms. To accommodate a dead-time settingof 10 ms the AE system must have a steady state throughputrate of 100 events/second (10 mseconds/event = 0.01seconds/event, 1/0.01 seconds/event = 100 events/second) To
48、 verifythat a system is capable of achieving a steady state data rate of100 events/second an electronic pulse generator (set to output100 pulses per second) and pulse transducer are utilized. Seeparagraph 5.1.2.6.1.3.1 An example of this process is provided in Table 3and Fig. 3 where the dead-time s
49、etting is specified at 10 ms.The procedure for this example is Test Method E 1419, TableX1.2.7. Factors that May Affect AE System Performance7.1 AE system performance may change as a result of time,physical and environmental factors. In some cases thesechanges can have a significant influence on the interpretation ofexamination results and the outcome of the examination. Apartial list of these factors is found in Table 4.8. Report8.1 Performance verification results should be in writtenform and included with the comprehensive test report that isTABLE 1 Example of P
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