1、Designation: E 750 04Standard Practice forCharacterizing Acoustic Emission Instrumentation1This standard is issued under the fixed designation E 750; 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 This practice is recommended for use in testing andmeasuring operating characteristics of acoustic emission elec-tronic components or unit
3、s. (See Appendix X1 for a descriptionof components and units.) It is not intended that this practice beused for routine checks of acoustic emission instrumentation,but rather for periodic evaluation or in the event of a malfunc-tion. The sensor is not addressed in this document other thansuggesting
4、methods for standardizing system gains (equalizingthem channel to channel) when sensors are present.1.2 Where the manufacturer provides testing and measuringdetails in an operating and maintenance manual, the manufac-turers methods should be used in conjunction with themethods described in this prac
5、tice.1.3 Difficult or questionable instrumentation measurementsshould be referred to electronics engineering personnel.1.4 The methods set forth in this practice are not intended tobe either exclusive or exhaustive.1.5 The methods (techniques) used for testing and measur-ing the components or units
6、of acoustic emission instrumenta-tion, and the results of such testing and measuring should bedocumented. Documentation should consist of photographs,charts or graphs, calculations, and tabulations where appli-cable.1.6 AE systems that use computers to control the collection,storage, display, and da
7、ta analysis are in common use. Featuresof the computer-based systems might include waveform col-lection as well as a wide selection of measurement parametersrelating to the AE signal. The manufacturer provides a speci-fication for each system that specifies the operating range andconditions for the
8、system. All calibration and acceptancetesting of computer-based AE systems must use the manufac-turers specification as a guide. This practice does not covertesting of the computer or computer peripherals.1.7 This standard does not purport to address all of thesafety concerns, if any, associated wit
9、h 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:E 1316 Terminology for Nondestructive Examinations22.2 ANSI Standard
10、:ANSI/IEEE 100-1984 Dictionary of Electrical and Elec-tronic Terms32.3 Other Documents:Manufacturers Operating and Maintenance Manuals perti-nent to the specific instrumentation or component3. Terminology3.1 DefinitionsFor definitions of additional terms relatingto acoustic emission, refer to Termin
11、ology E 1316.4. Apparatus4.1 The basic test instruments required for measuring theoperating characteristics of acoustic emission instrumentationinclude:4.1.1 Variable Sine Wave Generator,4.1.2 True RMS Voltmeter,4.1.3 Oscilloscope,4.1.4 Variable Attenuator, graduated in decibels, and4.1.5 Tone Burst
12、 Generator.4.2 Additional test instruments should be used for morespecialized measurements of acoustic emission instrumenta-tions or components. They are as follows:4.2.1 Variable-Function Generator,4.2.2 Time Interval Meter,4.2.3 Frequency Meter, or Counter,4.2.4 Random Noise Generator,4.2.5 Spectr
13、um Analyzer,4.2.6 D-C Voltmeter,4.2.7 Pulse-Modulated Signal Generator,4.2.8 Variable Pulse Generator, and1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission.Current edition approved May
14、 1, 2004. Published June 2004. Originallyapproved in 1980. Last previous edition approved in 1998 as E 750 - 98.2For 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
15、standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2.9 Phase Meter,4.2.10 El
16、ectronic AE Simulator.4.3 An electronic AE simulator is necessary to evaluate theoperation of computer-based AE instruments. A detailed ex-ample of the use of an electronic AE simulator is given in 5.5.3under dead time measurement. The instruction manual for theelectronic AE simulator provides detai
17、ls on the setup andadjustment of the simulator. Control of pulse frequency, risetime, decay, repetition rate, and peak amplitude in the simula-tor makes it possible to simulate a wide range of AE signalconditions.5. Tests and Measurements5.1 Required Measurements:5.1.1 Tests and measurements should
18、be performed todetermine the instrumentation bandwidth, frequency response,gain, noise level, threshold level, dynamic range, signal over-load point, dead time, and counter accuracy.5.1.2 Where acoustic emission test results depend upon thereproduced accuracy of the temporal, spatial, or spectralhis
19、tories, additional measurements of instrumentation param-eters should be performed to determine the specific limits ofinstrumentation performance. Examples of such measurementsmay include amplifier slew rate, gate window width andposition, and spectral analysis.5.1.3 Tests and measurements should be
20、 performed todetermine the loss in effective sensor sensitivity resulting fromthe capacitive loading of the cable between the preamplifierand the sensor. The cable and preamplifier should be the sameas that used for the acoustic emission tests without substitution.(See also Appendix X2.)5.1.3.1 Impo
21、rtant tests of a computer-based AE systeminclude the evaluation of limits and linearity of the availableparameters such as:(a) Amplitude,(b) Duration,(c) Rise Time,(d) Energy, and(e) Source Location.5.1.3.2 The processing speed of these data should be mea-sured as described in 5.5.3 for both single-
22、 and multiple-channel operation.5.1.3.3 The data storage capability should be tested againstthe specification for single- and multiple-channel operation.Processing speed is a function of number of channels, param-eters being measured, timing parameter settings, AE signalduration, front-end filtering
23、, storage device (RAM, disk), andon-line analysis settings (number of graphs, data listings,location algorithms, and more). If waveform recording is used,this may influence the processing speed further.5.2 Frequency Response and Bandwith:5.2.1 The instrumentation, shown in Fig. 1, includes thepreamp
24、lifier with amplification and signal filters, possiblyconnected to the AE system which might have additional signalfilters, amplification, and interconnecting cables. All measure-ments and tests should be documented. If the preamplifier is tobe tested without the AE system connected, it should beter
25、minated with the normal working load as shown on thebottom right of Fig. 1.5.2.2 An acceptable frequency response between cutofffrequencies is within 3 dB of the reference frequency. Thereference frequency is the geometric mean of the nominalbandwidth of the instrumentation. The mean frequency iscal
26、culated as follows:fM5 fLfH!12where:fM= mean frequency,fL= nominal lower cutoff, andfH= nominal upper cutoff.5.2.3 The bandwidth should include all contiguous frequen-cies with amplitude variations as specified by the manufacturer.Instruments that include signal processing of amplitude as afunction
27、of frequency should have bandwidth amplitude varia-tions as specified by the manufacturer.5.2.4 With the instrumentation connected to the oscillatorand attenuator, see Fig. 1 and the sine wave oscillator set wellwithin the instrumentations specified dynamic range, thefrequency response should be mea
28、sured between frequencylimits specified in 5.2.2. The oscillator is maintained at a fixedamplitude and the frequency is swept through the frequencylimits. The preamplifier or AE system voltage output ismonitored with an rms voltmeter. Values of amplitude areFIG. 1 Component Configuration Used for Te
29、sting and Measuring the Frequency Response, Amplification, Noise, Signal Overload,Recovery Time, and Threshold of Acoustic Emission InstrumentationE750042recorded for each of several frequencies within and beyond thenominal cutoff frequencies. The recorded values should beplotted. The amplitude scal
30、e may be converted to decibels. Thefrequency scale may be plotted either linearly or logarithmi-cally. Appendix X2 provides further discussion of wave shap-ing components.5.2.5 A spectrum analyzer may be used in conjunction witha white noise source or an oscilloscope may be used inconjunction with a
31、 sweep frequency oscillator to determinebandwidth. With a white noise source connected to the input, aspectrum analyzer connected to the output will record thefrequency response.5.2.6 The measured bandwidth is the difference between thefrequencies at which the response is 3 dB less than the response
32、at the reference frequency.5.3 Gain:5.3.1 The electronic amplification is comprised of thepreamplifier gain, the wave filters insertion gains or losses andthe AE systems gains or losses. (See Appendix X2 for anexplanation of gain measurements.)5.3.2 The electronic amplification may be measured witht
33、he test setup shown in Fig. 1, with the oscillator and attenuatorconnected. The sine wave oscillator is set to the referencefrequency. The oscillator amplitude is set well within thedynamic range of the instrumentation to avoid distortion due tooverload. With the voltmeter at Vosc, oscillator amplit
34、ude is setto 1 V. The attenuator is set for a value greater than theanticipated electronic amplification. Next, the voltmeter ismoved to Vout(preamplifier or AE system voltage outputdepending on the test being performed). The attenuator is nowadjusted until the voltmeter again reads 1 V. The electro
35、nicamplification is equal to the new setting on the attenuator. Awhite noise generator or sweep generator and spectrum or FFTanalyzer may be used in place of the oscillator and RMSvoltmeter.NOTE 1If the input impedance of the preamplifier is not both resistiveand equal to the required load impedance
36、 of the attenuator, propercompensation should be made.5.4 Dynamic Range:5.4.1 The criterion used for establishing dynamic rangeshould be documented as the signal overload point, referencedto the instrumentation noise amplitude, while keeping likemeasurements for both readings (for example, peak volt
37、age topeak voltage, peak-peak voltage to peak-peak voltage or rms torms readings). Alternatively, the reference amplitude may bethe threshold level if the instrumentation includes a voltagecomparator for signal detection. In addition, dynamic rangerelative to instrumentation damage may also be docum
38、ented.The total harmonic distortion criterion should be used forsignal processing involving spectrum analysis. All other signalprocessing may be performed with the signal overload pointcriterion.5.4.2 The dynamic range (DR) in decibels should be deter-mined as follows:DR 5 20 log10signal overload po
39、int voltage/background noise voltage!5.4.2.1 The dynamic range of instrumentation exclusive ofthreshold or voltage comparator circuits, is a ratio of the signaloverload level to the noise amplitude. (A brief description ofnoise sources appears in Appendix X4). An oscilloscope isusually required as a
40、n adjunct to determine the characteristicsof noise and to monitor the signal overload point.5.4.2.2 A field measurement of dynamic range may producesubstantially different results when compared with a laboratorymeasurement. This difference is caused by an increase in thereference voltage output, and
41、 may result from noise impulsesof electrical origin, or ground faults.5.4.2.3 For an amplifier that has a threshold comparator asits output device, the dynamic range is the ratio of maximumthreshold level to input noise level at the comparator. Excessamplitude range in the amplifier contributes to o
42、verloadimmunity but not to the dynamic range. The following mea-surement will give the effective dynamic range:DRe5 20log10MaxTh/MinTh!where:DRe= the effective dynamic range of the system,MaxTh = the highest settable threshold value that justpasses the largest undistorted peak signal input,andMinTh
43、= the threshold value that passes less than 1count/s with no input signal.This dynamic range is the difference between the largest andthe smallest AE input that can be reliably detected by thesystem.5.4.3 Measurement of instrument electronic noise is accom-plished by replacing the oscillator/attenua
44、tor of Fig. 1, with thesensor that will be used, including its cable (or with a lumpedequivalent capacitance). A lumped capacitance represents theelectrical characteristic of the sensor and cable combinationwithout adding mechanical noise interference. The rms noisevoltage is measured at the instrum
45、entation (preamplifier or AEsystem) output (Vout) per Fig. 1. Alternatively, a peak AEsystem noise measurement can be measured by setting thelowest possible AE threshold which passes less than one falsehit within ten seconds or by setting the AE system thresholdbelow the noise and recording the peak
46、 AE amplitude of hitsdetected in a ten second period.5.4.4 The signal overload level is measured by replacing thesensor with the sine wave oscillator as shown in Fig. 1. Thefrequency is set to the mid-band frequency of the instrumen-tation. The oscillator amplitude is fixed at 1 V peak to peakmonito
47、red at Vosc. The attenuator is adjusted to increase thesignal level to the preamplifier until the instrumentation output(Vout) is 0.5 dB less than the computed output.5.4.5 Should the peak amplitude of acoustic emission activ-ity exceed the dynamic range, several deleterious effects maybe produced;
48、these include clipping, saturation, and overloadrecovery time-related phenomena. (See Appendix X2 for adiscussion of overload recovery.) The instrumentation gainshould be adjusted to limit these effects to an absoluteminimum in order to increase the reliability of the data.5.5 Dead Time:5.5.1 The in
49、strumentation dead time may include variableand fixed components, depending on the instrumentation de-sign for handling the routine of the input and output dataprocessing. The components included in dead time are processE750043time and lock-out time. Process time varies from system tosystem and usually depends on the number of parametersprocessed for each AE hit. Lock-out time, which may beoperator controlled, is used to force a time delay beforeaccepting new AE hits.5.5.2 Dead time measurement in a counter type AE instru-ment should be conducted as follows: Set the instrumen
