1、Designation: E750 10Standard Practice forCharacterizing Acoustic Emission Instrumentation1This standard is issued under the fixed designation E750; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 units.
3、(SeeAppendix 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 meth
4、ods 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 practice
5、.1.3 The methods (techniques) used for testing and measur-ing the components or units of acoustic emission instrumenta-tion, and the results of such testing and measuring should bedocumented. Documentation should consist of photographs,screenshots, charts or graphs, calculations, and tabulationswher
6、e applicable.1.4 AE systems that use computers to control the collection,storage, display, and data analysis, might include waveformcollection as well as a wide selection of measurement param-eters (features) relating to the AE signal. The manufacturerprovides a specification for each system that sp
7、ecifies theoperating range and conditions for the system. All calibrationand acceptance testing of computer-basedAE systems must usethe manufacturers specification as a guide. This practice doesnot cover testing of the computer or computer peripherals.1.5 The values stated in SI units are to be rega
8、rded asstandard. No other units of measurement are included in thisstandard.1.6 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 determi
9、ne the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E1316 Terminology for Nondestructive Examinations2.2 ANSI Standard:ANSI/IEEE 100-1984 Dictionary of Electrical and Elec-tronic Terms32.3 Other Documents:Manufacturers Operating and Maintenance Man
10、uals perti-nent to the specific instrumentation or component3. Terminology3.1 DefinitionsFor definitions of additional terms relatingto acoustic emission, refer to Terminology E1316.4. Summary of Practice4.1 Tests and measurements should be performed to deter-mine the instrumentation bandwidth, freq
11、uency response, gain,noise level, threshold level, dynamic range, signal overloadpoint, dead time, and counter accuracy.4.2 Where acoustic emission test results depend upon thereproduced accuracy of the temporal, spatial, or spectralhistories, additional measurements of instrumentation param-eters s
12、hould be performed to determine the specific limits ofinstrumentation performance. Examples of such measurementsmay include amplifier slew rate, gate window width andposition, and spectral analysis.4.3 Tests and measurements should be performed to deter-mine the loss in effective sensor sensitivity
13、resulting from thecapacitive loading of the cable between the preamplifier andthe sensor. The cable and preamplifier should be the same asthat used for the acoustic emission tests without substitution.(See also Appendix Appendix X2.)4.3.1 Important tests of a computer-based AE system in-clude the ev
14、aluation of limits and linearity of the availableparameters such as:(a) Amplitude,(b) Duration,1This 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 Jan. 1,
15、 2010. Published February 2010. Originallyapproved in 1980. Last previous edition approved in 2004 as E750 - 04. DOI:10.1520/E0750-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info
16、rmation, refer to the 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.(c) R
17、ise Time,(d) Energy, and(e) AE Arrival Time.4.3.2 The processing speed of these data should be mea-sured as described in 7.4.3 for both single- and multiple-channel operation.4.3.3 The data storage capability should be tested againstthe specification for single- and multiple-channel operation.Proces
18、sing speed is a function of number of channels, param-eters being measured, timing parameter settings, AE signalduration, front-end filtering, storage device (RAM, disk), andon-line analysis settings (number of graphs, data listings,location algorithms, and more). If waveform recording is used,this
19、may influence the processing speed further.5. Significance and Use5.1 This practice provides information necessary to docu-ment the accuracy and performance of an Acoustic Emissionsystem. This information is useful for reference purposes toassure that the instrumentation performance remains consiste
20、ntwith time and use, and provides the information needed toadjust the system to maintain its consistency.5.2 The methods set forth in this practice are not intended tobe either exclusive or exhaustive.5.3 Difficult or questionable instrumentation measurementsshould be referred to electronics enginee
21、ring personnel.5.4 It is recommended that personnel responsible for carry-ing out instrument measurements using this practice should beexperienced in instrumentation measurements, as well as allthe required test equipment being used to make the measure-ments.6. Apparatus6.1 The basic test instrument
22、s required for measuring theoperating characteristics of acoustic emission instrumentationinclude:6.1.1 Variable Sine Wave Generator or Oscillator,6.1.2 True RMS Voltmeter,6.1.3 Oscilloscope,6.1.4 Variable Attenuator, graduated in decibels, and6.1.5 Tone Burst Generator.6.2 Additional test instrumen
23、ts may be used for morespecialized measurements of acoustic emission instrumenta-tions or components. They are as follows:6.2.1 Variable-Function Generator,6.2.2 Time Interval Meter,6.2.3 Frequency Meter, or Counter,6.2.4 Random Noise Generator,6.2.5 Spectrum Analyzer,6.2.6 D-C Voltmeter,6.2.7 Pulse
24、-Modulated Signal Generator,6.2.8 Variable Pulse Generator, and6.2.9 Phase Meter,6.2.10 Electronic AE Simulator (or an Arbitrary WaveformGenerator (AWG) can be used providing an automated evalu-ation).6.3 An electronic AE simulator (or AWG) is necessary toevaluate the operation of computer-based AE
25、instruments. Adetailed example of the use of an electronic AE simulator (orAWG) is given in 7.4.3 under dead time measurement. Theinstruction manual for the electronic AE simulator providesdetails on the setup and adjustment of the simulator. Control ofpulse frequency, rise time, decay, repetition r
26、ate, and peakamplitude in the simulator makes it possible to simulate a widerange of AE signal conditions.7. Measurement Procedure7.1 Frequency Response and Bandwidth Measurements:7.1.1 The instrumentation, shown in Fig. 1, includes thepreamplifier with amplification and signal filters, possiblyconn
27、ected to theAE 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 beterminated with the normal working load as shown on thebottom
28、right of Fig. 1.7.1.2 An acceptable frequency response should be flatbetween cutoff frequencies within 3 dB of the referencefrequency. The reference frequency is the geometric mean ofthe nominal bandwidth of the instrumentation. The meanfrequency is calculated as follows:FIG. 1 Component Configurati
29、on Used for Testing and Measuring the Frequency Response, Amplification, Noise, Signal Overload,Recovery Time, and Threshold of Acoustic Emission InstrumentationE750 102fM5 fLfH!12where:fM= mean frequency,fL= nominal lower cutoff, andfH= nominal upper cutoff.7.1.3 The bandwidth should include all co
30、ntiguous frequen-cies with amplitude variations as specified by the manufacturer.Instruments that include signal processing of amplitude as afunction of frequency should have bandwidth amplitude varia-tions as specified by the manufacturer.7.1.4 With the instrumentation connected to the oscillatoran
31、d attenuator, see Fig. 1 and the sine wave oscillator set wellwithin the instrumentations specified dynamic range, thefrequency response should be measured between frequencylimits specified in 7.1.2. The oscillator is maintained at a fixedamplitude and the frequency is swept through the frequencylim
32、its. The preamplifier or AE system voltage output ismonitored with an RMS voltmeter. Values of amplitude arerecorded for each of several frequencies within and beyond thenominal cutoff frequencies. The recorded values should beplotted. The amplitude scale may be converted to decibels. Thefrequency s
33、cale may be plotted either linearly or logarithmi-cally. Appendix X2 provides further discussion of wave shap-ing components.7.1.5 A spectrum analyzer may be used in conjunction witha white noise source or an oscilloscope may be used inconjunction with a sweep frequency oscillator to determinebandwi
34、dth. With a white noise source connected to the input, aspectrum analyzer connected to the output will record thefrequency response.7.1.6 The measured bandwidth is the difference between thecorner frequencies at which the response is 3 dB less than theresponse at the reference frequency.7.2 Gain Mea
35、surements:7.2.1 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.)7.2.2 The electronic amplification may be measured withthe test setup shown in Fig
36、. 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 amplitude is setto 1 V. The atte
37、nuator 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 electronicamplification is equal
38、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 of the attenuator, proper
39、compensation should be made.7.3 Dynamic Range Measurements:7.3.1 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 voltage topeak vo
40、ltage, peak-peak voltage or RMS to RMS readings).Alternatively, the reference amplitude may be the thresholdlevel if the instrumentation includes a voltage comparator forsignal detection. The total harmonic distortion criterion shouldbe used for signal processing involving spectrum analysis. Allothe
41、r signal processing may be performed with the signaloverload point criterion.7.3.2 The dynamic range (DR) in decibels should be deter-mined as follows:DR 5 20 log10signal overload point voltage/background noise voltage!7.3.2.1 The dynamic range of instrumentation exclusive ofthreshold or voltage com
42、parator 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 an adjunct to determine the characteristicsof noise and to monitor the signal overload point.7.3.2.2 A field measuremen
43、t of dynamic range may producesubstantially different results when compared with a laboratorymeasurement. This difference is caused by an increase in thereference voltage output, and may result from noise impulsesof electrical origin, or ground faults.7.3.2.3 For an amplifier that has a threshold co
44、mparator 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 overloadimmunity but not to the dynamic range. The following mea-surement will give the effective dynamic range:DRe5 20
45、log10MaxTh/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 = the threshold value that passes less than 1count/s with no input signal.This dynamic range is the difference between
46、 the largest andthe smallest AE input that can be reliably detected by thesystem.7.3.3 Measurement of instrument electronic noise is accom-plished by replacing the oscillator/attenuator of Fig. 1, with thesensor that will be used, including its cable (or with a lumpedequivalent capacitance). A lumpe
47、d capacitance represents theelectrical characteristic of the sensor and cable combinationwithout adding mechanical noise interference. The RMS noisevoltage is measured with a true RMS voltmeter (see 6.1.2)atthe instrumentation (preamplifier or AE system) output (Vout)per Fig. 1. Alternatively, a pea
48、k AE system noise measurementcan be measured by setting the lowest possible AE thresholdwhich passes less than one false hit within ten seconds or bysetting the AE system threshold below the noise and recordingthe peak AE amplitude of hits detected in a ten second period.7.3.4 The signal overload le
49、vel is measured by replacing thesensor with the sine wave oscillator as shown in Fig. 1. TheE750 103frequency is set to the mid-band frequency of the instrumen-tation. The oscillator amplitude is fixed at 1 V peak to peakmonitored 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.7.3.5 Should the peak amplitude of acoustic emission activ-ity exceed the dynamic range, several deleterious effects maybe produced; these include clipping, saturation, and overloadreco
