1、Designation: E750 15Standard 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. Scope*1.1 This practice is recommended for use in testing andmeasuring operating characteristics of acoustic emission elec-tronic components or units.
3、 (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 me
4、thods 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 practi
5、ce.1.3 The methods (techniques) used for testing and measur-ing the components or units of acoustic emissioninstrumentation, and the results of such testing and measuringshould be documented. Documentation should consist ofphotographs, screenshots, charts or graphs, calculations, andtabulations wher
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.)1This practice is under the jurisdiction of ASTM Committee E07 on N
14、onde-structive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved Dec. 1, 2015. Published December 2015. Originallyapproved in 1980. Last previous edition approved in 2010 as E750 - 10. DOI:10.1520/E0750-15.2For referenced ASTM standar
15、ds, 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.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, N
16、ew York, NY 10036.*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 States14.3.1 Important tests of a computer-based AE system in-clude the evaluation of limits and linearity of
17、the availableparameters such as:(a) Amplitude,(b) Duration,(c) Rise 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
18、 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, storage device (RAM, disk), andon-line analysis settings (number of graphs, data listings,loc
19、ation algorithms, and more). If waveform recording is used,this 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 purpose
20、s toassure that the instrumentation performance remains consistentwith 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 instr
21、umentation measurementsshould be referred to electronics engineering 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
22、make the measure-ments.6. Apparatus6.1 The basic test instruments 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 decib
23、els, and6.1.5 Tone Burst Generator.6.2 Additional test instruments 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 G
24、enerator,6.2.5 Spectrum Analyzer,6.2.6 D-C Voltmeter,6.2.7 Pulse-Modulated Signal Generator,6.2.8 Variable Pulse Generator,6.2.9 Phase Meter, and6.2.10 Electronic AE Simulator (or an Arbitrary WaveformGenerator (AWG) can be used providing an automated evalu-ation).6.3 An electronic AE simulator (or
25、AWG) is necessary toevaluate the operation of computer-based AE 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 simu
26、lator. Control ofpulse frequency, rise time, decay, repetition rate, 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 the
27、preamplifier with amplification and signal filters, possiblyconnected 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
28、beterminated with the normal working load as shown on thebottom 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 ofFIG. 1 Component Configuration Used for Testing and M
29、easuring the Frequency Response, Amplification, Noise, Signal Overload, Re-covery Time, and Threshold of Acoustic Emission InstrumentationE750 152the nominal bandwidth of the instrumentation. The meanfrequency is calculated as follows:fM5 fLfH!12where:fM= mean frequency,fL= nominal lower cutoff, and
30、fH= nominal upper cutoff.7.1.3 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 of frequency should have bandwidth amplitude varia-tions as specified by the manufac
31、turer.7.1.4 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 measured between frequencylimits specified in 7.1.2. The oscillator is maintained at a
32、fixedamplitude and the frequency is swept through the frequencylimits. 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
33、. The amplitude scale may be converted to decibels. Thefrequency scale may be plotted either linearly or logarithmi-cally. Appendix X2 provides further discussion of waveshaping components.7.1.5 A spectrum analyzer may be used in conjunction witha white noise source or an oscilloscope may be used in
34、conjunction with a sweep frequency oscillator to determinebandwidth. 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
35、dB less than theresponse at the reference frequency.7.2 Gain Measurements:7.2.1 The electronic amplification is comprised of the pre-amplifier gain, the wave filters insertion gains or losses and theAE systems gains or losses. (See Appendix X2 for anexplanation of gain measurements.)7.2.2 The electr
36、onic amplification may be measured withthe 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
37、the voltmeter at Vosc, oscillator amplitude 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 th
38、e voltmeter again reads 1 V. The electronicamplification 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 resistive
39、and equal to the required load impedance of the attenuator, propercompensation 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 likem
40、easurements for both readings (for example, peak voltage topeak voltage, 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 should
41、be used for signal processing involving spectrum analysis. Allother 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 dyn
42、amic 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 an adjunct to determine the characteristicsof noise a
43、nd to monitor the signal overload point.7.3.2.2 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 may result from noise impulsesof electrical origin,
44、 or ground faults.7.3.2.3 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 overloadimmunity but not to the dynamic range. The fo
45、llowing 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 = the threshold value that passes less than 1 count/
46、swith no input signal.This dynamic range is the difference between 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, inc
47、luding 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 with a true RMS voltmeter (see 6.1.2)atthe instrumentation (preamp
48、lifier or AE system) output (Vout)per Fig. 1. Alternatively, a peak AE system noise measurementcan be measured by setting the lowest possible AE thresholdwhich passes less than one false hit within ten seconds or byE750 153setting the AE system threshold below the noise and recordingthe peak AE ampl
49、itude of hits detected in a ten second period.7.3.4 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 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 ma
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