208 L. Dieng et al. Fig. 21.1 The principle of acoustic emission methods Table 21.1 Basic parameters used in AE methods Name Unit Description Threshold level [dB, ref 1 V] Parameter to detect AE signals. The threshold is set such as that the unwanted noise is minimized. In this project, the threshold is set to 45 dB Hits [ ] Number of AE burst signals Counts [ ] Number of threshold crossings within one discriminated burst signal Amplitude [dB, ref 1 V] Amplitude of AE signal Peak amplitude [dB, ref 1 V] It is the greatest measured voltage of signal. Signals with amplitudes above the threshold correspond to an event, if the amplitude is below the threshold, isn’t recorded Energy [J] Signal strength, approximation Rise time s Time between 1st threshold crossing and maximum amplitude (Amax) Duration s Signal length/time between 1st and last threshold crossing Background noise level V Background noise level at pre-amplifier input prior to a hit Fig. 21.2 Example of AE signal possible performed in accordance with ARCHES recommendations [4]. The main technical terms can be found in EN 1330-9:2009 Non-destructive testing—Terminology—Part 9: Terms used in acoustic emission testing (EN 1330-9:2009), recommendations of RIELM TC 212-ACD [13] and elsewhere [8]: The basic parameters of AE signals being usually measured are listed in Table 21.1 and presented in Fig. 21.2.
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