A Lab-scale Digital Acoustic Emission System for Source Location

coustic emission (AE) techniques have been used * of arrival-time differences (delta-T’s) for each mesh point. To in the study of crack location, cracking mecha‘ calculate the source position for a set of burst-type AE signisms, deformation of metals and leak detection. : nals, a straightforward “shift and a d d method was used. A In these techniques, AE sensors hit by transient . First, assuming the AE source is at a mesh point inside the stress waves generate AE signals, and then the AE signals . circle, the signal waveform of each channel was shifted forare analyzed with various methods. Conventional AE sys. ward in the time domain, with the corresponding delta-T tems only record some parameters of the AE signals, such * value. Each time-shifted waveform was added to that of the as peak amplitude, ringdown counts, duration, risetime, and * first-hit channel, and then the resultant additive waveform so on. On the other hand, a fully digital AE system can dig’ was squared to give the signal power from that mesh point. itize the waveforms of AE signals and perform various anal’ When these operations have been performed for all mesh yses. Since many versatile and relatively cheap personal : points, a power map can be created, and the peak of power computers (PC), analog-to-digital (A/D) cards, and digital . map is considered the closest point to the AE source. Figures signal processing (DSP) software packages for PC are avail. 2 shows a set of simulated signals, with the AE from (1, 21, able, a fully digital and PC-based lab-scale AE system for 3. propagating at 1480 m/s, of 10 kHz carrier frequency and D source location can be set up. With the results of DSP for . sampled at 100 kHz. With this sampling rate, a series of simulated and real AE signals, features of this AE system . location results for various carrier frequencies of signal (10, and critical factors involved are presented. . 20, and 50 kHz) are shown in Figure 3-5. It was found that when the sampling rate was CONFIGURATION OF 5 times the carrier frequency AE SYSTEM or higher, source location results were good no matter where the postulated source The configuration of our AE was. As the sampling rate system is shown in Fig. 1. lowered, other peaks began Appropriate AE sensors and to emerge on the power map. amplifiers can be employed,