## 4 Verification of High-Performance Measurements
### Actual Measurement with the Application of Acoustic Emission Monitoring  
In this case study, the program was used to detect and locate crack sources early by monitoring AEs during an in situ load test for a new hydraulic accumulator. The accumulator configuration is shown in Figure 11. During the testing, the operational oil was cyclically pumped into the accumulator. In each cycle, the oil pressure ascended to the peak amplitude, reaching 400 bar, and remained at this level for 0.2 s before declining to 100 bar. Each cycle was completed within approximately 0.8 s. These pressure settings were significantly more severe than those used in the operational design. The test was continued until the new accumulator was entirely broken.  
A simulation performed using ANSYS Workbench demonstrated that the greatest stress concentration occurred near the bottom thread of the lower shell under the test pressure conditions, as illustrated in Figure 11. Consequently, during the actual measurement, AE sensors were positioned around the accumulator at the bottom thread, as shown in Figure 12. Three types of 8152C Kistler sensors were installed at positions P1, P2, and P3. Two VS30-V Vallen sensors were placed at positions P1 and P3. The frequency range of the Kistler sensors was 100-900 kHz, whereas that of the Vallen sensors was 20-80 kHz. The measurement sampling rate was configured to be 2 MS/s per channel for eight activated channels using the DAQ device NI USB-6366. The 2-byte number format was selected to store the measurement data, which aligned with the 16-bit resolution of the DAQ device. These measurement configurations required an average write rate of 32 MB/s. Consequently, only HDD #1 was used for the measurements, with the specifications outlined in Section 3. Data were recorded every 10 min for 10 s, resulting in a data file size of 320 MB. The program successfully performed the measurements.  
After 18 h of testing, corresponding to 81,000 load cycles, the Kisler sensors detected AE events from the accumulator. Figure 13 illustrates a measured AE event indicating a potential crack in the accumulator that may not be visible yet. In the event, a burst wave was generated with frequencies greater than 120 kHz, beyond the detection range of the Vallen sensors. Although all eight channels were recorded to gather extensive information about the accumulator's condition and to verify the effectiveness of the data-writing algorithms, only the AE waves measured by the Kistler sensors were able to reveal the AE events. Figure 13d shows a comparison of the arrival times of the AE event waves at positions P1, P2, and P3, which are represented by black, red, and blue, respectively. The wave first arrived at P2, followed by P1, and finally at P3. The time differences in arrivals at P1 and P3 were minimal, suggesting that the fracture location was adjacent to P2 in the direction of P1.  
Figure 11: Configuration of the hydraulic accumulator.  
Figure 12: Installation of acoustic emission sensors.  
Figure 13: _Cont_.  
The load test was continued until the accumulator was completely broken, as depicted in Figure 14. The operational lifetime was approximately 29 h, which is equivalent to approximately 130,000 load cycles. A subsequent inspection after the test revealed that the initial cracking point was adjacent to P2 in the direction of P1, as previously indicated by the AE sensors. This test confirmed the ability of the program to perform AE measurements. In this case, the potential of the crack was accurately detected at an early stage, which was approximately 62% of the total operational lifetime. The total data size for all measurements was approximately 55.7 GB. This highlights the benefits of using a binary format for measurements with exceptionally high sampling rates.  
Figure 13: AE event wave measured by the Kistler sensors. (**a**) At position P1, (**b**) at position P2, and (**c**) at position P3. (**d**) Comparison of the arrival times of the AE event wave to positions P1, P2, and P3.