46 D.P. Rohe Fig. 5.5 Laser camera view showing points used for alignment (marked withplus) Fig. 5.6 Laser camera view showing measurement points for a given baseline scan poor signal return from the high AoI. The maximum AoI for a measured point in this test was 55ı. With 16 circumferential stations, this required four separate scans to measure the entire part with each scan measuring 40 points. Frequency response functions (FRFs) were measured up to 2000 Hz with a frequency resolution of 1.25 Hz. Random excitation was applied to the shaker and 20 averages were measured at each scan point. Hann windows were applied to the measured responses. For this test, all signal enhancement parameters were set to their highest levels. This allowed the laser system to detect when poor quality data were measured and add up to 100 total averages to improve the data. It became obvious during the test that the baseline system was struggling to get good measurements from the darker surface due to poor signal return. Signal dropouts and their resulting over-ranges were prevalent. The system was not able to measure FRFs for 10 of the 16 points on the darker surface, and the FRFs of the points that were measured were very noisy (see, for example, Fig. 5.7). 5.2.2 1D Test with New System The same test article was scanned with the new system in 1D mode to compare the results to the previous test. Due to lab space constraints, the original test setup had to be dismantled between tests, but the shaker hardware was left attached to the test article to ensure consistent drive point excitation locations. When the test was set back up, the same bungee cords were used to suspend the test article, and the stinger was simply re-attached to the force gauge that was left attached to the test article.
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