40 E. Proner and E. Mucchi The test specification used to generate the target vibration environment consists of flat uncorrelated profiles of 1 gRMS in the frequency range [20−600] Hz, replicated simultaneously on each direction the tab accelerometer. Figure 3 depicts the comparison of the response PSDs measured the tab accelerometer. The three subplots on the left show the acceleration PSDs along the three orthogonal direction measured by the response accelerometer. These include the target PSD (blue solid line), the PSD obtained using the MPM(orange dashed lines), the PSD obtained in the test performed controlling thetabaccelerometer and using theMDM(yellow dotted-dashed line) and the PSD obtained when controlling the tipaccelerometer and using the MDM(purple dotted line) . On the right side of Figure 3, the bar plot reports the acceleration RMS value measured by the tipaccelerometer for each direction. It can be observed that test performed using the MPMand the test performed using MDMand controlling the tip accelerometer (labeledMDMtip) both provide a good match with thetarget measurement PSDs. Furthermore, the acceleration RMS obtained by the MPMand the MDM tip tests is close to the target RMS for each direction. In particular, the target acceleration RMS are 8.57g, 20.01g and5.30g, the MPMtest achieved an acceleration RMS of 8.89g, 20.1g and5.05g, the MDMtiptest achieved an acceleration RMS of 8.77g, 19.71g and5.43g along the X, Y and Z axis, respectively. On the other hand, the MDMtabtest, performed controlling the tabaccelerometer by using the MDMand with the same excitation PSDs of the target, determined different results. In particular, the response of the specimen is lower than the response obtained during the target measurement. The difference is significant especially along the Y and Z direction where the acceleration RMS determined during the MDM tab test is 12.73g and 3.77g, respectively. In fact, changing the correlation of the refer100 200 300 400 500 600 Hz 10-6 10-4 10-2 100 102 g2/Hz PSD X Target MPM MDM tab MDM tip 100 200 300 400 500 600 Hz 10-6 10-4 10-2 100 102 g2/Hz PSD Y Target MPM MDM tab MDM tip 100 200 300 400 500 600 Hz 10-6 10-4 10-2 100 102 g2/Hz PSD Z Target MPM MDM tab MDM tip RMS X 0 2 4 6 8 10 g Target MPM MDM tab MDM tip Y 0 5 10 15 20 25 g Target MPM MDM tab MDM tip Z 0 1 2 3 4 5 6 g Target MPM MDM tab MDM tip Fig. 3 Acceleration PSDs measured by the tipaccelerometer during the tests and their respective RMS value
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