With this more accurate estimate, we find the Q level to be 140. Random Damage Random vibration is considered in terms of its 3 and 2 instantaneous amplitude values. So, at the resonant frequency, the PSD levels of the product will be amplified by Q2. Sine on Random is also frequently used to include vehicle engine vibrations in automotive tests. No, that is close but not quitecorrect. Recall from equations (1) and (4) above, that when we have resonances in the product, they will amplify the vibration levels. Using sine vibration to identify resonant conditions on the PCB or on other test item structures is an effective way to understand how mechanical vibration propagates through a device and can help designers stiffen or dampen elements of the product to reduce the probability of a fatigue failure. The simplest musical tones are sine waves at particular frequencies. This would lead us to believe that the random test was a more severe test. As expected, at the Control point, the peak G levels for the Sine test were of course 3.5 G peak and 1.5 G peak. A random test is defined in terms of a PSD, which is an amplitude-squared measure. In a swept sine test a vibration sine tone is ramped up and down through a range of frequencies and for a specified rate and duration. A major difference between sinusoidal vibration and random vibration lies in the fact that for the latter, numerous frequencies may be excited at the same time. Sinusoidal vibration tests are not as helpful as random testing, because a sine test focuses upon a single frequency at any one time. Sine testing is primarily useful in identifying resonant conditions within a test item. While running the tests, we also simultaneously streamed the accelerometer data to the hard disk drive for later analysis. The most effective vibration test to run is one based on actual field measurements of the specific environment where a product will be operated. This is an important point because quite often accelerometers are sized based on the test profile´s acceleration level, while the resonances may see 10x or 100x the profile acceleration level. Figure 3: Comparison of the Sine equivalents of the Random profile, with various Q. A quick calculation tells us that the random test, which can have peak values up to 4 or even 5 times the RMS level, will apply 4 x 1.05 G rms, or 4.20 G peak to our product. The road input vibration is random in nature, whereas the engine sine component is too strong to ignore. If the measured vibration environment has sinusoidal characteristics then the random vibration profile can also be tailored to include sine tones applied over the random vibration background. The relative severity of a sine test and a random test will vary depending on your product´s resonant frequencies and Qs. Vibration from tracked vehicles is typical of Random on Random (ROR), where narrowband random is superimposed on broadband random. 0.01500 G2/Hz at 40Hz to 0.00015 G2/Hz at 500Hz Broad-spectrum random vibration contains not sinusoids but rather a continuum of vibration (with differing amplitudes, VRC)” (pg. Sine-on-Random-on-Random (SoRoR) vibration testing contains both sine tones and narrow band random peaks superimposed on broadband random vibration. It will also be helpful to refer to the following relationship, which tells us that, for a given RMS level, the PSD level is inversely proportional to the full bandwidth of the random spectrum. Mixed Mode Vibration Testing: Sine-on-Random (SoR) & Random-on-Random (RoR) Sweeping Modes: sine tones can either be individually configured with sweeping speeds and schedules (Free Sweep mode), or jointly defined as harmonics of the first primary tone (Harmonic mode) Number of Sine Tones (SoR): 1 - 12 in free-sweeping mode; 1 - 20 in harmonic mode, up to 32 when RoR is disabled

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