Plus the exciteramplier system trying to maintain the

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Unformatted text preview: ion signal would be combined with cyclic averaging. 10 1 Power Spectrum − Burst Pseudo Random 10 0 Magnitude 10 −1 10 −2 10 −3 0 5 10 15 Spectral line (bin) 20 25 30 Figure 5-21. Signal Energy Content - Burst Pseudo Random Burst Periodic Random - Figure 5-22 shows the energy content of a hybrid excitation method that combines periodic random with burst random. This excitation signal would be combined with cyclic averaging. 10 1 Power Spectrum − Burst Periodic Random 10 0 Magnitude 10 −1 10 −2 10 −3 0 5 10 15 Spectral line (bin) 20 25 30 Figure 5-22. Signal Energy Content - Burst Periodic Random (5-55) +UC-SDRL-RJA CN-20-263-663/664 Revision: June 12, 2001 + 5.3.5 Deterministic Excitation Methods Slow Swept Sine - The slow swept sine signal is a periodic deterministic signal with a frequency that is an integer multiple of the FFT frequency increment. Sufficient time is allowed in the measurement procedure for any transient response to the changes in frequency to decay so that the resultant input and response histories will be periodic with respect to the sample period. Therefore, the total time needed to compute an entire frequency response function will be a function of the number of frequency increments required and the system damping. Periodic Chirp - The periodic chirp is a deterministic signal where a sinusoid is rapidly swept from F min to F max within a single observation period (T). This signal is then repeated in a periodic fashion. While this signal is not random in characteristic, it is often included in discussions of random excitation since it has similar properties as pseudo random. (5-56) +UC-SDRL-RJA CN-20-263-663/664 Revision: June 12, 2001 + Chirp Force Excitation 6 4 2 Amplitude 0 −2 −4 −6 0 1 2 3 4 5 6 Time (Seconds) 7 8 9 10 Figure 5-23. Typical Chirp Signal - Time Domain (5-57) +UC-SDRL-RJA CN-20-263-663/664 Revision: June 12, 2001 + 10 3 Chirp Force Excitation 10 Magnitude 10 2 1 10 0 0 1 2 3 4 5 6 Frequency (Hertz) 7 8 9 10 Figure 5-24. Typical Chirp Signal - Frequency Domain Impact (Impulse) - The impact signal is a transient deterministic signal which is formed by applying an input pulse to a system lasting only a very small part of the sample period. The width, height, and shape of this pulse will determine the usable spectrum of the impact. Briefly, the width of the pulse will determine the frequency spectrum while the height and shape of the pulse will control the level of the spectrum. Impact signals have proven to be quite popular due to the freedom of applying the input with some form of an instrumented hammer. While the concept is straight forward, the effective utilization of an impact signal is very involved [33,34,37] . (5-58) +UC-SDRL-RJA CN-20-263-663/664 Revision: June 12, 2001 + Step Relaxation - The step relaxation signal is a transient deterministic signal which is formed by releasing a previously applied static input. The sample period begins at the instant that the release occurs....
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This note was uploaded on 09/29/2013 for the course MECHANICAL ME taught by Professor Regalla during the Fall '11 term at Birla Institute of Technology & Science, Pilani - Hyderabad.

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