Tham khảo tài liệu 'harris' shock and vibration handbook part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EXPERIMENTAL MODAL ANALYSIS FOURIER ANALYZER SHAKER SYSTEM FIGURE Typical fixed-input modal test configuration shaker. Impact impulse . The impact signal is a transient deterministic signal which is formed by applying an input pulse lasting only a very small part of the sample period to a system. The width height and shape of this pulse determine the usable spectrum of the impact. Briefly the width of the pulse determines the frequency spectrum while the height and shape of the pulse control the level of the spec- FOURIER ANALYZER FIGURE Typical fixed-response modal test configuration impact hammer. TABLE Characteristics of Excitation Signals Used in Experimental Modal Analysis Slow swept sine Periodic chirp Impact Step relaxation Pure random Pseudorandom Periodic random Burst random Minimize leakage Yes No Yes Yes Yes No Yes Yes Yes Signal-to-noise ratio Very high High Low Low Fair Fair Fair Fair RMS-to-peak ratio High High Low Low Fair Fair Fair Fair Test measurement time Very long Very short Very short Very short Good Very short Long Good Controlled frequency content Yes Yes No No Yes Yes Yes Yes Controlled amplitude content Yes Yes No Yes No No Yes Yes No Removes distortion No No No No Yes No Yes Yes Characterize nonlinearity Yes Yes No No No Yes No No Special hardware .
