Text: A mathematically constructed diagram used in rotating machinery design as a tool for selecting and checking shaft rotative speeds so as to avoid excitation of natural resonance(s) in the system. The X axis represents the various excita-tion frequencies, i.e., rotative speed, misalignment (2X), oilwhirl (40-48% X), blade or vane passing frequencies, gear mesh frequencies, etc. The Y axis represents the lateral and torsional resonance frequencies. The term is sometimes used incorrectly to describe a CAMPBELL DIAGRAM plot of machine vibration frequency (X axis) versus vibration amplitude (Y axis) at various shaft rotative speeds. The accepted terms for the latter type of data presentation are Cascade plot and Waterfall plot.

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