Jun,29 3.5 critical speed A speed of a rotating system that corresponds to a natural frequency of the system. 3.6 damping The dissipation of energy with time. 3.7 displacement d A vector quantity that specifies the change of position of a body or particle and is usually measured from its position of rest. Displacement is expressed in mils (1 mil = 0.001 in.) or millimeters (1 mm = 1 0 ð3 m). 3.8 excitation An external force (or other input) applied to a system that causes the system to respond in some way. 3.93.9 filter An analog or digital device for separating signals on the basis of their frequency. It introduces relatively small loss to signals in one or more frequency bands and relatively large loss to signals at other frequencies. 3.10 forced vibration Oscillation of a system if the response is imposed by continuous excitation. 3.11 foundation support A structure that supports the loads of a mechanical system. It may be fixed in space, or it may undergo a motion that provides excitation for the supported system. 3.12 frequency f The reciprocal of the period of a function in time. NOTE 1 NOTE 2 The unit is cycle per unit time. The unit cycle per second is called Hertz (Hz). 3.13 fundamental frequency The lowest natural frequency of an oscillating system. 3.14 g The acceleration produced by the force of gravity, which varies with latitude and elevation at the point of observation. NOTE By international agreement, the value 32.1 739 ft/sec 2 = 386.087 in./sec 2 = 980.665 cm/sec 2 has been chosen as the standard acceleration due to gravity.
3.15 G The ratio of local acceleration to the acceleration of gravity. 3 NOTE For example, an acceleration of 38.6 in./sec 2 (98.1 cm/sec 2 ) is written as 0.1 G. 3.16 isolation A reduction in the response of a system to an external excitation, attained by the use of a resilient support. 3.17 natural frequency f n A frequency of free vibration of a system. NOTE There are a large number of natural frequencies in complicated systems, though normally only a few have energy contents high enough to be of concern. 3.18 oscillation The time variation of the magnitude of a quantity (e.g. displacement). 3.19 peak-to-peak displacement d pp The algebraic difference between the extremes of the displacement of a vibrating quantity. NOTE This is twice the amplitude of the sinusoidal displacement. 3.20 peak velocity The maximum velocity occurring during normal sinusoidal displacement. NOTE Housing or case vibration is normally measured in units of peak velocity. 3.21 period The time interval to complete one cycle of sinusoidal oscillation, usually expressed in seconds. 3.22 resonance Situation when the forcing frequency is at or near a system natural frequency when a forced vibration exists. NOTE Any change, however small, in the frequency of excitation results in a decrease in the response of the system. 3.23 rotating speed N The frequency at which the mechanical system rotates, generally expressed in revolutions per minute (RPM). 3.24 simple harmonic motion A motion in which the displacement is a sinusoidal function of time. NOTE Sometimes it is designated by the term harmonic motion.
3.25 steady-state vibration Vibration that exists when period and amplitude are constant. 3.26 stiffness The ratio of change of force (or torque) to the corresponding change in translational (or rotational) deflection of an elastic element. 3.27 subharmonic A sinusoidal quantity having a frequency that is a fraction of the fundamental frequency. 3.28 synchronous vibration The filtered component of vibration at the frequency that corresponds to the machine rotating speed. 3.29 transducer pickup A device that converts vibration or shock motion to an optical, a mechanical, or most commonly to an electrical signal that is proportional to a parameter of the experienced motion. 3.30 velocity v A vector quantity that specifies the time rate of change of displacement with respect to a reference time frame. 3.31 vibration A term that describes oscillation in a mechanical system. 3.32 vibration meter An apparatus for the measurement of displacement, velocity, or acceleration of a vibrating body.

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