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Fundamentals of vibration

Vibration - repetitive motion of a body around an equilibrium position. Vibration is generally represented as a sine wave.

Period (T) - time required for one complete cycle, in seconds.

Frequency (F) - number of cycles completed in one second and it is the reciprocal of the period, in Hertz.

Units of measure

  • Displacement (D) - deviation of measured point from rest position, in inches or millimeters. Typically used for applications where frequency is below 500 Hz.
  • Velocity (v) - rate of change of displacement (v = D / t), in inches per second or millimeters per second. Typically used for applications in the 2…2000 Hz range. Most motor-driven equipment from 600 to 3000 rpm will fall within this frequency range.
  • Acceleration (a) - rate of change of velocity (a = D / t2), in inches per second squared or meters per second squared. 1 g = 386 in / sec2=9.8 m / sec2. Typically used for applications in the 4…20,000 Hz frequency range.
  • Amplitude - distance from zero
          • Peak - zero to maximum positive or negative value.
          • Peak-to-Peak - maximum positive to maximum negative value.
          • RMS - 0.707 times peak value.