Noncontacting vibration pickups

THIS digest discusses a group of methods for the measurement of vibration by devices which make no mechanical contact with the vibrating object. These devices sense the vibrations by their effect on an electric field between the pickup and the object shaken and give the magnitudes of the frequency, amplitude, and waveform of the vibratory displacements. In spite of the disadvantage of determining accelerations by measuring the frequency, amplitude, and waveform of the displacements, owing to the very large range of displacements required to hold constant acceleration through considerable frequency changes, these devices are highly useful. Effectively, they are a class of transducers for converting mechanical displacement to electric output which do not load the vibrating object.