Abstract: Noise signals from a relatively moving object, such as those caused by eddies in a fluid or by protrusions and recesses or gradation on the surface of paper or an iron plate, are sensed at two or more points spaced in the direction of the motion. A difference signal is then obtained from the resulting two noise signals. The relative velocity of the object is detected from the difference signal by utilizing the autocorrelation function or the frequency spectrum of the difference signal.

Abstract: Noise signals from a relatively moving object, such as those caused by eddies in a fluid or by protrusions and recesses or gradation on the surface of paper or an iron plate, are sensed at two or more points spaced in the direction of the motion. A difference signal is then obtained from the resulting two noise signals. The relative velocity of the object is detected from the difference signal by utilizing the autocorrelation function or the frequency spectrum of the difference signal.

Abstract: A flow metering apparatus of the type having a vortex generating element with a generally elongate cylindrical shape placed in a stream of flowing fluid in a pipe so as to produce Karman's vortices at a rate proportional to the velocity of the flowing fluid, with ultrasonic means for detecting the rate of production of vortices to give a linearly related measure of fluid velocity. To improve the sensitivity of detection, especially at low velocities, the element is formed with a passageway transverse to the stream to produce therein an alternating fluid flow corresponding to the alternating shedding of vortices, and an ultrasonic generator and an ultrasonic receiver are positioned on opposite sides of the element so that the ultrasonic signal generated will be propagated through the passageway in the element and will be modulated by the alternating fluid flow therein.