Abstract: An apparatus and method for detecting a moving object as it passes through a light curtain generated by one or more emitters, by the means for detecting the light of the light curtain reflected by the passing object onto a photoelectric detector. The object sensing area is not constrained by mechanical means and is limited only by the light curtain shape. Velocity of the object is determined primarily by dividing the known distance between two or more parallel light curtains by the time of passage between the light curtains. Additional velocity measurement obtained from the known object length divided by the time of its passage through the light curtain allows verification of the primary velocity measurement. Direction of the object motion across the sensitive area is determined by implementing two or more uniquely identifiable, closely spaced parallel light curtains, and corresponding uniquely identifiable detectors.

Abstract: A method and apparatus for detecting a projectile or another moving object as it passes through a light curtain generated by one or more emitters, by the means of detecting the light of the light curtain reflected by the passing object onto a detector located in proximity to the emitter. The projectile or object sensing area of the apparatus is not constrained by any mechanical means and is limited only by the shape of the light curtain. Velocity of the projectile or object is determined by dividing the known distance between two or more parallel light curtains by the time of passage of projectile or object between the light curtains. Additional velocity measurement is obtained from the known projectile length and the time of passage of the projectile through the light curtain and allows verification of the primary velocity measurement.