Ballistic velocity measurement system having dual sensor unit with parabolic slit mirrors

摘要

A chronograph for determining the muzzle velocity of a projectile fired from either a small arm or a rifle includes two IR light beam assemblies attached to a platform with respective photodetection circuits and a clamp for holding a vertical shot dispersion monitoring target plate at a rear extremity of the platform. The photodetection circuits provide start and stop signals for gating clock pulses of known frequency to an internal counter, the velocity being a scaled inverse of the measured interval. Each light beam assembly has two facing parabolic slit mirrors or reflectors with a photoemitter placed at one focal point and a photodetector at the other focal point for forming thin spaced beams oriented orthogonal to an intended path of the projectile. The photodetector circuit responds to a rapid drop in the total photocurrent of the photodetector in response to the partial blocking of the beam by a passing projectile. The photodetector circuit is DC coupled to the photodetector for providing an unsaturated calibration output signal. Also disclosed are design parameters for the parabolic mirrors and a method for calibrating the chronograph.