Laser-based apparatus for measuring projectile velocity

The design and construction of a apparatus to accurately determine the velocity of a projectile by measuring the time of flight between two parallel laser screens is presented. Each screen is formed by a laser source, a large photodetector and a retro-reflector. Optical output of the laser source is a collimated beam. The beam passes through cylindrical lens and the slit of photodetector reach to retro-reflector. The energy, reflected by retro-reflector, focus on the active area of photodetector. Whenever a projectile crosses either of the screens, the corresponding photodetector senses the event, due to partial or full obscuration of the incident energy. The change of light flux is transformed by photodiode in to electronic signal and sampled by data acquiring card. Data processing is processed by professional software in computer. The results show that the system working properly, non-occurrence of false triggering. Data of velocity are within the ranges supplied by the manufacturers. The apparatus can perform satisfactorily in outdoor and indoor ranges with a wide range of ambient light conditions.