| Popis: |
The design and construction of a system to accurately determine the speed of a projectile (bullet) by measuring the time of flight between two parallel laser screens is described. Each screen is formed by a laser source and a set of prisms. At the detection end of each of the screens, a collector lens focuses the incident laser light beam onto a photodetector. The collector lens and detector are kept in a recess so that no stray or ambient light falls on the 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. An electronic circuit is used to accurately record the time when the projectile crosses each screen, and the time interval gives the time of flight. The distance between the screens being known, the velocity is displayed on a computer screen. Because a single collimated beam of light generates the entire optical curtain, the reduction in incident energy at the photodetector plane is independent of the entry point of the projectile into the screen. Due to the baffling of the photodetector from ambient light, the optical screens can be used at indoor or outdoor ranges equally effectively. |
