Model 57 Infrared Ballistic Screens

General The Model 57 Ballistic Screens are use to detect projectile passage through a reference plane. They use an infrared light source mounted at the top of the screen and a series of photodetectors mounted in the base. The screens will normally detect projectiles as small as .17 caliber at velocities as low as 250 fps. Sensitivity improves with larger projectile and higher velocities. Automatic gain control is included to compensate for effects such as dust in the light path. Ambient Light The screens will operate under reasonable conditions of ambient light from darkness to sun. The screens are not normally triggered by external fluorescent light under normal conditions. The screens can be easily triggered by fluorescent light while the detector portion is removed from the screen frame.

Output

The screen provides a nominal +12 volt pulse of approximately 2 ms duration from a panel mounted BNC connector. The output can be approximated by 50 ohms to +12v in the high state and by 10K ohms to ground in the low state. Rise time is approximately 0.1 microsecond. More than one pulse may occur for the passage of a single projectile.

Subsonic Bullets

For any projectile velocity less than 1200 fps and for automatic fire, you must place a wooden blast shield midway between the muzzle and the first screen. The shooting hole through the center of the baffle should be as small as is convenient. The hole need not be square or round; a vertical rectangle is often convenient and effective. The muzzle blast shock wave preceding a subsonic bullet often causes a light diffraction and false trigger at the screen. The muzzle blast wave from the preceding shot can cause problems during automatic fire.

240-volt Operation

The units are normally shipped set for operation from 120 volt ac power. Either 50 or 60 Hz is acceptable. To change to 240 volt, remove the fuse cover by prying up on the left-hand end. Pull up the white nylon pin located at the right-hand end to remove the small circuit board, change the orientation of the board so that the 240 volt legend points down, and replace the board. When the fuse holder is replaced, the white nylon pin should protrude through the hole marked "240". The provided line cord has the standard US three-conductor grounding plug; user must supply line cord for other local standards.

Infrared Lights

There is a line of 72 infrared emitting diodes in the top of the unit. These infrared diodes are arranged in 12 series strings, and each string includes a red diode visible from the front of the unit. The illumination of each red diode assures that the associated infrared diodes are operating.