Ballistic measurement systems: optically measuring the projectile velocity (1955)

Optically measuring the projectile velocity (1955)

This optical device measures flight times of projectiles coming from a cannon barrel. Two device sets were built for the Commission of Trials of the Royal Netherlands Army. The first device set was taken into use in 1955. The measurements can be performed when shooting at elevations from 0° to 85°. The equipment is composed of two parts, the photo bar and the main amplifier. The photo bar is placed under the projectile track. The photo bar consists of two measuring heads that are connected to each other by a steel tube with a fixed distance of two meters. Each measuring head contains two photomultipliers, preamplifiers and a double optical system so that projectiles can be measured over two independent measuring systems.

Construction of the photo bar and the schematic device setup
Construction of the photo bar and the schematic device setup

When the projectile passes, the light from the sky that falls on the photomultiplier is partly blocked. The amplified detector signal is converted into pulses in the main amplifier, which corresponds in time with the passing of the projectile through the “watched sky” by the front and rear detectors. The different pulses are used as start and stop signals for four electronic time interval meters (two front and two rear measurements). The speed of the projectile can be determined from the known base length (2 meters) and the measured flight time.

The photo bar on tripod, Doppler radar and tailstock for measuring projectile velocities under elevation
The photo bar on a tripod, Doppler radar and tailstock for measuring projectile velocities under elevation