A light screen device for measuring the velocity of a projectile comprising a laser disposed opposite to one end of a first plane reflecting mirror and inclined with respect thereto to cause a laser beam to strike the first plane reflecting mirror and in turn to reflect the beam to a second plane mirror and successively reflecting the beam back and forth vertically to higher points on each mirror surface forming a criss-cross rectangularly shaped light grid network therebetween. A light detector is disposed axially in line with a reflected beam to intercept and detect the continuing presence thereof and to generate a pulse signal in response to the projectile passing through the light screen to stop a counting circuit.
LASER SCREEN GOVERNMENTAL INTEREST
The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.
Various means have been used in the prior art to determine the velocity of projectiles undergoing development. Some prior art devices utilize large wire coils to insure the clearance of a magnetized projectile passing therethrough. Frequently these large coils had the problem of generating a reduced induced pulse signal. The small pulse signal necessitated the use of more powerful magnets within the projectile to produce a signal capable of being adequately measured. In cases where the projectile being tested was small, it was not possible to change the size of the permanent magnet contained therein. The problem with prior art devices utilizing the break paper technique frequently required a thicker or more supportive arrangement to stop flexing and vibration of the paper by the wind. These large sheets of break paper generally cut down the availability of down range camera coverage of the projectile firing.