Gun chronograph
Encyclopedia
A gun chronograph is an instrument used to measure the velocity of a projectile fired by a gun.
was used to measure the momentum
of the projectile
fired by a gun
; dividing the momentum
by the projectile mass
gives the velocity
.
An early chronograph that measures velocity directly was built in 1804 by Grobert, a colonel in the French Army. This used a rapidly rotating axle with two disks mounted on it about 13 feet apart. The bullet was fired parallel to the axle, and the angular displacement of the holes in the two disks, together with the rotational speed of the axle, yielded the bullet velocity.
that detect the passage of the bullet. The bullet is fired so it passes through both screens, and the time it takes the bullet to travel the distance between the screens is measured electronically.
The first electronic ballistic chronograph was invented by Kiryako ("Jerry") Arvanetakis in the 1950s. As consulting engineer under contract by NACA (later NASA
), he was asked to find a way to accurately measure the velocity of various projectiles fired at hyper-velocities
into a variety of engineered materials in anticipation of manned space flight. His first design was an open rectangular frame of square aluminum tubing with a screen of fine copper wire at both ends. Breaking the first wire started charging a capacitor
, breaking the second wire stopped it. Measuring the accumulated voltage and knowing the rate of charge the elapsed time could be accurately calculated.
History
Around 1800, the ballistic pendulumBallistic pendulum
A ballistic pendulum is a device for measuring a bullet's momentum, from which it is possible to calculate the velocity and kinetic energy. Ballistic pendulums have been largely rendered obsolete by modern chronographs, which allow direct measurement of the projectile velocity.Although the...
was used to measure the momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
of the projectile
Projectile
A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....
fired by a gun
Gun
A gun is a muzzle or breech-loaded projectile-firing weapon. There are various definitions depending on the nation and branch of service. A "gun" may be distinguished from other firearms in being a crew-served weapon such as a howitzer or mortar, as opposed to a small arm like a rifle or pistol,...
; dividing the momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
by the projectile mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
gives the velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
.
An early chronograph that measures velocity directly was built in 1804 by Grobert, a colonel in the French Army. This used a rapidly rotating axle with two disks mounted on it about 13 feet apart. The bullet was fired parallel to the axle, and the angular displacement of the holes in the two disks, together with the rotational speed of the axle, yielded the bullet velocity.
Modern chronograph
The modern chronograph consists of two sensing areas called chronograph screens, which contain optical sensorsPhotodetector
Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...
that detect the passage of the bullet. The bullet is fired so it passes through both screens, and the time it takes the bullet to travel the distance between the screens is measured electronically.
The first electronic ballistic chronograph was invented by Kiryako ("Jerry") Arvanetakis in the 1950s. As consulting engineer under contract by NACA (later NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
), he was asked to find a way to accurately measure the velocity of various projectiles fired at hyper-velocities
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...
into a variety of engineered materials in anticipation of manned space flight. His first design was an open rectangular frame of square aluminum tubing with a screen of fine copper wire at both ends. Breaking the first wire started charging a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
, breaking the second wire stopped it. Measuring the accumulated voltage and knowing the rate of charge the elapsed time could be accurately calculated.