Magnetic sensor arming apparatus and method for an explosive projectile

Abstract

A dipole magnet is placed in a sabot of an explosive projectile. The magnet is arranged and configured within the interior surface of the sabot--such that when the sabot is placed over the casing of the projectile, the majority of the magnetic flux tends to take a path through the projectile casing and between two sensing coils located within the fuze and within the projectile. The first sensing coil forms a larger circle which encompasses the aft end or outer diameter of the projectile which is made up of ferrous materials. The second sensing coil forms a smaller concentric circle (relative to the first sensing coil) and is situated inside the inner diameter of the after end of the projectile, thus encompassing no ferrous metal. The majority of the flux from the magnet enters the ferrous projectile casing, travels through the casing, and exits primarily between the two coils on a continuous path back to the magnet. In operation, as the sabot moves away from the casing after exit from the bore, the magnet also moves away. The result is that a change in the amount of flux flowing between the coils occurs. The change in flux moving between the two coils of wire creates a voltage that can be used to detect the sabot release. The second sensing coil is utilized to produce a gradiometer sensor. The output from the first and second sensing coils is provided to a summing block, the output of which is provided to a preamp/signal conditioning block. After the signal has been conditioned, the signals are provided to a differentiator and then to a threshold detector for subsequent transmission to the fuze logic.