Apparatus and method for calculating muzzle velocity
First Claim
1. Apparatus for measuring the muzzle velocity of a projectile, comprising:
- a washer-shaped magnet having a north pole and a south pole that is positioned on a projectile body so that its outside diameter is located close to that of the projectile'"'"'s outside diameter, and the south pole of said magnet faces the direction in which the projectile will exit the muzzle;
a position sensor having a first and a second inductive coil mounted a known separation apart, wherein a voltage is induced in each coil when said magnet passes through said inductive coil;
a first and a second wide bandwidth preamplifier, each having an input and an output;
first and a second comparator pairs, each comparator in said comparator pairs having a positive input, a negative input connected to and electrically coupled to ground voltage, and an output;
a digital counter having a start input, a stop input, an in input, a reset input and an output; and
a high precision frequency source connected to and electrically coupled to the input of said digital counter to provide a clock signal to said digital counter;
wherein the input of said first wide bandwidth preamplifier is connected to and electrically coupled to said first inductive pickup coil to amplify the voltage induced in said first inductive coil when said magnet passes through it and the input of said second wide bandwidth preamplifier is connected to and electrically coupled to said second inductive coil to amplify the voltage induced in said second coil when said magnet passes through it;
wherein the positive inputs of said first comparator pair are connected to and electrically coupled to the output of said first wide bandwidth preamplifier and the positive inputs of said second comparator pair are connected to and electrically coupled to the output of said second wide bandwidth preamplifier;
wherein the outputs of said first comparator pair are connected to and electrically coupled to the start input of said digital counter to start said counter when the voltage induced in said first inductive coil crosses zero; and
wherein the outputs of said second comparator pair are connected to and electrically coupled to the stop input of said digital counter to stop said counter when the voltage induced in said second coil crosses zero, and thereby generate a velocity count signal, corresponding to the velocity of the projectile, on said output of said digital counter.
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Accused Products
Abstract
Apparatus for measuring projectile muzzle velocity with an accuracy of ±0.1% is mounted in an easily portable muzzle attachment. It operates in the following manner. A washer shaped permanent magnet is positioned on a projectile body. A position sensor containing two inductive coils is located inside the muzzle. When the projectile is fired, the magnet mounted on the projectile passes through the inductive coils, inducing a voltage in each coil. Each voltage is amplified and then fed into hysteresis and zero crossing comparators corresponding to each inductive coil. The zero crossing comparator detects when the induced voltage crosses zero. The hysteresis comparator will gate out any noise induced zero crossings. The two zero crossings are used to start and stop a digital counter which generates a velocity count signal that corresponds to the velocity of the projectile. Further noise interference rejection is obtained by encasing the muzzle extension in a magnetic metal.
89 Citations
22 Claims
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1. Apparatus for measuring the muzzle velocity of a projectile, comprising:
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a washer-shaped magnet having a north pole and a south pole that is positioned on a projectile body so that its outside diameter is located close to that of the projectile'"'"'s outside diameter, and the south pole of said magnet faces the direction in which the projectile will exit the muzzle; a position sensor having a first and a second inductive coil mounted a known separation apart, wherein a voltage is induced in each coil when said magnet passes through said inductive coil; a first and a second wide bandwidth preamplifier, each having an input and an output; first and a second comparator pairs, each comparator in said comparator pairs having a positive input, a negative input connected to and electrically coupled to ground voltage, and an output; a digital counter having a start input, a stop input, an in input, a reset input and an output; and a high precision frequency source connected to and electrically coupled to the input of said digital counter to provide a clock signal to said digital counter; wherein the input of said first wide bandwidth preamplifier is connected to and electrically coupled to said first inductive pickup coil to amplify the voltage induced in said first inductive coil when said magnet passes through it and the input of said second wide bandwidth preamplifier is connected to and electrically coupled to said second inductive coil to amplify the voltage induced in said second coil when said magnet passes through it; wherein the positive inputs of said first comparator pair are connected to and electrically coupled to the output of said first wide bandwidth preamplifier and the positive inputs of said second comparator pair are connected to and electrically coupled to the output of said second wide bandwidth preamplifier; wherein the outputs of said first comparator pair are connected to and electrically coupled to the start input of said digital counter to start said counter when the voltage induced in said first inductive coil crosses zero; and wherein the outputs of said second comparator pair are connected to and electrically coupled to the stop input of said digital counter to stop said counter when the voltage induced in said second coil crosses zero, and thereby generate a velocity count signal, corresponding to the velocity of the projectile, on said output of said digital counter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of calculating a muzzle velocity comprising the steps of:
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generating a start input signal to a digital counter, when a voltage induced in a first coil decreases in magnitude from a positive voltage to a negative voltage crossing the zero voltage point, based on when a second pole of a magnet mounted on a projectile crosses said first inductive coil; commencing a counting operation of said digital counter based on said start input signal; generating a stop input signal to a digital counter when a voltage induced in a second coil decreases in magnitude from a positive voltage to a negative voltage crossing the zero voltage point, based on when the second pole of the magnet mounted on the projectile crosses said second inductive coil; ceasing the counting operation of said digital counter based on said stop input signal; determining a velocity count by retrieving an output of said digital counter; retrieving a known frequency of a high precision frequency source; calculating a time between said start input signal and said stop input signal by multiplying said velocity count by the output frequency of said high precision frequency source; and dividing a known separation apart distance by the time between said start input signal and said stop input signal.
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21. A method of calculating a muzzle velocity comprising the steps of:
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generating a start input signal to a digital counter when a voltage induced in a first coil decreases in magnitude from a positive voltage to a negative voltage crossing the zero voltage point, based on when a second pole of a magnet mounted on a projectile crosses said first inductive coil; commencing a counting operation of said digital counter based on said start input signal; generating a stop input signal to a digital counter when a voltage induced in a second coil decreases in magnitude from a positive voltage to a negative voltage crossing the zero voltage point, based on when the second pole of the magnet mounted on the projectile crosses said second inductive coil; ceasing the counting operation of said digital counter based on said stop input signal; determining a velocity count by retrieving an output of said digital counter; and calculating the muzzle velocity by dividing a known separation distance apart between said first inductive coil and said second inductive coil by the time between said start input signal and said stop input signal. - View Dependent Claims (22)
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Specification