Projectile Velocity Measurement.

This application specific configuration of Kaman's KD-2300 system
provides an analog signal to standard data acquisition equipment
allowing the user to very precisely calculate projectile velocity

With no target projectile present, the analog voltage output of the system is
zero. When a projectile enters the electro-magnetic field of the first coil, the
output increases until the projectile is at the axial center of the coil. As the
projectile leaves the coil field, the output returns to zero. The same occurs
when the projectile engages the electro-magnetic field of the second coil.
The difference is that the spike in the output is negative instead of positive.

The analog voltage output of the KD-2300 is captured by the customer's data
acquisition system. By dividing distance between the coils by time between
the positive and negative peaks in the output, the velocity of an electrically
conductive projectile can be detennined. Overall accuracy is dependent on the
distance between the sensor coils and the customer's data acquisition system.

The recommended velocity limits are based on the time it takes the KD-2300
circuit to come out of saturation when a projectile enters the coil's electro-magnetic
field, and the time of engagement as it passes through the coil. Considering that
a larger diameter projectile will cause the circuit to react to a greater degree than
a smaller diameter, and that the length of the projectile can vary, it is possible
that the limits identified can be exceeded.

Accuracy is dependent on the instrument used to capture the data, and the
distance between the coils.

Maximize the distance between the sensors, and ensure the sensors are
oriented identically. This can be verified by having the sensor connections
of both sensors on the same side of the mounting bar.
Check and adjust the gain setting every time a different material, size, or
shape of projectile is tested.
If a debris shield is used make sure that it is manufactured of non-conductive
material, or at least 3 times the sensor ID away from the sensor.

For more information contact:-

Malcolm Read at Ixthus Instrumentation

March 2002

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