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Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Ok, i only saw this type of triggering for multo stage coilguns on one site, and that didn't have much information. The triggering is done by wraping somewire around the barrel, and when the projectile moves through it, then voltage is induced. The only problem i see is distinguishing the projectile passing from the large EM field made by the coil.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
I worked for several months on such a system, and pretty much decided that it wasn't practical by any stretch of the imagination. The sensitivity of the trigger circuit must be so high in order to sense the projectile that even pulses 2 or 3 stages down (12" separation in one case) were sufficient to trigger it.
I do have a working prototype of an inductance based sensor, though. Essentially its just a simplified metal detector. A high frequency signal (10MHz, for instance) is passed through a series resonant LC tank circuit (Capacitor and inductor in series). The inductive element is the small sensor coil wrapped around the barrel, and the capacitive element is a small air variable capacitor.
The tank circuit is adjusted to resonate at the frequency of the oscillator, ensuring minimal attenuation when no projectile is present. When the projectile moves into the sensor coil, the coil's inductance climbs dramatically, dragging the resonant frequency of the filter down. This pulls the pass band down below the oscillator frequency, attenuating the 10MHz signal, which is sensed by a comparator or similar on the output of the filter.
Any induced current from the propulsion coil is severely attenuated, and any current that does manage to get to the comparator will be of little consequence, as the comparator ignores it, watching only for a voltage below a certain level from the filter output.
By adjusting the Q of the circuit, and the ratio of inductance to capacitance, along with the trigger level of the comparator, the circuit can be made to work in almost any circumstance, even virtually directly under the propulsion coil.
This is a fairly simplistic explanaition of the system, but it does work, and I've tested it on systems up to several hundred joules per stage. I'll draw up a schematic when I get a free moment in the next couple days.
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coil triggering via induced voltage.
