Until now I used railgun technology in pulse fusion tests, but unfortunately we had to move to design space and military railgun launchers
Recently I tested a railgun, but I can measure bullet speed after it goes out from the railgun by using high speed photodiodes and high speed camera.
It would be desirable to have the position of the bullet inside the railgun as a function of time.
During the measurement it is generated high power light and electromagnetic pulses.
The bullet speed from the first stage is about 500m/s
Use fiber optics for your light source and sensors so that the sensitive electronics are kept out of the field.
Simply, you can use photodiodes which connected to an oscilloscope or computer interface.
Would "measuring" position sensor-lessly meet your goals? You should be able to relate measured rail current = f(t) to bullet position and rail characteristics. Could you measure rail reaction force to measure bullet acceleration and so derive position? Would a high speed camera transverse to velocity show the rails bulging due to internal pressure?
David, you had a great idea, I can measure the magnetic field over the railgun as long as when the bullet passes under the receiving coil or sensor the magnetic field would changes its polarity
My problem was that I installed the photodiodes at the railgun exit over high power infrared diodes (see first photo)
But then there is a light burst in all the frequencies as can be seen in the attached scope plot. This burst hides the diode light in some shot (see the second figure):
The other idea that I had is to install a small mirror in front of the bullet to track it when it is moving (see third figure), but I am not sure that it could work.
I will increase the transmitting light at 10Mhz using high power diodes acquiring the light through a high pass filter
Depending on the reaction time of your components, you could use a lidar like approach to separate your signal from the noise. By pulsing your light source at a high frequency, it should be possible to differentiate it from the outside interference, assuming that the initial signal level is high compared to the interference. That does not appear to be the case from your plots. You could probably do background subtraction though to remove the ambient from the signal.
The discharge light and RF noise will make any approach problematic, but I also wonder if you couldn't use Doppler detection to isolate the moving object. The detector becomes more complicated, but it may be more sensitive than just an amplitude detection.
I supose the use of doppler detection of the bullet speed by using a rf emitter at the bullet, It could be don by mixing received signal from an antenna in front of the bullet again signal from rear antenna. With a frequency to voltage converter I could see the bullet speed directly at the scope.
What happend to high speed photography?
Using a strobe flashing at an adequate interval would "stop" the bullet on video or film.
Not with the burst of light being produced by the discharge itself. See the photograph Javier posted above. The trick here is to get information in the presence of a huge amount of interference.
Instead of measuring the projectile location within the barrel, I would sense the position of the armature by it's magnetic signature. You could place magnetic field sensors at fixed locations along the barrel normal to plane of the rails and they would indicate when the armature passed over them. This would enable you to derive the projectile's acceleration and velocity (well at least average velocity between 2 sensors) within the barrel.
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