Analysis of the Velocity and Current Measurement Method Based on B-Dot Probes for the Rail Gun

Measuring the velocity and displacement of the armature and current for a rail gun is important. The common method uses B-dot probes to acquire the discrete time points when the armature passes by them. These points can be interpolated into a curve of the armature's displacement. Actually, the common interpolation method has some disadvantages. Some probes may break down, and the interpolation method is regardless of the process between the discrete points. So it is difficult to get the armature's position at any time and the exact velocity at any position. Aiming at these disadvantages, this paper presents an improved method, which based on both B-dot points and the main current waveform. A B-dot probe beside the rails easily gives this waveform. The shape of the current waveform helps us to fit the curve with enough physical information. The new method can give a more precise velocity of the armature at an arbitrary position between two B-dot probes' positions. It is also practical outside of two B-dot probes' positions too. And it still works when some B-dot probes fail. Moreover, the current waveform with the adjusted amplitude is also calculated out. The launching experimental results and currents measured by Rogowski coils show that the improved method is highly suited for the velocity and current measurement for a rail-gun system.