Measurement of Solid Armature’s In-Bore Velocity Using B-Dot Probes in a Series-Augmented Railguns

The waveform of solid armature displacement and velocity can be obtained by arranging B-dot probe arrays along the barrel of a series augmented railgun. The moment of armature arrival can be detected by an evident change in the differential signal from the B-dot probe while armature passes by. However, it is difficult or even impossible in a railgun to directly pick up the arrival moment, because both armature movement and rail current are responsible for the change of differential signal, especially in the series-augmented railgun where currents in both outer rails and connecting conductors are probably sensed by the B-dot probe. A ratio function (RF) has been introduced to eliminate the influence of current change, which is the ratio of the integral of differential signal to the current. The RF of the armature probe aimed at the armature current will reach a maximum at the moment of armature arrival, while the one at the rail current will reach the median. Three shots with identical initial conditions were conducted in a series-augmented railgun, each of which had adopted the armature probe, rail probe, and Velocity Interferometer System for Any Reflector, respectively. The good agreement between the displacement and velocity waveforms derived from B-dot probes indicated that the method and measurement were valid. The accuracy of the B-dot method is mainly affected by probe dimension and position, railgun current distribution, and electromagnetic noise.