Measurement of solid armature´s in-bore velocity using B-dot probes in a series augmented railgun

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 arrive can be detected by an evident change in the differential signal from B-dot probe while armature passing by. However, it is difficult or even impossible in a railgun to directly pick up the arrive moment because of not only armature movement but also rail current contribution to the change of differential signal, especially in the series augmented railgun where all the time there are currents both in outer rails and connecting conductors to probably be sensed by the B-dot probe. To eliminate the influence of current change a ratio function has been introduced, which is the ratio of the integral of differential signal to the current. The ratio function of armature probe aimed at armature current will reach a maximum at the moment of armature arrive, while the one at rail current will reach the median. Three shots with identical initial conditions were conducted in a series augmented railgun, each of which had adopted armature probe, rail probe and VISAR, respectively. The well agreement with each other about displacement and velocity waveforms by B-dot probes indicated that method and measurement were valid. The accuracy of B-dot method is mainly affected by probe dimension and position, railgun current distribution and electromagnetic noise.