A Novel Measurement Method of Solid Armature's In-Bore Motion State Using B-Dot Probes for Rail Gun

Measuring the solid armature's in-bore motion state using B-dot probes is significant for studying the electromagnetic emission. 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. However, considering the rapid current changes, the points contain an error. What is worse, it is difficult to recover the armature's whole process motion by limited discrete points. In this paper, by deeply digging out the information contained in induced electromotive force curve of B-dot probes, a novel measurement method is proposed, which we can recover solid armature's in-bore whole process motion without any interpolation. At the beginning, considering the current skin and velocity skin effects, a precise 3-D model is built. By analyzing the effect of the current changing rate, the discrete precise time points when the armature passes by them are getting. Then, through the mathematical transformation and applying Newton's second law, a novel method to acquire velocity curve, displacement curve, and acceleration curve of armature's in-bore motion in the whole launch process is put forward. Finally, the simulation model of 9-m rail gun with 18 B-dot probes is built. Simulation shows that the proposed method can obtain precise armature's in-bore motion state in the whole electromagnetic emission process and can deduce in-bore force curve of the armature, which is significant for fault diagnosis of launcher.