Improvement of a Low-Cost Combined Fitting Method for the Armature Speed and the Rail Current Measurement

Measuring the armature speed in bore and the rail current is very important in doing a further research for the launcher design. The B-dot probe method we often used has limited number of probes and its mathematical fitting curve has no actual physical meanings. Therefore, the current waveform's shape information was used to improve the B-dot probe method's result. The combined method could give an armature's velocity at an arbitrary position, and the current waveform could also be calculated out at the same time. Although the combined method was suitable for the measurement, the transient situation limited the accuracy of the results. According to the transient current, the inductance gradient and the distance between rails and a probe are changing during the launching process. In this paper, this two varied parameters that influence the combined method are discussed. The experimental data shows that the improvement of the combined method is more reliable and suitable.