Inaccuracy in measuring solid armature velocity by B-dot probe in electromagnetic launch
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摘要: 对磁探针感应电压的原理进行分析,得出电枢电流变化率是磁探针测量电枢膛内运动位置误差的原因。通过简化,采用理想化的电枢电流波形和电枢位移曲线,不同电枢电流变化率条件下,在Matlab软件中对磁探针测量电枢位置进行仿真分析。结果表明:测量电枢位置误差与电枢电流变化率绝对值正相关,电枢电流变化率相同时,误差与电枢电流和电枢速度的乘积负相关。进一步对磁探针测量电枢膛内速度的误差进行仿真分析,理想电流曲线仿真结果表明:测速误差情况可分为三种,电枢电流变化率相近,则测速误差小,反之则测速误差大。Abstract: The B-dot probe is one of the most common measurements of velocity for armatures in the bore of a railgun. In this paper, we analyzed the principle of B-dot probe induced voltage, and found that the rate of change of armature current is the inaccuracy factor in locating moving armature by B-dot probe. Armature currents with different dI/dt were set in the Matlab simulation of locating moving armature by B-dot probe. The results show that the error in locating moving armature by B-dot probe is positively correlated to the absolute value of dI/dt, and is negatively correlated to the product of armature current and armature velocity if dI/dts are equal. According to the results, we performed a further simulation of inaccuracy in B-dot-probe measurement of armature velocity, and its results could be divided into three types. Real current data were utilized to replace the ideal current in the simulation, the results of which well matched the ideal one. In short, the error in measuring armature velocity by B-dot probe is small if dI/dts are similar, and the error is large if dI/dts are different.
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