The operating conditions in a permanent magnet were analyzed to quantity the magnetic induction changes on the surface with an alternating magnetic field.

针对电机的实际工作环境 ，研究了不同工作状态的磁体在交变磁场作用下表面磁感应强度随时间的变化。

The conventional demagnetizing method is not good at inner demagnetization using direct or alternating magnetic field.

常规的交、直流消磁方法对材料内部消磁效果欠佳.

The induction method for measuring the alternating magnetic field is improved with the oscillograph , the effect and precision of the experiment are improved.

采用示波器对感应法测交变磁场实验进行了改进，提高了实验的效果和精度。