Method and device for detecting geometric neutral line of direct-current motor

The invention discloses a method and a device for detecting a geometric neutral line of a direct-current motor. The method comprises the following steps of: S100, connecting an alternating-current power supply to a main exciting winding; s200, connecting an electronic tube voltmeter to the electric brush, and measuring the induced electromotive force of the electric brush through the electronic tube voltmeter; and S300, finding out the position with the minimum induced electromotive force of the electric brush by adjusting the position of the electric brush, and determining the position with the minimum induced electromotive force of the electric brush as the geometric neutral line of the direct-current motor. According to the method, a traditional direct-current power supply is replaced by an alternating-current power supply to be connected to the main exciting winding, the position of the electric brush with the minimum induced electromotive force is found by continuously adjusting the position of the elect