This invention mainly develops the multiple discharge-servo curve control method and device of electrical discharge machine. The impulse ring comprises at least one pair of magnetic poles or at least one magnet with north poles and south poles alternatively arranged along its circumference. The conductive contacts are disposed on the surface, and the conductive sealing ring is disposed on the surface and surrounds the conductive contacts. The compactness of the detector makes it ideally suited for utilization in a miniature electron beam column, such as a microcolumn. The isolation tool can control flow of the pulverized formation cuttings mixed with a drilling mud uphole through the drill string. A low voltage for avoiding occurrence of a high electric field is applied to the auxiliary transfer roller, while a high transfer voltage for realizing sufficient transfer is applied to the main transfer roller.