The power supply adopts hand-cranked DC generator G or rectified power supply. The measuring mechanism consists of two moving coils, both of which are in the magnetic field generated by the permanent magnet. Rc and RU are additional resistors, and Rx is the measured resistance. When current flows through the coil, the moving coil 1 generates a rotating moment M1, and the moving coil 2 generates a resisting moment M2; when the two moments M1 and M2 are balanced, the deflection angle α of the movable part α = f (I1 / I2), that is, the deflection angle It is related to the ratio of the current passing through the two coils, but not to the power supply voltage.
Such a magnetoelectric system measuring mechanism is called a magnetoelectric system current ratio meter. For different measured insulation resistance values Rx, the current ratio I1 / I2 is also different, so the movable part has different deflection angles, the pointer gives different resistance readings. When Rx = 0, I1 is the largest, the deflection of the movable part is also the largest, and the pointer turns to the far right of the scale. Conversely, if Rx = ∞, then I1 = 0, the movable part deflects under the action of I2, and the pointer turns to the far right end of the scale. Therefore, the scale of the high resistance meter is reversed.