In single-phase motor, another method of producing rotating magnetic field is called pole mask method, which is also called single-phase cover pole motor. This kind of motor stator is made into salient pole, there are two poles and four poles. Each pole has a small slot at the 1 / 3-1 / 4 full polar plane, dividing the magnetic pole into two parts, and putting a short-circuit copper ring on the small part, like putting this part of the pole hood together, so it's called a cap-type motor. The single-phase winding is set on the whole pole, each pole coil is in series, the polarity must be arranged according to N, S, N, S when connected. When the stator winding is electrified, the main flux is generated in the magnetic pole. According to Lenz's law, the main flux passing through the short circuit copper ring produces a 90 degree phase lag inductive current in the copper ring. The magnetic flux of this current also lags behind the main flux in phase, and its function is equivalent to that of the starting winding of capacitive motor, thus producing a rotating magnetic field to make the motor turn.