The buzzer can only judge whether the resistance of the line is larger or smaller (generally, it is about 30-50Ω as the dividing point, and different multimeters are a little different).

Assuming that the critical resistance of the buzzer gear of the multimeter is 50Ω, the buzzer gear will ring only when the resistance of the line or load is less than 50Ω, and the smaller the resistance, the greater the buzzer sound. But when the resistance of the line or load is more than 50Ω, the buzzer will not ring. Therefore, when the line resistance is greater than 50Ω or ∞, we can't distinguish it with the buzzer.

Single-phase motor quality judgment

From knowing that the motor has four wires in total, we can infer that the motor should be a single-phase motor (the specific type of single-phase motor can only be concluded after seeing the real thing).

Single-phase motor has two coil windings, one is the starting winding and the other is the running winding. Because the running winding is thicker and the starting winding is thinner, the resistance of the starting winding is larger than that of the running winding. The specific resistance value is related to the motor model and power, and it is possible from more than ten ohms to one or two hundred ohms. (The greater the motor power, the smaller the resistance; The smaller the power, the greater the resistance)

If the power of the motor is very small, its resistance will be very large. If the resistance is greater than 50Ω, the result we measured with the buzzer is no sound. Similarly, if the motor winding is burnt out, then we will not sound when we use the buzzer.

If the motor power is high, its resistance value will be very small. If the resistance value is less than 50Ω, the result we measured with the buzzer gear is a buzzer. Similarly, if there is a short circuit in the middle of the motor winding, then the result we measured with the buzzer gear is also a buzzer.