1. Power off method
Using the characteristics of electromagnetic noise that change with the strength of the magnetic field, the size of the load current, and the level of conversion, the power supply is suddenly cut off after listening to the no-load motor for a period of time, and some of the noise will disappear immediately as the power supply is cut off. After a power failure, the noise generated by the motor continuing to run by inertia is mechanical noise. Repeat several times to be determined.
2. Change the voltage method
When the power supply voltage is rapidly dropped to a certain limit (the speed does not change greatly), if the electromagnetic noise is the main part of the motor noise, it will vary greatly with the voltage, while the other causes of the noise are basically unchanged.
3. Current test method
If the stator winding of the miniature geared motor is asymmetrical, the internal phase is broken, or the inter-turn is short-circuited, the current is unbalanced; if the rotor cage is broken or the rotor of the wound motor is asymmetrical, the stator current fluctuates, so as to identify electromagnetic noise.
4. Drag method
Use a low-noise motor to drive the tested motor to rotate, and lift and lower the carbon brush several times to identify the effect of carbon brush noise.
5. Method of dismantling parts
The aerodynamic noise has stable characteristics, which can be identified by the noise change before and after removing the fan of the miniature geared motor or the external blower (large and medium-sized motors). In addition, by replacing fans with different outer diameters and types, the difference in noise can be distinguished at different speeds, and the fan noise can also be identified.