Secondly, the noise identification method

2.1 Power off method

Using the characteristics of electromagnetic noise that changes 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 part 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.

2.2 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 other noises are basically unchanged.

2.3 Current test method

If the stator winding is asymmetrical or the internal phase is broken, or the inter-turn short circuit, the three-phase current is unbalanced; if the rotor cage is broken or the three-phase of the wound motor rotor is asymmetrical, the stator current fluctuates, so as to identify electromagnetic noise.

2.4 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.

2.5 Disassembly method

For aerodynamic noise with stable characteristics, it can be identified by the noise change before and after removing the fan (small motor) or the external blower (large and medium motors). In addition, by replacing fans with different outer diameters and types, and distinguishing the difference in noise at different speeds, the fan noise can also be identified.