20 Jul A Brief Introduction to EMI of coin Motor
1.Basic theory of electromagnetic compatibility
In the same electromagnetic environment, the equipment can work properly under the interference of other equipment, and at the same time, it does not interfere with other equipment.
Electro Magnetic Compatibility (EMC)。
·Three Elements of EMC: Interference Source, Sensitive Equipment and Coupling Path.
·Coupling Path: Space Coupling, Wire Coupling (Power Line or Signal Line)
Electromagnetic compatibility evaluation index
2. Working Principle of coin Motor
DC current flows into the coil by sliding contact between the brush and the commutator (rectifier). The coils with different windings cut the magnetic force line in the permanent magnetic field formed by the stator assembly to produce electromagnetic force, which makes the rotor rotate. The current flowing through the brush makes this process circulate through the commutator, and the permanent motion of the rotor is realized.
3. Analysis of interference source of coin motor
According to the working principle of coin motor, coin motor belongs to brush motor, and its working resistance can be divided into single-phase and dual-phase, and it can be switched by cycle. When the brush transits from one part of the commutator to another, because of the instantaneous change of contact resistance, the current will suddenly change and the arc will be generated, resulting in steep pulsed electric field interference, which will cause high frequency interference harmonics in a wide frequency range, and the radiated interference will be transmitted through the power line.
4. Measures to Improve EMC
1. Principal and Break Coupling Path
For conductive coupling: adding filters between interference sources and sensitive devices.
For spatial coupling, interference sources need to be shielded.
2. Reducing the Intensity of Interference Sources
1) The arc of motor commutation is reduced by reducing carbon film resistance.
2) Adjust the elasticity of motor brush to reduce the fluctuation of contact resistance at the moment of commutation.
Due to the structural characteristics of coin motor, the electromagnetic interference can not be completely avoided in the motor body. At present, only adjusting the process parameters can reduce the intensity of electromagnetic interference.
5. Confirmation of Improvement Effect
Through the following Improvement Plan B , the customer confirms that the validation has passed and achieved the desired results.