§ electric Machine interference

One 、 Background introduction

   The motor discussed here is a small DC motor ,  The interference comes from the commutation ring inside the motor ,  Electric sparks caused by friction and commutation .  The interference signal can pass through the lead ,  Or the space electromagnetic wave is coupled to the circuit board of the accessory .  Let's test the size of this interference through experiments .

Two 、 measuring method

   Here are several small DC motors ,  Place an I-shaped inductor next to the motor ,  Test the electromagnetic field fluctuation caused by motor rotation .  The parameter of inductance is 0.319mH,  Equivalent series resistance ：1.339 ohm .  Now use an oscilloscope to observe the inductive signal output .

  
   Next, compare the rotation of small motors , Inductance output waveform .  This is the voltage waveform when the motor is not rotating ,  This is the voltage waveform when the motor rotates ,  You can see that there is not much difference between them .  Therefore, measuring with oscilloscope is different and reliable .

3、 ... and 、 Measurement results

   Use FLUK45 The effective value of the output signal of the inductance is measured by the AC Gear of . It can be seen that there is a great difference between the motor speed and the stop . When the motor stops , The output voltage is about 1.35mV; When the motor is running , The output voltage is about 17mV.

  
   Next, measure the motor under different voltages , Corresponding inductance output AC voltage . It can be seen that the amplitude of the output voltage is basically linear with the working voltage of the motor .  This is the working voltage from 0 Change to 6V The corresponding situation .  This shows the linear relationship between the external variable magnetic field of the motor and the working voltage of the motor .

Four 、 Apply capacitance

   Next, add a 0.1uF The ceramic chip capacitance of .  Compare the change of inductive output voltage before and after the increase .  This is in the case of adding capacitance , After the motor runs , Inductance output AC voltage , The maximum value is 12mV.  This is without adding capacitance , The output AC voltage amplitude of the inductor can reach 14mV, The interference increased slightly .
  
 

※ total    junction ※

   Here, I-type inductance is used to measure the external fluctuating electromagnetic field of the motor ,  It is seen that the increase of ceramic chip capacitance at the motor terminal has little effect on the magnitude of magnetic field fluctuation .  This may be because the inductance only measures the low-frequency magnetic field fluctuation signal .  If the measurement spectrum range is increased ,  You may see the function of the ceramic chip capacitor of the motor pin .