The reason is the same, that is, after the current passes through the switch, the original waveform is destroyed because of on and off, just like a stone thrown into the water, which produces ripples. Generally speaking, the amplitude and frequency of differential mode interference are small, and the interference caused is also small; * * * mode has large interference range and high frequency, and it can also generate radiation through wires, which has great interference. Methods to eliminate * * * mode interference: (1) Use shielded twisted pair and effectively ground. (2) Where the electric field is strong, galvanized pipes should be considered for shielding. (3) When wiring, stay away from high-voltage lines, and even more, do not tie high-voltage power lines and signal lines together for wiring. (4) Do not use the same power supply as the electronic control station. (5) Adopt linear regulated power supply or high-quality switching power supply (ripple interference is less than 50mV). The sensor requires high purity of power supply, and the switching power supply with poor quality has high harmonic content and is not suitable for supplying power to the sensor. In order to reduce interference, filter circuit, power supply and sensor grounding can be added, which has a certain effect on improving interference.