Analysis of impedance characteristics for the loop-cable position and speed detection system

The position and speed detection system based on the loop-cable is a non-contact method. It could fulfill the accuracy requirements of the position and speed for the mid-speed maglev train. This paper simply introduces its working principle and describes its basic structure. Considering the maglev train is one kind of traffic tool, the induction loop-cable has to adapt to the long-distance structure. The paper draws the theory about the lossless uniform transmission line and analyses the impedance characteristics of the loop-cable using Telegraphic equations (transmission line equation). As the loop-cable has a special periodic structure, it could be equivalent to the cascade of unit rings. Meanwhile, there is impedance mismatch connection point between the loop-cable and the trackside transmission cable, so the impedance converter is designed to prevent the signal reflection. Finally, the non-uniform factor of the unit ring is analyzed and the coefficients of reflection are given.