Author(s)

H. Zhao, Y. Liu & B. Liu

Abstract

A kind of onboard auto-test system was proposed so as to detect the track circuit compensating capacitors in real time. The system model and design were based on the resonance current detection method. The data acquisition card generated the actuating sine signal first, which was amplified and coupled onto the rail. Two wheels of the test vehicle, rail lines between and the capacitor connected between the rails formed a closed LC loop. If the actuating signal frequency coincides with the inherent resonance frequency of the loop, a reactive current will be produced within the loop. After the current is sampled and further processed, the capacitor value can be estimated. The system principle and architecture are described in detail. Experiments show the invalid capacitors can be efficiently detected and located in real time. Keywords: resonance current detection method, compensating capacitor, onboard auto-test system, track circuit, data acquisition. 1 Introduction Audio frequency jointless track circuits, i.e. UM71 and ZPW-2000A, are now widely used in the railway autoblock systems in China. As for ZPW-2000A, rail lines act as the transmission media for dedicated FSK signal which carried the vital autoblock information used for train control. Modeled as a kind of distributed transmission line with inductive characteristic impedance, rail lines are not a good transmission media for audio frequency, unfortunately. In order to weaken the negative effect of the inductive rail and prolong the transmission length of track circuit, compensating capacitors are evenly spaced and installed between the rail lines, as shown in Fig. 1.

Keywords

resonance current detection method, compensating capacitor, onboard auto-test system, track circuit, data acquisition.