Research on the 2-out-of-3 Speed Measurement Scheme in Metro Signaling System

Currently, the speed measurement system in the signaling system heavily relies on the height of the speed sensor (OPG). When any single OPG fails, the speed measurement system malfunctions. To address this issue, this paper proposes a 2-out-of-3 speed measurement method that integrates the speed information from two OPGs and one radar. By adopting the 2-out-of-3 speed measurement approach, the application scope of radar is expanded. Instead of merely serving as a speed compensation device during wheel spin or slip, the radar is used to measure speed. The healthy OPGs are compared with the radar measurements to determine the safe speed. This ensures that the signaling system can maintain normal speed measurement even when a single OPG fails, significantly enhancing the availability of the speed measurement system. Based on the analysis of the OPG speed measurement principle, radar speed measurement principle, and the safety speed calculation principle of the subway signaling system, and considering the speed measurement performance of existing radar systems, it is demonstrated that radar can be used for safe speed measurement not only during wheel idle or slide but also under normal operating conditions. The paper provides calculation methods for maximum and minimum speeds under different scenarios using the 2-out-of-3 speed measurement approach, covering low-speed, medium-speed, and high-speed scenarios. Finally, using fault tree analysis, the paper calculates the Tolerable Hazard Rate (THR) for the single OPG and radar configuration, proving that it meets the safety integrity level requirements of the signaling speed measurement system.