Objective As metro trains start and stop frequently, the stable input of P/B (traction and braking) signals directly determines operational safety. During the initial operation phase of Foshan Metro Line 3, some trains encountered P/B signal input faults. This issue involves complex systems and interfaces, with numerous interfering factors in the troubleshooting process. Therefore, it is necessary to make an in-depth summary and analysis based on multiple fault data.

Method Based on the on-site experience of Foshan Metro Line 3, the fault moment data of two types of P/B signal input faults are categorized, sorted and theoretically analyzed. According to the analog signal types and fault diagnosis logic, the fault locations are identified. Targeted improvement plans are further proposed, modification and corresponding testing are carried out on the train.

Result & Conclusion  The P/B signal input fault of the master controller is caused by the watchdog in the AIM (analog input module) triggering the module reset and the data-clearing during the reset. The firmware watchdog refresh time is subsequently optimized to avoid abnormal board card resets. The P/B signal input fault of the ATO (automatic train operation) system is due to the VCU (vehicle control unit) that identifies invalid digital quantities at certain specific moments after the ATO mode is established and judged to be valid, which results in an out-of-range judgment of the signal. To solve this problem effectively, in addition to optimizing the watchdog refresh time, it is necessary to adjust the fault diagnosis logic of the VCU and increase the diagnosis duration. No similar faults have occurred in the six months after the modification, indicating that the operational risks are eliminated.