15. Useful life evaluation method for electronic equipment of wayside signalling systems

Electronic equipment constituting the signalling systems used along a railway line is subject to operational stress due to energization as well as environmental factors including temperature and humidity, corrosive gases and vibration (Fig. 1). This has made it difficult to understand the main factor and the tendency of deterioration, leading to issues in determining the proper timing of updates.

Therefore, an investigation was conducted to better understand the environment in which wayside signalling systems are used and the actual conditions of failures. The results showed that the dominant deterioration factors impacting equipment useful life were operational stress due to energization and environmental stress caused by temperature and humidity changes.
Based on the results of the investigation, a method to evaluate useful life has been developed focusing on cracks generated in solder joints of electronic parts themselves consisting of electronic equipment and their substrates (Fig. 2).
With this method, not only can the useful life of an electronic part be calculated according to the usage environment by utilizing the results of a reliability test implemented by the part manufacturer, but also the useful life of solder joints can be calculated by accelerated tests to reproduce solder cracks caused by temperature change, so as to identify weak points based on each calculation result and estimate the service life of equipment. An evaluation was attempted by applying this method to train detectors for grade crossing in two types of equipment boxes under different usage conditions--with and without a shield to block direct sunlight. The results confirmed that weak points could be identified under each condition and the estimated useful life could be calculated (Fig. 3).

This method will help railway operators to quantitatively estimate the useful life of electronic equipment for signalling systems used along their railway lines and develop update schedules, if they use the evaluation tool implemented using this method in spreadsheet software along with the procedure manual.
This method is also applicable for electronic equipment other than signalling systems.