A simple "back-up" relay-circuit manages, that even when the "main filament" of the light bulb in a train signal fails, a "secondary filament" is powered to guarantee that the signal is still in a working order to be realized by the train driver. At the same time the secondary filament lights up, another relay gets activated so a "alarm" light lights up in the switch box, so the disponent knows that this signal is about to fail soon and the light bulb needs replacement.
29 сен 2024
