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| Does it need to be a controlled signal? 05/03/2014 at 00:31 #56549 | |
DaveBarraza
88 posts |
I see what you mean by guaranteed: The red indication in the signal icon is positive feedback that the action has occurred in the field (and with lamp-proving thrown in!) There are some plausible failures which could lead to the red panel lamp being spuriously lit - but the signalman should spot these quickly, especially when the signal should by-rights be clear. But most of the failures would lead to the red panel lamp being dark, and the signalman can proceed appropriately (cautiously) because he does not *know* the signal is displaying red. For the most part control panels and remote control schemes are very highly reliable, and can be relied upon to bring the signal to danger in almost every case without being SIL4... Thanks All! P.S: How is light-out protection done with LED's in the UK? with a current threshold? Are degraded LED arrays considered? Log in to reply |
| Does it need to be a controlled signal? 05/03/2014 at 01:19 #56552 | |
Stephen Fulcher
2078 posts 
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The red light in the signal indication will only show when the emergency replacement is operated, not when the signal is at red under normal running with the passage of trains. Lamp proving is done using current sensing for both LED and some conventional filament lamps, dependent on the age and type of interlocking. SSI signal modules have several "current path" inputs which will only work if a predetermined current is being drawn. Degraded LEDs draw less current and are detected as such by the interlocking. A Dorman LED head that falls below this threshold and therefore considered out by the interlocking is sometimes difficult to see as such by the naked eye relative to a signal that works. Log in to reply |