Flashing aspect lamp proving

[ewsclass]

Hi all,
Just wondering if anyone would be able to explain how lamp proving works for flashing aspects in RRI and SSI regions?
Cheers

 

[mr_towers]

You might have some luck at the signalbox forums as well, they’re pretty good for hard(ish) core technical questions! Equally someone like AnnetsKey I’m sure will have something to contribute here.

 

[Railsigns]

Lamp proving relays are slow to release, so they're unaffected by momentary drops in current as well as momentary interruptions when a change of aspect occurs.

 

[Annetts key]

The following applies to RRI areas:

The flashing yellow aspect of a conventional filament lamp is still supplied with a low current to keep the filament warn when its not “lit”.

Hence a special filament change-over relay is used in the head.

A flashing aspect unit has a separate output that feeds the flashing aspect lamp proving relay.

For SSI areas, everything is done by the SSI TFM signal module, including controlling the flashing and all lamp proving.

 

[MarkyT]

I recall that if the electronic flasher unit itself fails in a relay installation, it's designed to revert to providing a steady output, hence a steady single/double yellow, which is more restrictive than the flashing aspect intended, and thus a 'right side' failure.

 

[Annetts key]

Yes, on failure of the flashing aspect system, the system drops out a proving relay. The junction signal then goes back to red and normal approach release applies. Hence the flashing single yellow signal will now become a steady single yellow. A flashing double yellow signal will now become a steady double yellow aspect.