Dot matrix display on signal gantry

[Tom williams]

(Mods please move if not in the apropriate section)



Hi All,

I was trainspotting in hereford station the other day, and noticed this dot matrix display on the signal gantry to the south end of the station. I was just wondering if anyone knew what it was for? I've never seen it light up or do anything.

Thanks

Tom

 

[D6130]

They will be route indicators working in conjunction with the position light signals located to the left of the main running signal heads. It's a while since I last visited Hereford, but I suspect that they will be to advise a driver which of the sidings South of the station their empty train is signalled....and possibly also to indicate a shunt move across the main-to-main crossover at that end of the station . Someone more local than me will hopefully be able to confirm or otherwise.

 

[tomuk]

I think they are indicators

They will be route indicators working in conjunction with the position light signals located to the left of the main running signal heads. It's a while since I last visited Hereford, but I suspect that they will be to advise a driver which of the sidings South of the station their empty train is signalled....and possibly also to indicate a shunt move across the main-to-main crossover at that end of the station . Someone more local than me will hopefully be able to confirm or otherwise.

They look a bit small for route indicators, maybe that's ok if they are read in conjunction with the subs only? I thought they maybe C, S, W calling on indicators as these colour lights are a replacement for some earlier semaphores.

 

[zwk500]

I think they are indicators

They look a bit small for route indicators, maybe that's ok if they are read in conjunction with the subs only? I thought they maybe C, S, W calling on indicators as these colour lights are a replacement for some earlier semaphores.

If you do a google image search for 'hereford signal diagram' you get a Signalling Record Society diagram of the 1970's resignalling, which seems to still be the current design.
H51 will show 'S' when the Subsidiary aspect is illuminated for movements towards the Diesel Siding, on the Up side of the line. The Route Indicator would remain unlit when the subsidiary aspect is cleared for draw-ahead movements onto the Up Main.
(Sorry, I can't do a link and not sure if I'm meant to directly repost the document and don't want to accidentally subvert the SRS who do a fine job)

 

[King Lazy]

They are certainly route indicators.

These type are known as “stencil indicators”. They generally* work in conjunction with shunt signals (in this case the position light associated with the main aspect).

The larger square ones on the network are known as “Theatre boxes” and generally* work alongside the main aspects.

I don’t know of the layout in the picture attached but from a quick glance my guess is that only one route is available from either of the main aspects while more than one is available if either of the position lights illuminate.

Therefore only stencil indicators are provided for the position lights. If there were multiple routes from either main aspect then a theatre box or boxes would be provided as well.

It is quite common to see signals with both stencil indicators and theatre boxes.

* There are as ever exceptions to what I posted which was merely meant to explain how they are usually utilised.

 

[LNW-GW Joint]

It's a while since I passed through Hereford, but much of the siding infrastructure to the south west of the station is out of use, or nearly so.
You might be a long while waiting for those stencil indicators to be lit.

 

[Annetts key]

They are route indicators. There are various types/styles/versions/sizes. The current preferred term is “alphanumeric route indicators”.

King Lazy is correct in that the type in the picture are what (in the past) were known as “stencil indicators”. This type/style/size is only permitted when the approach speed is relatively low. So they are normally used with position light (PL) shunt signals.

Network Rail now however use the term “miniature alphanumeric route indicators” (MARI).

The larger type, “Theatre indicators” are now called “standard alphanumeric route indicators” (SARI). As King Lazy says, they are normally only used with main aspect signals. There is a maximum approach speed where these are normally permitted to be used. At higher speeds, only position light junction indicators (PLJI) or “feathers” are permitted.

Over the years, the technology has changed. The 1970s type stencils in the photo will have conventional filament lamps, with a plate that has a matrix of holes. Behind this plate is sheet that blocks the light from passing through some of the holes, but which allows light through others, hence a number, or letter can be shown. One ‘box’ is provided per route, as they can only show one route.

Later came Fibre optic types which use quartz halogen lamps. All are now being replaced with LED (light emitting diode) types.

Here is a modern LED equivalent:

The main aspect head is showing a green, as the route is set for the main line.
On the left of this, the top head is a LED MARI. This will show an ‘S’ only when the signal is routed into the sidings in combination with the LED position light head (shunting signal) that is mounted under the MARI.

More information on this web site.