[imatfaal (OP)]

Hello

I have noticed these strange devices on some London Underground Platforms for a few years now.  Not all have them - but the Jubilee Line (one of the more modern lines) has examples at most stations that I use.

Its is obviously some form of optical device - and some of them seem to have a paired device in the ceiling, but by no means all of them (or you just can't spot it).  Other info
- They do not move, although the paired devices seem to
- Actual size is about 12-13 cms cube with 5 cm cylindrical bit
- they are about 12-18 inches off the floor and attached to the wall
- the orange glow is real not a photo-artifact
- there seem to be optics inside - but I have never looked straight in (I like my retinas as they are)


Funny Bit of Platform.jpg (79.77 kB . 591x738 - viewed 3945 times)

I hope someone knows what they are - I have lots of ideas, but nothing concrete

Cheers

Matthew

[RD]

Optical smoke detector ?

Also seen in large rooms, such as a gymnasium or an auditorium, are devices to detect a projected beam. A unit on the wall sends out a beam, which is either received by a receiver or reflected back via a mirror. When the beam is less visible to the "eye" of the sensor, it sends an alarm signal to the fire alarm control panel

http://en.wikipedia.org/wiki/Smoke_detector

[imatfaal (OP)]

Optical smoke detector ?

Mmm I dunno - for the majority of the rush hour (now about two and half hours long in London) it won't see anything, too many people.  I would place it 8 foot up the wall (to stop idiots putting chewing gum on it) if that was the intention.  My crummy pictures makes it look distant and zoomed in - but it is on the wall of the platform where people stand.

[RD]

I would place it 8 foot up the wall (to stop idiots putting chewing gum on it).

Cold smoke will run along the floor, so putting the sensors/reflectors 8 feet up would reduce their usefulness.

[Bored chemist]

"Cold smoke will run along the floor, so putting the sensors/reflectors 8 feet up would reduce their usefulness."
By the time the smoke is cold...


The London underground has a degree of understanding of the way smoke behaves during fires.
http://en.wikipedia.org/wiki/King's_Cross_fire
Incidentally, if they were likely to damage anyone's retninnae they wouldn't be there (the lawyers would have banned them).
However, if you can point your camera into them then you can always get a new camera if I'm wrong.

[LeeE]

I would place it 8 foot up the wall (to stop idiots putting chewing gum on it).

Cold smoke will run along the floor, so putting the sensors/reflectors 8 feet up would reduce their usefulness.

Smoke, usually resulting from combustion, tends to be hot, and rises.

In large buildings where there's any sort of complex layout, and where people might not be able to find fire exits if there's a lot of smoke about, you'll often find little luminescent arrows stuck to the sides of corridors, just above the floor, leading to the exits so that people who have ducked down or who are crawling beneath the smoke can find their way out.

I've got a vague recollection of seeing these things too, but haven't been able to come up with a plausible explanation of what they are, other than being some sort of sensor.  Being near floor level really rules out smoke detectors, which only really leaves some sort of air quality monitoring/sensor device, possibly relying upon back-scattering.  It seems a bit strange that they're located where they can easily be obstructed by people standing near the walls of the platform while they wait for their train though, but this in turn suggests that whatever it is that's being monitored or detected, it isn't so vital that it needs constant sensing, or it isn't expected to change quickly so that shorts breaks in the sensing output can be ignored.

[RD]

Being near floor level really rules out smoke detectors

some of them seem to have a paired device in the ceiling

so the beam would cover from ceiling to floor.


beam.gif (51.57 kB . 800x413 - viewed 3584 times)

http://www.tycosafetyproducts-europe.com/english/pdf/Datasht/Fire/PSF085TFIS.pdf

[LeeE]

some of them seem to have a paired device in the ceiling

so the beam would cover from ceiling to floor.

Huh?

What about the ones that don't seem to have a paired device in the ceiling?

...and you wouldn't get coverage from ceiling to floor for the cases where there are paired devices anyway, because the devices are aimed along the platform, not towards each other (where there are a pair).

[CliffordK]

BrotherBloat,

The link you had attached was a generic link to a company and didn't seem to answer the question, so I've removed it.

If you've identified the sensor in the first post by imatfaal, we'd love to hear what it is.  Your link did suggest possible geostability monitoring, but none of the devices sold by the company seemed to match imatfaal's photo.

Otherwise I'll chalk it down to being an anti-personnel laser for use by Skynet.

[AdrianJC]

I have noticed these strange devices on some London Underground Platforms for a few years now.  Not all have them - but the Jubilee Line (one of the more modern lines) has examples at most stations that I use.

Its is obviously some form of optical device - and some of them seem to have a paired device in the ceiling, but by no means all of them (or you just can't spot it).  Other info
- They do not move, although the paired devices seem to
- Actual size is about 12-13 cms cube with 5 cm cylindrical bit
- they are about 12-18 inches off the floor and attached to the wall
- the orange glow is real not a photo-artifact
- there seem to be optics inside - but I have never looked straight in (I like my retinas as they are)

Looks like one of the geodetic prisms newbielink:http://www.soldata-ltd.co.uk/solfrey/iweb.nsf/pages/groundstructure.0E94484C784F8676C1257949007143E2 [nonactive]. A number of these geodetic prisms are newbielink:http://www.youtube.com/watch?v=tzy1lWrpZwc [nonactive] which is technically a very advanced type of newbielink:http://en.wikipedia.org/wiki/Theodolite [nonactive].

Soldata has been monitoring for unexpected movements in the London Underground tunnels and neighbouring buildings in connection with the building of The Shard and the demolition of the building that used to stand in its place. This is part of newbielink:http://de.soldatagroup.com/C1256954003EC4A6/type/96CAB84BBD1437DEC12576F500459C45/$File/London%20Shard%20of%20Glass-uk.pdf [nonactive] that also includes newbielink:http://www.homegardenguides.com/garden-forum/diy-forum/459650-what-street-furniture-3.html [nonactive].

Other major construction projects in London such as newbielink:http://www.vraco.fr/images/pdfs/UK/02%20-%20UK%20-%20London%20-%20Kings%20Cross%20-%20COMPLETE.pdf [nonactive], newbielink:http://monitoring.topcon.co.jp/at_work/Crossrail.html [nonactive], and newbielink:http://www.itmsoil.com/pages/Victoria+Underground+Station+Upgrade [nonactive] will also have similar monitoring networks installed by various construction related companies.

[Robert Fitzgerald]

Hello all, sorry to drag up such an old thread but I couldn't find any other more recent discussions on the topic and I wanted to answer this one.

I've been wondering the same thing for several years now and I see them on most of the stations I use (Victoria, Euston and Archway mainly but also on Green Park and others in the area) and I had a search and found this post.

I'd completely disagree with it being smoke detectors and the 'paired device' is actually a prism which reflects the light into another prism and bounces it around the platforms to a receiver somewhere else. I would think it uses either some form of invisible or safe laser beam, or that it is only made active when the station is closed overnight for example.

(remove spaces from links below, I couldn't work out how to verify my account to be able to post them properly)

I've had another search and found reference to an accident report: http : / /content.tfl.gov.uk/16-safety-alert-monitoring-prisms-in-passenger-areas-oct-2012.pdf where it was called a "monitoring prism" and from there, that led me to find that they are for surveying and monitoring measurements over a long period of time, there is some good information about them on this website: http : / / www .berntsen.com/Surveying/Survey-Prisms/Mini-Prisms but presumably they are to make sure that the station is not slowly sinking or collapsing over time and to monitor the structural integrity of the building. Normally they seem to have 3 or more on the ceiling above escalators going down towards the platforms, normally there is a transmitter near the bottom of escalators (the same as the one imatfaal pictured above as well but I'm unsure where the receivers are or how the system works. I would guess a laser point is projected on the centre of the receiver, and if the building were to move at all, it would cause the point to move slightly on the sensor and having several prisms reflecting off of each other allows it to give a much more accurate reading, because if even one of them moved by a less than a millimeter it could cause the end dot to move on the receiver a lot more and indicate a problem.

Mystery solved!

[chris]

Only just saw this thread resolution! Thanks @Robert Fitzgerald for solving it!