|
|
Post by ducatisti on Aug 9, 2009 15:34:13 GMT
Saw this on the Met line at West Hampstead on the baker Street-bound track. flickr.com/gp/27565507@N06/6279h8Looks like some kind of composite thing. Rattled when shoes went over it. Any ideas what it is and why it's there? |
|
metman
Global Moderator
5056 05/12/1961-23/04/2012 RIP
Posts: 7,421
|
Post by metman on Aug 9, 2009 20:36:23 GMT
Might be a temp. repair?
|
|
Tom
Administrator
Signalfel?
Posts: 4,196 
|
Post by Tom on Aug 9, 2009 20:37:01 GMT
It's a Speed Inductor. It measures the speed of a train passing over it by the shoes generating a small AC signal in magnets hidden in a dummy bit of conductor rail. The frequency generated is proportional to the train speed, hence the ability to measure speeds.
|
|
|
|
Post by ducatisti on Aug 9, 2009 20:56:07 GMT
Gosh... that's clever. Is it to enforce speed limits or to gather information (ie is it a speed trap equivalent or one of those two-wires-in-the-road council survey things)?
Was it's location on such a short piece of conductor rail coincidental, or are they all like that?
|
|
mrfs42
71E25683904T 172E6538094T
Big Hair Day
Posts: 5,922
|
Post by mrfs42 on Aug 9, 2009 21:41:39 GMT
AIUI the old-style inductors are all like that - it was things like these that were used to enforce the speed signalling on the District back in black-and-white days.
I think the 'magnets-generating a waveform' type were all on their own bit of rail, so the wave form could be generated by the unused positive shoebeam/shoe passing over and electromagnetically isolated when not in use. The generated signal is fed to an appropriately tuned relay. They appear on diagrams as |->-| with the arrow pointing in the direction they are active.
Such things are installed to enforce a delay in signals clearing - platform starters and draw-up signals for example. Cases where a train needs to achieve a target speed before a signal clears.
|
|
Tom
Administrator
Signalfel?
Posts: 4,196
|
Post by Tom on Aug 9, 2009 21:54:35 GMT
The patent for the Speed Inductor did envisage them being concealed in an appropriately insulated piece of current rail that was part of the main length of rail. Other than a couple of examples on the Jubilee line (both in the negative rail) I believe all inductors were on the opposite side to the real current rail.
They are progressively being removed and replaced with other methods of speed control as the power packs they use are becoming beyond economical repair.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Aug 10, 2009 17:21:12 GMT
just cant get the spares at all now this is the reason why ej100 at tower hill can be so slow when going into the bay road as 2 of those segments have got a open circuit somewhere in them and need replacing
|
|
Ben
fotopic... whats that?
Posts: 4,282
|
Post by Ben on Aug 10, 2009 18:44:47 GMT
Why can power packs not just be fabricated from other available parts?
|
|
mrfs42
71E25683904T 172E6538094T
Big Hair Day
Posts: 5,922
|
Post by mrfs42 on Aug 10, 2009 22:21:48 GMT
Well, in other countries the power packs [1] are still cited as current........
[1] or sensing devices (in this particular application). My German is a bit sketchy but Bahnübergänge mit EBÜT 80 und Radsensoren RSS (RSE45 mit ARS2/ARS4) would seem to be related, if not especially affordable.
|
|
