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Post by orienteer on Dec 4, 2022 20:56:11 GMT
Do track circuits become obsolete once moving block signalling and automatic train control are installed?
Can't think of any use they would be on the SSR, for example.
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Tom
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Post by Tom on Dec 4, 2022 21:02:38 GMT
By and large yes, though it depends on the flavour of moving block signalling you choose. If you're planning to have a purely CBTC railway then yes, if you're going to have inter-running then some form of detection mechanism is needed, be that Axle Counters or Track Circuits.
In some sections of the District line track circuits were going to be retained for Piccadilly line trains, but the project has been descoped to remove the inter-running sections.
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Post by jimbo on Dec 4, 2022 23:51:29 GMT
Does the new Victoria Line signalling still use track circuits? Or perhaps that was only in the change-over period when track circuits detected all trains, but codes were sent by both old and new systems.
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Post by 100andthirty on Dec 6, 2022 16:19:51 GMT
Victoria line uses a lot of track circuits. To allow trains to close up around stations, some of them are very short - circa 40m. I'm sure Tom will be able to give a lot more detail.
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Post by zbang on Dec 6, 2022 17:19:57 GMT
Without axle counters, track circuits, etc, how does CBTC determine the train position? Is there something like fixed transponders or optical targets with dead-reckoning between those monuments?
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Post by Dstock7080 on Dec 6, 2022 20:08:41 GMT
Without axle counters, track circuits, etc, how does CBTC determine the train position? Transponder tags fitted in the 4 foot provide the train with positional information. |
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Tom
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Post by Tom on Dec 6, 2022 21:04:47 GMT
Victoria line uses a lot of track circuits. To allow trains to close up around stations, some of them are very short - circa 40m. I'm sure Tom will be able to give a lot more detail. All I would add is some of them are even less than that - I've not done much on the Victoria line but the last time I worked on the line it involved some 30m track circuits that were misbehaving. |
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Tom
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Post by Tom on Dec 6, 2022 21:05:43 GMT
Without axle counters, track circuits, etc, how does CBTC determine the train position? Transponder tags fitted in the 4 foot provide the train with positional information. Which the train uses to report its position back to the control centre via radio link. |
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Post by jimbo on Dec 6, 2022 23:27:46 GMT
I presume the new Vic.Line track circuits are jointless, so no need to keep breaking the running rail for insulation.
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Post by 100andthirty on Dec 7, 2022 7:39:08 GMT
Transponder tags fitted in the 4 foot provide the train with positional information. Which the train uses to report its position back to the control centre via radio link. I'm not sure that the train does report its position to control. In this respect it's not as sophisticated as Thales Seltrac. What follows is a simplistic mechanical engineers understanding Hence the need for all the track circuits which give the signalling system comparatively fine information about train location. The trains get told by broadcast radio how far they can travel. The train's ATC has has its own map of the line (including RFID TAG locations and IDs) and works out where it is from odometry (tachos and dopplar radar) and the tags position codes. The tags also correct any errors in the odometry. Using all this info the train equipment decides what to do. In comparison, with the Seltrac system, the shore system builds a picture of where all the trains are based on feedback from trains passing 'nul' locations where the inductive loops cross (RFID tags perform this on 4LM), and the control centre tells trains how far they're allowed to travel. In short, Seltrac train needs to be told where it is. |
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Post by t697 on Dec 7, 2022 11:02:25 GMT
There might be a bit of confusion between different postings here.
In any case, different CBTC systems divide different amounts of location processing between train and wayside computers. As per post above, in Seltrac the trains are fairly 'dumb' and don't have a 'map'.
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Tom
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Post by Tom on Dec 7, 2022 18:05:14 GMT
Indeed so - zbang asked how CBTC establishes train position, which Dstock7080 and I replied to. Are you thinking about Siemens Traingard on the Elizabeth Line 100andthirty? |
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Post by zbang on Dec 7, 2022 19:04:13 GMT
Which leads to-
What's the rationale for placing the transponders? I'd assume that one or two per station, maybe another in longer sections between stations. More? That gets into how accurate the dead-reckoning* is between the known points; I'd assume that with almost constant error correction, it ought to be pretty good.
*using the nautical meaning since I don't think there's an equivalent term in railway use
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Post by Dstock7080 on Dec 7, 2022 20:15:11 GMT
Which leads to- What's the rationale for placing the transponders? |
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Post by zbang on Dec 8, 2022 3:43:09 GMT
Thanks, much closer than I had expected.
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Post by 100andthirty on Dec 8, 2022 7:14:19 GMT
Indeed so - zbang asked how CBTC establishes train position, which Dstock7080 and I replied to. Are you thinking about Siemens Traingard on the Elizabeth Line 100andthirty? No, Victoria line.......a Westinghouse/Invensys product unlike Trainguard MT which is a Siemens Germany product. |
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Post by 100andthirty on Dec 8, 2022 7:46:38 GMT
Which leads to- What's the rationale for placing the transponders? I don't think I was clear in my earlier post Following up Tom's and dstock7080's comments, each CBTC has its own rules: Dstock7080 cited the rules for RFID tags on the subsurface version of Seltrac. The Northern and Jubilee versions of Seltrac don't use RFID tags at all. They determine position by the wire loops crossing over every 25 m; these are called null points. On all these lines, the trains read the tags/null points to confirm their position ie to correct any inaccuracy that has built up in the odometry since the last tag or null point. These trains routinely report position to the shore side of CBTC. The system provides for a single missed tag/crossover to be ignored but the missed read is reported. No track circuits are necessary with Seltrac but LU closes to have some axle counters arranged in long blocks to help manage degraded conditions and movements of trains without Seltrac fitted (e.g. Bakerloo movements to/from Acton. Victoria is different. The shore system relies totally on track circuits for train detection. The large number is provided to allow trains to close up in places where they're expected to be close....around stations. The blockjointless track circuits have limits for both short and long lengths both of which are exploited. The RFID tags are read by and solely used by the trains to determine absolute position. Another feature of the Victoria line not shared with the Seltrac systems is automatic fine wheel size calibration which happens every time the trains leave the depot. |
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Post by Dstock7080 on Dec 8, 2022 8:10:15 GMT
I don't think I was clear in my earlier post Following up Tom's and dstock7080's comments, each CBTC has its own rules: Dstock7080 cited the rules for RFID tags on the subsurface version of Seltrac. The Northern and Jubilee versions of Seltrac don't use RFID tags at all. I therefore apologise for any misinformation and confusion on my part, as zbang had referred to the generic CBTC name rather than the separate CBTC/TBTC differentiation as used by LU. |
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Post by 100andthirty on Dec 8, 2022 9:41:09 GMT
It's understandable that people think CBTC is a generic product. More accurately, its a concept. Each supplier of metro CBTC has its own product or products which are, almost without exception, incompatible with each other. So, for example, a Victoria line train wouldn't recognise any of the Seltrac system, but then again, an S stock wouldn't recgnise the Jubilee line flavour of Seltrac and a 1996 tube stock wouldn't recognise the 4LM version.
For this reason, when thoughts turned to go anywhere battery locos it all got rather complicated (typical British understatement).
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Post by zbang on Dec 8, 2022 16:58:35 GMT
Dstock7080 cited the rules for RFID tags on the subsurface version of Seltrac. The Northern and Jubilee versions of Seltrac don't use RFID tags at all. I therefore apologise for any misinformation and confusion on my part, as zbang had referred to the generic CBTC name rather than the separate CBTC/TBTC differentiation as used by LU.
I was somewhat ignorantly thinking in the context of the TfL lines which use any form of TC which doesn't involve track circuits/axle counters/etc and hand-waving around any system differences.
After that, it seems that another point is being ignored- it appears all the systems use some form of fixed monument to determine & correct the assumed train position and that these monuments are fairly close together. It doesn't matter, conceptually, whether that monument is an RFID tag, an induction loop, some kind of active transponder, a barcode, or what; they all use a the spot on the ground that says "You are here".
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Post by Tom on Dec 8, 2022 17:47:35 GMT
For this reason, when thoughts turned to go anywhere battery locos it all got rather complicated (typical British understatement). If we were having a competition for understatements this would be a contender for the top 5. I hear a lot about battery locos and dealing with them is more of a 'dark art' than signalling is. |
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Post by d7666 on Dec 8, 2022 18:11:05 GMT
For this reason, when thoughts turned to go anywhere battery locos it all got rather complicated (typical British understatement). If we were having a competition for understatements this would be a contender for the top 5. I hear a lot about battery locos and dealing with them is more of a 'dark art' than signalling is. Engineers vehicles of any sort always lie in the dark art zone. I always liken them to engineer's laptops. Wholly alien entities to mainstream IT people. (Well mine are anyway !!!) MInd you, most of the LU signals control systems computing in SCCs would baffle mainstream IM people. Which is why we don't let them touch. What has been done with the TRU TRT ? I've lost track of that one with regard to assorted ATP systems. I remember joking with a cetain senior Jubilee manager by saying that if it could run in full TBTC ATO then, as it knows exactly where it is, why not set it up such that as it trundles along and finds a track defect, not just to record it, but to act on it, and automtically put on a TSR in exactly the right place there and then.  Anyway, the TRU TRT question is has it got all the same gubbins the battery locos have or fudged in some other way ? I sort of heard one - of many - reasons the MPUs got dumped was the escalating costs of all these different ATP systems - and not having all of them kind of made them useless. |
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Post by 100andthirty on Dec 8, 2022 22:09:52 GMT
d7666 and Tom have summed engineers trains up rather well! I believe some engineers trains have received Northern and Jubilee Seltrac kit. Similarly some have received SSR Seltrac kit. I don't know whether any have more than one type of equipment.
I vaguely recall that some engineers trains have Central line ATP - particularly the RATs.
No engineers trains have been fitted with the Victoria line ATP to the best of my knowledge.
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Post by t697 on Dec 8, 2022 22:35:23 GMT
All the (29) battery locos have been fitted with SSR CBTC and now Jub/Northern TBTC with a group still to have the TBTC commissioned I think. Some (or was it all?) have Central ATP. And correct, none have Vic line ATP.
Central line RATs have Central line ATP. D78 RATs are fitted with as yet uncommissioned SSR CBTC.
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Post by 100andthirty on Dec 9, 2022 7:51:45 GMT
Thanks for the correction t697.
How do drivers change ATP systems from, say, SSR Seltrac to the Jubilee variety, or from tripcock to Northern Seltrac?
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Post by t697 on Dec 9, 2022 8:13:29 GMT
A big selector switch basically. Used at the boundary between ATP system areas. Best not cover full details on here.
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Post by towerman on Dec 9, 2022 8:41:26 GMT
All the (29) battery locos have been fitted with SSR CBTC and now Jub/Northern TBTC with a group still to have the TBTC commissioned I think. Some (or was it all?) have Central ATP. And correct, none have Vic line ATP. Central line RATs have Central line ATP. D78 RATs are fitted with as yet uncommissioned SSR CBTC. Is it still the case when engineer’s trains are working on the Victoria Line there is a whole line possession?Was the the rule under the old signalling system. |
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Post by d7666 on Dec 9, 2022 12:24:17 GMT
All the (29) battery locos have been fitted with SSR CBTC and now Jub/Northern TBTC with a group still to have the TBTC commissioned I think. Some (or was it all?) have Central ATP. And correct, none have Vic line ATP. Central line RATs have Central line ATP. D78 RATs are fitted with as yet uncommissioned SSR CBTC. My gen - very old notes these - had L27-L32 as VLATP fitted but that gen is ancient and was always suspect (due to the line wide possession rule) and with hindsight possibly made its way into dud gen arising from terminological inexactitudes .... A more recent (2015) document immediately before any CBTC : L15-L19 Tripcock, CL-ATP and TBTC L20-L21 Tripcock, CL-ATP and TBTC L22-L26 Tripcock L27-L32 Tripcock and Victoria Line Safety BoxL44-L54 Tripcock, CL-ATP and TBTC What does "VL safety box" mean ? |
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Post by t697 on Dec 9, 2022 14:39:26 GMT
VL Safety Box was for the original Vic line signalling not the new system installed for 09TS. In any case, taken out of use long ago and Engineers trains had and still have to use a Possession.
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Post by d7666 on Dec 9, 2022 17:54:01 GMT
VL Safety Box was for the original Vic line signalling not the new system installed for 09TS. In any case, taken out of use long ago and Engineers trains had and still have to use a Possession. ta that explains that one then |
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