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Post by orienteer on Dec 9, 2022 18:11:56 GMT
At the risk of creating further confusion, I thought the SSR system used train detectors on poles to determine train positions. Or are those just for communication with the trains?
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Post by d7666 on Dec 9, 2022 18:24:02 GMT
At the risk of creating further confusion, I thought the SSR system used train detectors on poles to determine train positions. Or are those just for communication with the trains? Those are wifi antennae which is the first 'c' in CBTC. The S-stock antennae are those two little ears on the cab ends that were added in their return trips to Derby. |
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Post by zbang on Dec 9, 2022 18:38:07 GMT
I hope that it's not really 802.11 wireless networking (commonly known as WiFi) but rather a purpose-built radio system on different frequencies. (Might look this up later, but we're a long way from track circuits at this point.)
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Post by trt on Dec 9, 2022 19:45:23 GMT
I hope that it's not really 802.11 wireless networking (commonly known as WiFi) but rather a purpose-built radio system on different frequencies. (Might look this up later, but we're a long way from track circuits at this point.) 802.11 it is Eliz line is also 802.11 It is the de facto CBTC standard world wide [agreed long way off topic] 802.11 isn't limited to just the frequencies such as 2.4GHz, 5GHz etc. It's now a fairly robust set of protocols, but I don't like the idea of it sharing spectrum with home broadband WiFi etc! |
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Post by d7666 on Dec 9, 2022 19:49:15 GMT
I hope that it's not really 802.11 wireless networking (commonly known as WiFi) but rather a purpose-built radio system on different frequencies. (Might look this up later, but we're a long way from track circuits at this point.) 802.11 it is Eliz line is also 802.11 It is the de facto CBTC standard world wide [agreed long way off topic] |
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Post by d7666 on Dec 9, 2022 19:52:15 GMT
802.11 it is Eliz line is also 802.11 It is the de facto CBTC standard world wide [agreed long way off topic] 802.11 isn't limited to just the frequencies such as 2.4GHz, 5GHz etc. It's now a fairly robust set of protocols, but I don't like the idea of it sharing spectrum with home broadband WiFi etc! Methinks the collective brains of international signalling and communications systems engineers addressed such worries before any train turned a wheel. |
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Post by jimbo on Dec 10, 2022 2:16:14 GMT
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 I think I read that TfL expect another system for the Picc/Bloo lines, and that no room remains on the locos for a further system to be fitted. They therefore expect to build new locos before then to be equipped with the next system. I presume these trains do not drive automatically as the passenger trains do, but are still manually driven in accordance with line clear and point locked indications received from the auto-drive signalling systems. |
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Post by jimbo on Dec 10, 2022 2:40:12 GMT
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. Under PPP back in 2003, Westinghouse were to put the Vic. Line system on the sub-surface lines, to commence at Watford and resignal 41 stages over 6 years to ensure that new signalling was available before the new S stock entered service on each line. This would have enabled more frequent services to compensate for the lower seating capacity of the new trains. However, with the collapse of Metronet in 2007 this contract was abandoned by TfL as not value for money. After a four-year delay TfL came up with a low-cost contract from Bombardier to commence from Uxbridge and resignal 12 stages over 2 years. This was again abandoned in late 2013 with insufficient evidence of progress towards that goal. So now we have Thales commencing from Hammersmith to resignal 14 stages over 2.5 years! The idea was to resignal the Hammersmith & City and Circle Lines in 2017-18 to enable service increases there by the year previously promised for completion of all lines. The Metropolitan branches were to be resignalled in 2018-19! |
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gefw
Gone - but still interested
Posts: 210
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Post by gefw on Jan 5, 2024 21:02:12 GMT
A few thoughts/notes;
"track circuits" were classically used in a Signalling system to determine where trains are (or aren't) so it can route trains safety.
"track circuit" was used as a term for a specific section of track (eg Track Circuit "JA") when reporting its status. I've heard the term "block" now used instead (eg fixed BLOCK signal" signalling, axle counter block status).
I also consider it a generic term for various technical methods/equipment applying & using electrical signals in the rails to detect trains.
As such, I am unsure whether I consider it to include axle counters (now the most commonly used trackside mounted method of detecting trains for new BR ETCS level 2 systems and I suspect to be used on the roll out of 4LM to detect non equipped trains in the shared areas).
Perhaps trying to assist in answering your question.
A very highly respected Signals Principles Engineer did a lecture a few years back (for the Signal Technical society) "Signalling on London Underground Since the Early 1960's".
I recall his view that even though there has been (and continues to be) accepted safety cases where the primary method of the safety critical signalling control system ascertaining positions of trains is trainbourne equipment based (eg ETCS level 3), for the foreseeable future he expected additional/independent trackside based equipment to determine train position/absence in points & crossing areas to be required for LUL systems. On the 4LM and Eliz line I believe Axle counter technology is used for this purpose (rather than track circuits).
He didn't explain his reasoning behind this (would probably take hours!) but I suspect it is based on LUL's "belt and braces" approach in higher risk scenarios; providing suitable diversity of point locking, conflicting movement protection and dealing with failed trains came to my mind.
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Post by jimbo on Jan 6, 2024 7:36:40 GMT
It seems to me reasonable to take a 'belt & braces' approach on LU compared to elsewhere because of the higher risks with crowded trains at close intervals in confined tunnels.
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