Axle Counters

Discussion in 'Infrastructure & Stations' started by trac, 30 May 2015.

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  1. trac

    trac Member

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    For the uninitiated(me!), can someone discuss the benifits behind installing axle counters as part of the GWML upgrade. Do these replace the traditonal ways to detect trains or do they provide speed information etc?

    Are axle counters necessary for one of the forms of ECTMS? Are the counters widespread European practice?

    I see there are often delays attributed to the newly installed counters on the GWML upgrade. So at the moment they sound like something else to go wrong and require fixing :)
     
  2. edwin_m

    edwin_m Veteran Member

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    An axle counter consists of a detector at each piece of track going into or out of the section, which is able to detect a passing wheel and which direction it is travelling in. These are all connected to a central evaluator which increases and decreases its count of the number of axles within the section. When the total is equal to zero the evaluator tells the interlocking that the section is not occupied.

    Thus, although it has internal information about the size of the train, this is not used externally and from the interlocking's point of view it is equivalent to a track circuit. It has advantages of not being affected by leaf contamination, wet ballast, and other things that can cause failures of track circuits. It can also be infinitely long, where a long track circuit will actually comprise several separate ones combined together by the interlocking.

    The axle counter also has disadvantages. It will not detect a broken rail (which track circuits will sometimes but not always detect). Nor will it detect the track circuit clip that is traditionally put down on the adjacent track if a derailed train fouls it - drivers have to contact the signaller by phone or radio instead. Probably the worst problem is that if the axle counter loses power, or during engineering work, or sometimes even if a train stops on the evaluator, it could lose count and declare the section occupied when it is clear with even a small probability of declaring it clear when it is occupied. After these events the axle counter has to be reset manually after physically checking that there are no trains in the section. Obviously this is a major hassle especially if a wide-area problem affects many axle counters.
     
  3. MarkyT

    MarkyT Established Member

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    From a safety case perspective that can be covered by more frequent and thorough track inspections and sometimes an increased rate of rail renewal. Also specific products for the purpose of break detection can and are being developed, perhaps homing in more accurately on the precise position of damage than a track circuit's simple 'break somewhere' within a defined section. Even if electrically based, freed from the track circuits finely calibrated requirement to detect train axles at any point, such alternative systems might be much better optimised for the specific rail break detection task. There's a wide market for such systems, not just axle counter fitted main line railways but also long ore haulage lines in various remote parts of the world where the prospect of thousands of tonnes tipped off the rails in the middle of hard to access mountains or desert and blocking the supply route is a powerful incentive.

    Many track circuits, in electrified territory especially, are termed 'single rail'. For these example only one of the rails is series bonded. A break on the other rail will certainly be bypassed by parallel traction bonding so will not be detected at all.

    In modern control centres where full cab secure or GSM-R radio comms is provided the message can be passed verbally just as quickly, even by a driver or guard who may be trapped. Modern signalling then allows the signaller to replace any or all of the signals in an area and a radio mayday to all traffic can also be sent.

    This is no doubt their 'Achilles heal' but the miscount issue appears primarily to be a problem in permissive platforms at major stations where train detection is often split up into multiple separately indicated short sections so signallers have a better idea of free space available to accept multiple trains for splitting and joining, run-round and shunting operations. In this scenario it is very likely that a wheel may be stopped right above a sensor, and if the system cannot determine which direction the wheel moves away subsequently, that is when the evaluator fails safe and miscounts 'right side' leaving a section occupied when it should have been clear. Reset procedures today usually require a 'sweep train' to be authorised to pass through under verbal authority after which normal operations can be resumed. To get around this, the recent Nottingham area resignalling, which employed axle counters widely for the vast majority of the area concerned, substituted track circuits through the platforms themselves at Nottingham station. The relatively small numbers of short track circuits, confined to a well drained major station area, are likely to be fairly easy to maintain and to keep in adjustment compared to the numerous longer examples distributed along trunk stretches of main lines that were typical of first generation power signalling. Once set up and working, axle counters require significantly less routine testing and adjustment than their predecessors. Perhaps GWML resignalling will employ a similar strategy.
    --- old post above --- --- new post below ---
    The question is are the total signalling attributed delays improving or not? Many previous so called 'signalling failures' may actually have been down to the track circuits anyway, and the replacement systems are probably still on the leading edge of their new system reliability curve, whilst tweaks in installation and maintenance methods are being optimised and any rogue products from a large new batch are being weeded out.
     
  4. Yabbadabba

    Yabbadabba Member

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    A quick but not complete guide to Axle Counter operations.

    I would say most of the benefits would be form an instillation and maintenance point of view. As from a operation point of veiw they dispay the trains progreess and location in exactly the same as normal track circuits would.

    At our place we used to have 8 co-operative reset axle counters where by a technician and a signaller had to jointly reset the axle counter section by pushing their respective reset buttons for 10 secinds at the same time. To perform a reset the axle counter needs to have been disturbed or miscounted first. If all being well the axle section would the go clear and be reset, but an aspect restriction but be placed on the protecting signal forcing the 1st train to become a sweeper train starting a new count. With all being well the new count would be correct and the axle counter would be restored to the interlocking and the aspect restriction is removed from the signal. This style of axel counters would often show occupied after nighty engineering work which would require the local TOC to provide a sweeper train to clear the sections before the start of service to mitigate against service delays. All relevent forms must filled out and completed to keep the auditors happy lol

    But since our area of control on one of our panels has been extended all using axle counters which are of a non co-operative reset meaning that the signaller can perform the reset all by themselves our existing axle counter sections were also changed over to the new style. so we now have 65 of them (less than some locations but more than others). This new style of axle counters come with EPR (engineers possession reminder) of more later. Conditional resets, with this style of axle counter the actions of the reset are all permormed by the signaller by pulling up the relevent axle section button and then pressing the reser button for 10 seconds and all being well the section will go clear. As above you can only perform a reset if the axle counter has been disturbed or as been miscounted. Aspect restriction will aply as necessary and the 1st train will be required to sweep the section after passing the protecting signal at danger and examining the line. We now have axle counters through point work which means that in most cases but not all (depends on if the driver can see all of the axle counter section that they are sweeping) that every route through the points will need to be swept. The new count will start and and once clear will restore the axle counter back to the interlocking. As above all forms must be completed.

    Un-conditional resets, for booked enginnering work the signaller will apply an EPR to all axle sections before the block is granted. With these applied you can disturb and have as many miscounts as you like, as just before the possession is about the be handed back to the signaller, the PICOP ES and Signaller must complete the a line clear verification process that confirms that the line is clear of all engineers trains/machines. With this done and once the possession has been been given the signaller can remove all the EPRs, this will have the effect of resetting and restoring any axle counter sections to clear without any restrictions to the signalling and no sweeper train is required. On our panel with axle counters it takes a full 23 minutes to restore all 65 EPRs before you can run a normal train service after a possession, and if it is to be believed on the Pool to Wool re-signalling which is also a panel it takes the best part of 45 minutes to restore all EPRs after a possession. In contrast EPRs on workstations only takes a few minutes and all can be applied and taken off in geographic groups or on line of route depending on the setup. Even more forms and forms need to completed for engineers possession.
     
    Last edited: 2 Jun 2015
  5. carriageline

    carriageline Established Member

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    I was surprised when someone told me how long it takes you lot "over t'road" to remove your EPRs on all your axle counters, when we could probably have all ours done and dusted within about 2-3 minutes! But that's the limitations of the NX interface I suppose!

    I'm neither for or against. It's nice being able to reset them after a fault, but that's if the fault will allow them to be reset. Some faults still require techs to go out and reset the equipment on the ground.

    But on a day to day, normal running scenario they are no different to track circuits.
     
  6. Yabbadabba

    Yabbadabba Member

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    This is why I was very careful in choosing my words, as a signaller can only reset an axle counter if there has been a miscount or its been disturbed. If the axle counter has an actual fault or an evaluator has failed then that will require the technicians to fix it. We've only had that situation right at the beginning when 3 of our converted axle counters refused to work properly until the wiring was modified.

    All of our new axle counters have worked and reset properly apart from an smartlock (SSI) software problem that needed a rewrite because it prevented axle counters from being reset if they were separate axle counter section acting as an overlap. Where by the axle counter couldn't be reset without the protecting signal being at danger and the button pulled up. But the signal wouldn't time out as the overlap was still occupied, so it was a catch 22. The only way around it until the software rewrite was a release of signalling controls on the signal timeout circuit.

    We also right at the beginning asked the contractor plus the lead NR project enginner to have group EPR replacements and resets ((standard enginnering areas) S,E,As) as we could see this as a performance issue. We even got as far as working out how many we would need (7 in total) and what the controls would look like and the priciples of how to operate them. But as there are no group standards covering them on panels then someone would need to go through the expense of designing them and getting them approved. This is the stage we are at but the principle contractor for the re-signalling work is claiming a heavy workload and we and the Pool to Wool panel are not high up on the priority list for getting them anytime soon.
     
    Last edited: 2 Jun 2015
  7. alxndr

    alxndr Member

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    Some areas of the GWML also use track circuits which are not AC Immune, such as Asters, so these are being replaced ready for the impending electrification.

    Is there a link between the move to SSI has anything to do with the introduction of axle counters, or is it just coincidence?

    I believe that most of the issues are with the axle counters fitted with the older mushroom style EAKs rather than the new K type, such as we're fitted as part of the Kemble redoubling project.
     
  8. edwin_m

    edwin_m Veteran Member

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    I think all the areas of the GW signalling that are to be electrified and also old enough to include Asters etc are being re-signalled first. The equipment would date from the 60s and 70s so pretty much life expired anyway.

    SSI first appeared in the late 1980s and all installations used conventional track circuits until Stoke-on-Trent in about 2000 which was the first to use axle counters on a large scale. The original SSI had no logic to deal with axle counters (a trackside module including the evaluator function was developed in the late 80s but never introduced) so the evaluator output would be connected to a SSI module input as if it was a track circuit. I don't know if the computer-based interlockings that have largely superseded the original SSI include any better axle counter functionality.
     
  9. Bald Rick

    Bald Rick Established Member

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    I disturbed an axle counter once.

    I told him there was no God.

    (With apologies to Paul Merton). (Also getting coat).
     
  10. carriageline

    carriageline Established Member

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    With jokes like that you can stay out!! :lol::lol
     
  11. MarkyT

    MarkyT Established Member

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    Except for the Didcot - Swindon area (excluding Swindon station which is due for resignalling during 2015). That was resignalled using SSI in the early 1990s with control being transferred from Reading PSB to the new Swindon B IECC. AC traction immune track circuits were used, but clearly the bonding design (cables connecting equipment to rails and between rails) will have to be altered significantly to cater for the traction return current, or perhaps they will replace the track circuits entirely with axle counters. Note the signalling structures in the area were built for OHLE clearance as well.

    As far as I know axle counter equipment is still separate from the interlocking computers in offerings from all the main suppliers. Interface is via voltage free relay contacts.

    Before Stoke, early axle counters had been used in problem areas where environmental conditions made track circuits unreliable or otherwise difficult to apply. Examples include the Forth Bridge (wet and metallic), the Severn Tunnel (wet all the time) and the Dawlish Sea Wall (sometimes very wet and salty with wildly changing ballast resistance so impossible to keep in adjustment through stormy weather). They also found favour on long single line sections and long rural block sections on double track with no intermediate signals. Despite their relatively high cost in the beginning, they could save numerous individual track circuits in these applications and allowed many token and absolute block sections together with their local controlling signal boxes to be abolished economically. This process continues today with the modular signalling approach in rural areas, and the axle counter cost premium over track circuits has also narrowed markedly over time.
     
  12. edwin_m

    edwin_m Veteran Member

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    Yes that's an exception. I don't know how much would have to be done to the bonding but if the track circuits are immune that would remove a big part of the cost. Asters etc were well obsolete by that time.

    Yes, that's why I was careful to cite Stoke as the first use "on a large scale". The Newark flat crossing was (and I think still is) another isolated used of axle counters in an otherwise track circuit area - something to do with the complications of insulating and bonding for track circuit detection in all directions I think. Certainly I can't think how it would have been done without putting two more insulated joints in each ECML rail, in the four-foot of the two Nottingham-Lincoln tracks. The pounding they would have taken, would have made the whole thing much more prone to failure.
     
  13. DY444

    DY444 Member

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    Another advantage in 3rd rail areas is there is no need for impedance bonds
     
  14. class 9

    class 9 Member

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    Axle:lol:
     
  15. 68000

    68000 Member

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    The track circuit clip is an irrelevance now with GSM-R rolled out nationally. The driver presses the red button to protect the track - a much quicker way of protecting versus TC clip or asking the signaller to protect
     
  16. najaB

    najaB Veteran Member

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    Almost nationally.
     
  17. 68000

    68000 Member

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    Yes apart from the RETB lines
     
  18. carriageline

    carriageline Established Member

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    But, what if some sort of horrific accident caused the GSMR to be inoperable (equipment damaged etc) then a TCOC isn't so irrelevant then!

    I know nothing about the trainbourne stuff, but is the back cab GSMR 'live', at all times (ie displays "GSMR GB", but not registered)

    Also bit confused when you say "red button to protect the track"? As technically this does nothing signalling wise to stop trains, although any GSMR equipped unit will stop (hopefully!)
     
    Last edited: 3 Jun 2015
  19. Yabbadabba

    Yabbadabba Member

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    Mind still not much use in an axle counter area and on a GSM-R note, we've got a terminal that spends most of its time crashing and rebooting from windows.
     
  20. moggie

    moggie Member

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    What can be said is Stoke was the first area to use AzLm style Axle Counters now common throughout the country employing Conditional / Unconditional Reset rather than the Co-operative Rest method which was generally used up until the Stoke project.

    I understand all of the common use CBI's operate pretty much as those SSI area's when it comes to Axle Counter controls other than a few tweaks that have taken place over the years since Stoke.

    The newer Axle Counter systems are pretty clever bits of kit and in future their direction detection capabilities I'm sure will be put to use in conjunction with the Interlocking controls. The interface between the systems is the constraining feature but I'd not be surprised if this is one area of system development which is already underway but suppliers to make best use of the Axle Counter system capability.
     
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