Automatic SDO systems seem overly complex

[K.o.R]

Having read descriptions of how various SDO systems work they seem to be either over-engineered or vulnerable to problems (GPS systems allow the doors to be opened as long as the train is close enough to the platform location?).

Proposal: have a sensor positioned under each door, and on the track are pairs of beacons/balises/whatevers at each end of the platform. The outermost beacons are "off" switches for the doors and the innermost beacons are "on" switches, so if the last thing the sensor "saw" was an "on" beacon, then that door is alongside a platform. This obviously doesn't say which side the platform is on, but it seems a simple addition to such a system.

 

[Bletchleyite]

The problem with that is that you have a possible wrong-side failure if the "off" beacon isn't seen.

You could possibly have a variant that wouldn't, though - just have the one at the start of the platform as an "on" switch for any door that has passed it (the driver can see easily enough if he's overshot, so that doesn't need handling), and "off" is signified by the wheels moving. A wrong-side failure would then leave all doors locked and so fails safe.

 

[Great_Western]

Why can't you just have a system where the driver or guard selects what doors can be opened via the TMS? Surely it is safer to do it manually?

 

[Fincra5]

Why can't you just have a system where the driver or guard selects what doors can be opened via the TMS? Surely it is safer to do it manually?

Bit like a cl222?

The system on 377s via Mitrac is pretty reliable tbh. There's a few places were some beacons are defective but on the whole its a quick and efficient system.

 

[K.o.R]

Why can't you just have a system where the driver or guard selects what doors can be opened via the TMS? Surely it is safer to do it manually?

I'm thinking in terms of "if you must have an automatic SDO method".

 

[Bletchleyite]

Why can't you just have a system where the driver or guard selects what doors can be opened via the TMS? Surely it is safer to do it manually?

For DOO it's fairly susceptible to error, muscle memory etc. For guarded operation it works better as you can have a simple "open all doors forward of and including this one" option. While I'm sure it has happened I don't believe I've ever seen a LNR guard get UDS (Unit Deselect) wrong on the south WCML (prior to the platform extensions).

 

[K.o.R]

The problem with that is that you have a possible wrong-side failure if the "off" beacon isn't seen.

You could possibly have a variant that wouldn't, though - just have the one at the start of the platform as an "on" switch for any door that has passed it (the driver can see easily enough if he's overshot, so that doesn't need handling), and "off" is signified by the wheels moving. A wrong-side failure would then leave all doors locked and so fails safe.

By the wheels moving after the train has come to a stand otherwise that wouldn't work, but yes, that's good too.

I had another variant which involved there being a central rail and a shoe under each door, so if the shoe wasn't in contact with a rail then the associated door can't open, but that might be trouble when passing at high speed

 

[Bletchleyite]

By the wheels moving after the train has come to a stand otherwise that wouldn't work, but yes, that's good too.

I would suggest "after open has been pressed".

 

[43096]

This is pretty much the system implemented by SWT. Beacon on the track with sensors under each unit (Desiros) or car (Junipers). The Desiro version interfaces with the TMS and only releases the doors as per the beacon. The Juniper system just enables the doors on that car - which has an additional fail-safe advantage if a train stops short.

You don't need an "off" beacon at the end of the platform - the doors are only "primed" by the beacon and only release when the guard presses the door release. Of course, it's all cancelled when the guard closes the doors. So if a train passes a station non-stop, it will still read the beacons, but they have no effect until the guard releases the doors. At the next stopping point the train will pass the next beacon, which overrides that for the previous stop.

 

[K.o.R]

For DOO it's fairly susceptible to error, muscle memory etc. For guarded operation it works better as you can have a simple "open all doors forward of and including this one" option. While I'm sure it has happened I don't believe I've ever seen a LNR guard get UDS (Unit Deselect) wrong on the south WCML (prior to the platform extensions).

The only issue with the "forward of this panel" method is needing the guard to be in the right place for each station.

I've seen an interesting situation at Portsmouth & Southsea platform 3 which is an 8-car terminating platform, but the siding is long enough for 12 car, and they had to put a 12-car in there and release the doors. I think the guard had to tell the driver to wait and not shut his cab down before he could release the doors as otherwise it'd be in the "wrong" direction and there was no way to release what would become the rear 8 coaches.

 

[K.o.R]

This is pretty much the system implemented by SWT. Beacon on the track with sensors under each unit (Desiros) or car (Junipers). The Desiro version interfaces with the TMS and only releases the doors as per the beacon. The Juniper system just enables the doors on that car - which has an additional fail-safe advantage if a train stops short.

You don't need an "off" beacon at the end of the platform - the doors are only "primed" by the beacon and only release when the guard presses the door release. Of course, it's all cancelled when the guard closes the doors. So if a train passes a station non-stop, it will still read the beacons, but they have no effect until the guard releases the doors. At the next stopping point the train will pass the next beacon, which overrides that for the previous stop.

The "off" beacon is for if the train overshoots or for whatever reason needs to overhang the front end.

From what I've heard it's still rather more complex than it would seem to need to be, with talk of the beacons transmitting "what station is this, is the train supposed to be stopping here", etc. For me the only concern is is there a platform next to this door?

 

[TEW]

This is pretty much the system implemented by SWT. Beacon on the track with sensors under each unit (Desiros) or car (Junipers). The Desiro version interfaces with the TMS and only releases the doors as per the beacon. The Juniper system just enables the doors on that car - which has an additional fail-safe advantage if a train stops short.

You don't need an "off" beacon at the end of the platform - the doors are only "primed" by the beacon and only release when the guard presses the door release. Of course, it's all cancelled when the guard closes the doors. So if a train passes a station non-stop, it will still read the beacons, but they have no effect until the guard releases the doors. At the next stopping point the train will pass the next beacon, which overrides that for the previous stop.

It's actually the train travelling a certain distance, or reaching a certain speed that resets the system. If it were the doors closing you could potentially end up with a wrong side failure if a train passed through a station non stop, read and remembered the ASDO beacon, then failed to read the ASDO beacon at the next booked stop, whilst still remembering the old one. It would then open doors as if it were at the station it passed non stop, which could potentially mean too many doors opening. That it isn't reset by the guard closing doors also means that guards can safely re-release the doors at stations, and the ASDO system will still only open the correct number of carriages.

 

[hwl]

The "off" beacon is for if the train overshoots or for whatever reason needs to overhang the front end.

From what I've heard it's still rather more complex than it would seem to need to be, with talk of the beacons transmitting "what station is this, is the train supposed to be stopping here", etc. For me the only concern is is there a platform next to this door?

I disagree and I don't think you have fully understood, you also need to understand the rolling stock capabilities i.e. how smart the train is or isn't.
The original Bombardier system for Southern was just GPS and bit problematic at times (e.g. in Victoria P9-19 delaying door opening) the later Hima-Sella balise system also helps solve the multi platform issues (and allows correct side door enabling) and works best when the train has each set of doors is individually addressable by the TMCS (e.g. Electrostar, Movia for LU SSR or Juniper but not Desiro) so a single set of balises near the platform end (or other desired stopping point) can allow the train to sort the doors appropriately even if it isn't quite in the right place (Ditto the ETCS balises used for 700 positioning). This means far less equipment, improved reliability and reduced cost.

The problems is some older stock that doesn't have individually addressable doors like Desiros (Unit deselect instead etc.)

 

[swt_passenger]

The "off" beacon is for if the train overshoots or for whatever reason needs to overhang the front end.

From what I've heard it's still rather more complex than it would seem to need to be, with talk of the beacons transmitting "what station is this, is the train supposed to be stopping here", etc. For me the only concern is is there a platform next to this door?

There are no “off” beacons on the SWT/SWR system are there? AIUI bidirectional platforms have entry beacons at both ends, but ordinary one direction platforms don’t.

I think (and this has come up in previous threads) the Desiro system doesn’t deal with either stop shorts or overshoots. Which is why the guard still has a role to play.

Also, and AIUI from the published description, the information read is completely passive and always the same at each particular location, it doesn’t know whether a particular service is or isn’t stopping.

 

[TEW]

There are no “off” beacons on the SWT/SWR system are there? AIUI bidirectional platforms have entry beacons at both ends, but ordinary one direction platforms don’t.

I think (and this has come up in previous threads) the Desiro system doesn’t deal with either stop shorts or overshoots. Which is why the guard still has a role to play.

Also, and AIUI from the published description, the information read is completely passive and always the same at each particular location, it doesn’t know whether a particular service is or isn’t stopping.

All correct. Some platforms may have additional beacons. Guildford Platform 2 is an example, where it is possible to enter the platform via two different sets of points, which would mean a different number of coaches being on the platform.

 

[swt_passenger]

The problems is some older stock that doesn't have individually addressable doors like Desiros (Unit deselect instead etc.)

To clarify, although Desiro UK as delivered only had (whole) Unit Deselect, SWT’s had individual carriage level control retrofitted prior to the trackside hardware being installed. I’m surprised all the other classes you mention can control individual door sets within a particular carriage, The only Electrostars I’ve been on where individual doors were controlled was a 378?

 

[K.o.R]

To clarify: "Off" beacons don't, as far as I know, exist in any of the existing systems. They are part of the design I was proposing.

 

[swt_passenger]

To clarify: "Off" beacons don't, as far as I know, exist in any of the existing systems. They are part of the design I was proposing.

Ok thanks for explaining, I didn’t grasp that...

 

[Bletchleyite]

To clarify: "Off" beacons don't, as far as I know, exist in any of the existing systems. They are part of the design I was proposing.

Off beacons seem to leave you with a point of potential wrong-side failure, though? It's much safer for the default to be that no doors can be opened.

 

[K.o.R]

Off beacons seem to leave you with a point of potential wrong-side failure, though? It's much safer for the default to be that no doors can be opened.

Yes, you did mention. Although if the train overshoots with nothing to disable the doors that have overshot is also a problem. I was merely clarifying as some posters thought they already existed.

 

[Bletchleyite]

Yes, you did mention. Although if the train overshoots with nothing to disable the doors that have overshot is also a problem. I was merely clarifying as some posters thought they already existed.

Overshooting is less of a problem as the driver will know they have done as it's quite visible (though releasing on muscle memory is a possibility I suppose). A more likely error is stopping at the 4-car marker with a 12-car train and releasing with 2 units off the platform, perhaps.

 

[K.o.R]

Overshooting is less of a problem as the driver will know they have done as it's quite visible (though releasing on muscle memory is a possibility I suppose). A more likely error is stopping at the 4-car marker with a 12-car train and releasing with 2 units off the platform, perhaps.

Yes, but those units won't have passed the "on" beacon and so won't release their doors.

 

[hwl]

Yes, but those units won't have passed the "on" beacon and so won't release their doors.

That is a lot of extra reading equipment with a reader per set of doors...

The ORR won't like that solution given the risk of wrong side failure. It might have been approved in the 1990s but won't now. Most new implementations have correct side door enabling as well.

Far cheaper and easier to do it as the Southern / Thameslink / subsurface line implementations it really isn't that complex if the rolling stock computer system can cope

How would you deal with centre doors not opening on the Crossrail units on highly curved platforms with your suggested system?

 

[K.o.R]

How would you deal with centre doors not opening on the Crossrail units on highly curved platforms with your suggested system?

I'm not sure I follow. As I have described it, any door that has passed the "on" beacon when entering the platform and has not passed an "off" beacon afterwards can open.

As far as "failing to read an 'off' beacon" goes, don't these sorts of things reliably tell a Pendolino where to tilt while going at 125mph?

 

[TheManWho]

Having read descriptions of how various SDO systems work they seem to be either over-engineered or vulnerable to problems (GPS systems allow the doors to be opened as long as the train is close enough to the platform location?).

Proposal: have a sensor positioned under each door, and on the track are pairs of beacons/balises/whatevers at each end of the platform. The outermost beacons are "off" switches for the doors and the innermost beacons are "on" switches, so if the last thing the sensor "saw" was an "on" beacon, then that door is alongside a platform. This obviously doesn't say which side the platform is on, but it seems a simple addition to such a system.

This is pretty similar to how the DLR SDO works- beacons in the four foot and tag readers on the units

 

[rdeez]

As far as "failing to read an 'off' beacon" goes, don't these sorts of things reliably tell a Pendolino where to tilt while going at 125mph?

IIRC, each TASS balise transmits the location of the next balise, so if the system didn't pick up the next one when it expected to the tilt would be automatically disabled and limited to non-EPS speed. Also, I think each balise only provides tilt information for a certain distance, so if the next one had failed the train wouldn't tilt in that section anyway because it wouldn't have the required information to do so.

Any of the above may be wrong, just what I think I remember reading in the past!

 

[pompeyfan]

In regards to SWR and the story about platform 3 at Southsea, I think a lot of train crew don’t realise that the ASDO is actually quite clever. It doesn’t matter about the cab being on etc, a train will remember to open as many doors as it needs to no matter how many times doors are released, keys taken off etc, the ONLY exception to that is if the unit has to be rebooted or there’s an ESO, in which case the guard must do local door only, I’d assume the train will open in default but I wouldn’t know which end it would open from.

Also, the units can’t take into account permissive working, so for example if an 8 car needs to come on top of a 4 car at places such as Southsea platform 3, Harbour platform 1, or both platforms at Alton and countless other platforms that can do permissive working but can’t take 12 coaches, local door needs to be used as the train will otherwise put up the release that it’s programmed too.

 

[K.o.R]

In regards to SWR and the story about platform 3 at Southsea, I think a lot of train crew don’t realise that the ASDO is actually quite clever. It doesn’t matter about the cab being on etc, a train will remember to open as many doors as it needs to no matter how many times doors are released, keys taken off etc, the ONLY exception to that is if the unit has to be rebooted or there’s an ESO, in which case the guard must do local door only, I’d assume the train will open in default but I wouldn’t know which end it would open from.

Also, the units can’t take into account permissive working, so for example if an 8 car needs to come on top of a 4 car at places such as Southsea platform 3, Harbour platform 1, or both platforms at Alton and countless other platforms that can do permissive working but can’t take 12 coaches, local door needs to be used as the train will otherwise put up the release that it’s programmed too.

Conversely, when it's not working properly, you get situations like only the front 2 of a 444 on Platform 1 at PMS opening.

I'm fairly sure the Platform 3 story was before they had ASDO working, so only complete units could be released. It was certainly something none of the crew seemed to have encountered before; there was much flailing.

 

[pompeyfan]

Conversely, when it's not working properly, you get situations like only the front 2 of a 444 on Platform 1 at PMS opening.

I'm fairly sure the Platform 3 story was before they had ASDO working, so only complete units could be released. It was certainly something none of the crew seemed to have encountered before; there was much flailing.

The Desiro ASDO system is designed to fall back into default mode if there is a problem with the beacon or with the loop on the train. When a door release is put up and the TMS hasn’t received any ASDO data it will only open 4 coaches on a 450 train, or 3 on a 444, if it is a 9 car hybrid it would still only be 3 or 4, depending on what was leading.

 

[Alteran Ancient]

Occasionally when I am travelling to Victoria, I might get a 12-coach 375, which will automatically announce that you "cannot alight from the rear 3 coaches" but this is likely down to Platforms 3-4 only having space for a 9-coach train. This means that when we pull into platform 2, there's plenty of room and then some. Sure enough, only the first 9 coaches unlock, but then the ASDO is overridden by the driver and the rear 3 then subsequently unlock.

In this case, it works fail-safe, but this is presumably because the older Electrostars use a rudimentary form of GPS-assisted door opening and cannot necessarily tell what platform you are on.