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| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 09:04 #58478 | |
Peter Bennet
5402 posts |
I've edited it a bit and moved some of the content to the call-on section. That in turn may need further tweaking. Peter I identify as half man half biscuit - crumbs! Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 09:12 #58479 | |
Steamer
3986 posts |
Wiki said:The driver sees the standard shunt signal (maybe with a “C” to indicate a Call-on function):As far as I know, this is only used on some mechanical signals. On colour-lights, the letter/number displayed will generally be a route indicator (e.g. '1' for Platform 1, 'DM' for Down Main etc.). Wiki said: TC override buttons may be found where it is necessary for a signalman to send a train into an occupied platform - either to join there or just because two trains are booked to use the same platform at once. The second train usually arrives from a siding where its approach speed will be low (e.g., 15 mph) and entry is controlled by a Ground Position Light, rather than a subsidiary shunt signal attached below a main signal, minimizing the risk of colliding with the stationary train (see Call-On, also Huddersfield Control).I think you've got confused. A driver will interpret a shunt signal showing clear and a red+subsidiary at a main signal in the same way, and will drive slowly on passing either. The only function of the TCO is as an 'Are You Sure?' reminder for the signaller. At Hove, the TCO is only used with shunt signals, however at other locations it's used with main signals as well. Main signal with subsidiary lit:  Shunt signal:  In either case, two diagonal white lights mean the same thing, and the chance of collision is identical. "Don't stress/ relax/ let life roll off your backs./ Except for death and paying taxes/ everything in life.../ is only for now." (Avenue Q) Last edited: 06/04/2014 at 09:14 by Steamer Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 11:12 #58483 | |
Tempest Malice
122 posts |
I have possible idea as to why tco's are used instead of call on's. In most examples I've found on SimSig, tco's are used where that tc can be called on to from both ends. So on an nx panel you only need 2 route exits and one tco button rather than 2 standard route exits and two call on buttons so a tco svaes a button on the panel and with that time space and money. This is just a guess of course but I'm sure someone who designed nx panels might have more of a clue than me.
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| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 14:00 #58485 | |
Danny252
1461 posts |
" said:An irrelevant historical note: it wasn't always the case that a main signal couldn't be cleared in such circumstances, certainly on the GWR, but if a subsidiary signal existed it would always be used. The GWR rulebook made it clear that it was possible for permissive working for joining trains to be allowed at locations with only a main signal and no subsidiary, and that at such locations the signalman must clear the signal (rather than give a hand signal).Was that a GWR thing? I thought that "Station Yard Working" was standard practise wherever you went. Edit: From a bit of reading, it may have been that non-GWR practise was to caution the train and use handsignals for Station Yard Working where subsidiary signals were not available, although my current source is an Australian rule book and may not be representative of UK practise... Last edited: 06/04/2014 at 14:09 by Danny252 Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 14:00 #58486 | |
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Hooverman
306 posts |
For such a simple concept we appear to be going around in circles here. I can only speak from my experience at TBASC where we have TCOs at Norwood Junction, Purley, Redhill, Three Bridges and Hove stations. Our TCOs only have an effect on shunt signals (GPL) and not the calling on signals associated with a main aspect signals. Does anyone know a location elsewhere where a TCO needs to operated to get a calling on to clear? Our TCOs only appear where we have had or still have permisive working for both passenger and freight trians at a station. For the normal attaching of a passenger train we would still use the calling on signal as normal and set that in the normal way. But if we set into the occupied platform from a shunt signal then as part of the condition for the interlocking after setting the route then the TCO button would need to be operated (pulled up in our case) to get the shunt signal to clear. The only trains likely to be using the shunt signal at these locations would be either a light engine, engine + vans or engine + wagons. So they way I look at it, they are there as another layer of protection to ensure we don't permissively work a passenger and a freight class of trains into the same platform atvthe same time, bearing in mind that you might not have any decription in the TD berth for any local shunting taking place and will only have an occupied track circuit acting as your reminder as to what you have on the track. The last paragraph is just a personal opinion as all of our instructions explain how to use them and don't give a clue as to why we have them at only certain locations (and platforms within those locations) and not other locations within the ASC, Haywards Heath for instance. Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 14:58 #58491 | |
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Peter Bennet
5402 posts |
" said:Does anyone know a location elsewhere where a TCO needs to operated to get a calling on to clear?Edinburgh Sim has loads, both GPL and Subs. Peter I identify as half man half biscuit - crumbs! Last edited: 06/04/2014 at 15:06 by Peter Bennet Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 15:08 #58492 | |
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Hooverman
306 posts |
Ok thanks Peter, I've only used the ones at Dunbar which were the shunt ones and they operated in the way I expected of them. The ones on the calling ons where were they and what sort of traffic would be using them?
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| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 15:51 #58495 | |
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Peter Bennet
5402 posts |
As per linked photo - all the north-end bays had them. What I'm not 100 sure of is whether these specific ones were an override to the Lime Street overlengths trips or whether they were used for every call-on. They must override the LSs as locos would have dropped on carriages occupying nearly the full length of the platforms. There are other dotted around the place (Inverkeithing North Curve rings a bell). Peter I identify as half man half biscuit - crumbs! Last edited: 06/04/2014 at 15:51 by Peter Bennet Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 17:51 #58498 | |
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Hooverman
306 posts |
Hello Peter I note that where they have renewed Edinburgh's buttons they have given them a yellow insert at the top of the buttons and where they renewed the tiles at Edinburgh itself they have given them a yellow bezel but with "T" on them, our are still the older 1980 vintage buttons with a black bezel at the bottom and no letters printed on them. Looking at Dunfermline Townhill yard I see that there are TCOs applied to both Down & Up Cowdenbeath lines. Now if these behaved like the ones at Three Bridges then setting the calling on from the main aspect will just work as normal, but setting a route from the GPL signals reversing back into the occupied track will require the use of the TCO. But as we know everywhere operates differently so they may still apply to the calling on from the main signals. Going back to Inverkeithing north curve from the Up fife there is no calling on signal so the TCO can only apply from the GPL signal on the down Fife but on the Down & Up Cowdenbeath lines you have both a main aspect with a calling on and GPL signal, so that back to the old argument do TCO only apply to GPL signals or the associated calling on signal for main aspect signal as well. You seem to think that Edinburgh's apply to both so that means that two large power boxes operate differently, don't you just love UK signalling lol. Also I've been talking to one of our signallers who went into Three Bridges when it first opened and still works there (what he doesn't know isn't worth worrying about lol). He said that then TCOs are located at both Free Wire and Geographical interlocking areas so it can't be down to what type of interlocking is used at a location. No one said even back then why we had TCOs just you were shown how to use them like any other piece of equipment. Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 18:35 #58502 | |
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Forest Pines
525 posts |
" said:" said:I have to admit I don't know what the other 3 railways did, so I don't want to say it was a GWR-*only* practice.An irrelevant historical note: it wasn't always the case that a main signal couldn't be cleared in such circumstances, certainly on the GWR, but if a subsidiary signal existed it would always be used. The GWR rulebook made it clear that it was possible for permissive working for joining trains to be allowed at locations with only a main signal and no subsidiary, and that at such locations the signalman must clear the signal (rather than give a hand signal).Was that a GWR thing? I thought that "Station Yard Working" was standard practise wherever you went. Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 22:04 #58510 | |
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clive
2789 posts |
" said:I have possible idea as to why tco's are used instead of call on's. In most examples I've found on SimSig, tco's are used where that tc can be called on to from both ends. So on an nx panel you only need 2 route exits and one tco button rather than 2 standard route exits and two call on buttons so a tco svaes a button on the panel and with that time space and money. This is just a guess of course but I'm sure someone who designed nx panels might have more of a clue than me.You don't need a separate exit button for calling-on. The normal exit button can be used with track circuit occupation used to determine the route type. Certainly it's done that way on Cambridge panel. There's a TCO at Ely. It's used for a shunt route into one platform; there are also (I think) calling-on routes into that platform from both ends. Log in to reply |
| Purpose of Track Circuit Override (TCO)? 06/04/2014 at 22:06 #58511 | |
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clive
2789 posts |
" said:The one TCO on Cambridge panel applies to a GPL reading into a platform, and *not* to the calling-on route on the converging line (i.e. to the same platform starter signal). Log in to reply |
| Purpose of Track Circuit Override (TCO)? 07/04/2014 at 02:49 #58512 | |
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maxand
1637 posts |
After seeing what further edits were made to the glossary entry, the final result seems so similar to the original that I feel I needn't have bothered. Ha ha. Well, you can't please them all.
Last edited: 07/04/2014 at 02:51 by maxand Log in to reply |