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tynewydd
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This thread is to take the RR&Co discussion out of the layout thread Port Dinllaen layout thread as it is a fairly specialized topic.
As I am still wiring up the last (and most complex) modules of the layout, I thought it might be helpful to discuss/ ruminate on how to allocate track circuits to achieve good results operationally. This rethink is based on John's cautions about how long gaps between circuits can be problematic even though - theoretically - they don't inhibit TC from working. 

Background - 
  • I exclusively use BlockD8s to detect occupancy via current flowing to one rail. I will have 18 of these detectors in total providing about 120 track circuits. This sort of transformer detector is said to be superior to the diode drop type (like the DB4) because it does not reduce the delivered track voltage. 
  • I intend to ensure that all guard vans and brake coaches will be equipped with resistive wheels so that both ends of a train can be detected.  
The track plan for PD is pretty complex and is split into three sections - the approaches (including the two MPDs and goods yard), the throat and the station itself. The approaches are relatively simple because at this stage of the game I am choosing not to circuit the MPDs or Goods Yard - making working those areas an entirely manual process. The majority of the throat and the main station are intended to be capable of automated operation especially for DMUs and steam trains where the engines are not turned.



The basic PD design is a compressed rip-off of Holyhead with a two-track mainline, twin-sided goods facilities (customs in and out), 4 platforms (Pl1 <arrivals> subdivided into 3 sections, Pl2 <main departures> with Pl3 <parcels and sleepers> embedded along it, and Pl4 <in/out>)  Pl1 and Pl4 have run-around facilities, Pl2 and Pl3 are blind.  There is a special engine release road to access the MPD from Pl1, and in parallel a road from the MPD Out that allows Engines directly into Pl1-Pl4. An aim of the circuit design should be to permit as much parallel activity as possible with Engines being sent to the MPD and leaving the MPD at the same time, for example.  There is and added a single track secondary mainline, which adds a flavor of Bath Green Park.  

Anyway to business. Each of the two modules will have 16 track circuits available - it is possible that a small number could be located on one module and the detector be on the other. Let's look at the main station section first. 




The track circuits are shown in green with red numbers for the 16 circuits detected on the main board. On the second picture the circuits are numbered in orange for those 16 detected in the throat in this second picture. You'll see a few red circuits are used in the throat - this is to save on investing in yet another BlockD8 just for a couple of circuits. 

I'm still working on these diagrams - I just saw that I have to move red circuit 13 over to just the main board as I made a mistake and repeated red 6 in the diagram - so I am thinking of simplifying detection of the double crossover in the throat to be just one circuit and releasing orange 15 to replace it.

The principles I have adopted are -
  1. If a train can stop somewhere it must be a dedicated circuit for just that location. Examples orange 9, 10 and 5.
  2. The purpose of detecting elsewhere is that we want to know that certain tracks are empty before sending/signalling another train (or use a calling-on/ground signal rather than a main signal if the circuit is occupied). 
  3. Only those seperate tracks which will block the same set of other tracks are added together. Example orange 1 which is the Engine Release to MPD In road has several parts a train on any of them will stop cross traffic and vice-versa - but note that orange 2 is seperate so that trains on the way to the MPD from the Pl4 RR track don't block departures or engines being coupled at Plats 2, 3 and 4. 
  4. All areas of track that can be automated are detected.  
  5. Where I can I use the required IRJs (Insulated Rail Joiners) at points/switches to isolate the end of a track circuit. But if I need to, I will add extra IRJs to break up the track and create independent circuits. 
  6. For entrances and exits to manual areas a track circuit is needed - see Orange 6, 3, 12 and Red 3, 12.
Anyway, that's my start. Comments/brickbats, etc welcome!  I am just at the point of track wiring on the main board right now so this is very timely.

Adam

John Dew
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Hi Adam

What an impressive track plan........matches the benchwork :thumbs

These comments are based on the assumption that you are going down the RR&Co route.

As I wrote earlier it is not mandatory to detect turnouts, most people dont. If you choose to do so they really should not be associated with blocks

A picture is worth a thousand words. I spent a few minutes setting out how a section of your track plan would look on a Train Controller Switchboard using your circuit #s






Each numbered block should be electrically isolated and connected to a dedicated "track circuit".....in TC speak a contact indicator or CI

The lettered blocks are undetected but should be wired so that you can set them up with CIs later. Meantime you would have to use Flagman indicators if you will be using TC to send trains there.

The two double slips could be detected with one track circuit if you wish.....but I wouldnt bother.

Block 4 could possibly be redundant depends on how you treat the diamond Xing

Similarly not sure if you need both Block 12 and 16 Red. A single block would work ok and the circuit saved could be used to detect a lettered block.

Hope this helps

Regards

John








tynewydd
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Hi John,Thanks for these pointers and your mockup - I have tried to adjust the plan as below. I guess the point is that TC normally sees turnouts/points/switches as nodes in the graph that connect blocks - which have indeterminate length. So including them inside a block is potentially a problem as TC doesn't have the idea of contained switches. 

So, given that, I have reset to either not cover turnouts or have them seperate in cases where a circuit would be especially helpful. Those cases are - 
  • Platforms which have turnouts embedded - which may therefore be occupied by coaches. Platform 2/3 is one example - trains in Platform 2 may be long enough to block Platform 3. See Red 13. Also each sub-part of Platform 1. See Red 6, 3 and 15.
  • Places where an engine may stand on a turnout waiting for onward clearance. Examples are at MPD Out, and the carriage sidings entrance. See orange 10 and Red 9.
  • A place where it is important to know whether the rear of a long train has cleared a set of points so it can reversed (like when coaches are pulled out of Pl1 and then pushed into the CS. See Orange 13.
In these cases I would model those I would include as a TC of the length of the turnout with a turnout at the end.



John Dew
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Hi Adam

Thanks for your latest.....I now have a much clearer idea of why you want to have occupancy detectors on some turnouts.

TC will compute the length of a trainset from its components so you can also use this as a conditional tool.

However, assuming  the block has its own separate CI,  having a turnout associated with a different dedicated CI is a more elegant and precise method. 

I am not sure how much knowledge of TC you have so forgive me if I am now stating the obvious. :roll:  I think I may embed this in my signature :lol: or perhaps you can just assume I have always written it!

Each of your track circuits will be associated with a CI. If the CI is attached to a block you can either display the CI indicator (Red ON Black OFF) adjacent to the block or embed it within the block which saves cluttering the switchboard.......regardless the block symbol will be coloured Pink when the associated CI is on

You will not be able to embed a CI within the turnout symbol.....in fact TC will not recognise the CI is associated with the turnout ......the turnout symbol will not change colour when the CI is on......nevertheless if a current drawing loco or car touches the track and turnout that are wired to a particular track circuit then its CI symbol will turn Red.

Thus you will have a visual indicator on the switchboard if a long train overhangs the block........you will know when the train has cleared the turnout because the symbol will turn black (see comment below re CI memory)

In addition to it being a visual symbol you will be able to use it as a condition in schedules and as a trigger for flagmen.

If you are operating long trains you may want to add a few more resistive wheel sets to avoid the CI flickering on and off. You will also need to adjust the memory of CIs on through blocks from automatic to say 2 seconds to prevent TC from thinking a second train has entered the block

One final thought on block design....for trains to run automatically with TC they must start in one block and finish in a different block.......known as a schedule. The ability to automatically move a train in a single block is very limited.

Hope this helps

Regards

John    



John Dew
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Hi Adam

This may be of interest....... RR&Co operating quite a lot of trains.....8 locos in play

http://yourmodelrailway.net/view_topic.php?id=14663&forum_id=35

Happy to answer any queries even if its only to apologise about the music...again

John

tynewydd
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Thanks  that helps a good deal.  It is as I expected, so we'lll give this a go and see where we are. Armed with this I have got this far. 
I added about 7 IRJs and some extra droppers. In particular, I moved both TCs that have a catch point so that the catch point is not included. Need to finish wiring up the second BlocD8 and move the topmost Cobalt over a smidge to clear the support pillar and I'll be done with this module. Then onto the throat. 


  


                 

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