Signalling: Mechanical and electrical interlocking

[BrianR]

I have put together a computerized simulated signal box to run a small and simple layout. The intention is for me to work it in the way that a real box would be worked. It allows for routine operation and movements but there is no provision for emergencies, keys in glass cases or winding handles for two minutes etc.  It is intended to be a cut down and very much simplified equivalent of the L&Y training layout now in the NRM. I have no experience or knowledge of real signalling and I have put this together by reading information from the internet, much of it by searching on here (The Beast has already helped in the early stages) and the signal box forum, plus whatever books and other sources I can find.

It works according to my interpretation and understanding of signalling rules and practices, but I am working in the dark and may have misunderstood what is needed and got it wrong in all sorts of ways.

My request is for the experts to give me some feedback by looking at what I have done and pointing out where it is wrong or deficient so that I can correct my mistakes.  As it stands I do not know whether it is a reasonable simulation or no more than an elaborate toy.

I have attached (I hope) three pictures: A view of station B, a screenshot of the simulated box in the state when the previous view was taken, and a track plan.

The layout and signalling is to run a service with 2 car DMUs and nothing else. It is all I can do to set that up, there is no provision for shunting or any other unusual movements.

In normal operation it is possible to work the twelve signal and point levers and to press the brown push buttons to send and acknowledge messages. It is not possible to move or alter anything else.  The computer works boxes A and C, both of them imaginary and superimposed at the back of the layout, and drives the trains according to the signals. A train from B arriving in station C waits for a few seconds after C has sent Train out of Section to B, then is instantly transported to station A. After a few seconds A offers it as a new train to B and I am able to accept or refuse it as normal.

This video is 70sec long and shows the procedure as I understand it for a train offered by box A. The bell messages take about 40sec in total and the train movement about 30sec.

 

I have set up reciprocal mechanical (simulated) locking for the points and signals. Pressing the button simulating each lever will change the state if the lever is unlocked but has no effect if it is locked. There is normal control by Home signals, sequential locking of Home and Starting signals, and Line Clear release of the Starting signals, valid for one train.  The three track circuits shown on the diagram lock the appropriate Home signals.  The small blue square above the diamond crossing is a computer operated toggle switch simulating the point locking bars.  All of this is to my understanding of the rules and may not correspond to the way it works in reality, although I am trying hard to ensure that it does.

The small size means that clearing points are drastically shortened. On all lines they are at the right hand fouling points.

I would be very grateful for any help and advice anyone is prepared to give. I think that the above is probably enough detail for an initial post. If anyone is willing to help I can add as much detail as is needed.

I use TrainController software to make it all happen but I stress that this post is not about the software. I am hoping for reality checks from experts to tell me where what I have done differs from the way a real box of this size and limitations would operate.
 

[Miss Prism]

I appreciate your post is not intended to be 'about the software', but are the sounds the software plays .wav files?

[phil-b259]

Minor point, no. 6 points should be double ended (i.e. there should be a trap point at the exit of the bay worked by 6 lever) to prevent any movements out onto the main line if a SPAD should occur to the bay platform starter. No FPL is required for this as trains should never pass over it in the faceing direction (they either take the route through no. 8 points or they have SPADed the starter)

[BrianR]

The sound files are .wav files. I'm not sure that I should admit this, but i took them from demos on either simsig or pcrail, I can't remember which.

 

Re the trap point, when I started this layout it was going to be a cheap and disposable test to see if I could set up a signal box. As it became obvious that it would work I developed it further. I may yet put a trap point in, but to need it would be an admission of failure.

 

Rather than leave this as a vague request for help, here is my attempt to set out the "mechanical" locking:

All levers are locked until the conditions for release are satisfied. These are the conditions:

Lever     Conditions to release from this state
state
  1N        2R, 4R
  2N        1N, 3N, 4N, 5R, 6N, 8N, 10N
  2R        1N
  3N        1N, 2N, 5R, 6R, 8N, 10N
  4N        1N
  4R        1N
  5R        2N, 3N, locking bars UP
  6N        2N, 3N, 5N, 10N
  6R        2N, 3N, 5N, 8N, 10N, bars UP
  7R        10N, bars UP
  8N        2N, 6R, 7N, 9N, 10N, 11N, bars UP
  8R        2N, 3N, 7N, 9N, 10N, 11N, bars UP
  9N    *    8N, 10N, 12N    (bars?)
  9R        12N
  10N        2N, 3N, 7R, 8R, 9N, 11N, bars UP
  11N        8N, 9N, 12N
  11R        12N
  12N        9R, 11R

I have three questions/comments about the list;
1. Do I need locking bars on 8A? It will be locked by signal 9 and I would have to replace lever 9 quickly/too early to unlock it under the train. I assume that trying to move lever 8 then would break the linkage rather than cause any serious damage, apart from losing my job.
2. I did not expect to have to lock any signal in the proceed position. A book "Signalling in the age of steam" says that the locking required the distant to be returned to caution before the stop signals could be returned to danger, so that is what I have done.
3. On the Down line I have assumed that even if I stop a train at 11 I must not allow it to draw forward to 9 unless 8 is Normal. Does the concept of clearing points apply in advance of the section signal?

[beast66606]

Traps are not required on passenger only lines.

 

Due to BT I have no home Internet at the moment, so I'll try and look further tomorrow.

[The Stationmaster]

The sound files are .wav files. I'm not sure that I should admit this, but i took them from demos on either simsig or pcrail, I can't remember which.

 

Re the trap point, when I started this layout it was going to be a cheap and disposable test to see if I could set up a signal box. As it became obvious that it would work I developed it further. I may yet put a trap point in, but to need it would be an admission of failure.

 

Rather than leave this as a vague request for help, here is my attempt to set out the "mechanical" locking:

 

All levers are locked until the conditions for release are satisfied. These are the conditions:

 

Lever     Conditions to release from this state

state

  1N        2R, 4R

  2N        1N, 3N, 4N, 5R, 6N, 8N, 10N

  2R        1N

  3N        1N, 2N, 5R, 6R, 8N, 10N

  4N        1N

  4R        1N

  5R        2N, 3N, locking bars UP

  6N        2N, 3N, 5N, 10N

  6R        2N, 3N, 5N, 8N, 10N, bars UP

  7R        10N, bars UP

  8N        2N, 6R, 7N, 9N, 10N, 11N, bars UP

  8R        2N, 3N, 7N, 9N, 10N, 11N, bars UP

  9N    *    8N, 10N, 12N    (bars?)

  9R        12N

  10N        2N, 3N, 7R, 8R, 9N, 11N, bars UP

  11N        8N, 9N, 12N

  11R        12N

  12N        9R, 11R

 

I have three questions/comments about the list;

1. Do I need locking bars on 8A? It will be locked by signal 9 and I would have to replace lever 9 quickly/too early to unlock it under the train. I assume that trying to move lever 8 then would break the linkage rather than cause any serious damage, apart from losing my job.

2. I did not expect to have to lock any signal in the proceed position. A book "Signalling in the age of steam" says that the locking required the distant to be returned to caution before the stop signals could be returned to danger, so that is what I have done.

3. On the Down line I have assumed that even if I stop a train at 11 I must not allow it to draw forward to 9 unless 8 is Normal. Does the concept of clearing points apply in advance of the section signal?

re the questions -

1. No, it's a trailing point.  If it moves under a train it's unlikely to use a derailment (which was the reason for lock bars on facing points.

2. It would be unusual to backlock a signal at 'off' but it probably happened in some circumstances.  In most cases the release on Distant Signals was a simple one and it might not be possible to replace the stop signals without first replacing the distant.

3. This depends very much on the locking but firstly a Clearing Point only applies in connection with block working and is thus in advance of the outermost Home Signal although other signals might come within the Clearing Point.  Now to the other bit of the question - in semaphore signalling a protecting stop signal need only be in rear of the fouling point and technically under the Rules signal 11 could be cleared (after a train has been brought almost to a stand at it of course) with signal 9 at danger and points 8 standing reverse.  However in some instances the locking (e.g. the way the GWR and WR did it) would prevent 11 being cleared with 8 standing reverse.  In other cases a subsidiary might be specifically provide below 11 in order to signal a train forward towards 9 with a train crossing in front of it (but that was a fairly rare & unusual situation).

[TheSignalEngineer]

"Backlocking" of a signal usually refers to being unable to replace a signal lever to normal unless other conditions are satisfied. The locking between Distant and Home which required the Distant to be replaced is actually the converse of the release rather than true backlocking. The only other circumstances I can readily think of where a signal lever would be locked in the reverse position is when a signal is 'Preceded by' the next signal. This means for instance that to clear a signal for a move setting back from ground signal to ground signal along a running line, the second signal, e.g. the one into a siding or through a crossover to the right line must be 'Off'.

 

Backlocking would normally be achieved electrically by a lock with the slide notch cut from the reverse position to the 'B' which is just out of the Normal position. This enables the signal to be replaced to danger without releasing the locking of points or opposing routes which would allow the signalman to set a conflicting move with a train approaching the signal which has been replaced. In your example levers 2 and 3 would be held in the 'B' position unless the train had passed onto the track circuit locking 6 points if provided, or until the track circuit approaching the signal had been occupied for a time or the lever had been in the 'B' position for a length of time, variously between 2 and 4 minutes.

 

Locking of points ahead of the next signal e.g. 11 locking 8 normal was also provided on the LMR, alternatively delayed clearance of 11 could be used after the berth track circuit had been occupied for time. In semaphore signalling a Warning arm was sometimes provided under the main signal if there was no berth track circuit.

 

 

[beast66606]

Backlocking was also used when the points from a siding were set to the main and the starter cleared, the starter backlocked the points in reverse to stop them being replaced under a train.

[BrianR]

Thanks for the comments, I am learning a lot already.

Because it is so easy to set up sophisticated locking with the software, at no cost and little effort, the danger is of including far too much at a station that is little more than a rural tram stop, but this is an exercise in locking arrangements so rather too much than too little.

The replies indicate that the locking for a departure over 8A is sufficient, although not foolproof.
I think the discussion around Q2 concludes that 1R should lock 2R and 4R and that the reality would include this in the dog and tappet set up.
For Q3, I am relieved that there is a precedent for making 8R lock 11N, which I think is the reciprocal of 11R locks 8N. I chose that arrangement because it seemed the safest option, the GWR and LMR confirm that.
To guard against  replacing 11 so unlocking 8 as the train moves slowly towards 9 your suggestion of fitting a timed release to delay unlocking 8 until, say, 2 min after replacing 11 would seem the way to go on a full size installation. When I set up the locking I did not know about timed releases or any details about back locking. On the layout, the software tells the signalling when the train has stopped in the correct position in rear of 9. There is an additional lock on 8, releasing when either the berth track circuit is vacant OR the train has stopped at 9. I could change this to a timer, but I think this gives the same protection and almost the same visible effect as a timed delay with the advantage that there is no wait between the train stopping and the lock releasing.

I hope that all the simulated mechanical locking is acceptable.  I would like to get your collective approval for it before moving to the "Lock and Block" arrangements.

[TheSignalEngineer]

At the moment I am not sure that I would make 8A/B double ended. I have just tried to do a mechanical locking table for the layout using the rules I learned about 40 years ago and it didn't quite work. I will have another look later and see if I can see what the solution should be. The rules were different with regard to left-hand and right-hand junctions.

[The Stationmaster]

At the moment I am not sure that I would make 8A/B double ended. I have just tried to do a mechanical locking table for the layout using the rules I learned about 40 years ago and it didn't quite work. I will have another look later and see if I can see what the solution should be. The rules were different with regard to left-hand and right-hand junctions.

For Brian's info - in a  left hand junction the facing point releases the trailing point, in a right hand junction the trailing point releases the facing point (assuming in both cases that the points stand normal for the 'straight' route).  

 

There was another method - officially the Southern Railway standard according to their Signalling Principles but also used by the LNER and occasionally elsewhere - in which the two point ends were set for different directions.  Viewed as you approached a facing junction the left hand point stood normal set towards the left and the right hand point stood normal towards the right hand route - if either lever was reversed it locked the other one at normal.  This method reduced the number of lever movements, especially at busy junctions.  But I doubt very much this arrangement would be used for your bay platform as there is a clear mainline precedence.

[BrianR]

If I have to separate 8A and 8B it is not a serious problem. Each point is wired independently and has its own digital address. On screen it is simple to move a block of levers sideways and put a new one in the gap. Amending the locking gets easier every time I do it.

 

I am not sure where the problem lies because I can never be sure that I have found all (or any) of the rules. I suppose I must face the possibility that the track plan itself breaks some rules. I worked out the locking by looking for the safest option in each situation.

 

At this junction the basic lock, pending your amendments, is that 6N locks 8N. I chose this to eliminate conflict at the diamond, but it fits the LH rule that facing releases trailing. Its mechanical converse (reciprocal?) is 8R locks 6R. This also seems the safer alternative in that a SPAD through the Up Homes would be diverted towards the branch and would have slightly more stopping distance before the collision. 6R leaves 8 free to be set for either an arrival or departure and, so far as I can see, does not have any safety implications for trains on the Down line. Linking 8A and B also gives automatic flank protection for a Down train.

[BrianR]

I was concerned that my track plan would prove to be unrealistic, so I have been searching through John Hinson's diagrams on signalbox.org. On the Great Northern I found Mablethorpe Jct. c1950. The track plan and signalling are very similar, there are locking bars on the facing points but not the trailing and there are three levers for the three points. At least I know now that that my plan is feasible. I have no idea where to start looking for a locking table to match the diagram, or if one exists.

[Grovenor]

At the moment I am not sure that I would make 8A/B double ended.

What situation do you see where 8A would be reverse with 8B normal or vice versa? Double ended looks fine to me with 8 rel by 6 as the OP has done.

The junctions where the numbering was different depending on left or right hand were usually double crossovers on quadruple track. I'll dig out the diagrams when I get a chance.

Keith

[TheSignalEngineer]

I'm captive on a train for a couple of hours tomorrow so I will do a conventional locking table to try to get it clear in my head.

[BrianR]

I have set it up in Modratec's sigscribe and been able to reproduce the locking with one lever for 8A and B. It has settled my uncertainty about replacing the distants, the 6/8 locking works, but I cannot find a way to set up sequential locking with sigscribe.

[The Stationmaster]

I have set it up in Modratec's sigscribe and been able to reproduce the locking with one lever for 8A and B. It has settled my uncertainty about replacing the distants, the 6/8 locking works, but I cannot find a way to set up sequential locking with sigscribe.

I understand that sigscribe and Modratec do not include sequential locking?

[BrianR]

I understand that sigscribe and Modratec do not include sequential locking?

 

I cannot find any mention of it in their tutorials.  I have tried sketching the tappets and dogs for it. I can get 4 (starting signal) locks 2 (Home) and by putting a notch in the reversed position of tappet 2 I can clear 2 then 4, but that leaves me needing to replace 4 first in order to replace 2. I'm stuck.

[TheSignalEngineer]

In tappet locking it was done with a sprung nib. This paper shows some good examples of tappet locking. Sequential locking is Section 6 and Fig. 25 http://www.s-r-s.org.uk/SignallingPapers/02/3barV5.html

[micknich2003]

 A few sketches ex NERly locking. Of interest is the combineing of Sequantal and Conditional locking on the same tappet at Brough East. Also eleswhere the provision of fixed locks or tappets. Mick.

[LNERGE]

The locking between 15 and 16 is sequential with a lifting tappet. Other locks engage in 16 tappet and they are marked as 'thick locks'.. The tray at this end bulged upwards to give room for the tappet to lift.

 

 

Also something to note. Look at the play between the notch and the locking die. The lever could move a good inch out of the frame before being arrested. This is essential to ensure that when 16 lever is returned towards normal the sequential locking is engaged before any lever band makes up freeing up the block etc. This is a little something most text books omit to tell you. It's no good having mechanical sequential if the lever can be carefully returned to normal and the circuit band makes up before the tappet drops. I have just inspected a lever frame on a Heritage railway where this could be done. It is rather unpleasant to have to show the gaping whole it leaves between the block apparatus (in this case key token) and the mechanical locking. The home lever could be restored nearly to normal with the starter off, a long plunge given to the box in rear allowing a key to be extracted there, and the home pulled again.

[BrianR]

Thanks for that information.

The SRS paper is at about the right level for me, and the animated diagrams are very helpful.  Fig 25 could be tailor made for my little station and shows clearly how it works.  LNERGE's heritage railway experience has shown me  how to defeat the locking if port 3 is a standard size and there is no notch in port 2, so that is another question pre-empted.

 

I am trying to avoid mentioning my TrainController solutions, but this is my version of fig 25, bearing in mind that no conditions allow free movement:  "Condition to release lever 2: 3N". Job done.

In looking at the mechanical locking I intended to check that my software version complied with all the rules and practicalities (apart from cost) applying to the real thing - I want it to pass the sort of inspection that LNERGE mentioned. It is becoming obvious that I need to draw up a locking table, if the SignalEngineer doesn't beat me to it, and cross check it with the software conditions before I can move to the electrical locking

[TheSignalEngineer]

I've looked again at the layout, and whilst a Bay may be treated locally in a different way to a Branch, I have followed the principles as would have been applied in days of yore to the control questions used in the Institution of Railway Signal Engineers examination. This would have been considered conventional wisdom in the early 1960s

 

Points shown as 8A and 8B would have been single ended. 8B would lie towards the Down line so that anything running by Signal 10 would run away into section on the right line rather than the wrong line. Although this may increase the chance of a collision locally on the junction, it eliminates the risk of a head-on collision in section.

 

I have renumbered the frame to allow for detonator placers which would have been used pre-TPWS and spaces for the three signals which could be there but aren't.

 

No doubt someone will give me chapter and verse regarding it not being done like that at xxxxxxx, but there is rarely a 100% fixed answer to interlocking and control questions.

 

[micknich2003]

 The attached drawing of Kirk Smeaton H&B Rly 1900, illustrates a similar style of numbering and point layout. May be of interest to someone. Mick.  

[LNERGE]

46 KIRK SMEATON.jpg

 The attached drawing of Kirk Smeaton H&B Rly 1900, illustrates a similar style of numbering and point layout. May be of interest to someone. Mick.

Interesting that great lengths have been gone to to show the normal position of all the points except 33a. It clearly wasn't a wide to gauge. Was there ever a wide to gauge fitted with an FPL? <G>