Assume for purposes of discussion and explanation that there are 3 multi-homes (A, B, C), with each reading a track circuit that encompasses a third of the platform length (I suspect that 'C' also reads the starter overlap). As a train enters the platform ('A' track circuit) the 'A' home would go red. Would the B and C homes also go red at that point, or do they go red in sequence as the train progresses into the platform? I know they clear in sequence, but am not sure of the logic setting them to red (realizing that they also must each go red if 'their own' block is occupied). All wisdom gratefully received!
As you might imagine, this is so I can finally realize one of my 'holy grails' of implementing this in MSTS. I have the clearing logic working - just need to make the 'red' logic prototypical.
Post by railtechnician on Nov 4, 2007 22:30:20 GMT
c5 said:
They would each go to red when the train's wheels pass over the Replacement Block Joint surely?
Yes absolutely, it is the norm for each signal to be replaced as a train drops onto its replacing track, this is also generally true for repeaters.
There are some instances where a repeater will not be replaced immediately usually to do with its positioning and I have come across one location where the 'A' and 'B' signals of a multiple home installation are so close together that they have the same replacing track!
Brian
Always a company man, very much a lurker now as I slowly fade away.
platforms usually have 2 track circuits so as the train leaves the platform the A signal will clear once the platform is totally clear the B signal will clear and so on or in the case of bow road on the west that has 4 home signals most common on the district in the old days but usually removed when resignalling took place in the 60's
As a train enters the platform ('A' track circuit) the 'A' home would go red. Would the B and C homes also go red at that point,
I just had to pick up on this bit - for completeness - if 'B' & 'C' went red at the same time as 'A', the driver would have signals going back in his face!
Multi home signals work independently just like any other stop signal - the only thing that really links them is the train stop on the station starter. If the starter (and/or it's associated train stop) were to fail, all of the homes would be affected (and would remain at danger). The reason for this is that the outer home provides the full speed overlap for the platform - and that's why all the home's have associated numbering.
Here's hoping one our signal experts agrees with my understanding ;D ;D
Post by railtechnician on Nov 5, 2007 20:21:17 GMT
aetearlscourt said:
platforms usually have 2 track circuits so as the train leaves the platform the A signal will clear once the platform is totally clear the B signal will clear and so on or in the case of bow road on the west that has 4 home signals most common on the district in the old days but usually removed when resignalling took place in the 60's
I can't help asking if the District is still using BTD (berth track down) in its signal selections, although it was supposedly obsolete many years ago I know some areas still used it but has it gone yet?
(If this better belongs in the Sim threads, I apologize - I put it here as it's a follow-on to my original question, and I felt the experts might spot it here). BTW Colin - fully understood, and thank you! I plead a senior moment
I always felt this was possible in MSTS, with a little ingenuity. I based my implementation from the description in TubePrune's site:
(Click on the multi-home title at the top of that page to get to the relevant segment of the description.)
The homes each go red as the train passes (their own block being occupied), and then clear as the train progressively departs the platform.
So to test it out in MSTS, I designed and created the required components. 4 of them are hidden - 3 "track circuit detector" items, places at the platform edge and at 1/3 and 2/3 the way down the platform track, per the TubePrune diagram; and a "track circuit repeater" item that the 3 home signals test to determine what track circuits (A, B, C) in the platform are occupied. The homes (A/B/C) should clear to green in sequence as the train ahead departs the platform as each of the track circuits clears. As the video shows (see URL below) it looks easy - in fact there's a bunch of logic going on behind the scenes, as with the real thing. I approached the A home slowly and waited for it to clear, then I held about 15mph so as to approach the B and C homes as they cleared as the train ahead departed the platform. It appears to me to be prototypical behavior. Note that it is the train AHEAD that is causing the homes to clear, not our train! Note also the A/B/C plates on the signals showing their function. The example location (part of the extension to HSK etc. that Eddie is working on) was purely for test purposes.
Click the URL below (select 'save' to get it to your PC, then view it). It's about 11MB and runs about 2 minutes. If you have a fast enough connection, you can open it directly and it will play in Media Player.
MSTS District Line Video:
The video shows us from the cab of a train and another train ahead of us. It doesn't show the train ahead passing the homes on its way into the platform, but they do behave correctly in that respect. We then follow as the signals allow our progress. Did I get it right?
Dr Jimi, your 3-multi-home is very good but I must confess my diagram is a little off reality. I did it some years ago before I got to see the scale plans.
I have looked at Sloane Square EB as an example.
The outer home is A765. It will go to green as the rear of a departing train clears the middle of Sloane Sq EB platform.
The intermediate home is A767. It will go to green as the rear of a departing train clears the block joint of the starting signal (A771 or PNX771 I'm not sure which number it has now) 15m in advance of it.
The inner home is A769. It will go to green as the rear of a departing train clears the block joint of the starting signal overlap, which is 69m in advance of it. This distance is the standard overlap for starting signals where all trains must stop (on level track). It is based on a 35km/h approach speed. There's a whole story about this but it would probably send most of you to sleep so I'll leave it until you read Underground News in February next year.
I recall this run into Sloane Sq. very well because it was a good place to do a Westinghouse but it had speed controlled signalling then. However, it will be a lot faster than 15mph to run in after a stop at the outer home. The outer home is almost 260m from the platform end. If the train in front moves off in a sensible time, you shouldn't have to stop, just reduce speed to about 20mph. At the other end of the scale, Mansion House will be a very slow run in. The DR drivers on this forum could help with some sample speeds I am sure.
The whole thing is that it is a balance between the sections between stations and the stations themselves. It's very difficult to model except on a site by site basis.
"Rules are for the guidance of wise men and the observance of fools"
Tubeprune has the speeds about right - though of course in reality a good driver will still hold back a little as no signal is guaranteed to behave how you expect and SPAD's are not good! ;D ;D
The quoted station starter number at Sloane Square is an interesting point - I saw you put PNX771 and was gonna say it must be A771 as PNX denotes a possession................I've just looked in me line supplement to be sure and it dose indeed show it as PNX771.
Needless to say I'll be looking at that tomorrow whilst on the job.......
I can't help asking if the District is still using BTD (berth track down) in its signal selections, although it was supposedly obsolete many years ago I know some areas still used it but has it gone yet?
Sorry, would it be possible for you to clarify what BTD is?
TubePrune & Colin - thank you for the additional info! The test I showed was mainly to test the 'virtual technology', and I felt my track circuit spacing and home signal placement was a bit off. Fortunately, my implementation allows positioning the 'detectors' at any point along the platform, and the homes are not limited by distance. I think my next test will be to try and replicate the homes approaching ACT EB from ECM down the bank. My signal diagrams show a 20mph speed test followed by homes. I'll get the positions as close to the diagram as I can and test if a 20mph approach results in the expected behavior (assuming virtual Picc trains aren't blocking both platforms ;D)
Based on your comments it seems the virtual representation is reasonable, and I think the flexibility is there to suit prototypical use at various locations. I'd just always wanted to add this feature to the virtual LUL signal set. My next challenge is to correctly signal Triangle Sidings - once again the sim is lacking in intrinsic capability and a little ingenuity will be needed.
I greatly enjoy trying to model LUL operations in the sim, and the kind support of you professionals is warmly appreciated.
Best to all, Jimi
Post-traumatic déjà vu disorder: The feeling one gets after one has experienced trauma before it happens.
I can't help asking if the District is still using BTD (berth track down) in its signal selections, although it was supposedly obsolete many years ago I know some areas still used it but has it gone yet?
Sorry, would it be possible for you to clarify what BTD is?
This may be wrong - but I understand it as proving the train is stood (berthed) [1] at the signal that is about to clear.
[1] or on the berth track (circuit) on the approach, (or in older terms) in rear of, the signal about to clear.
If we can have A 244/R 246A, ODX 246A/R 246B, A 246B/ROD 1, OD 1/ROD 2 then I'm going to have A (7)88/R (7)90A, NHX (7)90A/R (7)90B, A (7)90B/RNH 1, NH 1/RNH 2 and hang the consequences!
Post by railtechnician on Nov 7, 2007 11:56:46 GMT
spooky said:
railtechnician said:
I can't help asking if the District is still using BTD (berth track down) in its signal selections, although it was supposedly obsolete many years ago I know some areas still used it but has it gone yet?
Sorry, would it be possible for you to clarify what BTD is?
Signals are controlled by track occupancy, point positioning, speed etc this being known as signal selection. When a clear signal is passed the replacing track is occupied and the 'selected' feed is removed from the signal relay. As long as conditions make it unsafe for a signal to be cleared again the feed will be disconnected. In BTD when a train occupied the berth track it would not only disconnect the feed from the signal relay but also short circuit the coil. It would thus be impossible for some extraneous condition to 'pick up' the signal relay while a train was occupying the berth track. I never had occasion to work on BTD but my understanding is that the circuit was applied to multi home signalling where trains would be occupying a berth track for more than a few seconds i.e. at station approaches. It was not unknown for induced extraneous voltages to 'pick up' track and signal relays so shorting the single coil relay was a way of ensuring that it did not happen while a train was stationary within the limit of control of the signal. Obviously the danger on the District line in particular was the nearby BR overheads. In modern signal circuits the selection simply disconnects the 'Q' coil of a double coil signal relay while the 'R' coil is directly fed from a separate supply. The two coils have to be energised and 90 degrees out of phase with each other for the relay to 'pick up' which is designed to prevent an extraneous source from picking up the relay. Modern relays also use a 125 Hz supply for the same reason. The equivalent of BTD in a modern signal circuit is known as TR-GR series and as long as the berth track is occupied not only is the feed disconnected from the 'Q' coil by breaking the selection path but also the feed to the 'R' coil is disconnected because that coil is shunted directly by the train shunting the track circuit of the berth track.
I'm sure others will correct me if necessary. The longer one is away from the railway the quicker the grey cells fade!
In BTD when a train occupied the berth track it would not only disconnect the feed from the signal relay but also short circuit the coil. It would thus be impossible for some extraneous condition to 'pick up' the signal relay while a train was occupying the berth track.
Thanks very much for your informative answer, Brian. I think I have some reading up to do :-)
;D ;D
