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Electric token block instruments

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Electric token block instruments 06/10/2019 at 13:55 #120758
Muzer
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I can find loads of websites explaining in great detail how electric token block works from the driver and guard's perspective and loads on different variations of instrument types, tokens, etc., but I can't find a page explaining simply the electrical principles behind the operation.

I'm sure I've found such a page in the past but I can't find it now and it's really annoying me. So could someone explain how electrically the token locking works?

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Electric token block instruments 06/10/2019 at 14:13 #120759
Edgemaster
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There's some circuit diagrams for various single line block systems here: http://dickthesignals.co.uk/onewebmedia/signalling%20a%20single%20line.pdf

(You've got me searching for more online resources, now too)

Also: http://dickthesignals.co.uk/onewebmedia/9%20operation%20of%20single%20lines.pdf

Last edited: 06/10/2019 at 14:15 by Edgemaster
Reason: None given

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Electric token block instruments 06/10/2019 at 14:24 #120760
Muzer
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Cheers, I saw the second one but not the first! My friend and I are still having great difficulty working out the non-standard symbols in that first one though...
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Electric token block instruments 06/10/2019 at 14:32 #120762
Edgemaster
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I'm less familiar with the electrical side of signalling, it's an area in which I've intended to do some further study. By non-standard, do you mean deviating from the electrical symbol standards, or the more specialist railway signalling wiring diagram standards?
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Electric token block instruments 06/10/2019 at 15:10 #120764
Muzer
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The former - I didn't know there was a standard for railway wiring diagrams but I suppose that makes sense! Maybe that will help me interpret it...
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Electric token block instruments 06/10/2019 at 21:10 #120772
clive
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The basic answer on how it works …

There are two wires from the internal logic to the lock where the tokens are inserted and removed and from there along the telegraph wires to the other machine. Every time a token is inserted or removed the connections between the internal and external wires are reversed (so instead of internal wire A connecting to external wire A and B to B, it changes to have A connected to B and B to A). Tokens can be inserted at any time by rotating the lock one way, but to remove one - by rotating the lock the other way - an electric latch on the lock must be energised. This latch, in turn, is powered from the wires through a diode.

So one signalman presses the button to release a token. This connects a battery to the wires with positive on line A and negative on line B. If both locks are in the same position (either A-A/B-B or A-B/B-A) then at the far end you'll get positive on line A and current will flow through the diode to lift the latch. The token can then be removed. But if the locks are in opposite positions then you'll get *negative* on line A, the diode will block the current, and the lock stays firmly locked.

So you can only release a token when the locks are in the same positions and that changes them to opposite positions. Putting the token back (in either machine) restores them to the same positions again.

Hope this makes the concepts clear. The rest is just details.

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The following users said thank you: Muzer, Steamer, TUT
Electric token block instruments 06/10/2019 at 21:45 #120773
Muzer
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Perfect, that's the sort of simple explanation that I knew I'd read somewhere in the past but couldn't find, much appreciated Clive!

One thing, I imagine they would have used some naturally polarity sensitive lock rather than specifically a diode back in the day since I don't imagine they had decent diodes when these were first invented!

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Electric token block instruments 07/10/2019 at 06:23 #120778
d233
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And if, the sent train on the token has broken and it needs to be towed, then how?

(text via Google translator)

Russian Railways
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Electric token block instruments 07/10/2019 at 09:35 #120781
jrr
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No idea for token but with a staff the fireman had to take the staff to the signal box. The rescue loco then took the staff and fireman back to the failure. This got used several times when I signalled on a heritage railway.
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Electric token block instruments 07/10/2019 at 10:14 #120784
headshot119
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d233 in post 120778 said:
And if, the sent train on the token has broken and it needs to be towed, then how?

(text via Google translator)
In simple terms.

In the scenario that the train has failed in the section between box A and box B the token remains with the failed train.

The signaller at Box A will agree with the signaller at Box B what is to happen, and allow an assisting train onto the single line without a token.

EDIT

This is under the current regulations, on a line signalled with Electric Token Block regs.

"CHECK Do you stop at Capenhurst?" - Opinions are my own and not those of my employer
Last edited: 07/10/2019 at 10:16 by headshot119
Reason: Edit to clarify era context

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Electric token block instruments 07/10/2019 at 12:33 #120788
clive
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Muzer in post 120773 said:
Perfect, that's the sort of simple explanation that I knew I'd read somewhere in the past but couldn't find, much appreciated Clive!
You're welcome.

Muzer in post 120773 said:

One thing, I imagine they would have used some naturally polarity sensitive lock rather than specifically a diode back in the day since I don't imagine they had decent diodes when these were first invented!
The actual term is "polar relay". I always think of it as a relay with a diode in series but it almost certainly isn't. Sorry for any confusion.

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Electric token block instruments 07/10/2019 at 21:30 #120819
Muzer
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headshot119 in post 120784 said:
d233 in post 120778 said:
And if, the sent train on the token has broken and it needs to be towed, then how?

(text via Google translator)
In simple terms.

In the scenario that the train has failed in the section between box A and box B the token remains with the failed train.

The signaller at Box A will agree with the signaller at Box B what is to happen, and allow an assisting train onto the single line without a token.

EDIT

This is under the current regulations, on a line signalled with Electric Token Block regs.
Presumably today with the network covered by radio you can have a much more positive assurance that the train is definitely broken and the driver isn't going to start moving again having fixed it! Back in the day I can certainly understand the taking the token to the box - without it the remaining traincrew know they're not to move!

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Electric token block instruments 07/10/2019 at 22:41 #120822
pedroathome
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I was reading not too long ago in an old sectional appendix for the Western end of the Western (1973 copy I think, given it still made reference of the former through platforms at Plymouth), on the Gunnislake Branch, if a train failed between Bere Alston and Gunnislake (i.e. after the train has reversed), that the token was to be walked to Bere Alston so the ground frame could be worked. There was no mention of returning it to St Budeaux (Whichever was the LSWR station)
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