LU signalling and freight trains

[Deleted]

On the parts of the network that were shared with freight trains, what sort of signalling modifications were needed? I already know of the yellow mechanical distant discs seen on the Central, Northern and Metropolitan Lines, as well as the auxiliary reds on the Met Main, but what else was used?

[q8]

ETD's were used at certain places like Newbury Park, Leyton. These were livened up by electric trains and the associated signal would only clear for the juiced route. If they were NOT livened up the signal would clear for the steam route. You had to have coincidence with the track circuit for the lock to release.

[russe]

ETD

What's an 'ETD'? Extra-terrestrial distant?

Russ

[Deleted]

russe said:

ETD

What's an 'ETD'? Extra-terrestrial distant?

Russ

Electric Train Detector

[Tom]

A number of trainstops were positioned where it was possible for the signal to return to danger before the tripcock had passed the stick, they had to be slugged and were commonly fitted with hold-off circuits.

[russe]

Electric Train Detector

Thanks Jim. How does an ETD work? (i.e. how does it distinguish between an electric and a non-electric train)

Russ

[Tom]

They used a dummy current rail which the shoes of an electric train energised, which in turn picked up a relay which was used in the control of the signal for the electric route.

[mandgc]

On the Barnet and Epping lines ' during Fog and Falling Snow' when a Goods train had been let out onto the Main Line the 'Station Master' had to caution the following Electric Driver that the Goods Train was ahead and did not have an Electric Tail Lamp.
PS- Old PW ditty- " During Fog and Falling Snow, Into the bothy you must go! When the Sun begins to shine, Out you go along the line ! :-)

[russe]

They used a dummy current rail which the shoes of an electric train energised, which in turn picked up a relay which was used in the control of the signal for the electric route.

Thanks Tom. Presumably this a single (or double?) short section of otherwise unconnected conductor rail? Anyone know of a picture of one of these ETDs?

Russ

[q8]

Dunno about a picture Russ but a description is like this. Just an ordinary plain piece of conductor rail about 12ft long with a ramp at both ends and not connected in any way to the current supply. Similar looking to the short lengths you see at points and junctions. They were only provided on the positive rail position outside the running rails.

Exactly the same as in this photo but in this case the function is different.

www.trainweb.org/tubeprune/Acton%20Home%20Sigs1.jpg

[Deleted]

thats a speed inductor you see in the picture

[q8]

thats a speed inductor you see in the picture
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Yes I know. I was just trying to explain to Russ that an ETD looks similar.

[Deleted]

sorry q8

[q8]

sorry q8.
----------------------------------------------------------------------

Wot are you sorry for? You done right by telling him what the thing in the picture was. If I can find a photo of an ETD I'll post it to show the fella how easily you can mistake the two. I've been looking for photo's of Newbury Park or Leyton westbound in the sixties which both had ETD's.

[banana]

What's a speed inductor?

[russe]

Just an ordinary plain piece of conductor rail about 12ft long with a ramp at both ends and not connected in any way to the current supply.

Ok. Just to make it clear for me, an ETD is a single piece of conductor rail in the positive position that will presumably make a circuit, via the shoes connected through the train to the energised positive rail, that will indicate the incoming presence of an electric train. Question: was there an associated 'exit' ETD that would clear/unlatch the electric train indication, or was this done in some way by the track circuit release lock?

www.trainweb.org/tubeprune/Acton%20Home%20Sigs1.jpg

Interesting. But how does this provide an indication of speed? Is there another one associated with it with a timer between the two? Do I see another one in the middle distance in that picture?

Russ

[mandgc]

Where is an ETD required now that Goods trains no longer run on DL Tube extensions ?

[q8]

No You have a misconception Russ. I will try to explain in a sequential manner (don't think I am being patronsing please)

At Newbury Park westbound there were two such ETD's. One was approaching the home signals and the second a third of the way along the westbound platform road. Now although the levers for the home and starting signals were reversed (I.E. in the "off" postion) the signals remained at danger. Now along comes a tube train and no matter what speed he was doing as soon as the shoes strike the ETD and liven it up the relay in the frame room below the cabin would close (you heard a distinct "tock") and the associated signals would clear. It was if you like a second "stick" relay.

A stick relay is what prevents a controlled signal from returning to clear automatically. After a controlled signal was returned to danger by the passage of a train the signalman had to "restroke" that signal lever. "Restroking" the lever meant it had the placed at danger and then pulled to "clear" again. In the case of an ETD the relay was controlled purely by the ETD and the track circuits.

After the ETD was livened up the signals then worked normally. As soon as the associated signals were returned to danger this opened the ETD relay in the frame room (you heard a "clack" as it opened) ready for the next train and the whole sequence was repeated.. Speed was not taken into account at all, just the fact that the ETD was "live" or dead.

The reason there were two ETD's was that the second acted as a "back up" for the first and confirmed that it was indeed an electric train. Another reason was that coupling up used to take place at Newbury Park and a four car unit would be in the platform awaiting a normal train from the rear. This unit had already operated the second ETD so it could not be used agian until the starting signal had returned to danger. So the approching train had to contact the first ETD to liven the relays up again. The starting signal would not be "clear" as it was held at danger by the signalman until the coupling up was complete. Once the units were coupled at it was OK for the (now 8 car) train to leave he pulled the lever to clear and the starter would go green as the ETD relay was already closed.

I know it's a bit long-winded but it's the simplest way to describe it.

The only place I can think of nowadays where an ETD woud be useful is at Harrow-on-the-hill southbound to prevent a Met train from toddlng off down the Chiltern Line to Marylebone. (Which I think happened a couple of years back)

[q8]

What's a speed inductor?
------------------------------------------------------------------------
Now Mr Banana I will answer your query. The short piece of conductor rail you see on the right in that picture had set in it some coils at a given spacing. The coils were insulated from the metal of the rail itself. This spacing was decided by the speed determined for an approaching train to clear it's associated signal.

Now If the speed to clear the signal was 25mph the spacing was thus determined. Now along comes a train and as the shoes pass over the coils set in the rail it livened each one up in turn. If the speed was 25mph or less the signal cleared. If not it stayed at danger.

[Harsig]

q8 said:

The only place I can think of nowadays where an ETD woud be useful is at Harrow-on-the-hill southbound to prevent a Met train from toddlng off down the Chiltern Line to Marylebone. (Which I think happened a couple of years back)

There are a couple of problems with this idea which is no doubt why there is no such device installed.
As far as I am aware in all cases where ETDs were installed the signalling was so arranged that signals for a particular route would not clear unless an electric train was detected. In the case of Harrow you are trying to achieve the opposite effect i.e. you want to prevent certain signals clearing if an electric train is detected. Now since the signalling on the Main lines through Harrow is Multi Aspect they can quite rightly be cleared some time in advance of the train's arrival so the question arises where would you put the ETD?
Secondly of course the only reason that you would normally be interested in whether or not a train is electric is, as in the case of Newbury Park, to determine whether or not the train will fit in the tunnels immediately beyond. i.e. at Newbury Park if the train is electric you are fairly safe in assuming that it will be tube stock gauge.

[q8]

Well Mr Harsig I would say that it does not matter where the ETD was placed. The only thing that mattered was wether the thing was livened up or not. I have seen empty trains at Newbury Park (and been on one) that approached the ETD at the homes near line speed and the signals still cleared as the drivers new how it worked.

As for Harrow the simple answer to that is if the ETD were put at the very beginning of the platform or just prior and an electric train was detected the starter , if clear, could return to danger. After the electric set had gone the starter would be cleared by a restroking the lever. No problem!

[Deleted]

the speed inductor sections are never different its just the FR (frequency relay) which is different as it depends what sort of speed the train should be travelling at its usually 25mph, so if it detects the train going faster then 25 then the signal will not clear nor will it if detects the train going too slow as theres not enough current draw from the coils in the inductor to pick up the FR. the voltage to operate the FR is tiny when it comes from the inductor rail so it has to go through a transformer which thats boosts it to 100v now the reason why most of inductors don't work is because of the power pack failing and having no spares in the stores so they will be eventually removed one by one as i had to remove WM400 inductor a few weeks ago now because of the power pack being faulty.
Now there is a backup system if the inductor fails or otherwise the signal would never clear this works on timing relays usually 4 1/2 secs, but in controlled areas if the signal infront of the spped control signal clears the speed control signal will automatically clear

[Tom]

q8 said:

As for Harrow the simple answer to that is if the ETD were put at the very beginning of the platform or just prior and an electric train was detected the starter , if clear, could return to danger. After the electric set had gone the starter would be cleared by a restroking the lever. No problem!

Unless of course the ETD relay fails to pick up.

[Harsig]

tom said:

q8 said:

As for Harrow the simple answer to that is if the ETD were put at the very beginning of the platform or just prior and an electric train was detected the starter , if clear, could return to danger. After the electric set had gone the starter would be cleared by a restroking the lever. No problem!

Unless of course the ETD relay fails to pick up.

That was going to be my other point, the system in this context is inherently not fail safe. To make it fail safe you would need find some method of giving a positive indication when non-electric train approaches.

[q8]

Have a double ETD. One on the positive and one on the negative.

[banana]

q8 said:

Now along comes a train and as the shoes pass over the coils set in the rail it livened each one up in turn. If the speed was 25mph or less the signal cleared. If not it stayed at danger.

Thanks for that Mr Q8. I always thought these things were achieved via Track Circuits.

However I'm sure you don't mean to imply that the signal stayed at danger - surely it cleared eventually

[q8]

However I'm sure you don't mean to imply that the signal stayed at danger - surely it cleared eventually --------------------------------------------------------------------------

Oh yes it does. But if the speed inductor did not work or the train was travelling too fast it would be brought to a stand and a timing relay would clear the signal. That is if the train has not passed the signal at danger.

[Tom]

q8 said:

Have a double ETD. One on the positive and one on the negative.

Unfortunately that doesn't make the situation any better as too much emphasis is placed on the same component type, in this case a double ETD. If a failure mode is common to the type (such as speed inductors and their associated power packs) a double ETD won't solve the problem.

[igelkotten]

tom said:

q8 said:

Have a double ETD. One on the positive and one on the negative.

Unfortunately that doesn't make the situation any better as too much emphasis is placed on the same component type, in this case a double ETD. If a failure mode is common to the type (such as speed inductors and their associated power packs) a double ETD won't solve the problem.

It could even be argued that such a setup would increase the risk of a failure within the system.