Stratford describer

[stapler]

At lunchtime today, viewed the tail end of an Epping-labelled train departing the EB. (Grrrr!). Glanced up at the describer to see 1 reading unusually "South Woodford", almost immediately replaced by "Via Newbury Park", which scrolled to Hainault.
What was happening here?

[spsmiler]

As the train was departing so maybe you saw it changing to the next trains - rather than the one that was leaving the station?

[xtmw]

Maybe the destination changed? As spsmiller said the describer could have changed.

[Colin]

Whilst I'm not particularly familiar with the Central line's Westcode signalling system, the basic principle is likely similar.....

Some basic signalling principles to note:

• Platform describer boards are generally driven by the signalling system
• The track is usually divided into track circuits with a signal placed at the start of each one
• In very basic terms, the signalling system can "see" a given train moving along the line as it operates the track circuits

Given the above information, hopefully you'll be able to understand that as a train departs the platform it moves onto the next track circuit. The signalling system can then work out that the train is departing the platform and will change the display on the platform indicator to show the details of the next train to arrive at the platform. This happens before the departing train has fully left the platform which creates what you probably saw - the platform display changing its information as the train you observed departed.

[d7666]

Jul 1, 2022 14:36:15 GMT Colin said:

Whilst I'm not particularly familiar with the Central line's Westcode signalling system, the basic principle is likely similar.....

Some basic signalling principles to note:

• Platform describer boards are generally driven by the signalling system
• The track is usually divided into track circuits with a signal placed at the start of each one
• In very basic terms, the signalling system can "see" a given train moving along the line as it operates the track circuits

Given the above information, hopefully you'll be able to understand that as a train departs the platform it moves onto the next track circuit. The signalling system can then work out that the train is departing the platform and will change the display on the platform indicator to show the details of the next train to arrive at the platform. This happens before the departing train has fully left the platform which creates what you probably saw - the platform display changing its information as the train you observed departed.

Nit pick : Westrace not Westcode, and /generally/ - without a site by site list - the east end of the line is Westrace interlocking but the west end relay interlocking. Cue someone to list it all out .......

In the control system software, outside of the interlockings, there are "prediction points" that, over simpyfying, are associated with specific track circuits, and not every track circuit contributes input to the passenger information systems.

The underlying principle is spot on as described though.

[Colin]

Jul 1, 2022 14:50:20 GMT d7666 said:

Nit pick : Westrace not Westcode

Indeed - the D stock braking system was Westcode - obviously mixed the two up in my mind!

[d7666]

Jul 1, 2022 14:55:23 GMT Colin said:

Jul 1, 2022 14:50:20 GMT d7666 said:

Nit pick : Westrace not Westcode

Indeed - the D stock braking system was Westcode - obviously mixed the two up in my mind!

And not the first time nor will it be the last time this confusion occurs.

Going into digression here .... tsk tsk ... even the term Westcode for braking has a history; a Westcode unit is only an air-electric translator, an electric actuated pneumatic valve for want of another term, not really the complete braking system.

An example of this is the erstwhile main line class 33/1 diesel locos, when their push pull kit was fitted, a Westcode device translates the EMU drivers all electric controller notch setting to an air pressure step for the diesel engine control.

It is quite common (indeed correct w.r.t. what drivers etc are taught ?) I know to refer to the entire braking system on D-stock, etc, as Westcode, just as it is on main line EMU from 313s etc onwards, but, strictly, pedantically, Westcode's origin lies with the electric command - air presssure translator only.

[Colin]

The Westcode term was certainly mentioned as a catch-all term but equally we were very much trained in the how the braking system worked. I’m getting rusty now but can recall the seven step relay and how we only used three of the steps on D stock, for example.

Anyway, we’ve drifted off topic somewhat….

[t697]

Jul 1, 2022 15:55:10 GMT Colin said:

The Westcode term was certainly mentioned as a catch-all term but equally we were very much trained in the how the braking system worked. I’m getting rusty now but can recall the seven step relay and how we only used three of the steps on D stock, for example.

Anyway, we’ve drifted off topic somewhat….

Westcode steps 3-6 are Service 1-4 on the Traction/Brake Controller. Westcode step 7 is Emergency. Had to stop and think it out though! Still in use on the Picc 73TS of course.
Anyway anyone want to return to why the Stratford indicator briefly showed the OP "South Woodford"?

[stapler]

Is it perhaps that, unusually, a Woodford bay terminator was the train whose tail I saw, and the T/op had merely made a mistake in setting the rear DMI?
Or is there a lunchtime terminator now scheduled? (I have lost my link to the current WTT in an extended absence from the Central Line.)

[Colin]

Jul 1, 2022 20:58:27 GMT stapler said:

Is it perhaps that, unusually, a Woodford bay terminator was the train whose tail I saw, and the T/op had merely made a mistake in setting the rear DMI?

On the modern stocks with electronic destination displays it’s not possible to deliberately set up one end different to the other.

[Westinghouse]

Jul 1, 2022 20:58:27 GMT stapler said:

Is it perhaps that, unusually, a Woodford bay terminator was the train whose tail I saw, and the T/op had merely made a mistake in setting the rear DMI?
Or is there a lunchtime terminator now scheduled? (I have lost my link to the current WTT in an extended absence from the Central Line.)

I might be able to take an educated guess.

There are predicted ONA's (train operator not available for specific duties) for each day - with these a plan can be put in place to stable the train early awaiting a train operator to bring it back into service.

There are also late notice ONA's, eg Train operator books off sick before their duty, is late to work due to service disruption on other lines or bad traffic etc.

In the late notice scenario, the relevent Trains Manager will contact the Controller to inform them that train XXX has no relieving driver at its booked point.

Sometimes this can happen as late as when the train sitting in the relevent platform waiting for the new driver.

If there is no relief available for the current driver, then they have to take the train to the nearest depot or sidings and stable the train.

In the case of Leytonstone, a train crew depot and relief point, the nearest sidings is Woodford, any train going into Woodford sidings will show as South Woodford on the train describer dot matrix as it has to detrain at the previous station before going into the sidings.

A train going through Stratford Eastbound is about the right time for the controller to find out about a late notice ONA, If that was the case, the signaller would be informed to divert the train to Woodford sidings and the train describer and dot matrix would change to say South Woodford, the Train Operator will then be informed about the situation.

Maybe in your case, the train operator was still in the process of being informed of the situation and you just happened to catch the discrepancy with the dot matrix and the train as it departed.

[stapler]

I think you have it -- thank you. There was no train in Woodford bay, but there were two in the sidings....