Train Describers

I have seen a Morden description quite a few times at London Bridge N/B.

As for the reason, pure guess, as I am not a techie, wrong PTI codes by the T/op?

As far as Sub-Surface Lines are concerned, except for the area controlled by Baker St SCC (Aldgate to Wembley) the train describer system in use was that installed circa 1960/61. This is relay based and uses five TD code lines known as ABCDE. Simple arithmetic shows that there are only 31 different combinations (the 32nd (00000) option indicates no code being transmitted). Thus on any given line there are only 31 different Train Descriptions that can be displayed. While you might think this is quite a lot those in regular use rapidly use up this allocation particularly when you allow for the fact that you have to be able to maintain this one code for the entire length of the journey of that train. e.g. the code for trains to Hammersmith via Kings Cross cannot be used on the WB District west of Tower Hill because any such destination might be required for a train starting it's westbound journey at a point east of Aldgate East where the code is in use for the Hammersmith trains.
Also being of such vintage the system still carries descriptions that are no longer used such as the Hounslow or Northfields descriptions you referred to earlier.
Baker St SCC does have a wider range of train descriptions, being computer based but when trains pass out of it's area of control it is back to the old ABCDE system and so even the SCC can only transmit the 31 different descriptions.
Oh and when circles are reformed to Districts on the Inner Rail, the driver and line controller may know well in advance but the signalman at Baker Street does not because no-one bothers to tell him more than to put train 2xx up as an Edgware Road. In theory this avoids confusion to passengers who are not expecting trains on the Circle or H&C to go to Wimbledon. Baker St SCC does have a Wimbledon via Kings Cross description but we are not sure what TD this transmits to the signalman at Edgware Road when reverting to the old ABCDE system.

Going back to the Northern Line's (and Victoria's) train identification system, I was under the impression that drivers switch the destination at the stop before the terminus e.g Waterloo SB, South Wimbledon SB on the Northern, Stockwell SB on the Victoria Line.

there should be a various points on the line PTI arriels on the line controllers diagram and signal diagrams it would look like a folk but yes manily from each control site to another

going back to the ABCDE codes the only one with a E code is anything displaying a MET/H&C/CIRCLE code for instance if at Earls court they recieved a ABCD and that turned out to be a Upminster (not sure what the code is) but instaed got a ABCDE it would not show nothing and the regulator would just get a red X on there diagram

<much whirring of cranial cogs> I think you might very well be right - however I say this guardedly; after looking at the various textbooks on programme machine wiring and a couple of Northern perils that give the ABCD(E) codes - there doesn't seem to be a 'don't send this code back in the other direction' code or a filter to initiate a fresh code. There is the push-button 'XCL' Kennington Loop via Charing Cross - which (of course) isn't programme-only operation. I hasten to add that I'm only looking at textbook examples rather than specific locations.

However, is there not the code ABD - Kennington Loop via CX? On further digging it seems that ABD was used from Finchley Central and ABCD from Edgware for this destination- could it be that these codes and anomalous descriptions are a hangover from the installation of the programme machines?

ABD was also used at Archway for the loop.

Hmm, think this is a 'two-pipe problem'

I've thought on this some more to-day and my gut feeling is that ABCD SB does get transmitted NB - but I've got to check through what few ABCD codes I've got a note of for the Northern. Sadly I've not got a copy of Peril 38/1968 [1] which I think will give the TD codes for the converging branches .

[1] in one of the documents I was looking at last night - think it was installation of programme machines at Golders - there was a helpful note saying 'Train descriptions will be transmitted in the manner outlined as per TC Supplement 38/68 for Camden Town' Grrrrrr. ;D

The answer (in part at least) I suspect lies in which machine does what at Kennington. And of course the PTI codes - I'm the wrong side of the village to read my set at the moment.

I think that I once saw a 1995TS heading southbound with a northbound description on the front that had the platform describers showing Kennington, but I can't remember clearly enough to say.

at belsize park northbound i saw a destination which read high barnet via charing x was it
the driver keying the wrong pti code?

One more example tonight-- got a S/B train at London Bridge about 2200. The Platform indicator said Edgware, although the train correctly said Morden. Upon arrival at Colliers Wood, the platform board said Edgware via Bank. There were a few confused faces at London Bridge this evening!

One at London Bridge NB used to show H[blank] NET and the scroll text was also missing where it passed the relevant section...