Train describers and timetables

right hey goes tom if i forget anything tom do please comment

right this is only for the old system i.e the district but the principle is still the same for more complex systems i.e central and jubby line

lets start at upminster theres a train in platform before the signalman can clear the station starter he must first select a t.d so he/she would press the revelant platform set up button aswell as the correct t.d button lets say its a ealing broadway and it has a t.d code of ABCD when he pushes the button this picks up small relays for each of the codes so for ABCD you would have ABCD relays pick up now he can clear the signal IF he forgot this when the signal cleared with no t.d he would get a warning alarm (usually a bell) and a red X in his panel to inform him that no t.d has been selected. when the train drops onto the replacing track circuit (the one after the signal) the t.d code in this case is ABCD would be transmitted to the next reciever which in this case is hornchurch and the process starts again and again and certain points though along the line the t.d can be changed i.e for service alterations and such like but the whole process begins at one end and finishes at the other usually flawlessly
the dot matrix signs take there information from the t.d system but when things go wrong its usually these what give out strange descriptions like northfields,ealing common

the thing regarding the circle line is that in the morning a couple of them start from barking but between barking and aldgate the system is not designed to put a t.d up so how they get round it is if the circle train is via tower hill they will put up a district description usually putney bridge or parsons green and if the circle lne train is for via liverpool street it will get either a baker street or hammersmith t.d so the computer at aldgate can route the train accordly

when the train either enters a depot or is terminated the t.d system knows this and of course it cannot transmit any further if its the end of the line and simply disappears but in the case of the depot aslong as the right signal is clears again it just disappears i.e for a w/b district going to ealing common depot the code is ES ealing stow that means the train goes up to ealing broadway tips out then proceeds to the depot at ealing common on the e/b if there is a barking train going into the sidings it will have a BS code barking sidings but if the train was going into the bay road at barking platform 3 it would have a B description this is for the signalman so he knows where to put the train

all the information for the t.d is inputted via signal operators not via programme machines the reason why programme machines have this is such that for the machine to work in programme only mode the train number,time of departure,t.d and sometimes the route all has to match and be correct before the machine would clear the signal if any of the above were missing i.e no t.d then the signal would not clear and again the signal operator would get a alarm, its the same for FCFS (first come first serve) mode for the machine if the t.d was missing it would not clear the signal for FCFS to work it only needs the t.d and will route the train accordly regardless if the t.d is right or wrong so in this mode the signal opertor has to keep on there toes

the programme machine rolls are punched every time there is a change in the timetable i.e engineering works this is done usually 3 weeks before any such working and we have to go round and change them every time for the case of computer sites i.e baker street the information is loaded onto a disk and installed via the tech officer/aet again when the timetable has changes

it sounds like a complex system at first but once you understand the basics it is very easy indeed and if everything works well and the line controller does not decide if the train has to alter from its timetabled path the signal opertor has a easy life and just keeps a eye of the t.d but when it goes wrong it can be a complete nightmare this is usually the main cause of wrong signals being lowered especially in programme machine areas when the machine is left in FCFS mode and the t.d is wrong especially hanger lane junction

seconded ;D