S-Stock 'Doors not in use' flashing

Or the train may be on the mark but not picking up the signal from the beacon for some reason, also flashes on when the train is opened up, just until it realises where it is.

hmm... the more the technology, the more there is to go wrong!

The doors system in a quick and simplified way is made up of relays and hard wired controls, once the appropiate beacon signal is gained it allows the correct doors to open. This is different to the system that controls the "doors not in use" panel, which is controlled solely by the train control management system (TCMS), without going into too much depth, it uses something called a Modular input/output or MIO to turn on/off. TCMS is software and there are quite a few components which is connected via the digital output e.g. outer door indicator lights (ODILS), audible alarms in the cab and even the lights for when the door open buttons are pressed in the cab.

When you start involving software, it starts to get rather complicated, however you may have noticed all the systems I have listed above aren't safety critical systems or anything that would stop the train from being moved. Apart from a few train tests that rely on the MIO to operate, it's essentially a nice to have information system.


Whilst that is true there is enough redundancy built in, so that key systems will continue to work to not leave a train stranded even if multiple systems fail. 

Given that this is not a safety critical system, it doesn't really matter that much, but it's an odd 'feature'*.

The logic for the light would be something like this for each set of doors:

IF

We within x metres of the stopping point for the next station and approaching or stationary

AND

This is a station where this set of doors are inhibited

THEN

Turn on 'door not in use' light.

-------

After turning on light:

IF

Light is on

AND

Train has started after docking

THEN

Turn off light.

----

It's rather hard to see how that logic can produce a flash of the lights when they are not required.



* In software terms, a 'feature' is any bug that you can convince higher management / customers is an intended function.

That reminds me.. I know it's slightly off-topic but I do miss the door open buttons on the exterior of the doors on the 1996TS. The light on the button would extinguish maybe ~0.5-1.5s before the doors closing chime and the doors closed.. precious little time that was useful in gauging if I should run or not and allowed me to catch a train that I would otherwise have missed!

Less useful but slightly more aesthetically pleasing also was that they would light before the doors opened (when the door open chime sounded). I miss seeing the occasional person trying to press the button.