Can anyone shed light on why signal 113 is causing every fast northbound WCML to come to a stand before clearing, costing most trains a 2 -3 minute delay. And furthermore why is it taking so long to be fixed. Surely it is coming up to a month this has been faulty?
Funny enough, I described it to a pal as seeming to clear in the same way as approach control. Is there no way of creating a slightly longer temporary block section linked to the signal after it?
Can anyone elaborate on what is meant by issues with the data links? Does that mean a cable is damaged from the relay room to the signal that tells it what aspect to display, or indeed suggest a problem in the relay room?
And is it a case after 5 weeks that the exact faulty component or cable has not been identified or that replacement requires parts that need to be manufactured or time requiring more than a night's possession to rectify?
Without design changes, no, it's not practical to alter the signal block sections. And even if this was done, I don't think it would help with this problem.
Think of datalinks as similar to a ADSL broadband using a conventional copper telephone cable. Except it's a party line with many "modems" connected to it.
A single datalink originates at the computer based interlocking. Then it either feeds copper lineside cables directly or goes via a telecoms transmission system (which could be via fibre optic cables) and then feeds copper lineside cables.
The copper lineside cables datalink feeds every trackside functional module (TFM) in every lineside location cupboard/cabinet or REB (relocatable equipment building) in an area. And this area can be many, many miles long. Datalink modules and line isolating transformers are used to break the system into sections (to limit induced voltage from OHL or power lines). Datalink modules also try to clean-up the digital signals.
If noise affects the digital signals carried by the datalink, this noise could be coming from any TFM, from a datalink module or from an external cause. Cable damage is also possible, but this is or should be easier to track down.
The reason the Approach Control is on is because the signal reverts to danger/randomly changes aspects then the drivers are approaching. WM116 on the UF is the same.
There is random electrical interference that causes the Datalink issue. The technicians have been working to find where that is coming from, but it covers the interlocking on the Fast Lines that goes from Park Street tunnels to Kensal Green Tunnel so it’s a large area to cover and it’s proving elusive. It’s frustrating for both drivers and us signallers.
This problem with noise causing problems is a real pain to track down. And I am not surprised it's taking this amount of time. I've worked on similar datalink faults in the past.
The biggest issue is that if too many messages between the interlocking and a TFM are lost or corrupted, the TFM that controls a signal will revert the signal to red. And the interlocking will treat any signals controlled by that TFM as unlit (black) or treat any track circuits as occupied. Similarity, for TFM controlling points, the interlocking will treat them as not being correctly detected. Either-way, the interlocking will command the relevant protecting signal(s) to red.
But once communication is re-established, everything returns to normal. Until the next time messages are lost/corrupted.
For any S&T reading, I have deliberately left out some of the normal terminology and not gone into the full details in an effort not to make it even harder to explain in simple terms.
