Signals - Weird but wonderful questions

[alxndr]

Are you surmising that RAIB derived the speed passing the red signal by calculating the average speed over the 183 metres (overlap distance?) and that the average speed has been derived from the signal timings. If the average speed over this distance was 22MPH then the train cannot have passed the red signal at 20MPH.

I was simply stating a fact based on calculation, and pointing out that the report acknowledges that both the distance and time are inexact.

 

[John Webb]

Any measurement involves inexactitudes, and it is common scientific practice to calculate for any measurement the possible error. For example, with what accuracy does signal data-logging record events? To the nearest second, tenths of a second or what? And known track-circuit (T-C) lengths - to the nearest metre, millimetre or what? And the train length needs to be considered as well since the T-C will operate on the first wheels of the train and only be released as the last wheels come off. I suspect the RAIB does these calculations including the errors, but their reports have to be reasonably clear and concise and such detail is omitted or given in a simplified form.

 

[GC class B1]

Any measurement involves inexactitudes, and it is common scientific practice to calculate for any measurement the possible error. For example, with what accuracy does signal data-logging record events? To the nearest second, tenths of a second or what? And known track-circuit (T-C) lengths - to the nearest metre, millimetre or what? And the train length needs to be considered as well since the T-C will operate on the first wheels of the train and only be released as the last wheels come off. I suspect the RAIB does these calculations including the errors, but their reports have to be reasonably clear and concise and such detail is omitted or given in a simplified form.

If the timing was from entering one track circuit section to entering the next track circuit section then the train length would not need to be known, only the distance between the start of each track circuit section.

 

[John Webb]

If the timing was from entering one track circuit section to entering the next track circuit section then the train length would not need to be known, only the distance between the start of each track circuit section.

Fair enough!

 

[Cowley]

We seem to have drifted off topic and into discussing the Loughborough SPAD quite a bit here. Perhaps we could leave that stuff there please.

Thanks everyone

 

[Annetts key]

Are all signals fitted with data recorder equipment?
No. Signals themselves are not normally fitted with any data recorder equipment.

Can I rephrase your question, ‘Are signalling systems fitted with data recorder equipment?’.
Some. It depends on the type of signalling system. And if the type does not record data as standard, if the powers that be decided to fit a ‘condition monitoring’ or ‘data logging’ / ‘monitoring system’.

Computer based interlocking signalling systems record a record of every event seen by the system.

Some remote control systems (a digital transmission system known in the industry as a Time Division Multiplex or TDM) where the route relay interlocking is remote from the signal box / panel / PSB can also record all transmissions in both directions (‘commands’ and ‘indications’).

Some other equipment (for example, such as computer based axle counter systems, HPSA point equipment) also logs data. However not all have a built in real time clock (RTC) as standard.

Also, not all systems are connected to a remote ‘server’. So some have to be visited by staff to get physical access to the system.

The time resolution depends on the system. A lot of systems have a resolution of one second.

Please note that there are many variations, so just knowing the signal box type is not always going to help. However modern signalling centres (regardless of what they are called) are very likely to use a computer based system.

Here’s a selection of photos:
SSI Technicians Terminal:

The system logs most (but not all) faults where it can detect them. It is also possible to examine the data from the live system. Additional equipment can play back the recorded data.

ATP Encoder

Very limited information is available, as it can only detect some types of faults. As it does not have a RTC it can’t say when a fault occurred.

HPSA handset (for points)

Again, limited information is available, as it can only detect some types of faults. As it does not have a RTC it can’t say when a fault occurred. Additional equipment can however send the data to a remote system, which does record the date and time.

SA380C data logger

Used to record the state of important relays, such as signal control, point control, level crossing control or track circuit relays.

VAMOS Level Crossing Equipment

As you can see, it can detect some types of fault. It has a mobile telephone data link to a remote system that records the data.

Within S&T, the term ‘destructive testing’ has a very specific meaning. It only applies when S&T staff are investigating a wrong side failure . That is, where an allegation has been made that the signalling system has or may have operated in an unsafe mode or manner. Signalling equipment is designed to fail safe, that is, every reasonable effort is made to design the equipment so that if/when it fails, it will fail in a mode where it’s self protecting. Hence if it fails on the wrong side of this, it’s failed the wrong side (the/a unsafe side) and hence trains, or other users (level crossings, railway staff) may be put in danger.

Officially it’s part of the signal failure investigation which is part the Signal Maintenance Testing Handbook (SMTH).

There are three stages to an investigation. First is the non-destructive part. This is evidence gathering, visual inspection of the signals controls (levers, buttons, switches or equivalents) and indications, visual inspection and examination of relevant equipment (signal(s), point(s), relay(s), cables, plus much more), downloading data, taking voltages. If any part of the non-destructive work may disturb the equipment, it’s deferred to the ‘destructive’ testing.

If the cause has not been found, then permission must be obtained before proceeding to the ‘destructive’ testing. This is where the equipment has to be disturbed in order to carry out checks and tests. It includes checks where wiring has to be disturbed, and where the equipment is operated to see if the fault can be recreated, to check how the equipment operates, to electrically test the insulation of the cables and wires, plus much more.

Lastly consideration is given to anything else that may have caused or contributed to the symptoms seen / reported.