I can only assume that a risk assessment was undertaken and this justified the functionality being implemented in a SIl2 system. However I have never worked for that company- but you did for some time, so perhaps you know different!
Agreed TORR isn't dependent upon it being in an ARS area; the functionality was included in Westpac 4 which I believe predates any ARS in the UK by quite a few years. However the converse applies: ARS does require TORR (as otherwise it will fall over itself by locking up the entire area because it never unsets routes).
Also the significance of TORR and potential risk I regard as much greater within an ARS area because once the route is freed then another machine will take advantage and the human may well not be playing any particular attention to the area (putting it diplomatically).
Yes as I attempted to say, by checking the GSR down, TORR is effectively checking that the train movement taking the route was valid and will not occur if there is something unusual happening.
In the world of legacy LU, the entrance signal lever cannot be returned fully normal until the route has been used effectively in its entirety- the track circuits up to and including the last points have become clear and the front of the train detected by a "delta track" or "PD= Position Detector" a train length beyond the last points (situation is a bit different where there are points in the overlap). The backlock is implemented on the mechanical interlocking frame by the safety circuitry. Conversely as soon as the train had entered the route by passing the signal, it is the non-vital circuitry / computer which gives a puff on the lever to take it out of the fully Reverse position and leaving it centre (so there is no possibility of the signal reclearing after the train has left the route, yet with all the locking still held). Although not called TORR, there are close analogies but in this scenario the route is being primed for release, waiting for the safety conditions to occur at some later time.
Agreed TORR isn't dependent upon it being in an ARS area; the functionality was included in Westpac 4 which I believe predates any ARS in the UK by quite a few years. However the converse applies: ARS does require TORR (as otherwise it will fall over itself by locking up the entire area because it never unsets routes).
Also the significance of TORR and potential risk I regard as much greater within an ARS area because once the route is freed then another machine will take advantage and the human may well not be playing any particular attention to the area (putting it diplomatically).
Yes as I attempted to say, by checking the GSR down, TORR is effectively checking that the train movement taking the route was valid and will not occur if there is something unusual happening.
In the world of legacy LU, the entrance signal lever cannot be returned fully normal until the route has been used effectively in its entirety- the track circuits up to and including the last points have become clear and the front of the train detected by a "delta track" or "PD= Position Detector" a train length beyond the last points (situation is a bit different where there are points in the overlap). The backlock is implemented on the mechanical interlocking frame by the safety circuitry. Conversely as soon as the train had entered the route by passing the signal, it is the non-vital circuitry / computer which gives a puff on the lever to take it out of the fully Reverse position and leaving it centre (so there is no possibility of the signal reclearing after the train has left the route, yet with all the locking still held). Although not called TORR, there are close analogies but in this scenario the route is being primed for release, waiting for the safety conditions to occur at some later time.
(27-07-2012, 03:25 PM)Jerry1237 Wrote: PJW,
I would be interested to hear more to the rationale in your last paragraph that route release can be driven by a SIL2 control system.
TORR isn't dependant upon being in an ARS area. Is the logic for TORR requiring signal off simply that it is checking a train has stepped through a set and valid route which would include passing a signal that isn't in the stop position? In other words, the movement was valid. This stops the route collapsing behind the train where a potential SPAD, or other unexpected event, has occured - belt and braces?
PJW