10-08-2012, 01:22 PM
I'll add my own rather simplistic views to the mix.
There needs to be a very high degree of assurance that TORR will not erroneously request a route cancellation when it is unsafe. For example, a failure/ rectification of the IRJ between the first two track circuits in the route could very easily falsely generate the approach locking release conditions even though the train in question is still speeding towards the route entrance signal at 200 Kmh. In this case, a human signaller could choose to pull the button and instantaneously cancel the route, but would be expected to apply common sense and choose not to pull the button. An "automatic button pulling" system should have extra safeguards to check that the genuine intended train really, really, really has just entered the route.
Using the stick feature as an extra piece of evidence, as well as release of approach locking, that the train has entered the route, is therefore a convenient "off the shelf" way of building up the evidence at little cost.
It seems to me therefore that the original specifiers of TORR envisaged that the extra path to pick up the signal NR would contain ALSR front contact, GSR back contact, plus the contact (s) needed for the additional TISP. However, instead of saying this, they turned it into a verbal description of the conditions for the GSR to be down: signal OFF when passed, button not yet pulled by signaller, auto working not selected. this is a classic case of a signalling principle being written to reflect what was easily acheivable in relay technology.
Interestingly, the "GSR down" condition is not a fail safe condition, as it could be induced by a simple high resistance contact/ broken wire in the GSR coil circuit. This can cause a very interesting fault - if the GSR fails to pick for some reason, the route instantly cancels as soon as you set it, because the TORR conditions are true at the instant the route has just set (approach locking free because the signal has not yet cleared, GSR already down). During this time, the nominal 1 second DJR timer is still running, so the route sets again - and the TORR cancels it again. No matter how long the DJR timer is, the TORR will win! the result is that the route repeatedly sets and cancels, white route lights coming in and out. Despite the spectacular symptoms, the fault is "right side", because the route can only self- cancel before the signal has cleared.
Finally, we must remember that TORR almost always requires the extra evidence of additional train in section proving, which was again originally envisaged to be most easily performed by re-using the lookback logic ( TAR and ATSR both up). Now in the circuit for the TAR is a front contact of the berth TPR, which is wired in a stick arrangement as anti-bobbing protection such that a momentary occupation of this or any approach track permanently throws the TAR down. So, if the berth track was needed to be occupied for the stick to drop, it must have forced the TAR to drop. If the TAR has now re-picked (train fully past the signal and approach locking now free), the berth track must have cleared again. The TORR has therefore indirectly required a cyclic occupation and clearance of this track circuit - further evidence of the genuine arrival of the train.
Reuben
There needs to be a very high degree of assurance that TORR will not erroneously request a route cancellation when it is unsafe. For example, a failure/ rectification of the IRJ between the first two track circuits in the route could very easily falsely generate the approach locking release conditions even though the train in question is still speeding towards the route entrance signal at 200 Kmh. In this case, a human signaller could choose to pull the button and instantaneously cancel the route, but would be expected to apply common sense and choose not to pull the button. An "automatic button pulling" system should have extra safeguards to check that the genuine intended train really, really, really has just entered the route.
Using the stick feature as an extra piece of evidence, as well as release of approach locking, that the train has entered the route, is therefore a convenient "off the shelf" way of building up the evidence at little cost.
It seems to me therefore that the original specifiers of TORR envisaged that the extra path to pick up the signal NR would contain ALSR front contact, GSR back contact, plus the contact (s) needed for the additional TISP. However, instead of saying this, they turned it into a verbal description of the conditions for the GSR to be down: signal OFF when passed, button not yet pulled by signaller, auto working not selected. this is a classic case of a signalling principle being written to reflect what was easily acheivable in relay technology.
Interestingly, the "GSR down" condition is not a fail safe condition, as it could be induced by a simple high resistance contact/ broken wire in the GSR coil circuit. This can cause a very interesting fault - if the GSR fails to pick for some reason, the route instantly cancels as soon as you set it, because the TORR conditions are true at the instant the route has just set (approach locking free because the signal has not yet cleared, GSR already down). During this time, the nominal 1 second DJR timer is still running, so the route sets again - and the TORR cancels it again. No matter how long the DJR timer is, the TORR will win! the result is that the route repeatedly sets and cancels, white route lights coming in and out. Despite the spectacular symptoms, the fault is "right side", because the route can only self- cancel before the signal has cleared.
Finally, we must remember that TORR almost always requires the extra evidence of additional train in section proving, which was again originally envisaged to be most easily performed by re-using the lookback logic ( TAR and ATSR both up). Now in the circuit for the TAR is a front contact of the berth TPR, which is wired in a stick arrangement as anti-bobbing protection such that a momentary occupation of this or any approach track permanently throws the TAR down. So, if the berth track was needed to be occupied for the stick to drop, it must have forced the TAR to drop. If the TAR has now re-picked (train fully past the signal and approach locking now free), the berth track must have cleared again. The TORR has therefore indirectly required a cyclic occupation and clearance of this track circuit - further evidence of the genuine arrival of the train.
Reuben