08-03-2018, 01:34 PM
I'd guess that this is not the way the question is intended.
Track circuits prove the absence of the train, if there is a power failure (example) the track section might be occupied or not.
Axle Counters also prove absence in that if the section is reset following a failure it indicates occupied util restored such that track clear can be proven.
Actually it looks like the question is focusing on Signalling functions rather than the type of train detection.
So for a signal to clear it needs the appropriate track sections proved clear (plus other things like points detection). So signalling function <Signal Off> is one that must prove track clear.
Approach release (Main Aspect Approach Released from Red for example) proves that a train has slowed down on the approach to a signal by testing Berth track occupied, or occupied for time, or (less common) by using a treadle.
To set a permissive move such as a call-on into a platform, various tracks need to be proven occupied or occupied for time. So <Set Call-on Route> must prove exit track occupied.
For the aspect <Signal Off for call-on move> must prove berth track occupied for time, permissive (exit) track occupied for time and the other tracks in route clear.
It doesn't matter in any of these cases whether track sections are TC, AxC or something else. Have a think about these cases and others, what happens if the track has failed [clear when occupied] or [occupied when clear] and what will happen. Is it a wrong-side or right-side failure?
Track circuits prove the absence of the train, if there is a power failure (example) the track section might be occupied or not.
Axle Counters also prove absence in that if the section is reset following a failure it indicates occupied util restored such that track clear can be proven.
Actually it looks like the question is focusing on Signalling functions rather than the type of train detection.
So for a signal to clear it needs the appropriate track sections proved clear (plus other things like points detection). So signalling function <Signal Off> is one that must prove track clear.
Approach release (Main Aspect Approach Released from Red for example) proves that a train has slowed down on the approach to a signal by testing Berth track occupied, or occupied for time, or (less common) by using a treadle.
To set a permissive move such as a call-on into a platform, various tracks need to be proven occupied or occupied for time. So <Set Call-on Route> must prove exit track occupied.
For the aspect <Signal Off for call-on move> must prove berth track occupied for time, permissive (exit) track occupied for time and the other tracks in route clear.
It doesn't matter in any of these cases whether track sections are TC, AxC or something else. Have a think about these cases and others, what happens if the track has failed [clear when occupied] or [occupied when clear] and what will happen. Is it a wrong-side or right-side failure?