It is my understanding that Absolute Permissive Block Signals protect bi-directional track where timetables, warrants, nor dispatch are used.BigDumbDinosaur wrote:Above are the two block occupancy detectors produced by BCS Technology Limited for riding scale railroads—these items have been available since 2006.
Can you link to a diagram that shows how you would use the BODs, Signal modules, etc. to implement the wiring of APB signals on a wye where there is a (right-hand running) passing siding at each apex of the wye (i.e.: 'outside' the wye) and it is desired to allow non-conflicting trains to travel all legs of the wye at the same time?
To clarify: Given wye apexes A, B, and C where each apex consists of a passing siding with a double-head signal S1 at the departure of the siding to enter the wye (facing point move on the route selection - the switch has a motor controlled by an engineer-operated toggle switch) and two single-head signals (S2 & S3) guarding the trailing-point moves from each leg (i.e.: exiting the leg to pass through the apex onto the passing siding). .. I hope that's clear.
Allowed at the same time: a train can proceed from S1a toward siding at B, from S1b toward siding at C, from S1c toward siding at A (i.e.: trains permitted to enter and travel separate legs at the same time)
Allowed at the same time: a train from S1a toward the siding at B and a train from S1c toward siding at B - when the trains get to apex B they should be be sequenced by S2b and S3b into the siding.
Not allowed: a train to be permitted to pass S1a towards siding at b at the same time as a train is permitted to pass through S1b towards siding at A (i.e.: conflicting trains).
There are no intermediate signals.
This while guaranteeing that no two trains are ever permitted into a conflicting section at the same time and it is not permitted to require a crew to backup to clear a blockage (i.e.: at large 7.5" meets people do not want to have to back up due to a red after they have been cleared into a block).