Semaphores explained?

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Steggy
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Re: Semaphores explained?

Post by Steggy »

DianneB wrote:A 3 position signalling system requires monitoring the three blocks beyond the signal. If it is a bi-directional track, that doubles the complexity.
Actually, two blocks are involved: a block governed by the signal and a "downline" block that follows.
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DianneB
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Re: Semaphores explained?

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BigDumbDinosaur wrote:Actually, two blocks are involved: a block governed by the signal and a "downline" block that follows.
Plus the block the train currently occupies.
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ChuckHackett-844
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Re: Semaphores explained?

Post by ChuckHackett-844 »

DianneB wrote:Plus the block the train currently occupies.
I assume you mean the block just prior to the signal - if so, to my knowledge, most signal systems do not use this occupancy to determine the aspect on the signal being approached other than to support "Approach Lit" signals.

In my system, the track just prior to the signal is used by the system as the "approach track". When a train is detected on the approach track the system checks the status of the block (occupied, other trains at other block entry points, priority of this signal, any dispatch holds in effect, etc.) to determine the primary aspect (Permitted or Stop) and uses the status of other tracks ('downline', etc.) to determine the actual aspect (Clear, Approach, Approach Distant, etc.).
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
Owner, MiniRail Solutions, LLC, RR Signal Systems (http://www.MiniRailSolutions.com)
"By the work, One knows the workman"
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Steggy
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Re: Semaphores explained?

Post by Steggy »

DianneB wrote:
BigDumbDinosaur wrote:Actually, two blocks are involved: a block governed by the signal and a "downline" block that follows.
Plus the block the train currently occupies.
No, Dianne. Only two blocks affect a given signal in a basic ABS using three aspect signals, "basic" meaning no APB or other complications. For discussion's sake, I'll refer to those blocks as "home" and "downline." It will be assumed that only one train is in the signaled territory.

When a train enters the home block the "governing signal" changes to STOP. As the train proceeds and enters the downline block, nothing happens until the last wheelset leaves the home block. At that time, the governing signal will change to APPROACH. As the train continues, its last wheelset will eventually leave the downline block, at which time the governing signal will change to CLEAR. Hence only two blocks affected the governing signal.
———————————————————————————————————————————————————————
Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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