Capture/Release type circuit?

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Capture/Release type circuit?

Post by Atkinson_Railroad » Sat Oct 28, 2017 6:44 pm

Does anyone have a circuit diagram of the popular “…engineer-operated ‘button’ blocks (the Capture/Release type)” circuit that could be posted?
How many line wires are typically required between the operating button stations?

I'm vaguely recalling a circuit in one of the magazines illustrating the diagram.
What refinements have been made to it, if any?


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Re: Capture/Release type circuit?

Post by jabsteam » Mon Dec 11, 2017 6:47 pm

Bump from 2 years ago.
I'd like to see a basic circuit diagram too.
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Re: Capture/Release type circuit?

Post by kcameron » Wed Dec 13, 2017 8:18 am

The circuit I've been using is from Michigan. It uses three wires between endpoints for the two lamp version, and four wires if you want three lamps. It uses an AC 24V feed and then a small rectifier and cap to feed the DC relay. The claim button energizes the relay which also interrupts the circuit for the far relay. The release buttons are in series with the relay circuit.

Result is whichever relay closes first prevents the other relay from closing. The release buttons at both ends will clear whichever relay is active.
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Re: Capture/Release type circuit?

Post by Patio » Sun Dec 17, 2017 12:40 am

I do not know the order of operation, for train signal lights, but wouldn't a electrical latching circuit, as used in industry, work?
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Re: Capture/Release type circuit?

Post by SCBryan » Sun Dec 17, 2017 2:11 pm

I was playing around in the lab one day during my lunch break and built a circuit on the bench using components we had on the shelf trying to make something that I thought might work. I built this circuit and it seemed to work perfectly for capturing and releasing so I drew it up.
Basic Schematic.pdf
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Re: Capture/Release type circuit?

Post by Patio » Mon Dec 18, 2017 1:57 am

Ken, do you have a drawing of the 3 and 4 wire circuit, you use? Or a link to it?
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Re: Capture/Release type circuit?

Post by ChuckHackett-844 » Mon Dec 18, 2017 7:05 am

One thing you have to deal with using "capture & release" systems:

Typically when someone captures a block the signal either comes on (red only systems) or it goes from red to green, etc. The point is, unlike automatic systems, the signal is the same after the train enters as it is to permit the train to enter.

This means that a following train must not enter the block if the signal is in the "permit" state (i.e.: green in a red/green system) if he did not cause it to go green by hitting the capture button -- even if he can see the train in front of him. This is because the first train will release the block not knowing that the second train is in the block. This would allow an opposing train to capture the block and - voila - you have a cornfield meet with that train encountering the 'second section'.

The exception to this is that the second train can enter on the "permit" signal if and only if the first train knows that the second section will clear the block (and thus the first train does not clear it when he exits).

As an added problem - if the second section decides to stop following the first train he must notify the first train. If he doesn't, blocks will be left captured (because the first train is not releasing them) and the railroad will soon come to a stop.

This issue - the near end signal indication not changing from a "permit" aspect to an "occupied" aspect when the train enters the block is one of the flaws in capture & release systems.

This is not usually an issue with a small number of engineers who know the system and obey the rules but it raises havoc at a large meet with visiting engineers that either are not aware of the rules, are inattentive, etc. ... and it only takes one to clog up the railroad.

There are ways of solving this issue but they all involve adding more hardware and, even then, they have their own issues. Before you go to that effort (beyond simple capture & release) you should examine automatic signal alternatives.

Automatic signals eliminate this issue - but, as I have said before - each railroad has to judge what will work best for them. Capture & Release, automatic, whatever - they all have their place. You just have to know their limitations.

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
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