SEMAPHORE SIGNAL 'LOGIC'?
This may well be a dumb question, except that it isn't really phrased as such!
I have just purchased an MTH semaphore signal, a single arm unit and the way its wired the green lamp shows constantly while the arm is vertical and when a train activates the pressure switch the light turns to red as the arm comes down to the horizontal. This strikes me as odd, though I'm not up on signalling at all, one would have thought the 'normal' position would be red-danger and the trains approach would cause it to go green (having presumably been given the go ahead by a signalman, or not as the case may be). Ideally, the track power would be cut to the following section of track covered by that signal unless it was green so if a driver missed the signal it still had to stop.
Unfortunately, the way the signal is constructed and the way in which it operates makes it difficult to change the sequence, though I suppose one could swap the lenses, I haven't yet investigated if that is possible.
So I suppose I could put the pressure plate AFTER the signal so that the passing of the last car in the train causes it to go red thereby safing that section. Either way though, using my fixed 18volt AC, the lamp gets very hot in only a minute or so and I dont suppose a solenoid is very happy either being held on for long.
I've always wanted to have semaphore signals, just because their operation fascinates me and I suppose when all's said and done, it's really only a gimmick as much as anything and if it goes into action as a train approaches (or passes) no one will be any the wiser or bent out of shape. However, on the other hand, it would be nice to have it working 'properly' whatever that is and I thought perhaps it should be wired to a turnout instead so that it only did its thing when commanded rather than 'dumbly' as a train passes in either direction.
Hence my opening disclaimer, although this isn't really a question as such, I would like to know what others do, what logic they use, how they trigger the signal and so forth in the hope of learning a bit more.
On a prototype railroad, a semaphore used as a block signal would typically turn from green to red as a train passed it and stay red while the train was in the block guarded by the signal. Then, as the train moved entirely into the next block, the signal would go to yellow. Finally, when the caboose is two blocks away, it would go back to green.
The usual toy semaphore is trying to approximate this behavior, with the signal green as the train approaches, then red as it passes. The long wait for yellow and then green is skipped, however, and it goes back to green quickly when the train has passed.
It is of course possible to rig up a semaphore to behave just like a prototypical one, but not easy. One problem is to get it to stop in the yellow position. I have been able to do this with a Marx semaphore operated by a Tortoise switch motor, which also gives it a realistic slow motion. But I have yet to tackle the difficult job of creating the blocks in my tubular-track layout.
Bob Nelson
Thanks Bob and Roger for your advice. Roger I like the Z signals too but for $14 I wasnt going to pass up this MTH one and besides, it looks right, a nice hefty metal job, except the arm.
Just in case anyone else is interested in this topic I found this page of signalling links:-
http://www.semaphores.com/resources/sites.html
Thor,
I wire my signals to my switches.
When the switch is straight through, the signal shines green, when the switch is switched to the diverging route, the signal goes to red.
This is a simple way to do it, plus it gives me another indication of how my switches are aligned.
That is the way I have my block signal wired, been doing it for years with no burnt out bulbs...try it for awhile and see how you like it.
How does the manual recommmend you wire that signal?
If this is indeed a 3 position semaphore ( MTH #30-11023? ), I wonder if there actually is a mechanism within the signal which postions it to yellow. Seems that you haven't been able to access the yellow position yet. If it simply goes between the 2 positions of red and green then the wiring will never allow it to work prototypically without some major fudging. For activation wihtout the use of relays or IR my suggestion would be to wire it to 2 sections of insulated outside rails. The insulated block ahead of the signal would give you your green signal then move the arm to red once the train hit the insulated block past the signal. When no train was over either insulated block the signal would be dark. It's a compromise but better than burning out the solonoid or overheating the bulb by having it on all the time.
On the MTH 2 head target signal I had to accept this type of compromise too. My Atlas track is wired as such that one outside rail is always insulated ( accept at switches). The MTH signal has an internal board that ,when energized, lights the yellow signal first. I connected the wire that energizes the yellow light 2 blocks ahead of the signal. There's a time delay of about 5-10 seconds and then the signal goes automatically from yellow to green. By this time my train is within the block immediately ahead of the signal. My trains are generally long enough to be momentarily in 3 blocks at once. Once the train passes the signal it energizes the next insulated block connected to the wire which energizes the red light while at the same time the end of the train exits the first block, turning off the green light. Yeah, it's not exactly prototypical postioning like Bob described but it does at least work....and as much as I know it works as MTH intended.
Bruce Webster
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