Speaking of Signalling....

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DianneB
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Speaking of Signalling....

Post by DianneB »

My club uses flat iron for rail and welded-in steel ties so we can't use electrical detection for trains. I tried electrical contacts to detect passing flanges but the contacts didn't stand up to weather and abuse.

We have one corner that has a level crossing and right after the crossing is the passenger loading/unloading area. The problem is that you can't see if a train is stopped for passengers (or just 'parked') until you are well into the corner.

Has anyone ever used a "car detection loop" (like used at intersections) to detect trains? It could be laid as a "square loop" along the track and SHOULD pick up the presence of a train within the loop.

If anyone has tried it and it doesn't work, I wont waste my time.
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Steggy
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Re: Speaking of Signalling....

Post by Steggy »

DianneB wrote: Sun Jun 17, 2018 3:26 pmMy club uses flat iron for rail and welded-in steel ties so we can't use electrical detection for trains. I tried electrical contacts to detect passing flanges but the contacts didn't stand up to weather and abuse.

We have one corner that has a level crossing and right after the crossing is the passenger loading/unloading area. The problem is that you can't see if a train is stopped for passengers (or just 'parked') until you are well into the corner.

Has anyone ever used a "car detection loop" (like used at intersections) to detect trains? It could be laid as a "square loop" along the track and SHOULD pick up the presence of a train within the loop.

If anyone has tried it and it doesn't work, I wont waste my time.
Traffic signal detection loops are basically large radio antennae that are attached to a "loop detector" in the traffic signal cabinet. The loop detector applies a low-frequency, low-power AC signal to the loop. When a sufficiently large metal object gets within the field of the loop the circuit characteristics are perturbed, causing a frequency shift that is interpreted as a vehicle being present. During initial installation, the loop detector will be tuned to the loop characteristics so as to establish a baseline.

Although I have not attempted what you want to do, I suspect, based upon prior experience with traffic loop detectors, that most of the RF radiation from the loop will be absorbed by the trackwork, leaving too weak a signal to produce reliable detection. In other words, the passage of a train won't be able to perturb the loop to a degree necessary to signal a change of state.

How difficult would it be to change that one section of track to wood or plastic ties so you can use a standard track circuit?
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DianneB
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Re: Speaking of Signalling....

Post by DianneB »

Thanks BDD.

Changing a section of track wouldn't go over with the club but maybe I will play with the metal-detector principle. A few smaller coils placed between the rails may well de-tune enough to detect a train.

(It helps to be a retired electronics designer LOL!)
Pontiacguy1
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Re: Speaking of Signalling....

Post by Pontiacguy1 »

Why not use several emitter/detector pairs placed along the track at some various locations, or something basically like a stretched-out light curtain. if you are worried about foot traffic fouling it, then make it such that it has to block two of the sensors before the light will change. It might not be the best thing, and I don't know how these would hold up out in the weather. I'm just trying to think of something other than track conductivity that might work. Of course, simple is better so, this may not be viable at all.
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ChuckHackett-844
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Re: Speaking of Signalling....

Post by ChuckHackett-844 »

Assumption: I assume that you were happy with the system functionality using the 'electrical contact' attempt except for the reliability of the contacts? i.e.: you didn't have problems with false occupied or false unoccupied situations. If you did, we need to discuss your approach in the circuit that the contacts feed ...

Since you are apparently skilled in electronics ...

You can try a coil in the track - I would try an oval coil (maybe 6" long) on top of the ties, keeping the coil an inch or so from the rails. Connect the coil as part of a tuned circuit (high audio, low RF). The circuit will undergo frequency/amplitude changes that you can detect with op-amps or 555 frequency discriminator.

Even simpler - arrange a very short section of one rail (4" or so) that is insulated from the adjoining rails (fiberglass 'joint bars, etc.) and use 'track circuit detection' from this rail to the other (common) rail. If you can't reliably detect the presence of a train let me know, I have a device that is guaranteed to do it reliably.
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rkcarguy
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Re: Speaking of Signalling....

Post by rkcarguy »

There are relay modules that can be purchased, that work similar to the sensors on a garage door opener to detect if anything is in the way.
Amazon has a lot of options, modules with time delays on/off, multiple relays, default off-on or on-off, etc.

https://www.amazon.com/OSOYOO-Infrared- ... lay+module

These for instance, work off of the reflected light, so you would only need to place a few of these close to one side of the train and use them to trip a relay for a red signal indicating a stopped train at the station.

Search for "infrared obstacle sensor" and there is tons of stuff to choose from.
Note that I feel that block detection is a better way to do things, but for this circumstance where you can't have it due to the steel ties, and have a train stopping at a set point(station), it should work good. If you get one with, or wire in an adjustable time delay on/off module, it can be adjusted to where it will take a couple seconds of sensing a train before it triggers, this would "filter" out birds leaves and people walking in front of the sensors for a moment, and then also give time(30 seconds?) for the train to clear before the signal would show clear.
How many sensors, and their position, could be experimented with for the best results.
SteveM
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Re: Speaking of Signalling....

Post by SteveM »

I have used Banner photodetectors. You have one on one side of the track and a reflector on the other side.

They are compact, rugged and reliable. Unless you hook them up backwards (don't ask how I know) they will last for years.

Downside is that it can't tell the difference between a train and a pedestrian.

Steve
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NP317
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Re: Speaking of Signalling....

Post by NP317 »

"Downside is that it can't tell the difference between a train and a pedestrian."

Perhaps use a time delay circuit?
Require the detector to be consistently blocked for longer than a pair of passing legs, to register as occupied. Like charging a capacitor.
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rkcarguy
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Re: Speaking of Signalling....

Post by rkcarguy »

They make the modules with time delay on/off just for that reason, so you can "filter" things out and the light doesn't blink on and off at everything. 2-3 seconds delay on, and maybe 30 seconds delay off so the train can clear the block?
As far as making them weatherproof, I had good luck with a similar project cutting a hole into a plastic electronics "project box", used JB weld to secure a piece of clear plastic over the hole, and then put the sensor behind it. Then I silicone sealed the halves of the box when I assembled it.
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DianneB
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Re: Speaking of Signalling....

Post by DianneB »

Optical detectors are out. The are simply a track-side obstruction and will get knocked over. If used between the rails, they will always be dirty.

I think I will make up some coils on wooden forms that will fit between the rails and measure the inductance change when a train passes over, sort of like a standard metal detector only with rectangular coils.
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Re: Speaking of Signalling....

Post by Atkinson_Railroad »

I Love Signaling and most everything related to it.

Yep!

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steamin10
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Re: Speaking of Signalling....

Post by steamin10 »

Teh use of inductance coils is getting pretty common now. It is the primary sensing rout for highway siganals having loops buried in the pavemetn post installation. They are simple and reliable for sensing. the passage of metallic objects. I worked with them and wired them up to controllers, but dont know the circuits. A loop between the rails would be unobtrusive and the signal cable run could be close to the ballast edge. Telephone wire comes to mind, it will last a good long time if it is hidden out of the sun. Two wires and a spare, cheap too.
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