Spring points!

[retbsignalman]

Good afternoon!

I would like to set up a bit of automation on a set of points powered by a Tortoise switch machine.

 

Basically, as the train approaches  in the trailing direction, it passes over a light sensitive diode which via a relay sets the point for the train. Once the train has passed clear, it passes over another light sensitive diode and the point resets itself.

 

I have uni directional line as far as a 'limit of shunt board' (from the lhs on the diagram), after which it becomes a headshunt. 

 

Can anyone assist with a wiring diagram please?

 

In anticipation! 

 

Thanks Graeme 

[Jeremy Cumberland]

What type of photo sensor are you using?

How is the train detected? Does it reflect light, or does it break a beam?

Can the exit sensor be positioned far enough away from the point so that when the front of the train reaches it, the rear of the train is guaranteed to be clear of the points, or do you need it to sense that the back of the train is clear?

Edited November 19, 2023 by Jeremy Cumberland

[RailWest]

2 hours ago, retbsignalman said:

......

I have uni directional line as far as a 'limit of shunt board' (from the lhs on the diagram), after which it becomes a headshunt. 

......

What diagram please?

[retbsignalman]

Ah, sorry! Here it is!!

What I have in mind is for the train to approach the point and pass over light sensitive diode A which will, via a relay activate the Tortoise motor to the points reverse position for the train to pass over it and once clear at B activate it to its normal position set for the sand drag.

The light sensitive diodes I have are 5mm 'photodiode photosensitive light sensitive diodes'

The distance between A and B is roughly 18" - roughly 6" before the point and 2" beyond it.

Hope this helps explain it better!

Thanks Graeme 

[RailWest]

Well, the first thing that seems 'obvious' - unless I've misunderstood something - is that if B is only 2" beyond the point, then as soon as the front of the engine passes over the point will start to reverse again long before perhaps even the engine, let alone the first carriage, is clear of the point.

 

What you need to create IMHO is the equivalent of a track-circuit extending from A to B, so that once the train runs onto the pseudo-TC at A the point reverses and is then held reverse by the continued occupation of the TC until its tail end clear the TC at B. Maybe several 'A's at intervals between A and B would do the trick ?

[retbsignalman]

Hi!

 

My initial thoughts were that A would be a 'strike in' to activate the points and B a 'strike out' which would reset them after the last vehicle had passed  clear.

If I were to use  say a DCC Concepts 'intelligent detection' track occupancy detector as a TC on the trailing approach to the points and carefully cutting the rail very close to where the switch rail meets stock rail. This would allow the last vehicle sufficient time to clear the switch rail before the Tortoise motor reset the point again (in theory)......

Hopefully my drawing will help!

G

[Jeremy Cumberland]

That would be a lot easier to wire - simply take the detection to feed the Tortoise DPDT relay. But why have the right hand break there, rather than at the toe of the point?

 

Your original suggestion would need four relays (one for each photodiode, a latching relay for A (reset by relay B being energised) and a DPDT for the Tortoise (powered by the latching relay or B). That is in addition to the photodiode relay circuits with their transistor and resistors.

 

Have you thought about simply trying a spring?

[Jeremy Cumberland]

You'll need to check that the track occupancy detector works with all of your vehicles (or, if the track circuit is longer than the longest train, it works with the first and last vehicles). It's no good simply detecting the locomotive, for then when the locomotive leaves the track circuit, the points will reset under the train.

 

From the DCC Concepts website

Quote

LM-iD reliably detects anything that alters the electrical state in the section: Examples are powered items such as Locomotives, illuminated coaches or rolling stock with resistive wheelsets. Even just a single tail lamp or a lamp in a Guards van or Caboose.

 

[retbsignalman]

If the break was at the toe of the point, anything that had passed the LOS board would be either be derailed as the blades were mid move or it would carry on along the uni directional line which is what I was trying to avoid. Hence the break where it is. 

I have experimented with springs but have yet to find one strong enough to hold the point in the correct position yet allow relatively light vehicles to pass without derailing.

[retbsignalman]

I have thought about that. The line is going to be solely used by EMUs, all of which have pick ups throughout. 

[Jeremy Cumberland]

Oh, you're expecting things to pass the limit of shunt board. Yes, that does make things a little trickier.

 

If you find that the Tortoise resets too soon with your track occupancy detector, then you could use two track occupancy detectors, one immediately after the other, with the right hand one providing a latching function. In terms of length and position, the left hand end of the left hand track circuit needs to be far enough away from the points for the Tortoise to motor them across before the train reaches them, and the right hand end of the right hand track circuit should be at the toe of the points. Both track circuits need to be at least as long as a coach wheelbase, but apart from that, it doesn't matter where you put the break between them.

 

The exact electrical configuration depends on whether you can get a 3PDT relay for the Tortoise, but you'll also need a relay (an SPST NO is all that is needed, but you may find a DPST NO easier to get hold of) to go with the right hand track circuit.

 

The idea is that the Tortoise relay is set by the left hand track circuit and is latched by the right hand track circuit. If you can get a 3PDT relay for the Tortoise, you want two feeds to the relay coil (just solder two wires to the same pin). One is from the left hand track occupancy detector. The other comes from the 12V power supply, passes through a spare NO contact in the Tortoise relay, and through an NO contact in the right hand track circuit relay. All the time that either the left hand track circuit is occupied, or that the point is already set and the right hand track circuit is occupied, the point will be set for normal running. However, simply occupying the right hand track circuit if the point isn't set for a train won't do anything.

 

If you can't get a 3PDT relay, then you can use a DPDT relay for the Tortoise, and have a DPST NO as a latching relay (as well as the SPST NO or DPST NO relay for the right hand track circuit). Have two feeds to the latching relay coil, one from the left hand track occupancy detector and the other from the 12V power supply, via an NO contact in the latching relay and an NO contact in the right hand track circuit relay. Then use the second NO contact in the latching relay to power the Tortoise DPDT relay coil.

 

As far as I can see, you can't use commercially-available latching relays because you will have times when set and reset will be powered at the same time.

 

The only thing I am a little unsure of is whether the left hand track occupancy detector can cope with the output being back-fed from the latching circuit. You can completely separate it electrically by having another relay, so that instead of taking a feed directly from the track occupancy detector to the latching relay or 3PDT Tortoise relay, you take it from an NO contact in the left hand track circuit relay.

[RailWest]

I'm confused now :-) As drawn, your uni-directional  line is for traffic moving from L to R. The LOS board, as drawn, applies to 'wrong direction' traffic from R to L.

 

Clearly you do not want the traffic moving from L to R to be still over the point when it moves back to normal. But if traffic goign 'wrong direction' from R to L inadvertently passes the LOS board, then why would the points be moving anyway?  And if they were, and the train was derailed, well isn't that purpose of the points anyway?

[retbsignalman]

The headshunt on the rhs is by its nature bidirectional up to the LOS board.  The line from the lhs is unidirectional as indicated by the arrow (as far as the LOS board).

The point is set normal to the sand drag in case the LOS board is passed  from the headshunt end. 

What I'm trying to create is a situation whereby a train approaches from the lhs, the point reverses and resets to the sand drag after it has passed.

[retbsignalman]

8 hours ago, Jeremy Cumberland said:

Oh, you're expecting things to pass the limit of shunt board. Yes, that does make things a little trickier.

It's not an expectation really, but just like on the 12":1' railway I've built in a run off/ trap. Just in case as its way more likely here!!

8 hours ago, Jeremy Cumberland said:

 

If you find that the Tortoise resets too soon with your track occupancy detector, then you could use two track occupancy detectors, one immediately after the other, with the right hand one providing a latching function. In terms of length and position, the left hand end of the left hand track circuit needs to be far enough away from the points for the Tortoise to motor them across before the train reaches them, and the right hand end of the right hand track circuit should be at the toe of the points. Both track circuits need to be at least as long as a coach wheelbase, but apart from that, it doesn't matter where you put the break between them.

 

The exact electrical configuration depends on whether you can get a 3PDT relay for the Tortoise, but you'll also need a relay (an SPST NO is all that is needed, but you may find a DPST NO easier to get hold of) to go with the right hand track circuit.

 

The idea is that the Tortoise relay is set by the left hand track circuit and is latched by the right hand track circuit. If you can get a 3PDT relay for the Tortoise, you want two feeds to the relay coil (just solder two wires to the same pin). One is from the left hand track occupancy detector. The other comes from the 12V power supply, passes through a spare NO contact in the Tortoise relay, and through an NO contact in the right hand track circuit relay. All the time that either the left hand track circuit is occupied, or that the point is already set and the right hand track circuit is occupied, the point will be set for normal running. However, simply occupying the right hand track circuit if the point isn't set for a train won't do anything.

 

If you can't get a 3PDT relay, then you can use a DPDT relay for the Tortoise, and have a DPST NO as a latching relay (as well as the SPST NO or DPST NO relay for the right hand track circuit). Have two feeds to the latching relay coil, one from the left hand track occupancy detector and the other from the 12V power supply, via an NO contact in the latching relay and an NO contact in the right hand track circuit relay. Then use the second NO contact in the latching relay to power the Tortoise DPDT relay coil.

 

As far as I can see, you can't use commercially-available latching relays because you will have times when set and reset will be powered at the same time.

 

The only thing I am a little unsure of is whether the left hand track occupancy detector can cope with the output being back-fed from the latching circuit. You can completely separate it electrically by having another relay, so that instead of taking a feed directly from the track occupancy detector to the latching relay or 3PDT Tortoise relay, you take it from an NO contact in the left hand track circuit relay.

I'm using Potter & Brumfield relays as in the attached picture. 

 

Graeme 

[Izzy]

I might just be my usual thick self but going by your original diagram of sensors at A & B can't you just move sensor B further along to the right so a complete EMU/your longest train passes the trap before reaching this sensor? There must be the room or does the full track layout prevent this somehow seeing as how you refer to it as the headshunt. 

 

Bob

[RailWest]

6 minutes ago, Izzy said:

I might just be my usual thick self but going by your original diagram of sensors at A & B can't you just move sensor B further along to the right so a complete EMU/your longest train passes the trap before reaching this sensor? There must be the room or does the full track layout prevent this somehow seeing as how you refer to it as the headshunt. 

 

But...what then happens if a shorter train goes from L to R and never reaches the relocated B?

In effect the system needs to detect 3 conditions:-

1. Train approaching (strike-in)

2 Train passing over the point (continuous detection)

3. Train clear of the point (strike out)

 

1 and 3 are easy, it's the 2 that may be harder :-)

[Jeremy Cumberland]

That's rather more meaty than I was expecting. That's a 4PDT so it's easy to make it into a latching relay.

 

If you want to try with one track circuit as per your earlier post, then connect the relay as follows (this isn't the only way of connecting it):

1: Tortoise 1 (or 8)

2: Tortoise 8 (or 1) - swap these over if the point moves the wrong way.

5 and 10: 12V supply

6 and 9: Common return

13: Track occupancy detector output

14: Track occupancy detector return (or common return)

 

I've looked at the Legacy Models Intelligent Detector instructions  - is this what you were thinking of using for detection? It looks ideal for the purpose, but I am not sure whether it has a switched power output or a switched NO contact. A switched power output seems more likely. Either way, you won't need a second relay if you want to use two track circuits.

 

For a single track circuit, and assuming a switched power output, the detector connections are as follows:

A: 12V supply and common return (or track bus or some other power supply)

C+: Relay terminal 13

C-: Relay terminal 14

Loop the track dropper wire through the LM-iD coil.

 

If you want to try with two track occupancy detectors, connect the left hand detector and the relay as above, connect power to the right hand detector terminals A and loop the right hand track circuit dropper wire through the coil, and then add these connections for the latching circuit:

Right hand detector terminal C+ to relay terminal 3

Relay terminal 7 to relay terminal 13 (there is already a wire here)

Relay terminal 14 (there is already a wire here, too) to right hand detector terminal C-

 

Personally, I would use two track occupancy detectors, because I think this provides exactly what you want, reliably and without any difficulty. One track occupancy detector might work, but I'd be worried about derailing the train. I can't say I much liked the idea of photo diodes. I've found them rather unreliable in other situations, unless paired with a transmitter, and the rest of the circuitry needed for your application is rather off-putting. Have you used them before with model railways? Perhaps your experience has been better than mine.

Edited November 21, 2023 by Jeremy Cumberland
Second thoughts about detector output

[Jeremy Cumberland]

I've just edited my last post, thinking it more likely that the detector terminals C are a switched power output rather than a switched contact. Also, this is the "safer" way of wiring them. If they are a switched contact, then you won't do any damage wiring them as above (but the circuit won't do anything) whereas if they are a switched power out and you wire them as a switched contact, you risk doing some damage.

 

If the above circuit does not work, then wire the coil as follows:

"Set" circuit:

12V to left hand detector terminal C-

Left hand detector terminal C+ to relay terminal 13

Relay terminal 14 to common return.

 

Latching circuit:

12V to relay terminal 3

Relay terminal 7 to right hand detector terminal C-

Right hand detector terminal C+ to relay terminal 13.

[retbsignalman]

Thank you Jeremy, this is going to be a project for next week when I can devote a bit of uninterrupted time to it.  

But first, a couple of questions about the placing of the TCs....as you'll have gathered from the foregoing I'm a novice at things like this.

1. TC A - the strike in TC (lhs) - this is approximately 3' and presumably excludes the point.

2. TC B - the latching TC - is the length of the point ( and I won't have to cut the rail near where the switch rail meets the stock rail)

Would that then mean that a train approaching from the headshunt would activate the sequence and the point move? 

Or, because of the latching process TC B won't activate unless TC A has been occupied? 

Thanks Graeme 

Edited November 21, 2023 by retbsignalman

[Jeremy Cumberland]

20 minutes ago, retbsignalman said:

Or, because of the latching process TC B won't activate unless TC A has been occupied? 

This. Strictly speaking, the track circuit activates, but it won't do anything. If the points are already powered across, it will hold them there, but if they aren't already powered across, then the track circuit output won't be connected to the relay coil.

[retbsignalman]

Thats spot on, thank you again Jeremy. I'll let you know how I get on! 

Graeme 

[The Stationmaster]

Late to the party but a simple question.  As the line is unidirectional why not use a signal to operate the catch point?   And if the line to the right of the point is actually bi-directional (as opposed to shunting moves being made in the wri=ong direction on a unidirectional line) why isn't there a signal fixed at danger protecting the point for a facing movement towards it?

[retbsignalman]

Hi Mike, 

 

The start of the unidirectional line is in the fiddle yard and, like a lot of good intentions was an extra siding which in the end was hardly used. So, it has to be imagined that the signal to access it is off scene. 

The L.O.S. board has since been upgraded to a PLS fixed at danger (!) as of yesterday, as in the second drawing which also shows the point as 'sprung' (for the want of a better description. 

 

Cheers G 

[5BarVT]

5 hours ago, retbsignalman said:

TCs....as you'll have gathered from the foregoing I'm a novice at things like this.

That’s cos RRTB doesn’t need any!

:-)

Paul. 

[retbsignalman]

8 minutes ago, 5BarVT said:

That’s cos RRTB doesn’t need any!

:-)

Paul. 

You say that Paul, but we have a smattering of such newfangled gizmos across the area, mostly to set routes at Dingwall and Georgemas, and others around level crossings!!

Graeme 😃