Switch Point Detection continued

This forum is dedicated to Riding Scale Railroading with propulsion using other than steam (Hydraulics, diesel engines, gas engines, electric motors, hybrid etc.)

Moderators: Harold_V, WJH

User avatar
Trainman4602
Posts: 3240
Joined: Sat Oct 16, 2004 9:26 pm
Location: New Jersey

Re: Switch point position detection

Post by Trainman4602 » Mon Oct 23, 2017 2:31 pm

I sort of trust the signal system but after throwing a switch to turn in a siding I always look at the points to make sure they are thrown completely

Your Eye is the best tell tail.
ALLWAYS OPERATING MY TRAIN IN A SAFE MANNER USING AUTOMATIC AIR BRAKES

User avatar
BigDumbDinosaur
Posts: 583
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Switch point position detection

Post by BigDumbDinosaur » Mon Oct 23, 2017 3:48 pm

ChuckHackett-844 wrote:I think you will find it difficult to find relays that will work on long sections of track under both wet and dry conditions - doable, but not easy.
ABS block occupancy detection at the Illinois Live Steamers is purely electromechanical and is based upon the well-known KISS principle. This modular ABS has been in service for more than a decade without failure, with the only issues coming from the occasional broken wire following a derailment or from cut wires caused by bull-in-a-china-shop track maintenance procedures.

The key to successful block occupancy detection is the use of very low track circuit voltage in concert with relatively high continuous current delivery capacity, as well as short-term surge current capacity. The resulting low impedance power source makes it possible for the track circuit to "overwhelm" the leakage across the ties and ballast, even during rainfall. Performance is enhanced by use of a specific type of track relay that tolerates a wider range of voltages than is customary. Further to the KISS principle, active electronics in the ABS logic are limited to timers whose failure will not compromise the failsafe nature of the system. No active electronics are used in system logic. It's all based upon full-sized practice that has existed from when William H. Taft was president, and continues to be used to this day.

Power distribution throughout the system is at line voltage, and is locally fused and stepped down at each instrument cabinet to power the ABS modules. This approach has minimized electrical losses by localizing high current flow to the instrument cabinet and the block(s) and turnout(s) it governs. Provisions are in place to prevent accidental contact with anything in the instrument cabinet that is energized at line voltage.

As the wiring that ties together the logic in the instrument cabinets is vulnerable to induced impulses from nearby lightning strikes, a basic design tenet is to only have relay contacts driving relay coils over such circuits. MOVs are used at both ends of each circuit to suppress transients. All relay coils that are attached to inter-cabinet wire runs are suppressed with high current Schottky diodes to prevent flyback voltage from being propagated back to the module at the other end of the circuit.

Speaking of wire, it is crucial in ABS circuitry to minimize wiring losses over long distances. The smallest gauge used in the ILS ABS is 16 AWG type TFFN for inter-cabinet logic and signal head connections. Track circuit and turnout position detection wiring is 14 AWG THHN, and power distribution is 12 AWG THHN. Rail joint bonding jumpers are made from 12 AWG wire, with heavy duty ring tongue terminals that are machine-crimped and then soldered with 20/80 solder to prevent long-term corrosion. There are bonding jumpers on the railroad that are approaching 15 years of exposure from the time when the prototype ABS was being tested. They have not deteriorated in any measurable way.

My point to all this is there is a tendency in the large-scale hobby to over-engineer ABS and make it into something akin to a computer. Most ABS installations are "static"—they are rarely reconfigured once installed and satisfactorily operating. Also, the logic that is implemented in a typical ABS can be generally realized with simple components that are tolerant of a wide range of ambient conditions. That too was an important consideration at the ILS, where the temperature may range from sub-zero to 90° F or more on a typical summer day.

A goal we had at ILS in developing an ABS was to avoid a level of complexity that would prevent someone with reasonable skills and electrical knowledge from maintaining and repairing the system, or adding to it in the future. This philosophy proved invaluable earlier this year when major track "upgrades" were made and one of the individuals involved didn't tag any of the trackside ABS wiring that he had cut and ripped out for expediency purposes. Two other members, one of whom has only basic electrical knowledge, were able to repair everything and restore operation.
Science makes it known. Engineering makes it work.

User avatar
ChuckHackett-844
Posts: 70
Joined: Wed May 03, 2017 3:54 pm
Location: Tampa, Florida

Re: Switch point position detection

Post by ChuckHackett-844 » Mon Oct 23, 2017 4:08 pm

I think this discussion has overstayed it welcome under "Live Steam". I will reply over under "Riding Scale Railroading" ...

Chuck H
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
"By the work, One knows the workman"

User avatar
BigDumbDinosaur
Posts: 583
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Switch point position detection

Post by BigDumbDinosaur » Mon Oct 23, 2017 4:09 pm

Trainman4602 wrote:I sort of trust the signal system but after throwing a switch to turn in a siding I always look at the points to make sure they are thrown completely

Your Eye is the best tell tail.
Full-sized railroaders do the same thing. Back in my railroading days, I was always looking at points to assure myself that turnouts were fully thrown and lined in the direction we were suppose go. That habit become doubly important when I got into large-scale railroading and saw how vulnerable turnouts were to debris between points and stock rails, as well as ballast stones lodged into guard rail and frog flangeways.

It should be noted that the methods by which point position on full-sized turnouts is annunciated is independent of the means by which turnouts are actuated. Also, that annunciation is not 100 percent foolproof, but in practice, very rarely causes a problem. Annunciation is through mechanically-operated contacts mounted in a separate enclosure from the switch machine, in the case of a powered turnout. Due to the inevitable tolerances of any mechanism, as well as accuracy of adjustment, annunciation hysteresis is unavoidable but in practice, does not compromise safety in full-sized applications. A gap of a quarter inch between a point and its mating stock rail will generally not pose a picking problem with a wheel that has a reasonable profile.

Unfortunately, scaling down full-sized practice also reduces that quarter inch gap to 1/32 inch. Devising an annunciation mechanism that has only 1/32 inch hysteresis would be no trivial task. I periodically give it some thought, but as there has been no real impetus to date to develop and test something, I haven't gone beyond superficial conjecture.
Science makes it known. Engineering makes it work.

User avatar
BigDumbDinosaur
Posts: 583
Joined: Tue Jun 28, 2011 9:19 pm
Location: Midwestern United States

Re: Switch point position detection

Post by BigDumbDinosaur » Mon Oct 23, 2017 4:10 pm

ChuckHackett-844 wrote:I think this discussion has overstayed it welcome under "Live Steam". I will reply over under "Riding Scale Railroading" ...

Chuck H
Hmm...didn't notice it was in the Live Steam forum.
Science makes it known. Engineering makes it work.

rkcarguy
Posts: 477
Joined: Tue Aug 22, 2017 10:33 am

Re: Switch point position detection

Post by rkcarguy » Mon Oct 23, 2017 5:33 pm

rkcarguy wrote:I've weighed many options for my soon to be RR as I am currently building signals and a relay system to control them. I have crossed out anything with complex electronics as I don't want a voltage spike to fry it all.
I think you will find it difficult to find relays that will work on long sections of track under both wet and dry conditions - doable, but not easy.

I have modified and tested my design for at least 5 years in Florida (lightning capitol of the world :-) ). I can now draw a 5,000 volt arc to a track terminal without damage. Direct strike - forget it, but anything would be fried then.

It's not easy to build a relay system that guarantees only one train permitted at a time with an arbitrary number of block entries (ABS signals do not).
rkcarguy wrote:I'm just going to use one of these:

https://www.amazon.com/Moroso-74120-But ... B000CON4MU
Wow, you are going to need a strong turnout motor to activate those! Also, I think you'll find that:
  • * they work fine for high currents but will eventually fail on low currents (which is what I need)
    * their hysteresis will prevent you from detecting down to 1/32"
Regards,

Chuck[/quote]

I won't be having any turnout motors, so I guess things are a bit different. My blocks are going to be 200' long tops, turnouts manually controlled at the switch stands. On the mainline turnouts, I'll probably use some rods and set the switch stands in front of the turnouts so I don't have to get off the riding car to change them.

Regarding lightning, I know on communications towers they set large "points" with a gap to a ground rod(like 1" bolts and/or rod turned to a 45* point on the end), under the idea that the voltage reaches a certain point and then jumps the gap to ground. Something to consider, maybe something you are doing already.

Can I ask, do you think the contacts on the switch motors are failing from wear, or from over-current draw through them indicating they should be triggering a relay instead?

User avatar
ChuckHackett-844
Posts: 70
Joined: Wed May 03, 2017 3:54 pm
Location: Tampa, Florida

Re: Switch point position detection

Post by ChuckHackett-844 » Mon Oct 23, 2017 5:57 pm

rkcarguy wrote:Can I ask, do you think the contacts on the switch motors are failing from wear, or from over-current draw through them indicating they should be triggering a relay instead?
They were failing because they are not designed for low current. If I connected a relay or lamp to them it would probably solve the problem but it would increase the power demands and we keep it very low because we only have access to 120vac at one end of the railroad.

As in most cases, different railroads have different needs and restrictions which determines the 'best' solution.

Regards,

Chuck
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
"By the work, One knows the workman"

User avatar
ChuckHackett-844
Posts: 70
Joined: Wed May 03, 2017 3:54 pm
Location: Tampa, Florida

Re: Switch point position detection

Post by ChuckHackett-844 » Mon Oct 23, 2017 5:58 pm

All ...

I should not have started this discussion here. If you have additional comments, let's take it over to "Riding Scale Railroading".

Regards,

Chuck
Regards,

Chuck Hackett, UP Northern 844, Mich-Cal Shay #2
"By the work, One knows the workman"

User avatar
Atkinson_Railroad
Posts: 159
Joined: Mon Jun 08, 2015 6:27 pm
Location: Michigan
Contact:

Switch Point Detection continued

Post by Atkinson_Railroad » Mon Oct 23, 2017 6:43 pm

Switch Point Detection conversation continued.

Atkinson_Railroad wrote:
"Also, further conversation on why separate (suitable) limit switches actuated by each rail point would not work,
will be helpful for clarification too."

Chuck, I just read the above and was confused too!
Something about staying up past dark thirty causes this problem.

I meant to say two suitable switches... one for each rail point providing "proof" they are in their proper position.
(or something like that ; )

JDA

Harold_V
Posts: 16664
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Switch point position detection

Post by Harold_V » Mon Oct 23, 2017 11:59 pm

As the discussion pertains to railroading, in general, it's fine where it is posted. That said, I will merge the topics, so they are in a common place, and will be found under the Riding Scale Railroading forum.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
Atkinson_Railroad
Posts: 159
Joined: Mon Jun 08, 2015 6:27 pm
Location: Michigan
Contact:

Re: Switch Point Detection continued

Post by Atkinson_Railroad » Tue Oct 24, 2017 5:57 am

Harold, thanks for the thread housekeeping. I knew you would fix it up.

As Chuck mentioned near the beginning of the thread, the switch point detection problem could be solved by spending [time] on the solution which is often just not available with so many other projects in progress.

A thought occurs to me the tight tolerance factor required could possibly be solved by “magnifying” the actuation so to speak.
I chopped away at the paint drawing posted earlier in the thread to help illustrate the thought.

I would tend to agree with dinosaur that there is a lot of “over engineering” that can take place.

The design of something spans philosophies from intelligence made visible, to the well doing of what needs doing.

Incidentally, for those of you (myself included) who may have left the printed periodical world in favor
of what’s available on your computer screen, Chuck’s very detailed computer solution to outdoor railroad
signaling is featured in the September /October 2017 issue of Live Steam & Outdoor Railroading.

Perhaps at some point when his project pile is reduced a half a notch or so, he might consider posting some computer screen shots,
or even some video of his computer system in operation.

And now… as Dave Sclavi has said, “NOW back to work.”

John
Attachments
SWITCH POINT DETECTION 2.jpg
Not illustrated to any scale or specific arrangement.

rkcarguy
Posts: 477
Joined: Tue Aug 22, 2017 10:33 am

Re: Switch point position detection

Post by rkcarguy » Tue Oct 24, 2017 1:24 pm

BigDumbDinosaur wrote:
ChuckHackett-844 wrote:I think you will find it difficult to find relays that will work on long sections of track under both wet and dry conditions - doable, but not easy.
ABS block occupancy detection at the Illinois Live Steamers is purely electromechanical and is based upon the well-known KISS principle. This modular ABS has been in service for more than a decade without failure, with the only issues coming from the occasional broken wire following a derailment or from cut wires caused by bull-in-a-china-shop track maintenance procedures.

The key to successful block occupancy detection is the use of very low track circuit voltage in concert with relatively high continuous current delivery capacity, as well as short-term surge current capacity. The resulting low impedance power source makes it possible for the track circuit to "overwhelm" the leakage across the ties and ballast, even during rainfall. Performance is enhanced by use of a specific type of track relay that tolerates a wider range of voltages than is customary. Further to the KISS principle, active electronics in the ABS logic are limited to timers whose failure will not compromise the failsafe nature of the system. No active electronics are used in system logic. It's all based upon full-sized practice that has existed from when William H. Taft was president, and continues to be used to this day.

Power distribution throughout the system is at line voltage, and is locally fused and stepped down at each instrument cabinet to power the ABS modules. This approach has minimized electrical losses by localizing high current flow to the instrument cabinet and the block(s) and turnout(s) it governs. Provisions are in place to prevent accidental contact with anything in the instrument cabinet that is energized at line voltage.

As the wiring that ties together the logic in the instrument cabinets is vulnerable to induced impulses from nearby lightning strikes, a basic design tenet is to only have relay contacts driving relay coils over such circuits. MOVs are used at both ends of each circuit to suppress transients. All relay coils that are attached to inter-cabinet wire runs are suppressed with high current Schottky diodes to prevent flyback voltage from being propagated back to the module at the other end of the circuit.

Speaking of wire, it is crucial in ABS circuitry to minimize wiring losses over long distances. The smallest gauge used in the ILS ABS is 16 AWG type TFFN for inter-cabinet logic and signal head connections. Track circuit and turnout position detection wiring is 14 AWG THHN, and power distribution is 12 AWG THHN. Rail joint bonding jumpers are made from 12 AWG wire, with heavy duty ring tongue terminals that are machine-crimped and then soldered with 20/80 solder to prevent long-term corrosion. There are bonding jumpers on the railroad that are approaching 15 years of exposure from the time when the prototype ABS was being tested. They have not deteriorated in any measurable way.

My point to all this is there is a tendency in the large-scale hobby to over-engineer ABS and make it into something akin to a computer. Most ABS installations are "static"—they are rarely reconfigured once installed and satisfactorily operating. Also, the logic that is implemented in a typical ABS can be generally realized with simple components that are tolerant of a wide range of ambient conditions. That too was an important consideration at the ILS, where the temperature may range from sub-zero to 90° F or more on a typical summer day.

A goal we had at ILS in developing an ABS was to avoid a level of complexity that would prevent someone with reasonable skills and electrical knowledge from maintaining and repairing the system, or adding to it in the future. This philosophy proved invaluable earlier this year when major track "upgrades" were made and one of the individuals involved didn't tag any of the trackside ABS wiring that he had cut and ripped out for expediency purposes. Two other members, one of whom has only basic electrical knowledge, were able to repair everything and restore operation.
BDD, the relays I have on hand require a 6 volt, one amp "trigger" to activate. It's my plan to use a couple 12 volt 6 amp power supplies that are used on several kinds of printers to power my system, and the detector circuits will contain a timed delay off module set for couple seconds to prevent flickering. I can of course, change relays if the above ones won't cut it. It's wet up here, so I don't know what the amount of leakage will be across wet ties and if it would be enough to false trigger the system or not.

Post Reply