Switch Point Detection continued

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BigDumbDinosaur
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Re: Switch point position detection

Post by BigDumbDinosaur » Tue Oct 24, 2017 3:56 pm

rkcarguy wrote:BDD, the relays I have on hand require a 6 volt, one amp "trigger" to activate.
What the heck kind of relays are these that would need a "one amp 'trigger' to activate"? What is it you are describing?

Track circuits are (should be) operated at very low voltages and the relays used in track circuits should be high sensitivity so they do not drag down the open circuit (unoccupied block) voltage. For example, in the MABS block occupancy detectors (BOD, illustrated below) made by my company, this hermetically sealed relay is used as a track relay.
bod_assy_1024x1024.jpg
MABS Non-directional Block Occupancy Detector (©2004-2017 BCS Technology Limited)
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MABS Directional Block Occupancy Detector (©2004-2017 BCS Technology Limited)
In the above devices, the track circuit power source is 3.3 volts and when the drop in the track circuit ballast resistor is accounted for, the theoretical voltage across the track relay coil is 3.1 volts, which is also the theoretical voltage between the rails in an unoccupied block.

The reason for keeping the voltage very low is to minimize the effects of leakage through the ties and ballast, which is present even when conditions are completely dry. The power loss due leakage increases with the square of the unoccupied block voltage, so it is advantageous to operate the track circuit at the lowest practical voltage consistent with reliable relay operation. If leakage is excessive, the losses caused by parasitic current drawn through the ballast resistor will reduce the open circuit voltage below the track relay's pickup point, resulting in a false occupied state.

Relays that are suitable for use in track circuits are usually not compatible with sizable loads, especially incandescent lamps. In full-sized practice, track relays control other relays that are responsible for handling signal lamp loads. The above relay I linked is specified by the manufacturer for use in "signal" applications, which in electronic parlance means controlling low power devices, such as other relays or the inputs of solid state devices. This relay has gold-flashed, crossbar contacts that allow it to switch extremely light loads, as low as one milliamp. Such a design by nature cannot safely switch heavier loads and attempting to drive an incandescent lamp would likely result in contact welding.
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...
Switch-mode power supplies of the type you describe will work but are gross overkill for the application, and contain a lot of electronics that can fail due to evinromental factors or line surges caused by nearby lightning strikes. Simple (and less failure-prone) linear supplies powered from readily-available transformers are more than adequate, less failure-prone, and can be made compact. Both of the BODs illustrated above have built-in regulated, linear power supplies and require only 12 volts AC input to operate. The non-directional BOD is about the size of the palm of my hand.
...and the detector circuits will contain a timed delay off module set for couple seconds to prevent flickering.
Delay-on-clear is also used in full-sized practice for the same reason. "Vital" (track) relays are gravity-released and often pneumatically damped so they are not affected by the variable contact resistance that occurs between the railhead and moving wheel. The damping prevents relay chatter when empties near the end of the train are about to exit the block, also the case if the last car is a caboose.

In hobby practice, where a pneumatically-damped, gravity release relay would be prohibitively expensive (and nearly impossible to obtain, not to mention it being a bulky relay), a solid state timer can be used, provide the timer circuit cannot start its sequence unless the track relay is truly actuated. Such a timer has to be fully resettable, which means each time the track circuit is cleared the timer must start from zero.

In an uninterrupted block, the delay-on-clear can be less than a second. More delay is required if the train must pass through dead sections, such as turnouts that are isolated from the track circuit. The above BODs have adjustable delay-on-clear that ranges from 0.8 seconds to 8 seconds. In uninterrupted blocks, we recommend setting them to the minimum to produce realistic operation.
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.
The degree of leakage you will experience is highly variable and will be influenced by block length, track construction methods, tie material, tie size, the type of ballast used (fines are particularly problematic), track gradient, right-of-way drainage characteristics and even the presence of weeds on the right-of-way. I can tell you that the trackwork at ILS uses 260 treated wooden ties per 100 linear feet—the ties are made from two-by-sixes that are ripped to make a two-by-three tie, with the narrow dimension being the surface that supports the rails. Such construction, along with medium grade ballast, has a dry leakage rate of approximately 60 milliwatts per 100 linear feet of track in a 3 volt track circuit. At 6 volts, the leakage would theoretically be 240 milliwatts. Testing at the ILS immediately following a soaking rainfall indicated the leakage increased to approximately 180 milliwatts per 100 linear feet of track, again in a 3 volt track circuit, and safely below the point where false occupied states would occur. Elevating the track circuit voltage to 6 volts would increase that leakage to 720 milliwatts—a 100 foot block would not clear with that much leakage.

I am in the process of evaluating a BOD design that would operate the track at 1.5 volts. Based upon theoretical computations and a certain amount of educated conjecture, I believe such BOD would successfully operate on a 1500 linear foot block in 7-1/2 inch gauge, assuming the construction characteristics described above (260 ties per 100 linear feet, etc.). That would be nearly 2.3 scale miles.
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rkcarguy
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Re: Switch Point Detection continued

Post by rkcarguy » Tue Oct 24, 2017 7:04 pm

To further clarify, I'm using a pair of SPDT relays to provide my signal control at each signal. The default setting(relay #1 at rest) is red the way I have my mockup wired at the moment on the workbench. When Relay #1 is energized(emulating a permissive system), green is shown and the red is dropped. But....the relay #1 output to the green is fed into relay #2's positive in-feed, which will switch the green to yellow if triggered from the adjacent block by another train.
The signal is unable to show two aspects at the same time, because if the signal is red, there is no power to relay #2, therefore green or yellow won't work.
Because this setup requires a minimum of +6 volts, 1 amp to activate the relays, I would much rather use a single pole single throw relay which is grounded by the train making the connection across the rails as my detection circuit, and allows me to use whatever voltage and sensitivity relay I want as long as it can output at least 6 volts and 1 amp to trigger the relays in the signal box. I'll toss a $6 amazon delay circuit on each one of these set to 1-2 seconds then off(and yes these have 4 configurations for time on, time off, instant reset or reset after off), to absorb any intermittent connections and prevent relay chatter.
Each signal will have +12V feed directly to it's relay box, so the only losses will be due to the lengths of wire runs in the detection system and any resistance across the rails.
Based on your info above, it looks like I'll need a relay capable of a 3 volt "trigger side" and 12 volt switched side of at least an amp if such a thing exists, so my ~200' blocks won't false detect in heavy rain?

I'd like a regular relay, not anything like above with all those chips capacitors and such.

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BigDumbDinosaur
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Re: Switch Point Detection continued

Post by BigDumbDinosaur » Wed Oct 25, 2017 2:51 am

rkcarguy wrote:Based on your info above, it looks like I'll need a relay capable of a 3 volt "trigger side"...
The correct terminology for the "trigger side" is the "coil."
...and 12 volt switched side of at least an amp if such a thing exists, so my ~200' blocks won't false detect in heavy rain?
Relays with 3 volt coils and 1 amp contacts do exist—the relay to which I previously linked has a 1 amp contact rating. BUT...it cannot switch a 1 amp lamp load. There's a lot more to relay selection than just the steady-state current flow, especially in a circuit powered by direct current. Also, I will reiterate that track relays should not direct control signal lamps. Track relays should drive relays that are capable of handling the lamp loads.
I'd like a regular relay, not anything like above with all those chips capacitors and such.
What do you call a "regular relay?" The relays used in the above BOD modules are off-the-shelf parts. The other components are the built-in delay-on-clear timer, which you are planning to do with a completely separate assembly, and the power supply that converts low voltage AC to the DC voltages that operate the module and power the track circuit. Just what do you think is inside that timer module you are considering?

I do not mean to sound condescending, but I suggest that you bone up a lot more on electrical theory and signal system design before you start buying parts and trying to build something from scratch. I can assure you it's not nearly as simple as it would seem.

Also, I'm ending this discussion here because it is not directly related to Chuck's topic, which was devising a method of turnout point detection.
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rkcarguy
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Re: Switch Point Detection continued

Post by rkcarguy » Wed Oct 25, 2017 3:26 pm

I apologize for thread jacking, I'll post in my signal thread.

Liesegang
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Re: Switch Point Detection continued

Post by Liesegang » Sat Nov 18, 2017 5:16 pm

Rather than all of this circuit design, why not use the engineers eyesight to determine if the points are position correctly? We have more than 400 spring switches on our railroad and the engineer must watch for points not aligned. Remember the KISS rule.

Terry

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ChuckHackett-844
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Re: Switch Point Detection continued

Post by ChuckHackett-844 » Sat Nov 18, 2017 5:27 pm

Liesegang wrote:Rather than all of this circuit design, why not use the engineers eyesight to determine if the points are position correctly? We have more than 400 spring switches on our railroad and the engineer must watch for points not aligned. Remember the KISS rule.

Terry
The detection is to control the double-head signal for the facing-point move. Yes, the engineer is told to always visually check the points ... but ...

Chuck
Regards,

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

Liesegang
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Re: Switch Point Detection continued

Post by Liesegang » Sun Nov 19, 2017 11:54 pm

On MLS switches, the throw arm indicates the position of the points. No signal heads required.

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ChuckHackett-844
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Re: Switch Point Detection continued

Post by ChuckHackett-844 » Mon Nov 20, 2017 10:00 am

Liesegang wrote:On MLS switches, the throw arm indicates the position of the points. No signal heads required.
The double-head signal is used to indicate the status of each route ahead, not just the turnout point status (for that I would use a dwarf at the turnout). If the turnout points are "against" the associated route the signal system will force the signal to a STOP* aspect and, if the points are closed for the other route, the other signal will indicate the status of that route (STOP, Clear, Approach, etc.). If the points are blocked (rock, etc.) or 'in transition' both signals will indicate STOP*.

It can get more complicated: In the case of a choice of one of three routes (i.e.: two turnouts, one right after the other) we use a triple-head signal at the points of the first turnout. In this case two of the signals will indicate STOP* and one (for the selected route) will indicate the actual route status.

*In actual use, the aspect will be "Points Against" indicating that the points are not closed for a given route. We define this aspect as a solid red that 'winks' off twice per second (in our system all aspects are "soft" and can be defined by the user, one could define it as just solid red). Engineers are told "proceed on Green or Yellow ... anything else means STOP" but the wink indication tells them why it's red if they care to know i.e.: on a double-head, if both signals are winking 2 for an extended period it indicates that there is a rock in the points or the turnout motor malfunctioned. This is not encountered in normal circumstances and the different wink codes (there are others) are used as an aid to diagnosing signal issues.

Usually the engineer wants to know "can I go that way" ... the answer to that question is a combination of turnout point position and route status so we combine that information for the engineer into a single indication in the signal head(s) to make things simpler.

You are quite right, one could just present the engineer with the status of the route and require him to check the points but, in my experience, if you do that at a large meet (especially at night) you will invariably have cases where someone goes on the ground and he says "but I had a green" - yes, he should have checked the points but now he is holding up others from having fun while he gets his engine back on the track ... that's what we are trying to avoid ...

As a side note: In our usage, these "route choice" signals are usually located at the clearance point on a passing siding exit where there is also a switch post that the engineer can use to select a route. Thus the signals will prevent him from leaving the passing siding until the route is aligned and clear. Keep in mind that he may not be able to see the points from that position since the turnout(s) may be some distance ahead.

Regards,

Chuck
Regards,

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

rkcarguy
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Re: Switch Point Detection continued

Post by rkcarguy » Tue Nov 21, 2017 6:38 pm

Chuck, how does one work with signaling the exiting of a siding back onto the mainline with sprung points(i.e. the train forces them open and back onto the mainline)? It seems like it would need to be dependent on the next mainline blocks being clear, instead of point position because we are forcing them open.
I think in my case and my "RR rules", I'd have the dwarf controlling the siding exit stay red until the 2 blocks ahead were clear(other train would have to be on the mainline beside the siding and clear of the turnout).

rkcarguy
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Re: Switch Point Detection continued

Post by rkcarguy » Tue Nov 21, 2017 7:14 pm

I got logged out, so in continuation....

I plan on having switch-stands on my turnouts with colored plates so I can see point position without signals, and set things up such that uphill trains will take the main and downhill the siding, as the default. The double headed signals guarding each end of the main/siding portion from oncoming trains will either get a green over red, or red over yellow when the switch is set to diverging. It will take some work with relays and diodes lol, but I'll get it:)

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ChuckHackett-844
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Re: Switch Point Detection continued

Post by ChuckHackett-844 » Tue Nov 21, 2017 7:27 pm

rkcarguy wrote:Chuck, how does one work with signaling the exiting of a siding back onto the mainline with sprung points(i.e. the train forces them open and back onto the mainline)? It seems like it would need to be dependent on the next mainline blocks being clear, instead of point position because we are forcing them open. ....
90% of the time the siding signals (exiting) do not care about point setting because it's a spring switch and it's a trailing point move.

Note: for 1" scale tracks they have requested controlled exits also because some light 1" scale cars are derailed when going through spring switches. In this case the exit ( trailing point) signal would also be at stop until the switch is set. In this case the signal system will align the turnout for exit when appropriate.

The point detection and signal control I mentioned was for facing point moves, typically at route choices, not passing sidings. For facing point moves, if the switch is against a route, the signal for that route is forced to stop. If the switch is set for that route, the signal indicates the ststus of the track ahead (stop, approach distant, approach, or clear).
Regards,

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

rkcarguy
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Re: Switch Point Detection continued

Post by rkcarguy » Wed Nov 22, 2017 6:53 pm

Ok, good to know. That's kind of what I figured, that trains approaching the turnouts/passing siding would face a signal illuminated as the turnout is set, and trains leaving the siding would face a signal showing a clear mainline with no relevance to the turnout position.

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