# occupancy detection



## bcer960 (Dec 27, 2007)

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I have an indoor layout and 1 BDL-168 and 5 BD-4's. The problem is lots of false detection and non-detection's. Most likely because these units are rated at 5 and 3 amps respectively and I know I am far above that. So the question is what are you guys using in the 10amp range?

Thanks
Ray 
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## krs (Feb 29, 2008)

I'm not into occupancy detectors, but does a single train on your layout really draw more than 5 amps? 

The 5 amp rating for the Digitrax detector that you quote is for each detection section I would hope. 
At that it should be adequate unless you're running more than two diesels per train. 

I would test the 5 amp detector with a 3-4 amp load first and also a much smaller load to see if it works properly then before thinking of investing more money buying something else. 

Knut


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## Greg Elmassian (Jan 3, 2008)

The guy who is an expert with these is Bob Grosh, but he's kind of fallen off the edge of the earth. 

I believe that George Schreyer is also knowledgeable, although I don't think he is using them in G scale. 

You might go to their respective web sites (Google them) and see if there is help there, maybe a mod. 

Many of these detectors use a low ohm resistor in series with the track power, and then measure the voltage across the resistor (sensing current). 

Maybe you can change the resistor to a lower value? 

Greg


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## krs (Feb 29, 2008)

Maybe you can change the resistor to a lower value? 

Ray seems to be getting problems at either ends of the sensitivity range. 
False detection to me means the detector provides an output with no train in that section - ie too sensitive 
No detection to me means the detector provides no output even though there is a train in the section - ie not sensitive enough 

Lowering the detector resistor value, if in fact Digitrax uses that design approach, would decrease the sensitivity. 

Maybe a bit more detail as to when there is false detection and no detection would help, but the bottom line is - I don't think it has anything to do with the 5 amp rating (although I didn't see a rating for the detectorswhen I glanced at the Digitrax info quickly; I'm sure it's there somewhere).


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## Greg Elmassian (Jan 3, 2008)

If the digitrax uses a sense resistor (which I believe it does) overcurrent would just melt and smoke the resistor. 

The system would be reading the voltage across the resistor... detecting when no loco means some current is flowing or is being detected, which would be independent of anything else now, since no loco in the circuit (or lighted cars, etc.)... 

We do need more information to help. 

Regards, Greg


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## krs (Feb 29, 2008)

I came across this partially completed technical article on the BDL-168 by Mark Gurris, but the technical detection parameters don't make any sense for our trains. 

https://sites.google.com/site/markgurries/home/dcc-problems/got-false-occupancy-detection/bd168 

This article lists the occupancy detection sensitivity as 1.2 ma and optional at 0.6 ma, I think that is far too sensitive for Large Scale. 

There was another thread on MLS just recently where someone measured 200 ohm leakage across the rails in wet conditions with a certain type of ballast. 
This occupancy detector would show that track as being occupied permanently. 
Ok, I agree, leakage of that magnitude, roughly 100ma, is somewhat unusual but a occupancy current design threshold of 1.2 ma doesn't sound reasonable for Large Scale especially when used outdoors. 
Begs the question, is that BDL-168 even meant for Large Scale applications? 

Knut 

Sorry - You have to copy and paste the link to read the details.


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## bcer960 (Dec 27, 2007)

Hi Guys,

Thanks for getting back to me on this. So first of all I am indoors and using hand laid aluminium track for everything you see on the layout and a combination of LGB, Aristo and some old Delton for everything under the layout i.e. storage tracks etc. I am running with Railroad & Co full computer animation, so the block detection has to work for the computer to line switches, start and stop trains etc. I am currently using all Digitrax DCC components as follows. 

1 DCS100( I know this is a 5 amp station, and have not measured the current when running, but the BD-4's are rated for 3 amps.)
1 DB-200+ (can't get this to work at all... different problem for later) 
1 BDL-168
1 DS-44 
7 DS-64
5 BD-4
Loco buffer II

All this is is a cabinet which I thought was about half way through my layout. However, right from the start I have had detection problems at the block furthest to the right of the cabinet. It is a section of LGB track about 60' long and on a 3.75% grade. I have replaced the wire, which is 14/2 and with track feeds every 6'. When I originally hook it up to the BDL-168 I could not get it to detect a train in that block. The train ran through the block fine, I could start and stop the train in the block, so the power/signal was there just no detection. After a lot of frustration I eliminated the block and just hard wired the section of track so the layout worked. ( In Railroad & Co, the program follows the trains around the blocks and highlights where they are. If they are not detected in a block but the train passes through it, the PC loses the train and it cannot complete it program. So, by removing the block the program still followed the train.) I ran this way for some time, but as the programs got more complicated I found I needed that block to stop trains in, so I experimented with a BD-4/ DS-64 combination, and wow it worked. I put it back into the BDL-168 and it didn't work. OK, back into the BD-4/DS-64 combo.

That is until I finally got my passenger train running. I had a USA Trains F-3, but needed a GP-7 to get enough traction to pull my full Aristo aluminium cars up the hill. This was fine for awhile, but the other day when I went to run, that block once again won't show detection, and the block before it (the 60' block got split as a siding was added between all this) is showing occupancy when there is none.They are on different BD-4/ CS-64 combos, but both on the grade.

Everything I have read including George's site talk about the high current USA Trains motors. My conclusion was that the 4 motors fried the BD-4, so back to the question of a high amp occupancy detector. I have to assume that someone out there is using the DB-200+ which is rated at 8amps (some say 7amps , but either way) with some form of detection. 

Thanks again

Ray 

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## Greg Elmassian (Jan 3, 2008)

The USA trains indeed have high stall currents, but running current is not that high... it's a complicated story, but I doubt your BD-4 is damaged. 

Why not experiment and twist the wires on the furthest block, like the HO scalers do? 

Greg


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## Axel Tillmann (Jan 10, 2008)

I am not familiar at all with the components you have listed, but what I am posting here is the information I was told by specialist in regards to using the block detection within a ZIMO environment.

1. The block detection electronic needs to be close to the block detection points.
2. No two block detection cables should run in parallel
3. No block detection cable should run in parallel with any DCC feeder line
4. No block detection cable should run in parallel with any regualr power liine

So if you have your block detection modules in a cabinet and all the wiring is going to the cabinet - I would be suspicous of that. In order to confirm Greg's suspicion that a BD4 is defective I would make a simple test track with the shortes wiring possible. If it works consistantly than of coure the BD4 is not your problem.

Hope this helps to point you into the correct direction.


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## krs (Feb 29, 2008)

Posted By bcer960 on 09 Jul 2011 08:25 PM 
.........so back to the question of a high amp occupancy detector. I have to assume that someone out there is using the DB-200+ which is rated at 8amps (some say 7amps , but either way) with some form of detection. 
The NCE occupancy detector is the only high current one I have come across.
Uses a different principle to detect absence or presence of current to the block.
But I don't know how you would tie that type into loconet and/or your computer program.

Have you looked at the problems and solutions people have posted on the net when it comes to these Digitrax detectors to see if any may apply to you?


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## Allen B (Sep 22, 2010)

You might try Tony's Train Exchange for the PSX series. They do have occupancy detection and will feed back to the Digitrax Loconet system. Just a thought. 
Allen B.


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## toddalin (Jan 4, 2008)

A possible solution for false detection is to use ferrite beads on your sensor wires.

I make lots of projects that use 555 chips. These chips are _severely prone to glitching_ and I must make all kinds of allowances to get many of my circuits to operate properly. Many of these "allowances" are not documented where I've seen them on the 'net. This is one reason that I don't often recommend untried 555 projects to beginners.

In building the motor and timing circuits for the aerial tramway, I had a problem in that I was burning out 555 chips when the motor had its current reversed to make the tram change direction. The motor used its own set of batteries and was completely separate from the 555 chip circuitry and its batteries that only switched a 4pdt relay armature to reverse the current. Yet, when the relay reversed the current, the motor would not reverse, but would start "skipping" and within about 20 seconds, the 555 chip would release the magic smoke. No one had an explanation.

A "ginormous box of parts" (~$12 at Goldmine Electronics), had several ferrite beads with wire stranded through them. With nothing to loose, I used these on the motor leads. (Yeah right, like that's going to do anything!) To my amazement, the circuit now worked perfectly and the motor ran forwards and backwards just like it should! In fact, with the beads, I was able to let the motor and electronics share a common power supply and it still worked/works fine!

When I later put the 555 circuits together for Gustav to push the block of ice into the reefer, I had a similar problem in that the solonoid produces so much "electricval kick back" that it would screw up the timing circuits leading to false triggering. I instantly reached for the ferrite beads and again to my amazement, they came to the rescue and Gustav works fine. You can see 7 orf them in this picture protecting the the 2 chips power taps, the relay power tap, and the solonoid power taps.

In your case, I guess you would just add them where your wire terminates at the module.


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## bcer960 (Dec 27, 2007)

Ok, 
I will try moving the BD-4 and DS-64 much closer. And I will go to my electronic supplier and find some beads. Is there any info on these beads? different sizes etc? 

Ray


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## Greg Elmassian (Jan 3, 2008)

Try twisting the wire between the sensors and the track first, cheaper. 

Greg


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## toddalin (Jan 4, 2008)

As I noted, my beads came in a "grab box" and I did not see them in the Goldmine Electronics catalog. This is to be expected as their grab boxes include lots that are too small to advertise.

I don't see any at the surplus houses, but on the 'bay the ones I'm using look just like this except there is an unstranded wire looped back and forth through the holes.


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