Digital Track sensor problem

Slawman

Slawman

Deckline
9 Apr 2018
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I am using a combination of the Massoth digital track contacts 8420102 and LGB 17100 reeds and experiencing the occasional "miss" ie. the detector does not trip when a loco passes.

As you can imagine, a missed detection can lead to some pretty crappy consequences up to and including a requirement for spare parts....

I am feeding the detectors through Massoth feedback modules and using level control signals. The longest cable run I have connecting the detectors to the modules is around 9 meters.

Has anyone else experienced any trigger reliability issues with this type of setup? Any tips?
 
Slawman

Slawman

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9 Apr 2018
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Quite right Greg, it is correctly the 8420502 digital contact. I would like to know if anyone else has ever had reliability issues with this setup or if it most likely something at my end....
 
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Slawman

Slawman

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9 Apr 2018
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Thanks John, thought provoking. I do not use diodes at the moment but at 8 dollars for 100 this is a good next step. The reeds look good as well although after giving the 17100s a good conformal coating I suspect they will last in the weather. The current detection is 100% but a real PIA. I have about 14 blocks now and only two are current detection...... I think I would prefer to put two reeds on every block for redundancy before I go down the current detection route. I have not (yet) had two fail in succession.
 
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Greg Elmassian

Greg Elmassian

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There are diodes in the LGB 17100's? If so it must be to protect the contacts. UGH. So diodes would work if you are switching DC, and would only really be needed with higher current or inductive loads.

But the application is using the Massoth modules, which surely are not inductive nor high current.

Using level control is trying to detect the transition from open to ground and from ground to open as 2 separate events... I would NOT do this with a reed switch which can be noisy and have the contacts bounce.

If these are just occupancy sensors, why are you using level control?

(perhaps I don't understand the finer points here)

Greg
 
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
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The biggest problem with DCC in general, is there is no hand-shake, or error correction.. Nothing to check if a 'message' gets to its' destination..
 
Slawman

Slawman

Deckline
9 Apr 2018
276
79
Sydney
There are diodes in the LGB 17100's? If so it must be to protect the contacts. UGH. So diodes would work if you are switching DC, and would only really be needed with higher current or inductive loads.

But the application is using the Massoth modules, which surely are not inductive nor high current.

Using level control is trying to detect the transition from open to ground and from ground to open as 2 separate events... I would NOT do this with a reed switch which can be noisy and have the contacts bounce.

If these are just occupancy sensors, why are you using level control?

(perhaps I don't understand the finer points here)

Greg

There is almost no load, this is just contact close in the case of the reeds and low voltage pulse in the case of the digital contacts directly into the feedback module. I am not using any of the detection circuit to throw switches directly.

I am using level so I am able to get 8 detectors with a discreet address through each feedback module. I am using this to feed into Traincontroller software. The following extract from the Massoth manual:

Every closing of the contact triggers
a signal. The usable contact number
may be doubled by programming the
module to level control (only DiMAX
bus). In case the reed switch is closed
the “a” contact is reported. In case the
reed relay is released the “b” contact
is reported.

I don't know why flank won't do this (this is what I setup first) as I only want an initial close. However based on my interpretation of the manual and my own experience you can only get 4 contacts through each module using flank. This seems to be specific to the Massoth unit as each input is paired. There is also a reasonably strong chance I have not properly understood what the manual is saying I find the language very confusing.

I can say after a good deal of trial and error the setup works perfectly aside from the fact that occasionally (maybe 1 in 20) the signal won't register.

It seems this now comes down to perhaps a de-bounce setting, magnet position, cable length, interference etc..... I am also going to experiment by increasing the strength of the magnetic field although I have no idea if the switch is not triggering or the signal is getting lost.
 
Greg Elmassian

Greg Elmassian

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Yep, my guess is debouncing... hard to believe the magnets aren't triggering it... I read the manual, there's nothing there I see to help, just a delay to send the trigger, but if you miss it, you miss it.

Greg
 
Slawman

Slawman

Deckline
9 Apr 2018
276
79
Sydney
Well I have a footnote for this one. I have found in my meandering tinkering that the reliability of a sensor triggering on my system is significantly increased if the magnet is offset from center. This goes for the large flat magnets mounted on locos as well. run a magnetic field down either the right hand or left hand of the sensor and I have yet to have a failed trigger.
 
Slawman

Slawman

Deckline
9 Apr 2018
276
79
Sydney
Easier to show with a video. I hooked an LGB 17100 up to a Multimeter continuity tester.

The magnet in the video is a little neodymium bar. Much stronger than the Massoth or LGB stick on plates.

You need sound on to hear the detection:


The Massoth/LGB plates will work "most" of the time however I am guessing whatever it is which is causing the dead spot in the middle will occasionally result in a no trigger.

** No trains were harmed in the filming of this video.
 
CharlieBear

CharlieBear

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7 Apr 2020
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Didsbury
I've had this problem, and its always the contact at the top of an end to end rack, I'll try repositioning the magnet under the loco