I will summarize all the options and offer the solution. It is left to=20
the authorities to choose which method.

Ravi

Isaac Marino Bavaresco wrote:
> This method seems to be the simplest, less expensive and safest.
>
> The OP says that he has approval from railroad authorities, so he should
> be able to get authorization to isolate electrically a section of the rai=
l.
>
> Just isolate electrically a 2km long section of just one of the rails
> between the 2km away point and where the detector will be installed.
> Connect one wire of the detector to the electrically isolated section
> and the other wire to the other rail. When the train arrives it shorts
> the isolated section with the other rail and closes the circuit.
>
> To avoid false positives the OP can use a moderately high current with
> a  very low voltage (thus low power) so leakage can be minimized and in
> the event of an accidental short circuit the intruder may be melted away
> and the problem self-corrects. Even moisture or a flood may not be able
> to give a false positive because a lot of current must flow for the
> detector circuit to trip.
>
>
> Isaac
>
>
>
> Em 18/07/2013 12:46, Dwayne Reid escreveu:
>> At 03:34 AM 7/18/2013, Ravi wrote:
>>> Hello all,
>>>
>>> Is there any method to detect an oncoming train about 2 KMs away?
>> The method that appears to be used in Western Canada is to use
>> wires.  A section of track is isolated electrically from the rest of
>> the track (easy to do - just insert a robust insulator between the
>> ends of the track section) and the train wheels bridge the circuit
>> when the train is present.
>>
>> This signal is used to cause the railway crossing lights to begin
>> flashing while the train is about a mile away from that
>> crossing.  Another isolated track section is used to automatically
>> turn the flashing lights OFF after the train has reached, then left
>> the crossing.
>>
>> There were always lots of telephone poles and wires that ran parallel
>> to the tracks in Western Canada - I assume that was part of the CNCP
>> Telecom group stuff.  I'm guessing that using one pair in one of
>> those cables was easy to do in those days.
>>
>> As a kid, I used to trick the crossing lights a mile away to begin
>> flashing by bridging the gap with a suitable conductor.  As an adult,
>> I now know how annoying that would be.  But the statute of
>> limitations on that misdemeanor has long since elapsed <grin>.
>>
>> dwayne
>>
>

--=20
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