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Treadles
#1
Hello,

This is Kannati, I am having a doubt on treadle operation i.e. where the QNR and QRR relays can use on signalling and also all treadles are having both detection contacts i.e.(QNR/QRR) or it depends upon type of treadle. I know that most of all treadles are using for Level crossings for strike in. and also I am using the treadle for replacement for distant signal in one of my project.

Can any one please clarify above and also requesting any documents regarding treadle operation having both QNR/QRR relays.

Many Thanks
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#2
Can't off the top of my head point you to any specific document I am afraid, however.......

Treadles generally have:

a) contacts that are made when the treadle is in its depressed position when actualted by a wheel flange of a passing train and for a duration afterwards (since the treadle is hydraulically damped and only rises slowly so that it is not physically hit by each and every wheel but actually is occasionally nudged as a long train passses and then rises some seconds after the last wheel has passed over it); these feed the QRR;
b) contacts that are made when the treadle is in its usual, fully raised, position and these feed the QNR relay.

The QRR contacts are used as proof of the detection of the presence of a train and may therefor initiate level crossing strike in or cause approach release of a signal.

The QNR contacts are generally used elsewhere as a safeguard, s that if the treadle sticks dwn for any reason and thereefore the QRR contacts are made invalidly that the situation is detected and a potentially dangersous situation is avoided by for example holding a signal in rear to danger, sounding an alarm to alert the signaller etc.


I have never considered how to use a treadle to replace a signal once a train has passed beyond it, but I would suggest that it would be appropriate to prove the QNR contacts made in that signal's aspect controls. Hence as soon as the arm is depressed by the first wheel of the train, the signal will revert to danger; it does not require the treadle to be fully depressed for this to occur. I would expect some form of stick relay to be disengaged and hence the signal to continue to be retained at danger, perhaps until the associated stop signal has been replaced to danger and then recleared.

Note that some treadles have two arms which is used to make them directional; they can be configured that is A is hit before B then the depression of B has no effect and the QNR contact is never broken and the QRR is never made, yet if B is hit before A then the treadle is effective and the QNR is broken and the QRR mde, just as it would have been in the case of a single arm treadle.




(19-02-2014, 10:40 AM)kannati Wrote: Hello,

This is Kannati, I am having a doubt on treadle operation i.e. where the QNR and QRR relays can use on signalling and also all treadles are having both detection contacts i.e.(QNR/QRR) or it depends upon type of treadle. I know that most of all treadles are using for Level crossings for strike in. and also I am using the treadle for replacement for distant signal in one of my project.

Can any one please clarify above and also requesting any documents regarding treadle operation having both QNR/QRR relays.

Many Thanks
PJW
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#3
Thanks PJW.. Yes, the same QNR contacts are using in the aspect controls and also using the QNSR for disengaging.
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