(03-09-2010, 10:02 AM)priyman Wrote: All,
We had a study group and were failing to understand the points (detection) section of the control tables.
We determined that when you put down the points normal or reverse, the interlocking circuits would check point are set, locked and detected.
But in the box labled 'detected normal or reverse'; the check is that the route is set only when the points are detected? But isn't that repetition because you have already checked that they are set locked and detected?
I'll give you the example I'm thinking of 2004 paper - route 142B(M) requires;
Assuming this is a swinging overlap for sake of understanding;
I wrote:
212N, 211N, 207R, 206N,
(203N, 205R, 201N) or (203R, 202N).
Then I would enter 203 in the detection box as well.
But I see repetition, is there supposed to be this additional check (and if this was RRI - a double inclusion of relay contacts 203 RLR in the route locking circuitry) or am I misunderstanding something?
Any input would be welcomed,
thanks,
Priyank
Not quite.
Firstly you wrote:
the box labelled 'detected normal or reverse'; the check is that the route is set only when the points are detected?.
That is either careless wording or you have actually completely misunderstood the overall CTs in a big way; the ROUTE setting depends only upon points AVAILABILITY; the parts of the Control Table to which you are referring are about the conditions under which the SIGNAL ASPECT can clear.
Secondly you wrote:
is there supposed to be this additional check (and if this was RRI - a double inclusion of relay contacts 203 RLR in the route locking circuitry) or am I misunderstanding something?
No there is no additional check, no there is no double inclusion of relay contacts in the circuit. Yes you are misunderstanding.
In fact it is worse than that; the RLR is the "interlocking set" rather than "points detected in position" relay and so that is something else you have not understood correctly, so perhaps it is not surprising that you have got yourself confused. Suggest you need to revisit some basic stuff before worrying about swinging overlaps- signs of "trying to run before you can walk".
You'll find that Merlin has put a
couple of very useful presentations on this website; suggest you study
them and other material to get things straightened out.
I am going for now to assume that you do actually appreciate the diffference between ROUTE and ASPECT and you just worded sloppily. This is pretty fundamental and there are other posts etc on the website that explain the distinction. Hence I am concentrating on the "swinging overlap" issue (again there are other relvant posts that use of the search facility should find for you to support the following comments).
The "Normal or Reverse" box is
only for facing points in overlaps which can be in either lie.
The heading is a bit of a shorthand and actually means "points proved:
a) set and detected normal or, alternatively
b) set and detected reverse or alternatively,
c) having been initially detected in either of these positions and the signal having cleared, then for a period of time not exceeding 8 seconds the proving is inhibited following a call on those points to the opposite position to which they are currently being assumed to be responding". Write that on your CT blank if you want to; most of us say "N or R or swinging"- a little inaccuracy being worth a ton of explanation. After all CTs are supposed to be utilised by those with adequate domain knowledge to interpret correctly rather than necessarly being a formal 100% specification for completely literal implementation.
This entry is the swinging overlap functionality which allows the overlap beyond the exit signal to be changed by
a) the signaller using the point key, or
b) by setting a forward route or
c) by the setting of another route which conflicts with the existing overlap but can be permitted to set provided it swings the hinge points of the existing overlap as flank
without the signal authorising the movement up to that exit signal changing aspect as soon as point detection is lost.
For a simple swinging overlap the hinge points are placed only in the "N or R" column rather than the normal columns for "set, proved locked and detected";
it is rediculous to put them in the "set/lock/detect" columns as well (without qualifying by a note such as "set only" )as otherwise the simple loss of detection will revert the aspect which is exactly what we do not want to happen
However in more complicated overlaps [i.e. if there are further points associated with one of the overlaps but not the other one(s)] then whilst these points are recorded within the usual N, R column(s) then they have to be associated via AND / OR conditions with the hinge points. Hence instead of just putting the hinge point number xyz in the "N or R" column, then have to write them in explictly as:
[xyz N associated with other points for the one overlap lie]
or
xyz R associated with other points for the other overlap lie]
and then bracket / dotted line the relevant condition with all the other assocuiated points.
An alternative presentation that you may sometimes see (and I guess you were trying to reproduce in your example quoted) would be to put the hinge points xyz in the "N or R or swinging" column as a free standing entry but also include those hinge points within the expression for the other overlap points BUT with a relevant $ note to qualify that it is just a pure "point set" condition to select the relevant one of the overlaps in the combinational locking rather than actually proving anything about the points trackside. This of course is where you'd use the points RLR within a relay circuitry.
So in a sense what you wrote was very nearly correct; however the fact that you could write it just as you did betrays the fact that it was "reproduction without understanding" and that is what the IRSE examiners are on the lookout for- for a candidate to be able to submit that is a give-away that there is a lack of overall comprehension. In the exam your written work is all they have to go upon to make a judgement; the advantage of this website is that there can be wider communication. All credit to you for recognising that things didn't make sense and flagging it up. Whereas the examiner wouldn't have had any evidence that you were even aware of the discrepency of your output, by posting here you have done the equivalent of a computer giving an error message having calculated the checksum of a downloaded file and identified that there must have been corruption- doesn't know what's wrong but has recognised discrepency and requesting attention before proceeding further!
I hope that this does make it a bit clearer for you. It is good that you are prepared to ask such questions and trying to resolve your understanding. My diagnosis of why you are having trouble is that you don't have a firm enough grasp of the fundamentals and your underpinning knowldege is weak with some confusions over terminology; think you are a clever chap but need to put a bit more effort in ensuring that you have really correctly understood the basics.
