Certainly where Network Rail use relays in a safety critical application, the philosophy is to use dependable relays (=non-weldable front contacts and the guarantee that no back contact on a relay can make at a time that any front contact is made). Sounds like India is more like most of the Continental railways where the relays could potentially weld as use all metal contacts and thus the safety is ensured by forms of sequential and cyclical checking, cross-proving etc.
Although this is a very important issue for interlocking design and certainly does require specific controls, this is more of a Module 1/7 question than Module 3 (it may be an essay question but not the Control Tables part).
The Control Tables are really about the Principles almost in ABSTRACT. Not so much the HOW they are achieved and the necessary TECHNOLOGY issues, more to do with the fundamental LOGIC of WHAT signalling element needs to interlock with any other. The purist would say that it doesn't matter if the interlocking "black box" uses computer data, bespoke electonic design, bespoke relay design- free wired or geograhical, compressed air, mechanical clockwork or indeed a little man inside it. Obviously the things that are technically possible differ in each case as indeed does the safety integrity (!- thinking of my dwarf!) and thus the reality is that any real Control Tables do have to reflect technology issues to some extent- often to make sure that the overall design mitigates identified hazards.
A very interesting argument and one that would make a good IRSE exam question which could with the correct "spin" arise in any of the modules except 2,4,6.
For Control Tables though, the examiners would not really be looking for the "technology specifics"- it could make the difference between Credit v Distinction, but not Fail v Pass.
To get a Pass you need to get the point calling and locking correct, inclusing trapping, flank, foul tracks, overlap locking annd releasing. You need to get opposing locking correct (direct, indirect, time out where applicable). You need to get the route setting conditions correct (point availability, opposing, crossproving). You need to get the aspect level correct (points including flank, tracks including foul, overlaps, approach release and route indicators). You need to get aspect sequence correct (in the NR UK case sequence, junction approach release, transitions etc).
Do this consistently and fast enough to attempt all the items set and you'll get a Pass; put a few of the frills on (e.g. swinging overlaps, permissive move locking etc) and you'll pic up those extra marks for a Credit. Show that you really know all the ins and outs of what you are doing as applicable to your sepcific railway and you'll get a Distinction BUT ONLY if you've got all the BASIC OK.
PJW
Peter
Although this is a very important issue for interlocking design and certainly does require specific controls, this is more of a Module 1/7 question than Module 3 (it may be an essay question but not the Control Tables part).
The Control Tables are really about the Principles almost in ABSTRACT. Not so much the HOW they are achieved and the necessary TECHNOLOGY issues, more to do with the fundamental LOGIC of WHAT signalling element needs to interlock with any other. The purist would say that it doesn't matter if the interlocking "black box" uses computer data, bespoke electonic design, bespoke relay design- free wired or geograhical, compressed air, mechanical clockwork or indeed a little man inside it. Obviously the things that are technically possible differ in each case as indeed does the safety integrity (!- thinking of my dwarf!) and thus the reality is that any real Control Tables do have to reflect technology issues to some extent- often to make sure that the overall design mitigates identified hazards.
A very interesting argument and one that would make a good IRSE exam question which could with the correct "spin" arise in any of the modules except 2,4,6.
For Control Tables though, the examiners would not really be looking for the "technology specifics"- it could make the difference between Credit v Distinction, but not Fail v Pass.
To get a Pass you need to get the point calling and locking correct, inclusing trapping, flank, foul tracks, overlap locking annd releasing. You need to get opposing locking correct (direct, indirect, time out where applicable). You need to get the route setting conditions correct (point availability, opposing, crossproving). You need to get the aspect level correct (points including flank, tracks including foul, overlaps, approach release and route indicators). You need to get aspect sequence correct (in the NR UK case sequence, junction approach release, transitions etc).
Do this consistently and fast enough to attempt all the items set and you'll get a Pass; put a few of the frills on (e.g. swinging overlaps, permissive move locking etc) and you'll pic up those extra marks for a Credit. Show that you really know all the ins and outs of what you are doing as applicable to your sepcific railway and you'll get a Distinction BUT ONLY if you've got all the BASIC OK.
PJW
Peter
Quote:I suppose the railway practice followed in UK & Australia would be similar and that to with Metal to carbon relay.
Indian Railways use metal to metal relay for interlockings.