<![CDATA[IRSE Exam Forum - General Circuit Design]]> https://irse.signalpost.org/ Tue, 11 Aug 2026 15:44:38 +0000 MyBB <![CDATA[Echo in DLMs]]> https://irse.signalpost.org/showthread.php?tid=2178 Mon, 30 Jan 2017 06:03:38 +0000 shekar413]]> https://irse.signalpost.org/showthread.php?tid=2178
What is the use of Echo in DLMs? Why is it disabled in Data link repeaters?

Also please confirm why Chassis Earth and Filter earths are used in DLMs?]]>
What is the use of Echo in DLMs? Why is it disabled in Data link repeaters?

Also please confirm why Chassis Earth and Filter earths are used in DLMs?]]> <![CDATA[UCR & USR relay interlocking circuit]]> https://irse.signalpost.org/showthread.php?tid=2102 Mon, 11 Jul 2016 10:11:00 +0000 onestrangeday]]> https://irse.signalpost.org/showthread.php?tid=2102
Can anyone explain the function of UCR Route Check Relay and USR Route Stick Relay, and the purpose of those 2 circuits?
and the meaning of these 2 relays when they are in the "pick up" state or "drop off" state? (i.e. route checked, or not checked etc.)




Thank you




Bill]]>
Can anyone explain the function of UCR Route Check Relay and USR Route Stick Relay, and the purpose of those 2 circuits?
and the meaning of these 2 relays when they are in the "pick up" state or "drop off" state? (i.e. route checked, or not checked etc.)




Thank you




Bill]]> <![CDATA[Basic Signalling Technology]]> https://irse.signalpost.org/showthread.php?tid=1940 Thu, 09 Jul 2015 23:52:45 +0000 CHALLIE2]]> https://irse.signalpost.org/showthread.php?tid=1940
Thanks

Jamie Newman]]>
Thanks

Jamie Newman]]> <![CDATA[Signalling Designs]]> https://irse.signalpost.org/showthread.php?tid=1939 Thu, 09 Jul 2015 23:41:57 +0000 CHALLIE2]]> https://irse.signalpost.org/showthread.php?tid=1939 would i be able to get

Scheme Plans
Location layout
Signal Circuits etc

Thanks


Jamie Newman]]> would i be able to get

Scheme Plans
Location layout
Signal Circuits etc

Thanks


Jamie Newman]]> <![CDATA[2014 Q8 Relay]]> https://irse.signalpost.org/showthread.php?tid=1913 Sat, 18 Apr 2015 06:22:59 +0000 asrisaku]]> https://irse.signalpost.org/showthread.php?tid=1913
Could you please help review my attempt? or any suggestion?

Thanks in advance!

Best regards,
Arnut]]>
Could you please help review my attempt? or any suggestion?

Thanks in advance!

Best regards,
Arnut]]> <![CDATA[Interface between SSI and RR]]> https://irse.signalpost.org/showthread.php?tid=1453 Sat, 17 Aug 2013 23:21:47 +0000 kannati]]> https://irse.signalpost.org/showthread.php?tid=1453
I would just like to know exact interface between the SSI and RRI particularly fringes ?]]>
I would just like to know exact interface between the SSI and RRI particularly fringes ?]]> <![CDATA[Maxmum number of contacts in series]]> https://irse.signalpost.org/showthread.php?tid=1117 Wed, 07 Nov 2012 20:24:30 +0000 PJW]]> https://irse.signalpost.org/showthread.php?tid=1117
Talking in terms of coil and contact resistance, how many contacts in series can make a relay drop (say Q series)??


It is a long time since I have been involved in New Works relay interlocking design, so don't know what current standards apply- hence would appreciate being directed to appropriate document. In the meantime I have given this response:

Firstly it is most unlikely that the relay will drop; what is far more probable is that it will fail to pick. That is because there is hysteresis- the pick up current of a relay is significantly greater (typically 150 percent) than the current required to keep the relay up.

The force required to pick the relay will require on such things a the number of contacts and the ratio of back contacts (whose pressure helps) and front contacts (whose pressure hinders), also crucially the coil resistance and number of turns. [Magnetic flux of coil given by "n" x "I"].

However giving some estimated typical figures, let us postulate that a relay will just pick when it has 40V across its coil connections and has a coil resistance of 800 ohms; we can therefore afford to drop 10V across the rest of the circuit. To be reliable, we need to make an allowance for the incoming power supply to be a little low, say 48V so we can therefore afford to drop 8V across the various contacts (assuming that the drop along the wires and spade connections is negligible in comparison). We have 50mA flowing through them, so that gives a total of 160 ohms. Contacts generally will have a low resistance, probably I guess rather less than 1 ohm.

The problem is that sometimes high resistance contacts develop (say 10 ohms) and too many of these in series mean the end function won't pick. Also when establishing contact, the higher voltage available as the surfaces approach each other, the better the chance of establishing good electrical contact as it may have to breakdown a thin surface film of contamination. The relay coil will present an inductive load; this will mean the build up of current will not be instantaneous.

Back contacts are especially prone to high resistance, particularly those used as "down-proving" as it is unlikely that they will ever switch the load- this causes wear but on the plus side ensures that the switching surface gets some cleaning as a result.

You can see that the circuit will continue to work even in the presence of several high resistance contacts of that sort of order, however if one contact deteriorates so much that its resistance gets higher than around 100ohms then we would be in trouble if there are also some others which are also not too good.

Actually I think the main determinant in selecting a maximum number of contacts is how long it would take the maintenance technician to locate the fault in a circuit; the more contacts in the circuit the longer it will take to go prodding around with a voltmeter to find where the voltage is being lost. Bear in mind that until the end relay is picked up, then a high input impedance meter will actually "see" effectively full voltage through a high resistance contact (as very little current is yet flowing). When a subsequent contact makes (i.e another relay was initially in the wrong state when the fault tracing commenced) to complete the link between the faulty contact and the end function, current will now attempt to flow across the high resistance of the previously checked function and suddenly voltage is lost across it. The technician could already have thought they had discovered this contact was ok and is directing their attention elsewhere.

Therefore many railways will specify what they think is a reasonable number of relay contact is in series in any end function. I seem to remember that the Western Region worked to a limit of 25 contacts, of which 5 could be back contacts, but the BR national standard was quite a bit lower, I think 10 or 12. I do not know whether NR's Design Handbook or any other documentation specifies a "good practice" limit.

I think however that a low (perhaps it was 5) limit was set for the number of point detection contacts which could be summated into an SSI points TFM input. Not sure where this came from, but certainly there are commissioned sites with double that number which haven't experienced any problems- also note that SSI input is a low voltage (5V) pseudo-random square wave code and the TFM input is probably higher input impedance than a relay, so there is little current available for "contact wetting" and hence more susceptible to high resistance contacts than a relay would be.

Hope someone can add to this........

Section 6.2.4 of 11600 states the max no of contacts as 20.
]]>
Talking in terms of coil and contact resistance, how many contacts in series can make a relay drop (say Q series)??


It is a long time since I have been involved in New Works relay interlocking design, so don't know what current standards apply- hence would appreciate being directed to appropriate document. In the meantime I have given this response:

Firstly it is most unlikely that the relay will drop; what is far more probable is that it will fail to pick. That is because there is hysteresis- the pick up current of a relay is significantly greater (typically 150 percent) than the current required to keep the relay up.

The force required to pick the relay will require on such things a the number of contacts and the ratio of back contacts (whose pressure helps) and front contacts (whose pressure hinders), also crucially the coil resistance and number of turns. [Magnetic flux of coil given by "n" x "I"].

However giving some estimated typical figures, let us postulate that a relay will just pick when it has 40V across its coil connections and has a coil resistance of 800 ohms; we can therefore afford to drop 10V across the rest of the circuit. To be reliable, we need to make an allowance for the incoming power supply to be a little low, say 48V so we can therefore afford to drop 8V across the various contacts (assuming that the drop along the wires and spade connections is negligible in comparison). We have 50mA flowing through them, so that gives a total of 160 ohms. Contacts generally will have a low resistance, probably I guess rather less than 1 ohm.

The problem is that sometimes high resistance contacts develop (say 10 ohms) and too many of these in series mean the end function won't pick. Also when establishing contact, the higher voltage available as the surfaces approach each other, the better the chance of establishing good electrical contact as it may have to breakdown a thin surface film of contamination. The relay coil will present an inductive load; this will mean the build up of current will not be instantaneous.

Back contacts are especially prone to high resistance, particularly those used as "down-proving" as it is unlikely that they will ever switch the load- this causes wear but on the plus side ensures that the switching surface gets some cleaning as a result.

You can see that the circuit will continue to work even in the presence of several high resistance contacts of that sort of order, however if one contact deteriorates so much that its resistance gets higher than around 100ohms then we would be in trouble if there are also some others which are also not too good.

Actually I think the main determinant in selecting a maximum number of contacts is how long it would take the maintenance technician to locate the fault in a circuit; the more contacts in the circuit the longer it will take to go prodding around with a voltmeter to find where the voltage is being lost. Bear in mind that until the end relay is picked up, then a high input impedance meter will actually "see" effectively full voltage through a high resistance contact (as very little current is yet flowing). When a subsequent contact makes (i.e another relay was initially in the wrong state when the fault tracing commenced) to complete the link between the faulty contact and the end function, current will now attempt to flow across the high resistance of the previously checked function and suddenly voltage is lost across it. The technician could already have thought they had discovered this contact was ok and is directing their attention elsewhere.

Therefore many railways will specify what they think is a reasonable number of relay contact is in series in any end function. I seem to remember that the Western Region worked to a limit of 25 contacts, of which 5 could be back contacts, but the BR national standard was quite a bit lower, I think 10 or 12. I do not know whether NR's Design Handbook or any other documentation specifies a "good practice" limit.

I think however that a low (perhaps it was 5) limit was set for the number of point detection contacts which could be summated into an SSI points TFM input. Not sure where this came from, but certainly there are commissioned sites with double that number which haven't experienced any problems- also note that SSI input is a low voltage (5V) pseudo-random square wave code and the TFM input is probably higher input impedance than a relay, so there is little current available for "contact wetting" and hence more susceptible to high resistance contacts than a relay would be.

Hope someone can add to this........

Section 6.2.4 of 11600 states the max no of contacts as 20.
]]> <![CDATA[650V POWER]]> https://irse.signalpost.org/showthread.php?tid=786 Mon, 11 Apr 2011 18:42:24 +0000 Archie]]> https://irse.signalpost.org/showthread.php?tid=786
Has it got anything to do with distance from the feed itself related to resistance?

I am not sure so any help would be greatly appreciated.

Many thanks]]>
Has it got anything to do with distance from the feed itself related to resistance?

I am not sure so any help would be greatly appreciated.

Many thanks]]> <![CDATA[Complete set of RRI circuits]]> https://irse.signalpost.org/showthread.php?tid=744 Sat, 12 Feb 2011 05:18:30 +0000 khalid]]> https://irse.signalpost.org/showthread.php?tid=744 I am new here and hope I am posting in the right place.

Would it be possible to get an entire set of British practice RRI circuits(of a single medium sized station) including the locking and selection tables,rack arrangements,etc?

If that is not possible then a set of typical circuits for route setting,locking and signal clearance?

Thanks,
Khalid,
India.]]> I am new here and hope I am posting in the right place.

Would it be possible to get an entire set of British practice RRI circuits(of a single medium sized station) including the locking and selection tables,rack arrangements,etc?

If that is not possible then a set of typical circuits for route setting,locking and signal clearance?

Thanks,
Khalid,
India.]]> <![CDATA[signalling circuitry to do with signal and point control and indication,]]> https://irse.signalpost.org/showthread.php?tid=404 Tue, 18 May 2010 19:51:46 +0000 Archie]]> https://irse.signalpost.org/showthread.php?tid=404
Many thanks
Archie]]>
Many thanks
Archie]]> <![CDATA[diagrams]]> https://irse.signalpost.org/showthread.php?tid=400 Sun, 16 May 2010 14:19:45 +0000 Archie]]> https://irse.signalpost.org/showthread.php?tid=400
Many thanks]]>
Many thanks]]> <![CDATA[Miscellaneous circuit design queries]]> https://irse.signalpost.org/showthread.php?tid=362 Tue, 23 Mar 2010 19:33:34 +0000 PJW]]> https://irse.signalpost.org/showthread.php?tid=362
Quote:I have doubt in these very basics one Kindly clarify.

a) Why these relays [WZR, GR, NR, TASR] made slow to release?
b) Why USR made slow to pick up?
c) Use and working of RDL?
d) TACL:For temporary approach control both berth track down and TACL shown parallel, Please explain the working?
e) Some times slow to release made external by adding
capacitor,resistor [DJR] with slow to release relay but for WZR, GR, NR, TASR only slow to release relay alone shown.why?
f) What is the slow to release timing of BR 934 relay?
g) ECR: - if green lamp fuses, yellow lamp lits automatically - why there is no provision in signal wiring circuit for this?
h) Please explain direct fed indirect fed?
j) Purpose of booster transformer?
k) Why TPR relay made slow to pick up in DC & AC traction area?
l) Purpose of V(M) GO resistor in TPWS?
m) How to find relay spaces of different equipment while keeping in location case?
n) Please explain how to calculate the fuse rating?
p)Explain the working of train describer?
q) Explain tollerton control?
r) Please explain why FB24 supply given to the RGKE indication?
s) What is the maximum distance of cable allowed while transferring the function from one location to other?

a) The simplistic answer is for the specific circuit to work; the precise rationale depends on the actual case. Generally however there is a need for there to be a short period of time during which something else is given the chance to change state- it takes time for a relay to change from breaking its back contacts to making its front contacts. If you actually understand the logic of how a particular circuit works, then you ought to be able to work out the precise reason for yourself. Hence I'll only give you an example: The TASR picks up when the first and second tracks beyond a signal are simultaneously occupied; a feed is given to the ALSR when the first track becomes clear. The memory of the simultaneous occupation must be destroyed so that it is not stored indefinitely and therefore a back contact of the ALSR is included within the TASR circuit. Therefore we have a front contact of the TASR trying to pick the ALSR but as soon as it starts to do so braking of the back contacts of the ALSR would then destroy the TASR condition before the ALSR had had time to make its front contacts and thus stick up. However by making the TASR slow to release then there is enough time for the ALSR to become fully energised and thus establish its alternative feed by the time that the TASR front contacts are broken.

See also http://www.irseexam.co.uk/showthread.php?tid=304

b) This is to give a small degree of protection against the loss of train shunt on a track circuit. There is generally a slow to pick TPR following the TR and then a slow to pick USR so that there are two delays- this means that a brief track "bob" doesn't result in the USR and thus all the route locking in front of the train being lost. This gives something like 1 second's protection; for places where Automatic Route Setting is provided then SSI includes a much enhanced "track bob protection"- it maintains the locking for 15 seconds in the event of a train "disappearing"

c) RDL= Route Disconnection Link. A simple way that a technician can ensure that the signal is held to danger for that particular route. The use may be to provide protection to staff working on the line (personnel safety) or when signalling alterations are being undertaken / there has been an alleged signalling irregularity which hasn't yet been fully investigated (system safety)

d) With the Temporary Approach Control Link inserted (which it normally is) then the contact of the berth track has no effect and signal clears normally; when it is withdrawn then approach release is imposed. In reality this facility is very rarely used- it can be potentially useful if there is a need to keep traffic moving at slow speed through the area (e.g. if alteration work on the signalling system has taken too long for all the required testing to be completed within the possession time- there is no need to have tested aspect sequence or approach locking look-back etc) and sometimes associated with imposing temporary speed restrictions.

e) Capacitors can give much longer delays than can be achieved by design of the magnetic circuit within the relay. However such slugging can not be relied upon in safety critical functions- the capacitor over time is likely to gradually lose capacitance or it might fail completely or become disconnected and the relay would then suddenly become normal acting. Need to evaluate what would be the effect on the circuit (and indeed the signalling system within which it is included) should this happen. Generally a capacitor slug will be for a period of a few seconds whereas slow to release relays only give delays of less than a second- generally just used to give a chance for other relays to change state rather than give a "functional" delay. The DJR gives the "time-out" function needed when using push-push panel for route setting and need to allow the signaller quite a few seconds to select the route exit after having selected the entrance; hence clear why we need a capacitor for this one. Also be aware that slow operating relays have less contacts available than normal acting relays (because of physical space issues and because the magnetism created by the current in the relay coil being deployed to do other things than just pull the armature).

f) Off the top of my head I do not know, but it is about 0.5 seconds. However I do know that some manufacturer]]>
Quote:I have doubt in these very basics one Kindly clarify.

a) Why these relays [WZR, GR, NR, TASR] made slow to release?
b) Why USR made slow to pick up?
c) Use and working of RDL?
d) TACL:For temporary approach control both berth track down and TACL shown parallel, Please explain the working?
e) Some times slow to release made external by adding
capacitor,resistor [DJR] with slow to release relay but for WZR, GR, NR, TASR only slow to release relay alone shown.why?
f) What is the slow to release timing of BR 934 relay?
g) ECR: - if green lamp fuses, yellow lamp lits automatically - why there is no provision in signal wiring circuit for this?
h) Please explain direct fed indirect fed?
j) Purpose of booster transformer?
k) Why TPR relay made slow to pick up in DC & AC traction area?
l) Purpose of V(M) GO resistor in TPWS?
m) How to find relay spaces of different equipment while keeping in location case?
n) Please explain how to calculate the fuse rating?
p)Explain the working of train describer?
q) Explain tollerton control?
r) Please explain why FB24 supply given to the RGKE indication?
s) What is the maximum distance of cable allowed while transferring the function from one location to other?

a) The simplistic answer is for the specific circuit to work; the precise rationale depends on the actual case. Generally however there is a need for there to be a short period of time during which something else is given the chance to change state- it takes time for a relay to change from breaking its back contacts to making its front contacts. If you actually understand the logic of how a particular circuit works, then you ought to be able to work out the precise reason for yourself. Hence I'll only give you an example: The TASR picks up when the first and second tracks beyond a signal are simultaneously occupied; a feed is given to the ALSR when the first track becomes clear. The memory of the simultaneous occupation must be destroyed so that it is not stored indefinitely and therefore a back contact of the ALSR is included within the TASR circuit. Therefore we have a front contact of the TASR trying to pick the ALSR but as soon as it starts to do so braking of the back contacts of the ALSR would then destroy the TASR condition before the ALSR had had time to make its front contacts and thus stick up. However by making the TASR slow to release then there is enough time for the ALSR to become fully energised and thus establish its alternative feed by the time that the TASR front contacts are broken.

See also http://www.irseexam.co.uk/showthread.php?tid=304

b) This is to give a small degree of protection against the loss of train shunt on a track circuit. There is generally a slow to pick TPR following the TR and then a slow to pick USR so that there are two delays- this means that a brief track "bob" doesn't result in the USR and thus all the route locking in front of the train being lost. This gives something like 1 second's protection; for places where Automatic Route Setting is provided then SSI includes a much enhanced "track bob protection"- it maintains the locking for 15 seconds in the event of a train "disappearing"

c) RDL= Route Disconnection Link. A simple way that a technician can ensure that the signal is held to danger for that particular route. The use may be to provide protection to staff working on the line (personnel safety) or when signalling alterations are being undertaken / there has been an alleged signalling irregularity which hasn't yet been fully investigated (system safety)

d) With the Temporary Approach Control Link inserted (which it normally is) then the contact of the berth track has no effect and signal clears normally; when it is withdrawn then approach release is imposed. In reality this facility is very rarely used- it can be potentially useful if there is a need to keep traffic moving at slow speed through the area (e.g. if alteration work on the signalling system has taken too long for all the required testing to be completed within the possession time- there is no need to have tested aspect sequence or approach locking look-back etc) and sometimes associated with imposing temporary speed restrictions.

e) Capacitors can give much longer delays than can be achieved by design of the magnetic circuit within the relay. However such slugging can not be relied upon in safety critical functions- the capacitor over time is likely to gradually lose capacitance or it might fail completely or become disconnected and the relay would then suddenly become normal acting. Need to evaluate what would be the effect on the circuit (and indeed the signalling system within which it is included) should this happen. Generally a capacitor slug will be for a period of a few seconds whereas slow to release relays only give delays of less than a second- generally just used to give a chance for other relays to change state rather than give a "functional" delay. The DJR gives the "time-out" function needed when using push-push panel for route setting and need to allow the signaller quite a few seconds to select the route exit after having selected the entrance; hence clear why we need a capacitor for this one. Also be aware that slow operating relays have less contacts available than normal acting relays (because of physical space issues and because the magnetism created by the current in the relay coil being deployed to do other things than just pull the armature).

f) Off the top of my head I do not know, but it is about 0.5 seconds. However I do know that some manufacturer]]> <![CDATA[Interesting One: Relay slugging]]> https://irse.signalpost.org/showthread.php?tid=304 Fri, 20 Nov 2009 14:29:56 +0000 SWer]]> https://irse.signalpost.org/showthread.php?tid=304 See attached scheme.

Thanks]]> See attached scheme.

Thanks]]> <![CDATA[Sequence of relay operation]]> https://irse.signalpost.org/showthread.php?tid=175 Thu, 19 Feb 2009 07:28:58 +0000 sugavanam nagarajan]]> https://irse.signalpost.org/showthread.php?tid=175 Hope it will be useful for all

Thanks for Mr.PJW for reviewing this document.]]> Hope it will be useful for all

Thanks for Mr.PJW for reviewing this document.]]>