I have been sent the following list of things to answer:
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
PJW
