<![CDATA[IRSE Exam Forum - TC Calcs]]> https://irse.signalpost.org/ Wed, 22 Apr 2026 13:59:45 +0000 MyBB <![CDATA[TC Calcs Britain vs Russia]]> https://irse.signalpost.org/showthread.php?tid=2202 Mon, 10 Jul 2017 13:15:17 +0000 yuriy]]> https://irse.signalpost.org/showthread.php?tid=2202 Could anyone give me some links on the most complete books and guides on calculating railway track circuits in Britain.
I'm trying to generalize the calculation methods that are used in Russia, with those used in other countries. I decided to start with Britain. Among the material that I could find, including the present site, I have realized that the general approach is very different. In Russia, there are five mandatory modes of operation of the rail circuits: normal, shunt, control, short circuit and continuous cab signalling mode. Each of the modes is calculated in a certain way.

Waiting for response]]> Could anyone give me some links on the most complete books and guides on calculating railway track circuits in Britain.
I'm trying to generalize the calculation methods that are used in Russia, with those used in other countries. I decided to start with Britain. Among the material that I could find, including the present site, I have realized that the general approach is very different. In Russia, there are five mandatory modes of operation of the rail circuits: normal, shunt, control, short circuit and continuous cab signalling mode. Each of the modes is calculated in a certain way.

Waiting for response]]> <![CDATA[Drop Shunt]]> https://irse.signalpost.org/showthread.php?tid=2082 Fri, 15 Apr 2016 18:45:57 +0000 Peter]]> https://irse.signalpost.org/showthread.php?tid=2082
Quote:You seem like the person to ask, what would cause the drop shunt to lower? i understand that lowering the voltage will increase the shunt and conditons of the track circuit equipment will effect the track, causing it to drop.
You have an idea of how the drop shunt varies with the voltage being lowered, so the converse is true - if you up the feed voltage, you end up putting more energy into the TC and hence a shunt that allows more current to be passed will be needed to divert the energy from the track relay.
If you assume that the feed voltage is fixed, think about what bits of the equivalent circuit work together with the shunt resistance. The obvious element is the ballast resistance so if you think of that as a simple resistance in parallel with the drop shunt, to keep the total resistance of this pair constant, it is obvious that to have a lower value of drop shunt, you would need a higher value of ballast resistance. Hence you get the fact that when ballast resistance rises, the drop shunt falls potentially leading to the track circuit tending to wrong side failure when one set up in wet conditions starts to dry out.
Hope that helps you to understand the relationship a bit better. Try playing with the values in the sheet posted in the General Track Circuit Calculations thread.
Peter]]>
Quote:You seem like the person to ask, what would cause the drop shunt to lower? i understand that lowering the voltage will increase the shunt and conditons of the track circuit equipment will effect the track, causing it to drop.
You have an idea of how the drop shunt varies with the voltage being lowered, so the converse is true - if you up the feed voltage, you end up putting more energy into the TC and hence a shunt that allows more current to be passed will be needed to divert the energy from the track relay.
If you assume that the feed voltage is fixed, think about what bits of the equivalent circuit work together with the shunt resistance. The obvious element is the ballast resistance so if you think of that as a simple resistance in parallel with the drop shunt, to keep the total resistance of this pair constant, it is obvious that to have a lower value of drop shunt, you would need a higher value of ballast resistance. Hence you get the fact that when ballast resistance rises, the drop shunt falls potentially leading to the track circuit tending to wrong side failure when one set up in wet conditions starts to dry out.
Hope that helps you to understand the relationship a bit better. Try playing with the values in the sheet posted in the General Track Circuit Calculations thread.
Peter]]> <![CDATA[2014 TC Calculation]]> https://irse.signalpost.org/showthread.php?tid=1865 Sun, 16 Nov 2014 11:39:12 +0000 nwbn]]> https://irse.signalpost.org/showthread.php?tid=1865 <![CDATA[2013 TC Calculation]]> https://irse.signalpost.org/showthread.php?tid=1745 Tue, 10 Jun 2014 10:46:43 +0000 NJK]]> https://irse.signalpost.org/showthread.php?tid=1745
I planned to sit module 5 exam this year. I made my first attempt on TC calculation. Please go through the attached document and give your valuable comments for my further enhancement.

In my attachement, I found the value of drop shunt resistance is 13.63 ohm but the permitted value of drop shunt resistance is 0.5 ohm. I given wrong information reg failure of TC for the higher value of drop shunt resistance.
The higher value of drop shunt resistance may lead to remain the track circuit is energized state after the occupation of train because of the relay voltage not to reduced below to the drop away voltage value.

Thanks & Regards,
NJK]]>
I planned to sit module 5 exam this year. I made my first attempt on TC calculation. Please go through the attached document and give your valuable comments for my further enhancement.

In my attachement, I found the value of drop shunt resistance is 13.63 ohm but the permitted value of drop shunt resistance is 0.5 ohm. I given wrong information reg failure of TC for the higher value of drop shunt resistance.
The higher value of drop shunt resistance may lead to remain the track circuit is energized state after the occupation of train because of the relay voltage not to reduced below to the drop away voltage value.

Thanks & Regards,
NJK]]> <![CDATA[Track circuit calculation]]> https://irse.signalpost.org/showthread.php?tid=1071 Wed, 12 Sep 2012 09:02:47 +0000 Murugesan india]]> https://irse.signalpost.org/showthread.php?tid=1071
I have a doubt regarding track circuit calculation.

Given : The minimum ballest resistance RB= 2.5 ohm.km

To calculate the length of track circuit L,

The formula is RB=(ρL)/a

where
ρ = Resistivity ohm meter
L = Length in meter
a = Cross sectional area in square meter

if we know the ballest resistance, how to find the length of track circuits.

i have verified in one of the calculations

the sample calculation conveys me

RB=ρ/L

how this is derived?
what abt the cross sectional area?

I got confused regarding this kindly clarifiy and also
what is the difference between ohm.km & ohm/km ?

Regards,

Murugesan]]>
I have a doubt regarding track circuit calculation.

Given : The minimum ballest resistance RB= 2.5 ohm.km

To calculate the length of track circuit L,

The formula is RB=(ρL)/a

where
ρ = Resistivity ohm meter
L = Length in meter
a = Cross sectional area in square meter

if we know the ballest resistance, how to find the length of track circuits.

i have verified in one of the calculations

the sample calculation conveys me

RB=ρ/L

how this is derived?
what abt the cross sectional area?

I got confused regarding this kindly clarifiy and also
what is the difference between ohm.km & ohm/km ?

Regards,

Murugesan]]> <![CDATA[2002 Track circuit cal.]]> https://irse.signalpost.org/showthread.php?tid=1042 Sun, 24 Jun 2012 16:49:37 +0000 leochungnet]]> https://irse.signalpost.org/showthread.php?tid=1042
Can i use the pickup current only as shown in the attachment to calculate the feed resistance? So, it will only include Ballast Resistance, Relay Resistance and Feed Resistance.

From another post, it shows an approach by assuming the drop away % is 65% of Pick-up current. It will include Shunt Resistance, Ballast Resistance, Relay Resistance and Feed Resistance in the calculation. The Feed resistance will be about 3.36ohm.

Which one is correct??

Thanks in advance!!]]>
Can i use the pickup current only as shown in the attachment to calculate the feed resistance? So, it will only include Ballast Resistance, Relay Resistance and Feed Resistance.

From another post, it shows an approach by assuming the drop away % is 65% of Pick-up current. It will include Shunt Resistance, Ballast Resistance, Relay Resistance and Feed Resistance in the calculation. The Feed resistance will be about 3.36ohm.

Which one is correct??

Thanks in advance!!]]> <![CDATA[2011 Qn5 T/C]]> https://irse.signalpost.org/showthread.php?tid=1037 Tue, 29 May 2012 12:48:11 +0000 hopkin]]> https://irse.signalpost.org/showthread.php?tid=1037 <![CDATA[redundancy for track circuit]]> https://irse.signalpost.org/showthread.php?tid=950 Thu, 29 Dec 2011 02:16:04 +0000 onestrangeday]]> https://irse.signalpost.org/showthread.php?tid=950
Recently, I have encountered a track circuit design philosophy which I have doubted the actual benefit that it brings to the railway system.

is it better to implement track circuit with redundant function ? (that's if one track receiver fails, the system will automatic change to other receiver unit for the same track circuit, so the track circuit will work normally as usual). Anyone got ideas ? or has anyone seen this kind of design philosophy implemented for track circuit ?

]]>
Recently, I have encountered a track circuit design philosophy which I have doubted the actual benefit that it brings to the railway system.

is it better to implement track circuit with redundant function ? (that's if one track receiver fails, the system will automatic change to other receiver unit for the same track circuit, so the track circuit will work normally as usual). Anyone got ideas ? or has anyone seen this kind of design philosophy implemented for track circuit ?

]]> <![CDATA[2004 Question 6 - Worked Example]]> https://irse.signalpost.org/showthread.php?tid=885 Mon, 22 Aug 2011 08:08:18 +0000 adikarina]]> https://irse.signalpost.org/showthread.php?tid=885
Regards
Aditi]]>
Regards
Aditi]]> <![CDATA[2010 Track Circuit Question]]> https://irse.signalpost.org/showthread.php?tid=676 Sun, 03 Oct 2010 06:45:43 +0000 Peter]]> https://irse.signalpost.org/showthread.php?tid=676 Relay resistance: 9 ohm
Track relay pick up current: 50 mA
Ballast resistance: 2.5 ohm/km
Feed end resistance: 6 ohm
Feed voltage: 5 V

a) Draw a physical representation of the track circuit and an electrical equivalent circuit;
b) Calculate the maximum length of track circuit for reliable operation (state any assumptions that you make);
c) For this maximum length calculate the drop shunt value.
[20 marks]

If the ballast resistance subsequently changes to 1.5 ohm/km what is the new drop shunt value? [5 marks]

Am I alone in wondering why the ballast resistance give in this years question is again given the wrong units like last year? The older exams (eg 2007) specify it correctly as ohm.km and I expect it would be argued that a good student should know what to expect and know that what was given in this year's paper cannot be right. Increasing the TC length decreases the effective resistance of the ballast, not as implied by the units given that each km presents 2.5 ohm, therefore 2 km would present 2 x 2.5 ohm.

I'm all for challenging students, but on an item where most people tend to struggle on the concept, giving them a duff steer in the specification is a bit off in my view. I wonder whether it was deliberate or a bad error. Throw into the mix that, as far as I can see, when you do the calcs properly, you end up with a surprisingly long TC.

What did any of the candidates find?]]> Relay resistance: 9 ohm
Track relay pick up current: 50 mA
Ballast resistance: 2.5 ohm/km
Feed end resistance: 6 ohm
Feed voltage: 5 V

a) Draw a physical representation of the track circuit and an electrical equivalent circuit;
b) Calculate the maximum length of track circuit for reliable operation (state any assumptions that you make);
c) For this maximum length calculate the drop shunt value.
[20 marks]

If the ballast resistance subsequently changes to 1.5 ohm/km what is the new drop shunt value? [5 marks]

Am I alone in wondering why the ballast resistance give in this years question is again given the wrong units like last year? The older exams (eg 2007) specify it correctly as ohm.km and I expect it would be argued that a good student should know what to expect and know that what was given in this year's paper cannot be right. Increasing the TC length decreases the effective resistance of the ballast, not as implied by the units given that each km presents 2.5 ohm, therefore 2 km would present 2 x 2.5 ohm.

I'm all for challenging students, but on an item where most people tend to struggle on the concept, giving them a duff steer in the specification is a bit off in my view. I wonder whether it was deliberate or a bad error. Throw into the mix that, as far as I can see, when you do the calcs properly, you end up with a surprisingly long TC.

What did any of the candidates find?]]> <![CDATA[2004 Track Circuit Calculations]]> https://irse.signalpost.org/showthread.php?tid=470 Tue, 13 Jul 2010 06:24:47 +0000 jenni.joseph9]]> https://irse.signalpost.org/showthread.php?tid=470
I have attempted 2004 Track Circuit calculations question.

The last bit of the question relates to the advantages of additional Relay end resistance.

Feed End resistance is used to operate the track in various ballast conditions but am not sure why the additional relay resistance is used for.

Please help and provide your valuable feedback/suggestion.

Thanks in advance.

Regards,
JJ]]>
I have attempted 2004 Track Circuit calculations question.

The last bit of the question relates to the advantages of additional Relay end resistance.

Feed End resistance is used to operate the track in various ballast conditions but am not sure why the additional relay resistance is used for.

Please help and provide your valuable feedback/suggestion.

Thanks in advance.

Regards,
JJ]]> <![CDATA[2005 Track circuit calculations]]> https://irse.signalpost.org/showthread.php?tid=462 Mon, 05 Jul 2010 12:17:35 +0000 PJW]]> https://irse.signalpost.org/showthread.php?tid=462
(1) With optimum feed voltage and maximum ballast resistance of the track, its relay voltage:-

(a) When the minimum permissible shunt resistance is connected across, shall not be more than 85% of its drop away value;

(b) Without a shunt across, shall not be more than 250% of its pick up value, and

(2) With normal feed source voltage and minimum permissible ballast resistance of the track, its relay voltage shall not be less than 125% of its pick up value.

Above values are matching with uk practice? Please clarify

=======================================================================
See attachments for an attempt and the feedback on that.]]>
(1) With optimum feed voltage and maximum ballast resistance of the track, its relay voltage:-

(a) When the minimum permissible shunt resistance is connected across, shall not be more than 85% of its drop away value;

(b) Without a shunt across, shall not be more than 250% of its pick up value, and

(2) With normal feed source voltage and minimum permissible ballast resistance of the track, its relay voltage shall not be less than 125% of its pick up value.

Above values are matching with uk practice? Please clarify

=======================================================================
See attachments for an attempt and the feedback on that.]]> <![CDATA[2002 Track Circuit Calculation]]> https://irse.signalpost.org/showthread.php?tid=453 Tue, 22 Jun 2010 19:34:48 +0000 adikarina]]> https://irse.signalpost.org/showthread.php?tid=453 Please see the attached attempted Track Cirucit calculation question for 2002.

For Part B, the comments are below:-

Wet weather has caused the increase in the ballast resistance from 5 Ohms to 40 Ohms, therefore, the current through the ballast resistance has reduced from 52mA to 6.5mA. The current through the relay resistance and feed resistance is the same, hence the additional current flows through the drop shunt resistance (i.e. the train wheels), hence the new drop shunt resistance value is lower than the original. The prsence of the train causes the track relay to de-energise and drop away its current.

Please provide your feedback.

Thanks
Regards
Aditi]]> Please see the attached attempted Track Cirucit calculation question for 2002.

For Part B, the comments are below:-

Wet weather has caused the increase in the ballast resistance from 5 Ohms to 40 Ohms, therefore, the current through the ballast resistance has reduced from 52mA to 6.5mA. The current through the relay resistance and feed resistance is the same, hence the additional current flows through the drop shunt resistance (i.e. the train wheels), hence the new drop shunt resistance value is lower than the original. The prsence of the train causes the track relay to de-energise and drop away its current.

Please provide your feedback.

Thanks
Regards
Aditi]]> <![CDATA[Question Papers: DC track circuit calcs questions]]> https://irse.signalpost.org/showthread.php?tid=443 Tue, 08 Jun 2010 17:19:05 +0000 Archie]]> https://irse.signalpost.org/showthread.php?tid=443
If so is there any chance of them being posted up on here for me to have a go at.

Many thanks
Arch]]>
If so is there any chance of them being posted up on here for me to have a go at.

Many thanks
Arch]]> <![CDATA[1995 Track circuit calculations]]> https://irse.signalpost.org/showthread.php?tid=380 Thu, 22 Apr 2010 19:44:08 +0000 Archie]]> https://irse.signalpost.org/showthread.php?tid=380
Many thanks
Archie]]>
Many thanks
Archie]]>