Intermediate Block Signaling using MSDAC

R Viswanath Reddy, IRSSE, DSTE/Co-ord/BZA

November 19, 2019

Abstract

For Intermediate Block signaling, various schemes arein use in Indian Railways based on different typesof vehicle detection devices and mechanism used todrive the remote IB Signals. Presently, the typicalIB signaling schemes in existence are i) ConventionalIB with copper cable ii) IB with Quad and coppercable iii) IB with EI and OCs iv) IB with UFSBI. Inall these above schemes, axle counters are used fortrack vacancy detection and to drive the signals atIB, to read the status back and for resetting mecha-nism, various schemes have been used. Multi SectionDigital Axle Counters (MSDACs), with dual detec-tion in distributed architecture can also be used fortrack detection as well as exchange of signaling infor-mation and resetting. This is successfully working inNW-WADI section of GTL division, with near zerofailures till date from the date of installation and sin-gle detection has been provided in 3 IBs of BZA di-vision, which are working successfully without manyhassles.

1 INTRODUCTION

Intermediate Block Section is one step advancementover absolute block system of working between twoblock stations in which, the block section is dividedinto two sections of approximately equal length wheretwo trains can be accommodated simultaneously ineach direction of traffic. The Intermediate block sig-nalling consists of two major components. A) Pro-vision of axle counters for track vacancy detectionin rear as well as advance sections B) Exchange ofsignalling and reset information between IB and sta-tions. In the present scheme, dual detection with re-dundancy at each level including communication me-dia has been adopted to achieve higher availability.Track vacancy detection has been achieved throughMulti Section digital axle counters and exchange ofsignalling information has been done through theutilization of IO-EXBs which are part of MSDAC.The typical scheme is explained using M/s Frauscher

make FAdC R2 system. The same scheme may beadopted to other MSDACs with slight modificationand tailoring to the needs of different makes.

2 DESCRIPTION OF THESHEME

A. Typical layout of the scheme: The IntermediateBlock Section between NW-WADI of GTL division isreffered for easy understanding. The typical layoutof the placement of different DPs and Signals is asfollows:

A Relay hut of size 12mx5m is provided tocater for RBG room at IB location. The IB homeSignals are typically planned in such a manner that,the UP and DOWN IB signals are near to Relayhut and as such both signals are driven from thehut including the corresponding distant signals.The nomenclature of DPs in DOWN direction isDN-DP1A, DN-DP1B, DN-DP2A, DN-DP2B, DN-DP3A, DN-DP3B, DN-DP4A, DN-DP4B. Similarnomenclature has been adopted for UP direction also.

B. Provision of MSDACs for track vacancy detec-tion and defining the boundaries of track section andSupervisory Track Sections:

Dual detection has been provided with redundancyfor all other equipment as well as communicationmedia. The Typical IB section consists of Threetrack sections in each direction. i) AS track section,which starts from the foot of LSS and ends at 400mahead of IB home signal (DN-AC) ii) IB tracksection, from the foot of the IB home signal to 400mahead of the signal (7 AC) iii) BPAC section, fromfoot of the IB home signal to 180m ahead of thehome signal of the ahead station for proving blockoverlap (DN-BPAC). A supervisory track section(DN-SPT) covers all these three track sections,which is used for second level of reset as explained inlater sections.

Why dual detection? :

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Figure 1: Typical Layout of IBS

There are few instances where it is observed singledetection (whether SSDAC or MSDAC) is prone tofailures irrespective of precautions taken. It may bedue to inherent design flaws, which might have nothave been envisioned during the design of the systemor due to external factors during real time working ofthe system.

i. whenever a loaded rake movement isthere over the coil portion, due to lightweight of the guard brake, there existsa considerable probability of the wheeljumping over the coil causing a mis-count and thereby counting mismatchand failure of axle counter.

ii. When there is a long haul movementor due to any unavoidable reasons, ifthe wheel traces a to and fro movementover the portion of coil, the system goesinto hang state which requires reboot-ing of the same. This is prevalently ob-served not only in SSDAC but also inMSDAC.

iii. Unintended count due to food foil: Ithas been an experience in few cases,where the Aluminum food foil whichruns along the track gets struck andattaches to the Rx Coil, which causesunintended outcount or in count lead-ing to failure of Axle counter.

In all above cases, if dual detection isprovided with staggering of coils, suchfailures shall be avoided through Auto-matic reset feature.

Why redundancy of other components ofMSDAC? :

In order to avoid other equipment failures suchas Power supply card, communication card, mother

board as well as relay driver card and relay failures,all are duplicated including communication media.

As shown in Fig.4, the redundancy at equipmentlevel is achieved as follows.

i. At wheel sensor level, dual detection isprovided with two DPs on either rail ineach direction of traffic.

ii. Two separate TLJBs are provided withIP65 protection for termination of eachDP.

iii. The 6quad cable from Relay hut to lo-cation box is duplicated and providedin two different paths to achieve pathredundancy.

iv. Each Coil/DP is connected to anAdvanced Evaluation Board(AEB)through a surge protection device, forprocessing of data received from coil.

v. Two evaluators (EVs), Main and Re-dundant (M&R) are provided in IB lo-cation as well as adjacent stations. Themain DPs of UP and DOWN direc-tion are connected to EV(M) and re-dundant(R) DPs of UP and DOWN di-rection are connected to EV(R). Theevaluated information is shared to Re-lay Driver card and COM-AdC. TheCOM-AdCs at IB as well as adjacentlocations are on a common networkthrough ethernet ports and in turnthrough dedicated OFC, via an unman-aged ethernet switch as shown in Fig.4.The COM-AdCs of both M & R EVsare hot linked and any failure of one ofthe board does not hamper the trackdetection.

vi. There are two ethernet switches avail-able for shared communication among

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Figure 2: Boundaries of Track Section

the MSDACs at all the three locations.One ethernet switch works on dedi-cated fibres(Tx &Rx). Another ether-

net switch works on a pair of quad ca-ble. Alternatively, the second one canalso be provided over redundant fibre.

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Figure 3: Dual Detection

vii. The Vital Relays (ACPRs) of eachtrack section are picked up at the En-try end of track section (either in IBlocation or station). The status of vi-tal relays exchanged between two lo-cation through IO-EXBs depending onthe need.

C. Exchange of signaling information between twolocations

The IB signal relay status has to be repeated fromrear station to IB location. Similarly the status ofIB signal as well as other vital and non vital indica-tions have to be exchanged between IB location andStations. In order to achieve this, the IO-EXBs areused in either location, with each pair exchanging 3vital I/Os between them. The vital mode is typi-cally termed as quad mode in which 3 I/Os of vitalinformation can be exchanged, where as the non vi-tal mode is termed as single mode, where 12 I/Oscan be exchanged between two locations with a pairof IO-EXBs. As these are under the approved listof components of FAdC R2 by RDSO, they can besafely used for this purpose. The typical Informationrequired to be exchanged between two locations is asfollows

D. Reset feautures of MSDAC

The reset arrangement is proposed at three levelsusing Track Sections and Supervisory Track Sections,two of which are automatic reset arrangements andone is manual reset.

1. L -I : Automatic reset with redundanttrack section :

Once the train has cleared both the track sec-tions, and any one of the track sections is infailure state, the track section, which is in clearcondition will reset the one in failed condition.The track section, which is under reset is keptin preparatory mode and the clear track sectioninformation is used to take off the signal.

2. L -II : Automatic reset with Supervisorytrack section:

When a supervisory track section is clear, all thetrack sections falling completely within the ju-risdiction of that supervisory track section canbe assumed to be clear. If any track sectionfails and it’s corresponding supervisory track sec-tion is clear, it will automatically reset the failedtrack section.

In case of automatic resetting with supervisorytrack section, the reset track sections will be keptunder preparatory mode, and the correspondingsignal will continue to be in ‘ON’ aspect, until atrain with low speed enters and exits the tracksection with equal count at the boundaries oftrack section.

As shown in Fig.2, DN-SPT is a supervisorytrack section which covers all the track sectionsof IB in DOWN direction. If any one of the tracksections fail, within the entire IB, DN-SPT re-sets that track section and keeps in preparatorymode.

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Figure 4: Typical equipment Block diagram

3. L -III : Manual Reset with Line verifica-tion :

In case of failure of Level -1 and Level -2 reset,manual resetting has to be carried out, which re-sets all the failed track sections in the section un-der consideration. One reset box at train sendingstation along with its corresponding Line verifi-cation(LV) box at other station is used to manu-ally reset all the track sections between both thestations of a particular direction of movement.This reset can be done only when Station Mas-ters of both the stations have ascertained thatall the track sections between the stations areclear of trains in that particular direction. Thiswill reset and set all the failed track sections inpreparatory mode. The clearance of train in each

section with balancing of count will make thetrack section clear and bring to its normal modeof working.

3 Power Supply Arrangement

The IB location is provided with a Mini IPS, forwhich the input supply of 230V AC is from UP ATand DN AT. The necessary power supplies for MS-DAC are derived from the Mini IPS. M/s Frauschermake MSDAC works on a voltage range of 19-72VDC. Hence 24V DC supply with suitable current ca-pacity from Mini IPS serves the purpose. In stations,the necessary power supplies are derived from the Ma-jor IPS.

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Figure 5: Vital and Non-Vital I/O between IB and station

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Figure 6: Termination box for DP

Figure 7: Ethernet Switch

4 Cable requirement

Signaling Cable : In the stations, Home & Advancestarter signals are directly fed from the EI/Relayroom with standard signaling cable, with aspect re-peating relays at signal locations. IB Signals at IBlocation are directly fed using a 12x1.5Sq.mm signal-ing cable from Relay Hut, without any repeater relayat site, as the distance is not more than 200m.

Quad Cable : MSDAC evaluator to each DP re-quires 1 quad of 4 conductors. A separate 6 quadcable is used for each DP of dual detection (main+ Stand-by) from the nearest Half location box pro-vided for Signal cable termination at signal location.From IB Hut to Half location box one 6 quad each isused for UP & DN directions.

The media between Station to IB location is dupli-cated by providing 6 Quad cable in addition to OFCcable. The OFC as well as Quad ethernet switcheswork in hot stand-by mode with seamless change overto each other without disturbing the communicationworking.

5 Conclusion

Reliability of conventional IB signaling suffers fromtwo problems. i) The SSDACs are provided withoutduplication, which may lead to intermittent failures,thus making the system less available. ii) Similarlythe Signaling and Power cables provided along the IBblock section are terminated in Quarter/Half locationboxes with atleast 2 RE cuts between Station and IB.These location boxes are in inaccessable locations forcarrying out preventive as well as break down main-tenance. Moreover as the number of location boxesand terminations increases, the probability of failurealso proportionally increases.

In view of the above, in the present scheme it isproposed to provide dual MSDAC for detection oftrack vacancy over OFC and IO-EXBs are used forexchange of signaling information between two loca-tions, duly eliminating signaling cables and RE cuts.

The information / views expressed in this pa-per is of the authors and are based on theirexperience. Comments / observations maybe sent to the author at vreddy.iitk@gmail.com

Shri R Viswanath Reddyis an IRSSE officer of 2010batch. He had received PostGraduate degree from IITKanpur, in Electronics andCommunication Engineeringin the year 2009. He startedhis career in Indian Railwaysas ADSTE/Kadapa in Gun-takal division of SCR in the year 2013. He is currentlyworking as DSTE/Co-ord/Vijayawada.

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