Computer Based Interlocking Systems

Challenges faced by Computer based Interlocking Systems

 

1. The wiring from the field object such as Signals, Points and tracks to the SSI Rack is still done using Copper cables which amounts to huge costs
2. The hardware reliability and availability  factor is low compared to the system availability given by RRI
3. The fail safe mechanisms employed  in processor based equipment is not standard and often get untested during V&V activities
4. Lack of formal methods in developing the control algorithms (Interlocking Logic)
5. Lack of domain Knowledge in Signalling and Traditional Route Relay Interlocking Systems, This creates a technological gap between the software programmers and the Domain consultants. This leads to Errors in software, which might lead to unsafe failures of the system
6. Extending the working scope of the Interlocking systems  for monitoring and  other non-Interlocking functions, which leads to degraded performance of the system
7. Employing Non-Formal Interlocking principles instead of traditional RRI Principles leads to software complexity. For Ex: The Geographical method needs every system that is installed for new Yard needs validation, which is not practicable.
8. Since the software and hardware is so complex, complete test of the system is not possible and most of the faults are revealed at the field Installation stage or during normal working of the system in field.
9. The software is to be changed for every yard, the software structure should be in a generic form, but we seldom see a generic form and at this stage errors creep in.
10. The lack of standardization in the railway working principles and the core Interlocking principles, the software developers are forced to do changes in the software for every yard in Different railway zones.
11. Increase in the complexity of the software leads to difficulty in testing, since most of the Interlocking systems are sequential machines they are error prone and are very difficult to test.

With Increasing speed of trains, there needs to be a direct communication with the on board computer of the train (Engine), so that there is less human involvement and thus less human errors. But Interlocking systems are mostly not capable of sending commands to the on board computer of the train (Engine).

 

Any queries mail me at sandeep.patalay@cmcltd.com

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Relay Interlocking

Historical Overview of  V&V of Relay Interlockings:

 

In the past relay interlockings were designed, installed and tested not only under the responsibility of a railway company but were actually carried out by the staff of this railway company. The people involved were educated and trained within the company, often by a training institute which also belonged to this same company. There was on the job training with a strong ‘father to son’ relationship and it took many years before an engineer was given the final responsibility of testing an installation. Common practice was that people required at least 7 to 10 years experience before they were allowed to take this responsibility. There was no official certification of engineers; it was well known who had the capability and experience to be responsible for such a job.

 

The design of a relay interlocking was carried out by a group of engineers and under the responsibility of an independent senior engineer a complete verification of the design took place. For these activities a set of design rules was available, which hardly changed for decades. After the approval of this design the installation was built on site, after which all wires and components were checked. After the completion of the installation, a test was carried out where not only the behaviour of the installation itself was tested, but also the correspondence with the outside elements (signals, point machines, track circuits, ATP-code, level crossings, bridges etc.) was checked.

 

This testing was the validation of the design; it was proven that the behaviour of the installations was in accordance to the (often implicitly) defined requirements for that location. The basis of these tests were not standardised; it was the experience and the knowledge of the senior tester in charge that assured the completeness and correctness of the test and therefore the quality of the final result.

 

Any queries mail me at sandeep.patalay@cmcltd.com

 

DISCLAIMER "The information contained in this e-mail message and/or attachments to it may contain confidential or privileged information. If you are not the intended recipient, any dissemination, use, review, distribution, printing or copying of the information contained in this e-mail message and/or attachments to it are strictly prohibited. If you have received this communication in error, please notify us by reply e-mail or telephone and immediately and permanently delete the message and any attachments. Thank you"