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

 

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