Ladder logic
The ElectroLogIXS interlocking is a
flexible, ‘ladder logic’ driven device
that deploys software written using
the Atkins Signalling Method (ASM).
The introduction of this interlocking in
the UK is intended to remove reliance
on existing interlocking products and
solutions, with the system enabling
the rationalisation and reduction in the
quantity of trackside cabling, along with
many other benefits.
Ladder logic was originally a
manufacturing industry and process
control method to document the
design and construction of relay racks.
Each device in the relay rack would be
represented by a symbol on the ladder
diagram, with connections between
devices shown. Other items external
to the relay rack, such as pumps and
heaters, would also be shown on the
ladder diagram. It then evolved into a
programming language based on the
circuit diagram relay logic hardware.
Ladder logic is now widely used in
other industries to develop software
for programmable logic controllers
(PLCs) that are being used in industrial
control applications. Ladder diagrams
were once the only available notation
for recording programmable controller
programs, but today other forms
are standardised in IEC 61131-3, the
international standard for PLCs that is
over 20 years old and is accepted in
many industries.
Less equipment
The standardisation of equipment and a
reduced number of trackside equipment
location cases is a major benefit, which
will deliver significant capital and
operating savings. There will also be no
reliance on bespoke software languages
used in previous electronic interlocking
technologies, with the system designed
to be future proof, scalable and ETCS
compatible.
Atkins has calculated that resignalling
all of the Feltham signalling project
area using conventional SSI would have
required in the order of 3,000 relays and
450 lineside equipment locations. Using
the new future signalling system, this
will reduce to approximately 130 relays
and 220 lineside equipment locations,
a reduction that will bring with it a step
change in reliability.The solution developed by Atkins is
based on a design using more readily
available non-discipline-specific software
engineers, rather than scarce signalling
designers, allowing the signalling
engineers to focus on the core functional
signalling requirements.
With traditional SSI interlockings, there
was also a large number of data errors
leading to failures resulting in significant
resources required to resolve. So, Atkins
has identified new methods of data
production and testing, using modelling
techniques and empirical processes as
part of their new way of working.
The design and testing of electronic
interlocking data was also taking too long,
so one requirement for the new way of
working was for repeatable data modules,
designed and tested once and then used
many times.
Some current interlocking technology
(SSI trackside functional modules, for
example) are reaching the end of their
life, so new equipment solutions are
also required. An interlocking capable of
communicating with a Radio Block Centre
(RBC) was essential to enable a future,
easy upgrade to ETCS, once compatible
rolling stock is available on a route.
Network Rail’s technology strategy
requires new interlocking technology
to comply with the EN 50128 functional
safety standard (Railway applications -
Communication, signalling and processing
systems - Software for railway control and
protection systems), so the ElectroLogIXS
interlocking creates a new solution that is
designed from the start using EN 50126
(Railway Applications - The Specification
and Demonstration of Reliability,
Availability, Maintainability and Safety), EN
50128 and EN 50129 (Railway applications- Communication, signalling and processing
systems - Safety-related electronic systems
for signalling standards).
FE ATURE 6565