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Signalling at the speed of light

Our new IoT control solution holds the key to fast and flexible signalling upgrades.

Railway signalling has become the focal point of modernisation efforts as infrastructure managers look to boost the resilience of their networks. Centralisation is a key trend: Europe’s major networks all have ambitious plans to concentrate control in a handful of digital interlockings – the new electronic “brains” of the railway.

New signalling needs

Centralisation presents a number of technical challenges. One of these is managing field elements, such as point machines and signals. New assets need to be installed and controlled, so cost-effective and standardised interfaces are needed.

Infrastructure managers also need options to link new interlockings to existing signalling assets. This is key, because a large national network may have up to 70,000 point machines and more than twice as many signals . These are capable of providing decades of useful service. 

In tandem with this, there is a growing requirement to reduce reliance on copper cabling. Copper prices rose sharply in 2020 and analysts expect further increases in 2021. Copper cabling not only adds to the cost of new signalling, but also exposes operators to the risk of metal theft. Solutions are needed that use high-capacity fibre optic cable instead.

Introducing Thales Distributed Control Architecture (DCA)

Thales Distributed Control Architecture (DCA) provides railway infrastructure managers with a cost-effective, flexible and standardised way for interlockings to control and monitor safety-critical field elements such as point machines and signals – no matter how far from the interlocking those elements are.


How does it work?

Put simply, DCA acts as a bridge between the digital world (the interlocking) and the analogue world (points and signals). 

The DCA field element controller receives digital commands from the interlocking, typically delivered via a fibre optic cable. When a command is received, the DCA controller switches an electric current to carry out a specific task – for example, to move a set of points or display a green signal aspect. There are no moving parts within the controller: current to the points and signals is switched via solid-state relays rather than electro-mechanical ones. 

As well as allowing the interlocking to control field elements, the DCA controller monitors the status of each field element in real time and reports this to the interlocking – for example, which way the points are set, or which signal aspect is being displayed.

DCA is a SIL4 system and it is built around Thales TransVital™ operating system for safety-critical applications. In common with all Thales solutions, DCA is “Cybersecured by Design”. This means that defence against cyberattacks is built-in to the solution from the ground up. 


From copper to fibre

Railways are moving towards distributed control of field elements. In the distributed model, field element controllers are located in cabinets in the immediate vicinity of the points and signals they control, rather than being housed within interlockings or technical rooms. Data from the interlocking to the DCA controller can be transmitted using dedicated fibre optic links or public networks. There is no distance limitation if dedicated fibre or public networks are used. One of the benefits of distributed control is that it results in a massive reduction in the need for copper power cables. Another is that it makes it easier to expand and adapt track layouts.

An alternative method is to centralise element controllers within the interlocking itself. This is the traditional approach. While this results in much longer power cable runs, it has the advantage of centralising the element controllers, which can ease maintenance. But with most infrastructure managers looking to reduce the number of interlockings, this approach is less and less adopted.

A hybrid arrangement can also be used with a mixture of both distributed and centralised controllers. The beauty of Thales DCA solution is that it permits any configuration the infrastructure manager chooses – controllers can be located in the field or in the interlocking.


Resilience made easy

Thales DCA supports infrastructure managers who require fully redundant systems. A single field element – such as a set of points – can be connected to a pair of DCA controllers to reduce the risk of failure.


IoT in the field

The DCA system generates diagnostics and maintenance notifications. This capability is of increasing interest to infrastructure managers, particularly if data from the field is used in conjunction with predictive maintenance tools. Data from point machines is particularly valuable because analysis of this can detect early signs of trouble, so assets can be repaired before they fail.


Seamless software management

All modern railway equipment requires software upgrades from time to time. This need typically arises when there are topology changes and track reconstructions, or when patches and new software features become available. Thanks to our Remote Upgrade capability, you can easily update and patch DCA software from a central node – with no need to go out into the field. This reduces deployment lead times, allows you to control exactly what software you are running and eliminates the need to send staff out into the hazardous trackside environment.


Interface standardisation


Infrastructure managers need the freedom to mix and match products from a range of different suppliers. They also need to be confident that solutions are capable of working on a plug-and-play basis. To meet these needs, Thales DCA conforms to EULYNX principles on the standardisation of signalling interfaces. DCA supports interfaces for interlocking, points, signals, diagnostics and maintenance.

The future: signalling unplugged?

Thales DCA solution underlines the way that digital technology is helping to accelerate the transformation of railways. But the story doesn’t end there. In the future, mobile radio technology such as 5G could be used to link interlockings with DCA controllers – further increasing flexibility and eliminating the need for fibre optic control cables. Our standardised interfaces are designed to make the transition from wired to wireless as easy as possible.