The hidden role of embedded computing in rail

PCBs are used everywhere, in all but all the simplest of electronic products, to mechanically support and electrically connect electronic components.

A basic PCB consists of a flat sheet of insulating material and a layer of copper foil, laminated to a substrate. The copper is divided into separate conducting lines - called tracks, circuit traces or pads - through chemical etching. This allows connections to pass between the layers of copper between solid conductive areas. It creates a more compact and reliable system compared with discrete wired enclosures, and also improves the overall reliability of the system.

Typical rail applications for PCBs include: in media converter boards that are  copper to fibre; isolated power supplies; multimedia gateways; or systems that monitor vibrations and other data from train engines or the rails of the track.

The latter scenario is where we might encounter the 'spilt coffee effect'. In such instances, data from vibration measuring computers, that are bolted inside the train, can be referenced. These log the amplitude, position and time of the fault. The data can then be assessed to determine whether the disruptive vibration was caused by the train’s wheels, the track or damaged components or infrastructure.

Flexible design

Since 1983, Recab UK, part of the international Addtech group, has been at the forefront of designing and manufacturing bespoke computer systems, including PCBs and enclosures, for Original Equipment Manufacturers (OEMs) and system integrators.

Heat is usually the biggest consideration when designing PCBs for extreme applications, like rail environments. In terms of designing the board, this entails laying out the components in such a way that heat generating components are not near other components that may be affected by heat.

Another requirement is that some power signals to the board’s inputs and outputs (I/O) must be isolated; after all, extreme rail environments can present extreme voltages in some cases. Recab UK tries to ensure that all analogue or digital I/O requirements are satisfied, within the desired voltage widths and ranges. This is where power filters designed for use with direct current to direct current (DC-DC) connections can be used according, to the RIA12 standard for protecting electronic equipment from transients and surges in DC control systems.

Cost is another primary driver, of course, and Recab UK puts cost-effectiveness at the forefront its design, development and supply for customers. This entails quick turnarounds, in terms of designs and prototypes, at a good price. Also integral to this is the company’s policy to develop long term relationships with customers by providing reliable products, quality system builds and responsive after sales services - all in line with BS EN ISO 9001-2008 Quality Management System requirements.

Recab UK’s product development is reinforced by extensive testing. Specifically, through the use of a temperature chamber that tests the PCBs, operating normally while specially-designed software exercises the memory, at temperatures of between 40 and 100°C. Testing can take place over periods of 24 to 48 hours to ensure there are no errors or out of the box failures.

Going underground

A good example of a system designed for the harshest of rail environments is the D2666 rugged rail computer. Essentially a boxed PC, the D2666 can be fitted under train carriages and used to record data from cameras and sensors - in the case of the latter, to monitor sound, vibrations or other data. The boxes have been shown to work reliably for many years.  

The design and development of the D2666 arose from an instance where a customer - the operator of a large underground rail network - approached Recab UK with a requirement for customised boxed PCs. These were to be fitted to trains and used to record data from cameras and sensors, including accelerometers and microphones, within the underground network.

The operator’s existing units had contained circuit breakers with a manual trip; a person would have to get under the train and flip it back on. The customer’s requirement was to replace this Circuit breaker arrangement so that, if the resettable fuse tripped, it would only need to cycle the power - or, turn the computer off then on again - to reset the fuse.

As well as being designed to fit to the underside of a train carriage, the boxed PCs needed to be able to work effectively in all conditions. Again, heat was the primary consideration here and certain fuses had to be selected that would work at high temperatures - as the hotter resettable fuses get, the lower the trip value.

The system would also have to use off-the-shelf I/O cards equipped for CompactPCI - the computer bus interconnect for industrial computers - with the assurance they would work reliably within the sealed, rugged and compact system enclosure. Furthermore, it would have to link up to a modern PC running Intel Core i7 and Solid State Drives (SSDs), and be compliant to EN50155, the international standard covering electronic equipment used on rolling stock for railway applications.

The development of the D2666 therefore married readily-available components with bespoke design. Recab UK took an off-the-shelf CPU board and conduction-cooled enclosure as a basepoint. The customer wanted all Ethernet to and from the box to be run over fibre, so a converter card was designed for this.

To meet RIA12 railway requirements, a customised power input filter board was designed. Additionally, an I/O transition card was designed to sit between the external connectors and the various internal CompactPCI cards. The boxed PCs are connected together by multiple MIL-DTL-3899 connectors. These are designed for power, signal and fibre optic applications in harsh environments, and are used frequently in military-grade applications.

Passenger comfort

While a passenger carriage or driver compartment isn’t as 'extreme' an environment as under the train, there are very strict regulations around power isolation, extended temperature range - again, units are sealed away from others to avoid 'interaction' - and radio frequency interference RFI/electromagnetic interference (EMI) emissions and immunity. That’s in order that these systems don’t interfere with any of the trains safety critical systems.

The D2557 railway grade computer can be used in these circumstances. The system was originally designed for passenger WiFi service provision; but Recab UK is now working on new designs to support 5G modems and provide more computing power, still in environmentally sealed and rugged units.

This type of system combines a powerful embedded processor, Ethernet switch with Power over Ethernet (POE, where electric power passes along with data through twisted pair Ethernet cabling) support and a removable SSD. Such systems are commonly-deployed for on-train CCTV applications, where WiFi or long-term evolution (LTE) connectivity is sometimes also needed, to enable offload of the video content without physical access to the drives.

Because of the power and space constraints of a train and the need for controlled emissions and power filtering, it’s common to design bespoke systems for on-train applications, using complete off-the-shelf (COTS) building blocks. They include COMexpress - the computer-on-module integrated and compact PC that is used much like an integrated circuit component - specifically, Compact Type 6 modules or, for smaller units, COMexpress Mini Type 10 modules.

Looking ahead

Going forward, DPI predicts an upswing in demand for PCBs driven by requirements surrounding the Internet of Things (IoT) and the need to mechanically support and electrically-connect components.

Britain’s exit from the European Union may also help in driving more inward investment towards UK companies, like Recab UK. For now, its support continues in varied applications where PCBs can prove so crucial - whether it’s monitoring vibrations in underground rail tunnels, or ensuring that passengers’ cappuccinos remain unspilled.