Signalling and control equipment assets normally have an expected service life of around 40 years. During the early stages of an asset’s life, the original equipment manufacturers (OEMs) are supportive with training for user staff, technical support and spare parts. However, as time progresses, OEMs tend to focus on new products, components become difficult to obtain or obsolete, both OEM and in house expertise reduces, and technical drawings and information become lost.

Not all the subsystems suffer the same issues and, while the overall asset condition may be acceptable and not justify re-signalling, there may be equipment whose reliability and performance deteriorates. So what’s to be done?

Fortunately, there are companies which specialise in this problematic area. One is Park Signalling Limited (PSL), based in a very impressive two floors of a refurbished mill in Reddish, Stockport, with excellent views across the Pennines.

Incidentally, the company is just a short distance away from Reddish South station, on the Stockport-Stalybridge Line, famous for having only one train a week in one direction! Don’t let this stop you visiting, however, as Reddish North is a more normal station with a regular service to Manchester Piccadilly. Even better, why not visit on a Friday morning via Reddish South and be one of the estimated 26 people a year who use the station, and then walk back down the hill to Heaton Chapel?

The company was formed in 2000 by key staff from the Manchester office of Alstom Signalling, and used the name Park after Trafford Park. Today, many of the engineers are still with PSL so the Company has many years’ experience of signalling systems which is supplemented by a number of associates and specialists who are called upon to provide expertise.

PSL operates in three main markets – extending useful life and enhancing performance, system upgrades and enhancements, and designing bespoke products and systems. The company has the capability to reverse engineer, replicate the form, fit and function of the existing equipment and remove obsolescence issues by using retro-engineering skills. PSL combines the service of supporting and designing new facilities and technology into old systems, while at the same time looking to the future, with developing innovative systems and products for both main line and metro.

SSI support

Many of the PSL engineers were responsible for the original design and development of SSI (solid state interlockings) for GEC/ALSTOM. They continue to design, develop and manufacture ‘smart tools’ that support and improve SSI, including test and repair. Knowing the design of SSI from first principles, combined with extensive specialist equipment resources, allows PSL to identify and diagnose the root cause of reliability and performance issues.

SSI accounts for approximately 45% of UK interlockings and is used throughout the world.

It is highly likely to be in use for many years to come, despite being a 30 year old electronic and software product. The typical life for this sort of technology in other industries is 10 years, so it is vital that the support that PSL provides is available for many years to come.

One aspect of SSI that heavily impacts on signalling availability is that the data links are remarkably tolerant of problems and performance issues which can be masked by the SSI diagnostic processor which only reports a complete failure.

There are standalone equipment systems available that monitor missing telegrams, but the systems require a technician to be present to read and assess the resultant output. ‘REMITdetect’ is PSL’s solution to monitor and report missing telegrams to a remote computer via a web-based programme. The system provides not only a continuous count of missing telegrams but also a count for individual telegram addresses, which
is particularly helpful in diagnosing the location of specific data link faults. This sort of facility is expected and standard on any modern computer- based system and is now available for good old SSI.


tt2 [online]

SSI data links are notoriously difficult to fault find, particularly when there are multiple faults present such as following a lightning strike. The current Network Rail maintenance regime requires that SSI data links are tested on a regular basis, which is expensive and time consuming. ‘REMOSdl’ is a tool to monitor the baseband links and (potentially) eliminate the need to carry out regular checking. It provides faulting assistance when data link problems occur, allowing faster restoration of the link, and monitors the ring actual data link performance, enabling viewing, analysing and recording, locally. Recordings can be wirelessly transmitted to allow more in-depth remote viewing, analysis and recording, via the ‘REMOSdl Viewer’.

PSL provides a data link modelling service where designs are theoretically tested for performance and robustness where the actual performance can be verified later, with the data link smart tools. Whilst this service is most useful in eliminating causes of faults, it is invaluable in pre-empting possible problems resulting from data link changes during system upgrades and/or new schemes.

REMITdetect and REMOSdl complement the SSI Data Link Analyser (SLA). This is a PC-based test tool that also provides the means to observe and record all messages being transferred on a Data Link in real-time. It has become the recognised data link analysis tool over the last decade.

Fibre optical cables have long been used in railway telecoms networks for the higher order SDH (Synchronous Digital Hierarchy) multiplex transmission systems carrying many gigabits of data. These networks carry SSI links and are able to provide diverse paths for the A and B SSI circuits. However SSI has very sensitive propagation time delay, which other systems carried over the telecoms network are not subject to. Hence, what is a fault to the SSI may not be picked up by the telecoms network diagnostics and monitoring. REMOSdl can diagnose such changes in circuit delay as a result of alterations to the path length due to diverse routing within the telecoms network.

Even with using telecoms based fibre optic networks for the higher order LDT (Long Distance Terminal) links, SSI has to be multiplexed down to a 64kbit/s connection for the data link distribution over twisted copper pair cables. The conventional copper data links are highly susceptible to interference and attenuation so PSL has developed an Optical Data Link Module (ODLM). This maintains plug compatibility with the original Data Link Module and allows the final data link to be connected by fibre. While this may appear wasteful to a telecoms engineer, it removes the conventional copper-wired data links which are highly susceptible to interference, attenuation and theft. The product has only recently been developed and, whilst UK benefits are obvious and will be exploited, there is already keen interest from countries with high instances of lightning strikes.

The original SSI Technicians Terminal from the 80s, with its green monochrome display and command text-based menu, is like something from another age (which it is in computer terms!) and is now obsolete. PSL has developed a modern replacement Technicians Terminal for up to six SSIs. This uses standard commercial off the shelf components, but is directly compatible at the electrical interfaces and replicates the feel and functionality of the original terminal with a modern graphical colour user interface.

The Technicians Terminal Replacement supports SSI logging and provides an external clock interface, and allows control and fault lists to be printed. It allows a user to perform all the functionality of the old Terminal through a user-friendly means of applying and removing technician controls including the stop/starting of interlockings, route barring, aspect disconnection and temporary approach control.

The system of PSL smart tools supplements the capability of existing SSI- based asset watch systems to detect and identify faulty data components, including data link modules, isolating transformers, surge protection units and cable faults and incorrect terminations.

Not just SSI or main line

PSL has life extended and enhanced other systems as well as SSI and one example is the Radio Electronic Token Block (RETB) which will still be used in some parts of the network for many years to come and was needed to interface with TPWS (Train Protection & Warning System). Currently, PSL is contracted by Telent to perform RETB works for the Far North Split contract for Network Rail.

The Trackside Radio Control Module (TRCM) forms part of the Trackside Radio Control Unit (TRCU) which interfaces TPWS with RETB signalled areas.

The TRCM ‘listens’ to the RETB radio traffic, using up to two radio receivers, in order to detect tokens transmitted for the particular sections that the TPWS equipment is protecting. Once an appropriate token has been detected, the TRCU will suppress the TPWS trackside equipment for a pre-determined time period to permit the train to pass over the train stop without being unnecessarily tripped.

PSL supports metro railways as well as main line. As part of an extensive network extension programme and signalling system upgrade for Manchester Metrolink, a temporary method of controlling junctions was required. PSL provided three temporary signalling interlockings to control Trafford Bar, Irk Junction and the single line at Dean Lane. Although the interlocking function was implemented using conventional relays, the PSL design was novel in that treadles were used for tram detection and the existing Vehicle Recognition System (VRS) was used to call the signalled routes from the tram. Treadle and conflict management was implemented using a Siemens programmable logic controller. The system was designed, manufactured and deployed within six months. It has proved very successful and has been in service for over two years.

And it’s not just about old stuff!

PSL’s own concept and innovation ideas include methods of controlling train movements using new technology and ways of working. These REMOS 5 [online]could be used to supplement the digital rail ETCS vision, for degraded mode operation or lightly used secondary routes. Verbal Exchange Radio Block (VERB) minimises, as far as reasonably possible, the quantity, complexity and cost of specialist railway signalling equipment fitted to track and trains, while maintaining safe, efficient railway operation.

The VERB concept is based on communications solely via audio channel radio and data channel to the limited trackside infrastructure.

One of the most unique systems in PSL’s portfolio is Virtual Lineside Signalling (VLS) ‘signals as pictures’ – which is a low-cost centralised signalling system with affordable operational enhancements primarily suited to, but not exclusively for, secondary and lightly- used routes.

This is achieved by using encrypted pictures, propagating central integrity out to commercial- off-the-shelf train-borne in-cab signalling equipment. Lineside signals and conventional train detection and train protection would be replaced with Radio Frequency Identification tags and/or GPRS to significantly reduce lineside infrastructure installation and maintenance requirements, and their costs, whilst increasing track availability.

There are circa 2,200km of secondary and rural track in the UK network, much of which would not normally attract enhancement investment. VLS would save somewhere in the region of £120,000 per kilometre in investment costs and £1,200 per kilometre annually on maintenance costs. So, if just one-fifth of Britain’s secondary and rural lines were signalled with VLS, there would be a saving of £57.3 million over the first five years when compared to conventional resignalling.

Track safety

As well as the smart tools for extending the life of systems, PSL has developed a number of innovative products including the very welcome introduction of new technology for track safety. ‘Vigil’ is a sentinel system for user worked crossings. Conforming to the Overlay Miniature Stop Lights for User Worked Crossing specification, Vigil ‘eavesdrops’ on the SSI data detecting track circuit occupation and operates the crossing miniature stop lights and audible alarm. Event logging and status reporting is also provided for an audit trail.

Optonator® provides a cost-effective track worker protection system, delivering a clear warning of approaching vehicles. This simple, completely independent, battery-powered product uses a fibre optic cable to detect approaching vehicles and remotely alerts track workers via an alarm siren and flashing siren.

It is a simple battery powered, hand-carried solution that provides protection against runaways, addresses procedural errors and rules out misunderstandings. Its continuous monitoring provides failsafe vehicle detection utilising wireless technology effective over 800 metres and is an effective alternative to conventional detonators providing advance warning of possession incursion directly at the work site.

Other markets?

Whilst PSL have a strong presence and reputation in the UK and business is developing overseas, in particular Australia and Indonesia, the company is keen to continue to develop and provide smart tools and techniques to keep the old stuff going, while looking to the future with new ways of working and other markets. Due to the parallels with the rail sector, this will include the power industry that has similar issues.

The views from the third floor of the mill in Reddish are spectacular, so why not take the unique journey (9:22 Fridays-only train from Stockport to Stalybridge – one way – and calling at 9:27!) to Reddish South and pay PSL a visit if you have a project requiring innovation and new ideas.