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Product category: Mid-range and Large PLCs
News Release from: Mitsubishi Electric Automation Systems | Subject: Bekonscot Model Railway
Edited by the Engineeringtalk Editorial Team on 04 March 2002

Train control is a model solution

A Mitsubishi PLC has brought a touch more realism to the UK's largest model railway.

The picturesque Bekonscot Model Railway at Beaconsfield, Buckinghamshire, is miniature in size only - and even that is debatable with over 450m of Gauge 1 track serving the Lilliputian towns of the Bekonscot Model Village Weaving it's way through some 3715m2 of landscaped garden; it is the most extensive outdoor public model railway in the UK

When it comes to its operation and function the railway is very much full-sized with some features that would make some real railway networks quite envious! Back in the early 1990s Beckonscots Railway was controlled in a manner befitting the Village's 1930s setting.

Unfortunately this led to parts of the track network never being used unless it was operated manually.

Moreover the visual appeal of the railway was severely impaired by unrealistic 'power on/off' train control and an unsightly 3rd rail attached to the track.

Bekonscot's fervent engineering team decided on a modular long term strategy to expand and completely modernise the railway, including its whole control philosophy.

This work had to be carefully phased, as it was not practical to have the major engineering works carried out during the open season to the public.

One of the engineering team had recently carried out a similar process in his full-time career for a railway signalling and control engineering company.

His company had decided to use Mitsubishi Electric products and services.

A main factor in their consideration was the recognition of Mitsubishi's policy of futureproofing its products, making them all backwards compatible, including software and programming.

Just as the "real world" railway, the Bekonscot team faced similar concerns and consequently also decided on Mitsubishi Electric as their partner in this long-term venture.

The first stage of the automation plan was to develop the "prime" signalling and train control system.

The Bekonscot engineers decided on using a Mitsubishi AnSH high-speed modular based PLC.

This PLC now controls the smooth operation of the entire railway track network.

The signalling functions managed by this PLC prevent train collisions and maximise the rail network capacity and service.

The train control manages the velocity of trains through each of the signal sections, obeying the signal status and, if required, additionally stopping the trains at station platforms.

It also manages the switching of 32 points and crossings giving a choice of over 40 routes along the track system.

Within the physical bounds of the track and signalling more than 16 trains can be simultaneously handled, quite comfortably, with the system minimising conflicts and hence not delaying trains.

To establish the position of each train the PLC monitors over 60 track occupancy zones.

The PLC sends, via custom interface boards, a 60V impulse signal to the track sections.

Since this process has to take into account resistance changes between the track rails, which vary considerably, detection is achieved by means of a "virtual short circuit".

"Virtual" because the impulse signal has to be mixed in with the 30V PWM motor power control that is also sent to the same track sections.

The pulses are too short to damage or power the locomotive motors, but enable occupancy detection within a section via a single discreet component carried by each and every vehicle that makes up a train.

The 30V PWM motor power is achieved with custom interface boards.

Due to the combinations of DC powered motors, rated between 40 and 100W, the drive and worm screw gearbox, the use of brass running rails for current pick-up and changeable environmental conditions, each train on the network has different and constantly varying driving characteristics.

This can be a problem and lead to the model equivalent of SPADs - signals passed at danger! The System has four operation modes, two manual and two automatic, with all four able to work quite happily together.

The first of the manual systems uses a Mitsubishi Electric Scada system to monitor, configure and manually command train movement.

The operator or signalman is shown a graphical representation of the track network, depicting which track zones are occupied and by what.

By clicking a mouse button the signalman can select any desired route, if available (no conflicting routes set).

Once a route has been chosen the Prime system controls the movement of the train through the route, switching all necessary points and also lineside animations such as model semaphore signals and level crossing gates.

The first of the automatic running modes is known as automatic routing setting (ARS).

When initiated, the ARS looks at the position of each train, decides which routes are available and how close to capacity advance areas of the network are.

Routes are then set for each train accordingly.

The ARS system does not discriminate what type of train is in each position, its main control philosophy being only to avoid conflicts to keep as many trains as possible moving at any one time.

The most recent stage of development of the system has provided the other two operating modes.

The "extended train operator" system uses a Mitsubishi AnS series PLC and is networked via Melsecnet B to the "prime" system.

Interfacing to this PLC is a genuine, full size 1950s Westinghouse signal lever frame which provides a more traditional manual control solution.

The lever frame is housed in Bekonscot's replica signal box, and functions exactly as it did when it was controlling trains through Purley in Surrey.

Basic signal and interlocking status is displayed to the signalman, some on the frame and others on an authentic track diagram above.

All points are moved and signals cleared, if not locked, by pulling the levers within the frame.

Signalling status indications are given to this system and the returning commands interpreted to produce route-setting calls.

This allows the railway enthusiasts to signal trains in the historic manner of yesteryear.

The final, and second automatic, train operating mode is known as coded routing setting (CRS) and is by far the most advanced mode.

The CRS has the same basic control as the ARS, but actually discriminates between each train to then select a predetermined route and station-stopping list.

The way the CRS identifies each individual train is by scanning a barcode mounted on the underneath of one of the vehicles making up the train consist.

This barcode also tags what type of train it is; freight, fast/local passenger etc.

to enable routing conflicts to be resolved based upon a trains priority within the system.

All of this information is then used to send route calls and station stopping flags to the prime system.

If a train is halted due to derailments (a common problem with young children so close to the trains), mechanical breakdowns, point failures etc, the CRS system is designed to reroute trains around the problem area so as to again keep as many trains running as possible at all times.

The barcode readers are housed under the track in the train storage area and read as the train departs the storage area ready for service and usually once per 'circuit' of the track system.

Additional barcodes attached to the locomotives allow the automatic train control in prime system to identify the associated locomotives mechanical performance characteristics.

This is then used as part of the automatic calculations to determine acceleration and deceleration rates that ensure accurate stopping at signal berths and at platforms - so fewer SPADS! The signalman can interact with the CRS through the Mitsubishi Scada system.

The signalman can interrogate the system for details of the train service provided, including what route the CRS requires for each train and where it will call at, thus enabling him or her to manually route trains through parts of the system without disturbing the operating pattern.

If he or she does, the system will attempt to route the train back onto its predetermined path as soon as possible.

A host of other useful information is available based on the CRS knowledge of individual locomotives and trains, for example, detailed information on "run times"; which is an important consideration as a locomotive may cover up to 5000km during an average season.

Using this information, the engineering team can ensure that locomotives receive regular maintenance and inspections.

For a final touch of realism an MP3 player has been added as an integral part of the CRS.

Just like a full size railway, announcements are made at the stations as to what is happening.

The MP3 player is driven off the barcode information.

The trains are now announced before they arrive and when they are leaving, stating their destination, route and at what stations they will call.

The Bekonscot engineering team felt they needed advanced control systems that allowed the modernised railway control system to be designed and built with flexibility.

The operating benefits that the technology has delivered are numerous, ranging from minimising the effects of perturbations, to freeing up skilled staff for more productive tasks.

In the 8 years that Bekonscot has been using Mitsubishi Electric equipment to control the track and the train routing, it has had trouble free control operation.

It has also been able to upgrade its application without fuss (due to the backwards compatibility of Mitsubishi Electric's products), with the bonus of superb quality and reliability.

The Bekonscot staff have always prided themselves on running competent rail service.

They take great care in the systems operation and even though the railway at Bekonscot is a miniature one, it is as reliable and flexible (if not more) as a full size railway network.

With the continued support of Mitsubishi the team is now looking at further enhancements and new additions to their system, all aimed at presenting an ever more impressive display of model train operation to their visitors. Request a free brochure from Mitsubishi Electric Automation Systems ...

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