British Waterways Scotland' Millennium Link project was a £84.5 million venture to join The Forth & Clyde and Union Canal navigational waterways together. This canal Link gives a sea to sea canal route, meeting at Falkirk and continuing on the Union canal to Edinburgh. Construction started in 1998, with a grand opening and inauguration of the Forth and Clyde Canal by the Prince of Wales on the 26th of May 2001. Funded by The Millennium Commission Lottery Fund, seven local authorities, Scottish Enterprise, The European Union and British Waterways, the re-opening of the whole canal network has been designed to encourage and promote tourism, and to create new opportunities for economic and social regeneration.
Along The Millennium Link, there were seven major obstacles that needed to be overcome by ingenious engineering. British Waterways Scotland set about the task of restoring the navigational canal by developing new engineering techniques to overcome some new and old obstacles in the canal's path. Working with Mitsubishi Electric as its chosen automation and control partner, it took on the challenge of some daunting engineering projects.
One of the first major challenges was the canal bridge at Dalmuir in Clydebank. The canal had not been used since the 1960s when official navigation ended, and here the council had built a new road and bridge over the canal. The road bridge prevented boats from passing underneath. Restrictions meant that the engineering team at British Waterways Scotland had to find another solution.
A unique lock system adopted:
The eventual design was a 'Drop Lock', a concept never used anywhere in the world before. Similar to normal locks in principle, this system drops the canal's water level in the lock low enough to allow boats to pass underneath the bridge. It then raises the level to the height of the canal when a boat has successfully navigated the bridge.
Using a Mitsubishi AnS PLC system allowed British Waterways Scotland to develop a system that could accurately raise and lower the water levels in the lock, with depths accurate to within millimetres. This creates a smooth operating system using minimum energy at optimum speed. The requirement was to have a 1.8m depth in the new navigable canal sections, and at least a 6m deep working environment for the boats in the locks.
Dalmuir is a completely automated drop lock solution, which uses a Lengthsman to start the sequence of events. When the process is started, the Lengthsman ensures that operation rules are adhered to by canal users. For safety reasons the operation is controlled by two Mitsubishi E200 HMIs. Each HMI controls one side of the lock only. When an operator wants a boat to enter, he or she goes to an E200 HMI terminal on the boat entry side, selects the action required and the AnS PLC takes care of the rest. The HMIs are connected to the PLC via an A1SJ RS422 module. This allows remote mounting of the HMI up to 500m. The HMI displays to the operator all real time water levels, gives operation instruction and advice, and provides all process statuses.
Safety barrier operation:
As boats enter the lock, a large boom is set across the canal. The boom prevents boats from trying to enter the lock without supervision. This also provides a safety barrier if the boat does not stop in time; gate breaches during operation are very dangerous. The PLC raises the appropriate inlet boom and opens the appropriate lock gates to allow a boat to enter.
Another variable height safety boom is set between the lock gate and the bridge, preventing boats from going under the bridge if the water level is not low enough. This process is controlled by the AnS which calculates the speed of raising and lowering to ensure accurate height control.
The height of the water level in the drop lock is monitored by a pressure sensor which constantly sends data back to a 12 bit A1S analogue module on the PLC that controls the whole filling process. A pressure sensor is used rather than a level sensor as it is unaffected by surface movement such as wind. The analogue module also reads pump current measurements. These are used to help calculate lock pressure levels.
The filling speed of the lock is controlled precisely by the PLC which increases flows gradually, stopping boats in the lock from being moved around in the swell that would be produced if not managed carefully. Emptying is also controlled by the AnS PLC.
A vertical lift bridge:
Some of the other complex obstacles along the length of The Millennium Link included a minor road crossing the canal at Bonnybridge. Here the engineers choose a vertical lift bridge (again the world's first), to allow boats to navigate this stretch of the canal. The 'Lift bridge' is lifted up by four huge hydraulic cylinders which use a Mitsubishi FX2N PLC system to control all operations. A E300 HMI is built into the bridge control podium. This shows the Banksman the status of the bridge and displays all alarm indications and sensor readings. The FX2N PLC monitors the position and pressure of all four hydraulic rams and compensates by increasing or decreasing pressure on the appropriate cylinder, ensuring the bridge raises smoothly and simultaneously to the correct height. The whole process is entirely automatically controlled.
Other major obstacles were overcome by creating swing bridges, a single leaf bastiol and a sea lock which together brought life back to these important navigational waterways.
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