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British Waterways
Control & Commuincations: Falkirk Wheel

The Challenge

·Improve realiability of communications between the wheel's main control station and the controlling electronics on the wheel
·Carry out any modification without shutting down the wheel's operation.

The Solution

·Employ a radio transmission system to replace the existing slip ring system

The Benefits

The new system provides much greater reliability over the original system.

The following extract is taken from an article published in Drives & Controls Magazine.

One of the most stunning Millenium projects in Scotland, the 35m-high Falkirk Wheel boat-lifting system, near Edinburgh, has been plagued with communications problems since it was commissioned in 2002. The Wheel, part of the £85m Millenium Link canal restoration project, moves two 22m-long gondolas - each carrying one or more canal boats and 300 tonnes of water - between a high-level canal and a lower one. The wheel has effectively replaced 11 locks that previously linked the Forth and Clyde Union canals.

Communication between the Wheel's main control station and the controlling electronics on the two gondolas is critical. Data is transmitted continuously to provide the instructions for each step of the complex process needed to operate the wheel safely and efficiently.

Soon after the Wheel began to operate, it became clear that achieving reliable communications was going to be difficult. Originally, slip-rings were to transfer data between the Wheel's main structure, and between the main axle and control colum. Despite frequent replacement of of the brushes and refurbishment of the slip-rings, problems persisted and were exacerbated by the use of two seperate slip-ring systems.

Laplace Control Sysyems, system integrators based in Glasgow, was asked to investigate ways of improving the communications. Laplace, in conjunction with Westermo Data Communications, reviewed the problem.

Radio was the first choice for a transmission medium, although there were several obsticles to overcome. for example the main control area was located inside a concrete structure which blocked hand-held radio communications and mobile phone frequencies. Also, the rotating structure made the selection of antenna systems tricky, because no direct, sustainable line-of-sight was possible. This resulted in the choice of a semi-directional antenna, and the use of radio signals bounced off the nearby visitor center, as the primary propagation route.

Laplace simulated the interface between the radios and controlling PLC, and non-invasive test system was installed temporarily, using the signal strength and bit-error-rate test routines built into an Elpro RM 805 radio modem. The results from the two-week test were good. Whereas the original systems failed to receive 25-30% of all the message packets, the new system had a sned-and-receive efficiency that was better than 99.99%.

The final installation was completed without interrupting the wheel's operation and has yielded several benefits. First, of course, communications between the two gondolas and the control point are now reliable. During the first few hours of testing, only one checksum error was recorded.

Originally, the communications rate was set at 1,200 bits/s. The radio modems immediately increased this to 19,200 bits/s, resulting in a 16-fold increase in speed, making it easier to resend corrupted packets - if any occur.

Key to the success of the project has been the ability of radio circuitry to resolve the multiple signal paths. The radio system is operating reliably, despite being feet away from mobile phones, walkie-talkies, high-power marine radios and even radar systems.

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