Radio modems improve canal link communications

A Westermo Data Communications product story

Edited by the Engineeringtalk editorial team Aug 31, 2004

Radio modems have been installed to improve datacommunications on the Falkirk Wheel, the massive structure that carries canal boats between the Forth and Clyde Canal and the Union Canal.

Scotland's pride, the Falkirk Wheel, was completed in 2002 as the crowning glory of the GBP 85 million Millennium Link Canal Restoration Project.

The magnificent structure stands over 35m in height, and rotates to elegantly carry two huge gondolas - each holding 300t of water, with canal boats and passengers - from the higher waterway to the lower, and vice versa.

The wheel has effectively replaced 11 locks that would have linked the Forth and Clyde Canal with the Union Canal.

Westermo Data Communications was approached to investigate possible improvements to the existing control communications.

Communications between the controlling electronics on the two gondolas and the main station is critical.

Data are sent between the areas continuously, for obvious safety reasons, and also to provide the instructions for each step of the complex procedure necessary to achieve safe and efficient operation of the wheel.

The reliability of the communications proved to be a problem virtually from the start.

Slip ring systems were employed to convey the data between the gondola and the main structure, and the main structures axle and the control column.

But two sets of slip rings offer the potential for twice as many errors.

Despite frequent replacement of brushes and refurbishment of the rings, problems persisted, to the frustration of all concerned.

Westermo was called in by Laplace, its Scottish systems integrator, to evaluate the site and see if an option was available to improve the situation.

Radio was the immediate choice of medium, although initially it looked like a major challenge with several obstacles to overcome.

The main control area deep inside the concrete structure was a problem as this blocked handheld radiocommunications and mobile phone frequencies.

The rotating structure made the selection of antenna systems a little tricky, as no direct sustainable line of sight was achievable.

This resulted in the selection of a semidirectional antenna, and the use of reflected radio signals - bounced off the adjacent visitor centre - as the primary propagation route.

Laplace, from its Glasgow head office, simulated the interface between the radios and PLC, and a noninvasive test system was temporarily installed, making use of the built-in signal strength and bit error rate test routines in the RM805 radio modem.

A two-week test was initiated.

The results were stunning.

The existing systems failed to receive between 25-30% of the total message packets sent, and by comparison the test showed a send and receive efficiency greater than 99.99% - a totally insignificant total error count.

It was then decided to proceed with the fitting of the Elpro RM805 series radios to upgrade the communications.

The final installation was completed without interruption to the wheel, and coming up to its busy tourist season, yielded a number of benefits.

First of course, the quality of the communication links between the two gondolas and the control point became reliable - perhaps for the first time.

During the initial two hours or so of testing, at high datarates and under working conditions, only one CRC checksum error was recorded by the central PLC.

The standard communications rate of the system had previously been set to 1200bit/s.

This was the most successful setting over the slip rings.

The radio modems went straight in at 19,200bit/s.

This gives a 16x increase in speed, allowing for a considerable number of resends of any corrupted packets (if ever required).

This application is a testament to the quality of the Westemo's Elpro radio modem Completech antenna combination, along with the engineering efforts of Laplace and Westermo.

Key to the success of the project is the ability of the radio circuitry to resolve complex RF signals - the result of multiple signal paths.

Secondarily, of course, the selectivity and noise immunity are important, with the radios and antenna operating just feet away from mobile phones, walkie-talkies, high-power marine radios and even radar systems.

The integrity of the data is assured with robust digital protocols developed by Elpro.