Case Study: Coleshill STW - Storm Tank Serial Radios

Client: Severn Trent Water
Client Contact: Matt Griffin
Date of Project: 25th November - 2nd December 2013

The Site: Coleshill STW is located in the county of Warwickshire, just off Junction 9 of the M42 Motorway. On site are 3 large Storm Tanks which provide relief from large volumes of sewerage during wet weather. The Storm Tanks (each approx 100 Metres long, 20 Metres Wide, >5 Metres Deep) have motorised gantry scrapers which move along the tanks.

Process Issues: The individual gantry scrapers are motion controlled (forward, reverse, raise scraper & lower scraper) by an on-board Allen-Bradley PLC. A Master Allen Bradley PLC providing the process co-ordination and ancillary controls back at the main MCC building. An existing radio link had been installed many years ago by an unknown supplier and it had never been fully operational. This meant that storm tank scraper operations were done by hand, with a Technician using the manual MCC controls on each gantry, to operate them.

Preliminary Works: There is a large mast present on site with many communications antenna's and dishes for third party operators e.g. Mobile Operators. With this in mind we completed a full and thorough radio survey to identify any frequencies that were to be blacklisted / avoided. We then proceeded to manufacture the radio systems at our facilities and provided a full and formal Factory Acceptance Test. A series of large SCADA screen's were used in conjunction with matching PLC processors and racks found on site, to provide proof of concept to the client.

Final Solution: The final solution was the provision of Elpro 805U Radios on a 869Mhz Frequency Range, with new RS232 Ruggedised Serial Cables attaching the Allen Bradley PLC's to the Radio System via DF1 Serial Protocol. Site Acceptance Testing took 1 day with a client ICA Technician present and formalised procedures were carried out such as Loss of Comms Fault Handling, Testing for Safe Remote Control of the Gantries from the Master PLC. We also provided Phoenix Contact IP65 Signal Towers on each Gantry to allow on-site Operators to identify when a gantry had a fault or automatic motion control processes were taking place.