Clear communications keep elevated motorways safe

Posted on 1 Jul 2014 by Tim Brown

The cathodic protection of elevated motorways north of Birmingham has been upgraded with a new remote monitoring and control system, based on more than 30 industrial PLCs (programmable logic controllers) feeding into a SCADA (supervisory control and data acquisition) software solution developed by Tritec Developments and Mitsubishi Electric.

Tritec Developments Ltd, of St Helens, developed the system in conjunction with Cathodic Protection Co. Ltd, the UK’s leading experts in impressed current cathodic protection of large structures.

Cathodic protection is a technique for controlling the corrosion of metal by making it the cathode of an electrochemical cell. Impressed current cathodic protection systems are used with large structures and their transformer-rectifier units are often fitted with remote monitoring and control, integral current interrupters and other features.

As part of the motorway project Tritec designed a module which provides data transfer to a local Mitsubishi Electric FX series PLC. The modules are built into small, impressed current cathodic protection units alongside the PLCs and supplied to Cathodic Protection.

These are installed on each of over 30 bents, the enormous reinforced concrete columns that raise the roadways above ground level. The PLCs communicate over telemetry links to a remote control centre, where the data is coordinated on a Mitsubishi MAPS SCADA solution running on a central server computer.

Tritec is recognized for its expertise in both control systems engineering and electronic product development. Specialisms include project management, design of control systems, electronics, software, firmware, opto-mechanical solutions and product compliance testing, all of which have been applied in manufacturing, aerospace, the nuclear industry and medical equipment.

As well as the module design Tritec also devised the system, developed its architecture and designed the electronics and firmware for all the MODBUS slaves that power the solution.

The Mitsubishi Electric FX PLC is a workhorse of many industries. The original model was developed over 30 years ago by Mitsubishi for controlling production lines in its own factories in Japan. It quickly proved its worth in-house, so was launched onto the global market to immediate acclaim. It has been updated and redeveloped several times since and has always maintained its position as the worldwide market leading compact PLC.

The Mitsubishi Electric FX3U variant that was used in the project was the world’s first dual system-bus, high-speed, fully expandable compact PLC
The Mitsubishi Electric FX3U variant that was used in the project was the world’s first dual system-bus, high-speed, fully expandable compact PLC.

The FX3U variant that was used in the project was the world’s first dual system-bus, high-speed, fully expandable compact PLC. It is designed to seamlessly control communication, networking, analogue and positioning systems. With up to 384 controllable local and networked inputs/outputs (I/O), the FX3U uses its power and flexibility to provide a solution for an enormous variety of applications. Most usually found controlling manufacturing and processing machinery, its logic switching operation means it has also been used in applications as diverse as stage sets, theme park attractions, retail displays, laboratory experiments, medical equipment, exercise and training equipment, etc.

Similarly, Mitsubishi’s MAPS SCADA has a distinguished industrial pedigree and can be found in manufacturing plants, power stations, waterworks and many other high-tech applications where multiple functions need to be controlled and synchronised with the utmost precision. Like the FX, it also finds uses in non-industrial fields, such as controlling multiple functions in airports and other large facilities, energy management and lighting control in TV studios.

The MAPS SCADA software provides an essential toolbox for visualisation, trending, alarm management and reporting. The software is scalable, so has been used on simple stand-alone equipment as well as multiple networked systems with many thousands of I/O.

For the communications between the PLCs and the MAPS SCADA, Tritec Developments used Mitsubishi’s M2M Machine to Machine communication driver.

M2M communication has expanded beyond a one to one connection and changed into a system of networks that transmits data to personal appliances (which is sometimes referred to as the Internet of Things).

The expansion of IP networks across the world has made it far easier for M2M communication to take place and has lessened the amount of power and time necessary for information to be communicated between machines.

The heart of the M2M is an intelligent link driver in MAPS which automatically and constantly monitors the connections between the server and the remote PLCs. Thus there is no need for continuous polling and also the ability to generate instant alerts if the link goes down. This means that management and diagnostic information from each PLC is always available in the control room.

The Mitsubishi M2M driver does not require a fixed IP or DNS middleware, allowing easy configuration. M2M communications expands conventional boundaries beyond one-to-one connection to create a system of networks that transmit data to both the central SCADA and to mobile devices. For the motorway monitoring installation, this means that technicians are not tied to the control room but are free to travel around while maintaining a perfect overview of the whole operation.

The potential for M2M to be used, in conjunction with globally expanding IP networks, in other wide area installations such as utilities, mines and pipelines means high level information can be freely available to engineers, technician and managers whether they are on-site or not.

In use at the motorway control room, an operator at the control desk only has to click on a graphical symbol for each bent to turn it on or off or to measure its current status. So, at a glance, operators can obtain an overall view of the whole flyover in a meaningful format. All the data is also logged so that it can be used for analysis.

Its datalogging facilities are fully automatic, allowing advanced alarm management, automated report generation and many other functions. It can even be operated via a mobile phone or tablet.

The Tritec system is currently being rolled out on the Wigmore Viaduct – a series of colossal concrete constructions supporting the M5 and M6 where they merge – part of the Midlands Link, a critical junction in the national motorways network that is both loved and loathed by the millions of motorists that use them.

Opened in the 1970s, the Midland Links motorway viaducts (MLMV) are a series of reinforced concrete structures, comprising 21km of elevated motorway around the outer circumference of Birmingham. Deterioration was identified early in their serviceable life, due to chloride-induced corrosion of the steel reinforcement.

An electrochemical treatment using an impressed current cathodic protection system was successfully trialed in 1987 with the first large-scale commercial application of the treatment on the network in 1991. These latest protection systems are to replace and improve the protection provided to the structures.