TRACK TECHNOLOGY
Michael Collett, a research scientist at the UK’s National Physical Laboratory (NPL) assesses the performance of Wireless Sensor Networks (WSNs) for environmental, acoustic or structural health monitoring.
T
he UK railway network is the oldest in the world. It consists of more than
10,000 miles of track, 2,500 stations and 40,000 bridges. It is designed to serve more than 1.3 billion passenger journeys every year.
Asset holders often have specifi c structures of interest, which they would like to characterise and understand. Critical bridges, embankments and tunnels are often inspected by hand, which can be expensive and time-consuming as well as only giving a snapshot of what’s happening over time. Distributed monitoring technologies such as wireless sensor networks (WSN) offer the potential to continuously gather data from remote and hard-to access locations.
NPL is the UK’s National Measurement Institute, providing independent and highly accurate measurement expertise and technology to benefi t industry and society in the UK. Through this role, NPL helps companies to have the confi dence required to successfully commercialise new materials, techniques and technologies.
For example, NPL recently worked with wireless sensor network developers Senceive. It helped them understand and improve the performance of their system. Senceive’s main application area is long- term infrastructure monitoring. The company’s meshed systems of wireless sensors are used to assess the condition of railway structures, track and bridges. The sensors are able to provide valuable information on the behaviour of the structures, potentially informing usage and maintenance. Wireless sensor networks
are highly complex embedded systems, so it can be a challenge to quantify the uncertainties involved. As the system is designed for structural health monitoring- type applications, generating reliable data is critical so Senceive asked NPL to help them improve their products by understanding their measurement challenges.
Initially the company needed NPL’s help to improve their tilt sensing system and verify its accuracy, precision and limits. NPL characterised the output of the tilt sensors in terms of linearity, jitter and overall uncertainty. NPL
also offered
advice on system improvements and on future deployments, giving a greater understanding of the measurement issues faced in preparing for an upcoming large- scale deployment.
The results from the work have given Senceive the confi dence of knowing how their sensors perform with real data to back up their datasheets. The company has now carried out a number of monitoring projects for Network Rail to detect such events as bridge strikes, changes in track geometry, or embankment landslides.
Such systems are also being used to learn more about understanding the long-term performance of structures. Being able to understand the response to loading and environmental conditions and how this changes over time could give invaluable information to inform usage, maintenance and future designs.
To develop understanding in this area and investigate emerging systems and technologies, NPL has developed a full-
scale demonstrator - a 15-tonne, fi ve-metre high, 20-metre long concrete bridge and one of the largest specimens ever tested at the laboratory. Researchers have over 150 sensors of 18 different technologies and are investigating the response of the bridge, and the sensors, to environmental and mechanical loading.
The results will provide real benefi ts to how we monitor critical structures within the rail infrastructure. Firstly, it will speed up the uptake of combined and multi- modal monitoring methods that support total life-cycle management of structures. Secondly, it will be used as reference specimen to provide sensor suppliers a test bed to assess the performance of their techniques throughout the year in varying climatic conditions. The bridge is representative of many bridges currently used in the UK’s transport infrastructure in terms of construction, age and exposure to corrosion. Due to this it will provide the basis for planners and surveyors to develop lifetime predictions for similar structures.
Maintenance and inspection programmes have to reveal potential problems well in advance to be truly effective. The work NPL is undertaking with its partners will help to supplement inspection and assessment procedures undertaken by staff. As monitoring systems become more distributed, remote and autonomous, understanding the performance is critical if the full benefi t of this technology is to be realised.
FOR MORE INFORMATION E:
Michael.Collett@
npl.co.uk
rail technology magazine Apr/May 11 | 167
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