Title: Design Issues and Experiences with BRIMON Railway BRIdge MONitoring Project
Abstract:
Structural health monitoring of railway bridges is an essential but currently expensive proposition. Current systems employing data loggers and analyzers are both labour intensive for setup and require trained manpower for deployment and usage.
In this work we propose a system design for remote, on-demand railway bridge monitoring system which is easier to deploy and autonomous in its operation. The system is low cost, as off the shelf equipments are used and expensive sensing equipments are replaced with Micro Electronic Mechanical Systems (MEMS) based sensors and Wireless Sensor Networks (WSN) replacing the cabling and data logging system for data transportation and collection. Current structural health monitoring systems are essentially wired solution or proprietary single hop wireless solutions. These systems are non-scalable and difficult to deploy on most of the structures. In contrast our approach using independent nodes attached with appropriate sensors and batteries for power make them easy to deploy without hassles of cabling. Using wireless data transmission and multi-hop data transport our solution is highly scalable. Use of low power devices also enable our design to have a longer maintenance cycle than existing methods which may require separate power generation units such as generators.
Due to challenges in wireless data transfer and distributed nature of data collection any designed system should have both reliable data transport and synchronized operation for data logging requirements. A reliable data transfer protocol called PSFS (Push Slowly Fetch Slowly) and an application specific data routing protocol have been designed for this purpose in a separate related work. In this work we focus on the problem of time synchronization and event detection for data collection. Flooding Time Synchronization Protocol (FTSP) has been used for time synchronization to achieve microsecond level accuracy on the multi-hop topology. We have modified the existing implementation to adopt it for our platform and work on the linear topology generated due to deployment pattern over bridge. We show that these modifications reduce the average error at nodes farther from the root as well as improve the network wide synchronization stability. We employ a Wake-on-WLAN based event detection mechanism for detection of incoming train. In our design the train acts both as mechanical shaker for data collection as well as data transporter from remote bridge location to a data repository. The event detection method also turns on the MEMS sensor just in time for data collection thus saving power. Results reflecting the achievable distances for successful operation of Wake-on-WLAN and comparison of MEMS accelerometers with existing Forced Balance Accelerometers (FBA) show that our design is viable for future deployment. Overall our approach achieves more than 96% cost savings over currently used wired solutions.