Lessons learned about wireless technologies for data acquisition

In recent years the electronics for developing sensor networks have become compact and cheaper. This has led to an interest in creating communities of distributed sensors that can collect and share data over a large area without being physically connected by wires. The Intelligent Systems Center at the University of Missouri-Rolla (UMR) has for several years been using commercial off-the-shelf (COTS) hardware and custom software to develop a system of stationary sensing nodes capable of pre processing their data locally and sharing processed data to produce global details. This distributed sensing and processing array is targeted for use in monitoring a wide variety of infrastructures. It has been laboratory tested for use in civil, automotive, and airframe monitoring. This paper is an overview of the technologies investigated and the level of functionality obtained from each hardware/sensor/target set. The current system consists of a web server, a central cluster and a collection of satellite clusters. The central cluster is a PC104x86 based computer with the satellite clusters being 8051 based single board computers. The satellite clusters are of the order 6"x5"x2" in size. There is an effort under way to place a short-range radio with a processor and a PZT sensor into a 2"x1.5"x.5" package. Exercises have been carried out to demonstrate the ability of the central clusters to remotely control the satellite clusters and the web server's ability to control the central cluster. Further work is under way to integrate the entire system into a web server attached to the Internet and to a long distance communication device, currently employed is a cellular modem into the monitoring array. The web server communicates over standard phone lines to the central cluster, which is equipped with a cellular modem. The central cluster communicates with the satellite clusters using short-range wireless equipment. Proxim rangelan, Erickson Bluetooth, and Linx Technologies RF modules have all been tested as short-range wireless communication solutions. We have demonstrated a system that consists of a structure with an array of smart sensors, preprocess and collect data, and post this data on a web server for global inspection and manipulation. This will enable data sharing and collaborative data analysis to extend the knowledge of structural health monitoring.