Wireless Sensors for Structural Monitoring

Abstract

A wireless sensor system is developed for structural monitoring purposes. This experimental system includes 5 monitoring stations and a main data collection and system control station. Each monitoring station has an accelerometer of 3-axis. Total number of channels is 15. This system uses 900 MHz ISM band spread spectrum digital radio transceivers for data transmissions. At each monitoring station, the analog signal from sensors is digitized using a 16-bit AID. A custom microcontroller (80C251 series) is designed and implemented to control the data collection and data transmission. A software for the sensor control, data collection, processing, coding, and transmission is inbedded into the microcontroller. A communication protocol is developed for the system. The central station is a PC with a radio module attached. Each monitoring station continuously collects data from the accelerometer, processes the collected data, and transmits processed data to main station when the monitoring station receives a data request command from the main station. The central station receives the data from each substation and stores them in a data file. The received data is analyzed by the main station. If one or more events exist in a period of time (e.g. 10 minutes), the data within this period will be stored. If no event is found, the data will be dropped. Received data can be analyzed using graphic display or computerized analysis. Initial lab tests show that this system is very efficient and reliable. The dynamic range of the wireless sensor is +/−4g, sensitivity is about 5 mg, and transmission distance is about 1000 ft indoor and 5 miles outdoor.