Study And Design For Bridge Structure Data Acquisition System Based On Wireless Sensor Network

In recent years, bridge accidents occur frequently, and bridge SHM (structural health monitoring) allows of no delay. With its self-organization, multi-hop routing and low power consumption, WSN (wireless sensor network) becomes more and more popular in the field of bridge SHM.Data acquisition system plays an important role in the bridge SHM, and is necessary for the bridge structure damage diagnosis and decision. In this article, it designs a data acquisition system for the acquisition of bridge strain signal and acceleration signal from practical aspect. The system consists of data acquisition network, data transmission network and user application interface. And since both data transmission network based on Internet and user application system based on database have been fully developed, the thesis will focus on the data acquisition network based on wireless sensor network. The main work is as following:1) According to the actual bridge environment and the wireless sensor network technology, it designed and developed a hardware platform in the paper, which consists of wireless acceleration sensor nodes, wireless strain sensor nodes, and Ethernet gateway, and mainly for acquisition of acceleration signal and strain signal.2) To meet the demand with high accuracies of time synchronization, it proposed a multi-subnet time synchronization algorithm, which including synchronization in three level in this paper. The first level is subnet synchronization based on GPS official calendar technology, the second level is node level synchronization based on wireless sensor network technology, and the third level is application level synchronization based on embedded technology. The time synchronization algorithm made cooperative work possible for data acquisition network.3) To meet the demand for reliability of the transmission system, it worked out three failure factors:the data sending bottleneck, wireless interference and node failure. In this paper, in order to eliminate the data sending bottleneck, it designed both the packet format to improve the payload transmission speed and local data storage system to ensure the data security; For wireless interference, frequency agility technology and data recovery mechanism are used to avoid interference; For the node failure problem, it proposed energy warning method for failure nodes based on RSSI and LQI, which contributes to self-heal.As experiment indicates, the4-hop time synchronization accuracy of WSN is below100microseconds. And the three unreliable situations of data transmission, data transmission bottleneck, wireless interference and node failure are greatly improved. Analyst strain and acceleration signals which were acquired, and the results show that the signals collected are of good quality and high signal to noise ratio and data precision, which could satisfy the basic needs of bridge structural health monitoring.