| Following by the rapid development of wireless communication technology, the wireless sensing network system depending on the merit of the flexible and simple system configuration, the convenient maintenance, the remote data acquisition, and so on, has become the focus of studying the strain measuring system applying in large engineering structure. However, the problems in existing wireless scheme including power consumption, the time offset between nodes, and so on, seriously impede the development of itself. In the meanwhile, the constant speed of strain acquisition would waste plenty of energy in the normal time. Moreover, when it comes to emergences, because of the relatively low strain acquisition rate, the actual situation cannot be detected reliable.For the drawbacks of current remote supervision system, after summarizing and analyzing the domestic and abroad relating studies, this article had designed a wireless strain acquisition system with high time synchronization precision. The system can use the low acquiring speed to reduce the power consumption under the normal situation. Nevertheless, when it encounters emergences, it can switch to the high acquiring speed mode automatically with the μs-grade synchronization. This system with low power consumption can guarantee the real-time capability and reliability of system.The results and study content of this article displayed below:1.The development of experimental platform of wireless strain acquisitionIn the hardware, the wireless strain acquisition system depending on the CC2530 as the main processor had been designed. The nodes contains strain acquisition circuit, signal conditioning circuit; at the same time, the SD card module was added to implement the data backtracking and avoid data loss causing by the power off; the CC2530 module is used to transmit data wirelessly. The 3G module can transmit the collected data to the Internet, therefore the system can be controlled through Internet; the GPS module was regarded as the base of the synchronization.2.The development of frequency conversion scheme with accurate time synchronizationThe foundation of system bases on the pulse per second from GPS. After nodes collecting the clock information of the coordinator, nodes can evaluate and adjust its own crystal drift to complete the time synchronization. In normal circumstance, the system uses the adaptive time window with twice weighing synchronization algorithm and the low acquiring frequency to reduce the energy consumption; When acquired strain exceed the threshold, the system can switch to the rapid acquisition model automatically. In this case, the system uses the least square method applying to the time synchronization, which not only can ensure the major resource of nodes applying to the strain acquisition, but also it can monitor the structure in high speed under the premise of high precision of time synchronization. This design has good adaptive ability and can provide supports towards the diagnosis of structure damage away from scene.3.The experimental test of wireless strain acquisition systemThrough the actual monitoring experiments, the stability and reliability of system had been tested. The precision of time synchronization between nodes can be controlled under 30μs through this plan. Compared with the expensively ms-grade scheme on the market, it has a great advantage in expense and precision. Furthermore, the experimental result of the reliability of data transmission has proved that the system has good immunity from interference. In addition, the precision of strain acquisition can be limited under ±1.5με. In conclusion, the system can meet the requirements of large structure monitoring in the aspects of the precision of strain acquisition, synchronization and the acquisition rate. |
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