Research On Key Technologies Of Wireless Sensor Network System For Structural Strain Monitoring

Engineering structures are indispensable for daily life of people, so its safecondition, durability and function attract more and more attentions recently. In order tomonitor the structure stress, the most effective way is strain measurement, becausestrain is the most important index of structure health condition. Most of the currentstrain measurement systems are wired, and site wiring is time-consuming duringassembling and disassembling period and difficult to extend. These disadvantages limitthe popularity of the wired system.Wireless sensor network (WSN) is a burgeoning research subject in the last decade.It is unnecessary to consider wiring by using this technology, which makes the gaugingpoints can be assembled soon and relocated freely, so WSN is applied in structuralhealth monitoring (SHM) systems. The obvious feature of WSN is that wireless node isdriving by batteries, so low power consumption is an essential requirement. Strainsensor is resistive element with high power consumption. The precision and powerconsumption restrict each other in the system, so it is a big challenge to get the balancebetween them during hardware design. Meanwhile, large scale structure is consisted ofmany components which are complex in the formation and function, which makes thestrain gauging points have the feature of large number and scattered distributed. A hugenumber of wireless nodes are needed to measure large scale structure, so it’s anotherchallenge to organize the network effectively.This paper has done some researches as follow to solve the key problem ofwireless structural strain measurement system.①Firstly, it is discussed the composition of analog and digital processing circuit,and the main influence factors of precision and power is calculated quantificationally.The expression of system precision is got by combining the error factors, and it showsthat the main factor is bridge voltage. The expression of system power is got bysumming power of each part of the circuit, and the way to reduce power is proposed.Then, the balance of precision and power can be got with diagram analysis base on thequantitative relationship between precision and power. The parameter of each element isoptimized for strain measurement. At last, the global system indexes and requirementsare determined.②The wireless network protocols in common use are classified with the analysisin their function and feature, and ZigBee is chosen to be the most suitable one which fits the requirement of WSN well. It is analyzed the topology models of wireless network,as well as the morphology characters of large scale structure. After that, it is proposedthe network topology for wireless structural strain measurement system, and the repairmechanism is studied to avoid communication disconnection caused by router failure.③The architecture of wireless node is designed based on theory analysis ofgetting balance of precision and power consumption. There is trade off betweenprecision and power consumption, which is considered during circuit design of the nodeand some novel circuit models are used with parameters and types of the elementsdetermined strictly. Meanwhile, the strain sensor is designed. The wireless node andcoordinator are embedded systems, and the software processes are designed withrequirements of data rate and network capacity. The software working on the PC of themonitoring center is designed, either.④To test the system design, some experiments are carried out, which areprecision and power test, comparison of wired and wireless systems test, stability andad-hoc of multi-node test. The sensitivity, linearity, precision and power are measuredby doing tensile test of a metal girder with WSSMS. The comparison result is got bymeasuring strain simultaneously. The drift of the strain is recorded by loading a fixedforce in long term. The network topology and networking time are observed wheninitialized multiple nodes one time.In this paper, it is analyzed the key technologies of WSSMS, which are balancemethod between precision and power, wireless network organization for large scalestructure. It is designed the network topology for large scale structure and proposed theoptimizing strategy for route repairing. Hardware and software are designed accordingto these theories. This research is supposed to not only guide design of low powerconsumption circuit, but also provide reference to popularize wireless technology instrain measurement.