The Design Of Bridge Strain Monitoring System Based On Vibrating Wire Sensor

With the rapid development of economy, there is tremendous achievement in our country bridge building. Inevitably, the bridge structure was damaged and its resistance was attenuated due to the destroy effect of environment. More and more people concerned how to measure and monitor the health of bridge. Through the monitoring and evaluation for the state of the bridge structure, the bridge healthy monitoring system will send out pre-alert signal when the bridge is under special climate, special traffic condition and the serious exceptions of running condition, and it analyses and evaluates the bridge life and supplies scientific evidence for the maintaining and management policy.At first the paper introduces the study background and the development actualities at home and abroad of the bridge strain monitoring, pointing out that the method in the paper has more advantages than traditional methods. Then the paper makes a deep study on the characteristics of vibrating wire sensors, including the analysis of the working principle and temperature characteristics of vibrating wire sensors, and thus providing a theoretical basis for the temperature compensation principle of vibrating. Then we analysis the functional requirements of the system and compares the advantages and disadvantages of various acquisition methods, a kind of disperses collection and centralized management's system structure is given, the structure includes 3 parts, that is field data acquisition subsystem, remote transmission subsystem and monitoring center subsystem. Finally, according to the working principle of vibrating wire sensors we complete the design of system's hardware circuit and software. The thesis emphasizes on the design of circuit to exciting coil and inspection circuit of vibrating wire sensor by analyzing the mathematical model of the vibrating wire strain sensor and its working principle. The exciting coil of sensor uses technology of hardware sweeping frequency to excite coil, the measurement of frequency uses equally accurate measuring frequency. Considered the effect of temperature, a measuring method based on ratio for sampling and the conversion of voltage to frequency is used to measure the temperature, to realize compensation of temperature. Two RS-485 bus conversion interfaces have been designed for the PC-side and MCU-side of the system, through converting signal circuit of RS-485/RS-232, PC can achieve multiple-access remote data acquisition and remote control. Based on the hardware, we have finished the design of software, including the slave device MCU software, the master PC software and the communication software between the MCU and the PC.According to the actualities of the bridge structural health monitoring, the paper aims at real-time, long-time and precision, designs a real-time bridge strain data acquisition system. The system uses vibrating wire sensor as the detection components, and makes full use of advanced microprocessor technology, modern communication technology, computer technology to achieve multi-point acquisition, data cable transmission, integrated processing and control of the detection process for the detected signal. And thus make a correct assessment for the health state and security life of bridge structure. So the system has theoretical significance and practical significance for many building's maintenance and security monitoring.