## long-distance and real-time monitoring of bridges

  
  
Abstract-Aiming at the disadvantage that traditional electrical sensors are not suitable for long-term long-distance real-time monitoring of bridges, this paper proposes an optical fiber bridge safety monitoring data collector based on STM32, which can realize data collection and upload of bridge structure parameters. In this paper,the hardware implementation and software design of the collector are mainly described, and the whole workflow is explained.  
  
Key words-bridge safety monitoring, fiber optic sensor, data acquisition  
I. INTRODUCTION  
As an important large-scale infrastructure, bridges play an important role in the transportation system and to a certain extent show the country's economic and technological strength. However, the complete construction of a large bridge will consume huge manpower and financial resources. Once the bridge is damaged or even collapsed due to construction errors, natural disasters, disrepair and other problems, it will bring great losses to people's lives and property and national economic construction. Therefore, it is very important to maintain and monitor the bridge after completion.  
  
However, most of the traditional methods use electrical sensors for measurement. The output signals of these sensors are weak, nonlinear, have zero drift problem and are vulnerable to electromagnetic interference. This has caused great waste of resources and increased the time and cost of detection. In recent years, optical fiber sensing technology has effectively solved the above problems due to the use of optical fiber as a transmission medium, and has been effectively applied in bridge detection.  
  
II. THE OVERALL DESIGN OF THE SYSTEM  
The overall structure of the optical fiber bridge safety monitoring data collector is shown in Figure 1. the collector is generally composed of two parts, of which the hardware part is the basis for ensuring the normal work of the software part, and is mainly composed of STM32 microcontroller and other basic circuits. The software part consists of each module program, and each module performs its own different functions.  
  
The collector is connected to the spectrum module through a parallel bus, is responsible for collecting wavelength data of the spectrum module, and uploads the collected wavelength data to the host computer according to a certain frame format through an RS232 serial bus.  
  
Fig.1 System architecture  
III. HARDWARE DESIGN  
As shown in Figure 2, the hardware of data collector of bridge safety monitoring based on optical fiber sensing technology consists of main control MCU, power circuit, data storage module, spectrum demodulation module and rs232 serial port module. This design chooses STM32F103ZET6 as the MCU. STM32F103ZET6 is a 32-bit microcontroller, which uses ARM Cortex-M3 high-performance core, operates at aclock frequency of up to 72MHz, and has high-speed memory,rich input and output ports and other peripherals. STM32F103ZET6 also has a static memory controller (FSMC), which can be used to control external memory.  
  
Fig. 2 Hardware schematic diagram  
A.Power circuit  
This design uses 10-30V DC power supply that is commonly used in the industrial field. In order to adapt to the wide voltage input range of 10-30V, the way of switching power supply with linear regulated is used to achieve DC/DC conversion. This design uses LM22679 as the switch power conversion chip, using LM1117 as the 3.3V regulator chip.The circuit is shown in Figure 3.  
  
Fig. 3 Power suppply circuit  
B.Spectrum module interface circuit  
The MCU is connected with the spectrum module by a parallel bus. This design uses the FSMC to control the timing sequence from the hardware level for reading and writing operations automatically.  
  
Fig. 6 Spectrum module interface circuit  
C.Data storage module  
This design chooses AT24C256, it is connected to the MCU through IIC bus.And it has a simple circuit structure.  
  
Fig. 7 Data storage module  
D.RS232 serial port module  
This paper uses MAX232 as the level conversion chip which can support up to 120kbps data transmission rate.  
  
Fig.8 serial communication circuit  
IV. SOFTWARE DESIGN  
As a bridge between the upper computer and the spectrum module, the collector first performs a series of initialization operations after power-on reset, and then waits for receiving the instructions sent to it by the upper computer. The command content will be analyzed only after the verification passes. If the command is collected, the spectrum data will be collected, and then the collected data will be sent to the upper computer through the serial port. The whole workflow of the collector is shown in figure 8.  
  
Fig. 9 system software flow chart  
I. SUMMARY  
In order to monitor the health condition of large bridges, this paper uses optical fiber sensors to measure the structural parameters of bridges, designs and implements an optical fiber bridge safety monitoring data collector with the functions of collection and upload, and focuses on the introduction of its hardware, completing a part of the bridge safety monitoring system. The collector has certain application value for bridge safety monitoring.