The bridge's health monitoring system requires 24 hours of continuous monitoring of a large number of different types of signals, and accurate and synchronized acquisition of vibration signals. This not only requires the collection terminal to have good openness, flexibility and stability to integrate different types of data collection modules for unified continuous collection of different types of signals, but also requires the collection terminal to provide high-performance clock and trigger synchronization functions. At the same time, the harsh marine environment and the impact of bridge deck road conditions also put high requirements on the environmental adaptability of the collection terminal.
Solution:
The solid CompactRIO control platform is used to establish a distributed real-time monitoring system to monitor the bridge 24 hours a day. In addition, the VI 6011 developed by Juxing can receive GSP signals and synchronize the time base.
Complete case analysis With the development of regional economy and engineering technology, and in order to meet the increasing traffic demand, more and more regions in the world began to build large bridges. According to statistics, in China, there are more than 60 extra-large bridges across the Yangtze River, and there have been many cross-sea bridges that have been built, are under construction or are in the project stage, such as Donghai Bridge, Hangzhou Bay Bridge, Humen Bridge . These bridge facilities not only have to resist natural disasters such as the impact and corrosion of seawater and rivers, earthquakes and typhoons, but also withstand the slow damage caused by various vehicles to the bridge structure. In recent years, many bridge collapse accidents at home and abroad have caused the relevant departments to attach great importance to the safety of bridges. Long-term health monitoring of bridges can allow bridge maintenance personnel to take timely measures on the abnormal conditions of the bridge, not only to extend the service life of the bridge It has also ensured the safety of people's lives.
A mature collection and recording system
Based on the NI CompactRIO hardware platform, we used NI LabVIEW to develop a multi-channel digital strong earthquake recorder suitable for all-weather seismic monitoring. The recorder can be distributed and expanded through the network to form a monitoring network, which provides the lowest level of data support for the monitoring, analysis and prediction of seismic signals.
Multi-channel digital strong earthquake recorder provides 16 & TImes; 3-channel acceleration signal access interface (including 16-channel accelerometer calibration signal output), external trigger signal interface, GPS antenna interface and Ethernet interface. The chassis and controller of the system are respectively selected cRIO-9104 and cRIO-9014; 3 cRIO-9205 are selected to collect 16 & TImes; 3-channel acceleration signal; 1 cRIO-9403 is selected to access external trigger signal and output 16-channel accelerometer Calibration signal; select a VISN GPS C87 (VI 6011) developed by Juxing Instruments that meets the cRIO module interface standard for GPS signal reception and time base synchronization.
The software structure of the system consists of two parts: data acquisition and communication. The data collection part can be divided into data collection module, data collection engine and data trigger engine. The communication part is composed of data interface, control interface and status interface. When implemented in LabVIEW, these different engines and interfaces are independent VIs that are executed by dynamic calls from the upper layer. This can take advantage of the multi-threaded nature of LabVIEW to avoid mutual blocking interference between various modules.
All of these engines and interfaces are implemented on the RT of cRIO-9014. They respectively complete specific tasks in real time with certain time characteristics. The cRIO-9401, cRIO-9215, cRIO-9203, and cRIO-9871 modules collect data on the corresponding signals on the FPGA of the cRIO-9104, with hardware-level synchronization, timing, and triggering features. They transfer the collected data to the data collection engine on RT through DMA for downsampling, filtering and other preprocessing.
GPS synchronous acquisition, remote processing is no longer a problem
In order to meet the requirements of bridge modal analysis, each data collection terminal needs to accurately and synchronously collect the vibration signals of the bridge. For the bridge health monitoring system, the distance of each data collection terminal is more than 100 meters, and the traditional master-slave terminal synchronization collection scheme is no longer applicable. We use the GPS synchronous acquisition solution based on cRIO-9401 and cRIO-9215 to solve the problem of synchronous acquisition of remote terminals. Specifically, we configure a GPS receiver for each data collection terminal, which respectively acquires the GPS absolute time signal and PPS second pulse signal that have been synchronized with the satellite, and sends it to the serial port and cRIO-cRIO-9014 of the corresponding collection terminal 9401 Collect, synchronize and count. We built a digital phase-locked loop and synchronous trigger module on the FPGA of cRIO-9104. With reference to the PPS second pulse signal introduced by cRIO-9401, through a series of hardware-level phase-locking, counting and triggering mechanisms, we ensure that different terminals All cRIO-9215 (including cRIO-9203) accurately and synchronously acquire the vibration signals of the bridge with the same frequency and phase sampling clock at the same absolute time.
Conclusion
Based on NI's excellent CompactRIO hardware platform and powerful LabVIEW software platform, we successfully developed a multi-channel digital strong earthquake that integrates uninterrupted data acquisition, strong earthquake signal recording and real-time transmission, strong earthquake signal warning and other functions in a short time Recorder, and successfully used in the monitoring of Shenzhen Bay Bridge, Jimei Bridge, Humen Bridge and many other sea-crossing bridges. In the past, almost all such equipment relied on the whole set of imports. The high cost burden and technical constraints have restricted the further development of our national defense and disaster mitigation work to a certain extent. The successful launch and application of a multi-channel digital strong earthquake recorder based on CompactRIO has filled a technological gap in the domestic seismic monitoring field. While various performance indicators have reached similar international advanced technology products, it has reduced application costs and formed an independent Intellectual property software and system products.
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