Design and application of digital earthquake monitoring system for nuclear power plants based on LabVIEW and PXI technology

　　During the three key periods of the Ninth Five-Year Plan, the Tenth Five-Year Plan, and the Eleventh Five-Year Plan, my country spent billions of yuan to build a national digital seismic network and crustal movement observation network, and implemented the China Earthquake Digital Network Project, in order to further study and understand the various internal mechanisms of the earth. Earthquakes always deal the heaviest blow to mankind. my country is one of the countries that suffers the most from earthquake disasters. In the 20th century, China accounted for 35% of the earthquakes above magnitude 7 that occurred in the world.

　　This article introduces a nuclear power plant digital earthquake monitoring system based on virtual instruments, which was successfully developed using LabVIEW, PXI technology and seismic measurement sensors. By using the LabVIEW system development platform (including signal processing software) of the American NI company, advanced PXI technology and seismic measurement sensors, a nuclear power plant digital earthquake monitoring system based on virtual instruments was successfully developed in a relatively short period of time, which strongly supports the development of China's nuclear power plants. The monitoring system has powerful seismic signal processing functions, rich and diverse information expression, and a friendly human-computer interface. Its main functions are to monitor the change of earthquake acceleration over time in real time and distinguish true and false earthquakes. When the earthquake signal exceeds the alarm threshold, it displays and records the peak value of earthquake acceleration and sends an alarm signal to the main control room; collects and records earthquake acceleration response time history data, calculates the acceleration response spectrum and design response spectrum of basic ground equipment, and compares them with the theoretical design response spectrum to verify whether the seismic design of seismic class I structures and equipment is reasonable, or to determine whether it is necessary to carry out post-earthquake inspections on certain items.

　　A virtual instrument is an instrument based on a computer. The close integration of computers and instruments is an important direction of instrument development at present. Roughly speaking, there are two ways to achieve this integration. One is to install a computer into an instrument, a typical example of which is the so-called intelligent instrument. As computer functions become increasingly powerful and their size becomes smaller, the functions of such instruments are becoming more and more powerful. Instruments with embedded systems have already appeared. Another way is to install the instrument into a computer. Relying on general computer hardware and operating systems, various instrument functions are realized. Virtual instruments mainly refer to this method.

　　Principle of ground motion measurement using basic ground equipment

　　Assume a single degree of freedom model of basic ground equipment as shown in Figure 1:

　　The two-order Newton forward interpolation formula is used to perform numerical calculations on the above equations (7), (8) and (9), and finally the acceleration response spectrum curve of the ground equipment is obtained.

　　According to the provisions of the ASME code, based on the calculated acceleration response spectrum curve, the peak points of the acceleration response spectrum are broadened by ± 15% of the frequency, and then connected in parallel to generate the corresponding design response spectrum curve.

　　Digital seismic monitoring system for nuclear power plants

　　At present, the basic framework of the earthquake network computing support platform has been completed, and the functions of computing application resource registration management, task distribution and scheduling management, cluster computing resource management, user authentication and access management of the computing application system have been preliminarily realized. The parallel reconstruction of the computing model and the design of the application program of "loading and unloading response ratio time-space scanning earthquake prediction", "anisotropic crust-mantle structure inversion", "crust stress field analysis" and "tectonic deformation field simulation" have been basically completed, and the network computing application test has begun. [page]

　　The main functions of the nuclear power plant digital earthquake monitoring system are:

　　(1) Real-time monitoring of the change of earthquake acceleration over time and identification of true and false earthquake signals; when the earthquake signal exceeds the alarm threshold, the peak value of earthquake acceleration is displayed and recorded, and an audible and visual alarm signal is sent to the main control room for the duty personnel to decide whether to issue an alarm or shut down the reactor;

　　(2) Collect and record the time history data of the ground earthquake acceleration response, calculate the acceleration response spectrum and design response spectrum of the ground equipment, so as to understand and verify whether the seismic design of Class I seismic-resistant structures and equipment is reasonable, or determine whether it is necessary to carry out post-earthquake inspection on certain items;

　　(3) Display and print the collected seismic acceleration signals and the data and graphics obtained through analysis, and store them for archiving.

　　System Components

　　The earthquake monitoring system is composed of LabVIEW6i, PXI-1010, PXIPCI18335, SCX1102, PXI3031E, MXI-3, Signal Processing Suite, triaxial acceleration sensor, industrial control computer and laser printer from NI Corporation of the United States (Figure 3).

　　Digital earthquake monitoring system platform

　　● Digital earthquake monitoring system panel

　　The digital earthquake monitoring system platform panel is shown in Figures 4 and 5. The system platform uses the tab page turning function of LabVIEW. The functions of the monitoring system are clear at a glance, and the relationship between the functions is clear and easy to select. For example, as shown in the panel of Figure 4, the monitoring system is in the earthquake monitoring function. At this time, the acceleration time history in the three directions of the free field, -15m and 11m foundation ground is measured and displayed, and the maximum and minimum values ​​of the acceleration are displayed at the same time. Figure 5 shows the calculated earthquake acceleration response spectrum of the equipment on the foundation ground at -15m and 11m in the free field when the damping ξ is 2%.

　　The main functions of the seismic signal analysis software completed by LabVIEW and signal processing package are: seismic signal conditioning, acquisition, storage, judgment of true and false earthquakes and alarm; generation of equipment calculation response spectrum and design response spectrum, and comparison of design response spectrum with theoretical response spectrum, and finally output of complete seismic data file.

　　The following example illustrates the application of joint time-frequency analysis and wavelet analysis in seismic signal analysis software.

　　● Joint time-frequency analysis

　　For the analysis of earthquake signals, in addition to knowing the amplitude and frequency of earthquake acceleration when an earthquake occurs, people also need to know the change of earthquake frequency over time during the earthquake period, that is, it is necessary to conduct joint time-frequency analysis on earthquake signals to obtain the relationship between earthquake frequency and time. We applied the joint time-frequency analysis software package of LabVIEW and used the earthquake test bench of Tongji University to simulate earthquake signals and obtained the frequency-time relationship of earthquake motion. Figures 6 and 7 are the analysis results obtained by using the STFT and ConeShaped algorithms. It can be seen from the figure that in the time range of about 0-20 seconds, the center frequency of earthquake motion is about 1.5HZ, and at about 8 seconds, the earthquake frequency is about 3.0Hz.

　　● Wavelet analysis

　　Since 1986, wavelet analysis has developed rapidly, and its application has gradually become more and more extensive. It has also achieved extraordinary results in noise elimination, weak signal extraction and image processing. Figure 8 (a) is the original data, Figure 8 (b) is the reconstructed signal, (c) is the signal after high-pass filtering, and (d) is the seismic signal after low-pass filtering. Applying wavelet analysis technology, the high-frequency and low-frequency parts of the signal are "refined and amplified", and the seismic signal after low-pass filtering (d) is clearer.

　　in conclusion

　　This paper applies advanced virtual instrument technologies such as LabVIEW and PXI from NI of the United States. LabVIEW provides many controls that look similar to traditional instruments (such as oscilloscopes and multimeters) and can be used to easily create user interfaces. The user interface is called the front panel in LabVIEW [2]. Objects on the front panel can be controlled by programming using icons and connections. In a relatively short period of time, a digital earthquake monitoring system for nuclear power plants based on virtual instruments was successfully developed. The digital earthquake monitoring system for nuclear power plants integrates computer data acquisition and processing of earthquake signals, has a large signal processing capacity, and intuitive and diversified data expression. The successful development of the digital earthquake monitoring system for nuclear power plants has strongly supported the development of China's nuclear power plants.