Energy spectrum nuclear well logging instrument based on embedded system

　　Civilian non-power nuclear technology is a high-tech technology that the country encourages to develop. Among them, nuclear logging technology is one of the cutting-edge logging technologies that has developed rapidly with the development of contemporary science and technology and its application in geological and mineral exploration fields such as petroleum, coal, and uranium. At present, there are few domestic instruments suitable for uranium nuclear logging , mainly including the HFC-1 type γ spectrum logging instrument developed by Chengdu University of Technology and the HD-4002 type comprehensive logging instrument developed by Beijing Institute of Geology of Nuclear Industry. Most of these instruments use laptop computers as the control core of the logging instrument system. In order to better adapt to the complex environment of field measurement work and facilitate field carrying and use, this article will use an embedded system based on a 32-bit processor ARM as the control core of the logging instrument system, and develop corresponding software and hardware on this basis.

　　2 Theoretical basis of spectral nuclear logging tool

　　As we all know, there are a certain amount of radioactive elements in the rocks and soil of the earth's crust, and they can spontaneously emit radioactive rays. In nature, these radioactive rays mainly come from natural radioactive elements such as the uranium-238 series, the thorium-232 series, and the potassium-40 series. These radioactive elements have different characteristic γ-ray peaks, such as the characteristic peaks of uranium, thorium, and potassium are 1.76 MeV, 2.62 MeV, and 1.47 MeV, respectively. Therefore, the radioactive element composition at the measurement point can be determined based on the energy spectrum data obtained by measurement, that is, the qualitative analysis of radioactive elements can be performed. At the same time, the content of radioactive elements is proportional to its γ-ray intensity. Therefore, as long as the γ-ray intensity of the radioactive element is calculated, the corresponding radioactive element content can be obtained. The quantitative interpretation methods of radioactive elements mainly include the average content method, the traditional stripping spectrum method, and the point-by-point stripping spectrum deconvolution interpretation method.

Energy spectrum nuclear logging is a non-destructive testing method 　　that determines the composition and content of certain elements in the formation by studying the distribution characteristics of the spectrum of naturally generated or artificially stimulated radioactive rays along the well axis. Energy spectrum nuclear logging instrument is an instrument that uses energy spectrum nuclear logging method to measure the gamma ray energy spectrum in the field and analyze the properties and content of radioactive elements such as uranium, thorium, potassium, etc.

　　3 Overall design of nuclear logging tool

　　Energy spectrum nuclear logging tools must meet the requirements of small size, stable performance, strong functions, high sensitivity, and easy to carry and use in the field. In response to these requirements, the following design scheme is proposed for energy spectrum nuclear logging tools:

　　3.1 Data Acquisition Hardware System Design

　　The data acquisition hardware system is mainly composed of downhole probe, automatic winch and spectrum acquisition circuit.

　　Downhole probe mainly includes nuclear radiation detector, preamplifier, probe housing, power supply, etc. At present, nuclear radiation detectors at home and abroad mainly include scintillator detectors (such as NaI (T1) inorganic crystal scintillator), semiconductor detectors (such as high purity germanium HPGe semiconductor detector, cadmium zinc telluride CdZnTe semiconductor detector), etc. Room temperature cadmium zinc telluride (CZT) semiconductor nuclear radiation detector is a new type of advanced detector developed after scintillator detector. Room temperature semiconductor nuclear radiation detector is considered to be an ideal detector. It has the advantages of good energy resolution of low temperature semiconductor detector and high detection efficiency of scintillation crystal detector. It also has the advantages of small size, light weight and easy to carry. Therefore, cadmium zinc telluride (CZT) semiconductor nuclear radiation detector is selected as the detector of energy spectrum nuclear logging instrument. The probe housing is made of stainless steel material, and it has good waterproof sealing performance, which can meet the normal operation under high temperature and high pressure conditions of logging.

　　The automatic winch is responsible for controlling the movement of the downhole probe, realizing the movement function of the probe in point-by-point or continuous measurement during well logging, and transmitting the depth value of the downhole probe to the embedded system control core.

　　The energy spectrum acquisition circuit realizes linear amplification, adjustment and signal noise removal of the electrical pulse signal output by the cadmium zinc telluride (CZT) detector, and divides the range of the measured pulse signal into multiple pulse amplitude intervals, and then counts the number of processed pulse signals in each pulse amplitude interval to form a count distribution curve of each pulse amplitude. The energy spectrum acquisition circuit is mainly composed of a linear amplifier, an over-peak detection circuit, a peak holding circuit, and a trigger ARM920T processor S3C2410A built-in A/D analog-to-digital conversion. Its circuit structure is shown in Figure 1.

　　3.2 Application of embedded systems in spectral nuclear logging tools

　　3.2.1 Embedded Hardware System

　　The control core ARM920T processor S3C2410A of the spectrum nuclear logging system is a high-end 32-bit low-power RISC microprocessor with a maximum operating frequency of 203MHZ, independent 16KB instruction cache and 16KB data cache. The storage system uses a combination of 2MB NOR Flash, 128MB NAND FLASH and 64MB SDRAM as program running and data storage space. Various corresponding peripheral interfaces are designed, mainly including LCD interface, SPI keyboard interface, USB interface, Ethernet interface, RS232 interface and multi-channel analyzer MCA interface. A 5.4-inch LCD true color display is used. Since the LCD controller is integrated inside the S3C2410A, various types of LCD displays can be easily controlled. [page]

　　3.2.2 Embedded Software System

　　The Bootloader is written on the nuclear logging instrument hardware platform to initialize the target board hardware, provide the operating system with on-board hardware resource information, and further load and boot the embedded Linux operating system. Because U-Boot has a wide range of versatility, U-Boot is selected for transplantation on this hardware platform. The transplantation of Flash driver and SDRAM driver is the key to the successful transplantation of U-Boot.

　　Embedded Linux supports multiple architectures, has powerful network function support, supports multiple file systems, and has rich peripheral drivers. In addition, Linux also has a complete set of tool chains, which makes it easy for users to establish development environments and cross-operation environments for embedded systems. Cut and transplant the Linux operating system kernel on the corresponding hardware platform, and transplant the Linux-based YAFFS embedded file system. The root file system uses the YAFFS file system, which has the characteristics of fast speed and low memory usage. It comes with a NAND chip driver. YAFFS is a log-structured embedded file system designed specifically for NAND flash memory and is suitable for large-capacity storage devices.

    3.2.3 Design of monitoring terminal based on MiniGUI

　　MiniGUI is a lightweight graphical user interface support system for real-time embedded systems. It is widely used in handheld information terminals, set-top boxes, industrial control systems and industrial instruments , portable multimedia players, query terminals and other products and fields. The monitoring terminal of the spectral nuclear logging instrument is written based on the MiniGUI graphical interface development library, which realizes the functions of spectral data collection, spectral curve display, data file management, spectral data analysis, etc. The basic structure of the monitoring terminal of the spectral nuclear logging instrument is shown in Figure 2.

　　3 Conclusion

　　This paper aims at the development trend of nuclear logging instruments at home and abroad, combines the characteristics of portable instrument field work and the development characteristics of embedded systems, takes the high-end ARM920T processor S3C2410A as the core, and transplants the embedded Linux operating system, YAFFS file system, MiniGUI graphical interface development library, writes the Bootloader system boot code, writes the device driver, and writes the logging instrument monitoring terminal software based on the Linux operating system and MiniGUI.

　　References

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