The Development Of Stray Current Detector In Coal Mine Based On Magneto Resistance Effects

This paper is an important part of "Research on the Distribution of Stray Current and Its Detection and Prevention Technologies in Sihe Coal Mine Power System", a scientific and technological project funded by JINCHENG ANTHRACITE MINING GROUP in Shanxi Province (project number: JMJS-JS-2012050), which is carried out in the context of frequent accidents, backward detection methods, unsatisfactory functions of relevant detection equipment in China’s coal mines caused by stray current. With the rapid development of China’s coal mine, higher requirements have been put forward for all kinds of underground disaster warning and prevention. In recent years, fire and explosion accidents resulting from stray current have accounted for a large proportion of various accidents. However, the research on stray current in domestic coal mines is lagging. The existing detection technology and equipments have poor security, low detection accuracy and poor anti-interference ability, which are not conducive to network analysis and remote monitoring. As a result, the development of a stray current detector to achieve high-precision and real-time detection of stray current is of great practical significance to the governance of underground stray currentThrough access to large quantities of related literature, identified the detection methods of underground stray current, developed the design scheme of detection equipment, designed the hardware circuit of detection unit, and prepared function programs of various parts of detection equipment. The experimental results showed that the current detection accuracy of this detection equipment met the needs of underground stray current detection. These main contents of this study are as follows:Combined with underground work environment, the causes of the underground stray current are analyzed and summarized. Based on these causes and research status at home and abroad, a detection method based on magneto resistance effect is proposed. The author expounded the basic principles of this detection method, established the framework of the formula derivation of anisotropic magneto resistance effect and related electromagnetic theory, laid the foundation of the detection equipments’design and development.According the principle of high resolution and strong stability, developed the hardware circuit design of the detector, drew the circuit principle diagram of each functional module, designed PCB circuit of each part, including magnetic field/temperature signal acquisition circuit, peripheral circuit of magneto resistive sensor, temperature signal conditioning circuit, minimum CPU system circuit, communications circuit, data storage circuit, clock circuit, display circuit and level conversion circuit, etc., conducted circuit debugging and verified the accuracy of design through experiments.This study also analyzed the refraction law of magnetic induction lines on the surface of magnetic media, designed magnetic gathering devices that bring magnetic fields together and magnetic shielding devices that shields irrelevant magnetic field functions, completed the selection of related materials, introduced the analysis of operating principles, and experimentally verified the functions and characteristics of magnetic gathering devices and magnetic shielding devices through the simulation software Ansoft Maxwell, finally designed the shell with function of magnetic gathering, magnetic shielding and explosion proof.Meanwhile, developed the software design of the detector and used C language and assembly language to write relevant software programs, which include the main program, A/D subprogram, digital filtering subprogram, asynchronous serial communications subprogram (RS-485), human-computer interaction system communication subprogram (SPI) and magnetic data correction subprogram. These programs are written in a modular way so good readability and portability is guaranteed.By means of the laboratory testing platform, the author conducted experiments to verify the characteristics and functions of the hardware circuit and magnetic gathering/shielding devices. The major experiments included magneto resistance sensor output linearity verification experiment, magneto resistance sensor temperature characteristics verification experiment, magneto resistance sensor set/reset circuit performance verification experiment, magnetic gathering/shielding device performance test experiment, detector’s output performance and detection effect verification experiment, etc. The experimental results showed that, the detector designed was able to accurately and stably measure the magnetic field of stray current, which had laid a good foundation for the governance of underground stray current.