Design Of Detecting Underground Metal And Imaging System

With the development of socio-economic and urban, there is a growing emphasison underground metal detection, especially in underground construction, mineralexploration and other fields.There are a variety of methods to detect undergroundmetal in geophysical field such as COD, seismic imaging method, electricalexploration. Each method has its characteristics and application areas. In contrast tothe various geophysical methods，TEM is the final selection.The underground metal detection system is a all-in-one device，based onprinciple of TEM. It consists of transmitting device components and receiving devicecomponents. The transmitter coil is accessed step current in transmittingdevice.There are eddy current in metal in the first current pulse.The eddy currentwill not disappear immediately during pulsed intermittent. The metal will form thesecondary magnetic field decayed with time. The law of the secondary magnetic fielddecayed depends on the metal conductivity, volume size, depth, the form of emissioncurrent and the frequency of current. The underground metal distribution can beknown through the secondary magnetic field measured by the receiving coil. The datacollected by the receiving device will be sent to the host computer for data processingrelated work. Finally the surfer imaging can help to determine the circumstances ofunderground metal objects. The whole system is very flexible and has strongresolutions, good stability and low power consumption.Analyzing the characteristics of transient electromagnetic instrument of previous,as well as the current development of new technologies, and consider the practicalapplication needs, this article designed an underground metal detective system. Thesystem chooses ARM as the controller, can quickly communicate with computer byUSB interface, and compatible with RS-232protocols. According to the features oftransient electromagnetic method, larger amplitude and faster decay of earlier signal,smaller amplitude and slower decay of later signal, I select the major chip first withanalyzing external relative factors. Then, hardware circuits of transmitter and receiverwere designed. Considering the characteristics of all-in-one system and the practicalapplication, the work installment has used the small coil overlap return wire, which reduced the weight and increased its flexibility. The key technology of the transmitteris to design the entire bridge connection, and it will have important effects on thetransient electromagnetic signals. Using new transmit bridge IGBT with shorterturn-off time, the needed square wave have been produced, in order to provideincentive magnetic field for receiver. At the same time, overflow protection andcushioning absorption circuits have been designed to ensure the safety of the system.At the receiving unit, signal collection circuits with a large dynamic range have beendesigned, and using24-bit A/D converter to increase the precision of the system. Forthe purpose of massive data transmission, USB interface was used to communicatewith computer. The collected data in computer need to be processed by mathematicmethod, then produce excel and import it into suffer. At last, get the cross-sectionalpictures and the relative information of underground metal.Receiver and transmitter have been made into one system, so it’s easier to use,flexible and convenient for practical detection.