Design Of Metal Detector Based On Balance Coil Technique

Metal detector is a kind of using the principle of electromagnetic induction, eddy current effect and so on detection of metal equipment, ore metal impurities(iron, copper, stainless steel, etc.) signal is induced by it, then the equipment alarms, and metal has been dropped.From the war of resistance against Japan’s mine detector to now mining production, food processing, etc, metal detector is widely used, action is more and more big, functionality and performance very attention by customer. Nowadays, high precision, fully functional metal detectors rely mainly on foreign imports, but the price is very expensive, technology strictly confidential. So, in view of the above problem, this paper designs a kind of relatively high accuracy, good stability, relatively low cost’s metal detector. It is not sensitive for high magnetic conductivity and electrical conductivity of material, so it can be applied to the place which traditional detector would produce the unacceptable high false alarm rate.This paper describes the development of metal detector, detector development present situation at home and abroad as well as the advantages and disadvantages are expounded.Using circular electric coil magnetic field characteristics, this paper analyzes the general balance of circular coil magnetic field distribution and deduces the metal into the coil coil magnetic field changes before and after the launch.According to the use of this topic research the probe field, probe using improved balance coil model is used to improve detection precision and increase the system stability. Based on the improved balance coil theory, this paper designs a new type of metal detector,which consists of control circuit, DSP, display circuit, probe and so on, and sensitivity can be adjusted. For the control circuit part, pulse signal through the gate and MOS tube production has the characteristics of less power consumption, strong anti-jamming capability, received signal through filtering and amplification, peak holding, signal conditioning, AD transform etc. can accurately reflect the features of testing materials, as far as possible eliminate interference, increase the stability. For the software design part, paper shows the flow chart of each module program, mainly to achieve self learning system, data processing, parameter Settings and calibration, signal alarm and display, and the digital filtering part design on the analog filter is added. For the probe part, the size and the position of transmitter coil and receive coils should be designed accurately to ensure their credibility and stabilization.On the basis of the hardware circuit and software program perfect, controller, probe and support parts has been installed into a complete metal detector. Through laboratory and field two stages of commissioning, it shows the effect of metal detector test and stable performance. And it indicates that the metal detector can work in the stable under the condition of high sensitivity and puts forward some improving measures.