Study On Detection Of Metal Impurities In Electrically Conductive Packaging Materials

Food is a fundamental need for human survival, and food safety problems pose a severe threaten to human survival and development, among which the mixing of foreign substance is particularly prominent. Through a great number of literature and data, this paper illuminated the dangers of mixing foreign matter in food, the development status of foreign substance detection technology, as well as the research significance of metal foreign substance detection in conductive packaging materials. By constructing the calculation model, this paper conducted the qualitative and quantitative analysis on the effect of eddy current on metal foreign substance detection in conductive packaging materials. The metal foreign substance packed in aluminum foil could not be effectively detected, because the aluminum foil packing may shield the high frequency magnetic field. For this issue, this paper proposed using low frequency magnetic field to detect the metal foreign substance packed in aluminum foil. Through the nonlinear characteristic of the magnetic field, this method generates tiny low frequency magnetic field by applying voltage to the test coil, and then generate tiny low frequency magnetic field, which will be taken as the detection field. It then detects the metal foreign substance through analyzing the output voltage of the test coil, so as to detect the metal foreign body foreign body.The results show that it is feasible to test the metal foreign substance packed in conductive packaging materials through the method of microscopic magnetic field detection. The test coil could achieve a better distinction degree under the best testing frequency, and it can detect the metal foreign substance. When use single coil in the test, the best distinction degree could be obtained under the testing frequency of 5.5 kHz; when use twin coil in the test, the best distinction degree could be obtained under the testing frequency of 7kHz. The distinction degree obtained by the twin coil is significantly higher than that of single coil, and the coil detection The size of the metal foreign substance does not affect the best testing frequency of the coil; the most testing result will be achieved when it is close to axis of the test coil.Based on the hardware design and production, this research has completed multiple output regulated power supply module, the signal producing module based on FPGA, and the data processing module based on STM32. On the software programming, it used Verilog HDL language and C language to control the FPGA and the STM32, respectively. On the digital filtering, it adopted an algorithm which combined the limiting amplitude wave filter and arithmetic mean filter, and realized the accurate output of the signal.