Design Of Nondestructive Detection System Based On GMR Sensor

Nondestructive testing system is used to determine the characteristics and the defects of the testedobject by measuring the changes of signals such as light, electricity, magnetic, heat and sound,which are caused by the anomalous or defects of the surface or the internal structure of the detectedobjects. Then the system can evaluate various performance of the object. With the development ofmodern electronic information technology and automation technology, nondestructive testingtechnology is becoming a very important technique in the controlling and ensuring the quality ofproduction in the current industrial automation and other aspects of production.Eddy Current Testing (Eddy Current Testing, ECT) is one of the five main methods used innondestructive Testing field (ultrasonic detection, radiation detection, magnetic particle detection,penetration, Eddy Current detection). It has the advantage of non-contact measurement, and will notpollute the environment. Thus, it become mainly used in detecting the surface or internal defects ofthe metal materials and semi or finished products such as some commonly used industrial products,machinery and equipment and are widely used in the aerospace industry, aerospace industry,automobile equipment production, the nuclear power plant inspection, and other important areas.However, conventional eddy current testing system can only detect the surface defects of metalobjects due to the influence of skin effect. At the same time, the data of the test can only beidentified by the experienced workers operating impedance plane diagram, inconvenient toautomatic testing.In order to reduce the degree of human intervention of conventional eddy current testing systemand favoring automatic detection, this paper designed a new type of nondestructive detection systemusing the highly sensitivity giant magneto resistance (GMR) chip as the sensitive element. Thesystem is based on the basic principle of eddy current testing, using direct frequency synthesizerAD9850and power amplifier chip TDA2030A to build alternating current signal generating circuitand GMR magnetic sensor to extract directly the eddy current magnetic field variation caused bythe defect of the metal to be tested. In this paper, the design of alternating current signal producingmodule can realize continuous adjustment of the output voltage. The output frequency can be set upaccording to the software with the step length of100Hz and range from100KHZ to20KHZ.In this paper, I used the Ansoft Maxwell software to verify the system. When the coil is energizedwith a200mA alternating current, quantity change of defects in a magnetic field of the object is0.3 mT. Through the GMR sensors I can detect the variation of the magnetic field very effectively sothat I can detect the defects of the metal according to the sensor output voltage signal. Finally, thepaper designed a physical test to the nondestructive detection system, the results of which show thatthe system measurement is reliable and can accurately identify the edge of the metal objects anddefects.