Based On The Alternating Magnetic Field Measurement Techniques Of The Metal Surface Defect Detection System

The Alternating Current Field Measurement (ACFM) technique is an electromagnetic nondestructive testing (NDT) technique used to detect and size surface cracks in electrically conducting, metallic components. In this paper, the status and the development home and abroad of the NDT technique and the ACFM technique are illustrated. The basic principle is discussed and the mathematical model is built up. Sensors are designed for varied occasions and the signal processing circuit is completed based on the characteristics of the signal. The lock-in amplifier realized via hardware, the orthogonal signal generator based on the Direct Digital Synthesizers improved, the system scheme for testing are presented and the instrument based on ACFM technique is made up. A large number of tests are carried out via the build-up system. This paper discusses the crack identification by qualitative analysis and gives methods of sizing the crack by quantitative analysis. And the results of the tests go along with the theory on the whole.In the end, the conclusions of this paper are given and the suggestions for further study are made.