Design And Experimental Study Of The ACFM Sensor

Alternating Current Field Measurement(ACFM) technique is a new developed non-destructive testing method for detecting surface defects. By detecting changes of the induced magnetic field of the workpiece surface to analyze whether the surface detects. The technology compared to traditional surface inspection technology, less demanding on the surface of the workpiece, easy to operate and intuitive test results and so on。Since the late development of the technology, most technical indicators still in the exploratory stage, the technology is not mature enough, especially in the country, mastery of the technology is still in its infancy, it has great significance for the study of the technology.This paper describes the technology in the current research. Base on the principle of the Alternating Current Field Measurement and Maxwell’s equations, Establish its mathematical model.Secondly, Based on the characteristics of the technology, built a Alternating Current Field testing platform. The testing platform includes five parts: excitation signal generator circuit, power amplifier circuit, probe, signal amplifier circuit and filter circuit. Excitation signal generator circuit through STM32 D/A implemented, as a reference for the design of portable disturbance magnetic field detector. Since output power of the excitation signal low, a low distortion and low power consumption power amplifier circuit is designed, to enhance the carrying capacity of the excitation signal source.Designed conventional probe of Alternating Current Field Measurement, and testing 45# steel which containing artificial defects of different length and depth. Using control variable method to analyze the relationship between the sensitivity of the probe with the defect length and depth. The probe along the reference line which is different offset distances from the position of the defect. By the size of the detection signal, analyzing the effective detection range of the probe. Scanning the defects in different depths, discusses the relationship between detection range and depth of the defect. Scanning that probe scanning direction at different angles to defect trend, analyzed the characteristics that Bx, Bz signal characteristic curve showing.Designed pen type probe of Alternating Current Field Measurement, for assisting conventional probe, to detect the parts where is difficult scanning for conventional probe. Tested 45# steel plates containing artificial defects. According to the defect signal characteristic curve, analyzes the sensitivity and the effective detection range of the probe, and discuss its positioning capabilities for defects.Designed ring probe of Alternating Current Field Measurement, to detect pipeline workpieces. Tested Seamless steel pipe containing artificial defects. Its good effect to make up for deficiencies that conventional detection probe in the detection of such workpieces, the detection signal prone to distortion, detection effect is not ideal.