第3章 涡流检测技术.ppt

Multi-Frequency Eddy Current Instruments (cont.) Advantages of Multi-frequency inspections: Allows increased inspection information to be collected from one probe pulling. Provides for comparison of same discontinuity signal at different frequencies. Allows mixing of frequencies which helps to reduce or eliminate sources of noise. Often improves detection, interpretation and sizing capabilities of discontinuities. Multi-Frequency Eddy Current Instruments (cont.) Screen of multi-frequency instrument during inspection. * Crack standards come in variety of shapes and sizes, which is controlled by the inspection application. The material should be the same or very close to the material of the component being tested. EDM notches are often used to represent the crack but it should be noted that EDM notches usually give a stronger signal that a crack will. The image on the left has EDM notches of various depths and the two on the right show EDM notches at fastener holes. 3.3.1 涡流检测仪 功能： ①产生激励信号； ②检测涡流信息； ③鉴别影响因素； ④指示检测结果。 组成（基本电路） 振荡器 信号检出电路 放大器 信号处理电路 显示器和电源电路 3.3.1 涡流检测仪 1 振荡器 高频振荡频率为2MHz一6MHz，适合于检测表面裂纹； 低频振荡频率为50kHz～100kHz，穿透深度较大，适合于 检测表面下缺陷和多层结构中第二层材质中的缺陷。 LC振荡器：起振容易、调整频率方便，振幅大、频率稳定 2 放大器 要求：低噪声、宽动态范围和低失真 3 抑止电路：通过信号叠加和平均消除干扰 4 检出电路：幅度探测器、相位探测器 5 显示：电流表显示、阻抗图显示、计算机数字处理和显示 3.3.2 涡流检测探头(检测线圈) 3.3.2.1 检测线圈的分类 3.3.2.2 检测线圈的使用方式 3.3.2.1 检测线圈的分类 1 穿过式线圈： 小直径管材、棒材、线材等检测 2 内通过式线圈：管件、深孔、螺纹孔内壁表面检测。 3 放置式线圈： 板材、带材和大直径管材、棒材的表面检测， 形状复杂的工件的特定区域局部检测。 3.3.2.1 检测线圈的分类 3.3.2.2 检测线圈的使用方式 3.3.2.2 检测线圈的使用方式 3.3.3 对比试样 检测和鉴定涡流检测仪的灵敏度、分辨力、端部不可检测长度等性能，用于： 选择检测条件 调整检测仪器 定期检查仪器 作为整个仪器的标准当量 Reference Standards Reference Standards (cont.) In order to give the eddy current inspector useful data while conducting an inspection, signals generated from the test specimen must be compared with known values. Reference standards are typically manufactured from the same or very similar material as the test specimen. Many different types of standards exist for due to the variety