Edge Detection of Metal Thickness of Electromagnetic Acoustic Transducer Based on Super-Heterodyne Phase-Sensitive Detector

In order to improve the thickness measurement accuracy of metal plate, a new method based on phase detection thickness is proposed. Two modes of ultrasonic echo are generated by electromagnetic acoustic transducer (EMAT) at the edge of specimen, and super-heterodyne phase-sensitive detection technique is used to collect the phases of the ultrasonic, then the thickness information of the tested specimen is obtained accurately. Firstly, the finite element model of EMAT is built, and the time-domain characteristics of acoustic echo are analyzed. Secondly, the 0∘ and 90∘ phase detection on echo signal are detected by the super-heterodyne phase-sensitive detection system. Finally, the relationship between phase information and specimen thickness is analyzed. The results show that the detection method, which based on super-heterodyne phase-sensitive detector of edge mode conversion, can realize the detection of metal plate thickness, and the phase error range is controlled within 0.23%.

Eddy Current Detection for Weld Defect and Automatic Separating System for Defective HFW Pipe

An eddy current detection and automatic separating system is developed to defect the weld defects in HFW pipe and separate the defective pipe. Application of phase sensitive detector, the pure signal of the weld defect is obtained through a low-pass filter. The information of the weld defect signal, the displacement of flying saw and the welding speed of welded pipe are fused together. The mathematical model is established for unfixed length truncation of the defective welded pipe. An automatic separating system is designed to cut and separate the defective welded pipes in the production line. The practice shows that this system can accurately detect the weld defect, cut the welded pipe in the perfect position and maximumly reserve the welded pipe without defect. This detection and separating system can improve the quality of the welded pipes and avoid the waste.