# The Rapid Detection Technology of Lamb Wave for Microcracks in Thin-Walled Tubes
## 3 Testing Equipment  
### Appearance and Core Components  
As shown in Figure 5, the testing equipment was mainly composed of three parts: a Programmable Logic Controller (PLC) control unit, a Personal Computer (PC) control unit, and a mechanical device. The control unit of the PLC was mainly responsible for the motion control of the mechanical device and communication with the PC through the RS232 serial module. The PC control unit mainly included a multi-channel pulse transmitter/receiver, the extraction device of the detection signal feature, the multi-channel data acquisition card, and the PC. The function of the multi-channel pulse transmitter/receiver was to detect the object using an excitation pulse to trigger the ultrasonic transducer and receive the detection signal from the detected object. The feature extraction device for the testing signal mainly ensured that only the defect echo signal was extracted through the hardware gate to reduce the amount of data acquisition and improve the speed of data processing. The mechanical device mainly performed the mechanical actions of grasping, rotating, and moving the thin-walled tube into place for testing. Figure 4: Relationship between the incident angle and frequency-times-thickness in steel (the P-wave velocity in water was 1480 m/s). Figure 5: Appearance of testing equipment (1. PLC control unit; 2. PC control unit; 3. mechanical device). The core components of the mechanical equipment are shown in Figure 6, which mainly include the material-preparation container, the testing container, the ultrasonic transducer, and the built-in manipulator. The material-preparation container was mainly used to place the thin-walled tube to be inspected. By moving up and down, the thin-walled tube was conveyed to a position that the built-in manipulator could grasp. There was an overflow outlet at the mouth of the testing container, which was used to discharge the overflow amount of water as the thin-walled tube slowly sank into the testing container. There was a water inlet at the bottom of the testing container, which was used to replace water when the thin-walled tube was removed from the testing container after the detection to ensure the coupling between the ultrasonic transducer and the thin-walled tube. A pair of ultrasonic probes were installed on the side of the testing container to scan the axial and circumferential distribution defects of the thin-walled tube. The movement of the testing container and the rotation of the built-in manipulator carrying the thin-walled tube could cooperate, which allowed the spiral scanning of the thin-walled tube by the ultrasonic probes. The built-in manipulator held the thin-walled tube from the inside. Meanwhile, an airbag at the top of the built-in manipulator sealed the opening of the thin-walled tube to prevent water from penetrating the thin-walled tube during the detection process. The built-in manipulator moved back and forth along the guide rail to grasp, rotate, and move the thin-walled tube into place. The detection process was as follows. Firstly, when all five material-preparation containers were placed into the thin-walled tubes, the built-in manipulator moved backward to the central position of the material-preparation container. When the material-preparation container rose to a certain position, the built-in manipulator held the thin-walled tube from the inside and allowed the top airbag to seal the opening of the thin-walled tube. The material-preparation container quickly dropped to the original position. Secondly, the built-in manipulator carrying the thin-walled tube moved forward to the center of the testing container and began to rotate at 320 rpm. The testing container quickly rose to a certain position, and the PLC control unit notified the PC through the RS232 serial port to begin the detection.