Research And System Implementation On Ultrasonic Nondestructive Testing Technology Based On Time Of Flight Transmission Method

This paper analyses an improved ultrasonic testing method called TOFT, time of flight transmission, combining with the engineering situation of ultrasonic nondestructive testing. Firstly, the paper analyzes the theoretical foundation on TOFT. Then, it designs an experiment system and carries out experiments on the drill collar tubing that texture is 4145H steel and nylon respectively. And, the experimental results prove the method is applicable and has some engineering values.(1) It analyses an improved ultrasonic testing method called TOFT, time of flight transmission, based on traditional ultrasonic testing method called TOFD. On one hand, the improved method can used to more testing objects, which breaks the limitation that the traditional TOFD method mainly applies in weld defect testing. On the other hand, it can simplify the testing process. Meanwhile, the paper makes the qualitative and quantitative description on the propagation process and propagation characteristics of ultrasonic in the detector, interface and work piece on theory.(2) It proposes an improved expression that matches the resonance of detector by connecting capacitor in series. The expression provides a scientific basis for parameter selection on core device of the ultrasonic transmitting circuit and improves the transmitting efficiency.(3) It develops an improved ultrasonic transmitting circuit. The circuit ensures the amplitude, drive ability and narrow pulses properties of control signal for MOSFET through monostable trigger circuit and differential circuit. It shortens conduction time and improves the circuit life by choosing the MOSFET that is lower on resistance. It improves lifetime of the detector by utilizing sheet wizard connectivity of the diode to allow the detector works only under negative voltage. However, the hardware cost does not increase obviously.(4) It develops a digital ultrasonic receiving conditioning circuit. The circuit ensures the flexibility and realizes the gain program-controlled by means of combining fixed gain with program-controlled gain. It also adds noise suppression circuit. It can control gate front and gate width of the echo signal through digital and automatic signal. Thus, the automatic regulation can reduce the operators'professional requirement greatly, and can be easy to maintain and engineering application. In addition, the engineering applications of the second phase of ultrasonic testing system for fine copper and ultrasonic testing system for profiled component, prove that the circuit has better stability and reliability.(5) It develops a special TOFT acquisition card which has 4 channels for ultrasonic testing. The card can measure echo's amplitude and time and provide program-controlled signals on gain, program-controlled signals on gate front and gate width. Thus we can say that it can provide a kind of platform for ultrasonic testing system based on TOFT method.(6) It proposes an improved median filtering algorithm. The algorithm is simple, fast and effective. It removes the noise and retains the defect information relatively complete. The maximal ranges about valid threshold between orders of magnitude on trial, so it improves engineering practicability and operability for the algorithm.