How to distinguish the echo wave from the transverse wave and longitudinal wave is essential for judging if the workpiece meets the requirement or not. By making the full use of the computer's storage and high speed comparison characteristics, we have designed a set of the advanced system.

After adjusting the relative location between the focused probe and tube, we make the tube rotating uniformly, recording the angular displacement of workpiece at any moment. So we can get frames of echo signal from the ultrasonic tester. With high speed A/D converter, the echo signal can be converted to digital signal, starting from surface echo wave and ending at bottom echo. We check all digital signal and send the echo's time, height and shape to memory in time if any flaw is discovered by computer.

As the workpiece is in uniform rotation, a series of flaw echo are sent to the memory. When a workpiece rotates a circle, there is a group of flaw echo signal in the memory.

According to acoustic velocity of the transverse wave and longitudinal wave and angle of incidence, location of the flaw is reconstructed on ring of the workpiece individually, resulting two flaw location graphics. According with a set of judge rules, the duplicate parts are rejected. Finally, we get an accurate flaw location graphic to judge if the workpiece is upto the standard.

With the basic principle, we have designed a immersion ultrasonic automatic testing system used for tube with thick wall and attained the goal of judging the flaw's location, size and quantity correctly and reliably.