Real time digital signal processing of on-line ultrasonic flaw detection

The authors have developed a real time digital signal processing system which improves signal-to-noise ratio (SNR) of online ultrasonic flaw detectors by synchronous averaging. The technique reduces not only electric noise but also echo noise. In online testing, although it also reduces flaw echoes because of the movement of flaws, the SNR can be improved if the average is optimum. The optimum number of average could be determined based on a beam profile calculation. The signal processing systems have been installed into online testing systems which inspect the welding area of electric resistance welding steel pipes. As a result, the SNR has been clearly improved