Operating principle of ultrasonic flaw detectors. 2) Operating algorithm

2) Operation algorithm of the ultrasonic flaw detector

UT-probe transmits a short ultrasonic signal into the tested object. The signal reflects from a flaw or the opposite surface and goes back to the receiver. The instrument registers time from the moment, the signal was issued to the moment the signal returned to the receiver.

Knowing the sound propagation speed for the particular material we can easily calculate the distance to the opposite surface, or a discontinuity in the body of the tested object as well as it’s exact position. Fig. 2.1.

Fig. 2.1 The principle of measuring the time and the way of the pulse

Time measurement starts simultaneously with the transmission of electrical impulse – excitation pulse. A very short electrical discharge causes a sound pulse in the piezoelectric elements in transducer. The sound pulse passes through the material, and being reflected from discontinuities (flaws) or the opposite surface returns back to the transducer. Received oscillations converted into an electrical impulse and stop the time measurement. The distance to the reflecting surface can be calculated with the following formula:

, where

S – the way of sound pulse [mm];

c – the speed propagation of sound in the material [km / s];

t – the duration time of pulse [c].

Simple model of the ultrasonic flaw detection is given on the next figure displaying timing, distance, and reflected impulse amplitude. Fig. 2.2.

Fig. 2.2. Graphical display of received ultrasonic signals