Ultrasonic Examination

Ultrasonic denotes high frequency sound waves beyond the audible range generally above 20,000 cycles per second Generation of Ultrasonic waves is done by means of Magnetostriction, or Piezoelectric Effect.

The waves are made to pass the material under checking through a coupling media. The waves propagate into the material in the form of bean resembling a solid cone diverging steadily from the source of generation

If the material is perfectly homogenous, the energy travels up back to the surface of specimen and is reflected and returns to the transducer. The transducer at once changes this mechanical energy into electrical energy which after amplification is routed through different electronic circuits. It ultimately reaches a vertical plate of cathode-ray tube in the form of unidirectional voltage. This is indirected by a pipe on the time base which is incorporated in between the horizontal plates of CPT to reckon the time of travel of the Ultrasonic energy into the material.

A part of the electrical pulse is fed into the vertical plates of the CRT simultaneously with the same being applied to the transducer. This gives the transmission echo on the time base which the starting point for measuring time of interval on the calibrated scale.

If now a discontinuity exists on the path of the Ultrasonic energy, part of it will be reflected and part of it will be transmitted depending upon the acoustic impendances of the material and the flaw. The energy reflected from the flaw and that from the back surface, having traveled different path lengths shall be indicated on the CRT screen by the two different echoes on the time base, the space between the echoes giving the difference of path traversed.

Graduations on the time base scale when calibrated with reference to the material under checking shall therefore readily give us the depth of flaw as well as thickness of the material.

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