ACS UK1401, Operation Manual, Page: 10 / 44

Ultrasonic tester UK1401
Operation Manual
10
ACOUSTIC
CONTROL
SYSTEMS
1.3.3 Operation modes
The instrument can be operated in the following modes:
- TIME –measurement of propagation time of ultrasonic waves in the material;
- VELOCITY – measurement of propagation velocity of ultrasonic waves in the material;
- CRACK – evaluation of the depth of the crack facing the surface;
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1.3.2 Operation principle
The instrument measures the time interval during which the ultrasonic pulse goes through the inspected object from
the transmitting transducer to the receiving transducer. The ultrasonic sound velocity is determined by dividing the distance
value between the points of emission and receiving points of ultrasonic waves, by the measured time value. The ultrasonic
pulse emission and reception are periodically repeated to increase the measurement reliability. The final value obtained after
processing of the sequence of several received ultrasonic signals is displayed on the screen.
Ultrasonic pulses go through the inspected object close to its surface in the form of elastic waves of various types. The
instrument counts the measured time interval according to the earliest impulse coming to the receiving transducer. Therefore,
the instrument measures velocity of the acoustic waves propagating through the given material with the highest velocity.
Primary energy of ultrasonic pulses propagates in the near-surface 2-3 cm thick layer of the material. If there is some kind
of imperfection of material (cavity or crack close to surface) in the way of the wave, then the wave will bypass it and will arrive
to the receiver in the weakened state or with delay as compared to the place without structural imperfection. In that case, the
lower velocity of sound or longer propagation time of the ultrasonic wave as compared to other spots (areas) are a sign of a
defect in the material structure invisible from the surface.
If the crack faces the surface, then it will completely block the path of the ultrasonic wave along the surface. In that case,
only a small part of the wave energy can bypass the crack within the material (up to 50 mm in the depth) and return to the
receiving transducer. Due to longer path, its propagation time will exceed the propagation time of the wave going the shortest
path (without a crack) between the transducers. The measurement process of the crack depth is based on comparison of these
time intervals.