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3.4
Operation principle of the thickness gauge is based on ultrasonic pulse-
echo method of measurement, which utilizes the property of ultrasonic waves to
reflect from interface of media with different acoustic impedances.
Piezoelectric plate of dual element transducer generates an ultrasonic pulse
through a delay line (wedge) in the direction of outer surface of a product, whose
thickness is to be measured. The ultrasonic pulse propagates in the product up to the
opposite surface, reflects from it, goes in reverse direction, and having passed the
delay line (wedge), it is accepted by receiving piezoelectric plate. Time of ultrasound
propagation from one surface of a product to another and back depends on the
product thickness:
where Н – thickness of test product;
С – velocity of ultrasound propagation in the product's material;
t – time of ultrasound propagation from one surface to another and back.
3.5
Schematic structure of the thickness gauge is shown on Fig.3.
3.6
The thickness gauge consists of a piezoelectric transducer and electronic
unit.
3.6.1 Piezoelectric transducer
Transducer types, ranges of thickness values to be measured, and dimensions of
work surfaces are listed in Table 1.
3.6.2 The electronic unit induces a high-voltage sounding pulse in order to
excite the transducer, amplify the signal exiting the transducer, generate and
measure a time interval, which corresponds to the time of ultrasound propagation
from one edge of a test product to another, as well as mathematical processing of
obtained data, storage of variable and intermediate measurement results, control of
operation modes, and display of measurement results in thickness units.
,
11
(1)
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