1.6 Design and operation
The device uses piezoelectric sensors that, when fed with a short electric pulse, emit sound waves
whose frequency is much higher than the upper limit of the range perceived by the human ear (that is –
US). The frequency values of the signal emitted by the sensor can be 1 MHz ... 20 MHz. Oscillations
of this frequency do not spread well in the air; therefore, to eliminate the air gap and ensure good
contact between the sensor and the surface of the object being inspected, a paste / gel layer (glycerin,
water, oil, special gels) is needed.
Ultrasonic signals generated by the generator enter the piezoelectric emitter. Further, they pass
through the outer surface of the object, propagate in the body of the object and are reflected from its
internal surface (that is, from the boundary of a significant difference in the "metal-medium"
densities). The sensor of the receiver perceives the reflected ultrasonic signal, converts it into electrical
signal and transmits it to the meter, in which the time interval is converted to a thickness measurement
result. The calculated thickness of the product is displayed on the device gauge.
Various factors can influence the operation of the device. If there are inhomogeneity in the
material of the investigated object, cavities, cracks, its surface is corroded (and others), the results can
be distorted.
In addition, in order to obtain reliable results of thickness measurement, it is necessary to use the
correct propagation velocity of US in this particular material. The actual speed of ultrasound in
different materials is very different both from material to material and from the reference data. The
best results can be obtained if the instrument is previously calibrated using an object of a known
thickness (reference) made of the same material as the object under study. The standard should have a
flat smooth surface and a thickness not less than the thickness of the object. It should be borne in mind
that the speed of sound in the same material can be unstable. For example, heat treatment of a material
can significantly change the sound propagation speed of that object. This should be taken into account
when assessing the accuracy of measurements. To reduce errors, it is useful to check the calibration
after measurements.
1.7 Means of measurement, device and accessories
To test the performance of the instrument, it is necessary to perform measurements on the
integrated calibration element (reference sample). The inconsistency of the readings of the device
should not exceed the permissible error (Table 1.2).
In the event of a malfunction, repair and adjustment of the device must be carried out by the
manufacturer.
1.8 Labeling and sealing
The symbol of the unit with the trademark of the manufacturer is applied to the front panel.
The serial number is printed on the back panel, under the battery compartment cover of the
instrument.
1.9 Packaging
The electronic unit and the probe are supplied in the packaging container, which excludes their
damage during transportation.
To avoid mechanical damage to the cable and connectors of the device, it is necessary to
disconnect the transducer from the device before packing.
