8
TN_EE-BA-e-2020
The upper figure shows the bottom view of a typical sound generator. The two half
circles are visible, visibly divided in the middle. One of the semicircles directs the
ultrasound into the material to be measured and the other directs the echo back to the
transducer. When the transducer is placed on the material to be measured, it is located
directly below the center of the area whose thickness is to be measured.
The picture below shows the top view of a sound generator.
It is pressed with the thumb or index finger from above on the sound generator to keep
it exactly placed. Only moderate pressure is required, as its surface only needs to be
positioned flat on the material to be measured.
Model
Frequency
MHz
Φ mm Measuring
range
Lower limit
Comment
P5EE
5
10
P-E: 2~600 mm
E-E:3~30/60 mm
Φ20 mm×3,0 mm Standard
measurement
3.2 Conditions and preparations for surfaces
For any kind of ultrasonic measurement, the condition and roughness of the surface to
be measured is of utmost importance. Rough, uneven surfaces can restrict the
penetration of the ultrasonic waves through the material, resulting in unstable, incorrect
measurement results. The surface to be measured should be clean and free of any
substances, rust or verdigris. If this is the case, the transducer cannot be placed cleanly
on the surface. Often a wire brush or scraper is helpful to clean the surface. In extreme
cases, belt grinders or the like can be used. However, it is important to avoid gouging
the surface, which prevents the sound generator from being placed cleanly. Extremely
rough surfaces like siliceous cast iron are very difficult to measure. These types of
surfaces behave like when light shines on frosted glass, the beam is scattered and
sent in all directions. In addition, rough surfaces contribute to considerable wear and
tear of the transducer, especially in situations where it is "scrubbed" over the surface.
They should therefore be checked at a certain distance, especially at the first signs of
unevenness on the contact surface. If it is worn down more on one side than the other,
the sound waves can no longer penetrate vertically through the material surface of the
test object. In this case, small irregularities in the material are difficult to measure
because the sound beam is no longer exactly below the sound source.
