Preparation For Commissioning; Selection Of The Measuring Probe - sauter TU-US Instruction Manual

4. Preparation for commissioning

4.1 Selection of the measuring probe

With this device you can measure a wide range of materials, from various metals to
glass and plastic. For different types of materials, different probes, i.e. US-measuring
heads, are required. The correct probe is crucial for reliable measurement success.
The following sections explain the important properties of the probe and what should
be considered when selecting a probe for a specific work object.
In general terms, this means that the best probe for a work object should send sufficient
ultrasonic energy into the material to be measured so that a strong, stable echo arrives
at the instrument. Certain factors influence the strength of the ultrasound as it is
transmitted.
These can be read below:
• The initial signal strength: The stronger a signal is from the beginning, the
stronger the returning echo will be. The initial signal strength is mainly a factor
of the size of the ultrasonic emitter in the probe. A strong emitting surface will
emit more energy into the material than a weak one. Consequently, a so-called
"1/2 inch" US probe will emit a stronger signal than a "1/4 inch" US probe.
• Absorption and scattering: When ultrasound passes through any material, it is
partially absorbed. In materials with a granular structure, the sound waves are
scattered. Both of these influences reduce the strength of the sound waves and
thus the ability of the device to detect or record the returning echo. Sound waves
with a higher frequency are "swallowed" more than those with lower
frequencies. So it might seem that it would be better to use a low frequency
probe in any case, but these are less alignable (bundled) than those with high
frequencies. Consequently, a high frequency probe would be the better choice
to detect small depressions or impurities in the material.
• Geometry of the measuring probe: The physical limits of the measuring
environment sometimes determine the suitability of the measuring probe for a
certain test object. Some measuring probes are simply too large to be used in
a fixed environment. If the available surface area for contact with the measuring
probe is limited, a measuring probe with a small contact area is required. If you
measure a curved surface, for example a drive cylinder wall, the contact surface
of the probe must also be adapted to this.
• Temperature of the material: If measurements are made on unusually hot
surfaces, high temperature probes are used. These are built in such a way that
they can be used at high temperatures without suffering damage, for special
materials and techniques. In addition, care must be taken when performing a
"zero calibration" or "calibration with known material thickness" using a high
temperature probe.
8 TU_US-BA-e-2020