ElektroPhysik
E-15
· Initial Signal Strength
The stronger a signal is to begin with, the stronger its
return echo will be. Initial signal strength is largely a
factor of the size of the ultrasound emitter in the trans-
ducer. A large emitting area will send more energy into
the material being measured than a small emitting area.
Thus, a so-called „1/2-inch“ transducer will emit a
stronger signal than a „1/4-inch“ transducer.
· Absorption and Scattering
As ultrasound travels through any material, it is partly
absorbed. If the material through which it travels has
any grain structure, the sound waves will also experience
scattering. Both of these effects reduce the strength of
the waves, and thus, the MINITEST 403’s ability to detect
the returning echo.
Higher frequency ultrasound is absorbed and scattered
more than ultrasound of a lower frequency. While it may
seem that using a lower frequency transducer might be
better in every instance, low frequencies are less
directional than high frequencies. Thus, a higher
frequency transducer would be a better choice for
detecting the exact location of small pits or flaws in the
material being measured.
· Geometry of the Transducer
The physical constraints of the measuring environment
sometimes determine a transducer’s suitability for a
given job. Some transducers may simply be too large
to be used in tightly confined areas. Also, the surface
area available for contacting with the transducer may
be limited, requiring the use of a transducer with a small
wearface. Measuring on a curved surface, such as an
engine cylinder wall, may require the use of a transducer
with a matching curved wearface.
· Temperature of the Material
When it is necessary to measure on surfaces that are
exceedingly hot, high temperature transducers must be
used. These transducers are built using special
materials and techniques that allow them to withstand
high temperatures without damage. Additionally, care
must be taken when performing a „Probe Zero“ or
„Calibration to Known Thickness“ with a high temperature
transducer. See Appendix B for more information on
measuring materials with a high temperature transducer.
Transducer Selection
