KERN & SOHN TN 60-0.01EE - Manual (Page 6)

6 TN_EE-BA-e-1410
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3 Preparation
3.1 Transducer Selection
The gauge is inherently capable of performing measurements on a wide range of ma-
terials, from various metals to glass and plastics. Different types of material, however,
will require the use of different transducers. Choosing the correct transducer for an
application is much important to perform easily accurate and reliable measurements.
The following paragraphs highlight the important properties of transducers, which
should be considered when selecting a transducer for a specific application.
Generally speaking, the best transducer for an application is one that sends sufficient
ultrasonic energy into the material being measured in the way that a strong, stable
echo is received by the gauge. Several factors affect the strength of ultrasound as it
travels. These are outlined below:
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 transducer. A large emitting area will send more energy into the materi-
al 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 ab-
sorbed. If the material through which the sound travels has any grain structure, the
sound waves will experience scattering. Both of these effects reduce the strength of
the waves, and thus, the gauge’s ability to detect the returning echo. Higher frequen-
cy 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 bearing face. Measuring on a curved surface, such as an en-
gine cylinder wall, may require the use of a transducer with a matching curved bear-
ing face.
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 tem-
peratures without damage. Additionally, care must be taken when performing a “Sen-
sor-Zeroing” or “Calibration to Known Thickness” with a high temperature transducer.
Selection of the proper transducer is often a matter of tradeoffs between various
characteristics. It may be necessary to experiment with a variety of transducers in
order to find one that works well for a given application.