Elcometer CG60DL Operating Instructions Manual page 41

The best measurement condition is one where sufficient ultrasonic energy is sent into the material being
measured such that a strong, stable echo is received by the gauge.
Several factors affect the strength of ultrasound as it travels. These are outlined below:
16.1 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 material being measured than a small emitting area. Therefore a 6 mm (1/4") transducer will emit a
stronger signal than a 3 mm (1/8") transducer.
16.2 ABSORPTION AND SCATTERING
As ultrasound travels through any material, it is partly absorbed. If the materials through which the sound
travels have any grain structure, the sound waves will experience scattering. Both of these effects reduce
the strength of the waves.
Higher frequency ultrasound is absorbed and scattered more than ultrasound of a lower frequency. It may
seem therefore that using a lower frequency transducer might be better in every instance, however low
frequencies are less directional than high frequencies.
16.3 GEOMETRY OF THE TRANSDUCER
The physical constraints of the measuring environment sometimes determine the suitability of a transducer
for a given job. The transducer may simply be too large to be used in confined areas. Also, the surface area
available for contacting with the transducer may be limited. Measuring on a curved surface may require the
use of a transducer with a matching curved wearface.
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