3
Preparation
3.1
Transducer
Selection
The UTG‐2900 is capable of performing measurements on a wide range of materials, from various metals to glass
and plastics. Different types of material, however, will require the use of different transducers. Choosing the correct
transducer for a job is critical to being able to easily perform accurate and reliable measurement. The UTG‐2900 is
supplied with a 5MHz dual sensor probe that is considered to be the general purpose probe of the group. The
following paragraphs highlight the important properties of transducers, which should be considered when selecting a
transducer for a specific job.
Generally speaking, the best transducer for a job is one that sends sufficient ultrasonic energy 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:
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. 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 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 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.
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