phase II+ UTG-2800 - Preparation; Transducer Selection

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3 Preparation

3.1 Transducer Selection

The gauge 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

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.