Checkline TI-25P - Manual (Page 10)

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7.0 T RANSDUCER S ELECTION
The TI-25P is inherently 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 reli-
able measurements. 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 ultra-
sonic energy into the material being measured such that a strong, stable echo is
received by the TI-25P. Several factors affect the strength of ultrasound as it trav-
els. 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 trans-
ducer. A large emitting area will send more energy into the material being meas-
ured 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 TI-25P'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 contact-
ing 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.
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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 tempera-
ture transducer.
NOTE: 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 job.
Electromatic can provide assistance in choosing a transducer, and
offers a broad selection of transducers for evaluation in specialized
applications.