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Dakota Ultrasonics MX-5 User Manual

Page 34

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Dakota Ultrasonics

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above this point, the change in sound velocity of the material being

measured starts to have a noticeable effect upon ultrasonic measurement.

At such elevated temperatures, it is recommended that the user perform

a calibration procedure (refer to page 14) on a sample piece of known

thickness, which is at or near the temperature of the material to be

measured. This will allow the MX-5 to correctly calculate the velocity of

sound through the hot material.

When performing measurements on hot surfaces, it may also be

necessary to use a specially constructed high-temperature transducer.

These transducers are built using materials which can withstand high

temperatures. Even so, it is recommended that the probe be left in contact

with the surface for as short a time as needed to acquire a stable

measurement. While the transducer is in contact with a hot surface, it will

begin to heat up, and through thermal expansion and other effects, may

begin to adversely affect the accuracy of measurements.

• Measuring laminated materials

Laminated materials are unique in that their density (and therefore

sound-velocity) may vary considerably from one piece to another. Some

laminated materials may even exhibit noticeable changes in sound-velocity

across a single surface. The only way to reliably measure such materials is

by performing a calibration procedure on a sample piece of known

thickness. Ideally, this sample material should be a part of the same piece

being measured, or at least from the same lamination batch. By calibrating

to each test piece individually, the effects of variation of sound-velocity will

be minimized.