Dakota Ultrasonics
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 15) on a sample piece of known thickness, which is at or near the temperature of the material to be measured. This will allow the MMX-6 DL 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.
