Dakota Ultrasonics PX-7 User Manual
Page 32
Dakota Ultrasonics
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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.
An additional important consideration when measuring laminates, is that
any included air gaps or pockets will cause an early reflection of the
ultrasound beam. This effect will be noticed as a sudden decrease in
thickness in an otherwise regular surface. While this may impede accurate
measurement of total material thickness, it does provide the user with
positive indication of air gaps in the laminate.