KERN & SOHN TN 60-0.01EE - Manual (Page 14)

14 TN_EE-BA-e-1410
6 Transport and Storage
Keep it away from vibration, strong magnetic field, corrosive medium and dust.
Storage in ordinary temperature.
Appendix A: Applications Notes
Measuring pipes and tubes
When measuring a piece of pipe to determine the thickness of the pipe wall, orienta-
tion of the transducers is important. If the diameter of the pipe is larger than approxi-
mately 4 inches, measurements should be made with the transducer oriented so that
the gap in the bearing face is perpendicular (at right angle) to the long axis of the
pipe. For smaller pipe diameters, two measurements should be performed, one with
the bearing face gap perpendicular, another with the gap parallel to the long axis of
the pipe. The smaller of the two displayed values should then be taken as the thick-
ness at that point.
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 calibrat-
ing 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.
Measuring through paint & coatings
Measuring through paints and coatings are also unique, in that the velocity of the
paint/ coating will be significantly different form the actual material being measured. A
perfect example of this would be a mild steel pipe with approximately 0.6mm of coat-
ing on the surface. Where the velocity of the pipe is 5920m/s, and the velocity of the
paint is 2300m/s. If the user is calibrated for mild steel pipe and measures through
both materials, the actual coating thickness will appear to be 2.5 times thicker than it
actually is, as a result of the differences in velocity. This error can be eliminated by
using a special echo-echo mode to perform measurements for applications such as