KERN & SOHN TN 300-0.01US - Manual (Page 9)

Sauter GmbH
Tieringerstr. 11-15
D-72336 Balingen
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Internet: www. sauter.eu
Instruction Manual
TN_US
TN_US-BA-e-1112 9
will be minimized by calibrating each test piece
individually.
An additional important consideration is, that any included
air gaps or air pockets will cause an early reflection of the
ultrasound beam. This will be noticed as a sudden
decrease in thickness in an otherwise regular surface.
While this may impede accurate measurement of the total
material thickness, it does positively indicate any air gaps
in the laminate.
Suitability of materials
Ultrasonic thickness measurement relies on passing a
sound wave through the material being measured. Not all
materials are suited to transmitting sound. Ultrasonic
thickness measurement is practically found in a wide
variety of materials including metals, plastic and glass.
Materials which are difficult include some cast materials,
concrete, wood , fibreglass and some rubber.
Couplants
Every ultrasonic application requires some medium to
couple the sound from the transducer to the tested
material. Typically, a high viscosity liquid is used as the
medium. The sound used in ultrasonic thickness
measurement doesn’t travel through air efficiently.
A wide variety of couplant materials may be used.
Propylene glycol is suitable for mostly all applications. In
difficult applications, where a maximum transfer of sound
energy is required, glycerine is recommended. However,
on some metals glycerine may promote corrosion by
means of water absorption, which is undesirable.
Other suitable couplants for measurements at normal
temperatures may include water, various oils and greases,
gels and silicone fluids. Measurements at elevated
temperatures will require specially formulated high
temperature couplants.
Inherent in ultrasonic thickness measurement is the
possibility that the instrument will use the second rather
than the first echo from the back surface of the material
being measured while being in standard pulse-echo mode.
This may result in a thickness reading that is TWICE what
it should be.
The responsibility of a proper use of the instrument and the
recognition of these types of phenomenon solely rest with
the user of the instrument.
7. Declaration of conformity