TN_EE-BA-e-2020
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example of this is a pipe made of mild steel with a layer about 0.6 mm thick. The speed
of sound propagation for the pipe is 5920 m/s, and for the paint layer 2300 m/s. If the
gauge is set to measure the thickness of a mild steel pipe and then the measurement
is made over both materials, the thickness of the layer will be 2.5 times greater than it
actually is due to differences in the speed of sound propagation. Such an error can be
avoided by selecting the 'Echo-Echo' measurement mode intended for measurement
under such circumstances. In this measurement mode, the thickness of the paint
coat/other coat is completely ignored and the measurement is concentrated on steel
only.
Material suitability
Ultrasonic material thickness measurements are based on the fact that a sound is sent
through the material to be measured. Not all materials are suitable for this. Ultrasonic
measurement can be applied practically to a wide range of materials including metals,
plastics and glass. Difficult materials include some cast materials, concrete, wood,
fiberglass and some rubber.
Coupling means
All ultrasonic applications require a medium to transmit the sound from the transducer
to the test material. Typically this is a very viscous medium. Ultrasound cannot be
efficiently transmitted through air.
A variety of coupling means is used. For most applications propylene glycol should be
used. Glycerine is recommended for difficult applications, as maximum sound
transmission strength is required. However, glycerine can cause corrosion due to water
absorption in some metals.
Other coupling agents for measurements at normal temperatures may include water,
various oils or greases, gels and silicone fluids. High temperature measurements
require special high temperature coupling agents.
A characteristic of ultrasonic measurement is that the instrument uses the second
rather than the first echo from the rear surface of the material to be measured when in
standard pulse-echo mode. This results in a reading that is
twice
as large as it should
be.
The responsibility for the appropriate use of the measuring instrument and the
detection of these phenomena lies exclusively with the user himself.
Note:
To view the CE declaration, please click on the following link:
