1. Getting Started
DMS 2 Operating Manual
Page 17
FIGURE 1-11—In the multi-echo measurement modes, an
ultrasonic pulse is transmitted by a probe into the material
being tested. The pulse first travels through the coating until
it encounters the interface of the coating and metal. At the
interface between the coating and the metal being tested,
some sound is transmitted through the metal being tested to
the backwall, some of the ultrasonic energy is reflected back
to the probe, and some is transmitted through the metal
being tested to the backwall.
The Multi-Echo Measurement Modes
The multi-echo measurement modes (there are actually three
multi-echo type modes) are called “multi-echo” because they
rely on multiple backwall echoes to determine material thick-
ness. Multi-echo modes are used to test materials that are
coated or painted. There are multi-echo modes that use either
single-element or dual-element probes.
In the multi-echo measurement modes, as in the dual-mea-
surement mode, a sound pulse is transmitted from a probe’s
element into the material being tested. However, in the multi-
echo modes, some of the energy in the sound pulse reflects off
the interface where the coating (or paint) and the metal being
tested meet. This first echo returns to the same element (or to
a second probe element). The rest of the energy in the first
transmitted pulse continues through the metal being tested and
returns as a backwall echo.
In the multi-echo modes, the time between the two returning
echoes, together with the speed of sound in the material being
tested, is used to determine the material’s thickness. Multi-echo
measurement using a single-element probe is shown in Figure
1-11.
Typically, a dual-element probe (such as the HT 400A) or a
single-element probe with a delay line is used to provide an
acoustic impedance match to the coating. This matching
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Страница 94: ...3 Setting Up the DMS 2 DMS 2 Operating Manual Page 83 FIGURE 3 11 An Auto Labeler screen is shown here ...