Dakota Ultrasonics PVX - Manual (Page 28)

Dakota Ultrasonics
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echoes are needed which requires a much stronger echo (reflection). In interface-
echo mode, it moves the interface further out in time eliminating any noise that’s
close to the initial pulse.
Important: The primary difference between interface-echo and echo -echo mode, is
interface-echo mode measures from the end of an interface (delay line), to the first
return reflection of the test material. However, in echo -mode, the measurement is
made between two return reflections (echoes). Although both modes use two gates
and virtually look the same on the scope, they are measuring in different ways and
are used to accomplish different application tasks. The diagrams below will offer an
additional explanation of the differences in these modes as follows:
Delay Line Single Element Transducer in Interface-Echo mode
Diagram 1
Refer to diagram 1. This diagram illustrates the sound path being measured in
interface-echo mode. (A) is the transducer. Point (B) is the piezoelectric crystal that
emits the sound wave. (C) is the delay line, most commonly made of acrylic or
graphite. The delay tip will act as the interface and the measurement will be made
starting from the difference of the reflection off the end of the delay tip (E). The
sound will also travel through the delay tip (C) and test material (F), and reflect back
to the piezoelectric crystal off the back wall of the test material. The measurement
will be made from the reflection off the end of the delay tip and back wall of the test
material.