Interface Blank; Table 12 Polarity Of Echoes - Olympus 45MG User Manual

DMTA-10022-01EN, Rev. C, January 2015
Measurement
mode
Mode 1
using contact
transducer
Mode 2
using delay line
or immersion
transducers
Mode 3
using delay line
or immersion
transducers
10.8.2

Interface Blank

The interface blank represents a blank or dead zone up to 20 µs long that follows the
leading edge of the interface echo. The interface blank is only available in mode 2 and
mode 3.
In mode 2, the interface blank prevents the detection of trailing lobes or cycles of the
interface echo which might otherwise be detected as back-wall echoes, which results
in a hang-up condition (see Figure 10-14 on page 181). The interface blank should be
180 Chapter 10

Table 12 Polarity of echoes

Echo 1
The back-wall echo is
normally negative, except
when measuring material of
low acoustic impedance
bonded to a material of high
impedance (such as plastic or
rubber over metal), where the
echo is phase-reversed.
The interface echo is
normally positive for high-
impedance materials such as
metals and ceramics, and
negative for low-impedance
materials such as most
plastics.
The interface echo is
normally positive for high-
impedance materials.
Echo 2
Not applicable
The back-wall echo is
normally negative, unless the
back-wall echo represents the
sort of low-to-high
impedance boundary.
The back-wall echo is
normally negative, except in
some special cases involving
difficult geometries in which
phase distortion may cause
the positive side of the back-
wall echo to be better defined
than the negative side.