8. Application Notes and Optional Features
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DMS 2 Operating Manual
method should be used when calibrating to a known thick-
ness (Section 3.3.4). When using a flat dual probe, position
the crosstalk barrier at a right angle to the long axis of the
part (see Figure 8-1). As a rule, smaller diameter probes
improve coupling and minimize “rocking” on curved parts. In
some cases , special probes with contoured faces to match
surface curvature may be needed. Practice may be helpful
to develop the proper technique.
8.2 Thickness Measurement on Hot Test Pieces
The DMS 2 can be used to measure the thickness of
materials with surface temperatures of up to 1,000
0
F (538
0
C)
with special, high temperature, dual element probe Model
HT400A, and also with single element, high temperature
delay line probes designed for such applications. A special
couplant, Krautkramer ZGM, and duty cycle are also re-
quired for high temperature use. The following procedure is
recommended.
Calibrate the DMS 2 according to the appropriate procedure
in Section 3.3.4.
Thoroughly clean the surface to be tested, using a wire brush
to remove any oxide layers.
Knead the ZGM high temperature couplant in the tube before
using. Then place a drop, about the size of a pea,
on the
contact face of the probe, not on the test piece.
Carefully couple the probe to the surface under test. To
prevent damage to the probe face, do not twist the probe while
it is in contact with the test surface. On a curved surface with a
dual probe, orient the cross-talk barrier as shown in Figure 8-1.
Allow 2 or 3 seconds for the ZGM couplant to melt and provide
good coupling. At temperatures above 1020°F (550°C), the
ZGM couplant may ignite spontaneously. This will not affect
quality of the coupling.
FIGURE 8-1—Crosstalk Barrier Orientation
