DeFelsko PosiTector UTG Guide D'utilisation page 5

When the probe senses echoed ultrasound, a coupled symbol
will appear on the display and thickness values will be
displayed. While the probe is coupled, the PosiTector UTG
continually updates the display.
3. When the probe is removed from the surface, the last
measurement will remain on the display.
Occasionally, excess couplant will remain on the probe when
the probe is lifted from the surface. This may cause the
PosiTector UTG to display a final measurement value different
from those observed when the probe was on the surface.
Discard this value and repeat the measurement.
Ultrasonic measurements are affected by the condition,
roughness and contour of the surface to be tested.
Measurement results may vary on coarse surfaces. Where
possible, it is recommended to seat the transducer on a smooth
flat surface that is parallel to the opposite side of the material.
On rough surfaces, the use of a generous amount of couplant
minimizes the surface effects and serves to protect the
transducer from wear, particularly when dragging the probe
across a surface.
UTG M Probes:
On smooth, uncoated metal surfaces the Gage (in multiple-echo
mode) may occasionally be unable to give a measurement result
even when the "coupled" symbol appears. Use additional
couplant and lighter pressure on the probe when measuring.
Alternatively, laying a plastic shim on the surface with couplant
applied to both sides to simulate a painted surface will help
produce a steel-only thickness measurement (multiple-echo mode).
Switching the Gage to single-echo SE mode (see pg. 9) will also
help produce a steel-only thickness measurement.
Surface Conditions
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