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The DIVE gauge uses negative ultrasound pulses to measure
thickness, so the A-scan display shows Half Wave Negative
Rectified signals.
Pits and Flaws
To obtain a reliable Multiple Echo thickness measurement the
gauge must be able to see three distinguishable equi-spaced
return echo pulses. The A-scan below shows the echo pulses of
ultrasound as measured in a flat, un-corroded, unpainted piece of
steel 12.5mm thick:
Flat, new steel 12.5mm thick.
You can easily identify the individual echo pulses and the gauge
correctly measures the thickness and marks the echo pulses it
used with three small squares (arrowed).
If we introduce a flat bottom hole into the steel, drilled half way
through we can have a situation where the echo pulses from the
hole are visible on the A-scan:
Flat, new steel 12.5mm thick with blind hole.
12.5mm
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