DeFelsko PosiTector 200 v.2.0 - Manual (Page 15)

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The PosiTector 200 probe emits a high frequency
sound pulse that travels into the coating via a
coupling gel and reflects from ANY surface that is
different in density. Coating thickness readings are
obtained by measuring the time taken for the
ultrasonic signal to propagate from the probe to the
coating/substrate interface and back. The travel time
is divided by two and multiplied by the velocity of
sound in the coating to obtain the thickness of the
coating. The strength of the reflected signal from the
coating/substrate interface determines the ability of
the instrument to measure the thickness of the
coating. Since most applications are not
homogeneous the gage will "hear" many echoes
when placed on a coating/substrate. The instrument
"hears" ALL reflections within the measurement
Application Notes Application Notes
The PosiTector 200 uses an ultrasonic principle to
measure coating thickness of most coatings on most
substrates. An ultrasonic signal is a very high
frequency sound wave. Like the echoes you hear
when you shout in a large hall or canyon the
PosiTector 200 listens for echoes from acoustic
boundaries within your application.
The PosiTector 200 is factory calibrated. But in
order for it to take accurate thickness measurements
of a particular material it might be necessary to
adjust the gage for that material. To determine if an
adjustment is necessary for your application,
measure a sample of known thickness of the coating
material to be measured. If the average of a series
of measurements is not close to the expected
thickness, adjust to the expected thickness.
Samples should be flat, smooth and as thick or
thicker than the maximum expected thickness of the
piece to be tested.