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the actual thickness. Another error result is called “pu
lse envelop, cyclic
leap”, its result is that the measured value is larger than the actual
thickness. To prevent these kinds of errors, please repeat the
measurement to check the results.
6.2 Rust, Corrosion and Pit
The rust and pit on the other surface of the object will cause irregular
change in readouts. In extreme situation, it will even cause no readout. It
is very difficult to find small rust. When one finds a pit or is in doubt, he
should be very careful in that area. In such situation, one can orient the
probe’s crosstalk interlayer plate in different directions to have multiple
measurements.
6.3 Error in Identifying Material
When calibrates the instrument with one material, and then uses it to
measure another material, error will occur. Please be careful in selecting
correct sound velocity.
6.4 Wear of Probe
The surface of the probe is allyl resin, after long time of usage, its
roughness will increase, and the sensitivity will drop. If the user can be
sure that this is the reason for error, he can grind the surface with sand
paper or oilstone to make it smooth and has good parallelism. If it is still
not stable, the probe must be replaced.
6.5 Overlapped Material and Compound Material
It is impossible to measure uncoupled overlapped material, because the
ultrasonic wave can’t pass an uncoupled space. Since the ultrasonic wave
can’t transmit in compound material in even speed, it is not applicable to
use ultrasonic thickness-gauge to measure overlapped material and
compound material.
6.6 Influence o
f Oxidation Layer at Metal’s Surface
Some metals can produce dense oxidation layer on its surface, such as
aluminum, etc. The layer is closely contacted with the substrate, and it
has no obvious interface, but the ultrasonic wave has different
