Dakota Ultrasonics CMX - Manual (Page 40)

Dakota Ultrasonics
36
Thru Paint & Coatings
Often times users will be faced with applications where the material will be coated
with paint or some other type of epoxy material. Since the velocity of the coating is
approximately 2.5 times slower than that of steel, pulse-echo mode will induce error if
the coating or paint is not completely removed. By using echo-echo mode, the user
is able to successfully measure through both, the coating and steel, and completely
eliminate the thickness of the paint or coating. Therefore, the steel can be measured
without having to remove the coating prior to measuring. Users will often use pulse-
echo mode and echo-echo mode in conjunction when performing inspections on
coated materials.
Thru coating measurements require special high damped transducers. The most
common transducers are the 3.5, 5, and 7.5MHz hi damped transducers. These
transducers are suitable for use in both pulse-echo and echo-echo modes. This
conveniently enables the user to accurately measure overall material thickness using
the thru Coating mode, and then conveniently switch to pit detection mode without
changing transducers. The ¼” 5MHz Hi damped transducer is the most commonly
used transducer for standard thru coating applications.
Coating Only
The coating only mode should be used when the application calls for coating
measurements only and the user is not interested in the thickness of the material the
coating has been applied to. This mode can also be used as a stand alone coating
thickness gauge, where the coating has not been applied to another material surface.
An auto identified coating probe must be attached to the CMX in order to enable this
mode.
Thin materials
Use pulse echo mode and a high frequency transducer for these types of
applications. The most common transducers are the 7.5MHz and 10MHz models
with extra resolution. The higher frequencies provide greater resolution and a lower
minimum thickness rating overall.
High temperature
Use and select a special 2.25MHz and 5 MHz High temperature transducer for these
types of applications. Both pulse-echo and echo -echo modes will also work for these
applications. However, echo-echo mode will eliminate error caused by temperature
variations in the delay line of the transducer.
Noisy Material
Materials such as titanium, stainless steel, and aluminum may have inherent surface
noise issues. This is a signal that appears at the surface of the material when using
a dual element delay line probe. Select a higher frequency transducer to reduce this
noise – 7.5MHz and higher for better resolution.