Dakota Ultrasonics UMX-2 - Manual (Page 32)

UMX-2 Underwater Material & Coating Thickness Gauge
28
measurement display. Note: Do not remove the transducer from the zero
reference standard.
4) When MANUAL is displayed, immediately press and release the button to
perform a manual probe zero.
5) Press and hold the button to escape out of the menu options at any time.
6) The UMX-2 in now ready to be calibrated for a given material type.
Note: The value that is displayed will change depending on the current velocity
setting in the UMX-2. Disregard the number that is displayed. It is not
important. What is important is accurately performing the steps outlined above
to insure reliability of the probe zero calculation.
7.3 Material Calibration
In order for the UMX-2 to make accurate measurements, it must be set to the correct
sound velocity of the material being measured. Different types of materials have
different inherent sound velocities. For example, the velocity of sound through steel
is about 0.233 inches per microsecond, versus that of aluminum, which is about
0.248 inches per microsecond. If the gauge is not set to the correct sound velocity,
all of the measurements the gauge makes will be erroneous by some fixed
percentage.
The UMX-2 has 8 preset material types with common fixed velocities to select from.
There is also 1 custom programmable velocity available for non-standard known
material velocities.
Basic Material Type
In order to calibrate the UMX-2 according to a specific material to be tested, the user
can select a basic material type from a list with approximate velocity values according
to various material types. It’s important to note that these velocities will not always
be an exact representation of the material being tested. They will typically be more
than adequate for ongoing ‘historical’ material degradation inspections. The following
is a list of the preset materials, and the procedure to select and calibrate the UMX-2:
UMX-2 Material Chart
Material Types Abbreviations Velocity Velocity m/sec