Dakota Ultrasonics MVX - Manual (Page 35)

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CHAPTER SIX
MAKING MEASUREMENTS
The steps involved in making measurements are detailed in this section. The
following sections outline how to setup and prepare your MVX for field use.
In pulse-echo modes, the probe zero must be measured on the reference disk
(battery disk) attached to the top of the instrument. This compensates for variation in
the transducer. In all modes the sound velocity must be determined. The sound
velocity is used to convert the transit time to a physical length. The sound velocity
can be selected from a material chart in the manual, selected from a material list in
the MVX, or for greater precision, determined from a sample of the test material that
has been mechanically measured. To enter the velocity from a table, look up the
material on the chart in the appendix of this manual and refer to the section below on
Calibration to a Known Velocity. To determine the velocity of a single sample, refer
to the Material Calibration section on page 39.
When measuring curved materials, it is more accurate to calibrate from two test
points, one at the minimum limit of the target thickness and one at the maximum limit.
In this case the reference disk mounted to the MVX is not used. This is called two-
point calibration and is described on page 40.
6.1 Selecting The Transducer Type
The first step in using the MVX is to select the transducer type from the transducer
list located in the tabbed menu items by frequency and diameter. By selecting the
transducer type from a predefined list, the MVX can recall specific properties about
the transducer. Note: Once the transducer has been selected, the MVX will store
and recall this transducer type every time the MVX is powered on/off. The type will
only change if the user physically selects another type from the list, or selects a
previously saved setup. Therefore, if you have previously gone through this section
and selected the transducer you are using, proceed to the next section. Use the
following steps to select your transducer type. Note: Be sure the transducer type
selected is the same as the transducer plugged into the MVX. Failure to do this will
result in erroneous measurements: