Dakota Ultrasonics CMX DL plus - Manual (Page 48)

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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 CMX
DL+
for field use.
An automatic or manual zero must always be performed. The auto zero is an off
block electronic zero that does not require a zero reference block. This will most
always be the zero option of choice, as it makes the zeroing process very easy and
convenient to perform. However, If the manual zero option is enabled, the probe
zero must be measured on the reference disk (battery disk) attached to the top of the
instrument. The zero compensates for variations 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 CMX
DL+
, 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 54.
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 CMX
DL+
is not used. This is called
two-point calibration and is described on page 56.
6.1 Auto Probe Recognition & Selecting The Transducer Type
The first step in using the CMX
DL+
is to plug the transducer into the gauge and power
the unit up. The CMX
DL+
has a special built-in automatic probe recognition feature
that will check to see if the probe plugged into the gauge is an auto recognized probe
type. If so, the CMX
DL+
will display a message indicating the transducer type and ask
the user for confirmation to use the identified probe. If the transducer is not an auto
recognized probe, the CMX
DL+
will display a message indicating the transducer type
has not been recognized, and force the user to select a transducer type from a list of
transducers according to frequency and diameter. Whether the transducer is auto
recognized or selected from a predefined list, the CMX
DL+
will recall specific
properties about the transducer. Note: Once the transducer has been selected, the
CMX
DL+
will store and recall this transducer type every time the CMX
DL+
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: If the
transducer is not identified on power up, be sure the transducer type selected is the
same as the transducer plugged into the CMX
DL+
. Failure to do this will result in
erroneous measurements: