Filter
Top Products
38
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 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, 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 45.
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 is not used. This is called two-
point calibration and is described on page 50.
6.1 Auto Probe Recognition & Selecting The Transducer Type
The first step in using the CMX is to plug the transducer into the gauge and power
the unit up. The CMX 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 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 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 will recall specific properties
about the transducer. Note: Once the transducer has been selected, the CMX will
store and recall this transducer type every time the CMX 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. Failure to do this will result in erroneous
measurements: