Checkline DFX-7 - 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 DFX-7 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 DFX-7, 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 DFX-7 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 DFX-7 is to plug the transducer into the gauge and power
the unit up. The DFX-7 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 DFX-7 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 DFX-7 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 DFX-7 will recall specific properties
about the transducer. Note: Once the transducer has been selected, the DFX-7 will
store and recall this transducer type every time the DFX-7 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 DFX-7. Failure to do this will result in erroneous
measurements: