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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
PVX-B
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
PVX-B
, 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 33.
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
PVX-B
is not used. This is called two-
point calibration and is described on page 34.
6.1 Selecting the Transducer Type
The first step in using the
PVX-B
is to select setup according to the type of
transducer, and or delay tip length from the list of factory setups. There are delay tip
lengths of 3/8” and ½”. There are also two different pencil style transducer options:
spherical focused (PTR-100E) and flat (PTR-300E). The PTR-100E is the most
common and popular option available. This option offers both a .060” and .125”
diameter contact area tip. By selecting the setup associated with a specific
transducer type, all the scope settings will also be loaded and setup. This will give
the user an excellent place to start, requiring only minor adjustments of the delay and
width, if any.
Note:
Once the setup has been selected, the
PVX-B
will store and
recall this setup every time the
PVX-B
is powered on/off. If changes are made to the
setup, they must be saved in a setup location in or to recall them at a later time. The
setup will only change if the user physically selects another setup from the list.
Therefore, if you have previously gone through this section and selected a setup,
proceed to the next section:
Selecting the Transducer Type & Setup
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