Dakota Ultrasonics PVX - Manual (Page 34)

30
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 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, 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 37.
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 is not used. This is called two-
point calibration and is described on page 38.
6.1 Selecting The Setup Based on Transducer Type
The first step in using the PVX 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: sphirical
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 will store and recall this setup every time
the PVX 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 a Setup for use with a specific Transducer Type