Nova Eclipse TG930 - Users Manual
32
5.4 Ultrasonic Velocity
Velocity Measurement:
To accurately measure the Longitudinal Ultrasonic
Velocity characteristic of any particular material, it is necessary to have a
sample of the material having known composition, and, if a metal, the heat
treatment condition. Case-hardened, coated, or plated samples are not
acceptable. Both front and back surfaces should have a fine finish, such as
that produced by finish surface grinding. The surfaces should be flat and
parallel. The ideal nominal thickness of the sample should be approximately
0.3 inch (7.5 mm) to 1.0 inch (25.4 mm). The precise thickness should be
determined to at least 0.xxxx inch (0.xx mm) accuracy using an appropriate
micrometer measurement tool.
Couple the probe to the surface of the reference sample, and, using the
Up/Down ARROW keys, scroll or toggle to the known thickness. As the
displayed thickness is adjusted to the known thickness, note that a velocity
value is displayed immediately below the thickness readout. If the gage has
been set to English units (inches), the velocity value will be displayed as a
number having four decimal places. If millimeters were set, the velocity will
have three decimal places. The units of velocity are inches per microsecond
(in/
μ
s), or millimeters per microsecond.
Velocity Calibration:
Though infrequently used, if the ultrasonic velocity of
the test material has been previously established or recorded, and reference
standards are unavailable, velocity calibration will produce accurate
measurements. To set velocity, while in the Measurement Display,
momentarily depress either of the Up or Down ARROW keys (VEL+ or
VEL
−
).
Velocity
, with the currently stored velocity value, is displayed
immediately below the thickness readout. The ARROW keys can then be
used to toggle or scroll velocity until the display precisely reads the known
velocity value.
Since many factors can affect ultrasonic velocity, the Velocity Measurement
procedure should produce significantly more accurate results than using
published velocity data. If approximate gaging accuracy is acceptable, the
use of published data, such as shown in the Longitudinal Ultrasonic Velocity
Table, below, can be considered.
This approach is reasonable for simpler, more-rugged applications; for
example, the gaging of mild steel or plain carbon steel alloys. Published
velocity data will be found to differ somewhat in different publications. This
is due to chemical or physical variations within the material that are within
the range of acceptable parameters for a particular alloy.
Nova Eclipse TG930 - Users Manual
33
Longitudinal Ultrasonic Velocity Table
(At Room Temperature)
Material
Velocity - in/
μ
s
Velocity - mm/
μ
s
Acrylic Resin
0.105
2.67
Aluminum
0.249
6.32
Naval Brass
0.174
4.43
Phosphor Bronze
0.139
3.53
Cast Iron
0.181
4.60
Copper
0.183
4.66
Window Glass
0.267
6.79
Inconel
0.225
5.72
Wrought Iron
0.232
5.90
Magnesium
0.248
6.31
Monel
0.237
6.02
Nickel
0.222
5.63
Mild Steel
0.232
5.90
4340 Steel
0.230
5.85
CRES 303
0.233
5.66
Titanium
0.239
6.07
Zirconium
0.183
4.65
