Dakota Ultrasonics PX-7 DL - Manual (Page 37)

PX-7 DL Ultrasonic Thickness Gauge
33
APPENDIX B
Application Notes
• Measuring tubing
When measuring a piece of tubing for wall thickness, it may prove
beneficial to have multiple delay lines with different radiuses for different
tubing diameters. The delay lines can be easily radiused by placing a
piece of emery cloth around the tubing and moving the transducer back
and forth until a radius has formed on the tip of the delay line.
• Measuring hot surfaces
The velocity of sound through a substance is dependant upon its
temperature. As materials heat up, the velocity of sound through them
decreases. In most applications with surface temperatures less than about
200
°
F (100
°
C), no special procedures must be observed. At temperatures
above this point, the change in sound velocity of the material being
measured starts to have a noticeable effect upon ultrasonic measurement.
At such elevated temperatures, it is recommended that the user perform
a calibration procedure (refer to page 13) on a sample piece of known
thickness, which is at or near the temperature of the material to be
measured. This will allow the PX-7 to correctly calculate the velocity of
sound through the hot material.
When performing measurements on hot surfaces, it may also be
necessary to use a specially constructed high-temperature delay line. It is
recommended that the probe be left in contact with the surface for as short