Application Notes - Elcometer 207 Operating Instruction

17 APPLICATION NOTES

17.1 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.
17.2 MEASURING HOT SURFACES
The velocity of sound through a material depends upon the temperature of the material. As materials heat
up, the velocity of sound in the material decreases. In most applications with surface temperatures less than
approximately 100° C (~200° F), no special procedures are required. At temperatures above 100° C
(~200° F), the change in sound-velocity of the material being measured starts to have a noticeable effect
upon the accuracy of ultrasonic measurement.
At such elevated temperatures, it is recommended that the user perform a calibration procedure (see
"Calibration" on page 15) on a sample piece of known thickness, which is at, or near, the temperature of the
material to be measured. This will allow the gauge 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
a time as needed to acquire a stable measurement. While the transducer is in contact with a hot surface, it
will begin to heat up, and through thermal expansion and other effects, may begin to adversely affect the
accuracy of measurements.
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