Checkline TI-25S - Manual (Page 6)

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IN/µs Symbol: When the IN
symbol is on, in conjunction with
the /µs symbol, the TI-25S is
displaying a sound-velocity value in
inches-per-microsecond.
M Symbol: When the M symbol is on,
in conjunction with the /s symbol, the
TI-25S is displaying a sound-velocity
value in meters-per-second.
3.3 Transducer
The transducer is the “business end” of the
TI-25S. It transmits and receives the ultra-
sonic sound waves which the TI-25S uses
to calculate the thickness of the
material being measured. The transducer
connects to the TI-25S viathe attached
cable and two coaxial connectors. When using the transducer, the
orientation of the dual coaxial connectors is not critical: either plug
may be fitted to either socket in the TI-25S.
The transducer must be used correctly in order for the TI-25S to produce
accurate, reliable measurements. Below is a short description of the trans-
ducer, followed by instructions for its use.
This is a bottom view of a typical transducer.
The two semicircles of the wearface are
visible, as is the barrier separating them. One
of the semicircles is responsible for conduct-
ing ultrasonic sound into the material being
measured, and the other semicircle is respon-
sible for conducting the echoed sound back
into the transducer. When the transducer is
placed against the material being measured,
it is the area directly beneath the center of the
wearface that is being measured.
This is a top view of a typical transducer.
Press against the top with the thumb or index
finger to hold the transducer in place.
Moderate pressure is sufficient, as it is only
necessary to keep the transducer stationary,
and the wearface seated flat against the
surface of the material being measured.
1.8.8.8.8
+ IN MM/ µs
1.8.8.8.8
+ INM M / µ s
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11.0 A PPENDIX A: A PPLICATION N OTES
Measuring pipe and tubing
When measuring a piece of pipe to determine
the thickness of the pipe wall, orientation of the
transducers is important. If the diameter of the
pipe is larger than approximately four inches,
measurements should be made with the transducer oriented so that the gap in
the wearface is perpendicular (at right angle) to the long axis
of the pipe. For smaller pipe diameters, two measurements should be
performed, one with the wearface gap perpendicular, another with the gap
parallel to the long axis of the pipe. The smaller of the two displayed
values should then be taken as the thickness at that point.
Measuring hot surfaces
The velocity of sound through a substance is dependent 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 9) on a sample piece of known
thickness, which is at or near the temperature of the material to be
measured. This will allow the TI-25S to correctly calculate the velocity
of sound through the hot material.
When measuring on hot surfaces, it may also be necessary to use a
specially constructed high-temperature transducer. These transducers are built
using materials which can withstand high temperatures. Even so, it is recom-
mended 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 itself, and through thermal expan-
sion and other effects, may begin to adversely affect the accuracy of measure-
ments.
Measuring laminated materials
Laminated materials are unique in that their density (and therefore sound-
velocity) may vary considerably from one piece to another. Some laminated
materials may even exhibit noticeable changes in sound-velocity across a sin-
gle surface. The only way to reliably measure such materials is by
performing a calibration procedure on a sample piece of known thickness.
Ideally, this sample material should be a part of the same piece being
measured, or at least from the same lamination batch. By calibrating to each
test piece individually, the effects of variation of sound-velocity
will be minimized.
Perpendicular Parallel