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6) The
and the
until it matches the sound velocity of the sample piece.
7) The
key has to be pressed. 1OF2 will be shown on the display. Steps 3 to 6 are
to be repeated on the second calibration point.
8) The
key has to be pressed, so that the symbol M/S (or IN/µS) is flashing. The
sound velocity value, which was calculated based on the thickness values being en-
tered in step 6, will now be displayed.
9) To quit the calibration mode, the key
ment is ready to perform measurements within its range.
4.4 How to perform measurements
The instrument always stored the last measured value until a new measurement is
made. In order for the transducer working in the right way there may not be any gaps
between the contact area of the sensor and the surface of the material being meas-
ured. This is accomplished with the coupling fluid, commonly called "couplant". This
fluid serves to "couple" or transfer the ultrasonic sound waves from the transducer,
into the material and back again.
Therefore a small amount of couplant should be applied onto the surface of the mate-
rial, before measurements are performed. Typically, a single droplet is sufficient.
After the couplant is applied, the transducer has to be pressed firmly against the area
being measured. The coupling status indicator should appear on the display as well
as a digit number. If the instrument has been "zeroed" properly and if it has been set
to the correct sound velocity, the actual thickness of the material directly beneath the
transducer will be indicated as a number in the display.
If the coupling status indicator doesn't appear or if it isn't stable or if the numbers on
the display doesn't seem to be correct, it has to be checked whether there is an ade-
quate film of couplant beneath the transducer and whether the transducer is placed
flat onto the material.
If conditions persist, sometimes it is necessary to select a different transducer (size
or frequency) for the material intended to be measured.
While the transducer is in contact with the material, the instrument will perform four
measurements every second, updating its display as it does so.
If the transducer is removed, the display will hold the last measurement performed.
Note: Occasionally a small film of couplant will be drawn out between the transducer
and the surface, as the transducer is removed. If this happens, the instrument may
perform a measurement through this couplant film, resulting in an erroneously meas-
urement. This is comprehensible because one thickness value is observed while the
transducer is in place and the other value is observed after the transducer is re-
moved.
In addition, measurements performed through very thick paint or coatings may result
in the paint or coating being measured rather than the material intended.
12
key have to be used to adjust the sound velocity up and down
has to be pressed again and the instru-
TN_US-BA-e-1814
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