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4.4.3 Two-point calibration
This procedure assumes that the user has two known material thickness points of the
test material and that these are representative for the measuring range.
1. The zero setting is made
2. Coupling agent is applied to the material sample.
3. The US measuring probe is placed on it (at the first or second calibration point)
and the correct position of the US measuring head on the material sample is
checked. The display should now show a (probably incorrect) measured value
and the coupling symbol should appear.
4. As soon as a stable measured value is reached, the sound generator is lifted
off. If the reading differs from that when the transducer was coupled, step 3 must
be repeated.
5. The key is pressed and the M/S (or IN/ µS) should start flashing.
6. The and keys
can now be used to correct the required material thickness
on the display until it matches that of the material pattern.
7. The key
is pressed and the display shows 1OF2. Steps 3) to 6) are now
repeated for the second calibration point.
8. The key is pressed so that the M/S (or IN/ µS) starts to flash. The instrument
now displays the sound velocity value that it has calculated based on the
material thickness value entered in step 6).
9. Press the key
again to exit the calibration mode. Measurement can now be
started in the preprogrammed measuring range.
4.5 perform measurements
The meter always stores the last measured value until a new value is added.
For the sound generator to function properly, there must be no air bridges between its
contact surface and the surface of the material to be measured. This is achieved with
the ultrasonic gel, the "coupling agent". This liquid "couples" or transmits the ultrasonic
waves from the transducer into the material and back again. Before the measurement,
a little coupling agent should therefore be applied to the material surface to be
measured. Even a single drop is sufficient.
Then the US measuring probe is carefully pressed firmly onto the material surface. The
coupling symbol and a number appear in the display. When the instrument has been
"properly adjusted" and the correct sound velocity has been determined, the number
in the display shows the current material thickness measured directly under the sound
source.
If the coupling indicator does not appear or the number on the display is questionable,
first check that there is sufficient coupling agent at the point under the US probe and
that it has been placed flat on the material. Sometimes it is necessary to try a different
transducer for the material in question (diameter or frequency).
While the US measuring probe is in contact with the material to be measured, four
measurements are taken per second. When it is lifted from the surface, the display
shows the last measurement.
