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7.3.2 Known Thickness Calibration
If the sound velocity of a material is unknown, a sample with one or two known thicknesses can be
used to determine the sound velocity.
Note: Known thickness calibration must be performed on material with the paint or coating removed.
Failure to remove the paint or coating prior to calibration will result in a multi-material velocity
calculation that may be different from the actual material velocity intended to be measured.
One-point Thickness Calibration: The one point calibration option is most suited for linearity over
large ranges. You should always calibrate on high side of the intended measurement range. For
example, if the measurement range is 2.54 mm to 25.4 mm (.100" to 1.0"), you should calibrate on
a known thickness sample close to 25.4 mm (1.0").
Note: Before you start this calibration procedure, perform a probe zero.
1. Physically measure an exact sample of the material or a location directly on the material to be
measured using a set of callipers or a digital micrometer.
2. Apply a drop of couplant on the transducer and place the transducer in steady contact with the
sample or the material being tested. Be sure that the reading is stable and the repeatability
indicator, in the top left corner of the display, is fully lit and stable.
3. Press
, scroll to the CAL menu and then highlight the ONE POINT function.
4. Press
to display the Digits Edit Box.
5. Use the
and
6. Use the
and
7. Repeat steps 5 and 6 until the known thickness value is correctly displayed.
8. Press
to calculate the velocity and return to the menu screen, or
9. Press
to return to the measurement screen.
Note: CHECK YOUR CALIBRATION! Place the transducer back on the calibration point. The
thickness reading should now match the known thickness. If the thickness is not correct, repeat the
steps above.
Two-point Thickness Calibration: For improved accuracy over a smaller measurement range,
conduct a one-point calibration followed by a two-point calibration. For example, if the measurement
range is 2.03 mm to 6.35 mm (.080" to 0.250"), perform a one point calibration on a known
thickness sample close to 6.35 mm (.250"), followed by a two-point calibration close to 2.03 mm
(.080").
Note: Before you start this calibration procedure, perform a probe zero.
1. Conduct a one point calibration routine as described previously in this section. You should
conduct this routine at the high end of the measurement range.
2. Physically measure an exact sample of the material or a location directly on the material to be
measured using a set of callipers or a digital micrometer. You should measure at the low end
of the measurement range.
arrows to scroll the highlighted value.
arrows to scroll the digit locations.
to cancel.
12
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