Checkline TI-25DL - Manual (Page 18)

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6.3 Changing Calibration - Acoustic Velocity Is Not Known
In applications where the type of material is not known or the material
is not listed in the Acoustic Velocity Table, the following procedure
can be used to calibrate the gauge for highest accuracy.
1. Obtain a sample of the material with a known thickness or use a
micrometer, caliper or similar device to accurately measure it.
2. Turn on the gauge by pressing the key.
3. Place a small amount of coupling fluid on the sample of known
thickness and place the probe on the sample. The Stability Indicator
should have nearly all its bars illuminated. Having achieved a stable
reading remove the probe from the sample.
4. Press the key.
5. The units of measure indicator “IN” or “MM” will be flashing
indicating that you are in the Measurement Calibration mode. (The
other calibration mode is the Acoustic Velocity Calibration mode, as
described in Section 6.2, which is used to adjust the acoustic
velocity to another known value.)
6. Use the and keys to adjust the displayed measurement
value to match the thickness of the known sample. By pressing and
holding the key, the numbers will change more rapidly.
7. Press the key again and the acoustic velocity units indicator
“IN/µs” or “M/s” will be flashing showing the acoustic velocity
value that was calculated for this sample. If desired, record this
value so it can be re-entered easily in the future.
8. Press the key again to exit the calibration mode and return to
the measurement mode.
Note: If the key is pressed while in the calibration mode, the
TI-25DL will be reset to the factory default calibration for common
steel (0.2330 IN/µs or 5920 M/s).
6.4 Performing a 2-Point Calibration
When desired, a user can perform a 2-Point Calibration using two
known samples with varying thickness. The two samples should be
representative of the thickness readings that will be enountered and the
thickness values should be known. Perform the following steps:
1. Turn on the TI-25DL power by pressing the key.
2. Perform a Probe-Zero (refer to Section 4.3).
3. Apply coupling fluid to the first sample of known thickness.
4. Measure the first sample as described in Section 3.3, making sure
that the probe surface is flat against the surface of the sample. The
display will show a thickness value (possibly inaccurate) and most
(or all) of the bars of the Stability Indicator will be illuminated.
5. Having achieved a stable reading, remove the probe. If the
displayed thickness reading changes, from the one previously
shown when the probe was in contact with the sample, repeat
step 4.
6. Press the key. The “IN” or “MM” indicator should begin
flashing on and off.
7. Press the or keys to change the currently displayed
thickness value until it matches the thickness value of the known
sample.
8. Press the key. The display will flash “10F2”.
9. Repeat steps 3 through 7 for the second sample of known
thickness.
10. Press the Probe-Zero key again and the display will now show the
sound velocity value it has calculated based on the two known
thickness values that were entered.
Upon completion of steps 3 through 7 for the second sample, the
TI-25DL will calculate and display the best acoustic velocity based
on the two samples. The TI-25DL is now ready for use.
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