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6.2 Material Velocity Calibration
This section presents the velocity calibration procedure for the Veo and Prisma test
instruments. The Velocity & Zero Wizard calibrates the material velocity and sets
the probe zero.
NOTE: While calibrating the material velocity, try to apply more or less the same pressure on
the probe handle.
To calibrate the velocity:
1 Select the correct calibration block according to the material to inspect.
2 On the test instrument, press the MENU key.
3 Select the Calibrate tab and, on the Calibration menu, select Velocity & Zero
Wizard.
4 Select a thickness reference.
5 Select 2 back-wall echoes.
The signals from these reflectors determine the velocity of the longitudinal wave in
the material.
NOTE: The zero calibration is not used since the IFT gate has been activated (refer to
section 7.1
"Interface Triggering (Zero Synchronization)").
6.3 TCG and Sensitivity Calibration
The TCG (time corrected gain) sets variable receiver gains over the time base of the
A-scan. Theprimary function of TCG is to compensate for signal attenuation as well
as variations in the energy of the sound field through the depth of a material.
Therefore, the amplitudes of echoes from reflectors of equal size at different depths
in the same material are display at the same full screen height.
Figure presents the signal when no TCG has been calibrated. Compare this images
to the three others that follow.
Figure
There are three types of TCG curve: automated, manual, and constant dB.
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