Adjusting The Extended Blank With Dual Element Transducers - Olympus 45MG User Manual

The gain value appears near the lower-right corner of the display. The waveform
display changes to the amplitude proportional to the gain mode.
2. Press [] or [] to adjust the gain in ±1 dB steps.
The gain value and the height of the echoes change accordingly.
• Increase the gain value when the peak amplitude of the echo that should be
detected is below 20 % of the waveform display height.
This prevents the gage from reading too high a value when skipping one
back-wall echo, and from measuring twice the correct thickness (doubling).
• Reduce the gain value when noise peaks are above 20 % of the waveform
display height.
This prevents the gage from detecting a noise peak rather than the correct
back-wall echo.
3. Press [2nd F], [GAIN/WAVE ADJ] again to restore the default gain value.
4. Press [GAIN/WAVE ADJ] again to return to the automatically adjusted echo
height mode.
The default automatic gain mode is indicated by a blank Gain field.
9.2

Adjusting the Extended Blank with Dual Element Transducers

Olympus recommends using the extended blank parameter only if you are an
experienced operator who thoroughly understands the acoustic properties of the
material being measured. Incorrect use of the extended blank can cause the gage to
misread areas of thin material.
Normally, the 45MG searches for echoes down to nearly zero thickness. However,
some special circumstances, such as a high degree of near-surface corrosion,
aluminum material, enclosed flaws, or laminations, can generate echoes that the
instrument may falsely detect as the low thickness. When these echoes are larger than
the sought after back-wall echo, the manual gain adjustment (see "Adjusting the Gain
with Dual Element Transducers" on page 149) cannot prevent this false detection.
However, the extended blank parameter allows you to define an early period, during
which the 45MG will not perform echo detection, thereby preventing erroneous
measurements.
CAUTION
DMTA-10022-01EN, Rev. C, January 2015
Using Advanced Gaging Features 151