shall be compensated for as specified below. However, for plates less than
25 mm 1 inch thick, no adjustment for loss of signal is required.
2.9.2
Calibration of Secondary Standard
After adjusting the first reflection from the reference hole in the
secondary standard to a 50-percent full-scale response for a shear or
longitudinal wave inspection, a maximized reflection from the 1.52 mm 0.060
inch reference hole in the primary standard shall be obtained without
changing the gain setting. This gain setting shall be readjusted to obtain
a 50-percent full-scale reflection. The readjusted setting shall be
recorded to provide a basis for recalibration when the secondary standard
is unavailable.
2.9.3
Equipment With a Calibrated Gain Control
When a calibrated gain control attenuator is used, the transducer shall be
positioned for maximum reflection from the reference hole in the secondary
standard representing approximately 1/2 the longest inspection distance.
This reflection shall be adjusted to mid-scale by varying the gain control
accordingly. The difference in decibels between this amplitude and the
signals obtained from the first, second, and longest distance reflections
obtainable on the secondary standard shall be measured. The differences
shall be recorded and plotted on a curve to determine the necessary
correction to the amplitude at the various inspection distances. A level
80 percent of the primary level, obtained from the corrected signal
heights, is equal to the reject/repair line.
2.9.4
Equipment With Electronic Distance Compensation Circuitry
If the distance in amplitude between the first reflection and the
reflection obtained from the maximum inspection distance is 1 dB or less,
the instrument may be used as is. If not, the procedure used for equipment
with a calibrated decibel control shall be used to determine the necessary
correction for the reflections obtained at the various inspection distances.
2.9.5
Longitudinal Wave Distance-Amplitude Corrective Curve
A longitudinal wave distance-amplitude correction curve shall be
constructed and drawn on the face of the CRT when longitudinal waves are to
be used in the inspection and when material thickness exceeds 50 mm 2 inches
if the test equipment design permits. The reference hole in the secondary
standard shall be used. The instrument sensitivity shall be adjusted to 50
percent full-scale of the maximized response from the reference hole at 1/2
maximum inspection distance. The reject/repair line shall be constructed
at 80 percent of the established distance-amplitude curve. The reflection
amplitudes to define this curve shall be taken from the faces of the
secondary sensitivity standard which are 25 mm 1 inch, 50 mm 2 inches, 1/2
maximum inspection distance, and the longest distance obtainable from the
secondary standard, respectively, from the reference hole. When a
correction curve cannot be drawn on the face of the CRT, an approved
distance-amplitude correction method shall be applied.
2.9.6
Longitudinal Wave Inspection Using Immersion Techniques
The reference hole in a secondary standard shall be used for each different
inspection distance. Reject/repair limits shall be established by
immersing both the search unit and secondary standard in the liquid bath in
which the inspection is to be conducted. The following procedure shall be
SECTION 05092A
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