least 13 mm 1/2 inch from one edge of the AWS D1.1/D1.1M, Type SC secondary
standards shall be used similarly. Acceptability shall be on the same
basis as in the primary standard.
2.8.2.4
Far-Surface Resolution
The equipment shall delineate the three resolution holes in the resolution
block appropriate for the angle of the transducer to be used in the
inspection.
2.8.2.5
Signal-to-Noise Ratio
With the search unit located as in the near-surface resolution tests, the
gain shall be set to obtain an 80-percent full screen height first
reflection from the respective reference reflector. The reference
reflection-to-noise shall not be less than 10 to 1.
2.8.2.6
Penetration
At least three multiple back reflections through plates up to 75 mm 3 inches
thick and at least one for plates greater than 75 mm 3 inches thick shall
be obtained. In either case, the initial or back reflection only shall
fall within mid-screen range with a gain input no greater than 50 percent
of the instrument capacity.
2.8.3
Immersion Testing
For immersion techniques, the back reflection from the interface between
the couplant and the plate surface is called the "first interface signal".
All measurements are to be referenced to this signal. The equipment shall
meet all requirements of paragraph EQUIPMENT SENSITIVITY CALIBRATION.
2.9
EQUIPMENT SENSITIVITY CALIBRATION
Sensitivity calibration shall be done immediately after a change of
operators and at least every 30 minutes thereafter as testing proceeds.
Recalibration shall also be required after any power interruption,
including a change of source, when the equipment is suspected of being in
error, or after relocation on the jobsite. The 30-minute and relocation
calibrations may coincide. Before calibration is attempted, the instrument
shall be allowed to warm up.
2.9.1
Calibration of Longitudinal Wave System
The instrument range and delay controls shall be adjusted to display
signals from the far surface of the plate to be inspected. The gain shall
be adjusted to produce a first back reflection 50 percent of full-scale.
The reject/repair line shall be established at 40 percent of full-scale or
2 dB below mid-screen height. The relationship between the 50-percent
reflection and the first back reflection from the 1.52 mm 0.060 inch
reference hole in the primary standard shall be determined in the following
way: without further adjustment of the instrument gain after the initial
sensitivity setting, the transducer shall be coupled to the primary
standard and positioned for a maximum first back reflection from the 1.52
mm 0.060 inch reference hole. The instrument gain shall be adjusted to
bring the maximum reflection to mid-screen height and this instrument gain
setting shall be recorded. A similar relationship, correlated with the
respective plate identifications, shall also be reported for each
subsequent plate inspected. Adjustment for loss of signal due to distance
SECTION 05092A
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