compensated as noted.
1.11.2
Calibration of the Secondary Standards
After adjusting the first reflection from the reference hole in the
secondary standard to 50 percent full-scale response for a sheer or
longitudinal wave inspection, a maximized reflection from the 1.524 mm 0.06
inch reference hole in the primary standard shall be obtained without
changing the gain setting. The gain setting shall be readjusted to obtain
a 50 percent full-scale reflection and the readjusted setting shall be
recorded as required by paragraph SUBMITTALS, SD-03, to provide a basis for
recalibration when the secondary standard is unavailable.
1.11.3
Equipment With a Calibrated Gain Control (Attenuator)
When a calibrated gain control attenuator is used, the transducer shall be
positioned for a 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 signal obtained from the first, second, and longest
distance reflection 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 of 80 percent of the primary level obtained from the corrected
signal heights, is equivalent to the reject/repair line.
1.11.4
Equipment With Electronic Distance Compensation Circuitry
If the difference 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 to the reflections obtained at the various inspection distances.
This characteristic of the equipment shall be re-examined on a monthly
basis or as otherwise stated in paragraph EQUIPMENT QUALIFICATION
REQUIREMENTS, and correction factors shall be modified accordingly.
1.11.5
Longitudinal Wave Distance-Amplitude Correction Curve
A distance-amplitude correction curve may be used instead of the calibrated
gain control or the electronic circuitry for either the shear or
longitudinal wave system as described below:
a. A shear wave distance-amplitude correction curve shall be
constructed and drawn on the face of the cathode ray tube (CRT) for
inspection of weldments in excess of 38 mm 1-1/2 inch thick when the
design of the test equipment permits. The reference hole in the
secondary standard [SC] [or] [DSC] shall be used to construct the
distance-amplitude correction curve for a minimum of three node points,
1, 2, and 3. The sensitivity of the instrument shall be adjusted to
produce 50 percent full-scale response for the maximized primary
reflection and the reject/repair line shall be constructed at 80
percent of the established distance-amplitude curve.
b. 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 for material thicknesses exceeding 25
mm 1 inch, if design of the test equipment permits. The reference hole
SECTION 05091A
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