1.10.3.7
Transducer Angle
The established exit point of the probe shall be set over the applicable
angle index line scribed on the 200 mm 8 inch or 300 mm 12 inch edge, as
appropriate, of the primary standard. The gain shall be set to obtain a
mid-screen first reflection from the 50 mm plexiglass-lined hole for search
units up to 70 percent with the search unit placed on the 200 mm 8 inch
edge. Search units of large angles that have been approved specifically by
the Contracting Officer shall be tested from the 300 mm 12 inch edge using
the 1.524 mm 0.06 inch reference hole. The search unit shall be moved back
and forth to maximize the first reflection. When the material to be
inspected is not acoustically similar to the primary standard, the
inspection angle shall be within plus or minus 2 degrees of the angle
specified in the approved procedure. Requalification is required after 40
hours or as otherwise stated.
1.11
SENSITIVITY CALIBRATION OF LONGITUDINAL AND ANGLE WAVE SYSTEMS
Sensitivity calibration shall be done immediately after a change of
operators and at least every 30 minutes thereafter as testing proceeds.
Recalibration will be required after any power interruption, including a
change of source, when the equipment is suspected of being in error, or
after relocation of the jobsite. The 30-minute and relocation calibrations
may coincide. The instrument shall be allowed to warm up before
calibration is attempted. The instrument range and delay controls shall be
adjusted to display signals from the reference hole in the primary (IIW
block) or secondary standard (DSC or SC block or both) on the viewing
screen for the range of distances to be inspected.
1.11.1
Calibration Procedure
The test instrument shall be calibrated as described below.
1.11.1.1
Longitudinal Wave
In calibrating with the primary standard, the transducer shall be
positioned on the 100 mm 4 inch edge for maximum reflection from the 1.524
mm 0.06 inch reference hole. The gain shall be adjusted so that the first
reflection is at 50 percent full scale. The top of that indication shall
be marked on the CRT with a wax pencil or by other means. This establishes
the standard reference level. A point at 80 percent of the standard
reference level shall be calculated and marked. This locates the
reject/repair line. If a secondary standard is to be used in the
inspection, the reject/repair line shall be established similarly. For the
DSC block, the transducer shall be positioned on the 100 mm 4 inch long
surface and with the SC degrees sound entry point lines. Adjustment for
loss of signal due to distance shall be compensated for as noted above.
1.11.1.2
Angle Wave
In calibrating with either the primary or secondary standard, the
transducer shall be positioned on the same surfaces as in the case of the
longitudinal wave system but over the sound entry point lines appropriate
for the angle of the transducer to be used in the inspection. The gain
shall be adjusted to give a first reflection that is 50 percent of
full-scale response. The top of that indication shall be marked with a wax
pencil or by other means. This establishes the standard reference level.
A point at 80 percent of the standard reference level shall be calculated
and marked. This locates the reject/repair line. Loss of signal shall be
SECTION 05091A
Page 17
Previous Page
