T.O. 33B-1-11.8.2.4.2.1Back Surface Resolution.a.Position the search unit on an IIW block, and peak the signal from ref lector A.b.Maximize the separation of the signals from the ref lectors A, B and C.c.Evaluate the resolution by matching the signal patterns. Good resolution is indicated by therespective signals returning to the baseline.d.If a test system with a 2.25 MHz search unit does not meet these resolution requirements, the searchunit and/or cable SHALL be replaced and the resolution checked again. If the inspection system stilldoes not meet the above requirements, the instrument SHALL be repaired or replaced.1.8.2.4.2.2EntrySurfaceResolution(DeadZone).a.Position the search unit on an IIW block at P-1 or P-2 as shown in Figure 1-14. P-1 gives 0.2 inchmetal travel distance to the edge of the large hole. P-2 gives 0.4 inch metal travel distance.b.Maximize the separation between the initial pulse and the hole signal. Evaluate the signal patternaccording to the criteria given in Figure 1-14.c.Check that the hole signal is actually the indication of the first echo from the hole by noting theposition of the hole signal on the calibrated distance scale of the waveform display. The distanceshould be the actual depth of the hole.d.The first echo from the edge of the hole shall be completely separate from the initial pulse. The initialpulse shall return to the baseline, as shown in the ‘‘good’’ example of Figure 1-14, for the followingconditions:(1)10 MHz:Good at P-1 and P-2(2)5 MHz:Good at P-2(3)2.25 MHz:Good at P-2e.If the first echo from the edge of the hole is not completely separate from the initial pulse as requiredabove, the search unit and/or cable SHALL be replaced and the dead zone checked again. If theinspection system still does not meet the above requirements, the instrument SHALL be repaired orreplaced.Change 21-61
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