Back Surface Resolution

T.O. 33B-1-1 1.8.2.4.2.1 Back 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 the respective signals returning to the baseline. d. If a test system with a 2.25 MHz search unit does not meet these resolution requirements, the search unit and/or cable SHALL be replaced and the resolution checked again. If the inspection system still does not meet the above requirements, the instrument SHALL be repaired or replaced. 1.8.2.4.2.2 Entry Surface Resolution (Dead Zone). 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 inch metal 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 pattern according 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 the position of the hole signal on the calibrated distance scale of the waveform display. The distance should 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 initial pulse shall return to the baseline, as shown in the ‘‘good’’ example of Figure 1-14, for the following conditions: (1) 10 MHz: Good at P-1 and P-2 (2) 5 MHz: Good at P-2 (3) 2.25 MHz: Good at P-2 e. If the first echo from the edge of the hole is not completely separate from the initial pulse as required above, the search unit and/or cable SHALL be replaced and the dead zone checked again. If the inspection system still does not meet the above requirements, the instrument SHALL be repaired or replaced. Change 2 1-61