MIL-STD-981C
5.6.7.2 Inspection lot.
5.6.7.2.1 Class B. An inspection lot shall include completely assembled devices of the same grade, construction, class, family, and electrical characteristics, manufactured under essentially the same conditions and having similar construction and materials. (Similar construction and materials shall be construed to include differences that will not affect test results.) Sample units shall be so selected as to be, as far as practicable, representative of the volt-ampere range of electrical values and physical dimensions included in the lot.
5.6.7.2.2 Class S. An inspection lot shall consist of completely assembled devices of a single grade, construction, class, family, and part number from one procurement document. Each lot shall meet all the lot controls specified in 5.6.1.1.1.2 for Class S devices.
5.6.7.3 Group A screening inspection. Screening inspections shall consist of the examinations and tests as specified in Tables V through X.
5.6.7.3.1 Lot acceptance. If, during the 100 percent inspection of subgroup I, 5 percent or (1) device whichever is greater, is discarded, the lot shall be rejected. NOTE: Radiographic and visual inspection shall not be included in the PDA calculation.
5.6.7.3.2 Rejected lots. For class B devices, if an inspection lot is rejected, the contractor may rework it to correct the defects, or screen out the defective units and resubmit for reinspection. Resubmitted lots shall be 100 percent inspected. Such lots shall be separate from new lots, and shall be clearly identified as reinspected lots. Rework of Class S devices shall not be permitted unless approved by the procuring activity.
5.6.7.3.3 Power transformers, power inductors, audio transformers, audio inductors, high power pulse
transformers, charging inductors, saturable transformers, and saturable inductors (families 03, 04, 20, 21,
36, 37, 40 and 41 respectively). These devices shall be subjected to the group A screening tests of
TABLE V.
5.6.7.3.3.1 Thermal shock. Thermal shock screening shall be in accordance with MIL-PRF-27, and as follows:
a. Number of cycles - The number of cycles shall be as specified in the procurement document but shall be restricted to 5, 10, 15, 25 or 50 cycles for Class B parts and 25 cycles minimum for Class S parts.
b. Continually monitor continuity during the entire final cycle to verify no intermittent conditions.
Continuity monitoring current shall not exceed 100 microamperes. Equipment shall be capable of detecting intermittent opens exceeding 100 microseconds.
NOTE: Continuity monitoring is not required for self-leaded parts with 26 gauge wire and heavier, or equivalent cross sectional area.
c. Class S parts using magnet wire smaller than AWG 38 shall have DC resistance measured before and after the thermal shock screen. The change in resistance shall not exceed ±3 percent.
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