MIL-PRF-21038/27 Inspection, Sampling, Testing

The original MIL specification for interface transformers used in MIL-STD-1553 applications was known as MIL-T-21038. Reflecting the diversity of applications utilizing the MIL-STD-1553 LAN by the late 1990s, the most recent revision, MIL-PRF-21038/27E (February 26, 2007), allows designers to select a QPL device and limit the testing to what is needed for the application:

Level C - for high reliability commercial/industrial applications. Level C parts are tested to the least stringent of the sampling plans. Level C calls for Hytronics to sample and test to internally established criteria assuring performance and reliability. Group A or B testing is not performed on Level C parts.

Level M - for general purpose military applications. A Level M part is exactly the same as the original QPL product that was defined by the earlier MIL-T-21038/27 specification. Level M requires Group A inspection and Group B inspection.

Level T - for high reliability critical military applications. A Level T part receives the most extensive testing along with thermal cycling. Level T requires Group A inspection and Group B inspection. The Level T transformer is subject to thermal shock screening in accordance with MIL-STD-202, method 107, test condition A (5 cycles). Following the thermal shock screening, the winding continuity test shall be performed on all transformers (MIL-PRF-21038, paragraph 4.7.2).

For a complete description of Level C, M, and T conformance and inspection requirements, see MIL-PRF-21038, paragraph 4.6 "Conformance Inspection."