Description: This revision added paragraphs on repeated circuits, selected and matched parts, and designation of deposited components on hybrid printed circuits. An appendix B was added covering the Item Designation system of IEC Publication 113-2. Supplement A of 1970 was incorporated into the text, along with minor clarifications and updating of references. Significant changes are marked by vertical black bars in the margin, adjacent to the changed text. The 1968 revision and its 1970 Supplement coordinated the title with the terms used in related standards, added the class letter U, identified names approved in the Federal Item Identification Guide (H6-1), and transferred the class letter list to IEEE Std 315 (ANSI Y32.2). The original issue of this standard was prepared by Subcommittee 16 on Reference Designations, appointed by Sectional Committee Y32 on Graphic Symbols and Designations for the purpose of preparing standard reference designations in the field of electrical and electronic equipment. Early work on reference designations, of the type herein standardized as the Unit Numbering Method, was done by the Symbols Committee of the Institute of Radio Engineers and was published in 1949 as Standards on Designations for Electrical, Electronic and Mechanical Parts and their Symbols, 49 IRE 21.SI. In 1951 the U.S. Department of Defense issued MIL-STD-16 which closely resembled the IRE Standard and acknowledged the pioneering work of the IRE Symbols Committee in this field. In order to minimize confusion, intensive and successful efforts have since been made to coordinate the two standards throughout their subsequent revisions. The work on this standard was greatly facilitated by the constant participation of representatives of the Department of Defense and the IEEE Symbols Committee. As in MIL-SfD-16C, the original Block Numbering Method of assigning reference designations has been deleted in favor of the more flexible and universally applicable Unit Numbering Method, whichis retained, with minor modifications, in Section 4 of this standard. The explanation of the Block Numbering Method appearing as Appendix A does not form a part of this standard, but is retained for reference in connection with existing equipment on which it was used. The subcommittee was assigned the task of standardizing means for physically locating, through a form of reference designation, the parts and divisions of an equipment. The Location Numbering Method in Section 5 and the Location Coding Method in Section 6 of this standard are based on existing industry practices which have been successfully used to facilitate manufacture and service of complex apparatus by providing such locating means. They are especially useful in designs making multiple use of identical or closely similar parts of subassemblies.
Oversight Committee: SASB
Sponsor: IEEE-SASB Coordinating Committees
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