MIL-DTL-24784 / 21B (SH)
e.
Function names. Each functional area of each unit shall be identified by a descriptive name.
These functional areas shall then be further broken into subfunctions, each being assigned a
descriptive name. Once a function name has been assigned, the identical name shall always
appear whether it appears on an FBD or on an FCD to identify the functional boundary. No
two functional areas may be assigned the same name.
f.
Diagram (drawing) numbers. In systems with fully implemented unit numbers, all FBDs shall
be numbered FBDXXXX, where XXXX is equal to the unit number (that is: 1001, 1002,
1107, and so forth), except for the master FBD or FCD. The master FBD or FCD shall be
numbered FBD0000 or FCD0000. For those cases where one FBD (or FCD) is used for
multiple and identical units, the lowest unit number shall be used (that is, units 1071 and 1072
shall be FBD1071). In other systems, FBDs shall be numbered chronologically.
g.
Sheet numbers. FBDs or FCDs having multiple sheets shall be assigned sheet numbers
starting with the number one. The drawing sheet number and zone number shall be used to
identify signal interconnections between sheets of the same FBD or FCD.
h.
Zone numbers.
1.
The zone number and sheet number shall be used to identify signal interconnections
between sheets of an FBD and when referencing between FBDs or from FBDs to FCDs
and vice versa. Sheet and zone numbers shall be as shown on figure 21-10.
2.
Zone number references shall call out the drawing coordinates of the referenced detailed
signal name rather than call out the drawing coordinates of the symbol itself. Brackets
may be used when all of a group of signals come from or go to the same place.
i.
Reference designations. Reference designations shall be used to correlate circuit symbols to
actual hardware locations. All hardware boundaries, logic symbols, electrical symbols, and
analog symbols shall be identified by the reference designations assigned to the hardware
being depicted.
3.5.1.1.3 Diagram drafting requirements. This subsection defines the requirements for line
weights, methods of depicting interconnecting lines, symbol sizes, lettering size, and notes in the
preparation of FBDs.
a.
Line weights. Hardware and functional boundaries and boundary titles shall be prepared as
described in the following paragraphs.
1.
Hardware boundary. A hardware boundary shall be a long-dash, short-dash light (0.005
inch) line. The length of the long dash in relation to the length of the short dash should
be drawn so that the long dash does not give the impression of a solid line. The
hardware boundary title shall be positioned as illustrated on figure 21-11.
2.
Functional Boundary. A functional boundary shall be a solid medium (0.01 inch) line.
The functional boundary title shall be positioned as illustrated on figure 21-12.
b.
Interconnecting lines. Interconnecting (data, signal and control) lines shall be prepared in the
following manner:
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