MIL-DTL-24784/20B (SH)
given in paragraph f.1 below. If FCDs are required for a unit having all three types of the above
circuits, all circuits shall be shown on the same drawing numbered FCD.
a.
Schematics are not required for unit wiring or similar interconnecting hardware devices
because complete interconnecting information appears on the FCDs. Components such as
switches, relays, terminating resistors, and so forth, mounted directly on the cabinet shall be
shown in schematic form on the FCD using the rules for detailed FCDs (refer to paragraph e
below).
b.
Layout techniques. An FCD shall be prepared for each function defined on the lowest level
of FBD where it is necessary to show circuits that are not located on pluggable modules and
for the power and grounding circuits. Layout of the symbols on the FCD shall provide a left-
to-right functional flow. Circuit symbols shall be functionally divided by thin lines in direct
relationship to a functional block on a related FBD, and the functional division on the FCD
shall be identified by the same function name. If the equipment is sufficiently complex, an
FCD may consist of multiple sheets; then, functional flow shall be left-to-right from sheet to
sheet. All inputs and outputs of the function depicted on the FCD shall be identified by signal
names. Inputs shall be referenced to the source FCD and outputs shall be referenced to the
destination FCD. For smaller systems or equipments, an FCD sheet may contain more than
one function and possibly the entire equipment.
c.
Analog functionalization. In analog functions, the FCD details the operating elements
(emitter followers, amplifiers, and so forth) within the function using special block symbols or
schematic symbols. The special block symbols shall be used to detail replaceable circuit
elements or modules that are used as building blocks in the analog equipment.
d.
Schematic symbols shall be used to detail circuits of assemblies or modules having
replaceable parts. The resulting FCD may have both symbolic and electrical schematic
characteristics with functional grouping techniques applied. Schematic representations on the
FCD shall be formed using the rules set forth for detailed FCDs.
e.
Detailed FCDs. Detailed FCD drawing techniques shall be used, where necessary, to show
cabinet-mounted components such as switches, relays, termination resistors, and so forth, and
for detailing circuits of assemblies or modules having replaceable parts. Separate detailed
FCDs are required for the unique repairable circuits used as building blocks for analog
equipment; one detailed FCD is required for each type of building block.
1.
Layout techniques. Detailed FCDs present all circuit information, including component
values, test points, and sensors (see figure 20-28). Circuit parts shall be grouped
functionally and arranged to make signal flow obvious from left-to-right and top-to-
bottom. Emphasis should be placed on arranging the circuit parts to enhance functional
understanding. One technique which simplifies the circuit presentation is to completely
separate each power and ground connection. Common ground or return points should
not be tied together merely to conserve symbols.
f.
Power and grounding circuits. The following paragraphs describe the preparation of power
and grounding circuit FCDs.
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