MIL-DTL-24784 / 21B (SH)
3.5.1.3), or to actual hardware by reference designator where the function depicted is
performed. The subfunctional segments illustrated on the secondary FBD shall often be
further subdivided to effectively depict equipment operation. In this case, the secondary FBD
provides the transition between the primary FBD and lower levels of FBDs (see figure 21-4).
1.
The secondary and lower-level FBDs are generated by dividing the functional elements
into discrete segment (subfunction) blocks. Each block shall be identified by a
descriptive name and referenced to a keyed text paragraph on the facing page. The
blocks shall also reference the paragraph number of the paragraph that describes the
block (not the keyed text paragraph). These segments shall be interconnected in the
same manner as the major blocks on the primary FBD; that is, with signal path and
control lines identified by names and having the proper line weights. Each subfunctional
block shall be identified by a descriptive name. A direct relationship shall be maintained
in regard to the number and nomenclature of interface lines between a secondary FBD
and other interfacing secondary FBDs. The lowest-level FBD block shall contain a
reference to an FCD, or to the hardware reference designator where the function
depicted is performed (see figure 21-5).
3.5.1.1.1 Power and grounding circuits. The following paragraphs describe the preparation of
power and grounding circuit FBDs.
a. Equipment power FBD. The equipment power FBD shall show the distribution of primary
power from the power source to the various units comprising the equipment. The FBD shall
be a part of the master FBD of the technical manual and shall reference the associated unit
power and grounding FBDs and FCDs. Power conversion and distribution within the
equipment units shall be shown by a separate power FBD for each unit unless the power
circuits within the unit do not warrant a separate FBD because of their simplicity.
b. Unit power FBD. This FBD shall show the distribution of primary power and control power
from the primary power source and associated interface units to the power elements within
each unit. The FBD shall represent the power elements as functional blocks and shall show
power conversion, power control monitoring and indicating between the unit power elements.
The diagram shall be laid out in a logical left-to-right sequence to clearly define the power
operations within the unit. Each functional block shall contain a reference to an FCD. This
FBD shall be the last sheet(s) of the FBDs (see figure 21-6).
3.5.1.1.2 Requirements for preparing FBDs. A clear and complete referencing system is
required for use on FBDs because of the interrelationship between FBDs and FCDs, and the
interconnection between sheets of FBDs. The referencing system shall include all or a portion of
the following reference information.
a.
Signal names.
1.
Signal names on FBDs shall be descriptive names. The Automated Interface Listing (AIL)
(the wire lists for the system cabling), or their equivalent, shall be used as the source of signal
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