Logic Diagrams
DOE-HDBK-1016/2-93
ENGINEERING LOGIC DIAGRAMS
Rev. 0
Page 1
PR-05
ENGINEERING LOGIC DIAGRAMS
This chapter will review the symbols and conventions used on logic diagrams.
EO 1.1
IDENTIFY the symbols used on logic diagrams to represent
the following components:
a.
AND gate
h.
Adder
b.
NAND gate
i.
Time-delay
c.
COINCIDENCE gate
j.
Counter
d.
OR gate
k.
Shift register
e.
NOR gate
l.
Flip-flop
f.
EXCLUSIVE OR gate
m.
Logic memories
g.
NOT gate or inverter
EO 1.2
EXPLAIN the operation of the three types of time delay
devices.
Introduction
Logic diagrams have many uses. In the solid state industry, they are used as the principal
diagram for the design of solid state components such as computer chips. They are used by
mathematicians to help solve logical problems (called boolean algebra). However, their principle
application at DOE facilities is their ability to present component and system operational
information. The use of logic symbology results in a diagram that allows the user to determine
the operation of a given component or system as the various input signals change.
To read and interpret logic diagrams, the reader must understand what each of the specialized
symbols represent. This chapter discusses the common symbols used on logic diagrams. When
mastered, this knowledge should enable the reader to understand most logic diagrams.
Facility operators and technical staff personnel commonly see logic symbols on equipment
diagrams. The logic symbols, called gates, depict the operation/start/stop circuits of components
and systems. The following two figures, which use a common facility start/stop pump circuit
as an example, clearly demonstrate the reasons for learning to read logic diagrams. Figure 1
presents a schematic for a large pump, and Figure 2 shows the same pump circuit using only
logic gates. It is obvious that when the basic logic symbols are understood, figuring out how
the pump operates and how it will respond to various combinations of inputs using the logic
diagram is fast and easy, as compared to laboriously tracing through the relays and contacts of
the schematic diagram for the same information.
