ENGINEERING LOGIC DIAGRAMS

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.