Symbology - h1016v2

Figure 2 Example of Figure 1 Pump Start Circuit as a Logic Diagram

Engineering Symbology Prints and Drawings Volume 2 of 2
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ENGINEERING LOGIC DIAGRAMS DOE-HDBK-1016/2-93 Logic Diagrams PR-05 Page 4 Rev. 0 Symbology There are three basic types of logic gates. They are AND, OR, and NOT gates. Each gate is a very simple device that only has two states, on and off. The states of a gate are also commonly referred to as high or low, 1 or 0, or True or False, where on = high = 1 = True, and off = low = 0 = False. The state of the gate, also referred to as its output, is determined by the status of the inputs to the gate, with each type of gate responding differently to the various possible combinations of inputs. Specifically, these combinations are as follows. AND gate - provides an output (on) when all its inputs are on. When any one of the inputs is off, the gate's output is off. OR gate - provides an output (on) when any one or more of its inputs is on. The gate is off only when all of its inputs are off. NOT gate - provides a reversal of the input. If the input is on, the output will be off. If the input is off, the output will be on. Because the NOT gate is frequently used in conjunction with AND and OR gates, special symbols have been developed to represent these combinations. The combination of an AND gate and a NOT gate is called a NAND gate. The combination of an OR gate with a NOT gate is called a NOR gate. NAND gate - is the opposite (NOT) of an AND gate's output. It provides an output (on) except when all the inputs are on. NOR gate - is the opposite (NOT) of an OR gate's output. It provides an output only when all inputs are off. Figure 3 illustrates the symbols covering the three basic logic gates plus NAND and NOR gates. The IEEE/ANSI symbols are used most often; however, other symbol conventions are provided on Figure 3 for information.

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