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As a consequence, the same terminal may appear more than once in a diagram. Each appearance shall be labelled with a terminal designation that relates it to all other appearances of the same terminal, but a connection to the repeated terminals need be shown in only one place.
However, a connecting line or another indication of the connection may be present at all additional occurrences of the terminal, provided no confusion is likely. For simplification, see 4. See also Figure If it is necessary to identify repetitive information, this shall be done by placing the repeated terminal designation in parentheses or by a special identifier explained in the diagram. Each of the symbols representing a part of the component shall have an item designation that relates it to all other symbols representing the same component.
For examples, see Table 2. However, in special cases the diagram can be better understood if these components are shown in the actuated or energized state. This shall be stated in the diagram3. For other switching devices that can rest in any one of two or more positions or states, an explanation shall be given in the diagram, if necessary. Control switches without a position designated OFF, in a position specified in the diagram.
Manually operated control switches for emergency operation, stand-by, alarm, test, etc. See Figure 11 and IEC For pilot switches, the diagram shall contain a description of the operation, adjacent to the symbol. This description may consist of: a graph, prepared in accordance with the examples in Figure 12 and in the left-hand column of Table 3.
In these examples, the indication 0 on the Y-axis stands for contact open and 1 for contact closed. For cam-operated or similarly operated devices, the symbol shown in the third column of Table 3 may be used; a note, designation or table.
For example, see Figure This is especially important if the symbol for the complete component contains symbols for a mechanical latch, blocking device, delay device, etc. However, when using detached representation in circuits with complicated contact arrangements but without mechanical latches etc.
The dot at one end of the arrows correlates the direction of rotation of the motor and the corresponding direction of motion of the sliding contact of the resistor. Rules for signal designations can be found in IEC There are two methods by which this may be done: 1 The use of the symbol for logic negation symbols and This requires the adoption of a single logic convention, either positive or negative, for the whole diagram or for a portion of the diagram see 2.
The terms states and levels are explained in IEC , section 3, with the help of this figure: 2. The connections may be shown graphically, or may be specified in a table or a note. For exampe, see Figure The supply lines should be shown at opposite sides of the circuit branches, see Figure 15, or grouped together to one side of, above, or below, the circuit, see Figure Supply lines may also be interrupted to aid the layout of the diagram, provided the requirements in 4.
Supply lines to a block symbol may be drawn at right angles to the signal flow. These methods may also be used inside a functional or constructional unit. A component may be represented as two or more symbols, one of them showing only the supply connections. Specifically, the presence of the logic negation symbol at an input or output signifies that the internal and external states are the complements of one another for that terminal.
The absence of the logic negation symbol signifies that the internal and external states are the same for that terminal. The symbol for logic polarity shall not be used with this method. See Figure 21 for an example of a diagram using a single logic convention the positive logic convention. The convention in use, either positive logic or negative logic, shall be clearly stated in the diagram or in referenced documentation.
This statement may include a small waveform graph with indications of the logic states and, if necessary, of the nominal value of corresponding physical quantities. NOTE Different logic conventions may be used for different portions of the same diagram; for example, on either side of an interface between contrasting technologies. The convention applying to each portion should be clearly shown, and the areas of the diagram to which each applies should be clearly delineated.
Specifically, the presence of the logic polarity symbol at an input or output indicates that the external low level corresponds to the internal 1-state for that terminal. The absence of the logic polarity symbol signifies that the external high level corresponds to the internal 1-state for that terminal.
No relationship between an external logic state and either an internal logic state or an external logic level is defined by the symbol. A relationship between the external logic level and a signal state is defined only by the signal designation see IEC In this system the symbol for logic negation shall not be used for external connections.
See Figure 22 for an example of a diagram using direct polarity indication. For diagrams prepared with direct logic polarity indication, but showing no logic polarity symbols, a statement indicating that direct logic polarity is employed shall be placed in the diagram or in referenced documentation.
For example, symbols for logic negation that would be shown at both the driving end and at the driven end of a connecting line double negation should be eliminated unless there are special requirements, such as if the function diagram is later to be converted to a circuit diagram. See Table 4. In a circuit diagram, the symbols should be chosen so that the logic polarity or negation indication at an input is the same as that at the source of a signal feeding that input. If this is done, a reader of the diagram can directly apply the internal logic state of an output as the internal logic states of the inputs fed by that output.
In the case of direct logic polarity indication, if the form of the signal name is chosen as described in IEC the signal designation, excluding the level indication, directly expresses the meaning of that internal logic state. See Figure The less positive value L-level corresponds to the external 0-state. The more positive value H-level corresponds to the external 0-state. This may be stated in a diagram thus: NEGATIVE LOGIC term direct logic polarity indication is used to contrast the method with the single logic convention, where the logic level can be obtained from an internal logic state only indirectly through an external logic state.
Direct logic polarity indication has been called mixed logic, implying that both positive and negative logic are present in a diagram using that method. This is misleading since the fixed relationship between logic levels and external logic states inherent in a single logic convention does not exist with direct logic polarity indication. Therefore, the term mixed logic is deprecated.
DIN EN 61082-1:2015-10;VDE 0040-1:2015-10