Circuit Symbols

4 Key excerpts on "Circuit Symbols"

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  eBook - ePub

  An Introduction to Electrical Science

  • Adrian Waygood(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  understand how that circuit works .

  Figure 2.3 is an example of a schematic diagram. It illustrates a basic rectifier (a.c. to d.c.) circuit for the current-measuring range of an analogue multimeter.

  Figure 2.3

  Circuit Symbols

  Whenever we create a schematic diagram we should always use standard Circuit Symbols to represent either the quantities (e.g. resistance , inductance , capacitance , etc.) or the circuit components (e.g. resistors , inductors , capacitors , switches, power supplies, etc.) we are using in that diagram. You could say that Circuit Symbols are the vocabulary of a schematic diagram, so they must be standardised so that they can be readily recognised by any trained person studying that diagram.

  So Circuit Symbols should comply with the relevant international standards. For example, in Europe, we use symbols which comply with standards approved by the IEC (International Electrotechnical Commission ). In North America, Circuit Symbols must comply with standards approved by ANSI /NEMA (American National Standards Institute /National Electrical Manufacturers Association ). Other countries may have their own standards but, in many cases, they are based on IEC or ANSI/NEMA standards.

  In any event, it is very important that, whenever we construct a schematic diagram, we are consistent by using Circuit Symbols from either one standard or another, and that we do not mix them .

  Figure 2.4 shows a selection of some of the most commonly used Circuit Symbols that accord with the relevant IEC standard.

  Figure 2.4

  Many of the more-complicated Circuit Symbols are actually created by simply combining related individual symbols. So, if we understand the functions of the individual symbols, then the function of any combination

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  eBook - ePub

  Circuit Analysis For Dummies

  • John Santiago(Author)
  • 2013(Publication Date)
  • For Dummies

    (Publisher)

  traces on a board. If you’ve ever opened up a desktop computer, you’ve seen traces on a big motherboard and wires connecting various devices like power supplies, sound cards, and hard drives.

  Gates: Control lines at the gate terminals of switches are represented by dashed lines (see the bottom-left diagram in Figure 2-5 ). By applying a voltage to the gate terminal, you can control the on and off states of the switch.

  Power supplies: Power supplies in schematics incorporate the device symbols I show you in Figures 2-2 and 2-3. You see power supply connections at the bottom right of Figure 2-5 . The left diagram shows a way to reduce the clutter found in schematics by not drawing the symbol for the power supply. The schematic on the right shows the ground symbol, which marks a reference point of 0 volts.

  Illustration by Wiley, Composition Services Graphics

  Figure 2-5: Connection Circuit Symbols.

  Additionally, circuit schematics often depict circular arrangements of electronic devices and junction points. The circular arrangements of electrical devices are called loops, and the junction or connection points are called nodes. I discuss these features next.

  Going in circles with loops

  When looking at a circuit schematic such as the one in Figure 2-6 , you often see a collection of resistors and a battery connected together in some configuration. The loops form circular connections of devices. By definition, a loop occurs when you trace a closed path through the circuit in an orderly way, passing through each device only once.

  This method of generating a closed path allows you to get consistent results when analyzing circuits. To form a loop or closed path, you must start at one point in the circuit and end up at the same place, much like going around the block in your neighborhood.

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  eBook - ePub

  Electric Circuits and Signals

  • Nassir H. Sabah(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  1

  Circuit Variables and Elements

  Overview

  Physically, an electric circuit is an interconnection of circuit elements of various types, such as sources of electric energy, resistors, capacitors, and inductors. In the presence of sources, current flows in different parts of the circuit, and voltages appear at the terminals of circuit elements. The circuit is described by a circuit diagram that specifies how the circuit elements are interconnected and on which are shown the values assigned to these elements. For each type of circuit element, voltage and current are related in a particular way that is characteristic of the given type. In the case of ideal resistors, for example, the voltage across a resistor and the current through it are related by Ohm’s law.

  A discussion of electric circuits logically begins with the definitions of the two basic circuit variables, namely current and voltage, and their relation to electric energy and power. It is emphasized in this discussion that the two fundamental laws of conservation of charge and conservation of energy must be satisfied in any valid electric circuit. Ideal circuit elements are also considered in this introductory chapter. Voltage sources, current sources, and resistors are presented in some detail. Capacitors and inductors are only briefly introduced at this stage in preparation for Chapter 5 on the sinusoidal steady state. A discussion of their general behavior is postponed to Chapter 11

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  eBook - ePub

  Renewable and Efficient Electric Power Systems

  • Gilbert M. Masters(Author)
  • 2013(Publication Date)
  • Wiley-IEEE Press

    (Publisher)

  The point here is simple. The combinations of resistors, capacitors, inductors, voltage sources, current sources, and so forth, that you see in a circuit diagram are merely models of real components that comprise a real circuit, and a certain amount of judgment is required to decide how complicated the model must be before sufficiently accurate results can be obtained. For our purposes, we will be using very simple models in general, leaving many of the complications to more advanced textbooks.

  2.2 DEFINITIONS OF KEY ELECTRICAL QUANTITIES We shall begin by introducing the fundamental electrical quantities that form the basis for the study of electric circuits. 2.2.1 Charge

  An atom consists of a positively charged nucleus surrounded by a swarm of negatively charged electrons. The charge associated with one electron has been found to be 1.602 × 10−19 coulombs; or, stated the other way around, one coulomb can be defined as the charge on 6.242 × 1018 electrons. While most of the electrons associated with an atom are tightly bound to the nucleus, good conductors, like copper, have free electrons that are sufficiently distant from their nuclei that their attraction to any particular nucleus is easily overcome. These conduction electrons are free to wander from atom to atom, and their movement constitutes an electric current.

  2.2.2 Current

  In a wire, when one coulomb's worth of charge passes a given spot in one second, the current is defined to be one ampere (A), named after the nineteenth-century physicist André-Marie Ampère. That is, current i is the net rate of flow of charge q past a point, or through an area:

  (2.1)

  In general, charges can be negative or positive. For example, in a neon light, positive ions move in one direction and negative electrons move in the other. Each contributes to current, and the total current is their sum. By convention, the direction of current flow is taken to be the direction that positive charges would move, whether or not positive charges happen to be in the picture. Thus, in a wire, electrons moving to the right constitute a current that flows to the left, as shown in Figure 2.2

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