A schematic, or schematic diagram, is a designed representation of the elements of a
system
A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment (systems), environment, is described by its boundaries, ...
using abstract, graphic
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
s rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the schematic is intended to convey, and may include oversimplified elements in order to make this essential meaning easier to grasp, as well as additional organization of the information.
For example, a subway map intended for passengers may represent a subway station with a dot. The dot is not intended to resemble the actual station at all but aims to give the viewer information without unnecessary visual clutter. A schematic diagram of a chemical process uses symbols in place of detailed representations of the vessels, piping, valves, pumps, and other equipment that compose the system, thus emphasizing the functions of the individual elements and the interconnections among them and suppresses their physical details. In an electronic
circuit diagram, the layout of the symbols may not look anything like the circuit as it appears in the physical world: instead of representing the way the circuit ''looks'', the schematic aims to capture, on a more general level, the way it ''works''. This may be contrasted with a
wiring diagram
A wiring diagram is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified shapes, and the power and signal connections between the devices.
A wiring diagram usually gi ...
, which preserves the spatial relationships between each of its components.
Types
Schematics and other types of diagrams, e.g.,
A semi-schematic diagram combines some of the abstraction of a purely schematic diagram with other elements displayed as realistically as possible, for various reasons. It is a compromise between a purely abstract diagram (e.g. the schematic of the Washington Metro) and an exclusively realistic representation (e.g. the corresponding aerial view of Washington).
Electrical and electronic industry
In electrical and electronic industry, a schematic diagram is often used to describe the design of equipment. Schematic diagrams are often used for the maintenance and repair of electronic and electromechanical systems.
[Thomas E. French, Charles J. Vierck (1975). ''Engineering Drawing and Graphic Technology, Eleventh Edition''. McGraw Hill. . pp. 621–624.] While schematics were traditionally drawn by hand, using standardized templates or pre-printed adhesive symbols, today
electronic design automation
Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...
software (EDA or "electrical CAD") is often used.
In electronic design automation, until the 1980s schematics were virtually the only formal representation for circuits. More recently, with the progress of computer technology, other representations were introduced and specialized
computer languages were developed, since with the explosive growth of the complexity of electronic circuits, traditional schematics are becoming less practical. For example,
hardware description languages are indispensable for modern
digital circuit In theoretical computer science, a circuit is a model of computation in which input values proceed through a sequence of gates, each of which computes a function. Circuits of this kind provide a generalization of Boolean circuits and a mathematical ...
design.
Schematics for electronic circuits are prepared by designers using EDA (
electronic design automation
Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...
) tools called
schematic capture tools or
schematic entry tools. These tools go beyond simple drawing of devices and connections. Usually they are integrated into the whole design flow and linked to other EDA tools for verification and simulation of the circuit under design.
Programmable logic controller
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity tha ...
s (PLC) can be programmed using
ladder diagrams.
In electric power systems design, a schematic drawing called a
''one-line'' ''diagram'' is frequently used to represent
substations, distribution systems or even whole electrical power grids. These diagrams simplify and compress the details that would be repeated on each phase of a
three-phase
Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, Electric power transmission, transmission, and Electric power distribution, distribution. It is a type of polyphase system empl ...
system, showing only one element instead of three. Electrical diagrams for switchgear often have common device functions designate by
standard function numbers. Another type of diagram used for power systems is a ''three-line diagram''.
For analysis purposes of a power system, from the one-line diagram, if the system is balanced, an ''equivalent per-phase'' (or ''single-phase'') ''schematic diagram'' can be obtained. If all of the parameters are represented as impedances and voltage sources, the equivalent per-phase schematic diagram is called an ''impedance diagram''. If all of the parameters are represented as admittances and current sources, the equivalent per-phase schematic diagram is called an ''admittance diagram''.
If the power system is unbalanced, but it is
linear
Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
(or can be approximated by a linear system), then Fortescue's theorem (
symmetrical components In electrical engineering, the method of symmetrical components simplifies analysis of unbalanced three-phase power systems under both normal and abnormal conditions. The basic idea is that an asymmetrical set of ''N'' phasors can be expressed as a ...
) can be applied. In this way, from the one-line diagram, three different per-phase schematic diagrams are obtained, known as ''sequence diagrams'': ''positive sequence diagram'', ''negative sequence diagram'', and ''zero sequence diagram''. Each of these diagrams can be represented as an impedance diagram or as an admittance diagram.
Schematics in repair manuals
Schematic diagrams are used extensively in repair manuals to help users understand the interconnections of parts, and to provide graphical instruction to assist in dismantling and rebuilding mechanical assemblies. Many automotive and motorcycle
repair manuals devote a significant number of pages to schematic diagrams.
See also
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Energy Systems Language
The Energy Systems Language, also referred to as Energese, Energy Circuit Language, or Generic Systems Symbols, is a modelling language used for composing energy flow diagrams in the field of systems ecology. It was developed by Howard T. Odum ...
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Chart
A chart (sometimes known as a graph) is a graphical representation for data visualization, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart". A chart can represent tabu ...
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Diagram
A diagram is a symbolic representation of information using visualization techniques. Diagrams have been used since prehistoric times on walls of caves, but became more prevalent during the Enlightenment. Sometimes, the technique uses a three- ...
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Straight-line diagram
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Topological map
In cartography and geology, a topological map is a type of diagram that has been simplified so that only vital information remains and unnecessary detail has been removed. These maps lack scale, also distance and direction are subject to change a ...
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Transit map
A transit map is a topological map in the form of a schematic diagram used to illustrate the routes and stations within a public transport system—whether this be bus, tram, rapid transit, commuter rail or ferry routes. The main components are ...
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Open-source hardware
Open-source hardware (OSH) consists of physical artifacts of technology designed and offered by the open-design movement. Both free and open-source software (FOSS) and open-source hardware are created by this open-source culture movement and a ...
References
{{Authority control
Diagrams
Electronic design automation
Technical communication
Infographics