Electronic symbols

An electronic symbol is a pictogram used to represent various electrical and electronic devices (such as wires, batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit. These symbols can (because of remaining traditions) vary from country to country, but are today to a large extent internationally standardized. Some symbols represent components which ceased to be used routinely as newer technologies were introduced (such as vacuum tubes).

Standards for symbols

There are several national and international standards for graphical symbols in circuit diagrams, in particular:

  • IEC 60617 (also known as British Standard BS 3939)
  • ANSI standard Y32 (also known as IEEE Std 315)
  • Australian Standard AS 1102

Different symbols may be used depending on the discipline using the drawing. For example, lighting and power symbols used as part of architectural drawings may be different from symbols for devices used in electronics. National and local variations to international standards also exist.

Reference designations

A reference designator unambiguously identifies a component in an electrical schematic (circuit diagram) or on a printed circuit board (PCB). The reference designator usually consists of one or two letters followed by a number, e.g. R13, C1002. The number is sometimes followed by a letter, indicating that components are grouped or matched with each other, e.g. R17A, R17B. IEEE 315 contains a list of Class Designation Letters to use for electrical and electronic assemblies. For example, the letter R is a reference prefix for the resistors of an assembly, C for capacitors, K for relays.

IEEE 200-1975 or "Standard Reference Designations for Electrical and Electronics Parts and Equipments" is a standard that was used to define referencing naming systems for collections of electronic equipment. IEEE 200 was ratified in 1975. The IEEE renewed the standard in the 1990s, but withdrew it from active support shortly thereafter. This document also has an ANSI document number, ANSI Y32.16-1975.

This standard codified information from, among other sources, a United States military standard MIL-STD-16 which dates back to at least the 1950s in American industry.

To replace IEEE 200-1975, ASME, a standards body for Mechanical Engineers, initiated the new standard ASME Y14.44-2008.

This standard along with IEEE 315-1975 provide the electrical designer with guidance on how to properly reference and annotate everything from a single circuit board to a collection of complete enclosures.

It breaks down a system into units, and then any number of sub-assemblies. The Unit is the highest level of demarcation in a system and is always a numeral. Subsequent demarcation are called assemblies and always have the Class Letter "A" as a prefix following by a sequential number starting with 1. Any number of sub-assemblies may be defined until finally reaching the component. Note that IEEE-315-1975[1] defines separate class designation letters for separable assemblies (class designation 'A') and inseparable assemblies (class designation 'U'). Inseparable assemblies—i.e., "items which are ordinarily replaced as a single item of supply"[1]—are typically treated as components in this referencing scheme.

Examples:

  • 1A12A2R3 - Unit 1, Assembly 12, Sub-assembly 2, Resistor 3
  • 1A12A2U3 - Unit 1, Assembly 12, Sub-assembly 2, Inseparable Assembly 3

Especially valuable is the method of referencing and annotating cables plus their connectors within and outside assemblies. Examples:

  • 1A1A44J5 - Unit 1, Assembly 1, Sub-Assembly 44, Jack 5 (J5 is a connector on a box referenced as A44)
  • 1A1A45J333 - Unit 1, Assembly 1, Sub-Assembly 45, Jack 333 (J333 is a connector on a box referenced as A45)

A cable connecting these two might be:

  • 1A1W35 - In the assembly A1 is a cable called W35.

Connectors on this cable would be designated:

  • 1A1W35P1
  • 1A1W35P2

ASME Y14.44-2008 continues the convention of Plug P and Jack J when assigning references for electrical connectors in assemblies where a J (or jack) is the more fixed and P (or plug) is the less fixed of a connector pair, without regard to the gender of the connector contacts.

The construction of reference designators is covered by IEEE 200-1975/ANSI Y32.16-1975[2] (replaced by ASME Y14.44-2008[3]) and IEEE-315-1975.[1] The table below lists designators commonly used, and does not necessarily comply with the standard.

Designator Component Type
A Separable Assembly or Sub-assembly (e.g. printed circuit assembly)
AT Attenuator
BR Bridge rectifier
BT Battery
C Capacitor
CN Capacitor network
D Diode (including Zeners, thyristors and LEDs)
DL Delay line
DS Display
F Fuse
FB or FEB Ferrite bead
FD Fiducial
J Jack (least-movable connector of a connector pair) | Jack connector (connector may have "male" pin contacts and/or "female" socket contacts)
JP Link (Jumper)
K Relay
L Inductor
LS Loudspeaker or buzzer
M Motor
MK Microphone
MP Mechanical part (including screws and fasteners)
P Plug (most-movable connector of a connector pair) | Plug connector (connector may have "male" pin contacts and/or "female" socket contacts)
PS Power supply
Q Transistor (all types)
R Resistor
RN Resistor network
RT Thermistor
RV Varistor
S Switch (all types, including push-buttons)
T Transformer
TC Thermocouple
TUN Tuner
TP Test point
U Inseparable Assembly (e.g., Integrated circuit)
V Vacuum tube
VR Variable resistor (potentiometer or rheostat)
X Socket connector for another item not P or J, paired with the letter symbol for that item (XV for vacuum tube socket, XF for fuse holder, XA for printed circuit assembly connector, XU for integrated circuit connector, XDS for light socket, etc.)
Y Crystal or oscillator
Z Zener diode

Component name abbreviations widely used in industry:

Gallery of common electronic symbols

Symbols shown are typical examples, not a complete list.

Resistors

Capacitors

Transistors

Diodes

Vacuum tubes

Switches

Circuit Breakers

Transformers

Miscellaneous

See also

Electronics portal

References

External links

  • International standard IEC 60617 DB Graphical symbols for diagrams
  • Electrical Circuit's Schematic Symbols
  • Circuit Symbols of Electronic Components
  • Circuit Symbols for all Electronic Components
  • List of Circuit Schematic Symbols
  • Electrical & Electronic Drawing Symbols
  • Collection of Electronic Symbols
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