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A reference designator unambiguously identifies a component in an electrical schematic or on a printed circuit board. 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.
Designator |
Component Type |
|---|---|
A |
Separable assembly or sub-assembly (e.g. printed circuit assembly) |
AT |
Attenuator or isolator |
BR |
Attenuator or isolator |
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 |
FL |
Filter |
G |
Generator or oscillator |
GN |
General network |
H |
Hardware |
HY |
Circulator or directional coupler |
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 or contactor |
L |
Inductor or coil or ferrite bead |
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 |