9
\$\begingroup\$

I've seen some circuit diagrams on-line that appear to use the units prefix symbol as the decimal point. So a 6.8kΩ resistor is shown as 6k8 and a 1.2nF capacitor is shown as 1n2. Is this an accepted practice, and am I interpreting the values correctly?

\$\endgroup\$
5
  • \$\begingroup\$ Both of them are representing the same values and yes, accepted. \$\endgroup\$
    – OJazz
    May 17 at 14:36
  • \$\begingroup\$ I've written a little python library that generates and parses this type of string. \$\endgroup\$
    – Neil_UK
    May 17 at 18:19
  • 2
    \$\begingroup\$ Note that this is even accepted/common practice enough to be supported by many tool like circuit designers or simulators as input format. \$\endgroup\$
    – PlasmaHH
    May 18 at 10:06
  • \$\begingroup\$ Also, some components also have markings in this format. I think I've first seen it on '70-'80 era soviet resistors. It's an intuitive notation in my opinion. \$\endgroup\$
    – Sasszem
    May 19 at 12:19

2 Answers 2

17
\$\begingroup\$

Yes, the practice is certainly accepted although there may not be a formal standard or requirement. You are interpreting the values correctly. Note that when no prefix is needed we use the quantity symbol instead, so \$1.1\Omega\$ is written as 1R1.

\$\endgroup\$
10
  • 2
    \$\begingroup\$ Sometimes R is used even when it's not a resistor, though. I've seen it used for inductors too. \$\endgroup\$
    – Hearth
    May 17 at 14:50
  • 4
    \$\begingroup\$ @Hearth - You've actually see this for ferrite beads, I would think. They are typically referred to by their impedance (say, 100R) over a certain frequency range. Actual inductors will be marked in Henrys. \$\endgroup\$
    – SiHa
    May 18 at 6:08
  • \$\begingroup\$ is it always the quantity symbol? would you write 1H1 or 1L1? hopefully your diagram does not include a current source \$\endgroup\$
    – user253751
    May 18 at 9:19
  • 2
    \$\begingroup\$ Using R instead of Ω comes from the fact that Ω may not be available in the typeset or on the keyboard or in the character encoding. These conventions predate unicode. \$\endgroup\$
    – Rodney
    May 18 at 10:06
  • 3
    \$\begingroup\$ @ElliotAlderson I have never seen a 100nH inductor labelled as 100nL on a schematic, it's either 100nH or 100n. So it's always the unit, or nothing. So we would expect H as the decimal point substitute, 1H1 not 1L1. (Resistance is different because it's a special case of avoiding the Ω symbol.) \$\endgroup\$
    – Rodney
    May 18 at 10:24
7
\$\begingroup\$

This improves the readability of printed values on components. A decimal point may be overlooked or is just missing on bad printing quality. You can even find this practice on schematics, BOMS and components, that are 50+ years old. If you see 470 printed on a capacitor the value is not 470pF! You must read it in the code of the color rings on resistors: 4, 7 and no zero digits behind. It's 47pF then, 471 would be 470pF and 475 is 4.7uF. The same on inductors: 101 is 100uH, R27 is 270nH. Using R on an inductor is absurd but very common.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.