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I have a package of 10 inductors, all of which are supposed to be 22µH, but they all have "220" printed on the case. It does not seem right when I compare to an otherwise identical (same type) inductor with an inductance of 3.3µH, which has "3R3" printed on it. Is it just odd ordering or am I missing something? Inductor is an SDR0604 type.

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    \$\begingroup\$ I don't get it, what else would you expect the marking "220" to mean? In most electronics contexts it means 22. \$\endgroup\$
    – Nick T
    Commented Mar 1, 2011 at 22:26
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    \$\begingroup\$ @Nick T, given that the other one was "3R3" I'd expect "220" to mean "220R" or 220µH. \$\endgroup\$
    – Thomas O
    Commented Mar 1, 2011 at 22:28
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    \$\begingroup\$ Maybe it's 22 Henries. Were the inductors delivered with a forklift? \$\endgroup\$
    – markrages
    Commented Mar 2, 2011 at 1:44
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    \$\begingroup\$ With +/-5% components, all you need are 2 digits plus one for order-of-magnitude. Just like on resistors and capacitors, there are 2 mantissa digits and one for radix. \$\endgroup\$
    – Nick T
    Commented Mar 2, 2011 at 3:10
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    \$\begingroup\$ MEasure them. It's the only way to know. \$\endgroup\$ Commented Mar 2, 2011 at 7:32

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That should be read as 22 × 100 µH and 3.3 µH respectively. The R is a decimal, the last digit otherwise is an exponent.

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There are two ways of marking parts...

A Three digit code for values from 10 and up

X Y Z
X - First digit
Y - Second digit
Z - Power of ten

220 would be 22 = 22 x 10^0 (1)
221 would be 220 = 22 x 10^1 (10)
222 would be 2,200 = 22 x 10^2 (100)
223 would be 22,000 = 22 x 10^3 (1000)

The Minimum for this coding would be 100 = 10 x 10^0 and the Maximum would be 999 = 99,000,000,000 = 99 x 10^9 (1,000,000,000)

For values under 10

you use a character to replace the decimal point

e.g. 3R3 = 3.3 R33 = 0.33

R is used for Ohms.

For resistors the value is usually in Ohms For Capacitors the value is usually in pico farads

e.g. a Capacitor marked 103 would be 103 pF = 10 x 10^3 (1000) pF = 10nF = 0.01uF

For Inductors the value is usually in micro henrys e.g. a Inductor marked 220 woulf be 22uH = 22 x 10^0 (1) uH

The part marked 3R3 is a 3.3 ohm resistor as R is used on resistors.

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    \$\begingroup\$ I think "R" can be used on inductors too, but I have no idea why they use that convention. Maybe "L" wouldn't be clear enough; suppose it could be read as a 7 upside down... \$\endgroup\$
    – Thomas O
    Commented Mar 1, 2011 at 22:34
  • \$\begingroup\$ Why couldn't they just write 22 µH as "22"? \$\endgroup\$
    – endolith
    Commented Mar 2, 2011 at 16:11
  • \$\begingroup\$ @Wonko The Sane: You say the minimum for this coding is 100 (meaning 10 x 10^0 = 10)... but why can't you have 010 (meaning 01 x 10^0 = 1)? \$\endgroup\$
    – BG100
    Commented Mar 2, 2011 at 16:14
  • \$\begingroup\$ @BG100: If you did that then you lose significant digits as you're putting useless leading zeros in your mantissa (significand). How would you express 1.5, or 3.3 as in the OP question? \$\endgroup\$
    – Nick T
    Commented Mar 2, 2011 at 16:40
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    \$\begingroup\$ @endolith "I suffered for my knowledge, now it's your turn" \$\endgroup\$ Commented Sep 25, 2012 at 19:47
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220 means that the value is 22 times 10^0, or 22uH. It's a similar notation to that used for small value capacitors. If they were really 220uH they would have the value 221.

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Panasonic SM inductors use R in the part marking (for example, 2R6 corresponds to the 2.6 microhenry part on the specified datasheet).

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