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SMD resistors

by iainhendry

All surface mount resistors have a 3-digit or 4-digit code.

Here is a picture of a 3-digit surface mount resistor

 

smd resistor

smd resistor

The first and second figures indicate the significant figures and the third one, is the multiplier. As an example, if the SMD resistor has the figures 102, it indicates 1, 0 = 10 x 102 ohms. That is the value is 1K. This next example can catch people out at first , 100 is not in fact a 100 ohm resistor but is in fact a 10×100 = 10 ohms or 10×1 = 10 ohms. In the case of resistors less than 10 ohms, the letter R is used in the position of decimal. For example, 4R7 represents 4.7 Ohms.

3-digit code examples:

330 = 33 × 100 (1) = 33Ω
331 = 33 × 101 (10) = 330Ω
332 = 33 × 102 (100) = 3300Ω or 3k3
3R3 = 3.3Ω

4-Digit markings are used to denote high tolerance SMD resistors. In these resistors, the first, second and third figures represent the significant values while the fourth is the multiplier. For example, if the figures are 3302 then the value is 330 x 102 ohms or 33K. In 4 figure marking, the values less than 100 ohms use the letter R at the position of the decimal point.

4-digit code examples:

3300 = 330 × 100 (1) = 330Ω
3301 = 330 × 101 (10) = 3300Ω or 3k3Ω
3302 = 330 × 102 (100) = 33000Ω or 33KΩ
33R0 = 33.0Ω

EIA 96 marking system is used in resistors with 1% tolerance. In this marking scheme the first and second digits indicate the resistor value and the third character is a letter that indicates the multiplier. This scheme can be hard to get used to at first.

Here is a table to help with the first 2 digits

Code Value Code Value Code Value Code Value Code Value Code Value
01 100 17 147 33 215 49 316 65 464 81 681
02 102 18 150 34 221 50 324 66 475 82 698
03 105 19 154 35 226 51 332 67 487 83 715
04 107 20 158 36 232 52 340 68 499 84 732
05 110 21 162 37 237 53 348 69 511 85 750
06 113 22 165 38 243 54 357 70 523 86 768
07 115 23 169 39 249 55 365 71 536 87 787
08 118 24 174 40 255 56 374 72 549 88 806
09 121 25 178 41 261 57 383 73 562 89 825
10 124 26 182 42 267 58 392 74 576 90 845
11 127 27 187 43 274 59 402 75 590 91 866
12 130 28 191 44 280 60 412 76 604 92 887
13 133 29 196 45 287 61 422 77 619 93 909
14 137 30 200 46 294 62 432 78 634 94 931
15 140 31 205 47 301 63 442 79 649 95 953
16 143 32 210 48 309 64 453 80 665 96 976

 

Here is the multiplier

Letter Multiplier Letter Multiplier Letter Multiplier
Z 0.001 A 1 D 1000
Y or R 0.01 B or H 10 E 10000
X or S 0.1 C 100 F 100000

Lets look at some examples

01C = 10kΩ (100×100)
01B = 1kΩ (100×10)
01D = 100kΩ

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