Resistors are available in surface mounted form. They are minute in size and consume less space. Other resistors like carbon composition resistors and wire wounded types have their resistance values printed on them in form of color codes unlike the surface mounted resistor which just have figures printed on them. Surface mounted resistors have their resistance code written on them which can help in replacement when faulty and troubleshooting of malfunctioning electronic boards.
During manufacturing it is always helpful in determining whether the correct resistor is soldered in a certain point on the board or not. Not all surface mounted resistors are printed with their resistance values, because of their tiny shape and size they might not be easy to print at so they are left blank.
Some SMD resistors are printed with "000" which means that it's just a mere conductor of zero resistance, they are us as fuse in some circuits or just a brigde between two lines on a circuit. There are three systems in which resistor's resistance are indicated which are;
- Three figures SMD resistor coding system.
- Four figures SMD resistor coding system.
- EIA96 SMD resistor coding system.
1. Three figures SMD resistor coding system.
This system uses three digits to represent the resistance value in ohms. The three figures Surface mounted resistor coding is normally use for standard tolerance resistors. It contains three digits with the first two serving as a whole number and the last number as the multiplier. For example, a resistor labelled with a code of 247 resistance value can be calculated by writing 2 followed by 4 then multiplied by ten raised to the power of 7. The resistor code above can be calculated as, 24×10^7 = 24× 100000000= 240000000= 240MΩ
Examples.
1.calculate the resistance value of the resistor below.
Solution.
The resistor above is a three figure system.the first two digits are significant while the third is the multiplier.
105= 10×10^5 = 10×100000 =1000000 =1M ohms
2.calculate the resistance value of the resistor below.
Solutions.
a. The first resistor is 104, it value is calculated by 10×10^4=100000 =100kohms. b. 4R7 resistor code is calculated by replacing R with dot. Resistance =4.7ohms. Note: For example a resistor code of R47 will be equal to 0.47ohms.
Some resistors which have their resistance less than 10 ohms resistance codes are usually in form of two digits seperated by an R, for example 2R5, their resistance value is calculated by replacing the R with a dot thus the resistance is 2.5 ohms.
2. Four figures SMD resistor coding.
This system is use for marking high tolerance resistors. Four figures are usually printed on them. Their resistance values can be calculated by writing the first three digits and the last as the multiplier.
For example, a resistor with code of 3799 resistance value can be calculated by writing three followed by seven the nine, the last nine is the multiplier, therefore the resistance value is; 379×10^9= 379× 1000000000= 379000M ohms. ✔️
Examples.
1. Calculate the resistance value of the resistor below.
Solutions.
2512 =251×10^2 =25100 =25.1k ohms.
2. Calculate the resistance value of the resistor below.
Solutions.
0805 =080×10^5 =8000000= 8M ohms.
3. EIA96 SMD resistor code system.
There are some resistors with extremely low size, but their full resistance value can't be printed on them, however manufacturers thought of using a more short numbering system than other systems to calculate their resistance value, this system is called EIA96. This system is use for SMD resistors with a tolerance value of 1%.
Resistors using EIA96 have high tolerance thus their figure increases, and smaller resistors are difficult to read. The EIA69 SMD resistor coding system uses two figures and a letter, thus having a total code character of three e.g 56x.
The first two digits indicates three significant figures of the resistor's value, the third character is a letter which serves as the multiplier. In this system it won't be mistaken to a three figures SMD system because the letter will differentiate it. To calculate the resistance of a resistor printed in the EIA69 system, the significant figures is equivalent to a code and also the letter. So you need to memorise this characters and their values.
EIA6 SMD figures and their values.
EIA69 SMD letters and their values.
Tags:
Basic Electronics