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How to Calculate the Value of an SMD Resistor?

Writer:Microhm Page View:Date:2019-06-18
Most chip resistors are marked with a 3-digit or 4-digit code - the numerical equivalent of the familiar color code for through-hole components. A new coding system (the EIA-96) has also appeared on precision SMDs.
The Three and Four Digit System
In this system the first two or three digits indicate the numerical resistance value of the resistor and the last digit gives a multiplier. The number of the last digit indicates the power of ten by which to multiply the given resistor value. Here are some examples of values under this system:
450 = 45Ω x 100 is 45Ω
273 = 27Ω x 103 is 27,000Ω (27kΩ)
7992 = 799Ω x 102 is 79,900Ω (79.9kΩ)
1733 = 173Ω x 103 is 173,000Ω (173kΩ)
The letter “R” is used to indicate the position of a decimal point for resistance values lower than 10 ohms. Thus, 0R5 would be 0.5Ω and 0R01 would be 0.01Ω.

The EIA-96 System
Higher precision resistors, combined with the decreasing sizes of resistors, have created the need to have a new, more compact marking for SMD resistors. Therefore the EIA-96 marking system has been created. It is based on the E96-series, thus aimed at resistors with 1% tolerance.
In this system, the marking exists out of three digits: 2 numbers to indicate the resistor value and 1 letter for the multiplier. The two first numbers represent a code that indicates a resistance value with three significant digits. In the table below the values for each code is given, which are basically the values from the E96 series. For example, the code 04 means 107 ohms, and 60 means 412 ohms. The multiplying factor gives the final value of the resistor, for example:
01A = 100 Ω ±1%
38C = 24300 Ω ±1%
92Z = 0.887 Ω ±1%

The usage of a letter prevents the confusion with other marking systems. However, pay attention because the letter R is used in both systems. For resistors with tolerances other than 1%, different letter tables exist.

Keywords:SMD resistor

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