EMC Question of the Week: June 5, 2023

Components on a circuit board

The circuit board component labeled R20 in the photo is a 

  1. 0.20 Ω resistor
  2. 2.0 Ω resistor
  3. 20 Ω resistor
  4. 2.0 μH inductor


The correct answer is “a.” The standard 3-digit code for marking SMD resistors puts an "R" in the location of the decimal point for small-valued resistors. So R20 represents a 0.20-Ω resistor. The resistors labeled 1R0 are 1.0-Ω resistors.

Larger valued resistors may use a "K" or "M" to represent kΩ or MΩ, respectively. For example, 4K7 may be used to indicate a value of 4.7 kΩ. However, there are competing standards for marking resistors. Depending on the standard applied, letters (including R, K and M) in the last position may indicate a tolerance. The EIA-96 standard (for resistors with a 1% tolerance) uses a letter in the last position to indicate a multiplier. 

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