The resistor color code is a method used to represent the resistance values of tiny resistors, where printing the actual resistance values would be impractical. Instead, color bands are used to encode the resistance. These bands are collectively known as resistor color codes.
The resistor color code system was developed in the 1920s by the Radio Manufacturers Association (RMA). This system not only specifies resistance but also provides information about tolerance and, in some cases, reliability or failure rates.
Number of Bands in a Resistor
Resistors can have between three to six color bands. The first two bands indicate the resistance value, while the third band serves as a multiplier. Additional bands, if present, specify tolerance or other characteristics.
Decoding the Resistor Color Code
To decode the resistor color code, one can use a resistor color table. This table correlates the colors with their corresponding numerical values, making it easier to determine the resistor’s specifications.
How to Read a Resistor Color Code
To accurately read a resistor color code:
- Hold the resistor such that the tolerance band is on the right. The tolerance band is typically gold or silver and is slightly separated from the other bands.
- Starting from the left, note the sequence of colors on the bands.
- Use the resistor color table to determine the digits associated with each color.
- Identify the multiplier band, which is next to the tolerance band. For example, if the multiplier band is red (representing 2), the value is calculated as 102.
Practical Example: Reading a Resistor
To illustrate how to decode resistor color codes, consider a resistor with a value of 22 ohms ± 5%. The tolerance band, which determines the permissible variation in resistance, is typically gold, indicating a minimal variation.
Calculating Tolerance
The tolerance of a resistor can be calculated using the formula:
Tolerance = Value of resistor × Tolerance percentage
For a 22-ohm resistor with a 5% tolerance:
- Tolerance = 22 ohms × 5% = 1.1 ohms
This calculation means the resistor’s actual resistance can range from 20.9 ohms to 23.1 ohms.
Key Points to Remember
- The band adjacent to the tolerance band represents the multiplier.
- The bands to the left of the multiplier band represent the significant digits of the resistance value.
