Reading a resistor involves interpreting the colored bands printed on its body. These bands encode the resistor's resistance value, tolerance, and sometimes its temperature coefficient.
Understanding Resistor Color Codes
Resistors typically have 3, 4, 5, or 6 color bands. Each band represents a specific part of the resistor's value or characteristic.
- Digits: The first one or two bands represent the significant digits of the resistance value.
- Multiplier: A subsequent band indicates the power of 10 by which the digit value is multiplied.
- Tolerance: A band, usually separated or wider, indicates the percentage tolerance (how much the actual resistance can vary from the stated value).
- Temperature Coefficient: On 6-band resistors, the final band indicates the temperature coefficient, showing how much the resistance changes per degree Celsius.
Determining the Reading Direction
The bands are read from left to right. The first band is typically located closer to one end of the resistor than the last band. Sometimes, the tolerance band is wider or has a greater separation from the other bands.
According to the reference, the bands are read in a specific direction, with the first band indicating the first digit value.
Interpreting the Bands: Color Code Table
To read the resistor, you need to know the value assigned to each color for digits, multipliers, and tolerance.
Here is a standard resistor color code table:
| Color | Digit | Multiplier | Tolerance | Temperature Coefficient (ppm/°C) |
|---|---|---|---|---|
| Black | 0 | 10⁰ (1) | - | - |
| Brown | 1 | 10¹ (10) | ±1% | 100 |
| Red | 2 | 10² (100) | ±2% | 50 |
| Orange | 3 | 10³ (1k) | - | 15 |
| Yellow | 4 | 10⁴ (10k) | - | 25 |
| Green | 5 | 10⁵ (100k) | ±0.5% | - |
| Blue | 6 | 10⁶ (1M) | ±0.25% | 10 |
| Violet | 7 | 10⁷ (10M) | ±0.1% | 5 |
| Gray | 8 | 10⁸ (100M) | ±0.05% | 1 |
| White | 9 | 10⁹ (1G) | - | - |
| Gold | - | 10⁻¹ (0.1) | ±5% | - |
| Silver | - | 10⁻² (0.01) | ±10% | - |
Reading Different Types of Resistors
While the principles are similar, the number of bands changes the interpretation:
- 4-Band Resistors:
- Band 1: First digit
- Band 2: Second digit
- Band 3: Multiplier
- Band 4: Tolerance
- 5-Band Resistors: (Common for higher precision)
- Band 1: First digit
- Band 2: Second digit
- Band 3: Third digit
- Band 4: Multiplier
- Band 5: Tolerance
- 6-Band Resistors:
- Band 1: First digit
- Band 2: Second digit
- Band 3: Third digit
- Band 4: Multiplier
- Band 5: Tolerance
- Band 6: Temperature Coefficient
Practical Example
Let's use the example mentioned in the reference:
- "the first band is red so the first digit. Value is two"
- "the second band is violet. So digit two is seven"
- "the third band is yellow."
Assuming this is a standard 4-band resistor:
- Band 1 (Red): According to the table, Red corresponds to the digit 2.
- Band 2 (Violet): According to the table, Violet corresponds to the digit 7.
- Band 3 (Yellow): According to the table, Yellow corresponds to the multiplier 10⁴ (or 10,000).
- Band 4 (Tolerance): (Not mentioned in the reference, but let's assume it's Gold for a common value). Gold corresponds to a tolerance of ±5%.
Combining these:
- Digits: 2 and 7 combine to 27.
- Multiplier: Multiply the digit value by 10⁴.
- Value: 27 * 10,000 = 270,000 Ohms (or 270 kOhms).
- Tolerance: ±5%.
So, a resistor with Red, Violet, Yellow, Gold bands is a 270 kOhm resistor with a ±5% tolerance. This means its actual resistance is between 270,000 (1 - 0.05) = 256,500 Ohms and 270,000 (1 + 0.05) = 283,500 Ohms.
Reading resistors correctly is a fundamental skill in electronics, allowing you to identify the correct component for a circuit.
