Resistors are among the most often used parts in electrical and electronic circuits. When putting together a circuit, it’s critical to correctly identify the different resistance values of these resistors.
Manufacturers employ colour codes to identify their resistance levels because it is impractical to print them on a small resistor. The Colour Code for Carbon Resistors is the name of this scheme.
Introduction to Carbon Resistors
The most popular fixed resistors are carbon resistors. They are composed of insulating material (often clay or ceramic) and finely powdered carbon.
The resistance value is determined by the carbon to insulating material ratio. A strong, coloured insulating covering is applied to these resistors to shield them from environmental and mechanical harm.
The resistance value and tolerance cannot be printed directly on them because to their extremely small surface area. To illustrate the resistance value and its tolerance, coloured rings are positioned around the resistor body using a standardised colour band system.
Need for Colour Coding
Without the use of extra instruments, the colour-coded system makes it simple to interpret resistance values rapidly and precisely. Because of its global acceptance, this standardised approach guarantees resistor identification that is consistent and uniform.
According to the colour chart established by international standards like the Electronic Industries Association (EIA) and the International Electrotechnical Commission (IEC), the colour bands stand for digits, multipliers, and tolerance.
Colour Code Table
The colour code system uses ten standard colours to represent digits from 0 to 9. Each colour corresponds to a specific number as shown below:
Colour | Digit | Multiplier | Tolerance |
Black | 0 | 10⁰ | — |
Brown | 1 | 10¹ | ±1% |
Red | 2 | 10² | ±2% |
Orange | 3 | 10³ | — |
Yellow | 4 | 10⁴ | — |
Green | 5 | 10⁵ | ±0.5% |
Blue | 6 | 10⁶ | ±0.25% |
Violet | 7 | 10⁷ | ±0.1% |
Grey | 8 | 10⁸ | ±0.05% |
White | 9 | 10⁹ | — |
Gold | — | 10⁻¹ | ±5% |
Silver | — | 10⁻² | ±10% |
No Colour | — | — | ±20% |
Reading the Colour Code
A carbon resistor generally has four or five colour bands printed around its body.
* Four-band resistors are the most common type used in basic circuits.
* Five-band resistors are used where more precision is required.
Let’s understand both:
Four-Band Resistor:
* First Band: Represents the first significant digit of resistance.
* Second Band: Represents the second significant digit.
Suppose a resistor has the following colour bands: Red, Violet, Orange, Gold
* Red → 2
* Violet → 7
* Orange → 10³
* Gold → ±5%
So,
Resistance ( R = 27 × 10³ = 27,000 Ω = 27 kΩ ± 5% )
Hence, the resistor value is 27 kΩ with a tolerance of ±5%.
Five-Band Resistor:
In precision resistors, the first three bands represent the significant digits, the fourth band represents the multiplier, and the fifth band represents the tolerance.
If the colour bands are Brown, Black, Black, Red, Brown, then
* Brown → 1
* Black → 0
* Black → 0
* Red → 10²
* Brown → ±1%
Therefore,
Resistance ( R = 100 × 10² = 10,000 Ω = 10 kΩ ± 1% )
Tolerance and Its Importance
Tolerance indicates the possible variation of the actual resistance value from its nominal value.
For instance, a resistor of 100 Ω ±5% can have an actual resistance between 95 Ω and 105 Ω.
Lower tolerance values mean higher accuracy and better quality resistors.
Typical tolerance values are ±1%, ±2%, ±5%, ±10%, and ±20%.
Special Cases: Temperature Coefficient
In some precision resistors, a sixth colour band may also be present, which indicates the temperature coefficient (ppm/°C). It tells how much the resistance changes with temperature. For example, a brown band in this position means a temperature coefficient of 100 ppm/°C.
Advantages of Colour Coding
Compact representation: Saves space on small resistors.
Universal standard: Easy identification across all manufacturers.
Quick reading: Enables technicians to recognise resistance values instantly.
Durability: The colours are heat-resistant and long-lasting.
Summary
Without the need for written labels, the colour-coding scheme for carbon resistors is a clever and useful way to identify resistance levels and tolerances. For students, engineers, and technicians working in the electronics industry, it is essential to comprehend this system. In circuit design and sort out, it encourages uniformity, precision, and effectiveness.
