Resistors are electrical circuit components that restrict current flow and generate a voltage drop. Carbon resistors are colour-coded to determine their resistance value in ohms due to their tiny size. The most popular method of indicating a resistor’s value is utilising colour bands on the resistor’s body. The Electronic Industries Association has standardised colour coding (EIA). In the year 1920, a resistor colour coding was established. The body of micro resistor components has these colour bands printed on it.

Colour bands’ definitions

The colour of the multiplier band denotes multiples of ten or the decimal point’s location. ORANGE (3), for example, symbolises 10 to the third power or 1,000. The tolerance specifies how much a resistor can vary above or below its value in percentage terms. A gold band represents ±5%, a silver band represents ±10% and if no fourth band appears, it is believed to represent ±20%. Consider the following scenario. A 5 percent resistor with a resistance of 100 ohms can have a resistance of 95 to 105 ohms and yet be regarded within the specified tolerance. The temperature coefficient band defines the greatest change in resistance with temperature change, expressed in parts per million per degree Celsius (ppm/°C).

Following are the Types of Resistors based on the number of bands

• The multiplier is represented as the third band in a three-band resistor. A high-resistance multiplier is used to convert a galvanometer to a voltmeter. It also moves the decimal point to alter the value from megaohms to milliohms. 
• The most popular version is the four-band colour coding. There are two resistance bands, one multiplier and one tolerance band on these resistors. The four bands in this example are green, blue, red and gold. Using the colour code for the carbon resistors chart, one can see that green represents 5 and blue represents 6. 
• An additional band indicates a third significant digit on high-precision resistors. As a result, the first three bands denote significant digits, the fourth band denotes the multiplication factor and the fifth band denotes tolerance.
• High precision resistors with an extra band to define the temperature coefficient (ppm/C = ppm/K) are commonly seen in resistors with six bands. Brown (100 ppm/°C) is the sixth band’s most prevalent colour. This indicates that the resistance value can change 1000 ppm = 0.1 per cent with a temperature change of 10 °C when it comes to the 6-band resistor.

A five-band resistor with a gold or silver fourth band

The anomalies seen on specialist and older resistors are five-band resistors with a gold or silver fourth band. The first two bands represent the significant digits; the third band represents the multiplication factor; the fourth band represents the tolerance and the fifth band shows the temperature coefficient (ppm/C).

E-series or Preferred Values

In 1952, the IEC (International Electrotechnical Commission) set tolerance and resistance standards for resistors to make mass manufacturing easier. Select values, often known as E-series, are defined in the standard IEC 60063:1963. These standards are also used in capacitors, Zener diodes and inductors. This was done so that when firms made resistors with varying resistance levels, they would be evenly spaced on a logarithmic scale. This assists the provider in stocking various values. Because standard values are used, resistors from different manufacturers are compatible with the same designs.

The formula for Resistor Colour Coding

To calculate the colour code for the carbon resistors calculator, we must first group the values of the significant digits bands. This means taking the values of the first two or three bands from the left, depending on the total number of bands and multiplying that value by the multiplier to obtain the resistor’s resistance value.

• It’s possible that the reading orientation isn’t always obvious. The increased gap between bands 3 and 4 can sometimes be used to determine the reading direction. In addition, the first band is often the closest to a lead. The last band is always a gold or silver band (the tolerance).
• It’s good to double-check the manufacturer’s paperwork to ensure you’re using the right resistance colour coding method.
• When in doubt, use an ohmmeter to check the resistance. This may be the only method to determine the resistance in rare circumstances, such as when the colour bands have been burned out.

Conclusion 

Electrical circuits require resistors as a basic component. Soon after completing studies to ascertain the consequences of passing electricity through various materials and discovering electrical current, early scientists came to comprehend the idea of resistance and colour code for carbon resistors. While copper, gold and aluminium were discovered to be excellent conductors with minimal resistance, air, mica and ceramics were labelled as resistors due to them significantly reducing the flow of electrical current. Boykin’s novel resistor began to be implemented into everything from domestic appliances and computers to guided missiles as the US military, IBM and numerous consumer electronics manufacturers placed orders for it.