tolerances

Resistor Colour Code are uses colour bands to quickly identify a resistors resistive value and its percentage of tolerance with the physical size of the resistor indicating its wattage rating. Generally, the resistance value, tolerance, and wattage rating are printed on the body of a resistor as numbers or letters when the resistors body is big enough to read the print, such as large power resistors. Resistors are usually very tiny, and it is challenging to print resistance values on them. So, colour bands are printed on them to represent the electrical resistance. These colour bands are known as resistor colour code. The resistor colour code was invented in the 1920s by the Radio Manufacturers Association (RMA). All leaded resistors with a power rating up to one watt are marked with colour bands. They are given by several bands and together they specify the resistance value, the tolerance rate and sometimes the reliability or failure rates. The number of bands present in a resistor varies from three to six. Resistor Colour Code Table ColourDigitMultiplierToleranceBlack01 Brown110± 1%Red2100± 2%Orange31000 Yellow410,000 Green5100,000± 0.5%Blue61,00,000± 0.25%Violet710,000,000± 0.1%Grey8 ± 0.05%White9 Gold 0.1± 5%Silver 0.01± 10% How to Read Resistor Colour Code? To read them, hold the resistor such that the tolerance band is on your right. The tolerance band is usually gold or silver in colour and is placed a little further away from the other bands.Starting from your left, note down all the colours of the bands and write them down in sequence.Next, use the table given below to see which digits they represent.The band just next to the tolerance band is the multiplier band. So if the colour of this band is Red (representing 2), the value given is 102. Learning with an example Here’s an example to get you started: The band colours for resistor colour code in the order: Band colours in orderREDREDBLACKGOLDDigit representation221±5%Value22 Ω ±5 % The tolerance values represent by how much the resistance can vary from its mean value in terms of percentage. A gold band represents the lowest variation, so be sure to buy these at the electronics store. The value of the given resistance is: 22 Ω ± 5% . The tolerance of the resistor can be calculated as follows: ToleranceValue of resistor × value of tolerance band 22 Ω × 5% 1.1 Ω This means that the 22 Ω resistor with a tolerance value of 1.1 Ω could range from the actual value as much as 23.1 Ω to as little as 20.9 Ω. It is important to note that the band next to the tolerance band represents the multiplier. All the bands to the left of this band represent the significant digits. There can be more than two such bands. Resistor colour code Mnemonic You can remember the colour code values using the following mnemonic: BB ROY of Great Britain had a Very Good Wife The capital letters represent the first letters of the colours and their positions the digit values. Now that we have an idea to determine the resistance value of a given resistor. Let us solve some problems related to this in the next section. Resistor Colour Code Examples Q) Determine the resistance of the given resistor with the given colour sequence (Red, Green, Red, Gold). As we know, the first two colours represent the significant digits of resistance value so the given colours represent digits 2 and 5. The third band is a multiplier band. Hence, the colour red represents a multiplier factor of 102. The last band represents the tolerance level and the tolerance level of the resistor is ±5%. Hence, the resistance value of the given resistor is 2500 ± 5% Ω or 2.5 kΩ.