Resistor

Identifying resistors

Most axial resistors use a pattern of coloured stripes to indicate resistance. SMT ones follow a numerical pattern. Cases are usually brown, blue, or green, though other colours are occasionally found like dark red or dark gray.

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4-band axial resistors

4 band identification is the most commonly used colour coding scheme on all resistors. It consists of four coloured bands that are painted around the body of the resistor. The scheme is simple: The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value. Each colour corresponds to a certain number, shown in the chart below. The tolerance for a 4-band resistor will be 2%, 5%, or 10%.

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The Standard EIA Color Code Table per EIA-RS-279 is as follows:

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Note: red to violet are the colours of the rainbow where red is low energy and violet is higher energy.

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Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent; 6.8, 68, 680, etc. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colours, which make them easier to recognize.

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Preferred values

Standard resistors are manufactured in values from a few milliohms to about a gigohm; only a limited range of values called preferred values are available. In practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined above. Resistors are often marked with their tolerance (maximum expected variation from the marked resistance). On color coded resistors the color of the rightmost band denotes the tolerance:

Related Topics:
Preferred values - Tolerance - Color coded

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: silver 10%

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: gold 5%

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: red 2%

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: brown 1%.

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Closer tolerance resistors, called precision resistors, are also available.

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5-band axial resistors

5-band identification is used for higher tolerance resistors (1%, 0.5%, 0.25%, 0.1%), to notate the extra digit. The first three bands represent the significant digits, the fourth is the multiplier, and the fifth is the tolerance. 5-band standard tolerance resistors are sometimes encountered, generally on older or specialized resistors. They can be identified by noting a standard tolerance color in the 4th band. The 5th band in this case is the temperature coefficient.

Related Topics:
Tolerance

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SMT resistors

Surface-mount resistors are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance SMT resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten. For example, "472" represents "47" (the first two digits) multiplied by ten to the power "2" (the third digit), i.e. 47 imes 10^2 = 47 imes 100 = 4700 mbox{ ohms}. Precision SMT resistors are marked with a four-digit code in which the first three digits are the first three significant digits of the value and the fourth digit is the power of ten.

Related Topics:
Surface-mount - Significant digit

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Industrial type designation

• In industrial type designation, the first two digits represent the significant figures and the third gives the number of zeros to folow.
• For resistance value less than 10$Omega$, the letter (G) substituted in place of the third digit signifies a decimal multiplier of 0.1

e.g.: 27G represents a resistance of 2.7Omega.

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• Another digit following the resistance value code gives the percentage tolerance.
• Digits used to represent the tolerances of $pm$5%, $pm$10% and $pm$20% are 5, 1 and 2 respectively.
• The power rating is expressed by two letters preceding the resistance value code. These letters are BB, CB, EB, GB, HB, GM and HM respectively for , 1, 2, 3 and 4 W resistors.

spadesuit The operational temperature range distinguishes commercial grade components from the industrial grade components.

Related Topics:
Temperature - Commercial

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Commercial grade: 0^circC to 70^circC

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Industrial grade: -25^circC to +85^circC

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