## Resistors And The Colour Code

### Resistors

These are components made to provide resistance in circuits. They are made in various resistance values, physical sizes, and can be of fixed or variable value.

The circuit symbols used for different types of resistors are shown in the diagram The symbols at A are those used for fixed value resistors, at B are those for variable resistors, at C those for preset resistors or trimpots, and at D a variable resistor used as a potentiometer, with provision for tapping off part of the voltage across the resistor, and being able to vary the tap.

### Resistor Power Ratings

Fixed resistors are available in a wide range of power ratings. The power rating of a resistor depends on its ability to dissipate heat and to keep its operating temperature below a value at which its resistance value is seriously affected. To do this, it must have a certain surface area. The larger the power rating, the larger the resistor.

Usual ratings are 0.125, 0.25, 0.5, 1, and 2 watt in carbon resistors; above these levels, wire-wound or other types are used.

### Resistor Markings

Sometimes the value of a resistor is printed on the component itself. The letters R and k have a purpose here. Note in this table how these letters act as the decimal indicator:

 Marking Resistance Values in Circuits R05 0.05 ohms 1R5 1.5 ohms 15R 15 ohms 1k5 1500 ohms or 1.5 kilohms 15k 15 000 ohms or 15 kilohms 1M5 1.5 megohms

### The Resistor Colour Code

Resistor values are usually marked on the resistor itself by using colour rings or bands. Because the range of resistor values used in electronics goes from fractions of an ohm to tens of megohms, it is impossible to manufacture resistors in every possible value, so resistors are produced in preferred values. Resistors are marked with their preferred value, and a tolerance value, which indicates the spread of the resistance value you can expect.

 1st ring = 2nd ring = 3rd ring = 4th ring = Colour 1st digit 2nd digit multiplier tolerance of value of value % None ±20% Silver 10-2 Ω = 0.01 Ω ±10% Gold 10-1 Ω = 0.1 Ω ±5% Black 0 0 100 Ω = 1.0 Ω Brown 1 1 101 Ω = 10 Ω ±1% Red 2 2 102 Ω = 100 Ω ±2% Orange 3 3 103 Ω = 1 k Ω Yellow 4 4 104 Ω = 10 k Ω Green 5 5 105 Ω = 100 k Ω ±0.5% Blue 6 6 106 Ω = 1 M Ω Violet 7 7 107 Ω = 10 M Ω Grey 8 8 108 Ω = 100 M Ω White 9 9 109 Ω = 1000 M Ω

The Table shows the colour code and the tolerance colours for the four ring colour code

Some equipment requires increased precision. To meet this need resistors with a precision of ±0.5% are required. For these types of resistor a five ring or band colour code is used to give a third digit value for more precise resistor values and tolerances.

### Remembering the Colour Code

The colouring starts with Black (which is Zero). The sequence is:

 0 1 2 3 4 5 6 7 8 9 Black Brown Red Orange Yellow Green Blue Violet Grey White

Just remember the ditty

Better Be Right Or Your Great Big Venture Goes West

Remember that it starts at Zero which is Black.

### An Example

This figure below shows a fixed resistor with its colour rings. To read the colour code, put the tolerance ring to your right and read off the colours as number values. The first two rings give a number between 10 and 100 and the third ring is the power of 10 or multiplier needed for the final value. The fourth ring indicates the tolerance.

For example, a resistor coded brown, red, yellow, silver is a 12 x 104 or 120 kilohm resistor, and the tolerance of 10% indicates that the value could lie between 108 kilohms and 132 kilohms.

Gold and silver are also used as multipliers. Gold = multiply the value by l0-1 (multiply the value by 0.1) and silver = multiply the value by 10-2 (multiply the value by 0.01).

### Preferred Ranges For Resistors

The preferred ranges depend on the tolerance.

For 10% resistors the preferred values are 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82, and multiples of each value. For example, you can have a 10 ohm, a 10 kilohm, and a 10 megohm resistor value.

For 5% resistors the preferred values are 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91, and multiples of each value.

For 1% resistors the Preferred values of Resistor are 100, 102, 105, 107, 110, 113, 115, 118, 121, 124, 127, 130, 133, 137, 140, 143, 147, 150, 154, 158, 162, 165, 169, 174, 178, 182, 187, 191, 196, 200, 205, 210, 215, 221, 226, 232, 237, 243, 249, 255, 261, 267, 274, 280, 287, 294, 301, 309, 316, 324, 332, 340, 348, 357, 365, 374, 383, 392, 402, 412, 422, 432, 442, 453, 464, 475, 487, 499, 511, 523, 536, 549, 562, 576, 590, 604, 619, 634, 649, 665, 681, 698, 715, 732, 750, 768, 787, 806, 825, 845, 866, 887, 909, 931, 953, 976, and multiples of each value. For example, you can have a 16.5 ohm, a 165 kilohm, and a 16.5 megohm resistor value.

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Compiled Thu Jan 20 2011 at 9:07:41pm

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