Color Code Resistors

The value of the resistor, its wattage rating and tolerance are commonly printed on the body of the resistor as numbers/figures only if the resistor's body is large enough to read the print, such as high wattage resistors. But if the resistor is tiny such as a 1/4 W carbon/film type, the specifications can not be printed and even if they are printed, they can not be read. The value of the given resistor must be shown in other way. So to overcome this problem, the value of tiny resistors (1/4 W) are written in color-coded bands to indicate their resistive value & their tolerance. These color-coded bands produce a system of identification generally known as a Resistor's Color-Code.

The international & universally accepted resistor color coding system was developed long time ago as a simple and convenient way of identifying a resistor's value and its tolerance, no matter what its size or condition is. The color-code resistor consists of a set of individual colored rings/bands in spectral order representing each digit of the resistor's value. The resistor's color-code is always read one band at a time starting from the left to the right, keeping the tolerance band at the right. The tolerance band is either identified by its color (golden or silver) or by its spacing; the tolerance color is placed abit further from other value colors. By matching the color of the first band with its associated number in the digit column of the color chart, the first digit is identified and this represents the first digit of the resistance value. Again, by matching the color of the second band with its associated number in the digit column of the color chart we get the second digit of the resistance value and so on as illustrated in the figure.

Calculating Resistor's Value

The Resistor Color Code System is an easy and the most convenient way to mention the value of a resistor. We need to have a good knowledge about the color codes and the we need to understand how to apply it in order to get the correct value of the resistor. The color-coded resistor is read from left to the right. Below is an example showing how to read the value of the resistor with 4-bands of color:

Example:
COLOR   Red   Yellow   Blue   Silver
VALUE      2        4          6       10% Tolerance
Total: 24 × 106 = 24000000Ω or 24MΩ 

In the four band color-coded resistor, the first and second color value is written as usual but the third value is written in the ten times power of the value. For example: If the third color(color before the tolerance value) is green, its value is five zeros at the end. That gives the value of the resistor in ohms(Ω). The last value of the resistor determines its tolerance. Tolerance of a resistor is the error of the resistor. It means, the tolerance of a resistor in percentage is the value by which a resistor differs from its printed value. For instance, if the last color is silver, its tolerance is +-10% which means the value of the resistor may differ by 10% above or below.

The color code of the resistor with its value is hard to memorize. It is easier to remember the resistor color code by using mnemonics or certain phrases that have a sparate word in a phrase to represent each of the ten + Two colors in the code. These phrases are quite simple and easy to learn and to memorize the value of the color codes.

Some of the phrases are:
BB ROY of Great Britain has a Very Good Wife
Bad Boys Ring Our Young Girls But Vicky Goes Without
Bad Booze Rots Our Young Guts But Vodka Goes Well


The British Standard Code [BS1852]

Larger power resistors are bigger in size and their resistance value, wattage and tolerance are generally printed onto the body of the resistor. However the values are represented as codes using numbers and alphabets. In this system of coding, the decimal values are represented in terms of suffix letters. 

Let us look at an example:

If the printed value is 4K7  J
When an alphabet (here, K) comes in between the numbers, it is the decimal value. So, the value is 4.7. To know its unit we need to again see the alphabet. In this case the alphabet is K which means the unit is Kilohms. So, the value of the resistor is 4.7KΩ. The alphabet J represents its tolerance which is 5%.


The following table makes it clear:

I hope this post helps you a lot to find the exact value of the resistor. Have a happy reading. If you have any comments or suggestions regarding this post you can directly comment on the comment box. Feedback are welcomed. Please do not forget to share and like this post. Read my other post to know more about other electronic components and some useful electronic projects.

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Introduction to Resistors

A resistor is a component of an electrical circuit that resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next. A resistor is primarily used to create and maintain a known safe current within an electrical component.

Resistance is measured in ohms, after Ohm's law. This rule states that electrical resistance is equal to the drop in voltage across the terminals of the resistor divided by the current being applied to the resistor. A high ohm rating indicates a high resistance to current. This rating can be written in a number of different ways depending on the ohm rating. For example, 81R represents 81 ohms, while 81K represents 81,000 ohms.

The amount of resistance offered by a resistor is determined by its physical construction. A carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around the outside. Metal film or metal oxide resistors are made much the same way, but with metal instead of carbon. A wire wound resistor, made with metal wire wrapped around clay, plastic, or fiberglass tubing, offers resistance at higher power levels. For applications that must withstand high temperatures, materials such as cermet, a ceramic-metal composite, or tantalum, a rare metal, are used to build a resistorthat can endure heat.

A resistor is coated with paint or enamel, or covered in molded plastic to protect it. Because resistors are often too small to be written on, a standardized color-coding system is used to identify them. The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is to its ohm value. This is important for two reasons: the nature of resistor construction is imprecise, and if used above its maximum current, the value of the resistor can alter or the unit itself can burn up.Every resistor falls into one of two categories: fixed or variable. A fixed resistor has a predetermined amount of resistance to current, while a variable resistor can be adjusted to give different levels of resistance. Variable resistors are also called potentiometers and are commonly used as volume controls on audio devices. A rheostat is a variable resistor made specifically for use with high currents. There are also metal-varistor, which change their resistance in response to a rise in voltage; thermistors, which either raise or lower resistance when temperature rises or drops; and light-sensitive resistors.

Resistors are "Passive Devices", that is they contain no source of power or amplification but only attenuate or reduce the voltage signal passing through them. This attenuation results in electrical energy being lost in the form of heat as the resistor resists the flow of electrons through it.

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Welcome to Electronics club

Electronics Club

This blog is designed in order to provide information to the you about electronics. Electronics is an interesting in the field of physics. The giant strides that we have made in the areas of communications and computers are possible only because of the great success that we have achieved in the field of electronics.

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