The common fixed resistor comes with a variety of colorful bands. Do they mean anything? Yes, they do! These colors give vital information about the resistor. Read this article to learn what they mean.
What Is a Resistor?
A resistor is an electrical component that is used to create resistance in circuits. This resistance can be utilized in many ways, like dividing the voltage or reducing the current. There are many types of resistors. However, the one that we're going to work with in this article is the most common one: the 4-band fixed resistor. A resistor works by changing the three factors in the resistance formula. R = pL / A Based on this formula, to create and increase resistance, you can:
- Increase the p or resistivity by using a less conductive material.
- Increase the L or length.
- Reduce the A or cross-section area.
A fixed resistor basically does all three of these at the same time. The resistor uses carbon, which is a less conductive material, and has a thin long structure that increases the length while reducing the cross-section area.
Fixed resistors have color bands to inform you of their properties. Each band adds one piece of information to the whole picture, depending on its position and its color. There are three major types of fixed resistors:
- 4-band: This is the most common type of resistor. The first two bands indicate the significant digits, the third band indicates the multiplier, and the fourth band indicates the tolerance.
- 5-band: This is similar to the 4-band, except that it has three bands for significant digits. The fourth band indicates the multiplier and the last band indicates the tolerance.
- 6-band: This one introduces an entirely new band type. Aside from all the bands in the 5-band resistor, this resistor also has a sixth band, indicating the temperature coefficient.
You'll have to put together the numbers each band represents to calculate the resistance.
First digitFirst digitFirst digit
Second digitSecond digitSecond digit
MultiplierThird digitThird digit
The Digit Bands
The digit bands use the same color codes for the digits they want to express. In a 4-band resistor, the digit bands are the first two bands, and in a 5- or 6-band resistor, the first three will be the digit bands. The digit bands can be in any of the 10 colors, which represent the digits 0 to 9. The first digit, however, can't be black (which represents zero) since it would be quite pointless.
Brown1Red2Orange3Yellow4Green5Blue6Violet7Gray8White9Black (never in the first band)0
Once you put the digits each color represents together, you have the significant digits for your resistance value in ohms. All that remains is to find out the multiplier.
The Multiplier Band
The multiplier band indicates the value your digits are multiplied with. This is the third band in a 4-band resistor type and the fourth band in 5- or 6-band types.
For example, if you have an orange multiplier band it means your resistor is in the kilohm scale.
The Tolerance Band
Tolerance is basically the error margin of your resistor. This means that your resistor won't always be resisting exactly with the value it's supposed to. A tolerance of 10% on a 100 ohm resistor means that the resistance can be anywhere from 90 to 110 ohms.
The least tolerance in typical resistors is ±0.05%, represented by gray, and the most is ±10%, represented by silver. Silver and gray may sound like they can be mistaken for one another, but the metallic glow of the silver band color easily distinguishes it from gray. The tolerance band is the last band in a 4-band resistor type and the fifth band in a 5- or 6-band type.
The Temperature Coefficient Band
The 6-band resistors have a special final band that indicates the temperature coefficient of the resistor. Resistance changes when the temperature changes; the amount (how much the resistance changes per each unit of temperature) and direction (whether the resistance increases or decreases) both depend on the material. The common fixed resistors are made of carbon and their resistance decreases with heat. The sixth band, combined with the first four bands, can tell you how much exactly it changes per temperature unit.
Black250 ppm/ºCBrown100 ppm/ºCRed50 ppm/ºCOrange15 ppm/ºCYellow25 ppm/ºCGreen20 ppm/ºCBlue10 ppm/ºCViolet5 ppm/ºCGray1 ppm/ºC
The temperature coefficient is expressed in ppm/ºC, which is parts per million per degree Celsius. To translate this to ohm/ºC, all you need to do is to multiply the temperature coefficient with the resistance of the resistor, and then divide it by a million. This will give you a value in ohm/ºC which tells you how much the resistance will drop with every degree Celsius of increased temperature.
Putting It All Together
When it comes to resistor bands, each color represents a number. The number a color represents depends on the band's position. For instance, in a 4-band resistor, violet on the first band means 7, whereas violet on the third band means x10,000,000. To interpret the resistor band colors, you'll have to consider the color and the sequence. Let's put it all together with two examples.
Resistor Example 1
Here's a simple 4-band resistor. Let's see if we can determine its properties just by looking at it.
- The first band: The first band is in orange, and according to the table in the previous sections, orange stands for 3.
- The second band: The second band is in orange as well, so this is another 3. So far we have 33.
- The third band: Since this is a 4-band resistor, the third band is the multiplier. A green multiplier band means x100,000. By now we know that we have a 3,300,000 ohm or 3.3 megohm resistor.
- The fourth band: The final band in a 4-band resistor is the tolerance band. This is going to indicate the error margin for your resistor. The fourth band in this resistor is gold, and that means ±5%. Gold and silver tolerance bands are the most common.
So then, the resistor in the picture is a 3.3 megohm resistor with a tolerance of ±5%. The tolerance combined with the resistance value means that the minimum resistance for this resistor is 3.135 megohms (-5%) and the maximum is 3.465 megohms (+5%).
Resistor Example 2
Here's another 4-band resistor. The waypoint is just like the previous example:
- First band: The first digit band is brown, which represents 1.
- Second band: The second digit band is green, which represents 5.
- Third band: The multiplier band is orange, which represents x1,000. So far we have 15,000 ohms (15 kilohms).
- Fourth band: The tolerance band is gold, like the previous example, which means the tolerance is ±5%.
So if you put all this information together, you'll know that this is a 15 kilohm resistor. The minimum resistance is 14.25 kilohms (-5%) and the maximum resistance is 15.75 kilohms (+5%).
No Need for an Ohmmeter
You don't always need to use an ohmmeter to find out the resistance of a resistor. If your resistor has color bands on it, you can tell how much resistance it's packing just by simply observing it. Now that you know what resistor you have, it's the right time to solder it into your circuit.