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Resistor resistance determination

Published 15.07.2010 Presenter Anton Pankratov

Often when we replace a broken resistor, it is necessary to determine its nominal resistance. We can use an ohmmeter for this. What is more, it's possible to use a standard multimeter.
Let's set it to the ohmmeter mode and measure the nominal resistance of our resistor.
We see that its value is approximately 100 ohms.
There are two ways of marking the values and tolerances on resistors: using the color code or the alpha-numeric code.
First, let's consider the color code.
The resistor body is marked with 4 or 5 color bands. The resistance in ohms is expressed by two or three digits and the multiplier 10 in the n-th power, where n is an integral number from -2 to +9.
The marks are located on one end of the resistor and arranged left to right in the following order.
The first band is the first nominal value digit.
The second band is the second nominal value digit.
The third band is the third nominal value digit which does not equal zero.
The fourth band is the multiplier.
And the fifth band is the deviation tolerance.
If the nominal value of a resistor has only two significant figures, the third band is not applied and there are only 4 color bands: two digits of the nominal value, the multiplier and the tolerance.
If the resistor size does not allow applying color bands asymmetrically, closer to one of the resistor ends, then the first band is approximately twice as wide as the other bands.
The other coding scheme is the alphanumeric code.
Let's consider the resistor color coding scheme.
There are two red bands, a black one and a gold one.
The red bands mean two times two, or twenty-two.
The black band is the multiplier. It equals one
That is, the nominal value is 22 Ohm.
And the gold band means 5%.
Thus, our 22 Ohm resistor has a 5% tolerance.
SMT resistors are marked with the digital code.
The first and the second figures are the first two digits of the nominal value. The third figure is the multiplier: 10 in the n-th power.
Thus, if we see 105 on the chip, it means 10 in the 5th power, or 1 Mohm.
So, we have described how to determine the nominal resistance of a resistor.
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