Standard resistor values
- the E series for preferred resistor values
The values given to resistors (and capacitor) fall into a number of standard
or preferred values. They have a logarithmic sequence related to the component
accuracy, enabling the standard values to be values to be spaced according to
the tolerance on the component.
Component values such as resistor values can never be manufactured exactly,
each resistor has a tolerance associated with it. These may typically be �20%, �
10% and �5%. Other tolerances such as �2% are also available.
In order to enable the standard resistor values to be spaced apart according
to their tolerance, a series known as the E series for standard or preferred
values is used. Resistors are spaced apart so that the top of the tolerance band
of one value and the bottom of the tolerance band of the next one do not
overlap. Take for example a resistor with a value of 1 ohm and a tolerance of
20%. If the actual resistance of the component falls at the top of the tolerance
band then it will have a value of 1.2 ohms. Take then a resistor with a value of
1.5 ohms. Again it is found that the value at the bottom of its tolerance band
is 1.2 ohms. By calculating a range of values in this way a series can be built
up. This is repeated for each decade.
The series generated in this way is known as the E series and these are
preferred values. If a �40% tolerance is used there will only be 3 values in
each decade (1, 2.2. and 4.7), and the series is known as the E3 series as there
are three values in each decade. There is also an E6 series with six values in
each decade for a �20% tolerance, E12 series with 12 values in each decade for a
�10%, E24 series with 24 values in each decade for a �5% tolerance. Values for
resistors in these series are given below. Further series (E48 and E96) are
available, but are not as common as the ones given below.
The E6 and E12 resistors are available in virtually all types of resistor.
However the E24 series, being a much closer tolerance series is only available
in the higher tolerance types. Metal oxide film resistors that are in common use
today are available in the E24 series as are several other types. Carbon types
are only available in the lower tolerance ranges as their values cannot be
guaranteed to such a close tolerance.
| E6 Series: |
|
|
|
1.0 |
1.5 |
2.2 |
|
3.3 |
4.7 |
6.8 |
| |
|
|
| E12 Series: |
|
|
|
1.0 |
1.2 |
1.5 |
|
1.8 |
2.2 |
2.7 |
|
3.3 |
3.9 |
4.7 |
|
5.6 |
6.8 |
8.2 |
| |
|
|
| E24 Series: |
|
|
|
1.0 |
1.1 |
1.2 |
|
1.3 |
1.5 |
1.6 |
|
1.8 |
2.0 |
2.2 |
|
2.4 |
2.7 |
3.0 |
|
3.3 |
3.6 |
3.9 |
|
4.3 |
4.7 |
5.1 |
|
5.6 |
6.2 |
6.8 |
|
7.5 |
8.2 |
9.1 |
|
