What Are The Standard Resistors?

**What are the standard resistors?

Resistors are fundamental components in the world of electronics and are used extensively to control the flow of current in circuits. They come in various types, sizes, and resistance values, but there are some standard resistors that are commonly used in electronic devices. In this article, we will delve deeper into these standard resistors and understand their characteristics, applications, and limitations.

**Types of Resistors:

There are mainly two types of resistors - fixed resistors and variable resistors. Fixed resistors have a specific value of resistance that cannot be adjusted, whereas variable resistors have a variable resistance value that can be adjusted by users. Variable resistors are further divided into potentiometers and rheostats, depending on their usage.

**Fixed Resistors:

Fixed resistors come in various sizes and shapes, but their resistance value is fixed and cannot be changed. They are made of various materials, including carbon, metal film, and wire-wound, each with their own specific properties. The most commonly used fixed resistors are carbon composition and metal film resistors.

Carbon Composition Resistors:

Carbon composition resistors are made of a mixture of carbon particles and a binding material that holds them together. They were once the most commonly used resistors due to their low cost, but their popularity has decreased over time due to their relatively poor stability, high noise level, and non-linear characteristics.

Metal Film Resistors:

Metal film resistors are made by depositing a film of metal on a ceramic substrate. They offer better stability, lower noise level, and more uniform characteristics than carbon composition resistors. Metal film resistors are available in various tolerances, ranging from 1% to 10%, and are used in various applications, including audio amplifiers, power supplies, and timing circuits.

Wire-Wound Resistors:

Wire-wound resistors are made by wrapping a wire around an insulating core. They offer high precision and low temperature coefficient of resistance but have relatively high cost due to their need for precision winding. Wire-wound resistors are used in applications demanding high precision, such as medical equipment, aerospace, and military applications.

**Variable Resistors:

Variable resistors are devices that allow users to vary the resistance value by rotating their shafts. These are further classified into potentiometers and rheostats, depending on their applications.

Potentiometers:

Potentiometers, commonly known as pots, are variable resistors that are used to control the voltage level in a circuit. They consist of a resistive element, consisting of carbon or metal film, and a movable contact, which is connected to a knob that users can turn to change the resistance value. Potentiometers are widely used in audio equipment, tone controls, and voltage regulators.

Rheostats:

Rheostats are variable resistors that are used to control the current flow in a circuit. They are similar to potentiometers but have a higher resistance value and can dissipate more power than pots. Rheostats are used in various applications, including heating elements, motor speed control, and lighting dimmers.

**Standard Resistor Values:

Resistors are available in a wide range of values ranging from milliohms to megaohms. However, there are some standard resistor values that are commonly used in electronic devices due to their availability and ease of use.

The standard resistor values are based on the E-series, which is a set of preferred values used in electronic devices. The E-series resistor values are based on a logarithmic scale and have a specified tolerance value, ranging from 1% to 20%.

The most commonly used E-series values are E6, E12, E24, E48, E96, and E192, representing the number of values within each series. For instance, E6 series has 6 standard values, E12 series has 12 standard values, and so on.

The most commonly used standard resistor values are:

E6 series: 10, 15, 22, 33, 47, 68

E12 series: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

E24 series: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91

**Resistor Color Code:

Resistors are identified by their color code, which is printed on their bodies using colored bands. The color code represents the resistance value, tolerance, and sometimes the temperature coefficient of resistance.

The color code of resistors follows a standard scheme, with the first two bands indicating the first two digits of the resistance value, the third band indicating the multiplier, and the fourth band indicating the tolerance value. For example, a resistor with the color code brown, black, red, and gold represents a resistance value of 1,000 ohms, with a tolerance of 5%.

The color code for resistors may differ slightly between different manufacturers, but the scheme is standardized to ensure easy identification and compatibility.

**Limitations of Resistors:

Resistors have some inherent limitations that can affect their reliability and performance in electronic devices. Some of the limitations are:

Temperature Coefficient of Resistance:

The resistance value of a resistor changes with temperature due to the temperature coefficient of resistance. The temperature coefficient of resistance is the rate at which the resistance value changes with temperature and is expressed in parts per million per degree Celsius. Resistors with high temperature coefficient of resistance can cause errors in electronic devices, especially in precise applications.

Power Rating:

The power rating of a resistor is the maximum amount of power it can dissipate without being damaged. Resistors with low power rating values can be damaged or burnt if subjected to higher power levels.

Noise:

Resistors generate thermal noise due to the random motion of electrons within their resistive material. This noise can affect the performance of electronic devices, especially in audio applications, where it can be audible.

**Conclusion:

In conclusion, resistors are essential components in electronic devices that are used to control the flow of current in circuits. They come in various types, sizes, and resistance values, and there are some standard resistors that are commonly used in electronic devices. Fixed resistors include carbon composition, metal film, and wire-wound, whereas variable resistors include potentiometers and rheostats. The standard resistor values are based on the E-series, and resistors are identified by their color code. Resistors have some limitations, including temperature coefficient of resistance, power rating, and noise, but their benefits outweigh their limitations, and they play a crucial role in the world of electronics.