There are a large variety of fixed and variable resistor types with different construction styles available for each group of resistors, with each one having its own particular Characteristics, Advantages and Disadvantages. To include all types would make this section very large so I shall limit it to the most commonly used, and readily available general purpose resistor types.
Composition Resistors
Carbon Resistors are the most common type of Composition Resistors as they are a cheap general purpose resistor. Their resistive element is manufactured from a mixture of finely ground carbon dust or graphite (similar to pencil lead) and a non-conducting ceramic (clay) powder to bind it all together. The ratio of carbon to ceramic determines the overall resistive value of the mixture and the higher this ratio is the lower the resistance. The mixture is then moulded into a cylindrical shape and metal wires or leads are attached to each end to provide the electrical connection before being coated with an outer insulating material
and colour coded markings.
Carbon Resistor
Carbon Composite Resistors are low to medium power resistors with low inductance which makes them ideal for high frequency applications but they can also suffer from noise and stability when hot. Carbon composite resistors are prefixed with a "CR" notation (eg CR10kΩ) and are available in E6 (±20% tolerance (accuracy)), E12 (±10% tolerance) and E24 (±5% & ±2% tolerance) packages with power ratings from 0.125 or 1/4 Watt up to 2 Watts.
Film Resistors
The generic term "Film Resistor" consist of Metal Film, Carbon Film and Metal Oxide Film resistor types, which are generally made by depositing pure metals, such as nickel, or an oxide film, such as tin-oxide, onto an insulating ceramic rod or substrate. The resistive value of the resistor is controlled by increasing the desired thickness of the film and then by laser cutting a spiral helix groove type pattern into this film. This has the effect of increasing the conductive or resistive path, a bit like taking a long length of straight wire and forming it into a coil.
This method of manufacture allows for much closer tolerance resistors (1% or less) as compared to the simpler carbon composition types. The tolerance of a resistor is the difference between the preferred value (i.e, 100 ohms) and its actual manufactured value i.e, 103.6 ohms, and is expressed as a percentage, for example 5%, 10% etc, and in our example the actual tolerance is 3.6%. Film type resistors also achieve a much higher maximum ohmic value compared to other types and values in excess of 10MΩ (10 Million Ω´s) are available.
This method of manufacture allows for much closer tolerance resistors (1% or less) as compared to the simpler carbon composition types. The tolerance of a resistor is the difference between the preferred value (i.e, 100 ohms) and its actual manufactured value i.e, 103.6 ohms, and is expressed as a percentage, for example 5%, 10% etc, and in our example the actual tolerance is 3.6%. Film type resistors also achieve a much higher maximum ohmic value compared to other types and values in excess of 10MΩ (10 Million Ω´s) are available.
Film Resistor
Metal Film Resistors have much better temperature stability than their carbon equivalents, lower noise and are generally better for high frequency or radio frequency applications. Metal Oxide Resistors have better high surge current capability with a much higher temperature rating than the equivalent metal film resistors.
Metal Film Resistors are prefixed with a "MFR" notation (eg MFR100kΩ) and a CF for Carbon Film types. Metal film resistors are available in E24 (±5% & ±2% tolerances), E96 (±1% tolerance) and E192 (±0.5%, ±0.25% & ±0.1% tolerances) packages with power ratings of 0.05 (1/20th) of a Watt up to 1/2 Watt. Generally speaking Film resistors are precision low power components
Wirewound Resistors
Wirewound Resistor is made by winding a thin metal alloy wire (Nichrome) or similar wire onto an insulating ceramic former in the form of a spiral helix similar to the Film Resistors. These types of resistors are generally only available in very low ohmic high precision values (from 0.01 to 100kΩ) due to the gauge of the wire and number of turns possible on the former making them ideal for use in measuring circuits and Whetstone bridge type applications.
resistors of the same ohmic value with power ratings in excess of 300 Watts. They are also able to handle much higher electrical currents than other
These high power resistors are moulded or pressed into an aluminum heat sink body with fins attached to increase their overall surface area to promote heat loss. These types of resistors are called "Chassis Mounted Resistors". They are designed to be physically mounted onto heatsinks or metal plates to further dissipate the generated heat increasing their current carrying capabilities even further.
Wirewound Resistor
Wirewound resistor types are prefixed with a "WH" or "W" notation (eg WH10Ω) and are available in the WH Aluminium Cladded package (±1%, ±2%, ±5% & ±10% tolerance) or the W Vitreous Enamelled package (±1%, ±2% & ±5% tolerance) with power ratings from 1W to 300W or more.
