Metal Film vs Carbon Resistors
Resistors are commonplace components in a wide range of electronics, serving to implement electrical resistance as a means of managing current flow, adjusting signal levels, terminating transmission lines, and much more. Film type resistors in particular are those that are manufactured through the deposition of pure metals or oxide film onto an insulating ceramic or substrate, and carbon film and metal film resistors are two primary variations. While belonging to the same general category of resistors, each type differs in its construction and capabilities, allowing them to benefit different applications. In this blog, we will provide a brief overview of both resistor types, allowing you to have a better understanding of their advantages, applications, and more.
Carbon film resistors can be considered to be the most commonly used type, featuring low wattage and fixed operations. Fixed resistors are generally components that feature an unchanging resistance value that is determined by their materials and makeup. For the carbon resistor, a solid ceramic core is covered with carbon film that is electrically resistant in its properties. By making a helix cut on the carbon film resistor, a narrow resistive path can be created along the length of the component. While the resistive material of the resistor is made up of a carbon clay composition, the leads are all produced from tinned carbon. Generally, the thin carbon film is added to the ceramic rod during the production stage, and the resistive coating is spiraled away so that the resistance between each end of the rod is as accurate as possible.
Due to having safety features such as heat radiation and fire retardation, carbon film resistors are commonly used for low-power applications as a result of their safety benefits. Despite this, they are known to be somewhat noisy during standard operations, thus they can be detrimental for some applications. For their characteristics, such film type resistors may be procured with values ranging between +5% to +10% of their nominal value.
The metal film resistor, on the other hand, is a type that is often manufactured by coating small rods of ceramic with nickel alloy or another metal type. The film will typically be homogeneous in nature, and it may be deposited over glass, ceramic, or another form of insulating material core. As compared to carbon film resistors, metal film resistors exhibit more optimal temperature characteristics, current-noise suppression, accuracy, and linearity. Despite these advantages, metal film resistor components are typically more expensive.
To control the overall resistance value of the metal film resistor, one may adjust the thickness of the coating layer. Additionally, a fine spiral groove cut can be made along the core, allowing for the coating to be cut into a long spiral strip. This is done with the use of a laser or diamond cutter, and establishing such strips will determine the resistance value. For their applications, metal film resistors commonly find use in assemblies where high tolerance or high accuracy values are required. As such, they are often implemented within filter circuits, bridge circuits, and low-noise analog signal circuits.
Metal oxide film resistors are another form of metal film resistor, differing in the fact that they feature a stable ceramic core that is coated with tin oxide or another metal oxide type. As a result, they surpass their counterparts with higher stability and reliability. Coupled with a small design and low annual shifts, such resistors may benefit applications that have high endurance demands. Additionally, metal oxide film resistors also provide high stability in diverse environments, ample safety, high ohmic values, a flame retardant coating, and more. Despite this, they are known for radiating heat when they are mounted.
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