Maya Ellison
Resistors are made from a variety of materials, including metal and plastic. The type of material used depends on the specific application and requirements, such as tolerance, voltage coefficient, temperature coefficient, stability, and cost. Metal film resistors, for example, are made by placing a layer of metal such as ruthenium or nichrome onto an insulating substrate. They offer high precision, low TCRs, and better temperature coefficients than carbon film resistors. Carbon composition resistors, on the other hand, consist of a mixture of powdered carbon and an insulating material, typically ceramic, and are known for their reliability but poor accuracy. Plastic may be used as a protective coating for the resistor body, as seen in wirewound resistors, which have a plastic or fiberglass core.
| Characteristics | Values |
|---|---|
| Type | Carbon composition, carbon film, metal film, wirewound, foil, thick film, thin film |
| Composition | Metal, carbon, ceramic, fiberglass, plastic, nickel-chromium alloy, vitreous enamel, tantalum nitride, ruthenium oxide, tin oxide, silver-palladium alloy |
| Manufacturing Process | Sputtering, printing, laser trimming, injection moulding, stamping, soldering |
| Properties | High precision, low TCR, low ESR, low noise, high stability, high endurance, temperature stable, high power, low inductance, high-frequency applications, high voltage |
| Applications | Electrical engineering, power supplies, welding controls, audio devices, voltage dividers, load banking, power devices, electronic circuits, computer networks, telecommunications equipment |
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What You'll Learn
Metal film resistors are more common than carbon film resistors
Metal film resistors are more widely used than carbon film resistors due to their superior performance characteristics. Metal film resistors are made by depositing a thin metal film onto a cylindrical or flat insulating substrate, typically ceramic or glass. This process results in a more compact design compared to carbon film resistors.
Metal film resistors offer several advantages over carbon film alternatives. Firstly, they exhibit less thermal noise, making them ideal for devices such as radios, intercoms, and radars. This reduced noise is a result of their lower temperature coefficient of resistance, which also contributes to their reliability under extreme temperatures. Metal film resistors also demonstrate better stability, voltage coefficient, and tolerance than carbon film resistors. These factors make metal film resistors more consistent in performance, with less variation in sound from amp to amp.
In terms of cost, metal film resistors can be more expensive than carbon film options. However, metal film resistors are still cost-effective, especially when considering their improved performance characteristics. Additionally, metal film resistors have higher power dissipation, which can be advantageous or disadvantageous depending on the specific application.
While carbon film resistors have their advantages, such as performing well in high-voltage applications and withstanding high-energy pulses, the overall superiority of metal film resistors in terms of stability, noise characteristics, and tolerance has led to their increased usage.
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Carbon composition resistors are reliable but inaccurate
Carbon composition resistors (CCR) are made from conductive carbon particles mixed with a binder, such as clay or ceramic. They are remarkably reliable, with the ability to withstand high energy pulses. This makes them useful for certain applications, such as power supplies, welding controls, and medical defibrillators.
However, CCRs have poor accuracy, with a maximum tolerance of around 5%. This is due to the inherent design of the resistor, which contains materials with different heat expansion properties. When the conducting carbon particles and the non-conducting binder heat up or cool down, stresses arise in the resistor body, leading to a change in resistance value. The resistance value can change up to 5% over a shelf life of one year, and even more with heavy use.
The noise properties of CCRs are also poor due to the mixture of different materials. The noise level increases when the current flows. Additionally, CCRs have a high temperature coefficient of around 1200 ppm/°C and a poor insulation resistance of 109 Ω.
While CCRs were once the standard for general applications, they have lost market share to other resistor types that offer better properties in terms of tolerance, voltage coefficient, temperature coefficient, stability, and cost. CCRs are becoming scarcer, and design engineers are encouraged to explore alternative options.
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Metal oxide film resistors have a higher operating temperature
Resistors are made from a wide variety of materials and manufacturing processes. Each type of resistor has its own unique properties and specific areas of use. Metal oxide film resistors are made of metal oxides, which result in a higher operating temperature and greater stability and reliability than metal film.
Metal oxide film resistors were the first alternatives to carbon composition resistors. They are produced using chemical deposition methods, with a ceramic carrier as the substrate. The deposition process involves the reaction of a pure metal with a gas at high temperatures and low pressure. Tin oxide is a very common metal oxide film, and the film is established by heating the resistor body in a tin chloride vapor. Metal oxide film resistors have a temperature range of -55°C to 175°C, making them suitable for a wide range of environmental conditions.
The ceramic substrate of the metal oxide film resistor provides thermal stability, allowing the resistor to maintain its performance even in extreme temperatures. This broad temperature range makes them ideal for aerospace, automotive, and industrial applications where temperature fluctuations are common. Metal oxide film resistors are also known for their low noise and low inductance characteristics, which are crucial in applications where signal integrity is essential.
Metal film resistors, on the other hand, are usually made of Nichrome, a combination of ceramic material and metal. They possess very good noise characteristics and low non-linearity, with excellent parameters such as tolerance, temperature coefficient, and stability. However, when metal film resistors are loaded with higher power, the temperature increases, which decreases stability. Thus, metal film resistors often have a lower tolerance than metal oxide film resistors.
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Metal resistors are used for specialist applications
Metal film resistors are made of Nichrome, a combination of ceramic material and metal, or other materials such as tantalum nitride. The resistance value is adjusted by cutting a spiral pattern in the film. Metal film resistors have excellent parameters such as tolerance, temperature coefficient, and stability. They are available as leaded kinds for through-hole mounting and as MELF-style SMD devices.
Metal-oxide film resistors are made of metal oxides, which result in a higher operating temperature and greater stability and reliability than metal film. They are used in applications with high endurance demands.
Foil resistors, invented in the 1960s, are used for applications with high precision requirements. They are made of a thin bulk metal foil that is cemented onto a ceramic substrate.
In heavy-duty industrial high-current applications, a grid resistor is a large convection-cooled lattice of stamped metal alloy strips connected in rows between two electrodes. They are used in applications such as dynamic braking and load banking for locomotives and trams, neutral grounding for industrial AC distribution, and control loads for cranes and heavy equipment.
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Metal resistors are more stable and accurate
Metal resistors offer greater stability and accuracy than plastic resistors. Metal film resistors are made by depositing a thin film of metal or metal oxide over a ceramic core. The resistance is controlled by cutting a helical path into the deposited metal. The performance of metal film resistors is determined by the quality of the materials and processes used in their manufacture.
Metal film resistors possess very good noise characteristics and low non-linearity. Parameters such as tolerance, temperature coefficient, and stability are excellent. Metal film resistors are available as leaded kinds for through-hole mounting and as MELF-style SMD devices. They are also beneficial due to their long-term stability.
Metal-oxide film resistors are made of metal oxides, which results in a higher operating temperature and greater stability and reliability than metal film. They are used in applications with high endurance demands. Metal oxide film resistors have overall better properties than carbon film, and have therefore gained more popularity.
Foil resistors are another type of metal resistor and are the most accurate and stable type of resistor today. They are made by gluing a thin metal foil to a ceramic substrate. They feature a very low temperature coefficient of resistance and are used for applications with high precision requirements.
Wirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. They are often produced for high precision or high power applications. They have low noise, are robust, and are temperature stable.
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Frequently asked questions
Metal film resistors are made by placing a layer of metals such as ruthenium or nichrome onto an insulating substrate. They are available in a large number of types and packages and are smaller and simpler to mass-produce than carbon film resistors. Metal film resistors have replaced carbon film resistors in most standard applications due to their lower noise, tighter tolerances, and better temperature coefficients.
Metal film resistors include wirewound resistors, foil resistors, and cermet resistors. Wirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. Foil resistors are made by gluing a thin bulk metal foil to a ceramic substrate and are the most precise and stable type of resistor. Cermet resistors are made from a combination of ceramic and metal materials.
Plastic is used in the construction of some resistors, such as carbon composition resistors, to protect the resistive element. The body of the resistor is coated in paint or plastic.
Yes, resistors are produced with a wide variety of materials and manufacturing processes. Other materials used in resistors include carbon, fiberglass, glass, and metal oxides such as ruthenium oxide and tin oxide.
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