The first alternative to a carbon composition resistor is a metal oxide film resistor. These resistors are very easy to manufacture as compared to metal film resistors. Firstly we have to know that metal oxide is one kind of metallic compound that is formed due to the chemical bonding among the oxygen atom as well as other elements. So it includes a minimum of two or above different kinds of atoms like a tin with oxygen. Thus, tin oxide is utilized for designing these resistors. These resistors are the most frequently used resistors because they have superior performance as compared to carbon film & carbon composition resistors. So this article discusses an overview of a metal oxide film resistor, it&#;s working, and its applications.
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What is Metal Oxide Film Resistor?
Metal oxide resistor definition is; the fixed value and axial resistors which are made with the ceramic rod that is covered with a metal oxide thin film like tin oxide are known as metal oxide film resistor. These resistors should not be confused with metal oxide varistors because they are made with silicon carbide or zinc oxide. These resistors are used mostly wherever power dissipation is necessary. The metal oxide resistor diagram is shown below.
Specifications
The performance guide of the metal oxide film resistor is given below.
- The available tolerance typically is ±1%, ±2%, ±5%, ±10%,
- Its resistance value ranges from 1Ω to 10MΩ.
- Maximum noise is 0.2 µV/V.
- The temperature coefficient is ±300 ppm/°C.
- The voltage coefficient is 0. %/V.
- The resistor temperature maximum is 300°C.
- It has outstanding long-time stability.
- It has overload or high surge capability.
- The standard resistance tolerance is ±5%.
Construction of Metal Oxide Film Resistor
The metal oxide film resistor construction is the same as the metal film resistor except for the material used to construct the film. This resistor uses tin oxide to construct the film which is made with tin oxide as well as antimony oxide which works as the resistive element for the electric current. Thus, this material restricts the current flow to a certain level.
The manufacturing procedure of a metal oxide film can be done with chemical deposition techniques & almost ceramic carriers are used as substrates always. The deposition procedure is obtained by the pure metals reaction with gas at low pressure & high temperature. The metal oxide film is most frequently produced with a chemical deposition process. Here tin oxide is the common metal oxide film that is created by heating the body of this resistor within a tin chloride steam.
Usually, other metal oxide film uses a different deposition procedure. Initially, a thin metal film is applied, after that it is reacted by oxygen. So the desired composition is attained by simply measuring the resistance.
The working of this resistor is; once the film is applied to the body of the resistor then the final value of resistance can be achieved by applying a helical cut. Usually, this can be done by laser cutting but earlier it was done by sandblasting or grinding. Here, the spiral cut on the resistor will make the resistance path longer & also increases the value of resistance up to a hundred times higher. The value of resistance can be controlled precisely by cutting. The resistance of his resistor mainly depends on the antimony oxide amount of added to the tin oxide; the helical metal oxide film cut width & the metal oxide film layer thickness.
Characteristics
The characteristics of a metal oxide film resistor are given below.
- These resistors give better performance as compared to other resistors like carbon film & metal film resistors like voltage rating, power rating, surge capacity, high-temperature operation & overload capabilities.
- So these resistors are preferred mainly for high-endurance applications.
- These resistors&#; stability properties are lower than metal film resistors.
- These have very poor properties for tolerance & low values.
- The temperature coefficient of metal oxide film resistors is higher as compared to metal film resistors like 300 ppm/0C.
- These resistors use tin oxide as a resistive material that is contaminated by antimony oxide to enhance resistivity.
- The antimony oxide amount added will determine the resistance level, the metal oxide film layer thickness & the helical metal oxide film cut width.
- These resistors can withstand high temperatures as compared to metal film or carbon resistors. The noise property of these resistors is the same of carbon resistors.
Metal Oxide Film Resistor Color Code
Generally, cylindrical resistors are color coded with bands/markings to identify the values of resistance & tolerance very quickly like metal film, carbon film, fuse, winding, metal film, and metal oxide film resistors. So the resistance value can be found based on the color code of the resistor. Resistors are available in four to six color bands on the resistors which specify the value of resistance.
Please refer to this link for: Resistor Color Code.
Please refer to this article for the Difference between Metal Oxide Resistor & Metal Film Resistor.
Advantages & Disadvantages
The advantages of a metal oxide film resistor are discussed below.
- The performance of this resistor is high compared to metal film & carbon film resistors.
- These resistors are used by many designers in high-endurance applications.
- These are not expensive as compared to carbon composition type resistors.
- They have superior high surge current capacity.
- These operate at higher temperatures.
- They have high stability & reliability.
- These are available in small sizes.
- They produce less noise.
The disadvantages of a metal oxide film resistor are discussed below.
- These are not appropriate for high-frequency-based applications.
- Nowadays these are not commonly used.
- Its installation is difficult.
Applications
The applications of a metal oxide film resistor are discussed below.
- These are the main types of resistors within basic circuits.
- These resistors are used where power dissipation is required above 1 W.
- These are used where high stability is necessary.
- These are used in medical equipment & telecommunication.
- These are used in power applications around several watts
Thus, this is an overview of a metal oxide film resistor &#; working, characteristics, advantages, disadvantages, and its applications. This is a fixed-type resistor that uses a resistive element like metal oxide film to restrict the electric current flow to a certain level. Here is a question for you, what is a carbon film resistor?
28 August
Metal film resistors are a kind of film resistors. Metal film resistors are resistors in which special metals or alloys are used as resistor materials, and the resistor film layer is basically formed on ceramic or glass by vacuum evaporation or sputtering.
Catalog
&#; Basic introduction
Metal film resistors are a kind of film resistors. Metal film resistors are resistors in which special metals or alloys are used as resistor materials, and the resistor film layer is basically formed on ceramic or glass by vacuum evaporation or sputtering. Because it is a lead type resistor, it is convenient for manual installation and maintenance and is used in most household appliances, communications, and instruments. Metal film resistors are widely used resistors so far, with high precision, stable performance, simple and lightweight structure. It plays an important role in the electronics industry and military aerospace under high-precision requirements.
&#; Thin film resistor
There are mainly four types of thin film resistors
1.Carbon film resistor
Metal film resistors are made by depositing crystalline carbon on the ceramic rod skeleton. Carbon film resistors are low in cost. It has stable performance, a wide resistance range, and low-temperature coefficient and voltage coefficient. It is currently the most widely used resistor.
2.Metal film resistor
Metal film resistor
Metal film resistors are the main type introduced today. The alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation. Metal film resistors have higher accuracy, better stability, noise and temperature coefficient calibration than carbon film resistors, and are widely used in instrumentation and communication equipment.
3.Metal oxide film resistor
The feature of a metal oxide film resistor is that a layer of metal oxide is deposited on the insulating rod. Since it is an oxide itself, it is stable at high temperatures, heat shock resistant, and has a strong load capacity.
4.Synthetic film resistor
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Synthetic film resistors are made by coating a conductive composite suspension on a substrate, so it is also called paint film resistance. Because its conductive layer presents a granular structure, it has high noise and low accuracy. It is mainly used to make high voltage, high resistance, and small resistors.
&#; Structure of metal film resistor
The production of metal film resistors is to deposit a nickel-chromium alloy on a round base rod to obtain excellent performance. The usual tolerance is ±1%, and tolerances of ±0.1%, ±0.2z5%, and ±0.5% can also be obtained. The temperature coefficient can be as low as ±15ppm/&#;. After cycling and aging, the change will not exceed 0.25%. The typical structure is shown in the figure.
Structure of metal film resistor
Metal film resistors are resistors in which special metals or alloys are used as resistance materials, and the resistance film layer is basically formed on ceramic or glass by vacuum evaporation or sputtering. This type of resistor is generally made by a vacuum evaporation process, that is, heating the alloy in a vacuum, the alloy is evaporated, and a conductive metal film is formed on the surface of the porcelain rod. Grooving and changing the thickness of the metal film can control the resistance. Its heat resistance, noise potential, temperature coefficient, voltage coefficient, and other electrical properties are better than carbon film resistors. The manufacturing process of metal film resistors is relatively flexible. Not only can its material composition and film thickness be adjusted, but also the resistance value can be adjusted through grooves, so that a resistor with good performance and a wide resistance range can be made.
Metal film resistors generally have cap structure, cylindrical structure, chip structure, and leadless structure, as shown in the figure
&#; Features of metal film resistor
&#;Good heat resistance, rated working temperature is 70&#;, maximum working temperature can reach 155&#;.
&#;Good voltage stability and small temperature coefficient.
&#;Wide working frequency range, low noise electromotive force, can be used in high-frequency circuits.
&#;Under the same power condition, it is much smaller than the carbon film resistor, about half of the carbon film resistor.
&#;It can adjust the precision resistance value by cutting butterfly and pattern method, and the accuracy can reach ±0.5%, ±0.05%.
&#;The resistance range is very wide, and can be made into 1Ω -MΩ resistors.
&#;The rated power is 0.125W, 0.25W, 0.5W, lW, 2W, lOW and 25W, etc.
&#;The pulse load stability is poor, not as good as carbon film resistors.
&#;The application is very wide, suitable for AC, DC, and pulse circuits.
&#; The difference between carbon film resistors and metal film resistors
For carbon film resistors, it uses carbon to be deposited on a magnetic rod or ceramic tube, and at the same time, a layer of the crystalline carbon film is formed on the surface. The thickness of the carbon film and the method of notching the carbon film are used to change the degree of the carbon film resistor and finally, get the required resistance value. The surface is coated with epoxy resin to strengthen the seal. The appearance color is basically khaki, of course, there are other colors, such as pink.
The color band is four bands, the resistance range is 1Ω~10MΩ, the rated power is 0.125W, 0.25W, 0.5W, 1W, etc., the accuracy range: ±10%, ±5%, ±2%. This kind of resistor is universal larger, often used in cheap products, such as power supplies, chargers. It is not recommended for starting resistance, because the impact resistance is relatively defective.
For metal film resistor, it uses vacuum evaporation or burning infiltration to form a metal film on the ceramic tube frame. This film is attached to the surface of the white ceramic. The resistor is cut and adjusted to obtain a more precise resistance. This kind of resistor has high precision, small size, good stability, and high cost. It is usually used in wireless electronic equipment, especially on occasions with higher precision requirements.
&#; Distinguish between carbon film resistors and metal film resistors
1. According to the temperature coefficient of resistor
We can distinguish the two types of resistors by carbon film resistors with negative temperature coefficient characteristics, and metal film resistors with small positive temperature coefficients, which can distinguish these two resistors well.
2. According to resistance accuracy
The manufacturing process of each type of resistor is different, and the accuracy of the resistor is also different. We know that carbon film resistors are very common resistors, and their accuracy is generally not high. The production requirements of metal film resistors are higher and the resistance accuracy is higher than that of carbon film resistors. It is also an identification method to judge the resistance accuracy.
4. According to resistor color
Common carbon film resistors have low precision and low production costs, so their appearance is mostly khaki or pink, while the appearance of metal film resistors is mostly blue. We can clearly distinguish the two resistors through color.
5. According to resistance painting
Carbon film resistors have a layer of black protective paint on the surface. We can distinguish by looking at the color of the protective paint. Metal film resistors usually use a bright white protective film. Through the protective painting of these two resistors, we can also distinguish the two well.
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