Carbon vs Metal Film Resistors: Differences

Carbon Film Resistor VS Metal Film: Definition

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A carbon film resistor is a type of resistor that slows the flow of electricity by using a thin layer of carbon. Unfortunately, carbon film resistors are more expensive to make than other types of thin film resistors. They also generate a lot of thermal noise and can portray low accuracy. 

(carbon film resistor)

Despite its challenges, it can withstand high-energy pulses and thus are suitable for applications like surge protection electronic circuits, computers, test equipment, DC power supplies, and high-frequency applications. 

A metal film resistor limits the flow of electricity by using a thin metal film. It is also the most popular type of thin film resistor. Moreover, metal resistors are cost-effective, compact, have low tolerance, generate less noise, and operate widely compared to carbon resistors. 

(metal film resistors)

Therefore, you&#;ll find them in bridge circuits, active filters, and high-frequency applications. 

Carbon Film Resistor vs Metal Film Resistor: Side-by-Side Comparison

Now that we&#;ve defined these resistor types individually, let&#;s look at a head-to-head comparison of them both. This will make it easier to know which use cases would suit each resistor type best. The properties this section will focus on are the voltage coefficient of resistance, stability, and temperature coefficient of resistance.

Temperature Coefficient of Resistance (TCR)

Similar to how the amount of voltage applied to a resistor can affect its resistance, changes in temperature have an effect, too.

Of course, this phenomenon isn&#;t exclusive to resistors. All conductors have resistance of some sort which increases in high temperatures and decreases in low temperatures.

We express this value as parts per million per degree Centigrade (ppm/°C) or Kelvin (ppm/K). As with the previous property the resistance value of metal film resistors is less susceptible to change in temperature than carbon film resistors.

Metal film resistors have a TCR between  ± 20 and ± 200 ppm/k. On the other hand, carbon film resistors have a TCR between -200 to - ppm/k.

As such, the carbon film resistor TCR is substantially greater than the metal film resistors. This makes metal film resistors more reliable under extreme temperatures (both hot and cold).   

Moreover, metal film resistors produce less thermal noise. This makes them ideal for devices such as radios, intercoms and radars. 

Carbon Film Resistor Green Color

Voltage Coefficient of Resistance (VCR)

Applying voltage to a resistor may cause changes in its resistance value. Usually, applying voltage to a resistor causes the resistance to drop in near proportionality.

Regardless of decrease or increase, we represent the change in resistance against each applied volt (per volt).

This measurement is known as the Voltage Coefficient of Resistance (VCR) and is represented by the metric: parts per million per volt (ppm/V).

The VCR is important because it helps us predict and determine how well a resistor performs in high-voltage situations. While carbon film resistors perform well in high-voltage applications, their metal film counterparts perform even better. Metal film resistors have a VCR of just under 1 ppm/V, whereas carbon film resistors have a -10 ppm/V. This means metal film resistors are less susceptible to changes in resistance caused by applied voltage.

Stability

Since resistors are a part of machinery and electronics operating in various environments, we must know how they are fair against external stressors. These stressors can (potentially) affect the resistance value of the resistor. We refer to a resistor&#;s tolerance to environmental stressors over time as stability.

Some of the most common stressors are exposure to radiation, heat (high temperatures), and cold (low temperatures). Sudden or prolonged power spikes can also be categorized as stressors that can challenge the stability of the resistor.

Nevertheless, stability is another area in which metal-film resistors outperform carbon-film resistors. This is not to say that carbon-film resistors are unstable. They have moderate stability. On the other hand, metal film resistors exhibit good to exceptional stability.

Carbon Film Resistor VS Metal Film: Construction

The two resistor types have different processes.

Carbon film resistor construction

Manufacturers make carbon composition resistors from a solid, cylinder-shaped resistive element with wire leads and metal caps on the ends. Further on, the materials in the resistive element are a mixture of clay-based ceramic and graphite or carbon powder. Generally, the carbon powder lets electricity flow through it well.

(Internal part of a carbon film resistor) 

So, during the deposition process, manufacturers start by heating the ceramic substrate in a hydrocarbon like methane. Next, at high temperatures of approximately °C, cracking reactions will occur in the gas. The pure graphite&#;s crystalline carbon then sticks to the ceramic. 

Afterward, the resistive material gets a plastic covering to keep it safe from the heat generated from outside. Manufacturers finally apply copper to make the wire leads at both ends of the resistive element. 

Metal film resistor construction

Contrarily, manufacturers use a special method for metal film resistors, where they artificially age the deposited metal in low temperatures for an extended time. 

Here, the material employed as the resistance material is Nickel chromium (NiCr). However, in other applications, you&#;ll find other materials like tantalum nitride, gold with platinum, and tin plus antimony.

Then, the resistor&#;s stability and resistance often depend on the metal film thickness. Thus, a larger thickness will mean a lower resistance value and greater stability on both films ends. 

Manufacturers use connection leads to press a metal cover for the final touches. They can now achieve the desired resistance via a spiral-shaped slot cut in the thin metal thickness.

Carbon Film Resistor VS Metal Film: Availability

Carbon Film Resistor

You&#;ll find carbon resistors in 1 ohm to 25megaohms with a power rating ranging between one-quarter watt and five watts. 

The three factors affecting the resistance of carbon film resistors are;

• The solid cylindrical rod&#;s cross-sectional area is inversely proportional to the resistance of the resistor.
• Then, we have the rod&#;s length directly proportional to the resistance.
• Lastly, the amount of carbon you add to the resistor is inversely proportional to the resistor&#;s resistance.

Metal Film

Usually, the available metal film resistors in the market have tolerances of 2%, 1%, 0.5%, 0.25%, and 0.1%. Additionally, the resistors are likely to have temperature coefficients ranging from 10 to 100 ppm/K and some resistance. 

The two main factors affecting the resistance of metal film resistors include:

• The width of the spiral metal film cut is inversely proportional to the metal film resistor resistance.
• Secondly, the layer of the metal film is also inversely proportional to the resistance. 

Carbon Film Resistor VS Metal Film: Similarities and Differences

• Similarities

The film resistors are similar in the following ways;

• First, you can regulate both by controlling their thin film thickness.
• Then, their non-conducting material is ceramic.
• They also have the same size.
• Lastly, their shape and appearance are similar. 

(Film resistors in a circuit board)

• Differences

We have summarized the differences between the metal film and carbon film resistors in the table below.

Carbon Film Resistor VS Metal Film: Drawbacks

Both these resistor types have advantages. While metal film resistors have the best frequency response of all resistors, carbon film resistors are more affordable and have high resistance. However, both these resistor types have drawbacks and limitations.

For instance, as we previously discussed, one of the biggest disadvantages of using carbon film resistors is their high-temperature coefficient of resistance. In addition to this drawback, they also have comparatively subpar stability, especially when compared against wire-wound and metal-film resistors.

Another somewhat cumbersome feature of carbon-film resistors is their bulkiness.

As a consequence of their larger size, they can be a little difficult to maneuver and place, especially by hand. Contrastingly, metal-film resistors are compact, which makes them ideal for smaller electronics.    

While, in many ways, metal-film resistors may be superior to carbon-film and carbon-composite resistors, they aren&#;t without their own drawbacks.

For one, they&#;re generally more pricier than carbon film resistors. Moreover, they have higher power dissipation.

Some may see this as an advantage, but it&#;s an attribute that makes them unsuitable for use cases that require low-power dissipation resistors.

Metal Film Resistor On Green Blur

Conclusion

Both carbon film and metal film resistors limit current flow through circuits. However, carbon film resistors use carbon, while metal film resistors use metal to reduce current flow.

For more information on the resistors, kindly reach out to us. 

What is the difference between metal film and metal oxide resistors?

The difference between metal film and metal oxide resistor include the following.

Metal Film Resistor

Metal Oxide Resistor Metal films are the most common type of resistor. Metal oxide resistors are also popular and often used for high-power applications. Metal films typically have a smaller tolerance. Metal films typically have a higher tolerance but they handle higher power ratings. These are cylindrical axial resistors. These are axial & fixed value resistors. These resistors are applicable where a more precise value and high tolerance value are necessary within a circuit. These resistors are used for high endurance applications. The frequency response of these resistors is about 100 MHz. The frequency response of metal oxide resistors is about 100 MHz. These resistors have good characteristics for stability, TCR & tolerance. In addition, these resistors feature high linearity & low noise properties due to a low voltage coefficient. These resistors will exceed both the resistor&#;s performance like carbon film & metal film for different properties like voltage rating, power rating, surge capacity, high-temperature operation & overload capabilities. The maximum temperature of the metal film resistor operates up to 150°C & with platinum sensors, they work up to 600°C. The temperature coefficient of the metal oxide resistor is approximately 300 ppm/°C.

Advantages

Metal Film Resistors have the following advantages:

High Precision: Film thickness is easy to control, the manufacturing process is mature, with stable performance.

Low Noise: The temperature coefficient of resistance is small, it is not easy to produce a microphonic effect.

High Stability: High purity ceramic core, film-coated on the surface, no oxygen in the air will not oxidize the surface of the resistor, it has good anti-vibration and anti-shock performance.

High Power Rating: Metal film resistors also have a high power-rating, which means they can be used in high-power applications. They tend to have a lower temperature coefficient than carbon film resistors, which makes them ideal for use in precision circuits where a low-temperature coefficient is essential.

Disadvantages

The disadvantages of metal film resistors include the following.

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Metal film resistors are more expensive than carbon composition and carbon film resistors because there&#;s a higher cost to precision.

Metal film resistors have a limited power rating of 3 watts or less. If you require more power, you&#;ll need to use a wire wound resistor instead.

They are sensitive to temperature changes, both within their environment and in the current they conduct.

They need to be regularly maintained, cleaned, and checked to make sure they work correctly.

The resistor will fail before it reaches its maximum power rating if there is a sudden surge in current or voltage.

The metal film will erode over time due to high temperatures caused by prolonged use at higher power levels than those specified on the resistor itself

Metal film resistors can only operate up until temperatures around 200°C (392°F).

They are not suitable for use in high-frequency circuits because their parasitic capacitance limits them from being able to handle frequencies above about 100 MHz (Megahertz).

Where are Metal Film Resistors Used/ Applications?

The applications of metal film resistors include the following.

Metal-film resistors are used in almost every circuit where resistance is required, including power supplies and other circuits.

They are also used to protect sensitive electronic components from dangerous voltages.

Metal-film resistors have been around for a long time, but only in recent years has their popularity begun to increase. The reason for this is because they are less expensive than other types of resistors and they are very reliable. This means that they can be used in a wide variety of applications including automotive electronics and computer circuitry.

Its resistance to currents makes it useful in a variety of situations, from industrial equipment to consumer electronics.

These resistors are used in different types of equipment in different fields like Industrial, military Automotive, Professional audio & video.

Industrial Applications: Metal film resistors are commonly used in industrial equipment. They help regulate the flow of current and prevent damage by overheating. Metal film resistors are also frequently employed in appliances, as they help to protect motors and other components of the machines.

Consumer Electronics Applications: Metal film resistors are used in a wide range of consumer electronics, including cell phones, laptops, and televisions. They help regulate the current flow in these devices and prevent them from overheating when they are used for extended periods at high power levels.

What is the Difference Between Metal Film Resistor and Other Types of Resistors?

Metal film resistors are more precise than carbon composition or wire-wound resistors, but they are not as precise as thin-film resistors. There is a wider tolerance range for metal film resistors than most other types of resistors, but the tolerance can be adjusted by adjusting the process used to make them.

What should I know before selecting a metal film resistor?

There are many factors to consider when choosing a metal film resistor. Here are some considerations:

How much power will the resistor dissipate?

Is there an issue with temperature rise?

How accurately does the value need to be?

Does it need to work at high frequencies?

Is moisture resistance required?

How Much Power Can I Use With a Metal Film Resistor?

The amount of power that can be used with a metal film resistor depends on the size of the resistor and its temperature rating. A smaller resistor will have a lower power rating than a larger resistor because it will have less surface area over which to dissipate heat. As temperatures rise, power ratings drop because it becomes harder for heat to dissipate through the air or other means.

Thus, if you&#;re looking for a way to add resistance to your circuit without spending a lot of money, metal-film resistors may be just what you&#;re looking for. They are very durable and dependable, which means that you can use them for years without having to replace them or fix them often. Even though metal film resistors aren&#;t cheap, they do make up for their cost by being able to stand up to harsh conditions and still perform well. Here is a question for you, what is a metal oxide resistor?

Metal Film Resistor : Construction, Working & Its Applications

Metal film resistor is the most common type of resistor used in electronics. They have been widely used since their development in the s, and are very popular for their consistency and accuracy. This is a type of resistor that has a metal oxide film deposited on the surface of a ceramic core. This is different from carbon film resistors, which have a layer of carbon instead of metal.

Metal film resistors have better performance than carbon or wire wound resistors. They are also more dependable and reliable than other types of electronics parts. For these reasons, metal film resistor is often used as replacements for other types of electronic components.

Metal Film Resistor Definition:

A metal film resistor is a passive two-terminal electrical component. It is designed to provide a specific resistance. The metal film resistor is constructed by depositing an insulating layer of oxide or nitride, which is then covered with a resistive metal film and terminated with a second insulating layer, usually oxide. These components are used in active filters, precision circuits, and timing applications.

The metal film resistor symbol is similar to a normal resistor which includes two connecting terminals like anode and cathode shown below.

Metal Film Resistor Construction

Metal Film Resistors are made of a metal film on an insulating substrate, similar to a thin-film resistor. The metal is deposited by evaporation onto the substrate. The metal film is typically 0.1 µm or thicker and has a much higher resistance than the substrate.

The resistors are formed by screen printing carbon paste onto the substrate in a shape that cross-sections the metal film, creating two parallel conductors with a uniform gap between them. The resistor body is coated with an epoxy coating for environmental protection and insulation.

Metal film resistors are manufactured using a photolithography process that creates high-accuracy and low-tolerance resistors. Photolithography is a photographic process that transfers images to semiconductor wafers during integrated circuit development. Metal film resistors have resistance values ranging from 0.1 ohms to 100 MΩ, with tolerances of ±0.1% or less at operating temperature ranges from -55°C to 155°C.

Working

The working of a metal film resistor is similar to the normal resistor to restrict the flow of electric current through it. So, it functions as the resistive element for the flow of electric current. The ceramic substrate of this resistor does not let heat throughout it.

Specifications

The specifications of the metal film resistor include the following.

The availability of typical tolerance is ±0.1%, ±0.25%, ±0.5%, ±1% & ±2%,

Resistance value ranges from >1Ω < 10MΩ

Max resistor temperature is175 °C

Load life (% change over h) is 1

Voltage coefficient is 0.0 %/V

Max noise is 0.2 µV/V

Temperature coefficient ±50 to ±100 ppm/°C

Metal Film Resistor Tolerance

Metal Film Resistor tolerance is the highest level of deviation from the nominal value of a resistor. This tolerance represents an accuracy standard for resistors, and it determines how much the measured resistance will vary from the ideal resistance. The tighter the tolerance, the more accurate your measurement will be.

The tolerance of a metal film resistor is the amount the resistance of the resistor can vary from its nominal value. This is usually expressed as a percentage, and can be calculated using the formula:

(Measured Value &#; Nominal Value)/Nominal Value)×100

If you measure 10kΩ and it has a 5% tolerance, then you know that tolerance is 500Ω. The highest possible value would be 10.5kΩ and the lowest possible value would be 9.5kΩ.

Metal Film Resistor Power Rating

The maximum power a resistor can handle is known as the power rating for that resistor.

The power rating is determined by how much heat the resistor can take before it fails. Heat causes the resistance in the resistor to rise, which causes it to dissipate more power, which causes it to get hotter, and so on. If this process runs away, the resistor&#;s temperature rises quickly and it fails catastrophically.
The maximum power (Pm ) a Metal Film Resistor can handle is calculated by dividing the maximum working voltage (Um ) by the resistance value (R):

Pm = Um/R

Metal Film Resistor Size Calculation

The size of a metal film resistor can be calculated from its power rating.

After the power rating (power = voltage x current) and the maximum possible temperature rise are known, the resistor size can be calculated by adding the thermal resistance RTH of the resistor to the thermal resistance RθJA of the mounting surface.

Rth = (TJ &#; TA)/Pd

Here, Rth is thermal resistance

&#;Tj&#; is Junction temperature

&#;TA&#; is ambient temperature

&#;Pd&#; is power dissipation

Size limitation is given by:

RTHmax = (TJmax &#; TA)/Pd

Resistor size = Rthmax + RθJA

Metal Film Resistor Color Code

The color code for metal film resistors consists of three bands and a fourth band indicating tolerance.
The first two bands indicate the first two digits of the value.

The third band indicates the number of zeros following those first digits. For example, if the third band is red, there are two zeros following the first two digits. If it is gold, there are five zeros following those first two digits.

The fourth band indicates tolerance in percent. A brown or red band represents a 1% tolerance, while a gold or silver band represents a 10% tolerance.

If additional bands are present, they typically indicate temperature coefficient, but this varies based on the manufacturer and part number.

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