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Understanding carbon firm resistor

Over the years, the carbon film resistors have taken over from the carbon composition resistor, due to their portability and ability to provide a much better performance level. These types of resistors can be compared with metal film and metal oxide film, and they are widely used in electronics. This is because they provide better performance in many respects than the carbon compositing resistor. However, the metal oxide film is adopted more because they give better levels of performance than carbon film. Today you’ll get to know the definition, applications, functions, symbols, components, diagram, characteristics, working, specifications, and construction of carbon film resistors. You’ll also get to know the advantages and disadvantages of a carbon film resistor.

carbon film resistors

Read more: Understanding carbon composition resistor

What is a carbon film resistor?

Carbon film resistors are types of fixed value resistors that are constructed out of a ceramic or former carrier with a thin pure carbon film around them. This thin carbon film functions as resistive material. A helical cut is normally made into the film to enable the carbon film to have the correct resistance. With this, the length of the path is increased and the width of the resistive element reduces. The resistance of these types of resistors is governed by the length of the path, the width of the resistive element, and also the thickness of the deposited carbon film.

When the resistive element forms a coil, these resistors have an inductance that may affect their operation in RF circuits. The value may reach several µH, although there are uncut resistors and their level of self-induction can be around 0.01 µH. the capacitance may be around 0.5pF.

Pure carbon is used here to ensure carbon film resistors have a negative temperature coefficient which is higher than that of carbon composition resistors. The value may range between -1×10-4 Ω/°C and -8×10-4 Ω/°C. other properties of these types of resistors include pure carbon, less noise, etc.

Read more: Understanding resistors

Applications

The applications of carbon film resistors are common in high voltage and high-temperature applications. They can operate at the voltage of up to 15 kV with a nominal temperature of 350 oC are feasible for carbon film resistors. With this property, some applications of carbon film resistors include radars, x-rays, and lasers. In other words, The applications of carbon film resistors include x-rays and lasers devices, also radar and welding technology makes use of these resistors.

Symbol

Components of a carbon film resistor

components of carbon film resistors

Diagram:

diagram of carbon film resistors

Read more: Understanding ultracapacitors

Construction of a carbon film resistor

The construction of carbon film resistors is achieved through a deposition process. A ceramic rod or carrier is placed in a high temperature and pressure environment. Also, hydrocarbon gas, typically methane or benzene is passed over the rods at a temperature of around 10000C. With this level of temperature, the hydrocarbon gas breaks down and a thin carbon film is deposited onto the rods.

After the rods have been obtained, end caps are placed onto the rods to connect to the carbon film, and the resistance value may be trimmed by making a helical cut in the carbon. Once complete, the resistors are coated in a resin to protect the resistive element from handling, moisture, and other contaminants.

Read more: Understanding capacitor

Watch the video below to learn the working of carbon film resistors:

Specifications

The table below shows the typical performance figures for carbon film resistors as a guide to the performance.

CARBON FILM RESISTOR PERFORMANCE GUIDE
CARBON FILM RESISTOR PARAMETER CARBON FILM RESISTOR PERFORMANCE
Typical tolerance availability ±2%, ±5%, ±10%, ±20%
Value range <1Ω – ~10MΩ
Load life (% change over 1000h) 2
Max noise (µV/V) 20.
Temperature coefficient (ppm/°C) ±200 – >±1500
Voltage coefficient (%/V) 0.0005
Max resistor temperature (°C) 150

 

Advantages and disadvantages of a carbon film resistor

Advantages:

The benefits of carbon film resistors include:

  • Lower noise
  • Lower tolerance
  • Cost is low
  • Very tiny – large amount can be transport
  • It is widely use
  • Wide operating range

Disadvantages:

Despite the good advantages of these types of resistors, some limitations still occur. Below are the disadvantages of carbons film resistors:

  • High negative temperature coefficient of resistance
  • The metal film and metal oxide film are better options
  • Have lower capacity compared to the resistance of the same range
  • Installation requires a highly skilled person.

That is all for this article where the definition, applications, functions, symbols, components, diagram, characteristics, working, specifications, and construction of carbon film resistors are being discussed. I hope you get a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!

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