What is Flame Sensor ? | Principle | 4 Important Types | Application


What is a flame sensor?

A flame sensor, as the name suggests, is used for detecting and responding to the presence of a fire or flame.

The flame sensor usually responds in the form of sound alarms, fuel line deactivations (such as a natural gas  line or a propane line), and activation of different types of fire suppression systems.

Flame sensors are commonly used to check whether the furnaces are working properly. These sensors are also employed in an ignition system to take accurate actions or to notify the operator.

Flame sensors or flame detectors are comparatively more accurate and swifter than smoke or heat sensors.

flame sensor
A flame igniter and a rectifying flame sensor. Image source: AlexBwineglass – Own work
CC BY-SA 4.0


What is the working principle of a flame sensor?

  • Flame sensors are constructed with an electronic circuit that receives electromagnetic radiations.
  • The sensor comprises of an isolated metal rod that directs an alternating current signal into the flame.
  • The flame receives this alternating current and injects its direct current part to the burner.
  • The burner is then responsible for conducting the received dc signal first to the burner rack and then to the control by using aground wire.
  • The control then detects the current loop and locks on the gas valve in order to continue the run. This returns in the form of a small amperage/voltage signal that has high chances of signal degradation.
  • The flame detector follows the infrared flame flash method that makes it capable of working through a coating of dust, oil, water vapor, and at times ice.

What are the types of flame sensors?

The Types of Flame sensors :

  1. Ultraviolet sensors
  2. Infrared sensors
  3. Visible sensors
  4. IR3 Flame detector

Ultraviolet sensors:

Ultraviolet (UV) sensors detect the emitted UV radiation during the time of ignition. UV flame sensors can detect fires and explosions within 3–4 milliseconds. However, it is considered better to include a time delay of about 2–3 seconds for minimizing false alarms that can occur due to the radiations generated by other UV sources such as lightning, radiation, arc welding, and sunlight. UV detectors generally work better with wavelengths that are shorter than 300nm for reducing the effects of natural background radiation. Oily contaminants can easily blind the solar-blind UV wavelength band.

Infrared sensors:

Infrared (IR) or wideband infrared (more than 1.1 μm) flame detectors sense and analyze the infrared spectral band for finding certain predefined patterns given off by hot gases. These patterns are sensed or detected by using thermographic cameras or thermal imaging cameras. Near-Infrared flame sensors work with flame recognition technology to detect the near-IR radiations by using a CCD or a Charge-coupled device. Water vapor significantly affects the infrared radiation sensors because water absorbs a major portion of the received IR radiation. For this reason, infrared sensors are not capable of providing accurate results in an outdoor environment.

Thermal image of a flame.
Image source: Hugues CREPINAllumette img ptCC BY-SA 3.0

Visible sensors:

Visible flame or radiation sensors are used for providing an output image of radiation patterns that can be understood by humans. These types of sensors are often disturbed by smoke and fog. Visible sensors are often combined with UV sensors or IR sensors collecting information, improving detection output, and sensing false alarms. The corona camera is an example of a combination of UV and visible sensors. These sensors are especially capable of detecting flames over long distances.

IR3 Flame detector:

IR3 flame detectors can compare the radiation patterns between three different IR spectral bands and the ratio of the radiation bands with respect to each other. Generally, such sensors are programmed to detect one radiation band belonging to the 4.4 micrometer range and the other two bands belonging to the range above and below the 4.4 micrometer spectrum. By this, the detector is able to separate the actual flames and the non-flame radiations that affect the results. These detectors are therefore able to provide better flame detection results by ignoring the background radiations.

Apart from the UV, IR, visible and IR3 flame detectors, several other detectors are also found; like 3IR+UV flame detectors, IR/IR flame detectors, UV/IR flame detectors, and Infrared thermal cameras.

What is the detection range of a flame sensor?

The range of detection of a flame sensor depends on where it is mounted, the accessibility of the detector, and the surrounding atmosphere of the detector. The range of flame detection is shown in the image below.

The flame detector is placed at a height that is twice of the object. The depression angle is fixed at 45 degrees for maximum range coverage,. Image source: Jan.NijkampFlame detection rangeCC BY-SA 3.0

What are the applications of a flame sensor?

Applications of flame sensor :

  • Industrial gas turbines.
  • Hydrogen stations.
  • Fire detection devices.
  • Fire alarms.
  • Domestic and industrial heating systems.
  • Fire fighting robots.
  • Industrial furnaces.
  • Drying systems.
  • Gas-powered cooking devices.
  • Radiation research labs.
  • Mines.
  • Ignition systems.

To know more about sensors visit https://lambdageeks.com/photocell-sensors/

About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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