Flame detector

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A flame detector is a device which will detect the presence of a flame due to combustion. It detects the flame by optical sensing, ionization, or by heat detection means, and often form part of system of active fire protection used in fire alarm systems and in applications where the presence of a flame, such as a pilot light is necessary for operational safety.

Optical Flame Detectors[edit]

Flame detector type regions

Ultraviolet[edit]

Ultraviolet (UV) detectors work with wavelengths shorter than 300 nm. These detectors detect fires and explosions within 3–4 milliseconds due to the UV radiation emitted at the instance of ignition. False alarms can be triggered by UV sources such as lightning, arc welding, radiation, and sunlight. In order to reduce false alarm, a time delay of 2-3 seconds is often included in the UV flame detector designs.

Near IR Array[edit]

Near infrared (IR) array flame detectors, also known as visual flame detectors, employ flame recognition technology to confirm fire by analyzing near IR radiation via the pixel array of a charge-coupled device (CCD).

Infrared[edit]

Infrared (IR) flame detectors work within the infrared spectral band. Hot gases emit specific spectral patterns in the infrared region, which can be sensed using a specialized thermal imaging camera (TIC) for fire-fighting, a type of thermographic camera. False alarms can be caused by other hot surfaces and background thermal radiation in the area, as well as blinding from water and solar energy. A typical frequency in which a single frequency IR flame detector is sensitive lies within the 4.4 micrometer range. Typical response time is 3-5 seconds.

UV/IR[edit]

UV and IR flame detectors compare the threshold signal in two ranges in "AND" configuration and their ratio to each other to confirm the fire signal and minimize false alarms.

IR/IR flame detection[edit]

Dual IR (IR/IR) flame detectors compare the threshold signal in two infrared ranges. In this case one sensor looks at the 4.4 micrometer range. The other sensor looks at a reference frequency.

IR3 flame detection[edit]

Triple IR flame detectors compare three specific wavelength bands within the IR spectral region and their ratio to each other. In this case one sensor looks at the 4.4 micrometer range and the other sensors at reference bands above and below. This allows the detector to distinguish between non flame IR sources, and flames that emit hot CO2 in the combustion process (which have a spectral characteristic peak at 4.4 micrometer). As a result, both detection range and immunity to false alarms can be significantly increased. IR3 detectors can detect a 0.1m2 (1ft2) gasoline pan fire at up to 65m (215ft) in less than 5 seconds.

Most IR detectors are designed to ignore constant background IR radiation, which is present in all environments. Instead they measure the modulated part of the radiation. When exposed to modulated non flame IR radiation, IR and UV/IR detectors become more prone to false alarms, while IR3 detectors become somewhat less sensitive, and more immune to false alarms. Triple IR, like other IR detector types, is susceptible to blinding by a layer of water on the detector's window.

Visible sensors[edit]

In some detectors a sensor for visible radiation is added to the design in order to better discriminate against false alarms or to improve the detection range. Example: UV/IR/vis, IR/IR/vis, IR/IR/IR/vis flame detectors.

Video[edit]

Closed-circuit television or a web camera can be used for video detection (wavelength between 0.4 and 0.7 µm). Like humans, the camera can be blinded by smoke or fog.[1]

Other types[edit]

Ionization current flame detection[edit]

The intense ionization within the body of a flame can be measured by means of the current which will flow when a voltage is applied. This current can be used to verify flame presence and quality. They are normally used in large industrial process gas heaters and are connected to the flame control system and act as both the flame quality monitor and the "flame failure device".

Thermocouple flame detection[edit]

Thermocouples are used extensively for monitoring flame presence in combustion heating systems and gas cookers. They are commonly used as the "flame failure device" to cut off the supply of fuel if the flame fails. This prevents the danger of a large explosive mixture building up, or the hazard of asphyxiation in a confined space due to exclusion of oxygen.

Applications[edit]

UV/IR flame detectors are used on hydrogen stations.[2]

  • Gas fueled cookers
  • Industrial heating and drying systems
  • Domestic heating systems
  • Industrial gas turbines

See also[edit]


Noted Manufacturers[edit]

References[edit]

  1. ^ Töreyin, B. Ugur; Dedeoglu, Yigithan; Cetin, A. Enis (2005). Flame detection in video using hidden Markov models. "IEEE International Conference on Image Processing 2005". IEEE International Conference on Image Processing, 2005 (Piscataway, N.J.: Institute of Electrical and Electronics Engineers) 2: 1230–3. doi:10.1109/ICIP.2005.1530284. ISBN 0-7803-9134-9. 
  2. ^ Karner, Don; Francfort, James (December 2003). Arizona Public Service—Alternative Fuel (Hydrogen) Pilot Plant Design Report. U.S. Department of Energy FreedomCAR & Vehicle Technologies Program. pp. Appendix F (pdf).