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Flame detector
A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line (such as a propane or a natural gas line), and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.
Ultraviolet (UV) detectors work by detecting the UV radiation emitted at the instant of ignition. While capable of detecting fires and explosions within 3–4 milliseconds, a time delay of 2–3 seconds is often included to minimize false alarms which can be triggered by other UV sources such as lightning, arc welding, radiation, and sunlight. UV detectors typically operate with wavelengths shorter than 300 nm to minimize the effects of natural background radiation. The solar blind UV wavelength band is also easily blinded by oily contaminants.
Near infrared (IR) array flame detectors (0.7 to 1.1 μm), also known as visual flame detectors, employ flame recognition technology to confirm fire by analyzing near IR radiation using a charge-coupled device (CCD). A near infrared (IR) sensor is especially able to monitor flame phenomena, without too much hindrance from water and water vapour. Pyroelectric sensors operating at this wavelength can be relatively cheap. Multiple channel or pixel array sensors monitoring flames in the near IR band are arguably the most reliable technologies available for detection of fires. Light emission from a fire forms an image of the flame at a particular instant. Digital image processing can be utilized to recognize flames through analysis of the video created from the near IR images.
Infrared (IR) or wideband infrared (1.1 μm and higher) flame detectors monitor the infrared spectral band for specific patterns given off by hot gases. These are sensed using a specialized fire-fighting thermal imaging camera (TIC), a type of thermographic camera. False alarms can be caused by other hot surfaces and background thermal radiation in the area. Water on the detector's lens will greatly reduce the accuracy of the detector, as will exposure to direct sunlight. A special frequency range is 4.3 to 4.4 μm. This is a resonance frequency of CO2. During burning of a hydrocarbon (for example, wood or fossil fuels such as oil and natural gas) much heat and CO2 is released. The hot CO2 emits much energy at its resonance frequency of 4.3 μm. This causes a peak in the total radiation emission and can be well detected. Moreover, the "cold" CO2 in the air is taking care that the sunlight and other IR radiation is filtered. This makes the sensor in this frequency "solar blind"; however, sensitivity is reduced by sunlight. By observing the flicker frequency of a fire (1 to 20 Hz) the detector is made less sensitive to false alarms caused by heat radiation, for example caused by hot machinery.
A severe disadvantage is that almost all radiation can be absorbed by water or water vapour; this is particularly valid for infrared flame detection in the 4.3 to 4.4 μm region. From approx. 3.5 μm and higher the absorption by water or ice is practically 100%. This makes infrared sensors for use in outdoor applications very unresponsive to fires. The biggest problem is our ignorance; some infrared detectors have an (automatic) detector window self test, but this self test only monitors the occurrence of water or ice on the detector window.
A salt film is also harmful, because salt absorbs water. However, water vapour, fog or light rain also makes the sensor almost blind, without the user knowing. The cause is similar to what a fire fighter does if he approaches a hot fire: he protects himself by means of a water vapour screen against the enormous infrared heat radiation. The presence of water vapor, fog, or light rain will then also "protect" the monitor causing it to not see the fire. Visible light will, however be transmitted through the water vapour screen, as can easily been seen by the fact that a human can still see the flames through the water vapour screen.
The usual response time of an IR detector is 3–5 seconds.
MWIR infrared (IR) cameras can be used to detect heat and with particular algorithms can detect hot-spots within a scene as well as flames for both detection and prevention of fire and risks of fire. These cameras can be used in complete darkness and operate both inside and outside.
Hub AI
Flame detector AI simulator
(@Flame detector_simulator)
Flame detector
A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line (such as a propane or a natural gas line), and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.
Ultraviolet (UV) detectors work by detecting the UV radiation emitted at the instant of ignition. While capable of detecting fires and explosions within 3–4 milliseconds, a time delay of 2–3 seconds is often included to minimize false alarms which can be triggered by other UV sources such as lightning, arc welding, radiation, and sunlight. UV detectors typically operate with wavelengths shorter than 300 nm to minimize the effects of natural background radiation. The solar blind UV wavelength band is also easily blinded by oily contaminants.
Near infrared (IR) array flame detectors (0.7 to 1.1 μm), also known as visual flame detectors, employ flame recognition technology to confirm fire by analyzing near IR radiation using a charge-coupled device (CCD). A near infrared (IR) sensor is especially able to monitor flame phenomena, without too much hindrance from water and water vapour. Pyroelectric sensors operating at this wavelength can be relatively cheap. Multiple channel or pixel array sensors monitoring flames in the near IR band are arguably the most reliable technologies available for detection of fires. Light emission from a fire forms an image of the flame at a particular instant. Digital image processing can be utilized to recognize flames through analysis of the video created from the near IR images.
Infrared (IR) or wideband infrared (1.1 μm and higher) flame detectors monitor the infrared spectral band for specific patterns given off by hot gases. These are sensed using a specialized fire-fighting thermal imaging camera (TIC), a type of thermographic camera. False alarms can be caused by other hot surfaces and background thermal radiation in the area. Water on the detector's lens will greatly reduce the accuracy of the detector, as will exposure to direct sunlight. A special frequency range is 4.3 to 4.4 μm. This is a resonance frequency of CO2. During burning of a hydrocarbon (for example, wood or fossil fuels such as oil and natural gas) much heat and CO2 is released. The hot CO2 emits much energy at its resonance frequency of 4.3 μm. This causes a peak in the total radiation emission and can be well detected. Moreover, the "cold" CO2 in the air is taking care that the sunlight and other IR radiation is filtered. This makes the sensor in this frequency "solar blind"; however, sensitivity is reduced by sunlight. By observing the flicker frequency of a fire (1 to 20 Hz) the detector is made less sensitive to false alarms caused by heat radiation, for example caused by hot machinery.
A severe disadvantage is that almost all radiation can be absorbed by water or water vapour; this is particularly valid for infrared flame detection in the 4.3 to 4.4 μm region. From approx. 3.5 μm and higher the absorption by water or ice is practically 100%. This makes infrared sensors for use in outdoor applications very unresponsive to fires. The biggest problem is our ignorance; some infrared detectors have an (automatic) detector window self test, but this self test only monitors the occurrence of water or ice on the detector window.
A salt film is also harmful, because salt absorbs water. However, water vapour, fog or light rain also makes the sensor almost blind, without the user knowing. The cause is similar to what a fire fighter does if he approaches a hot fire: he protects himself by means of a water vapour screen against the enormous infrared heat radiation. The presence of water vapor, fog, or light rain will then also "protect" the monitor causing it to not see the fire. Visible light will, however be transmitted through the water vapour screen, as can easily been seen by the fact that a human can still see the flames through the water vapour screen.
The usual response time of an IR detector is 3–5 seconds.
MWIR infrared (IR) cameras can be used to detect heat and with particular algorithms can detect hot-spots within a scene as well as flames for both detection and prevention of fire and risks of fire. These cameras can be used in complete darkness and operate both inside and outside.