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Kinds of Flame Detector

9/4/2013 3:31:19 PM | by Anonymous

Detectors: Flame

A flame detector is a device used to detect flames, to monitor or prevent fires. Hazardous processes and manufacturing industries such as the oil and gas industries have a great need for flame detectors to prevent disasters from taking place. There are different types of flame detectors that use different technologies to sense the flames, some of which are optical, ionization and thermocouple flame detectors.


In optical flame detectors, there are four main kinds of technology in use today, which all work on being able to detect the ultraviolet, visible and infrared spectral bands emitted by the flames in their line-of-sight.


The first, ultraviolet, detects radiation at a range of 0-50ft and wavelengths shorter than 300nm. They have a very fast response and are very sensitive. Things such as lightning or halogen lamps might trigger a false alarm, so these are usually used indoors. Another disadvantage is that in thick, sooty, conditions, ultraviolet flame detectors will not work due to the smoke affecting the radiation.


Another optical flame detector is the infrared flame detector, which work within the infrared spectral band. These can be used to detect hot gases, as they emit a specific spectral pattern. However, false alarms can be caused by background thermal radiation from other hot surfaces.


The UV/IR flame detector combines both ultraviolet and infrared sensors, so both types of radiation can be detected when being emitted by a flame. Its reaction speed is moderate and it reduces false alarms.


Visual flame imaging detectors do not depend on any product of the flames to detect it. They work using an image sensor, commonly found in closed-circuit televisions and algorithms that detect the presence of flames. The live feed from the cameras is analyzed by the algorithms to detect the shape and progression of any fires. Thus, these are commonly found in industries where flames are used as part of the process and it is necessary to discriminate between the process flames and accidental ones. However, these detectors cannot detect flames that are invisible, such as hydrogen flames and heavy smoke would also impair the detector as then the camera cannot see the flames.


The ionization current flame detectors are usually connected to large industrial gas heaters. Intense ionization takes place in a flame, due to the particles becoming charged and when a voltage is applied, current will flow. These detectors measure the current and use it to measure the strength and quality of the flame.


Thermocouple flame detectors are commonly used as fail safes in combustion heating systems and gas cookers. When the flame fails, the thermocouple stops the supply of fuel, preventing the fuel from building up, which might cause an explosion or asphyxiation.


Other factors that are important to consider when a flame detector is being chosen include the reaction time and the range of its detection. Different types of detectors have different ranges and reaction times and these also depend on the situation, but usually the detectors that have the shortest response time over the largest range are the ones that are more effective at warning against fires. Other things like the field of view of the detector should also be taken into consideration. The number of false alarms caused by the detector is also important as they are costly and affect productivity.


Flame detectors can make the difference between life and death, so when choosing one it is incredibly important to ensure the principles on which the flame detectors works are understood so that the flame detector chosen will best fit the situation it will be used in and the type of hazards it is expected to combat and prevent.

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