Flame detector - AbsoluteAstronomy.com

There are several types of flame detector. The optical flame detector is a detector that uses optical sensors to detect flame

Flame

A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...

s. There are also ionisation flame detectors, which use current flow in the flame to detect flame presence, and thermocouple

Thermocouple

A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...

flame detectors.

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

(UV) detectors work with wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

s shorter than 300 nm

Nanometre

A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

. These detectors detect fires and explosions within 3–4 milliseconds due to the UV radiation emitted at the instant of their ignition. False alarms can be triggered by UV sources such as lightning

Lightning

Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

, arc welding

Arc welding

Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

, radiation

Radiation

In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

, and sunlight

Sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

. In order to reduce false alarm a time delay of 2-3 seconds is often included in the UV Flame detector design.

Near IR Array

Near Infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

(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

Pixel

In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

array

Array

In computer science, an array data structure or simply array is a data structure consisting of a collection of elements , each identified by at least one index...

of a charge-coupled device

Charge-coupled device

A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

(CCD).

Infrared

(IR) flame detectors work within the infrared spectral band. Hot gases emit a specific spectral pattern in the infrared region, which can be sensed with a thermal imaging camera

Thermal imaging camera

A Thermal Imaging Camera is a type of thermographic camera used in firefighting. By rendering infrared radiation as visible light, such cameras allow firefighters to see areas of heat through smoke, darkness, or heat-permeable barriers. Thermal imaging cameras are typically handheld, but may be...

(TIC) a type of thermographic camera

Thermographic camera

A thermographic camera or infrared camera is a device that forms an image using infrared radiation, similar to a common camera that forms an image using visible light...

. False alarms can be caused by other hot surfaces and background thermal radiation

Thermal radiation

Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....

in the area as well as blinding from water and solar energy. A typical frequency where single frequency IR flame detector is sensitive is in the 4.4 micrometre range. Typical response time is 3-5 seconds.

UV/IR

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

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

IR/IR/IR flame detection

Triple IR flame detectors compare three specific wavelength bands within the IR spectral region and their ratio to each other to reliably detect flames while attempting to reduce false alarms. In this case one sensor looks at the 4.4 micrometre range and the other sensors at reference frequencies above and below. Triple IR detectors are also susceptible to blinding by water and reduced sensitivity from sunlight. False alarms can be caused by other hot surfaces and background thermal radiation in the immediate area.

Visible sensors

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

Video

Closed-circuit television

Closed-circuit television is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors....

or a web camera can be used for video detection (wavelength

Wavelength

between 0.4 and 0.7 µm). Like humans, the camera can be blinded by smoke

Smoke

Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

or fog

Fog

Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...

Ionisation current flame detection

The intense ionisation 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

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

UV/IR flame detectors are used on hydrogen station

Hydrogen station

A hydrogen station is a storage or filling station for hydrogen, usually located along a road or hydrogen highway, or at home as part of the distributed generation resources concept. The stations are usually intended to power vehicles, but can also be used to power small devices. Vehicles use...

Gas fuelled cookers
Industrial heating and drying systems
Domestic heating systems

Ultraviolet

Near IR Array

Infrared

UV/IR

IR/IR flame detection

IR/IR/IR flame detection

Visible sensors

Video

Ionisation current flame detection

Thermocouple flame detection

Applications

See also