Flame detectors and methods of detecting flames

Flame detectors and methods of detecting flames are described herein. One device includes an optical element configured to process mid wave infra-red light and long wave infra-red light emitted from an area, and a bolometer configured to detect a flame in the area based on the mid wave infra-red light and long wave infra-red light processed by the optical element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of U.S. Provisional Application Ser. No. 61/504,645, filed Jul. 5, 2011, the entire specification of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to flame detectors and methods of detecting flames.

BACKGROUND

Flame detectors can be used to detect the presence of flames (e.g., fires) in a number of different environments, such as, for instance, oil platforms. For example, a flame detector can detect the presence of a flame by detecting the light (e.g., radiation) emitted by the flame.

Because the main emission of a flame is mid wave infra-red (MWIR) light (e.g., light having a wavelength of 3.0 to 5.0 micrometers), previous flame detectors may be configured to detect and/or process only MWIR light. That is, previous flame detectors may not be able to detect and/or process light outside of the MWIR range.

Detecting and processing only MWIR light, however, can decrease the effectiveness of a flame detector. For example, previous flame detectors that can detect and/or process only MWIR light may have a high false alarm rate (e.g., such previous flame detectors may frequently indicate that a flame has been detected in circumstances in which no flame is actually present).

DETAILED DESCRIPTION

Flame detectors and methods of detecting flames are described herein. For example, one or more embodiments include an optical element configured to process mid wave infra-red light and long wave infra-red light emitted from an area, and a bolometer configured to detect a flame in the area based on the mid wave infra-red light and long wave infra-red light processed by the optical element.

In addition to detecting and/or processing mid wave infra-red (MWIR) light (e.g., light having a wavelength of 3.0 to 5.0 micrometers), flame detectors in accordance with one or more embodiments of the present disclosure can detect and/or process light outside of the MWIR range. For example, flame detectors in accordance with one or more embodiments of the present disclosure can detect and/or process long wave infra-red (LWIR) light (e.g., light having a wavelength of 8.0 to 12.0 micrometers). Accordingly, flame detectors in accordance with one or more embodiments of the present disclosure can have increased effectiveness as compared to previous flame detectors. For example, flame detectors in accordance with one or more embodiments of the present disclosure may have a lower false alarm rate than previous flame detectors.

For instance, because the main emission of other objects in an area in addition to a flame (e.g., objects at ambient temperature, background objects in the area, and/or people in the area) may be LWIR light, flame detectors in accordance with one or more embodiments of the present disclosure can detect the presence of such objects in the area in addition to detecting the presence of the flame. Accordingly, flame detectors in accordance with one or more embodiments of the present disclosure can provide information on (e.g., identify) the location (e.g., source) of the flame in the area and/or a view of the area (e.g., the scene) in which the flame is burning.

The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures may be identified by the use of similar digits. For example,102may reference element “02” inFIG. 1, and a similar element may be referenced as202inFIG. 2.

As used herein, “a” or “a number of” something can refer to one or more such things. For example, “a number of optical elements” can refer to one or more optical elements.

FIG. 1illustrates an exploded view of a portion of a flame detector100in accordance with one or more embodiments of the present disclosure. As shown inFIG. 1, flame detector100can include an optical element102and a bolometer104.

Optical element102can include, for example, a lens106and an optical filter108, as shown in the embodiment illustrated inFIG. 1. However, embodiments of the present disclosure are not so limited. For example, in some embodiments, optical element102may not include an optical filter. For instance, optical element102may only include a lens (e.g., lens106) in some embodiments. As an additional example, optical element102can include a shutter in place of optical filter108in some embodiments.

Lens106can be, for example, a dual mid wave infra-red (MWIR) and long wave infra-red (LWIR) lens (e.g., a lens through which both MWIR light and LWIR light can pass). Additionally and/or alternatively, lens106can be, for example, a chalcogenide and/or silicon lens (e.g., lens106can include a chalcogenide and/or silicon material).

Lens106can have a diameter of, for example, 5 millimeters. However, embodiments of the present disclosure are not limited to a particular diameter for lens106.

Optical filter108can be, for example, a sapphire and/or aluminum oxynitride (AION) filter, and/or can include silicon dioxide (SiO2) and/or cadmium sulfide (CdS). In some embodiments, optical filter108can have a fixed intensity ratio and/or a fixed infrared emission line.

In some embodiments, optical filter108can be a fixed (e.g., unmovable) filter positioned above bolometer104(e.g., between bolometer104and lens106). In some embodiments optical filter108can be a movable filter. For instance, optical filter108can be moved from a position not between bolometer104and lens106(e.g., from the position illustrated inFIG. 1) to a position between bolometer104and lens106.

In the embodiment illustrated inFIG. 1, optical element102includes a single optical filter (e.g., optical filter108). However, embodiments of the present disclosure are not so limited. For example, in some embodiments, optical element102can include multiple (e.g., two) optical filters.

Although not shown inFIG. 1for clarity and so as not to obscure embodiments of the present disclosure, in some embodiments optical element102can include a wide band reflector adjacent (e.g., on and/or attached to) a first side of optical filter108, and a wide band transmitter adjacent a second (e.g., opposite) side of optical filter108.

In the embodiment illustrated inFIG. 1, lens106and optical filter108are separate (e.g., not attached). However, embodiments of the present disclosure are not so limited. For example, in some embodiments, optical filter108can be attached to (e.g., applied to the face of and/or superimposed on) lens106.

Bolometer104can include, for example, an array110of pixels, as shown inFIG. 1. In the embodiment illustrated inFIG. 1, bolometer104includes a single array (e.g., array110) of pixels. However, embodiments of the present disclosure are not so limited. For example, in some embodiments, bolometer104can include multiple (e.g., separate) arrays of pixels.

In some embodiments, bolometer104can include a number of different materials (e.g., layers) not shown inFIG. 1for clarity and so as not to obscure embodiments of the present disclosure. For example, in some embodiments, bolometer104can include a reflector, a vacuum gap, an absorber, a silicon nitride (Si3N4) material, a vanadium oxide (VOx) material, and an additional Si3N4material. The reflector can have a thickness of, for example, 100 nanometers (nm). The vacuum gap can have a thickness of, for example, 400 nm or 2800 nm. The absorber can have a sheet resistance of, for example, 90 Ohms per square (Ω/sq). The Si3N4materials can each have a thickness of, for example, 200 nm. The VOxmaterial can have a thickness of, for example, 10 K/sq. In contrast, the thickness of the vacuum gap of previous bolometers may be, for example, 1800 nm, the thickness of the Si3N4materials of previous bolometers may be, for example, 300 nm, and previous bolometers may not include an absorber.

Optical element102(e.g., lens106and/or filter108) can process (e.g., capture) MWIR light (e.g., light having a wavelength of 3.0 to 5.0 micrometers) and LWIR light (e.g., light having a wavelength of 8.0 to 12.0 micrometers) emitted from an area (e.g., an area in which a flame is or may be present). The MWIR light (e.g., MWIR radiation) can include light emitted by a flame in the area, and the LWIR light (e.g., LWIR radiation) can include light emitted by one or more objects in the area in addition to the flame (e.g., objects in the area that are at ambient temperature, background objects in the area, and/or people in the area).

The light emitted by the flame can have a wavelength of 2.7 micrometers or 4.2 to 4.4 micrometers, for example. That is, the flame can be, for example, a hydrogen flame whose major emission is from H2O, or a hydrocarbon flame whose major emission is from CO2. However, embodiments are not limited to a particular type of flame or light wavelength emitted by the flame.

The temperature of the flame can be, for example, 150 degrees Celsius or 400 degrees Celsius. That is, the flame can be emitted from, for example, a lighter or a torch. However, embodiments are not limited to a particular flame source or temperature.

Bolometer104can detect (e.g., determine the presence of) a flame in the area based on the MWIR light and LWIR light processed by optical element102. For example, in embodiments in which optical element102does not include optical filter108(e.g., optical element102includes only lens106), array110of pixels can absorb a portion of the MWIR light processed by optical element102and a portion of the LWIR light processed by optical element102. The portion of the MWIR light absorbed by array110can be greater than the portion of the LWIR light absorbed by array110(e.g., array110can be more sensitive to MWIR light than LWIR light). For instance, array110can absorb 100% (e.g., all) of the MWIR light processed by optical element102, but only 50-60%, 5-20%, or 5-10% of the LWIR processed by optical element102. Embodiments of the present disclosure, however, are not limited to particular portions of MWIR or LWIR light absorbed by array110.

Bolometer104can then generate an image (e.g., a single image) combining the portion of the MWIR light absorbed by array110and the portion of the LWIR light absorbed by array110. That is, the image combines the light emitted by the flame with the light emitted by the objects in the area in addition to the flame. Accordingly, the image can display both the flame and the overall scene in which the flame is burning (e.g., the MWIR light emitted by the flame can be seen against and/or discriminated from the lower intensity LWIR spatial background).

In embodiments in which bolometer104includes multiple arrays of pixels, a first array (or a first number of the arrays) can absorb the MWIR light processed by optical element102, and a second array (or a second number of the arrays) can absorb the LWIR light processed by optical element102. Bolometer104can then generate an image combining the MWIR light absorbed by the first array (or the first number of arrays) and the LWIR light absorbed by the second array (or the second number of arrays).

As an additional example, in embodiments in which optical element102includes optical filter108, the optical filter can alternatively prevent (e.g., block) the MWIR light and the LWIR light from reaching bolometer104. That is, optical filter108can alternatively act as an MWIR filter that blocks MWIR light and an LWIR filter than blocks LWIR light. In some embodiments, optical filter108can comprise a single filter (e.g., a single combined MWIR and LWIR filter), and in some embodiments, optical filter108can comprise two filters (e.g., separate MWIR and LWIR filters).

In such an example, bolometer104can generate separate images of the MWIR light and the LWIR light. For instance, bolometer104can generate a first image of the MWIR light when optical filter108is blocking the LWIR light, and bolometer104can generate a second image of the LWIR light when optical filter108is blocking the MWIR light. That is, the light emitted by the flame and the light emitted by the additional objects in the area can be displayed at full intensity in separate images (e.g., the scene can be decoupled to provide the MWIR flame image separately from the LWIR scene image).

In embodiments in which optical element102includes a shutter in place of optical filter108, the shutter can alternatively prevent the MWIR light and the LWIR light from reaching bolometer104in a manner analogous to optical filter108. Bolometer104can then generate separate images of the MWIR light and the LWIR light (e.g., a first image of the MWIR light when the shutter is blocking the LWIR light and a second image of the LWIR light when the shutter is blocking the MWIR light).

FIG. 2illustrates a side view of a flame detector200in accordance with one or more embodiments of the present disclosure. Flame detector200can be, for example, flame detector100previously described in connection withFIG. 1.

As shown inFIG. 2, flame detector200includes a number (e.g., plurality) of optical elements202. The number of optical elements can be, for example, twelve. However, embodiments of the present disclosure are not limited to a particular number of optical elements.

Optical elements202can be analogous to optical element102previously described in connection withFIG. 1. For example, optical elements202can include a lens, an optical filter, and/or a shutter, and can process MWIR light and LWIR light, in a manner analogous to optical element102.

As shown inFIG. 2, optical elements202(e.g., the lenses of optical elements202) can be positioned on a hemispherical surface220of flame detector200. Hemispherical surface220can have a diameter of, for example, 32 millimeters. However, embodiments of the present disclosure are not limited to a particular diameter for hemispherical surface220.

Positioning optical elements202on a hemispherical surface (e.g., hemispherical surface220) as in the embodiment illustrated inFIG. 2can increase (e.g., widen) the field of view of flame detector200. For example, flame detector200can have a field of view of 120×60, with a 320×240 25 micrometer pitch array. However, embodiments of the present disclosure are not limited to a particular field of view or pitch array for flame detector200.

Although not shown inFIG. 2for clarity and so as not to obscure embodiments of the present disclosure, flame detector200can include a bolometer (e.g., a single bolometer) analogous to bolometer104previously described in connection withFIG. 1. For example, the bolometer can detect a flame based on the MWIR light and LWIR light processed by optical elements202, in a manner analogous to bolometer104.

FIG. 3illustrates a method330of detecting a flame in accordance with one or more embodiments of the present disclosure. Method330can be performed by, for example, flame detectors100and/or200previously described in connection withFIGS. 1and/or2, respectively.

At block332, method330includes detecting mid wave infra-red (MWIR) light and long wave infra-red (LWIR) light emitted from an area (e.g., an area in which a flame may be or is present). The MWIR and LWIR light can be detected, for example, using (e.g., by) an optical element (e.g., optical element102and/or202) in a manner analogous to that previously described herein in connection withFIGS. 1and/or2.

At block334, method330includes determining whether a flame is in the area based on the detected MWIR light and LWIR light. The determination can be made, for example, using a bolometer (e.g., bolometer104) in a manner analogous to that previously described herein in connection withFIG. 1.