FI129348B

FI129348B - An ultraviolet flame detector

Info

Publication number: FI129348B
Application number: FI20206045A
Authority: FI
Inventors: Heikki Sipilä
Original assignee: Fenno Aurum Oy
Priority date: 2020-10-22
Filing date: 2020-10-22
Publication date: 2021-12-15
Also published as: FI20206045A1

Abstract

The invention relates to an ultraviolet flame detector (100). The ultraviolet flame detector comprises: a cylindrical outer tube (102) acting as a window structure, a photocathode (106) arranged on an outer surface of a cylindrical inner tube (104) arranged inside the outer tube (102), and a plurality of anode wires (108) arranged between the outer tube (102) and the photocathode (106). The plurality of anode wires (108) are parallel to the inner tube (104) and encircle the photocathode (106) arranged on the outer surface of the inner tube (104). The outer tube (102) is filled with a gas.

Description

An ultraviolet flame detector

TECHNICAL FIELD The invention concerns in general the technical field of detectors. Especially the invention concerns flame detectors.

BACKGROUND Typically, ultraviolet (UV) sensitive detectors may be used to detect flames or sparks. The detectors may typically be used for detecting the flames in indoor spaces, e.g. buildings, or outdoor spaces. Typically, the flames are emitting UV radiation at a wavelength band between 185 and 280 nanometers. For example, lamps used for lighting, do not emit UV radiation at said wavelength band due to a strong UV absorption in their materials, such as glass. This enables that the UV radiation from the flames may be detected by means of the flame detectors in indoor spaces. Moreover, because the ozone layer in the atmosphere absorbs the UV radiation from the sun at said wavelength band, the UV radiation from the flames may also be detected by means of the flame detectors outdoor spaces (e.g. forest fires, etc.). In order to be able to detect the flame as far away as possible, the flame detector should be sensitive to the UV wavelength band radiation and as insensitive as possible for radiation at longer wavelengths which dominates daylight light. The sensitivity of the flame detector may typically be limited by a background radia- tion caused by the daylight and pulses caused by the cosmic radiation. Thus, there is a need for developing solutions in order to improve at least partly N sensitivity of the flame detectors.

N O SUMMARY

N N 25 The following presents a simplified summary in order to provide basic under- E standing of some aspects of various invention embodiments. The summary is 0 not an extensive overview of the invention. It is neither intended to identify key 3 or critical elements of the invention nor to delineate the scope of the invention. N The following summary merely presents some concepts of the invention in a N 30 simplified form as a prelude to a more detailed description of exemplifying em- bodiments of the invention.

An objective of the invention is to present an ultraviolet flame detector. Another objective of the invention is to provide the ultraviolet flame detector with an im- proved sensitivity. The objectives of the invention are reached by an ultraviolet flame detector as defined by the respective independent claim. According to a first aspect, an ultraviolet flame detector is provided, wherein the ultraviolet flame detector comprises: a cylindrical outer tube acting as a window structure, a photocathode arranged on an outer surface of a cylindrical inner tube arranged inside the outer tube, and a plurality of anode wires arranged between the outer tube and the photocathode, wherein the plurality of anode wires are parallel to the inner tube and encircle the photocathode arranged on the outer surface of the inner tube, wherein the outer tube is filled with a gas. The material of the outer tube may be fused silica. Alternatively or in addition, the material of the photocathode may be cesium io- dide (Csl) or any other solar blind material. Alternatively or in addition, the gas may be a mixture of the following gases: argon (Ar), isobutane (iC4H10), and hydrogen gas (H2). Alternatively or in addition, the material of the plurality anode wires may be tung- sten. Alternatively or in addition, the plurality of anode wires may be coated with a metal having a work function of at least 5 eV.

O O The metal coating may be gold. 2 Alternatively or in addition, the plurality anode wires may be arranged at a pre- 3 determined distance from the photocathode, wherein the predefined distance =E 25 may be between 10 and 15 millimeters. a O Alternatively or in addition, the outer tube may comprise an end plate at each

O O end of the outer tube, wherein the end plates may be made of Kovar.

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O N Alternatively or in addition, the ultraviolet flame detector may further comprise a metal disc transversally inside the outer tube to each end of the outer tube,

wherein each metal disc may comprise a through hole for each wire of the plu- rality of anode wires. The metal discs may be coated with a metal having a work function of at least 5 eV.

Alternatively or in addition, the ultraviolet flame detector may further comprise a mesh tube arranged between the outer tube and the plurality of anode wires and configured to protect one or more components of the flame detector from elec- tromagnetic interferences.

Alternatively or in addition, the outer tube may comprise an interference filter.

Alternatively or in addition, each anode wire of the plurality of anode wires may be separately electrically connected to a preamplifier.

Alternatively or in addition, the plurality of anode wires may be configured to be positively biased, wherein a preamplifier may be electrically connected to the plurality of anode wires via a coupling capacitor.

Alternatively, the photocathode may be configured to be negatively biased, wherein a preamplifier may be electrically connected directly to the plurality of anode wires.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non-limiting embodiments when read in connection o with the accompanying drawings.

O

N O The verbs “to comprise” and “to include” are used in this document as open W limitations that neither exclude nor reguire the existence of unrecited features. N 25 The features recited in dependent claims are mutually freely combinable unless E otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” 0 or “an”, i.e. a singular form, throughout this document does not exclude a plural- 3 ity.

S N BRIEF DESCRIPTION OF FIGURES

The embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. Figures 1A and 1B illustrate schematically an example of an UV flame detector according to the invention. Figure 2A illustrates schematically a simple example of biasing an UV flame detector according to invention. Figure 2B illustrates schematically another simple example of biasing an UV flame detector according to invention. Figure 3A illustrates schematically another example of an UV flame detector according to the invention. Figure 3B illustrates schematically an example of an end disc of an UV flame detector according to the invention. Figure 4 illustrates schematically yet another example of an UV flame detector according to the invention. Figure 5 illustrates schematically yet another example of an UV flame detector according to the invention.

DESCRIPTION OF THE EXEMPLIFYING EMBODIMENTS Figures 1A and 1B illustrate schematically an example of an ultraviolet (UV) flame detector, i.e. a solar blind UV detector, 100 according to the invention. Figure 1A illustrates schematically a perspective view of the UV flame detector N 100. Figure 1B illustrates schematically a transverse cross-sectional view of the N UV flame detector 100 of Figure 1A. The UV flame detector 100 comprises a 2 cylindrical outer tube 102 acting, i.e. functioning, as a window structure of the N UV flame detector 100. In other words, the whole outer tube 102 is configured z 25 to act as the window structure of the UV flame detector 100. For sake of clarity so ends of the outer tube 102 are not shown in Figure 1A. The ends of the outer 3 tube 102 will be discussed later in this application. The UV flame detector 100 S comprises further a cylindrical inner tube 104 arranged inside the outer tube 102. A photocathode 106 is arranged on an outer surface of the inner tube 104, i.e. on a surface of the inner tube 104 facing towards the outer tube 102. The pho- tocathode 106 may be implemented as a coating on the outer surface of the inner tube 104 as illustrated in the examples of Figure 1A and 1B. The photo- cathode 106 may be arranged on, i.e. coated on, the outer surface of the inner tube 104 so that the entire area of the outer surface of the inner tube 104 is covered by the photocathode 106. In other words, an area of the photocathode 5 106 corresponds to the area of the outer surface of the inner tube 104. This enables that the area of the photocathode 106 may be substantially large. More- over, this enables that the photocathode 106 and thus the UV flame detector 100 is sensitive to radiation incoming from almost all directions. The UV flame detector 100 comprises further a plurality of anode wires 108 arranged between — the outer tube 102 and the photocathode 106. The plurality of anode wires 108 are parallel to the inner tube 104 in the longitudinal direction of the inner tube

104. The plurality of anode wires 108 encircle, i.e. surround, the photocathode 106 arranged on the outer surface of the inner tube 104 as illustrated in Figures 1A and 1B. In other words, the photocathode 106 arranged on the outer surface of the inner tube 104 is encircled by the plurality of anode wires 108 being par- allel to the inner tube 104. The plurality of anode wires 108 may be evenly or unevenly spaced so that the plurality of anode wires 108 encircle the photocath- ode 106. The plurality anode wires 108 may be arranged at a predetermined distance D from the photocathode 106. The predefined distance D may be e.g. between 10 and 15 millimeters. Figures 1A and 1B illustrate only a non-limiting example number of anode wires 108 and the UV flame detector 100 may also comprise any other number of anode wires being at least two. The UV flame detector 100 is filled with a gas. In other words, the outer tube 102 of the UV flame detector 100 is filled with the gas. The UV flame detector 100 according to the invention may be used for detecting 2 flames or sparks. Although, hereinafter throughout the application the detection S of the flames is discussed, all the same applies also for the detection of the O sparks. Typically, the flames are emitting UV radiation, i.e. UV light, at a wave- N length band between 185 and 280 nanometers. The UV flame detector 100 ac- I 30 cording to the invention 100 is sensitive to UV radiation at a solar blind UV wave- & length band, i.e. UV wavelengths below 300 nanometers. The UV flame detector O 100 according to the invention 100 is especially sensitive to the UV radiation 3 emitted by the flames. The UV flame detector 100 according to the invention is O capable to detect the flames indoors and/or outdoors. The operation of the UV flame detector 100 according to the invention may be implemented as a gas- filled proportional counter configured to detect the flames. The UV radiation emitted by the flames penetrates through, i.e. passes through, the window struc- ture, i.e. the outer tube 102, and reaches the photocathode 106. The plurality of anode wires 108 are biased in relation to the photocathode 106 to create an electric field inside the UV flame detector 100. Because of the created electric field, photoelectrons detaching from the photocathode 106 drift towards the plu- rality of anode wires 108 and positive ions drift from the anode wire 108 towards the photocathode 106. Near the plurality of anode wires 108 the electric field is high, i.e. the strength of the electric field is large, causing amplification of a signal via a gas amplification.

The signal may be induced to a preamplifier 202 (for sake of clarity not shown in Figures 1A and 1B) electrically connected to the plurality of anode wires 108, when positive ions drift from the plurality of anode wires 108 to the photocathode 106. The gas amplification must be higher than 2000 to resolve it from background noise of the electronics of the UV flame de- tector 100 and lower than 20000 so that the gas amplification stays in the pro- portional mode and not reach a Geiger mode, where amplitude information will be lost.

In the Geiger mode the gas amplification saturates causing that a signal induced by a single photoelectron cannot be distinguished from a signal induced by background radiation, e.g. a cosmic background radiation caused by thou- sand(s) of electrons.

When the gas amplification is in the proportional mode, i.e. in a linear mode, the signal induced by the single photoelectron may be distin- guished from the signal induced by the cosmic background radiation.

A diameter of the outer tube 102 may be e.g. between 70 and 80 millimeters.

A diameter of the inner tube 104 may be e.g. between 45 and 55 millimeters.

Pref- erably the diameter of the inner tube 104 may be 50 millimeters.

The outer tube 102 and the inner tube 104 may be substantially concentric.

In other words, the 2 inner tube 104 may preferably be arranged substantially concentrically inside S the outer tube 102. The outer tube 102 and the inner tube 104 may have sub- O stantially egual length.

The length of the outer tube 102 and the inner tube 104 N may be e.g. between 200 and 300 millimeters.

E 30 The material of the outer tube 102, i.e. the window structure, may be selected 0 so that the outer tube 102 is transparent to the UV radiation, especially UV radi- 3 ation at the wavelength band between 185 and 280 nanometers, to enable the N UV radiation emitted by the flames to enter inside the detector 100 and to reach N the photocathode 106. The material of the outer tube 102 may be e.g. fused silica.

The fused silica enables that the outer tube 102 is transparent to the UV radiation emitted by the flames.

Alternatively or in addition, the material of the photocathode 106 may be se- lected so that the photocathode 106 is sensitive to the UV radiation emitted by the flames, i.e. the UV radiation at the wavelength band between 185 and 280 nanometers.

The material of the photocathode 106 may be e.g. cesium iodide (Csl) or any other solar blind material.

These materials enable that the photo- cathode 106 is sensitive to the UV radiation emitted by the flames.

The material of the inner tube 104 may be metal, such as stainless steel.

The inner tube 104 may preferably be hollow to enable a lightweight inner tube structure.

Alterna- tively, the inner tube 104 may be solid, but it may increase the weight of the inner tube 104. According to an example embodiment of the invention, the gas with which the UV flame detector 100, i.e. the outer tube 102, is filled may be a gas mixture of argon (Ar), isobutane (iC4H40), and hydrogen gas (Hz), i.e. the gas mixture of Ar + iC4H+0 + Ha.

Preferably, the UV flame detector 100 may be filled with the gas — mixture of Ar + (4-8%)iC4H1o + (1-3%)H>. Alternatively, the gas may be e.g. a gas mixture of argon (Ar) and carbon dioxide (CO>) or any other suitable gas.

By filling the UV flame detector 100 with the gas mixture of Ar + iC4H1o + H2 enables that the UV flame detector 100 expires more slowly, i.e. a lifetime of the UV flame detector 100 filled with the gas mixture of Ar + iC4H10 + Ho may be over an order of magnitude longer than a lifetime of the UV flame detector 100 filled e.g. with the gas mixture of Ar + iC4H10 without Ha.

Moreover, the gas mixture of Ar +iC4H10 + Ha is radiation-resistant and enables substantially low high voltage (HV) for the gas amplification.

The mixture of Ar + iC4H:o is so called Penning mixture.

In the gas amplification process the argon atom either ionizes or ex- cites.

The ionization energy of the isobutane is lower than the excitation energy 2 of the argon.

Thus, the excited argon atoms ionize the isobutane (so called Pen- S ning process). Because of this more powerful ionization process, the needed HV O for the gas amplification may be substantially low, i.e. lower in comparison to N other gas mixtures, e.g. with the gas mixture of Ar + CO? higher HV is needed.

E 30 The material of the plurality anode wires 108 may be e.g. tungsten, i.e. wolfram. 0 Tungsten itself is a strong material.

The plurality of anode wires 108 may be 3 coated with a metal having a work function of at least 5 eV, e.g. gold.

The work N function of the gold may be from 5.1 to 5.3 eV.

The coating of the plurality of N anode wires 108 enables that the surface of the plurality of anode wires 108 maintains stable and does not react with the gas.

A diameter of each wire of the plurality of anode wires 108 may be e.g. from 13 to 25 micrometers.

The plurality of anode wires 108 may be positively biased, e.g. by means of a positive HV, wherein the preamplifier 202 may be electrically connected to the plurality of anode wires 108 via a coupling capacitor 204. Figure 2A illustrates schematically a simple example of biasing the UV flame detector 100 according to invention, wherein the plurality anode wires 108 are positively biased by a voltage source 206. Alternatively, the photocathode 106 may be biased nega- tively, e.g. by means of a negative HV.

This enables that the preamplifier 202 may be electrically connected directly to the plurality of anode wires 108 without the coupling capacitor 204, which in turn reduces input capacitance and sub- stantially also microphonism of the UV flame detector 100. Figure 2B illustrates schematically another simple example of biasing the UV flame detector 100 ac- cording to invention, wherein the photocathode 106 is negatively biased by the voltage source 206. As discussed above the outer tube 102 comprises ends, e.g. an end plate 310a, 310b, at each end of the outer tube 102. The end plates 310a, 310b may pref- erably be made of Kovar.

Because of the thermal expansion of the Kovar, the end plates 310a, 310b may be easily joined, i.e. attached, to the outer tube 102 made of the fused silica, e.g. by gluing or using any known heat sealing tech- nique between Kovar and fused silica.

The Figure 3A illustrates an example of the UV flame detector 100 according to the invention, wherein the end plates 310a, 310b are also shown.

Figure 3A illustrates a longitudinal cross-section of the UV flame detector 100. The UV flame detector 100 may further comprise a metal disc 320a, 320b arranged transversally inside the outer tube 102 close to each end plate 310a, 310b, of the outer tube 102 as illustrated in the example of Figure 3A.

Each metal disc 320a, 320b may be arranged at a second prede- 2 termined distance D> from the respective end plate 310a, 310b, of the outer tube S 102. The second predetermined distance D> may be e.g. from 5 to 15 millime- O ters.

Figure 3B illustrates schematically a transverse cross-sectional view of the N metal disc 320a, 320b according to the invention.

Each metal disc 320a, 320b I 30 — may comprise a through hole 330 for each wire of the plurality of anode wires E 108. This enables that the electric filed may be maintained constant also at end O areas of the outer tube 102. A diameter of each through hole 330 may be e.g. 3 from 2 to 10 millimeters.

Preferably the diameter of each through hole 330 may O be e.g. approximately 5 millimeters.

In addition, each metal disc 320a, 320b may comprise an opening 340 for the inner tube 104. The inner tube 104 passing through the openings 340 of the metal discs 320a, 320b may be attached to the end plates 310a, 310b.

Alternatively or in addition, the metal discs 320a, 320b may be attached to the inner tube 104. Each end plate 310a, 310b may comprise at least one connector for providing electrical connections to the plurality of an- ode wires 108 and/or the photocathode 106, e.g. the electrical connection to the preamplifier 202 and/or the electrical connection for biasing the anode wire 108 and/or the photocathode 106. For sake of clarity the connectors are not shown in Figure 3A.

The plurality of anode wires 108 passing through the respective through holes 330 of the metal discs 320a, 320b may be electrically connected to the preamplifier 202. The plurality of anode wires 108 may be electrically con- nected to the preamplifier 202 together.

Alternatively, each anode wire of the plurality of anode wires 108 may be separately electrically connected to the pre- amplifier 202. Connecting each anode wire of the plurality anode wires 108 sep- arately to the preamplifier 202 enables that a direction of the incoming UV radi- ation may be defined, which in turn enables that a direction of the flames emitting — the UV radiation in relation to the UV flame detector 100 may be defined.

The metal discs 320a, 320b may be coated with a metal having a work function of at least 5 eV, e.g. with gold.

This eliminates or at least reduces background radia- tion caused by daylight penetrated through, i.e. passed through, the outer tube

102, i.e. the window structure, and hit to the metal discs 320a, 320b.

According to an example embodiment of the invention, the UV flame detector 100 may alternatively or in addition comprise a mesh tube 410 arranged inside the outer tube 102 so that the mesh tube 410 is between the outer tube 102 and the plurality of anode wires 108. Figure 4 illustrates schematically an example of the UV flame detector 100 according to the invention, wherein the UV flame detector comprises the mesh tube 410. The mesh tube 410 may be arranged 2 inside the outer tube 102 so that a gap exists between the outer tube 102 and S the mesh tube 410 as illustrated in the example of Figure 4. The gap between O the outer tube 102 and the mesh tube 410 may be for example, but is not limited N to, less than 1 millimeter.

Alternatively, the mesh tube 410 may be arranged I 30 inside the outer tube 102 so that the mesh tube 410 is substantially in contact E with the outer tube 102, i.e. no gap is existing between the outer tube 102 and O the mesh tube 410. The mesh tube 410 may be configured to protect one or 3 more components of the flame detector 100 from electromagnetic interferences.

O Especially, the mesh tube 410 may be configured to protect the plurality of an- ode wires 108 from the electromagnetic interferences.

Moreover, the mesh tube 410 may prevent the outer tube 102, i.e. the window structure, to be charged and by this way the mesh tube 410 enables that the electric field inside the UV flame detector 100 may be maintained stable. At the same time, the mesh tube 410 allows the desired radiation, i.e. UV radiation emitted by the flames, to pass, i.e. penetrate, through the mesh tube 410 so that the desired radiation reaches the photocathode 106. The mesh tube 410 may be made of metal, e.g. stainless steel or nickel. The mesh tube 410 may be coated with a metal having a work function of at least 5 eV, e.g. with gold. The work function of the gold may be from 5.1 to 5.3 eV as discussed above. The coating of the mesh tube 410 elim- inates or at least reduces the background radiation as discussed above. The — mesh tube 410 may preferably be substantially sparse, e.g. an area formed by openings of the mesh tube 410 may be at least 95 % of the area of the mesh tube 410. The mesh tube 410 may comprise e.g. hexagonal openings. Accord- ing to a non-limiting example, the diameter of the hexagonal openings may be approximately 5 millimeters and the metal forming the hexagonal openings may have a width of approximately 0.5 millimeters and a thickness of approximately

0.5 millimeters. The mesh tube 410 may be substantially equally long as the inner tube 104. Alternatively, the mesh tube 410 may be shorter than the inner tube 102 so that the mesh tube 410 may be arranged in the longitudinal direction between the metal discs 320a, 320b, i.e. the length of the mesh tube 410 may be the length of the outer tube 102 minus two times the second predetermined distance Da. According to an example, the mesh tube 410 may be manufactured by cutting the openings to a metal plate and scrolling the metal plate into a tube after the cutting of the openings. This enables a simple and inexpensive way to manufacture the mesh tube 410. Alternatively or in addition, according to an example embodiment of the inven- 2 tion, the outer tube 102, i.e. the window structure, may comprise an interference S filter 510. In other words, the interference filter 510 may be integrated to the O outer tube 102. Figure 5 illustrates schematically an example of the UV flame N detector 100 comprising the interference filter 5410. In the example of Figure 5 r 30 the mesh tube 410 is not illustrated, but the UV flame detector 100 may also E comprise both the mesh tube 410 and the interference filter 510. The interfer- O ence filter 510 may be a multilayer interference filter that may be grown on top 3 of the outer tube 102 by using the outer tube 102 as a substrate for the growing O of the interference filter 510. The interference filter 510 may be grown on top of the outer tube 102 e.g. by sputtering or by using thin film manufacturing tech- nigues, e.g. atomic layer deposition (ALD). The interference filter 510 of outer tube 102 may be facing outwards from the UV flame detector 100 as illustrated in the example of Figure 5. Alternatively, the interference filter 510 of the outer tube 102 may be facing inside the UV flame detector 100, i.e. inside the outer tube 102. The integration of the interference filter 510 to the outer tube 102 en- ables that a separate interference filter is not needed to be used with the UV flame detector 100. In other words, the integrated interference filter 510 elimi- nates the need for a separate interference filter. The illustrated dimensions in Figures are not to scale and not comparable to each other; they have been selected only for graphical clarity in the drawings. The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

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Claims

1. An ultraviolet flame detector (100) comprising: - a cylindrical outer tube (102) acting as a window structure, - a photocathode (106) arranged on an outer surface of a cylindrical inner tube (104) arranged inside the outer tube (102), and - a plurality of anode wires (108) arranged between the outer tube (102) and the photocathode (106), wherein the plurality of anode wires (108) are parallel to the inner tube (104) and encircle the photocathode (106) arranged on the outer sur- face of the inner tube (104), wherein the outer tube (102) is filled with a gas.

2. The ultraviolet flame detector (100) according to claim 1, wherein the ma- terial of the outer tube (102) is fused silica.

3. The ultraviolet flame detector (100) according to any of the preceding claims, wherein the material of the photocathode (106) is cesium iodide (Csl) or any other solar blind material.

4. The ultraviolet flame detector (100) according to any of the preceding claims, wherein the gas is mixture of the following gases: argon (Ar), isobutane (iC4H10), and hydrogen gas (Hz).

5. The ultraviolet flame detector (100) according to any of the preceding claims, wherein the material of the plurality anode wires (108) is tungsten.

N S

6. The ultraviolet flame detector (100) according to any of the preceding ro claims, wherein the plurality of anode wires (108) are coated with a metal having < a work function of at least 5 eV. z

7. The ultraviolet flame detector (100) according to claim 6, wherein the metal 0 25 coating is gold.

O S

8. The ultraviolet flame detector (100) according to any of the preceding N claims, wherein the plurality anode wires (108) are arranged at a predetermined distance from the photocathode (106), wherein the predefined distance is be- tween 10 and 15 millimeters.

9. The ultraviolet flame detector (100) according to any of the preceding claims, wherein the outer tube (102) comprises an end plate (310a, 310b) at each end of the outer tube (102), wherein the end plates (310a, 310b) are made of Kovar.

10. The ultraviolet flame detector (100) according to any of the preceding claims further comprising a metal disc (320a, 320b) arranged transversally in- side the outer tube (102) to each end of the outer tube (102), wherein each metal disc (320a, 320b) comprises a through hole (330) for each wire of the plurality of anode wires (108).

11. The ultraviolet flame detector (100) according to claim 10, wherein the metal discs (320a, 320b) are coated with a metal having a work function of at least 5 eV.

12. The ultraviolet flame detector (100) according to any of the preceding claims further comprising a mesh tube (410) arranged between the outer tube (102) and the plurality of anode wires (108) and configured to protect one or more components of the flame detector (100) from electromagnetic interfer- ences.

13. The ultraviolet flame detector (100) according to any of the preceding claims, wherein the outer tube (102) comprises an interference filter (510).

14. The ultraviolet flame detector (100) according to any of the preceding claims, wherein each anode wire of the plurality of anode wires (108) is sepa- rately electrically connected to a preamplifier (202).

N

15. The ultraviolet flame detector (100) according to any of the preceding N claims, wherein the plurality of anode wires (108) are configured to be positively 3 25 biased, wherein a preamplifier (202) is electrically connected to the plurality of 3 anode wires (108) via a coupling capacitor (204).

I &

16. The ultraviolet flame detector (100) according to any of claims 1 to 14, 2 wherein the photocathode (106) is configured to be negatively biased, wherein

O O a preamplifier (202) is electrically connected directly to the plurality of anode QA .

o 30 wires (108).