Flame detector for radiation-based detection of a flame and method for its manufacture

Abstract

A flame detector for detecting a flame (20) comprises a waveguide (110) with a first end (111) and a second end (112), wherein the first end (111) is configured to thermally couple to the flame (20), and the waveguide (110) is configured to guide electromagnetic radiation (40) from the first end (111) to the second end (112); a sensor (130) configured to detect electromagnetic radiation (40); and a sensor attachment (135) for attaching the sensor (130) to the second end (111) of the waveguide (110), wherein a length (L) of the waveguide (110) is selected such that the sensor (130) is thermally decoupled from the flame (20).

Description

[0001] The present invention relates to a flame detector for radiation-based detection of a flame, a combustion control unit, a method for manufacturing a flame detector and in particular to flame detection by means of infrared measurement. BACKGROUND

[0002] Currently, several flame detector concepts exist. Classical flame monitoring methods use thermocouples or acoustic flame detection. While thermocouples are frequently used for flame monitoring, they have some disadvantages when used as flame detectors.

[0003] Maintainability is thus determined by the sensor's positioning. Since the sensor requires a short response time, it should be mounted close to the flame. This increases the stress on the thermocouple and reduces its lifespan. However, because the sensor is inaccessible during operation, replacement can only be performed when the unit is shut down. Should the sensor fail before this can be done, the flame can no longer be monitored.

[0004] A problematic aspect of thermocouples is their aging process. This is a temperature-dependent process (high temperatures accelerate it) in which foreign atoms from the environment (for example, from the conductor's sheathing) diffuse into the thermocouple. This causes the thermoelectric properties of the conductors to become uniform, leading to inaccurate measurements. Furthermore, this measurement method is unreliable under certain environmental conditions such as rain, wind, or steam. Finally, in large-scale plants, the pilot flare flame is only distinguishable from the main flame to a limited extent.

[0005] A conventional acoustic flame detector (flame monitor) for heating appliances is disclosed, for example, in DE 3 447 754 A1. The acoustic signal can be transported through a channel or hose to a remote location where there is no thermal stress. An airborne sound sensor in the form of a microphone can then be mounted there. The microphone signal is monitored in the frequency range of 0 to 2 kHz. DE 69 810 072 T3 discloses another conventional flame detection device, specifically designed for industrial flares or their pilot burners. Here, the sound is directed downwards through a tube acting as an acoustic conductor, where an acoustic sensor is mounted.

[0006] However, acoustic flame detectors also have several disadvantages. Firstly, flames are not a very intense source of acoustic signals. Especially in environments with background noise – such as industrial plants – false detections occur frequently because ambient noise masks the sound of the flame. Furthermore, there are no easy ways to shield acoustic noise from the environment, particularly when it comes to the application of detecting pilot flares. Vibrations of the acoustic conductors can also lead to background noise that must be filtered out in a complex process.

[0007] Therefore, there is a need for alternative ways to reliably detect the state of a flame, which are particularly suitable for industrial applications. BRIEF DESCRIPTION OF THE INVENTION

[0008] At least some of the aforementioned problems are solved by a flame detector for detecting a flame according to claim 1, a combustion control unit according to claim 11, and a method for manufacturing a flame detector according to claim 13. The dependent claims define further advantageous embodiments for the subject matter of the independent claims.

[0009] The present invention relates to a flame detector for detecting a flame. The flame detector comprises a waveguide with a first end and a second end, the first end being configured to thermally couple to the flame. The waveguide is configured to transmit electromagnetic radiation from the first end to the second end. The flame detector further comprises a sensor configured to detect electromagnetic radiation and a sensor mount for attaching the sensor to the second end of the waveguide. The length of the waveguide is selected such that the sensor is thermally decoupled from the flame.

[0010] It is understood that the waveguide is designed to transmit electromagnetic radiation of a specific wavelength, such as thermal radiation in the infrared (IR) spectrum, over longer distances, even around bends. In some embodiments, the distance is at least 10 m. The thermal decoupling of the sensor at the second end means, for example, that the temperature of the waveguide at the second end is essentially independent of whether the burner is burning or not. If any heating occurs, it is primarily due to the received thermal radiation. Therefore, any waveguide suitable for transmitting thermal radiation can be used, but not necessarily one suitable for data transmission (e.g., optical or acoustic waveguides). It is understood that, for efficient transmission, the dimensions can be selected according to the expected thermal radiation.Depending on the temperature, different IR wavelengths are excited, which are then transmitted via the waveguide.

[0011] Optionally, the waveguide is a hollow conductor (e.g., a tube), with the hollow conductor being closed at least at its first end. In particular, the hollow conductor can be hermetically (airtight) sealed at its first end, thus reliably preventing the ingress of soot, dirt, or other contaminants such as environmental influences or precipitation. The first end of the hollow conductor can, in particular, be windowless. This reliably prevents leaks from occurring at the window, even with continuous temperature fluctuations resulting from the ignition and extinguishing of a burner flame. It is therefore advantageous if the hollow conductor is monolithic. The waveguide can thus be inserted into the flame at its first end, where it heats up (significantly), emitting thermal radiation from within, which is then detected by the sensor.Therefore, the heat radiation from the flame is not passed on directly, but rather heat radiation generated by the heat conductor (inside) is passed on to the sensor.

[0012] Optionally, the waveguide has a treated inner surface. This can be located entirely or only partially within the waveguide. Compared to an untreated inner surface, it exhibits a reduced absorption coefficient for electromagnetic radiation. In other words, the treatment reduces absorption and thus the transmission loss of electromagnetic radiation from one end to the other. This treatment can, for example, involve electropolishing, which modifies the surface properties. Treating the waveguide can result in: increased inner surface smoothness, reduced micro-roughness, higher strength, and increased durability.

[0013] Optionally, the waveguide is at least partially flexible. Optionally, the first end of the waveguide has an angled tip. This allows the tip at the first end to be positioned in and / or near a critical area of ​​the flame, enabling very rapid heating of the first end and thus allowing a measurement signal to be received at the sensor with minimal time delay.

[0014] The first end of the waveguide can be bent at various angles. Preferably, the first part of the waveguide can be bent at an angle of 5 to 25 degrees relative to the second part of the waveguide. Preferably, the angle of the first part of the waveguide is between 10 and 20 degrees. The angled tip of the first end of the waveguide can be bent at various angles. Preferably, the tip of the waveguide can be bent at an angle of 0.2 to 10 degrees. Preferably, the angle of the tip is between 0.5 and 5 degrees.

[0015] The waveguide can optionally be metallic. It is understood that the waveguide is configured to withstand high temperatures. Therefore, glass waveguides, plastic waveguides, or other temperature-sensitive materials are less suitable as transmission media for electromagnetic radiation.

[0016] Optionally, the waveguide can have a round, oval, or rectangular cross-section, or another shape that can be produced by machining the metal. The metal waveguide could, for example, be heated to incandescence by the flame and would then be highly visible to the sensor. However, according to some embodiments, even lower temperatures are sufficient to generate enough thermal radiation to be detected by appropriate sensors (e.g., IR cameras). Often, even small temperature differences (e.g., 10°C or 20°C) are enough to generate a clear sensor image of the burning or extinguished flame.

[0017] Optionally, the waveguide has at least one of the following dimensions: - a length of at least 1 m or at least 2 m; - an inner diameter in a range of 2 mm to 10 mm or between 4 mm and 8 mm; - a wall thickness in a range of 0.3 mm to 5 mm or between 0.5 mm and 3 mm.

[0018] The dimensions of the waveguides can also be chosen differently, as long as the thermal radiation is conducted well. With these dimensions, exemplary embodiments are very well suited for industrial plants, e.g., for monitoring a pilot burner of industrial flares. A pilot flame (also called ignition flame) is a small, continuously burning flame that serves to ignite burner flames. According to an advantageous embodiment, the waveguide has an inner radius of approximately 6 mm and an outer radius of approximately 8 mm. Tests have shown that reliable detection is possible even over greater distances with these dimensions.

[0019] Unlike conventional systems (e.g., using thermocouples), where the sensor requires a direct line of sight to the flame, the sensor in these embodiments does not need direct contact with the flame. Instead, the sensor can be placed far away from the pilot flame. This allows for almost unlimited sensor placement. The length of the waveguide simply needs to be adjusted accordingly (e.g., 10 m or more).

[0020] Optionally, the waveguide may be made of at least one of the following materials: - Steel; - Copper alloys; - Aluminum; - Titanium.

[0021] It is known to those skilled in the art that the waveguide materials can be selected to be suitable for a wide range of applications. For example, corrosion is highly dependent on environmental conditions and gas flow. According to an advantageous embodiment, the waveguide comprises at least one of the following materials: austenitic steel, such as stainless steel types 304, 316, 1.43XX, 1.44XX, 1.45XX (e.g., 1.4571, where "XX" represents any two digits from 1 to 9); alloy steels, in particular copper alloys, aluminum, or titanium. These materials are very well suited for outdoor applications, even under adverse weather conditions.

[0022] According to further embodiments, it is also possible that the waveguide has other metals that are suitable for transmitting the electromagnetic radiation, especially in the infrared spectrum, from the first end of the waveguide to the sensor.

[0023] Optionally, the sensor is designed to detect infrared radiation as well as electromagnetic radiation. Optionally, the sensor includes one or more of the following components: - a pyrometer; - a thermal imaging camera (e.g. a CCD camera); - an infrared sensor; - a thermometer; - a thermal radiation thermometer.

[0024] The sensor can therefore be, in particular, a camera that captures at least part of the infrared spectrum and can generate an image.

[0025] Optionally, the waveguide has several components or sections connected to each other via connectors. It is understood that the connectors between the waveguide sections are also designed to enable the transmission and detection of electromagnetic radiation. Optionally, the connector can be made of the same material as the waveguide.

[0026] Exemplary embodiments also relate to an evaluation unit, wherein the sensor converts the electromagnetic radiation into a sensor signal and transmits or provides it to the evaluation unit via a line. The evaluation unit can include a processor which, via software from a data storage device, is able to perform its functions of evaluation, detection, and warning.

[0027] Optionally, the flame detector also includes an analog-to-digital converter and / or an environmental sensor. The analog-to-digital converter is designed to convert the sensor's analog signals into digital signals and provide these digital signals to the evaluation unit. The environmental sensor can detect at least one environmental condition, namely temperature and / or precipitation (e.g., rain, snow, fog, etc.) and / or wind. The flame detector can optionally also access an external temperature sensor. The optional precipitation sensor can detect rain, snow, fog, and wind, allowing the flame detector to take measurements more frequently.

[0028] Optionally, the evaluation unit is configured to issue an alarm if it does not receive a processable sensor signal from the sensor (e.g., if the flame is out), or if the sensor does not send a sensor signal (e.g., if the sensor is defective), or if signal transmission is not possible.

[0029] The evaluation unit can be positioned far away from the sensor using a line or cable. The length of the line or cable can range from a few centimeters to several meters.

[0030] Exemplary embodiments also relate to a combustion control unit (e.g., an industrial flare device) with a burner, at least one flame detector as described in this disclosure, and at least one pilot flame device for the flame that serves to ignite the burner. The pilot flame is thus an ignition flame for the actual burner. The burner combusts, for example, the harmful gas (environmentally harmful and / or toxic).

[0031] Optionally, multiple pilot flame devices are provided for the burner (enabling higher reliability), and the burner control unit features an orifice between any two of these pilot flame devices. Optionally, the burner control unit includes multiple burners with multiple pilot flames, with orifices between the pilot flames. The primary pilot flame should be distinguishable from other sources of interference (e.g., secondary pilot flame and / or other flames) that might disrupt detection. This could be achieved by shielding against these sources of interference using an orifice. The orifice should be capable of shielding heat sources of at least 200 °C or higher.

[0032] Exemplary embodiments also relate to a method for manufacturing a flame detector as described in this disclosure. Optionally, the method may include further steps, such as: - Electropolishing an inner surface of a waveguide and / or - Bending one end of the waveguide and / or - Angle one tip of the first end of the waveguide to position the tip in or near the critical area of ​​the flame.

[0033] Methods for polishing metallic surfaces, such as electropolishing, are well known to those skilled in the art. Electropolishing is a widely used surface treatment process for producing highly passive and glossy metal surfaces. This galvanic process, which can also be applied to the inner surfaces of waveguides, creates or enhances the effect of passivation layers that reduce surface roughness and / or increase corrosion resistance. Unlike mechanical processing, electropolishing smooths the surface without mechanical or thermal stress, and without contamination or chemical damage.

[0034] According to further embodiments, the inner surface of the waveguide can also be treated differently, e.g., by coating. The coated surface layer can be formed in such a way that it is very well suited for IR radiation (e.g., reflects very well and hardly absorbs).

[0035] Reflective surfaces (e.g., those treated by electropolishing and / or painting) are well suited to reducing the absorption coefficient and thus keeping the infrared radiation intensity received by the sensor as high as possible.

[0036] Advantageously or alternatively, the waveguide can be filled with dry air or nitrogen to eliminate humidity and other gases (e.g., CO2). Replacing air with dry air or nitrogen can improve the stability and reliability of the measurement. In some embodiments, the waveguide is vacuum-sealed, and the sensor is located outside this vacuum.

[0037] According to further embodiments, the angled tip of the first end of the waveguide can have a roughened inner surface configured to increase the emission of infrared radiation from the heated metal. BRIEF DESCRIPTION OF THE FIGURES

[0038] The embodiments of the present invention are better understood with reference to the following detailed description and the accompanying drawings of the different embodiments, which, however, should not be understood as limiting the disclosure to the specific embodiments, but merely serve for explanation and understanding. Fig. Figure 1 shows an embodiment of a flame detector for detecting a flame. Fig. Figure 2 shows another flame detector for detecting a flame according to a further embodiment. Fig. Figure 3 shows the steps of a method for manufacturing a flame detector according to an exemplary embodiment. DETAILED DESCRIPTION

[0039] Fig. Figure 1 shows an embodiment of a flame detector for detecting a flame. The flame detector is configured to detect a flame 20 and comprises a waveguide 110 with a first end 111 and a second end 112. The first end 111 is configured to thermally couple to the flame 20. The waveguide 110 is configured to transmit electromagnetic radiation 40 (e.g., IR radiation or thermal radiation) from the first end 111 to the second end 112. The flame detector further comprises a sensor 130, which is configured to detect electromagnetic radiation 40 and transmit a sensor signal to an evaluation unit 150. The sensor 130 is attached to the second end 112 of the waveguide 110 by a sensor mount 135, the length L of the waveguide 110 being selected such that the sensor 130 is thermally decoupled from the flame 20.The sensor 130 therefore heats up only (at most) through the received electromagnetic radiation 40 - but not through heat conduction or direct radiation from the flame 20. The temperature at the second end 112 of the heat conductor 110 is therefore independent of the presence or absence of the flame 20.

[0040] In the simplest case, the sensor mounting 135 can comprise a printed circuit board on which both the sensor 130 (e.g., an IR sensor or a CCD chip) and a processor or microcontroller are mounted as an evaluation unit 150. The evaluation unit 150 can perform the evaluation and optionally output or forward a warning (e.g., a warning signal, a visual or audible signal). The evaluation unit 150 can access or include a corresponding network interface for this purpose.

[0041] The concept of flame monitoring using IR measurement utilizes the measurement of IR radiation 40, caused by the heating of the first end 111, to determine the presence or absence of a flame 20. The emitted IR radiation 40 can be detected by the sensor 130. This measurement signal is processed by measuring electronics in the evaluation unit 150. The evaluation unit 150 can also be located at a considerable distance from the sensor 130 (e.g., several meters). Advantageously, at greater distances, an analog-to-digital conversion is performed in close proximity to the sensor 130 to transmit digital sensor signals without loss even over longer distances.

[0042] In the immediate vicinity of the flame 20, there is a high thermal load which could damage the measuring electronics. Exemplary embodiments offer the advantage that all electronic components can be mounted outside the critical area around the flame 20. Although the exact distance varies depending on the application and the size of the flame 20, exemplary embodiments allow the measuring electronics (the sensor 130 and the evaluation unit 150) to be positioned even at a considerable distance from the flame 20 (e.g., 10 m or more).

[0043] According to further embodiments, the evaluation unit 150 uses calibration data to determine the state of the flame 20. This calibration data can be stored in the evaluation unit 150 or externally. This calibration data can be generated in a calibration process, whereby, according to the embodiments, the calibration can be performed on-site or under laboratory conditions to determine, for example, changes or extent in the IR spectrum when the flame 20 is extinguished. During the calibration, a selection of criteria can also be made (what, where, and to what extent changes in the received IR signal) that are particularly suitable for a specific flame detector or for the specific environment.

[0044] Fig. Figure 2 shows another flame detector or further details of the flame detector according to further embodiments. The waveguide 110 is designed as a tube 110 and runs parallel to a fuel supply line 60 with an opening 65 for the flame 20. The waveguide 110 has at least one bend, and the flame 20 is protected by a cup-shaped wind guard 50 with ventilation openings. The wind guard 50 also includes a flame plate from below. The first end 111 can be inserted into the wind guard 50 from below and projects at least partially directly into the flame 20 in order to heat up sufficiently. The term "sufficiently" can be understood to mean that the heated first end 111 becomes a source of thermal radiation sufficient to be detected by the (remote) sensor 130.

[0045] At the second end 112 of the tube 110, the sensor 130 is located outside the critical zone. The signal can be captured at the sensor end 130 using a thermal imaging camera, and the sensor signal can then be forwarded to the evaluation unit 150 (which can also be a remote server). Using the example thermal imaging camera 130, the flame 20 can be observed very clearly through the waveguide 110 (e.g., a stainless steel tube).

[0046] The tip of the tube 111 (first end) is positioned in the flame 20 to be monitored, and the first end 111 can optionally be angled. This can be achieved, for example, by further bending, or the end 111 can run at a non-perpendicular angle to the axial axis of the tube 110, so that the end surface is heated more intensely and radiates heat over a larger area.

[0047] The tip of the tube 111 is positioned so far within the flame 20 that, despite disturbances such as environmental influences, the flame 20 continues to heat the first end 111. The wind guard 50 also provides protection against environmental influences such as wind. When using multiple thermal sources (e.g., several burners with multiple pilot flames), the end of the tube 111 can be positioned to prevent confusion regarding the radiation source. The wind guard 50 can also serve as a shield or baffle against interference. Separate baffles can also be designed.

[0048] As in the Fig. As can be seen in Figure 2, the pipe end 111 is closed, thus preventing the ingress of soot, dirt, or other contaminants. The closed pipe end 111 can also advantageously shield against bypass influences such as water or sunlight.

[0049] Alternatively or additionally, the outside and / or the inside of the pipe end 111 can be roughened to increase the absorption coefficient and thus the radiation emission.

[0050] Advantageously, the tube 110 can be made of or formed from titanium, copper, aluminum, or a high-temperature stainless steel such as 1.4302 (or an alloy thereof). To form a good waveguide for IR radiation, the inner surface of the tube 110 can be treated. For example, electropolishing can improve the internal surface finish of the tube 110 to reduce the absorption coefficient.

[0051] Fig. Figure 3 shows the steps of a method for manufacturing a flame detector according to an exemplary embodiment. The method comprises the following steps: - Providing S110 of a waveguide 110 with a first end 111 and a second end 112, wherein the waveguide 110 is configured to guide electromagnetic radiation 40 from the first end 111 to the second end 112; - Coupling S120 of the first end 111 thermally to the flame 20; - Attaching S130 of a sensor 130 to the second end 112 to detect electromagnetic radiation 40, wherein a length L of the waveguide 110 is chosen such that the sensor 130 is thermally decoupled from the flame 20.

[0052] Optionally, the procedure includes one, more, or all of the following steps: - Electropolishing S140 of an inner surface of a waveguide 110; - Bending a first end 111 of the waveguide 110; - Angle one tip of the first end 111 of the waveguide to position the tip in or near the critical area of ​​the flame 20.

[0053] According to the described embodiments, an indirect measurement of the flame 20 is thus performed by a signal receiver (e.g., sensor 130) for a transmitted heat radiation 40. This makes it possible for the combustion point to be located far enough away so that the electronics or the signal acquisition are not disturbed or influenced by interference such as flames 20 or high temperatures. This allows maintenance work on the signal receiver (sensor 130) without having to switch off the burner. All electronics (cables, sensor 130, etc.) are not located in the immediate vicinity of the flame 20 and are therefore very well thermally shielded.

[0054] Tests have shown that, according to the exemplary embodiments, the flame detector can register a temperature drop of 50 K within a range of seconds. This makes it readily possible to conclude that flame 20 is absent from the pilot burner.

[0055] Compared to conventional flame monitors (flame detectors), exemplary designs offer at least the following additional advantages: - Even if the waveguide 110 is bent several times by different angles (1, 2, 4 degrees), reliable flame detection can be guaranteed over a distance of 10 m. - The temperature drops immediately as soon as flame 20 goes out, thus providing a high-resolution temporal indication of the presence of flame 20. Conversely, the temperature rises again as soon as flame 20 is ignited. - Thus, it becomes possible to obtain a signal 40 through a bent tube 110 and with an optionally angled measuring tip of the tube 110, which has only slight time deviations. - Even under the influence of thermal disturbances, a drop in temperature is immediately noticeable. - Flame sensors can be monitored more stably and with less error. - Monitoring of flame activity by the flame detector according to the exemplary embodiments leads to a higher availability of upstream plants (refineries, steam crackers, etc.) and longer maintenance intervals.

[0056] These embodiments can be used for various applications. One specific application is found in pilot burners for industrial flares or combustion control units. Industrial flares are found in chemical / petrochemical plants, oil and gas production facilities, refineries, and chemical plants, and are designed to burn off unusable and / or environmentally harmful gases before they are released into the environment. Emergency flares also exist, which, in the appropriate situation, can quickly vent and flare off large quantities of process gases. These embodiments can also be used in various types of gas boilers.

[0057] To ensure combustion when needed, such flare systems are equipped with one or more pilot burners that ignite and maintain the main flame. Since the pilot burners must not fail during operation, flame detectors are used, as shown in the exemplary embodiments. Their function is to ensure the presence of the flame and, in the event of a failure, to initiate a new ignition. The exemplary embodiments also describe the operation of a robust flame detector as a flame monitor.

[0058] The flame detector's function is therefore to detect a flame and transmit this information to a combustion control unit, which then evaluates it. This unit can then initiate appropriate measures to ensure the safe operation of the flame. Possible applications for flame detectors include boiler systems, gas burners, furnaces, and industrial flares.

[0059] Compared to conventional flame detectors, these exemplary designs offer at least the following advantages: The flame detector according to the exemplary embodiments requires little maintenance. Access to towers in industrial plants is often severely restricted, and the corresponding system may be inaccessible for more than five years. Therefore, flame monitors often have very long maintenance intervals depending on the application, making flame detectors according to the exemplary embodiments advantageous. The flame detector according to the exemplary embodiments is interference-proof and environmentally robust, as it functions reliably even under extreme external influences. It also functions reliably in extreme wind speeds or storms, fog / steam, rain, snow / ice, lightning, sunlight, and / or infestation by pests (e.g., insects). Even high thermal loads from -50 °C in winter or in cold regions up to several hundred degrees Celsius with full flame development do not compromise the reliability of the exemplary embodiments. - The flame detector also exhibits high chemical resistance to process gases. - The flame detector according to the exemplary embodiments measures very reliably. This means, among other things, that the flame detector enables reliable detection of the flame 20. In particular, the flame 20 is not confused with other sources of ignition or interfering environmental influences.

[0060] In laboratory tests, various measurement scenarios were conducted and tested. The test examined whether a sensor 130 could detect flame activity over a length of 10 meters through a pipe 110. Subsequently, several modifications to the measurement setup were made to test the measurement under more challenging and realistic conditions. In the following examples, a photocell was used as the sensor. Standard software was used to evaluate the measurement data. The following tests were conducted with exemplary implementations: Attempt 1

[0061] In this experiment, signal 40 was transmitted as light waves through a 10 m long pipe 110 and an externally heated measuring sleeve to sensor 130. The inside of the pipe 110 was untreated. The image produced by sensor 130 was analyzed using computer software. This allowed the area that changed color due to the thermal radiation from the sleeve of the waveguide 110 to be clearly identified. Attempt 2

[0062] In this experiment, the first end 111 of the waveguide 110, to which the sleeve to be heated was attached, was bent at an angle of 15°. This meant that neither the sleeve nor the first end 111 of the waveguide 110 was directly within the field of view of the sensor 130. Nevertheless, during heating, an area (e.g., the critical area of ​​the flame 20) could again be identified on the measurement image, confirming the flame activity and the presence of the flame 20. Attempt 3

[0063] To simulate environmental influences such as solar radiation and high ambient temperatures, additional ignition sources were used on the outside of the pipe 110 in this experiment. Although two heat sources (main flame 20 and interference source) are now visible in the evaluated images with the sensor 130, the flame detector was nevertheless able to clearly distinguish the main flame from the interference source, according to the exemplary embodiments.

[0064] During the tests, a waveguide wall thickness of 1.5 mm proved effective in shielding thermal interference, simulated by a continuous heat source of 200 °C, to such an extent that it had only a minor influence on the measurement results. Initial tests under laboratory conditions also detected the infrared light waves 40 over a length of 10 meters through a stainless steel tube 110.

[0065] Further tests led to the conclusion that a connection using a pipe connector 115 between two pipes 110 (e.g., between the first end 111 and the second end 112 of the waveguide 110) still allows for good detection of the IR radiation. Therefore, the coupling losses at such a point can be considered negligibly small.

[0066] It has proven advantageous to position or mount the sensor 130 at a sufficient distance from the flame 20 or flame source at the end of the tube (second end 112 of the waveguide 110) for infrared radiation measurement. This achieves a good "distance-to-spot" ratio, i.e., measurements are taken at a sufficient distance.

[0067] The sensor signal can also be transmitted via cable from sensor 130 to the ground, where it can be read out by a measuring unit (e.g., evaluation unit 150). During calibration, initial images can then be used to determine the area of ​​the image where the radiation from the flame 20 to be detected is detected. Software can then be used to restrict the image analysis to this area, thus further increasing the sensitivity of the measurement. This also allows the influence of interference sources to be further limited. Optionally, the evaluation unit contains calibration data and is designed to detect when the flame has extinguished based on this data.

[0068] In summary, exemplary implementations offer the following advantages over existing systems: - The flame detector has a short response time, which means that a flame failure is detected quickly. Furthermore, it is very robust against environmental influences; in particular, the surrounding tube provides excellent protection for the entire sensor system. The evaluation electronics are also not exposed to thermal influences. - It allows for good differentiation between the main flame and sources of interference (other flames and environmental influences); - The flame detector or sensor system has a long lifespan.

[0069] The features of the invention disclosed in the description, claims and figures may be essential for the realization of the invention, either individually or in any combination. REFERENCE MARK LIST 20 flames 40 electromagnetic radiation, sensor signal 50 aperture, windbreak 60 Supply pipe or line 65 Opening for the flame 110 waveguides, pipeline 111 first end of the waveguide 112 second end of the waveguide 115 connectors 130 Sensor 135 Sensor mounting 150 evaluation units S110, S120, S130 Steps of a procedure L Length of the waveguide QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 3 447 754 A1

[0005] DE 69 810 072 T3

[0005]

Claims

Flame detector for detecting a flame (20) comprising: a waveguide (110) with a first end (111) and a second end (112), wherein the first end (111) is configured to thermally couple to the flame (20), and the waveguide (110) is configured to guide electromagnetic radiation (40) from the first end (111) to the second end (112); a sensor (130) configured to detect electromagnetic radiation (40); and a sensor attachment (135) for attaching the sensor (130) to the second end (111) of the waveguide (110), wherein a length (L) of the waveguide (110) is selected such that the sensor (130) is thermally decoupled from the flame (20). Flame detector according to claim 1, wherein the waveguide (110) is a waveguide which is closed at least at its first end (111). Flame detector according to claim 1 or claim 2, wherein the waveguide (110) has a treated inner surface which has a reduced absorption coefficient for the electromagnetic radiation (40) compared to an untreated inner surface. Flame detector according to one of claims 1 to 3, wherein the waveguide (110) has an angled tip at the first end and / or is at least partially bendable to position the first end (111) of the waveguide in the vicinity of a critical area of ​​the flame (20). Flame detector according to one of claims 1 to 4, wherein the waveguide (110) is metallic and has a round or square cross-section. Flame detector according to one of claims 1 to 5, wherein the waveguide (110) has at least one of the following dimensions: - a length (L) of at least 2 m; - a maximum inner diameter of 4 mm to 10 mm; - a wall thickness in a range of 0.5 mm to 5 mm. Flame detector according to one of claims 1 to 6, wherein the waveguide (110) comprises at least one of the following materials: - austenitic steel; - alloy steel; - copper alloys; - aluminium; - titanium. Flame detector according to one of claims 1 to 7, wherein the sensor (130) is configured to detect infrared radiation as the electromagnetic radiation (40). Flame detector according to any one of claims 1 to 8, wherein the sensor (130) comprises at least one of the following: - pyrometer; - thermal imaging camera; - infrared camera; - thermometer. Flame detector according to one of claims 1 to 9, wherein the waveguide (110) has several components which are connected to each other via connectors (115). Automatic burner with: a burner; at least one flame detector according to one of claims 1 to 10; and at least one pilot flame device for igniting the burner, wherein the at least one flame detector is configured to monitor a state of the flame (20) of the pilot flame device. Burner control unit according to claim 11, wherein several pilot flame devices are provided for the burner and the burner control unit has an aperture between two of the several pilot flame devices. A method for manufacturing a flame detector according to any one of claims 1 to 10, wherein the method comprises the following steps: - providing (S110) a waveguide (110) to a first end (111) and a second end (112), wherein the waveguide (110) is configured to guide electromagnetic radiation (40) from the first end (111) to the second end (112); - thermally coupling (S120) the first end (111) to the flame (20); and - attaching (S130) a sensor (130) to the second end (112) to detect electromagnetic radiation (40). Method for manufacturing according to claim 13, further comprising at least one of the following steps: - electropolishing (S110) an inner surface of the waveguide (110); - bending (S120) a first end (111) of the waveguide (110); - angled (S130) a tip of the first end (111) of the waveguide to position the tip in or near the critical region of the flame (20).

Images