Optical gas sensor with led emitter for emitting light of narrow bandwidth

Abstract

The invention relates to an optical gas sensor (1) for quantitatively measuring the concentration of one or more gases, having a radiation source (2) for emitting light waves (L), a sample cell (3) for accommodating the gas (G) to be measured, and a detector (4) for measuring the light intensity. The radiation source (2) has at least one emitter (5) of light waves (L) and is configured to emit light waves (L) of at least one first wavelength and at least one second wavelength different from the first wavelength simultaneously and separately from one another. Furthermore, the emitter (5) is also configured to emit a spectrum whose full width at half maximum is at most 50% of the center wavelength and to emit light waves (L) with a guided light path. The detector (4) is configured to quantitatively detect the intensity of the emitted light waves (L) of the first and second wavelengths.

Description

Technical Field

[0001] This invention relates to an optical gas sensor for quantitatively measuring the concentration of one or more gases.

[0002] Optical gas sensors can not only qualitatively determine the presence of one or more gases, but also quantitatively determine the concentration of one or more gases. Such gas sensors are used, for example, in gas detection devices in equipment used for transporting and handling flammable and / or toxic gases, to detect unwanted gas escape. Background Technology

[0003] Optical gas sensors are known to include an emitter, a sample cell (Küvette), and a detector. In the case of an optical gas sensor, the emitter is a light source, such as an incandescent lamp, that emits light waves with a broad spectrum, i.e., light waves with a large number of different wavelengths. The sample cell is preferably a substantially enclosed space within which the gas to be measured is contained. The sample cell may have an opening to the outside, which allows gas exchange between the sample cell and the surrounding environment of the gas sensor. The detector is a light sensor, which preferably measures the intensity of light incident on it. To detect light of a specific wavelength, a bandpass filter is connected before the corresponding detector. Such a bandpass filter can be configured to allow one or more wavelengths to pass through.

[0004] During operation, the gas or gas mixture to be measured is introduced into a sample cell. For this purpose, the sample cell may have one or more openings. Light waves emitted from the light source are absorbed more or less strongly by the corresponding gas depending on the concentration of the components of the gas mixture and the absorption wavelength, and then strike a photosensitive sensor that measures the intensity of the light waves. In this way, it can be determined which wavelengths have been absorbed by the gas and how strongly. Due to the known specific absorption characteristics of different gases, the composition of the gas mixture can be determined from the results.

[0005] An optical gas sensor is known from DE 202 02 694 A1, which has a cylindrical sample cell for containing the gas to be measured. At the sample cell, a plane mirror is arranged on one side along the longitudinal axis, and a concave mirror is arranged on the other side. The concave mirror has multiple recesses for accommodating an incandescent lamp and a light detector. Light waves emitted from the incandescent lamp are first radiated multiple times between the plane mirror and the concave mirror until they reach the light detector. This extends the optical path through which the light waves can be absorbed by the gas or gas mixture to be measured. Therefore, weakly absorbing gases can be measured more effectively.

[0006] Such optical sensors suffer from several drawbacks. The arrangement of the incandescent lamp and light detector at the concave mirror necessitates high-cost manufacturing due to the curved surface of the mirror. Furthermore, the light sources widely used in optical gas sensors emit a relatively broad light spectrum. This means they emit not only wavelengths necessary for measuring gas concentration but also wavelengths that are less important for concentration measurement and must be filtered out by bandpass filters to avoid measurement errors. This negatively impacts the efficiency of the optical gas sensor. In addition, incandescent lamps are particularly problematic because a large portion of the electrical energy is converted into heat, which must be dissipated as heat loss. This results in excessive energy consumption for the gas sensor, which is particularly detrimental for mobile applications powered by an internal current source such as a battery. Increased power consumption significantly reduces battery life and, consequently, the operating time of the mobile gas sensor. Summary of the Invention

[0007] Based on the prior art, the objective of this invention is to provide an optical gas sensor that at least partially avoids these drawbacks. Therefore, the objective of this invention is to provide an optical gas sensor capable of quantitatively measuring the concentration of weakly light-absorbing gases, and with improved efficiency.

[0008] The aforementioned task is accomplished by an optical gas sensor having features according to the invention for quantitatively measuring the concentration of one or more gases. Further features and details of the invention are derived from the specification and accompanying drawings.

[0009] Therefore, this task is solved by an optical gas sensor for quantitatively measuring the concentration of one or more gases, the optical gas sensor having a radiation source for emitting light waves, a sample cell for containing the gas to be measured, and a detector for measuring the light intensity. The radiation source has at least one emitter of light waves, such as an LED, and is configured to simultaneously and separately emit at least one first wavelength and at least one second wavelength different from the first wavelength. The emitter is preferably configured to emit a spectrum with a full width at half maximum (FWHM) of at most 50% of the centroid wavelength. Furthermore, the emitter is preferably also configured to emit a discrete spectrum with a FWHM of at most 20% of the centroid wavelength. The detector is configured to quantitatively detect the intensity of the emitted first and second wavelength light waves. The emitter is preferably configured to convert at least 80% of the electrical energy consumed by the emitter into light waves.

[0010] The idea behind this invention is that the efficiency of optical gas sensors can be significantly improved by using such an emitter. This results in less heat generation and therefore less electrical energy consumption when generating light waves. When converting electrical energy into light waves via an LED, less heat is generated compared to, for example, via an incandescent lamp used in many conventional gas sensors. Therefore, the gas sensor consumes less power during operation. This is particularly advantageous for mobile applications, as it significantly extends the charging cycles or battery life of the mobile application's battery.

[0011] By separately emitting light waves of different wavelengths, a main signal and a reference signal can be generated, wherein the reference signal can be used to verify the measurement results of the main signal. Here, an embodiment for quantitatively determining methane should be exemplified. Here, the measurement wavelength of the measurement signal is selected to have approximately 3.2 μm, and a suitable reference wavelength for the reference signal is derived to be 3.1 μm and / or 3.9 μm.

[0012] The more different wavelengths of light that can be generated more separately, the more gases can be quantitatively determined using the gas sensor according to the invention. This results in the emitter emitting only a relatively narrow bandwidth spectrum. The light waves are preferably in the infrared range due to the absorption characteristics of the gas.

[0013] The emitter configured as an LED has the advantage that it can emit relatively short light pulses, and unlike incandescent lamps, it does not have afterglow after the light pulse. Individual LEDs can therefore emit light pulses substantially sequentially, allowing, for example, measurement and reference signals to extend through a substantially constant gas mixture arranged in a sample cell. This avoids or reduces measurement errors. Furthermore, LEDs are suitable for emitting relatively narrow bandwidth spectra and exhibit particularly good efficiency in converting electrical energy into light waves. The special optical characteristics of LEDs in their emitter configuration are known, for example, from the field of optical signal transmission using optical waveguides. In particular, the narrow bandwidth of the emitted spectrum due to the full width at half maximum (FWHM) and centroid wavelength is illustrated, for example, in DE 40 11 462 C2.

[0014] The detector is, for example, a photodiode that generates an electric current when light waves strike it, the intensity of which is related to the intensity of the light waves. Therefore, the absorbance of light waves of a given wavelength through a gas, as well as the type of gas or the composition of a gas mixture, can be determined. Preferably, at least one detector is configured to detect a large number of different, preferably non-overlapping, wavelength ranges. Thus, at least two different gases can be detected in a simple and cost-effective manner using a sample cell and a detector.

[0015] A corresponding bandpass filter can be placed before the detector, for example, to avoid interference. Depending on the design of the gas sensor, the bandpass filter can be constructed according to the radiation source. Therefore, in the case of a radiation source capable of emitting, for example, light waves of four different wavelengths, a bandpass filter is preferably arranged in front of the detector that allows all four wavelengths to pass through. Another advantage of the bandpass filter is that light waves that do not pass through it can be reflected by the bandpass filter. Therefore, it can be advantageous to arrange the bandpass filter at the emitter or radiation source so that, in the case of multiple radiation sources with bandpass filters arranged in front of them, less reflective surface loss occurs compared to the absence of a bandpass filter. The sample cell is preferably constructed such that interference, such as light waves from the surrounding environment of the gas sensor, cannot penetrate the sample cell or reach the detector. This ensures the necessary accuracy of the gas sensor's measurement results. Furthermore, the air exchange between the sample cell and the surrounding environment of the gas sensor is preferably adjustable or relatively small, so that the gas mixture in the sample cell remains substantially constant during a measurement cycle in which the measurement signal and reference signal are emitted at least once. In this way, measurement errors are also avoided or reduced.

[0016] Furthermore, it can be specified that the radiation source has at least one first emitter and at least one second emitter, wherein the first emitter is configured to emit light waves of a first wavelength and the second emitter is configured to emit light waves of a second wavelength. The detector and / or at least one emitter has at least one optical filter, such as a bandpass filter. The emitter is preferably configured as an LED. Such a radiation source can be easily manufactured and requires relatively little structural space. Particularly preferably, it can be specified that the radiation source is configured to emit a discrete light spectrum. Thus, the radiation source is configured to generate light waves of only specific wavelengths or a relatively narrow wavelength range. Furthermore, it can be specified that a bandpass filter is arranged in front of the radiation source, which further narrows the wavelength range generated by the radiation source. Particularly preferably, a large number of light waves with wavelengths spaced apart from each other within the IR spectrum can be generated by the radiation source.

[0017] Preferably, the sample cell may be configured with a mirror assembly comprising a plane mirror and a concave mirror arranged opposite the plane mirror, wherein the optical axis of the concave mirror is arranged substantially perpendicular to the plane mirror. The distance between the concave mirror and the plane mirror preferably corresponds to an integer fraction of the radius of curvature of the concave mirror. Before the light beam reaches the photosensor, it passes through the sample cell multiple times, for example, four or six times, between the mirrors. This arrangement has the advantage that weakly absorbing gases can be measured even within the relatively compact structural dimensions of the gas sensor. Preferably, the radius of curvature of the concave mirror can be changed, or the concave mirror can be replaced with concave mirrors having different radii of curvature.

[0018] In this way, the optical path of the light wave within the gas sensor can be configured to be variable, such that the light wave is reflected at different frequencies between the concave and plane mirrors depending on the adjustment of the radius of curvature of the concave mirror, until the light wave reaches the detector. This has the advantage that the gas sensor can be used not only for measuring gases with weak light absorption but also for measuring gases with strong light absorption.

[0019] Alternatively, the mirror assembly can have two plane mirrors arranged substantially facing each other, wherein corresponding reflections of the light beam can be achieved, for example, by adjusting the radiation source or at least one mirror. This variant can be manufactured particularly simply and cost-effectively.

[0020] Preferably, the angle of incidence with respect to the surface normal of the mirror is as small as possible, that is, the light wave is incident on the mirror approximately perpendicularly. This reduces the influence of interfering factors that cause light wave absorption, such as moisture on the mirror surface.

[0021] Furthermore, it is preferable to specify that the radiation source and / or detector is arranged at the plane mirror. Therefore, the radiation source and detector arranged in this way can be easily isolated from the interior of the sample cell, for example, by means of transparent glass or a bandpass filter, so that they do not come into direct contact with the measuring gas. This is particularly advantageous when the fluid arranged in the sample cell may potentially damage the radiation source or detector. Furthermore, arranging the radiation source and detector on a plane has the advantage that they can be arranged on a common plate. Such an arrangement can therefore be manufactured particularly simply and cost-effectively. More preferably, the distance between the radiation source and the point where the optical axis intersects with the plane mirror corresponds to the distance between the detector and that intersection point. Such a plane mirror can be installed particularly easily due to its symmetry.

[0022] In a particularly preferred design of the gas sensor according to the invention, the radiation source and detector are arranged at the sample cell such that light waves emitted by the radiation source directly strike the detector. In this advantageous arrangement, the radiation source and detector are not arranged at the same mirror, so that light waves strike the detector without being reflected. This has the advantage of identifying particularly strongly absorbing gases. Such a gas sensor preferably has at least two radiation sources spaced apart from each other, at least one of which is arranged at the sample cell such that light waves emitted by the radiation source strike the detector only through the mirror assembly.

[0023] The gas sensor is preferably configured such that the radiation source and the detector are spaced apart at the sample cell.

[0024] The emitter is configured to emit light waves with a guided light path. Here, the plane mirror and concave mirror are considered components of the sample cell for the purposes of this invention. Particularly advantageously, such an arrangement is suitable for gas sensors designed to measure gases that absorb light waves only weakly. The light waves are emitted as a guided light path that has essentially no diffuse radiation. This has the advantage that the emitted light is used particularly efficiently to detect the gas. Furthermore, this is especially advantageous for gas sensors suitable for detecting gases with weak light absorption, as it allows for a particularly compact type of gas sensor structure.

[0025] Advantageously, exactly one detector is positioned at the sample cell. This detector is configured to quantitatively detect light waves emitted essentially only by the radiation source. For this purpose, the detector can, for example, have a corresponding bandpass filter. Such a sensor is particularly suitable for applications requiring high precision. Alternatively, the detector can be configured to quantitatively detect a broad spectrum of light waves of different wavelengths, where the light waves emitted by the radiation source are a portion of this spectrum. Such a sensor can be manufactured at a particularly cost-effective rate. Using only one detector has the advantage of saving the cost of other detectors. Furthermore, the sample cell has a larger reflective surface than the mirror with only one detector and the same structural dimensions, since the detector is located in only one position on the mirror. This, in particular, improves the accuracy when measuring gases that absorb only weak light waves.

[0026] In another embodiment of the invention, at least two radiation sources are arranged spaced apart from each other at the sample cell. This has advantages, for example, that each radiation source can have a less complex structure. Furthermore, defective radiation sources can be replaced independently of each other. This reduces maintenance or replacement costs. In a preferred improvement of the invention, four radiation sources are arranged at the sample cell.

[0027] Particularly preferred is that the sample cell has two detectors configured to measure the light intensity of different radiation sources or different emitters (such as different LEDs) of the two radiation sources. Here, the detectors are preferably arranged such that each detector can detect only the light wave from one radiation source. Alternatively or additionally, the radiation sources can be switched or modulated differently. This arrangement has the advantage that multiple measuring gases arranged in the sample cell can be simultaneously and quantitatively determined.

[0028] Particularly preferably, the gas sensor has at least one dual bandpass filter, which is preferably arranged at the radiation source. More preferably, the gas sensor has at least one triple bandpass filter, which is preferably arranged at the radiation source. In this way, the spectrum of light waves emitted by the respective radiation source can be divided into wavelengths or wavelength spectra that are clearly separated from each other. Attached Figure Description

[0029] Other improvements to the invention will be derived from the following description of several embodiments of the invention, illustrated in the accompanying drawings. All features and / or advantages known from the specification or drawings, including structural details and spatial arrangements, can reflect the essence of the invention not only individually but also in different combinations. The drawings are as follows:

[0030] Figure 1 A side view of a first embodiment of the gas sensor according to the present invention is shown schematically;

[0031] Figure 2 The schematic diagram shows the response from... Figure 1 A top view of the plane mirror of the gas sensor according to the present invention;

[0032] Figure 3 A top view schematically illustrating a plane mirror of a second embodiment of a gas sensor according to the invention; and

[0033] Figure 4 A top view of a plane mirror according to a third embodiment of the gas sensor of the present invention is shown schematically. Detailed Implementation

[0034] The optical gas sensor 1 according to the present invention is in Figure 1The first embodiment shown in the drawing has a sample cell 3 that is substantially cylindrical, in which the gas G or gas mixture to be measured is arranged. The sample cell 3 has at least one opening not visible in this view for exchanging the gas G arranged in the sample cell 3 with gas G from the surrounding environment of the gas sensor 1. A plane mirror 6 is arranged at one end face of the sample cell 3, and a concave mirror 7 is arranged at the other end face. The plane mirror has a radiation source 2, which is configured to emit light waves L of two different wavelengths in the IR spectrum and is aligned with the direction of the concave mirror 7. The radiation source 2 has an emitter 5 configured as an LED and is configured such that the light waves L of different wavelengths can be emitted independently of each other. An optical filter, such as a bandpass filter, a double bandpass filter, or a triple bandpass filter, is optionally arranged in front of the emitter 5. A detector 4 is arranged at the plane mirror 6 spaced apart from the light source and aligned with the direction of the concave mirror 7. The detector 4 is configured to measure the intensity of the light waves. The concave mirror 7 has an optical axis 8, which is arranged substantially perpendicular to the plane mirror 6. In the first embodiment, the distance between the concave mirror 7 and the emitter 5 is approximately half the radius of curvature of the concave mirror 7. When using an optical filter arranged in front of the emitter 5, this distance is slightly greater than half the radius of curvature of the concave mirror 7. Two distinct light beams L emitted by the radiation source 2 are depicted in the figure, with the first beam L schematically represented by a solid line and the second beam L schematically represented by a dashed line. The emitted light beams L are reflected from the concave mirror 7 onto the plane mirror 6 and then back onto the concave mirror 7, until they reach the detector 4. This arrangement is particularly advantageous when the gas G to be measured absorbs only a weak amount of light wave L and when the gas sensor 1 must have the most compact possible structural dimensions.

[0035] Figure 2 A planar mirror 6 of a first embodiment of the gas sensor 1 is shown in top view. The planar mirror 6 has: a first aperture 9 in which a radiation source 2 having a first emitter 5a and a second emitter 5b is arranged; and a second aperture 10 in which a detector 4 is arranged. The first embodiment of the gas sensor 1 according to the invention is particularly suitable for quantitatively measuring gas concentration or for detecting a single gas G. For this purpose, light waves L of different wavelengths can be emitted alternately by the first emitter 5a and the second emitter 5b and / or modulated with different frequencies. The detector 4 determines the intensity of the light waves L that are partially absorbed. Here, the light wave emitted by the second emitter 5b can be used as a reference signal. In this embodiment, the first emitter 5a and the second emitter 5b are configured as LEDs.

[0036] exist Figure 3The planar mirror 6 of a second embodiment of the gas sensor 1 according to the present invention is illustrated in a top view. The planar mirror 6 has: a first aperture 9 in which a radiation source 2 having a first emitter 5a, a second emitter 5b, and a third emitter 5c is arranged; and a second aperture 10 in which a detector 4 is arranged. Optical filters, such as bandpass filters, dual bandpass filters, or triple bandpass filters, are optionally arranged in front of the first emitter 5a and / or the second emitter 5b and / or the third emitter 5c. In this embodiment, the first emitter 5a, the second emitter 5b, and the third emitter 5c are configured as LEDs. The difference between the second embodiment of the gas sensor 1 and the first embodiment is that the radiation source 2 additionally has a third emitter 5c. The second embodiment of the gas sensor 1 according to the present invention is particularly suitable for quantitatively measuring or detecting two different gases G. For this purpose, light waves L of different wavelengths can be emitted by the first emitter 5a, the second emitter 5b, and the third emitter 5c. The detector 4 determines the intensity of the light waves L that are partially absorbed. Here, for example, the light wave emitted by the third emitter 5c is used as a reference signal.

[0037] exist Figure 4 The planar mirror 6 of a third embodiment of the gas sensor 1 according to the present invention is illustrated in a top view. The planar mirror 6 has two first holes 9 and two second holes 10. A first radiation source 2a having a first emitter 5a and a second emitter 5b is arranged in one of the first holes 9. A second radiation source 2b having a third emitter 5c and a fourth emitter 5d is arranged in the other first hole 9. A first detector 4a is arranged in one of the second holes 10, and a second detector 4b is arranged in the other second hole 10. The difference between the third embodiment and the first embodiment of the gas sensor 1 is that the gas sensor 1 has two radiation sources 2 and two detectors 4. The light wave emitted by the first radiation source 2a can preferably be detected only or substantially by the first detector 4a, while the light wave L emitted by the second radiation source 2b can be detected only or substantially by the second detector 4b. During operation, the first radiation source 2a and the second radiation source 2b can simultaneously emit light wave L. The first emitter 5a, the second emitter 5b, the third emitter 5c, and the fourth emitter 5d are configured as LEDs in this embodiment. The third embodiment of the gas sensor 1 according to the present invention is particularly suitable for simultaneously and quantitatively measuring or detecting two different gases G in a gas mixture. A bandpass filter arranged in front of the radiation source 2 or detector 4 acts as a mirror for the light waves from the other radiation source 2. This improves the efficiency of the gas sensor 1.

[0038] List of reference numerals

[0039] 1 Gas sensor

[0040] 2. Radiation source

[0041] 2a First radiation source

[0042] 2b Second radiation source

[0043] 3 Sample Cell

[0044] 4 Detectors

[0045] 4a First Detector

[0046] 4b Second Detector

[0047] 5. Launchers

[0048] 5a First Launcher

[0049] 5b Second Launcher

[0050] 5c Third Launcher

[0051] 5d Fourth emitter

[0052] 6. Plane mirror

[0053] 7. Concave mirror

[0054] 8 optical axes

[0055] 9 First Hole

[0056] 10 Second Hole

[0057] G gas

[0058] L light wave

Claims

1. An optical gas sensor (1) for quantitatively measuring the concentration of one or more gases, the optical gas sensor (1) comprising: a radiation source (2) for emitting light waves (L), a sample cell (3) for containing the gas (G) to be measured, and a detector (4) for measuring light intensity, characterized in that, The radiation source (2) has at least one first emitter (5a) configured as an LED for emitting light waves (L) and a second emitter (5b) configured as an LED. - The first emitter (5a) is configured to emit light waves (L) of a first wavelength as the main signal. - An optical filter is arranged in front of the first emitter (5a). - The second emitter (5b) is configured to emit a second wavelength of light (L) that is different from the first wavelength as a reference signal for verifying the measurement results of the main signal. - An optical filter is arranged before the second emitter (5b), wherein the first wavelength and the second wavelength light waves (L) are emitted separately from each other, wherein the emitters (5a, 5b) are respectively configured to emit a spectrum with a full width at half maximum of 50% of the centroid wavelength, wherein the detector (4) is configured to quantitatively detect the intensity of the emitted first wavelength and the second wavelength light waves (L), and wherein the sample cell (3) has a mirror device, the mirror device having a plane mirror (6) and a mirror with respect to the sample. A plane mirror (6) is positioned opposite a concave mirror (7), wherein the optical axis (8) of the concave mirror (7) is arranged perpendicular to the plane mirror (6), and the radiation source (2) and the detector (4) are arranged at the plane mirror (6). The optical path of the light wave (L) within the gas sensor is configured to be variable, such that the light wave is reflected at different frequencies between the concave mirror (7) and the plane mirror (6) according to the adjustment of the radius of curvature of the concave mirror (7) until the light wave hits the detector (4). - Wherein the first emitter (5a) and the second emitter (5b) are arranged in the first hole (9) arranged in the plane mirror (6), - The detector (4) is arranged in the second hole (10) arranged in the plane mirror (6), At least two radiation sources (2) are arranged at intervals between each other in the sample pool (3). And the sample cell (3) has at least two detectors (4), wherein the detectors (4) are configured to measure the light intensity of different radiation sources (2) or the light intensity of different emitters (5) of the two radiation sources (2).

2. The optical gas sensor (1) according to claim 1. Its features are, The radiation source (2) is configured to emit a discrete optical spectrum with a maximum full width at half maximum (FWHM) of 20% of the centroid wavelength.

3. The optical gas sensor (1) according to claim 1 or 2. Its features are, The radiation source (2) and detector (4) are arranged at the sample cell (3) such that the light wave (L) emitted by the radiation source (2) directly hits the detector.

4. The optical gas sensor (1) according to claim 1 or 2. Its features are, The radiation source (2) and the detector (4) are arranged at the sample cell (3) at a distance, wherein the first emitter (5a) and the second emitter (5b) are respectively configured to emit light waves (L) with guided light paths.

5. The optical gas sensor (1) according to claim 1 or 2. Its features are, Exactly one detector (4) is placed at the sample cell (3).

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