Method and apparatus for determining the concentration of a component in a fluid

Abstract

A method and apparatus for determining the concentration of a component in a fluid are described. The method comprises the following steps: providing a first light intensity (IR1A) interacting with the fluid at a first time point (A) from a first optical sensor (1), and providing a second light intensity (IR1B) interacting with the fluid at a second time point (B), wherein the first light intensity (IR1A) is different from the second light intensity (IR1B); and providing a third light intensity (IR2A) interacting with the fluid at the first time point (A) from a second optical sensor (2), and providing a fourth light intensity (IR2B) interacting with the fluid at the second time point (B). The method further comprises determining the concentration of the component in the fluid at the first time point (A) and / or the second time point (B) measured by the first optical sensor (1) based on the first light intensity (IR1A), the second light intensity (IR1B), the third light intensity (IR2A), the fourth light intensity (IR2B), the first concentration function (func1), the second concentration function (func2) and the correlation information (Corr).

Description

Technical Field

[0001] The invention relates to a method and a device for determining the concentration of a component in a fluid, the method compensating for measurement errors due to aging of a sensor for measuring the component, and to a sensor device in which the method is implemented. Background Art

[0002] The present invention relates to a maintenance-free sensor with a self-calibration function for compensating for measurement errors such as drift errors that occur over time. The present invention is applicable to any type of sensor, but may be particularly applicable to gas sensors, and more specifically carbon dioxide (CO2) sensors. Today, measurement errors can be handled in a variety of ways as described below:

[0003] The current standard method for calibrating sensors is the so-called ABC method (Automatic Baseline Correction), where the background level is monitored by finding the minimum reading of the sensor. This is assumed to be 400 ppm and is used as the calibration point.

[0004] Some sensors use dual sources, where one source is rarely activated and is therefore assumed to be drift-free. This source is used to calibrate the other source. This approach can compensate for aging of the primary source.

[0005] Some sensors use dual detectors, where one detector measures a reference wavelength outside the IR-active region of the target gas. The reference signal is used to normalize the light intensity to compensate for light intensity drift.

[0006] Other sensors use dual detectors with the same filters on both detectors and different path lengths, where the closest detector measures the light intensity and can be used for normalization. The effective path length will then be the difference between the two detectors. Such a sensor is described in WO 2012166585 A2.

[0007] Another known solution is a scanning filter, such as an adjustable Fabry Perot-filter, which can work according to the same principle as 3. (https: / / www.vaisala.com / en / vaisala-carbocapr-technology-demanding-envir onments), scanning between a reference wavelength and a measurement wavelength.

[0008] Another solution is to use pressure modulation for drift compensation. Summary of the invention

[0009] The object of the present invention is to provide a method and an optical sensor device for determining the concentration of a component in a fluid, which method and sensor device take into account drift errors of the optical sensor device, wherein the drift errors are taken into account in an alternative manner to prior art methods and devices.

[0010] The above objects are achieved by a method and an apparatus according to the independent claims.

[0011] Further advantages are provided by the features of the dependent claims.

[0012] According to a first aspect of the present invention, a method for determining the concentration of a component in a fluid is provided. The method comprises the following steps: providing a first light intensity of light interacting with the fluid at a first time point from the first optical sensor, and providing a second light intensity of light interacting with the fluid at a second time point, the first optical sensor being configured to measure the intensity of the light interacting with the fluid, wherein the first light intensity is different from the second light intensity. The method further comprises the following steps: providing a third light intensity of light interacting with the fluid at a first time point from the second optical sensor, and providing a fourth light intensity of light interacting with the fluid at a second time point, the second optical sensor being configured to measure the intensity of the light interacting with the fluid. The method further comprises the following steps: providing a first concentration function, the first concentration function defining the concentration of the component in the fluid as a function of the light intensity from the first optical sensor. The method further comprises the following steps: providing a second concentration function, the second concentration function defining the concentration of the component in the fluid as a function of the light intensity from the second optical sensor, wherein the first concentration function and the second concentration function have different dependencies on light intensity. The method also includes the following steps: providing correlation information, which defines the correlation between the first concentration function and the second concentration function, and determining the concentration of the component in the fluid measured by the first optical sensor at the first time point and / or the second time point based on the first light intensity, the second light intensity, the third light intensity, the fourth light intensity, the first concentration function, the second concentration function and the correlation information.

[0013] With the method according to the first aspect, the advantage is provided that compensation of the drift can be achieved simply by measuring two different concentrations of a component at two different points in time.

[0014] This method relies on measuring a component at different times and at different unknown concentrations to deduce the concentration of that component. In contrast, prior art methods may have different concentration functions but only measure at one point in time.

[0015] With this method, maintenance can be avoided whenever there is a change in the gas concentration in the environment.

[0016] The time difference between the first time point and the second time point depends on how fast the concentration of the component changes. If the change rate is fast, the time difference may be on the order of seconds. If the change rate is slow, the time difference may be on the order of hours or days. The most important factor is that the first light intensity is different from the second light intensity. However, the time difference should be short enough so that drift of the optical sensor device does not affect the light intensity. Drift of the optical sensor device typically has an effect on the light intensity on a time scale of weeks or months.

[0017] The fact that the first concentration function and the second concentration function have different dependencies on light intensity means that a change in the concentration of the component will result in a ratio between the first light intensity and the second light intensity that is different from a ratio between the third light intensity and the fourth light intensity.

[0018] The feature of providing information defining a correlation between the first concentration function and the second concentration function means that the relationship between the first concentration function and the second concentration function is known.

[0019] The first optical sensor and the second optical sensor may be configured to measure the concentration of the same component. In this case, the correlation information defines that the first concentration function provides the same concentration as the second concentration function.

[0020] If the first optical sensor and the second optical sensor are configured to measure concentrations of different components, the correlation is a function that describes the relationship between them. An example of this is a device configured to measure ethanol and carbon dioxide in a person's breath. The ethanol concentration close to the mouth depends on the ethanol concentration in the person's blood. Further away from the mouth, the concentrations of carbon dioxide and ethanol decrease by the same factor. Therefore, the concentration of carbon dioxide can be expressed as:

[0021] CmeasCO2=Cbackground+k CmeasEtOH,where

[0022] In this case, k is an unknown constant that depends on the intoxication level of the subject. In this case, "k" can be obtained by including data from more concentrations during the breath. k is constant during the test because the intoxication level remains constant.

[0023] The step of determining the concentration of a component in the fluid measured by the first optical sensor may include the following steps: determining a first zero signal from the first optical sensor in the absence of any component in the fluid, and / or determining a second zero signal from the second optical sensor in the absence of any component in the fluid, wherein the first concentration function is also a function of the first zero signal, and the second concentration function is also a function of the second zero signal.

[0024] Determining the first and second zero signals may be advantageous when determining the concentration of a component in a fluid, but depending on how the determination is performed, it is not always necessary to determine the first and second zero signals as part of the result.

[0025] A pair of light intensities from a first optical sensor and a light intensities from a second optical sensor may be provided at a plurality of time points, wherein the first time point and the second time point are selected such that the first sensor signal is different from the second sensor signal. Providing this pair of light intensities continuously facilitates providing the light intensities. These light intensities may be stored in a computer file and may be retrieved when necessary.

[0026] According to a second aspect of the invention, there is provided an optical sensor device for determining the concentration of a component in a fluid. The optical sensor device comprises a first optical sensor configured to measure the intensity of light interacting with the fluid, wherein the concentration of the component in the fluid is defined by a first concentration function, which is a function of the light intensity from the first optical sensor. The optical sensor device further comprises a second optical sensor configured to measure the intensity of light interacting with the fluid, wherein the concentration of the component in the fluid is defined by a second concentration function, which is a function of the light intensity from the second optical sensor, wherein the first concentration function and the second concentration function have different dependencies on the light intensity. The optical sensor device is characterized in that it is configured to measure a first light intensity of light interacting with the fluid at a first point in time with the first optical sensor, and to measure a second light intensity of light interacting with the fluid at a second point in time, wherein the first light intensity is different from the second light intensity. The optical sensor is configured to measure a third light intensity of light interacting with the fluid at a first time point with a second optical sensor, and to measure a fourth light intensity of light interacting with the fluid at a second time point, and to determine the concentration of a component in the fluid at the first time point and / or the second time point measured by the first optical sensor based on the first light intensity, the second light intensity, the third light intensity, the fourth light intensity, the first concentration function, the second concentration function, and correlation information defining the correlation between the first concentration function and the second concentration function.

[0027] With the optical sensor device according to the second aspect, the advantage is provided that compensation of the drift can be achieved simply by measuring two different concentrations of a component at two different points in time.

[0028] The invention relies on measuring a component at different times and at different unknown concentrations to deduce the concentration of that component. In contrast, prior art devices may have different concentration functions but only measure at one point in time.

[0029] With the optical sensor according to the second aspect, maintenance can be eliminated whenever there is a change in the gas concentration in the environment.

[0030] The optical sensor device knows the first concentration function and the second concentration function so that the concentration of the component can be determined.

[0031] The optical sensor device can be arranged so that the time difference between the first time point and the second time point depends on the rate of change of the concentration of the component. If the rate of change is fast, the time difference may be of the order of seconds. If the rate of change is slow, the time difference may be of the order of hours or days. The most important factor is that the first light intensity is different from the second light intensity. However, the time difference should be short enough so that drift of the optical sensor device does not affect the light intensity. Drift typically has an effect on a time scale of weeks or months.

[0032] The first concentration function and the second concentration function have different dependencies on light intensity, which means that a change in the concentration of the component will result in a different ratio between the first light intensity and the second light intensity than a ratio between the third light intensity and the fourth light intensity.

[0033] The feature of providing information defining a correlation between the first concentration function and the second concentration function means that the relationship between the first concentration function and the second concentration function is known.

[0034] The first optical sensor and the second optical sensor may be configured to measure the concentration of the same component. In this case, the correlation information defines that the first concentration function provides the same concentration as the second concentration function.

[0035] If the first optical sensor and the second optical sensor are configured to measure concentrations of different components, the correlation is a function describing the relationship between them, as explained and exemplified above in relation to the first aspect of the invention.

[0036] The optical sensor device can be configured to determine the concentration of a component in a fluid measured by a first optical sensor by determining a first zero signal from the first optical sensor in the absence of any component in the fluid, and / or determining a second zero signal from the second optical sensor in the absence of any component in the fluid, wherein the first concentration function is also a function of the first zero signal and the second concentration function is also a function of the second zero signal.

[0037] The optical sensor device may be configured to measure a pair of light intensity from a first optical sensor and light intensity from a second optical sensor at a plurality of time points, and wherein the first time point and the second time point are selected such that the first sensor signal is different from the second sensor signal. This provides the same advantages as described above in relation to the first aspect of the invention.

[0038] The first optical sensor may include a fluid cavity and a first light detector configured to measure the intensity of light interacting with the fluid in the fluid cavity. The second optical sensor may include a second light detector configured to measure the intensity of light interacting with the fluid in the fluid cavity. By having such a fluid cavity, the absorption length in the fluid is well defined. The difference between the first concentration function and the second concentration function can be obtained by changing the cross-section of the fluid cavity.

[0039] The first optical sensor and the second optical sensor may be configured to measure light intensity in the same wavelength range. It is preferred if the first optical sensor and the second optical sensor are to measure the same component in the fluid.

[0040] The optical sensor device may comprise a first band pass filter in front of the first light detector and a second band pass filter in front of the second light detector. Band pass filters in front of the light detectors are a simple way to provide filtering in a wavelength range. Another way to provide wavelength filtering is to use a light source that emits light in the desired wavelength range.

[0041] Advantageous detection wavelengths are in the wavelength range of 1-10 μm, and preferably in the wavelength range of 2-6 μm.

[0042] The optical sensor may be configured such that light has a longer travel distance through the fluid to the first light detector than to the second light detector.Alternatively or additionally, the filters may have different filtering properties.

[0043] The optical sensor device may include a first light source and a second light source, the light emitted by the first light source interacting with the fluid in the fluid cavity, and the light emitted by the second light source interacting with the fluid in the fluid cavity, wherein the first light detector is configured to measure the intensity of light from the first light source, and wherein the second light detector is configured to measure the intensity of light from the second light source. Arranging the sensors in this manner allows the optical sensors to be separated from each other.

[0044] The optical sensor device can be configured with two light sources and one light detector. According to one approach, wavelength filtering can be performed at the light source side, each detector has a different wavelength range, and a single detector detects both wavelength ranges. According to another approach, wavelength filtering can be performed anywhere, and a single detector detects light from both light sources. In both approaches, the first light source can be pulsed with a first frequency, and the second light source can be pulsed with a second frequency. The detector separates the different detection signals by electronically separating the detected signals.

[0045] In the following description of embodiments of the present invention, reference is made to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 An optical sensor device according to one embodiment of the present invention is shown.

[0047] Figure 2 An optical sensor device according to an alternative embodiment of the invention is shown.

[0048] Figure 3 An optical sensor device according to an alternative embodiment of the invention is shown.

[0049] Figure 4 An optical sensor device arranged at a road intersection is shown according to an alternative embodiment. DETAILED DESCRIPTION

[0050] In the following description of embodiments of the present invention, reference will be made to the accompanying drawings. Similar features in different drawings will be given the same reference numerals.

[0051] Figure 1 An optical sensor device 100 for determining the concentration of a component in a fluid is shown. The optical sensor device 100 comprises a first optical sensor 1 comprising a first light source 3, a first light detector 4, a second light source 5 and a second light detector 6. The optical sensor device 100 further comprises a fluid chamber 7 arranged to carry a fluid. Figure 1In the embodiment of the embodiment, the fluid cavity 7 is shown as a space into which the fluid enters. The first light source 3 is configured to emit light to the fluid cavity, the light interacts with the fluid in the fluid cavity 7 and is directed toward the first light detector 4. The second light source 5 is configured to emit light to the fluid cavity 7, the light interacts with the fluid in the fluid cavity 7 and is directed toward the second light detector 5. The first light source 3 is configured to emit light of a wavelength corresponding to the absorption peak of the component to be detected in the fluid. In the embodiment described, the second light source 5 is configured to emit light of the same wavelength as the first light source 3. The first light detector 4 (and therefore the first optical sensor 1) is configured to measure the intensity of the light from the first light source 3. The second light detector 6 (and therefore the second optical sensor 2) is configured to measure the intensity of the light from the second light source 5. The width of the fluid cavity 7 defines a first absorption path length L1 of the light from the first light source 3 to the first light detector 4. The height of the fluid cavity 7 defines a second absorption path length L2 from the second light source 5 to the second light detector 6. The first absorption length L1 is greater than the second absorption length. In the present embodiment, the first light source 3 and the second light source 5 are configured to emit light of the same wavelength, which is adapted to the absorption peak of the component to be detected. The first light detector 4 and the second light detector 6 are arranged to detect light interacting with the fluid in the fluid cavity. The first zero signal is represented as I01, that is, the light intensity detected by the first light detector 4 when there is no component in the fluid. The second zero signal is represented as I02, that is, the light intensity detected by the second light detector 6 when there is no component in the fluid. The first light detector 4 and the second light detector 6 are both connected to a control unit 20, which is configured to analyze the detected signals. The control unit 20 can be implemented as, for example, a computer or an FPGA. The dotted line 21 illustrates that the first optical sensor 1, the second optical sensor 2 and the control unit 20 can be integrated in a common envelope.

[0052] When a certain component is present in the fluid, part of the light from the first light source 3 and the second light source 5 will be absorbed by the component in the fluid. The part of the light absorbed in the fluid depends on the length of the absorption path and the concentration of the component in the fluid. The light intensity IR1 detected by the first light detector 4 is a function of the component concentration Cmeas1 and the first zero signal I01. The light intensity detected by the second light detector 6 is a function of the component concentration and the second zero signal I02. Alternatively, the concentration Cmeas1 of the component can be expressed as a function of the light intensity detected by the first light detector 4, that is, Cmeas1=func1(IR1, I01), where func1(IR1, I01) is a function determined in advance. Accordingly, the concentration of the component measured by the second optical sensor 2 can be expressed as Cmeas2=func2(IR2, I02), where func2(IR2, I02) is a function determined in advance. Due to the different absorption path lengths L1 and L2, the first concentration function (func1) and the second concentration function (func2) have different dependencies on light intensity.

[0053] The optical sensor device 100 is configured to measure, with the first optical sensor 1, a first light intensity IR1A of light interacting with the fluid at a first time point A, and to measure a second light intensity IR1B of light interacting with the fluid at a second time point B, the first light intensity IR1A being different from the second light intensity IR1B. The optical sensor device 100 is configured to measure, with the second optical sensor 2, a third light intensity IR2A interacting with the fluid at the first time point A, and to measure a fourth light intensity IR2B interacting with the fluid at the second time point B. The third light intensity IR2A will be different from the fourth light intensity IR2B.

[0054] Different light intensities can be achieved in many different ways. The optical device 100 can be configured to measure a pair of light intensity IR1 from the first optical sensor 1 and light intensity IR2 from the second optical sensor 2 at multiple time points. The selection of the first time point and the second time point makes the first sensor signal IR1A different from the second sensor signal IR1B. The pair of light intensity IR1 from the first optical sensor 1 and light intensity IR2 from the second optical sensor 2 can be stored in a memory in the order of occurrence time.

[0055] Then, the concentration of the component in the fluid at the first time point A and / or the second time point B measured by the first optical sensor 1 can be determined based on the first light intensity IR1A, the second light intensity IR1B, the third light intensity IR2A, the fourth light intensity IR2B, the first concentration function func1, the second concentration function func2, and the correlation information Corr defining the correlation between the first concentration function func1 and the second concentration function func2.

[0056] This determination can be made according to the following description.

[0057] The concentration Cmeas1 measured by the first optical sensor 1 at the first time point A A must be equal to the concentration Cmeas2 measured by the second optical sensor 2 at the first time point A A , because they measure the same fluid, namely Cmeas1 A =Cmeas2 A And, at the second time point B, the concentration Cmeas1 measured by the first optical sensor 1 is B must be equal to the concentration Cmeas2 measured by the second optical sensor 2 at the second time point A B As long as the first time point is not too far from the second time point, the first zero signal I01 will not change, and the second zero signal I02 will not change. The time difference between the first time point and the second time point is usually less than one day. Knowing that Cmeas1 = func1 (IR1, I01) and Cmeas2 = func2 (IR2, I02), we get the following equation:

[0058] Cmeas1 A =Cmeas2 A ,Right now,

[0059] func1(IR1 A ,I01 A )=func2(IR2 A , I02 A )

[0060] Cmeas1 B =Cmeas2 B ,Right now,

[0061] func1(IR1 B ,I01 B )=func2(IR2 B , I02 B )

[0062] I01 A =I01 B

[0063] I02 A =I02 B

[0064] Only when Cmeas1 A With Cmeas1 BThe above equations can only be solved if the dependence of func1 on IR1 is different and the dependence of func2 on IR2 is different. The latter requirement can be expressed as: the relative derivative of the IR signal between the two sensors is different in the concentration region A to B. We can rewrite the function func1 as IR1=funcinv(Cmeas1, I0), where Cmeas1 is the concentration of the component measured by the first optical sensor. The derivative [dIR / dC] / IR of the first optical sensor 1 and the second optical sensor 2 must be different, that is, the first optical sensor 1 and the second optical sensor 2 should absorb different parts of the light when going from concentration A to concentration B.

[0065] Cmeas1 A With Cmeas1 B A larger difference between will result in reduced sensitivity to measurement errors (such as sensor noise) and therefore more accurate estimates of I01 and I02 as well as Cmeas1 and Cmeas2.

[0066] The above system of equations can be solved to obtain a unique solution for Cmeas and the value of I0. The resulting I0 can be used to compensate for long-term drift by updating the sensor's calibration parameters.

[0067] A calculation method implemented in a computer or microcontroller can be used to update I0. This can be done using a single event, or incrementally, or through iterations.

[0068] As an example, we may assume that the relationship between concentration and IR signal is described by the Beer-Lambert relationship.

[0069] IR1=I01·e -Cmeas1·Sens1 ,as well as

[0070] IR2=I02·e -Cmeas2·Sens2 .

[0071] As an example, we can assume the following. From the factory calibration we know that Sens1 = 0.001 [ppm-1], Sens2 = 0.0005 [ppm-1]. Therefore, they have different relative sensitivities, i.e. the derivatives [dIR1 / dC] / IR1 and [dIR2 / dC] / dIR2 are different.

[0072] At time A, we know that the signals of the two sensors are IR1 A =0.9836 and IR2 A = 0.7288. We also know that they are exposed to the same concentration of the target gas. At time B, the gas concentration changes, and we have IR1 B=0.7412 and IR2 B =0.6326. We can assume that the first zero signal I01 and the second zero signal I02 do not change at two moments because the drift is very slow. We also know that the two sensors are exposed to the same gas concentration. Then the equations become:

[0073] CA=-ln(IR1 A / I01) / Sens1=-ln(0.9836 / I01) / 0.001

[0074] CA=-ln(IR2 A / I02) / Sens2=-ln(0.7288 / I02) / 0.0005

[0075] CB=-ln(IR1 B / I01) / Sens1=-ln(0.7412 / I01) / 0.001

[0076] CB=-ln(IR2 B / I02) / Sens2=-ln(0.6326 / I02) / 0.0005

[0077] If we equate the top two equations with the bottom two, we get:

[0078] -ln(0.9836 / I01) / 0.001=-ln(0.7288 / I02) / 0.0005

[0079] -ln(0.7412 / I01) / 0.001=-ln(0.6326 / I02) / 0.0005

[0080] The system of equations can be solved, and we get the unknown first zero signal I01 and the unknown second zero signal I02 as:

[0081] I01=1.5

[0082] I02=0.9

[0083] The sensor may update the first zero signal I01 and the second zero signal I02 and thus compensate for the drift.

[0084] The first zero signal I01 and the second zero signal I02 can also be used to calculate the concentrations CA and CB as follows:

[0085] Cmeas1 A =-ln(IR1 A / I01) / Sens1=-ln(0.9836 / 1.5) / 0.001=422ppm

[0086] Cmeas2 A =-ln(IR2 A / I02) / Sens2=-ln(0.7288 / 0.9) / 0.0005=422ppm

[0087] Cmeas1 B =-ln(IR1 B / I01) / Sens1=-ln(0.7412 / I01) / 0.001=705ppm

[0088] Cmeas2 B =-ln(IR2 B / I02) / Sens2=-ln(0.6326 / I02) / 0.0005=705ppm

[0089] In reality, the function is more complicated than Beer-Lambert, but is still known and unique. Computational methods are used to solve the system of equations.

[0090] The optical sensor device 100 in the above example is configured to determine the concentration of a component in the fluid measured by the first optical sensor 1 by determining a first zero signal I01 from the first optical sensor 1 when no component is present in the fluid, and / or a second zero signal I02 from the second optical sensor 2 when no component is present in the fluid. However, it is also possible not to determine the first zero signal I01 and the second zero signal I02 separately, but to integrate them when calculating the concentrations Cmeas1 and Cmeas2.

[0091] The optical sensor device 100 may be configured to measure a pair of light intensities IR1 from the first optical sensor 1 at a plurality of time points. A and the light intensity IR2 from the second optical sensor 2 A , and wherein the first time point and the second time point are selected so that the first sensor signal IR1 A With the second sensor signal IR1 B different.

[0092] In such Figure 2 In the optical sensor device 100, the first optical sensor 1 and the second optical sensor 2 are configured to measure light intensity in the same wavelength range because the measured components are the same in the first optical sensor 1 and the second optical sensor 2. Therefore, the first bandpass filter 8 is the same as the second bandpass filter 9.

[0093] It is also possible to measure the concentrations of different gases with the first optical sensor 1 and the second optical sensor 2 if there is a known relationship between the concentrations of the two components, i.e. if the first component is correlated with the second component. The first optical sensor 1 is configured to measure component X and the first bandpass filter 8 is adapted to the absorption wavelength of component X. The second optical sensor 2 is configured to measure component Y and the second bandpass filter 9 is adapted to the absorption wavelength of component Y. For example, when analyzing breath, there is a known correlation between CO2 and humidity (i.e. H2O) which can be used for self-calibration. In this case, we have a correlation function "Corr" to describe the relationship between CO2 (component X) and H2O (component Y), so:

[0094] Cmeas1=Corr(Cmeas2)=Corr(CmeasY(IR2,I02))

[0095] Four measurements of two different gases at two different times can in this case be described as:

[0096] Cmeas1 A (IR1 A ,I01 A )

[0097] Cmeas1 B (IR1 B ,I01 B )

[0098] Cmeasas2 A (IR2 A , I02 A )

[0099] Cmeas2 B (IR2 B , I02 B )

[0100] And the resulting system of equations becomes:

[0101] Cmeas1 A (IR1 A ,I01 A )=Corr(Cmeasas2 A (IR2 A , I02 A ))

[0102] Cmeas1 B (IR1 B ,I01 B )=Corr(Cmeas2 B (IR2 B , I02B ))

[0103] I01 A =I01 B

[0104] I02 A =I02 B

[0105] This equation can be solved if the correlation function Corr is known. The correlation function Corr can be obtained from calibration or physical correlation. It can also be obtained from self-characterization by adding more data points with different concentrations.

[0106] The first zero signal I01 and the second zero signal I02 can be used to recalibrate the first optical sensor 1 and the second optical sensor 2. In this way, the drift of the first zero signal I01 and the second zero signal I02 can be compensated. The determination of the first zero signal I01 and the second zero signal I02 can be performed regularly, for example once a day.

[0107] In a breathalyzer, when ethanol vapor and CO2 are sensed, the correlation between these two gases is known. The first optical sensor 1 measures the concentration of carbon dioxide CO2, and the second optical sensor 2 measures the concentration of ethanol. We can write Cmeas1 as CmeasCO2 and Cmeas2 as CmeasEtOH. We can get:

[0108] CmeasCO2=Corr(CmeasEtOH)=Cbackground+k CmeasEtOH,where,

[0109] In this case, k is an unknown constant that depends on the intoxication level of the subject. In this case, "k" can be obtained by including more concentration data during the breath. The unknown constant k is constant during the test because the intoxication level remains constant.

[0110] Figure 3 An optical sensor device 100 consisting of a first optical sensor 1 and a second optical sensor 2 and a control unit 20 is schematically shown. Figure 3 The optical sensor device 100 and Figure 1 The only difference between the optical sensor device 100 is that Figure 3 The first optical sensor and the second optical sensor are arranged side by side, as indicated by the dotted line.

[0111] Figure 4The optical sensor device 100 including a first optical sensor 1, a second optical sensor 2 and a control unit 20 is schematically shown, and the optical sensor device 100 is arranged at a road intersection 13. The first optical sensor 1 and the second optical sensor 2 may be as follows: Figure 3 As shown, the difference is that they are Figure 4 are separated by a large distance. The control unit is configured to wirelessly communicate with the first optical sensor 1 and the second optical sensor 2. The first optical sensor 1 is arranged at a corner of the first building 11, and the second optical sensor 2 is arranged at a corner of the second building 12. A plurality of cars 14. The carbon dioxide emitted by these cars 14 is monitored by an optical sensor device. The first optical sensor 1 and the second optical sensor 2 are configured to measure the same absorption wavelength of carbon dioxide. Normally, the traffic volume at night is lower than that during the day, which will cause a change in the carbon dioxide concentration at the road intersection, and the carbon dioxide concentration is higher during the day. The concentration of carbon dioxide tends to balance at the road intersection, resulting in substantially the same concentration at the first optical sensor 1 and at the second optical sensor 2. The concentration is continuously registered by the two optical sensors 1, 2 at fixed time intervals and sent to the control unit 20. By selecting the first time point A to be during the day and the second time point B to be at night, the concentration of carbon dioxide will be different, so that the first zero signal I01 and the second zero signal I02 and the measured concentration Cmeas1 can be determined by the above method. A ,Cmeas1 B , Cmeas2 A , Cmeas2 B .and Figure 1 and Figure 2 Compared to the embodiment shown, Figure 4 The first optical sensor 1, the second optical sensor 2, and the control unit of the optical sensor device 100 in the illustrated embodiment are separated from each other.

[0112] The embodiments described above may be modified in many ways without departing from the scope of the present invention, which is limited only by the accompanying claims.

Claims

1. A method for determining the concentration of a component in a fluid, the method comprising the steps of: - providing, from a first optical sensor (1), a first light intensity (IR1A) of light interacting with the fluid at a first point in time (A), and a second light intensity (IR1B) of light interacting with the fluid at a second point in time (B), the first optical sensor (1) being configured to measure the light intensity of the light interacting with the fluid, wherein the first light intensity (IR1A) is different from the second light intensity (IR1B), - providing a third light intensity (IR2A) of the light interacting with the fluid at the first point in time (A) and a fourth light intensity (IR2B) of the light interacting with the fluid at the second point in time (B) from a second optical sensor (2), the second optical sensor (2) being configured to measure the light intensity of the light interacting with the fluid, - providing a first concentration function (func1) defining the concentration Cmeas1A of a component in the fluid as a function of the light intensity (IR1A) from the first optical sensor (1) and defining the concentration Cmeas1B as a function of the light intensity (IR1B) from the first optical sensor (1), - providing a second concentration function (func2) defining the concentration Cmeas2A of a component in the fluid as a function of the light intensity (IR2A) from the second optical sensor (2) and defining the concentration Cmeas2B as a function of the light intensity (IR2B) from the second optical sensor (2), wherein the first concentration function (func1) and the second concentration function (func2) have different dependencies on the light intensity, - providing correlation information, said correlation information defining a correlation between said first concentration function (func1) and said second concentration function (func2), -Determine the concentration of the component in the fluid at the first time point (A) and / or the second time point (B) measured by the first optical sensor (1) based on the first light intensity (IR1A), the second light intensity (IR1B), the third light intensity (IR2A), the fourth light intensity (IR2B), the first concentration function (func1), the second concentration function (func2) and the correlation information (Corr).

2. The method according to claim 1, wherein: The first optical sensor (1) and the second optical sensor (2) are configured to measure the concentration of the same component, and wherein the correlation information defines that the first concentration function (func1) provides the same concentration as the second concentration function (func2).

3. The method according to claim 1 or 2, wherein: The step of determining the concentration of a component in the fluid measured by the first optical sensor (1) comprises the following steps: determining a first zero signal (I01) from the first optical sensor (1) when no component is present in the fluid, and / or determining a second zero signal (I02) from the second optical sensor (2) when no component is present in the fluid, wherein the first concentration function (func1) is also a function of the first zero signal (I01), and the second concentration function (func2) is also a function of the second zero signal (I02).

4. The method according to claim 1 or 2, wherein: A pair of light intensities (IR1A) from the first optical sensor (1) and light intensities from the second optical sensor (2) are provided at a plurality of time points, and wherein the first time points and the second time points are selected such that the first sensor signal (IR1A) is different from the second sensor signal (IR1B).

5. An optical sensor device (100) for determining the concentration of a component in a fluid, the optical sensor device comprising: - a first optical sensor (1) configured to measure the light intensity of light interacting with the fluid, wherein the concentration Cmeas1A of a component in the fluid is defined by a first concentration function (func1) as a function of the light intensity (IR1A) from the first optical sensor (1), and the concentration Cmeas1B is defined by a first concentration function (func1) as a function of the light intensity (IR1B) from the first optical sensor (1), - a second optical sensor (2) configured to measure the light intensity of light interacting with the fluid, wherein the concentration Cmeas2A of a component in the fluid is defined by a second concentration function (func2) as a function of the light intensity (IR1A) from the second optical sensor (2), and the concentration Cmeas2B is defined by a second concentration function (func2) as a function of the light intensity (IR1B) from the second optical sensor (2), wherein the first concentration function (func1) and the second concentration function (func2) have different dependencies on the light intensity, The optical sensor device (100) is configured to measure, with the first optical sensor (1), a first light intensity (IR1A) of light interacting with the fluid at a first time point (A), and to measure a second light intensity (IR1B) of light interacting with the fluid at a second time point (B), wherein the first light intensity (IR1A) is different from the second light intensity (IR1B), wherein the optical sensor device (100) is configured to measure, with the second optical sensor (2), a third light intensity (IR2A) of the light interacting with the fluid at the first time point (A), and to measure a fourth light intensity (IR2B) of the light interacting with the fluid at the second time point (B), -Determining the concentration of a component in the fluid at a first time point (A) and / or a second time point (B) measured by the first optical sensor (1) based on the first light intensity (IR1A), the second light intensity (IR1B), the third light intensity (IR2A), the fourth light intensity (IR2B), the first concentration function (func1), the second concentration function (func2), and correlation information (Corr) defining the correlation between the first concentration function (func1) and the second concentration function (func2).

6. The optical sensor device (100) according to claim 5, configured to determine the concentration of the component in the fluid measured by the first optical sensor (1) by determining a first zero signal (I01) from the first optical sensor (1) when no component is present in the fluid, and / or determining a second zero signal (I02) from the second optical sensor (2) when no component is present in the fluid, wherein: The first concentration function (func1) is also a function of the first zero signal (I01), and the second concentration function (func2) is also a function of the second zero signal (I02).

7. The optical sensor device (100) according to claim 5 or 6, configured to measure a pair of light intensity (IR1A) from the first optical sensor (1) and light intensity from the second optical sensor (2) at a plurality of time points, and wherein, The first point in time and the second point in time are selected such that the first sensor signal (IR1A) is different from the second sensor signal (IR1B).

8. The optical sensor device (100) according to claim 5, wherein: The first optical sensor (1) comprises a fluid cavity (7) and a first light detector (4), the first light detector (4) being configured to measure the intensity of light interacting with the fluid in the fluid cavity (7), and wherein the second optical sensor (2) comprises and a second light detector (6), the second light detector (6) being configured to measure the intensity of light interacting with the fluid in the fluid cavity (7).

9. The optical sensor device (100) according to claim 8, wherein: The first optical sensor (1) and the second optical sensor are configured to measure light intensity in the same wavelength range.

10. The optical sensor device (100) according to claim 9, comprising a first band pass filter (8) in front of the first light detector (4) and a second band pass filter (9) in front of the second light detector (5).

11. The optical sensor device (100) according to claim 6, wherein: The distance that light propagates through the fluid to the first light detector (4) is longer than the distance that light propagates through the fluid to the second light detector (6).

12. The optical sensor device (100) according to claim 6, the optical sensor comprising a first light source (3) and a second light source (5), the light emitted by the first light source (3) interacting with the fluid in the fluid cavity (7), and the light emitted by the second light source (5) interacting with the fluid in the fluid cavity (7), wherein The first light detector (4) is configured to measure the intensity of light from the first light source (3), and wherein the second light detector (6) is configured to measure the intensity of light from the second light source (5).

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