Gas sensor and method for detection

Abstract

To detect condensation in a measurement.SOLUTION: The gas sensor for detecting a detection target gas includes: a light-emitting unit for emitting light; a first light reception unit for receiving at least a part of the light which passed through the detection target gas and outputting a first light reception signal according to the result of light reception; a second light reception unit for receiving at least a part of the light which passed through the detection target gas and outputting a second light reception signal according to the result of light reception; and an operation unit for detecting generation of condensation in an optical path from the light-emitting unit to the first light reception unit on the basis of the first light reception signal and the second light reception signal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a gas sensor and a method of sensing. [Background technology]

[0002] 2. Description of the Related Art Conventionally, measuring devices for measuring the concentration of respiratory gas or gases are known (see, for example, Patent Documents 1 to 3). [Patent documents] Patent Document 1 Patent No. 5351583 Patent Document 2: JP 2022-3321 A Patent Document 3: JP 2019-174152 A Summary of the Invention [Problem to be solved by the invention]

[0003] In the measurement, it is preferable to detect condensation. [Means for solving the problem]

[0004] In order to solve the above problems, an embodiment of the present invention provides a gas sensor for detecting a target gas. The gas sensor may include a light emitting unit that irradiates light, and a first light receiving unit that receives at least a portion of the light that has passed through the target gas and outputs a first light receiving signal according to the light receiving result. Any of the gas sensors may include a second light receiving unit that receives at least a portion of the light that has not passed through the target gas and outputs a second light receiving signal according to the light receiving result. Any of the gas sensors may include a calculation unit that detects the occurrence of condensation in the optical path from the light emitting unit to the first light receiving unit based on the first light receiving signal and the second light receiving signal.

[0005] In any of the above gas sensors, the calculation unit may calculate a fluctuation rate of the first light receiving signal and a fluctuation rate of the second light receiving signal. In any of the above gas sensors, the occurrence of condensation may be determined based on a condensation determination evaluation value using the fluctuation rate of the first light receiving signal and the fluctuation rate of the second light receiving signal.

[0006] In any of the gas sensors described above, the condensation determination evaluation value may be a ratio of a fluctuation rate of the first light receiving signal to a fluctuation rate of the second light receiving signal.

[0007] Any of the gas sensors described above may determine that condensation has occurred when the condensation determination evaluation value is 2 or more.

[0008] In any of the gas sensors described above, the second light receiving portion may receive light that has not passed through a space in which the target gas is present.

[0009] Any of the gas sensors described above may be provided in a microphone device. Any of the gas sensors described above may be provided in a device worn on the head.

[0010] In any of the above gas sensors, the calculation unit may calculate a baseline of a waveform of the first light receiving signal based on a frequency component of the first light receiving signal that is lower than a set first cutoff frequency, and detect the occurrence of the condensation based on a signal obtained by removing the baseline from the first light receiving signal. In any of the above gas sensors, the first cutoff frequency may be set in response to a change in a signal value of the first light receiving signal.

[0011] In any of the gas sensors described above, the calculation section may change the first cutoff frequency when the condensation is detected.

[0012] In any of the above gas sensors, the calculation unit may calculate a baseline value for each of the signal values ​​of the first light receiving signals. In any of the above gas sensors, the calculation unit may set the value of the first cutoff frequency to be higher than the first cutoff frequency when the condensation is detected when the signal value of the first light receiving signal for which the baseline value is calculated has decreased by a second set value or more from the signal value at an immediately preceding timing in the time waveform of the first light receiving signal.

[0013] In any of the gas sensors described above, the calculation section may calculate at least one of a cycle and a length of breathing containing the target gas, using the first light receiving signal from which the baseline has been removed.

[0014] In any of the gas sensors described above, the calculation section may determine whether or not the condensation is caused by exhaled air, based on a fluctuation in the signal value of the first light receiving signal.

[0015] In order to solve the above problems, in another aspect of the present invention, a detection method for detecting a target gas is provided. In the detection method, at least a portion of light that is irradiated onto a path through which the target gas passes and that has passed through the target gas may be received, and a first light receiving signal corresponding to the light receiving result may be output. In any of the detection methods, at least a portion of the light that has not passed through the target gas may be received, and a second light receiving signal corresponding to the light receiving result may be output. In any of the detection methods, the occurrence of condensation in the optical path through which the light passes may be detected based on the first light receiving signal and the second light receiving signal.

[0016] The above summary of the invention does not list all of the necessary features of the present invention. Also, subcombinations of these features may also be inventions. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a gas sensor 10 for detecting a target gas. [Diagram 2] 13 is a diagram showing a change in signal value when condensation occurs on the light-emitting unit 16 or the first light-receiving unit 18. FIG. [Diagram 3] FIG. 13 is a diagram showing calculation of a baseline. [Figure 4A] FIG. 13 shows the results of using a constant first cutoff frequency in the baseline calculation. [Figure 4B] 4B is a diagram showing the results of calculating the ratio between the first and second received light signals and the difference between the baseline calculation values ​​from FIG. 4A. FIG. [Figure 5A] FIG. 13 is a diagram showing the results of changing the first cutoff frequency in baseline calculation depending on the magnitude relationship of the immediately preceding signal value. [Figure 5B] 5B is a diagram showing a determination signal calculated from the received light signal ratio and the baseline shown in FIG. 5A. FIG. [Figure 6A] FIG. 13 is a diagram showing a baseline calculation when condensation occurs. [Figure 6B] 6B is a diagram showing an example of a determination signal obtained by taking the difference between the light receiving signal ratio in FIG. 6A and a baseline calculation value. FIG. [Figure 7A] FIG. 13 is a diagram showing the results of changing the first cutoff frequency in baseline calculation when condensation occurs. [Figure 7B] 7B is a diagram showing an example of a determination signal calculated from the light receiving signal ratio in FIG. 7A and a baseline calculation value. FIG. [Figure 8] 1 is a diagram showing another embodiment of the gas sensor 10. FIG. [Figure 9] 2 is a diagram showing an example of the configuration of a light-emitting unit 16. FIG. [Figure 10] FIG. 1 is a block diagram showing an example of a gas sensor 10 according to an embodiment of the present invention. [Figure 11] FIG. 13 is a diagram illustrating an example of a flowchart of a detection method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. In this specification, the same parts in each figure are given the same reference numerals, and the description may be omitted. In addition, some configurations may not be illustrated for convenience of explanation.

[0019] In this specification, technical matters may be explained using an orthogonal coordinate system of X-axis, Y-axis, and Z-axis. The orthogonal coordinate system merely specifies the relative positions of components, and does not limit specific directions. For example, the Z-axis direction does not limit the height direction relative to the ground.

[0020] 1 is a diagram showing a gas sensor 10 that detects a target gas. The gas sensor 10 includes a light-emitting unit 16, a first light-receiving unit 18, and a calculation unit 20. The light-emitting unit 16, the first light-receiving unit 18, and the calculation unit 20 may be attached to a support member 30. In this example, the light-emitting unit 16 is attached to one of the support members 30 facing each other, and the first light-receiving unit 18 and the calculation unit 20 are attached to the other. In this example, a plane parallel to the main surface of the support member 30 is defined as an XY plane, and a direction perpendicular to the main surface of the support member 30 is defined as a Z-axis direction.

[0021] The gas sensor 10 is an optical gas sensor that utilizes a specific absorption wavelength of a component contained in the gas to be detected. The light emitting unit 16 irradiates light 14 toward a path 12 through which the gas to be detected passes. The light emitting unit 16 is, for example, an LED. The wavelength of the light 14 may be appropriately selected according to the absorption wavelength of the gas to be detected. A portion of the light 14 passes through the path 12 and enters a first light receiving unit 18. A portion of the light 14 enters a second light receiving unit 22, which will be described later.

[0022] The first light receiving section 18 receives at least a portion of the light 14 to which the target gas has been added, and outputs a first light receiving signal according to the light receiving result to the calculation section 20. The first light receiving section 18 is, for example, a photodiode.

[0023] The calculation unit 20 performs calculations on the first light receiving signal. The calculation unit 20 is, for example, an IC. Since the amount of light received at the absorption wavelength of the target gas decreases as the target gas absorbs the light 14, the calculation unit 20 can calculate the concentration of the target gas or a value corresponding to the concentration from the value of the first light receiving signal.

[0024] Here, as an example of a calculation performed on the first light receiving signal, a specific example of calculation of the first light amount information Φ1 relating to the amount of light absorbed by the gas to be detected will be shown. The intensity of the light that reaches the first light receiving unit 18 out of the light 14 emitted from the light emitting unit 16 in the absence of a detectable gas is expressed as Φ 1 (λ), and the sensitivity of the first light receiving unit 18 is Ri 1 Let Φ(λ) be the optical path length from the light-emitting unit 16 to the first light-receiving unit 18. Let μ(λ) be the absorption coefficient of the detected gas, and c be the concentration of the target gas. Here, Φ(λ) is the case when no detectable gas is present, but it may also be the case when some standard concentration of target gas is present.

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[0025] Here, Φ1 may be corrected based on temperature information. In this case, the gas sensor 10 may further include a thermometer, and the calculation unit 20 may receive a temperature signal from the thermometer. When the term due to temperature is taken into consideration, Equation 1 becomes Equation 2.

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[0026] The first light amount information Φ1 of any one of formulas 1 to 3 may be used to detect condensation, which will be described later. The detection of condensation may be performed by comparing the first light amount information Φ1 with a first set value A1. The first set value A1 is determined based on the fact that when condensation occurs, a further signal fluctuation occurs with respect to the amount of absorbed light expected by gas detection, and the threshold value is determined based on this. For example, in the case of a carbon dioxide sensor used in a breath detection sensor, the first set value A1 is determined based on the amount of absorbed light due to a carbon dioxide concentration of 40,000 ppm contained in breath. The carbon dioxide concentration contained in normal breath does not exceed approximately 40,000 ppm. On the other hand, when condensation occurs, a signal fluctuation greater than the fluctuation in the amount of absorbed light due to 40,000 ppm of carbon dioxide may occur.

[0027] The gas sensor 10 may include a second light receiving section 22. The second light receiving section 22 may be built in the light emitting section 16. The configurations of the light emitting section 16 and the second light receiving section 22 will be described later. The second light receiving section 22 receives the light 14 emitted by the light emitting section 16 that has not passed through the path 12 through which the target gas passes, and outputs a second light receiving signal according to the light receiving result. The second light receiving section 22 may receive at least a part of the light 14 that has not passed through the target gas. The second light receiving signal may be output to the calculation section 20. The calculation section 20 may correct the first light receiving signal using a signal value of the second light receiving signal. The correction may be to divide the value of the first light receiving signal by the value of the second light receiving signal. By providing the second light receiving section 22 and performing the correction, it is possible to correct the change in the amount of light of the light emitting section 16 and the output fluctuation due to temperature.

[0028] The calculation unit 20 may correct the first light amount information by using the second light receiving signal. Here, as an example of the correction, a specific example of calculation of the second light amount information Φ2 related to the light amount information absorbed by the gas to be detected is shown. When the light 14 emitted from the light emitter 16 in the absence of the gas to be detected is expressed as Φ 1 (λ), and the intensity of the light reaching the second light receiving section is Φ 2 (λ), and the sensitivity of the first light receiving unit 18 is Ri 1 (λ), the sensitivity of the second light receiving unit 22 is Ri 2(λ). The optical path length from the light-emitting unit 16 to the first light-receiving unit 18 is L. The absorption coefficient of the detection gas is μ(λ), and the concentration of the detection target gas is c. Here, Φ 1 Although (λ) is set to the case where no detection gas is present, it may be set to the case where a target gas of a reference concentration is present, etc. The second light quantity information Φ2 is calculated by Equation 4.

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[0029] Here, the second light amount information Φ2 may be corrected based on temperature information. In this case, the gas sensor 10 may further include a thermometer, and the calculation unit 20 may receive a temperature signal from the thermometer. When the term due to temperature is taken into consideration, Equation 4 becomes Equation 5.

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[0030] The gas sensor 10 may further include an optical filter 24 disposed between the light emitting section 16 and the first light receiving section 18. In this embodiment, the optical filter 24 is provided on the surface of the first light receiving section 18. The optical filter 24 limits the wavelength of the light 14 incident on the first light receiving section 18. An example of the optical filter 24 is a bandpass filter. The transmittance of the bandpass filter is T BPF (λ), Equation 1 becomes Equation 8.

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[0031] In general, the sensitivity of the first light receiving section 18 changes due to the influence of temperature. In a sensitivity curve with the horizontal axis representing the wavelength of light and the vertical axis representing the sensitivity of the first light receiving section 18, the influence of temperature appears as a shift of the sensitivity curve along the horizontal axis. On the other hand, the sensitivity curve has a wavelength range in which the sensitivity value is almost flat. By using the optical filter 24 to allow only light with wavelengths in that wavelength range to enter the first light receiving section 18, the influence on sensitivity can be suppressed even if the temperature of the first light receiving section 18 changes.

[0032] The type of gas to be detected is not particularly limited, but in this specification, the gas to be detected is exhaled air as an example. In this specification, when the gas to be detected is exhaled air, carbon dioxide contained in the exhaled air is assumed to absorb the light 14, but alcohol or the like may also absorb the light 14. The gas sensor 10 that detects the exhaled air may be provided in a microphone device or in a device worn on the head. The gas sensor 10 may be provided in the microphone portion of headphones.

[0033] FIG. 2 is a diagram showing a change in signal value when condensation occurs on the light-emitting unit 16 or the first light-receiving unit 18. In FIG. 2 and the following figures, the first light-receiving signal is represented as IR1, and the second light-receiving signal is represented as IR2. The horizontal axis of FIG. 2 represents time, the vertical axis on the left represents the signal strength (%) of the value of the first light-receiving signal and the signal strength (%) of the value of the second light-receiving signal, and the vertical axis on the right represents temperature. The reference of the signal strength may be the signal value when no breath is present. The signal strength in this example is a value that represents the value of each signal as a percentage when the value of each signal when no breath is present is normalized to 100% (reference value). The difference between the reference value and the signal strength is the fluctuation rate. In this example, it is expressed as the fluctuation rate (%) = reference value (100%) - signal strength (%). The more the signal strength deviates from 100%, the larger the fluctuation rate, which indicates a large fluctuation from the reference value. However, the reference value may be a value other than 100%. The solid line in the figure represents the first light receiving signal, the dashed line in the figure represents the second light receiving signal, and the dotted line in the figure represents the temperature of the gas sensor 10. The figure also shows the fluctuation rate ΔIR1 of the first light receiving signal and the fluctuation rate ΔIR2 of the second light receiving signal. The calculation unit 20 may calculate the fluctuation rate ΔIR1 of the first light receiving signal and the fluctuation rate ΔIR2 of the second light receiving signal. In this specification, the value of the first light receiving signal may be simply referred to as the first light receiving signal, and the value of the second light receiving signal may be simply referred to as the second light receiving signal. The calculation unit 20 may use the signal value as it is in the calculation, or may use a value obtained by converting the signal value into a fluctuation rate in the calculation. The terms "signal value" and "fluctuation rate" may be interchangeable.

[0034] In FIG. 2, exhaled air is blown onto the gas sensor 10 cooled to about 0° C. Breathing occurs from 40 seconds to 2 minutes 20 seconds in the figure, and the gas sensor 10 detects the exhaled air during the above period. The above period is shown in the figure as the breathing period. The amount of light received by the first light receiving unit 18 decreases due to the absorption of carbon dioxide, so the first light receiving signal decreases when exhaled air is detected. In addition, since the exhaled air is quickly diffused into the air, the first light receiving signal increases (recovers) immediately after decreasing. The small increases and decreases in the first light receiving signal from 40 seconds to 2 minutes 20 seconds in the figure correspond to breathing. One valley-shaped portion in the first light receiving signal corresponds to one breath. In FIG. 2, about 40 breaths are taken during the breathing period.

[0035] The second light receiving signal represents the result of receiving light 14 that has not passed through the path 12 through which the target gas passes. Therefore, no fluctuation in the value of the second light receiving signal due to breathing is observed. The temperature of the gas sensor 10 rises from around 0°C after breathing starts due to the temperature of the exhaled air, and repeatedly increases and decreases while breathing continues, and gradually decreases when breathing ends.

[0036] When detecting breath, moisture contained in the breath may cause condensation on the gas sensor 10. In FIG. 2, breath is blown onto the gas sensor 10 at 0°C to intentionally cause condensation on the gas sensor 10. When condensation occurs on the light emitting section 16 or the first light receiving section 18 of the gas sensor 10, part of the light 14 is absorbed, reflected, or refracted by the condensation and bent in an unintended direction, affecting the first received light signal. In FIG. 2, the first received light signal drops significantly around 40 seconds and continues to drop thereafter throughout the breathing period. This drop in the first received light signal is thought to be due to the effect of condensation caused by breath.

[0037] When condensation occurs, the S / N ratio of the first light receiving signal decreases, and the false detection rate increases. The occurrence of condensation on the light-emitting unit 16 or the first light-receiving unit 18 may also include the occurrence of condensation on the optical path through which the light 14 passes between the light-emitting unit 16 and the first light-receiving unit 18. As an example, it may also include the occurrence of condensation on the optical filter 24. Furthermore, the condensation in this example is not limited to condensation caused by exhaled breath, and may also include condensation caused by other factors, and may also include dirt that occurs on the light-emitting unit 16 or the first light-receiving unit 18.

[0038] The calculation unit 20 may detect that condensation has occurred in the optical path from the light emitting unit 16 to the first light receiving unit 18 based on the first light receiving signal and the second light receiving signal. The optical path may include the light emitting unit 16, the first light receiving unit 18, and an optical filter 24. The calculation unit 20 may detect condensation occurring in the light emitting unit 16 or the first light receiving unit 18 based on the fluctuation rate ΔIR1 of the first light receiving signal and the fluctuation rate ΔIR2 of the second light receiving signal. The calculation unit 20 may calculate the above-mentioned first light amount information based on the first light receiving signal, and obtain a condensation determination evaluation value based on the first light amount information. The condensation determination evaluation value may be the first light amount information itself, or may be second light amount information obtained by correcting the first light amount information using the second light receiving signal. The condensation determination evaluation value may be any value calculated by Equation 1 to Equation 8. The condensation determination evaluation value may be a value using the fluctuation rate ΔIR1 of the first light receiving signal and the fluctuation rate ΔIR2 of the second light receiving signal. The condensation determination evaluation value may be a ratio (ΔIR1 / ΔIR2) of the fluctuation rate of the first light receiving signal to the fluctuation rate of the second light receiving signal. The calculation unit 20 may detect that condensation has occurred in the optical path from the light emitting unit 16 to the first light receiving unit 18 based on the condensation determination evaluation value. This makes it possible to know whether the gas sensor 10 has a high false detection rate or not. The calculation unit 20 may determine that condensation has occurred when the condensation determination evaluation value is 2 or more. The value may be 3 or more, or 4 or more. The calculation unit 20 may notify the detection result to the outside. The calculation unit 20 calculates the fluctuation rate ratio (ΔIR1 / ΔIR2) using the fluctuation rates ΔIR1 and ΔIR2 at the same timing. The calculation unit 20 may sequentially calculate the fluctuation rate ratio (ΔIR1 / ΔIR2) in chronological order.

[0039] The calculation unit 20 may determine that condensation has occurred when the fluctuation rate of the first light receiving signal is equal to or less than a first set value. The calculation unit 20 may determine that condensation has occurred when the condensation determination evaluation value is equal to or more than a first set value. The first set value may be, for example, the value of the fluctuation rate of the first light receiving signal or the condensation determination evaluation value when a carbon dioxide concentration of 40,000 ppm is detected. The carbon dioxide concentration in a human lung is approximately 40,000 ppm. When exhaled air is released from the lungs into the atmosphere, the exhaled air diffuses into the atmosphere, so that a carbon dioxide concentration of 40,000 ppm or more is not detected by the exhaled air. Therefore, it is possible to determine that condensation has occurred based on the above-mentioned first set value.

[0040] The calculation unit 20 may determine that condensation has occurred when the rate of change of the second light receiving signal is constant and only the rate of change of the first light receiving signal is decreasing, and when the rate of change of the first light receiving signal is equal to or less than a first set value or when the condensation determination evaluation value is equal to or more than a first set value. A constant rate of change may indicate that the signal value varies by 5% or less during a predetermined period. The above-mentioned predetermined period may be 30 seconds, 60 seconds, or a period ten times the respiratory cycle. The calculation unit 20 may determine that condensation has occurred when the difference between the rate of change of the first light receiving signal and the rate of change of the second light receiving signal is equal to or more than a predetermined value. The above-mentioned predetermined value may be the value of the rate of change of the first light receiving signal when a carbon dioxide concentration of 40,000 ppm is detected (i.e., the first set value).

[0041] FIG. 3 is a diagram showing calculation of the baseline. The horizontal axis of FIG. 3 indicates time, and the vertical axis indicates the value of the ratio of the intensities of the first and second received light signals. In this specification, the ratio of the intensities of the first and second received light signals may be referred to as the received light signal ratio. As described above, by dividing the first received light signal by the second received light signal, it is possible to correct the change in the amount of light of the light emitting unit 16 and the output fluctuation due to temperature. In FIG. 3, the fluctuation of the received light signal ratio around 10 to 20 seconds corresponds to breathing. One valley in the received light signal ratio corresponds to one breath. In FIG. 3, five valleys appear in the waveform of the received light signal ratio, so the received light signal ratio for five breaths is shown.

[0042] In the following figures, the embodiment will be described using the light receiving signal ratio between the first light receiving signal and the second light receiving signal, but it is not essential to use the second light receiving signal. Instead of the light receiving signal ratio, the signal value of the first light receiving signal may be used. In this case, the term "light receiving signal ratio" may be read as "first light receiving signal." In this specification, even if processing is performed on the light receiving signal ratio, the same processing may be performed on the first light receiving signal, and even if processing is performed on the first light receiving signal, the same processing may be performed on the light receiving signal ratio.

[0043] The solid line in the figure indicates the light receiving signal ratio. The dashed line in the figure indicates a judgment threshold value, which will be described later. The calculation unit 20 calculates the baseline of the waveform of the first light receiving signal from the light receiving signal ratio. The dotted line in the figure indicates the calculated baseline.

[0044] The baseline refers to a signal waveform due to factors (disturbances) other than the gas to be detected. When the gas to be detected is exhaled breath, the baseline refers to a signal waveform due to factors other than the carbon dioxide contained in the exhaled breath. The baseline is a waveform in which the components due to the carbon dioxide concentration are reduced or excluded from the waveform shown by the solid line in Fig. 3. The baseline may include a component of the intensity of light 14 irradiated by light-emitting unit 16 and a fluctuation component due to factors other than changes in the carbon dioxide concentration.

[0045] When the gas sensor 10 detects exhaled breath, the temperature of the exhaled breath may change the temperature of the light-emitting section 16 and the first light-receiving section 18, causing a change in characteristics. The baseline may be a signal waveform that includes the influence of such characteristic changes and does not include the influence of carbon dioxide. Although the baseline caused by disturbances whose frequency deviates from the breathing cycle may also include the influence of humidity and deterioration of elements, in this specification, it is assumed to mainly include fluctuations due to the temperature of the exhaled breath or the temperature of the exhaled breath and condensation. In this specification, factors other than the gas to be detected are temperature or temperature and condensation. In the following explanation, we will first discuss fluctuations due to the temperature of the exhaled breath, and then fluctuations due to temperature and condensation.

[0046] The calculation unit 20 may calculate the baseline based on the light receiving signal ratio. This allows the influence of temperature due to exhaled breath to be appropriately reflected. Even when detecting other target gases, if there is a correlation between the disturbance and the target gas, the influence of the disturbance can be appropriately reflected by calculating the baseline based on the signal value of the target gas.

[0047] The baseline calculation value in Fig. 3 is calculated from the light receiving signal ratio, and therefore varies according to the respiratory cycle, but this represents the effect of temperature due to exhalation. A parameter for baseline calculation may be experimentally determined so that the change in the light receiving signal ratio due to factors other than carbon dioxide is represented. One example of the parameter is the coefficient b0 described later.

[0048] The calculation unit 20 may calculate the baseline by removing disturbance frequency components that are out of frequency with respect to the respiratory cycle from the time waveform of the light receiving signal ratio. As an example, the calculation unit 20 calculates the baseline by filtering expressed by infinite impulse response (IIR). An example of the process of calculating the baseline in IIR filtering is shown in Table 1. [Table 1]

[0049] In the table, x represents the signal value of the received signal ratio, and y represents the calculated baseline value. b0 is the filter coefficient. The number after x and y represents the sampling point n. Table 1 shows up to n=3.

[0050] The calculation unit 20 calculates the baseline value yn for each signal value xn of the light receiving signal ratio. As shown in Table 1, the calculated baseline value yn is calculated by multiplying the corresponding signal value xn by a coefficient b0 and the calculated value yn-1 of the previous baseline by (1-b0). In other words, the coefficient b0 determines the percentage of the corresponding signal value to be reflected in the calculated value of the previous baseline. The coefficient b0 takes a value of 0 or more and 1 or less. When the coefficient b0 is made larger, the corresponding signal value is more reflected, and the baseline can easily follow the fluctuation of the signal value. In the example of Table 1, the calculated value yn of the baseline reflects the value of one previous baseline yn-1, but in other examples, the calculated value yn of the baseline may reflect the values ​​of multiple previous baselines.

[0051] The baseline may be calculated by the following method other than IIR filtering: As an example, the baseline may be calculated by a moving average filter (MA) shown in equations (9) and (10).

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[0052] As another example, the calculation may be performed using a weighted moving average filter (WMA) shown in equation (11).

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[0053] As another example, the calculation may be performed using a finite impulse response (FIR) filter shown in equations (12) and (13).

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[0054] As another example, the calculation may be performed using a Butterworth filter shown in equation (14).

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[0055] Alternatively, the baseline may be determined based on values ​​when there is little signal variation, such as data from a time when breathing is not occurring during baseline calculation. At least one of an upper limit and a lower limit may be set for the baseline. Multiple baseline calculation methods may be changed depending on signal values ​​and environmental values.

[0056] Here, the calculation of the immediately preceding baseline is not limited to calculating the baseline of xn by xn-1. Any baseline calculation method that is difficult to follow the respiratory signal may be used. For example, for xn, the baseline calculation may be performed using all signals from xn-1 to further prior data xn-m, where m is a natural number. For example, if data is acquired every 0.1 seconds, the baseline calculation of the signal xn may be performed using the data of signals xn-1, xn-2, and xn-3 with m=3. The immediately preceding range may be determined so that it is difficult to follow the respiratory signal but can follow slower temperature fluctuations. The calculation of the baseline may be performed based on the light receiving signal ratio in the past Tn, or based on the light receiving signal ratio in a specific period shorter than the respiratory cycle in the past Tn.

[0057] The calculation unit 20 removes the baseline from the light receiving signal ratio. Removing the baseline may mean subtracting the baseline value at each time from the signal value at that time. By calculating and removing the baseline, it is possible to correct changes in the signal value due to factors other than carbon dioxide contained in the exhaled breath, and more accurate measurements can be performed, including the detection of condensation described above. The calculation unit 20 may detect the occurrence of condensation using the first light receiving signal from which the baseline has been removed, and may calculate a condensation determination evaluation value. In this specification, the signal obtained after removing the baseline from the light receiving signal ratio may be referred to as a determination signal.

[0058] The calculation unit 20 may calculate at least one of the breathing cycle or length. The calculation unit 20 may calculate at least one of the breathing cycle or length using the judgment signal. When the value of the judgment signal is lower than the judgment threshold, the calculation unit 20 may determine that exhalation has been detected. The calculation unit 20 may calculate the breathing cycle or length based on the period during which the value of the judgment signal is lower than the judgment threshold. The calculation unit 20 may determine the breathing length as one continuous period during which the value of the judgment signal is lower than the judgment threshold. The calculation unit 20 may calculate the breathing cycle as the sum of one continuous period during which the value of the judgment signal is higher than the judgment threshold and one continuous period during which the value of the judgment signal is lower than the judgment threshold. The calculation unit 20 may calculate the average value within a predetermined measurement period as the breathing cycle or length. By calculating the breathing cycle or length, it is possible to determine whether the person breathing is excited or relaxed. When measuring the cycle or length of breathing, it is sufficient to compare the value of the determination signal with the determination threshold, and it is not necessary to calculate the amplitude of the determination signal, and the measurement accuracy of the value of the determination signal does not need to be high.

[0059] Here, setting the coefficient b0 in the infinite impulse response corresponds to removing frequency components equal to or higher than a predetermined frequency from the signal value in calculating the baseline. If the predetermined frequency is the first cutoff frequency, the relationship between the first cutoff frequency and the coefficient b0 is expressed by the formula shown in formula 15. In formula 15, a1=b0-1.

[0060]

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[0061] The calculation section 20 may calculate the baseline based on the frequency components of the time waveform of the light receiving signal ratio that are lower than the first cutoff frequency that is set. By setting a coefficient b0 in the infinite impulse response, the baseline can be calculated based on the frequency components of the light receiving signal ratio that are lower than the first cutoff frequency. Specific examples of the coefficient b0 and the first cutoff frequency will be described later.

[0062] FIG. 4A is a diagram showing the result of using a constant first cutoff frequency in the baseline calculation. The axis of FIG. 4A and the solid and dotted lines in the figure are the same as those in FIG. 3. In this example, the baseline calculation is performed by setting the first cutoff frequency constant for the baseline value yn at each time. For example, in the example of Table 1, b0 is a constant value for all n. In FIG. 4A, the baseline does not track well when the light receiving signal ratio is increasing. Therefore, during the period when breathing is continuous, the baseline does not return to the original level (IR1 / IR2=about 1 to 1.01) and remains at a relatively low level. Also, immediately after the period when breathing is continuous ends, there are some points where the baseline is lower than the light receiving signal ratio.

[0063] FIG. 4B is a diagram showing an example of a judgment signal obtained by taking the difference between the light receiving signal ratio and the baseline calculation value from FIG. 4A. Since the judgment signal indicates a signal component due to exhalation, the judgment signal when there is no exhalation ideally coincides with the reference point (IR1 / IR2=0). Furthermore, the judgment signal when there is exhalation ideally becomes smaller than the reference point. In FIG. 4B, a part of the judgment signal is located above (on the positive side) the reference point (IR1 / IR2=0). In other words, the judgment signal is shifted upward. This is thought to be because the baseline does not track well when the light receiving signal ratio increases, and the baseline is evaluated to be smaller than it actually is.

[0064] The dashed-dotted line in the figure indicates the determination threshold value. As an example, when the signal value is lower than the determination threshold value, it is determined that exhalation is detected. In FIG. 4B, since only a part of the variation in the signal value due to exhalation is below the determination threshold value, it may not be possible to detect some breaths. Therefore, it is preferable to calculate the respiratory cycle etc. more accurately.

[0065] FIG. 5A is a diagram showing the result of changing the first cut-off frequency according to the magnitude relationship of the immediately preceding signal value in baseline calculation. The arithmetic unit 20 may change the first cut-off frequency according to the change in the signal value of the received light signal ratio. In other words, the first cut-off frequency may be set according to the change in the signal value of the received light signal ratio. In the arithmetic unit 20 of this example, when the signal value of the received light signal ratio for which the baseline value is to be calculated is increasing with respect to the signal value at the immediately preceding timing in the time waveform of the received light signal ratio, the first cut-off frequency is set higher than the first cut-off frequency when it is decreasing with respect to the immediately preceding signal value.

[0066] Using the symbols in Table 1, the first cut-off frequency when xn > xn-1 is set higher than the first cut-off frequency when xn < xn-1. The arithmetic unit 20 may set the first cut-off frequency higher by making the coefficient b0 when xn > xn-1 larger than the coefficient b0 when xn < xn-1. By increasing the first cut-off frequency, relatively high frequency components in the signal waveform of the first light emission signal can be reflected in the baseline. Therefore, the followability of the baseline when the signal value of the first light emission signal increases is improved. In FIG. 5A, the baseline follows well with respect to the increase in the signal value of the first light emission signal. Therefore, during the period when breathing is continuous and in the period immediately after that, compared with the example of FIG. 4A, the baseline returns to the vicinity of the original value (1 to 1.01).

[0067] Furthermore, when exhaled air flows into the gas sensor 10, after carbon dioxide is detected, the temperature of the element rises due to the temperature of the exhaled air. For this reason, it is considered that the influence of the temperature characteristics of the element appears in the time waveform of the baseline. Since the temperature of the element changes in synchronization with respiration, a valley portion synchronized with respiration appears in the time waveform of the baseline as shown in FIG. 5A. It is considered that the influence of the temperature of the exhaled air appears later than the detection of carbon dioxide. By setting the first cutoff frequency as described above, during the period when the signal value of the light receiving signal ratio is decreasing, the baseline calculation value is less likely to follow the fluctuation of the signal value due to the detection of carbon dioxide, so that the baseline calculation value is less likely to include the influence of carbon dioxide and appropriately reflects the influence of the temperature of the exhaled air.

[0068] The calculation unit 20 may set the first cutoff frequency higher when the signal value of the light receiving signal ratio for which the baseline value is calculated is increasing relative to the past signal value in the time waveform of the light receiving signal ratio than when the signal value is decreasing relative to the past signal value. The past signal value may be the average value of the light receiving signal ratio in a period shorter than the respiratory cycle in which the immediately preceding light receiving signal ratio is the end of the period, or may be the signal value of any of the light receiving signal ratios in the period, or may be the signal values ​​of all the light receiving signal ratios in the period. Using the symbols in Table 1, for example, the first cutoff frequency when xn is higher than the average value of xn-1, xn-2, and xn-3 may be set higher than the first cutoff frequency when xn is lower than the average value.

[0069] FIG. 5B is a diagram showing a determination signal calculated from the received light signal ratio and the baseline shown in FIG. 5A. In FIG. 5B, the determination signal is located below the reference point (IR1 / IR2=0) at all times, except for minute noise components. The dashed line in the figure indicates the determination threshold value, as in FIG. 4B. According to this example, it is possible to suppress the shift of the determination signal, to more accurately detect breathing, and to calculate the breathing period and length.

[0070] When the signal value of the received optical signal ratio for which the calculation unit 20 calculates the baseline value increases with respect to the signal value at the immediately preceding timing in the time waveform of the received optical signal ratio, the first cut-off frequency may be set to be 10 times or more higher than the first cut-off frequency when it decreases with respect to the immediately preceding signal value. As an example, the first cut-off frequency when xn > xn-1 may be 1 Hz or more (for example, about 1.8 Hz (coefficient b0 = 0.24)), and the first cut-off frequency when xn < xn-1 may be 0.1 Hz or less (for example, about 0.06 Hz (coefficient b0 = 0.01)). Thereby, the followability of the baseline is further improved. The magnification may be 2 times or more, may be 5 times or more, and may be 20 times or more. The first cut-off frequency may be 3 Hz or less. Note that the signal value at the immediately preceding timing may be the above-described past signal value.

[0071] FIG. 6A is a diagram showing baseline calculation when condensation occurs. The horizontal axis in FIG. 6A represents time, the left vertical axis represents the received optical signal ratio, and the right vertical axis represents temperature. The solid line in the figure represents the received optical signal ratio, the dashed-dotted line in the figure represents the baseline, and the dotted line in the figure represents the temperature of the gas sensor 10, respectively.

[0072] In FIG. 6A, exhaled air is blown onto the gas sensor 10 at about 0° C. in the same manner as in FIG. 2. Breathing is performed from about 40 seconds to about 2 minutes and 20 seconds in the figure, and the gas sensor 10 detects exhaled air during the above period. The above period is shown in the figure as the breathing period. The minute fluctuations in the received optical signal ratio during the breathing period correspond to breathing. One valley portion in the received optical signal ratio corresponds to one breath. In FIG. 6A, about 40 breaths are performed during the breathing period.

[0073] Also in this example, exhaled air is blown onto the gas sensor 10 at about 0° C., and condensation is intentionally generated. In FIG. 6A, the received optical signal ratio greatly decreases around 40 seconds, and continues to decrease until about 2 minutes and 20 seconds when breathing ends. This decrease in the received optical signal ratio is considered to be the influence of condensation due to exhaled air.

[0074] 6A, the calculation unit 20 calculates the baseline. The calculation method is the above-mentioned IIR filtering. In this example, the baseline calculation is performed by setting the first cutoff frequency constant for the value yn of the baseline at each time.

[0075] In Figure 6A, condensation occurs, so the light receiving signal ratio continues to decrease during the respiration period. Therefore, there are some parts where the baseline cannot follow the decrease in the light receiving signal ratio during the respiration period. In particular, it cannot follow the decrease in the light receiving signal ratio due to the condensation at the beginning of the respiration period (40 seconds to 1 minute) where the decrease is large.

[0076] FIG. 6B is a diagram showing an example of a judgment signal obtained by taking the difference between the light receiving signal ratio in FIG. 6A and the baseline calculation value. Since the judgment signal shows the signal component due to exhalation, the judgment signal when exhalation does not exist ideally coincides with the reference point (IR1 / IR2=0). Even when exhalation exists, carbon dioxide diffuses between breaths (peaks between valleys), so ideally it coincides with the reference point (IR1 / IR2=0). However, in FIG. 6B, many peaks are located below the reference point (negative side). This is thought to be because the fluctuation in the signal value due to condensation cannot be properly reflected in the baseline. The number of peaks located on the lower side (negative side) is particularly high in the early period of the breathing period (40 seconds to 1 minute).

[0077] The dashed line in the figure indicates the judgment threshold. As an example, it is judged that exhalation is detected when the signal value is lower than the judgment threshold. In FIG. 6B, only a part of the fluctuation of the light receiving signal ratio due to exhalation crosses the judgment threshold, and the other fluctuation is located below (on the negative side) the judgment threshold. In this case, the period during which the light receiving signal ratio is below (on the negative side) the judgment threshold is judged to be the time when one breath is being taken, which may lead to erroneous detection of the breathing cycle and length. Therefore, it is preferable to calculate the baseline more accurately.

[0078] FIG. 7A is a diagram showing the result of changing the first cutoff frequency in the baseline calculation when condensation occurs. Each axis and each line in FIG. 7A are the same as those in FIG. 6A. The calculation unit 20 may change the first cutoff frequency when condensation is detected. The calculation unit 20 may set the first cutoff frequency when condensation is detected higher than the first cutoff frequency when condensation is not detected. This makes it easier for the baseline to follow the fluctuation of the light receiving signal ratio due to condensation. In other words, the influence of condensation can be appropriately included in the baseline. Condensation may be detected by the method described in FIG. 2. In addition to the cutoff frequency, the attenuation tendency, the filter order, and the type of low-pass filter may be changed.

[0079] FIG. 7B is a diagram showing an example of a judgment signal calculated from the light receiving signal ratio and the baseline calculation value in FIG. 7A. In FIG. 7B, the interval between breaths (the peak between the valleys) roughly coincides with the reference point (IR1 / IR2=0). In other words, the effect of condensation is appropriately corrected. Note that the judgment threshold is not shown in FIG. 7B.

[0080] The decrease in the light receiving signal ratio due to the occurrence of condensation is particularly large in the early period of the respiration period (from 40 seconds to 1 minute in FIG. 6A and FIG. 7A). When the signal value of the light receiving signal ratio for which the baseline value is calculated is decreased by more than the second set value from the signal value at the immediately preceding timing in the time waveform of the light receiving signal ratio, the calculation unit 20 may set the value of the first cutoff frequency to be higher than the first cutoff frequency at the time when condensation is detected. This makes it possible to improve the tracking ability of the baseline even in the early period of the respiration period when the fluctuation is particularly large.

[0081] As described above, the carbon dioxide concentration in the lungs is approximately 40,000 ppm. When carbon dioxide flows from the lungs to the gas sensor 10 as exhaled air, it diffuses into the atmosphere, and the concentration detected by the gas sensor 10 is considered to be approximately 10,000 ppm. The second set value may be, for example, a signal value when a carbon dioxide concentration of 20,000 ppm or 30,000 ppm is detected.

[0082] The calculation unit 20 may determine whether condensation is due to exhalation based on the fluctuation of the light receiving signal ratio or the baseline signal value. In the case of condensation due to exhalation, the initial decrease in the light receiving signal ratio during the breathing period is larger than in the case of condensation due to other factors. Therefore, when the decrease in the light receiving signal ratio or the baseline within a predetermined time from the start of the breathing period is equal to or greater than a predetermined value, the calculation unit 20 may determine that condensation due to exhalation has occurred. The predetermined time may be the average value of the breathing cycle, or may be 10 seconds, 20 seconds, or 30 seconds. The predetermined value may be the amount of fluctuation in the signal value when a carbon dioxide concentration of 20,000 ppm, 30,000 ppm, or 40,000 ppm is detected.

[0083] The calculation unit 20 may determine whether the condensation is due to exhalation based on the ratio between the absolute value of the slope of the baseline from the start of the breathing period until a predetermined time has elapsed and the absolute value of the slope of the baseline from the end of the breathing period until a predetermined time has elapsed. As described above, if the condensation is due to exhalation, the absolute value of the slope of the baseline immediately after the start of the breathing period becomes relatively large. The calculation unit 20 may determine that condensation due to exhalation has occurred when the value obtained by dividing the absolute value of the slope of the baseline for a predetermined period after the start of the breathing period by the absolute value of the slope of the baseline for a predetermined period after the end of the breathing period is equal to or greater than a predetermined value.

[0084] FIG. 8 is a diagram showing another embodiment of the gas sensor 10. In the gas sensor 10 of this embodiment, the light emitting section 16, the first light receiving section 18, and the calculation section 20 are attached to the same support member 30. The gas sensor 10 of this embodiment has a mirror 32, and the path 12 through which the target gas passes is between the support member 30 and the mirror 32. In the gas sensor 10 of this embodiment, a part of the light 14 emitted by the light emitting section 16 is reflected by the mirror 32, and the first light receiving section 18 receives the reflected light 14. The other parts may be the same as those of the gas sensor 10 of FIG. 1. With such a configuration, the gas sensor 10 can be made smaller in size.

[0085] 9 is a diagram showing a configuration example of the light-emitting unit 16. The light-emitting unit 16 of this example has a substrate 40, a light-emitting element 44, and a second light-receiving unit 22. The substrate 40 may be transparent to the light 14. When detecting breath, the substrate 40 is, for example, a GaAs substrate.

[0086] The substrate 40 has a first main surface 41 and a second main surface 42. The first main surface 41 and the second main surface 42 are two main surfaces that constitute the substrate 40. In this example, of the two main surfaces, the first main surface 41 is the main surface on the positive side in the Z-axis direction, and the second main surface 42 is the main surface on the negative side in the Z-axis direction. The first main surface 41 faces the path 12 through which the target gas passes.

[0087] The light-emitting element 44 and the second light-receiving portion 22 may be provided on the same substrate. In this example, the light-emitting element 44 and the second light-receiving portion 22 are provided on the second main surface 42 of the substrate 40. The light-emitting element 44 has a laminated structure of a PN junction or a PIN junction. By supplying power to this laminated structure, the light-emitting element 44 operates as an LED and emits light 14 with a wavelength according to the band gap of the material of the laminated structure. When detecting exhaled breath, the light-emitting element 44 may use InAlSb as the laminated structure, which can output light in the vicinity of the absorption wavelength of carbon dioxide. The light-emitting element 44 described above is called a quantum infrared light-emitting element.

[0088] A portion of the light 14 travels through the substrate 40, passes through the first main surface 41, and is emitted to the path 12. Meanwhile, another portion of the light 14 travels through the substrate 40, is reflected by the first main surface 41, and is incident on the second light receiving section 22.

[0089] The second light receiving section 22 receives the light 14 that has traveled through the substrate 40. In other words, the second light receiving section 22 receives the light 14 that has not passed through the path 12 through which the target gas passes (the space in which the target gas exists). This makes it possible to correct output fluctuations due to changes in the light amount of the light emitting element 44 and temperature. The second light receiving section 22 may only receive the light 14 that has not passed through the space in which the target gas exists.

[0090] The second light receiving section 22 may also have a laminated structure. The laminated structure of the second light receiving section 22 may be a PN junction or PIN junction diode structure. The laminated structure and material of the second light receiving section 22 may be similar to the laminated structure and material of the light emitting element 44. This allows the temperature characteristics of the second light receiving section 22 and the temperature characteristics of the light emitting element 44 to be aligned. The above-mentioned second light receiving section 22 is referred to as a quantum infrared light receiving element.

[0091] Fig. 10 is a block diagram of a gas sensor 10 according to an embodiment of the present invention, which shows a light emitting section 16, a first light receiving section 18, a second light receiving section 22, and a calculation section 20 of the gas sensor 10.

[0092] As described above, the first light receiving unit 18 receives at least a portion of the light 14 that is irradiated from the light emitting unit 16 and passes through the target gas. The first light receiving unit 18 outputs a first light receiving signal to the calculation unit 20 according to the light receiving result.

[0093] As described above, the second light receiving unit 22 receives at least a portion of the light 14 that is irradiated from the light emitting unit 16 and has not passed through the target gas. The second light receiving unit 22 outputs a second light receiving signal to the calculation unit 20 according to the light receiving result.

[0094] The calculation unit 20 acquires a first light receiving signal from the first light receiving unit 18 and acquires a second light receiving signal from the second light receiving unit 22. As described above, the calculation unit 20 detects the occurrence of condensation in the optical path from the light emitting unit 16 to the first light receiving unit 18 based on the first light receiving signal and the second light receiving signal. The calculation unit 20 may detect condensation by the various methods described above. The calculation unit 20 may also calculate and remove the baseline described above. The calculation unit 20 may also calculate the respiratory cycle or length described above.

[0095] 11 is a diagram showing an example of a flowchart of a detection method. The detection method of this example includes a first light receiving step S102, a second light receiving step S104, and a condensation detection step S106. In the first light receiving step S102, light 14 is irradiated onto the path 12 through which the gas to be detected passes, at least a portion of the light 14 that has passed through the gas to be detected is received, and a first light receiving signal according to the light receiving result is output. The first light receiving step S102 is performed by the first light receiving unit 18 described above.

[0096] In the second light receiving step S104, at least a portion of the light 14 that has not passed through the target gas is received, and a second light receiving signal according to the light receiving result is output. The light 14 may be light that has not passed through the path 12. The second light receiving step S104 is performed by the above-mentioned second light receiving unit 22. In FIG. 11, the second light receiving step S104 is performed after the first light receiving step S102, but the order may be reversed, or the two steps may be performed simultaneously.

[0097] In the condensation detection step S106, it is detected that condensation has occurred in the optical path through which the light 14 passes, based on the first light receiving signal and the second light receiving signal. The condensation detection step S106 is performed by the above-mentioned calculation unit 20. In the condensation detection step S106, condensation may be detected by various methods including the above-mentioned condensation determination evaluation value. Furthermore, in the condensation detection step S106, the above-mentioned baseline may be calculated and removed. In the condensation detection step S106, the above-mentioned breathing period or length may also be calculated.

[0098] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the claims that such modifications and improvements can also be included in the technical scope of the present invention. [Explanation of symbols]

[0099] REFERENCE SIGNS LIST 10 gas sensor, 12 path, 14 light, 16 light emitting section, 18 first light receiving section, 20 calculation section, 22 second light receiving section, 24 optical filter, 30 support member, 32 mirror, 40 substrate, 41 first main surface, 42 second main surface, 44 light emitting element

Claims

1. A gas sensor for detecting a detection target gas, A light emitting unit that emits light; a first light receiving unit that receives at least a portion of the light that has passed through the target gas and outputs a first light receiving signal according to a result of the light receiving; a second light receiving unit that receives at least a portion of the light that has not passed through the target gas and outputs a second light receiving signal according to a result of the light receiving; a calculation unit that detects the occurrence of condensation in an optical path from the light emitter to the first light receiver based on the first light receiving signal and the second light receiving signal; A gas sensor comprising:

2. The calculation unit calculates a fluctuation rate of the first light receiving signal and a fluctuation rate of the second light receiving signal, The occurrence of condensation is determined based on a condensation determination evaluation value using the fluctuation rate of the first light receiving signal and the fluctuation rate of the second light receiving signal.

2. The gas sensor according to claim 1.

3. The condensation determination evaluation value is a ratio of a fluctuation rate of the first light receiving signal to a fluctuation rate of the second light receiving signal.

3. The gas sensor according to claim 2.

4. When the condensation determination evaluation value is 2 or more, it is determined that the condensation has occurred.

4. The gas sensor according to claim 3.

5. The second light receiving unit receives the light that has not passed through a space in which the target gas exists.

2. The gas sensor according to claim 1.

6. The gas sensor is provided in a microphone device.

2. The gas sensor according to claim 1.

7. The gas sensor is provided in a head-mounted device.

2. The gas sensor according to claim 1.

8. The calculation unit calculates a baseline of a waveform of the first light receiving signal based on a frequency component of the first light receiving signal that is lower than a first cutoff frequency that is set, and detects the occurrence of the condensation based on a signal obtained by removing the baseline from the first light receiving signal. The gas sensor according to claim 1 .

9. The first cutoff frequency is set in response to a change in the signal value of the first light receiving signal.

9. The gas sensor according to claim 8.

10. The calculation unit changes the first cutoff frequency when the condensation is detected.

10. The gas sensor according to claim 9.

11. The calculation unit calculates a value of the baseline for each of the signal values ​​of the first light receiving signal, When the signal value of the first light receiving signal, which is the object of calculating the baseline value, is decreased by a second set value or more from the signal value at the immediately preceding timing in the time waveform of the first light receiving signal, the calculation unit sets the value of the first cutoff frequency to be higher than the first cutoff frequency at which the condensation is detected. The gas sensor according to claim 10.

12. The calculation unit calculates at least one of a period or a length of a breath containing the detection target gas, using the first light receiving signal from which the baseline has been removed.

9. The gas sensor according to claim 8.

13. The calculation unit determines whether the condensation is caused by exhalation based on a fluctuation in a signal value of the first light receiving signal.

2. The gas sensor according to claim 1.

14. A method for detecting a detection target gas, comprising: receiving at least a portion of the light that is irradiated onto a path through which the target gas passes and that has passed through the target gas, and outputting a first light receiving signal in accordance with the light receiving result; receiving at least a portion of the light that has not passed through the target gas, and outputting a second light receiving signal in accordance with the light receiving result; The occurrence of condensation in an optical path through which the light passes is detected based on the first light receiving signal and the second light receiving signal. Detection method.

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