Gas sensor and detection method

Abstract

The invention relates to a gas sensor and a detection method, preferably for detecting condensation in assays. This gas sensor for detecting a gas to be detected is provided with: 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 gas to be detected and outputs a first light-receiving signal corresponding to a light-receiving result; a second light receiving unit that receives at least a portion of the light that has not passed through the gas to be detected, and outputs a second light receiving signal corresponding to a light receiving result; and a calculation unit that detects, on the basis of the first light reception signal and the second light reception signal, the occurrence of condensation in an optical path from the light emission unit to the first light reception unit.

Description

Technical Field

[0001] The invention relates to a gas sensor and a detection method. Background Art

[0002] Conventionally, there is known a measuring device for measuring respiratory gas or gas concentration (for example, refer to Patent Documents 1 to 3).

[0003] Patent Literature

[0004] Patent Document 1: Japanese Patent No. 5351583

[0005] Patent Document 2: Japanese Patent Application Publication No. 2022-3321

[0006] Patent Document 3: Japanese Patent Application Publication No. 2019-174152 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In the measurement, detection of condensation is preferred.

[0009] Solutions for solving problems

[0010] In order to solve the above problems, in an embodiment of the present invention, a gas sensor for detecting a detection target gas is provided. The above 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 detection target gas and outputs a first light receiving signal corresponding to the light receiving result. Any of the above gas sensors may include a second light receiving unit that receives at least a portion of the light that has not passed through the detection target gas and outputs a second light receiving signal corresponding to the light receiving result. Any of the above gas sensors may include a computing 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.

[0011] In any of the above-mentioned gas sensors, the calculation unit may calculate the variation rate of the first light receiving signal and the variation rate of the second light receiving signal. In any of the above-mentioned gas sensors, the occurrence of condensation may be determined based on a condensation determination evaluation value obtained using the variation rate of the first light receiving signal and the variation rate of the second light receiving signal.

[0012] In any of the above-mentioned gas sensors, the condensation determination evaluation value may be a ratio of a change rate of the first light receiving signal to a change rate of the second light receiving signal.

[0013] Any of the above-mentioned gas sensors may determine that the condensation has occurred when the condensation determination evaluation value is 2 or more.

[0014] In any of the above-mentioned gas sensors, the second light receiving unit may receive light that has not passed through a space where the detection target gas exists.

[0015] Any of the above-mentioned gas sensors can be provided in a microphone device. Any of the above-mentioned gas sensors can be provided in a device worn on the head.

[0016] In any of the above-mentioned gas sensors, the operation unit may calculate a baseline of the 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-mentioned gas sensors, the first cutoff frequency may be set according to a change in a signal value of the first light receiving signal.

[0017] In any of the above-mentioned gas sensors, the calculation unit may change the first cutoff frequency when the condensation is detected.

[0018] In any of the above-mentioned gas sensors, the calculation unit may calculate the value of the baseline for each of the signal values ​​of the first light receiving signal. In any of the above-mentioned gas sensors, when the signal value of the first light receiving signal, which is the object of calculating the value of the baseline, decreases by more than a second set value relative to the signal value at the immediately previous moment in the time waveform of the first light receiving signal, 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.

[0019] In any of the above-mentioned gas sensors, the calculation unit may calculate at least one of a cycle and a length of a breath containing the detection target gas, using the first light receiving signal from which the baseline has been removed.

[0020] In any of the above-mentioned gas sensors, the calculation unit may determine whether the condensation is caused by exhalation based on a change in the signal value of the first light receiving signal.

[0021] In order to solve the above-mentioned problem, in another embodiment of the present invention, a detection method for detecting a detection target gas is provided. In the above-mentioned detection method, at least a portion of the light that is irradiated to the path through which the detection target gas passes and passes through the detection target gas can be received, and a first light receiving signal corresponding to the light receiving result can be output. In any of the above-mentioned detection methods, at least a portion of the light that does not pass through the detection target gas can be received, and a second light receiving signal corresponding to the light receiving result can be output. In any of the above-mentioned detection methods, the occurrence of condensation in the optical path through which the light passes can be detected based on the first light receiving signal and the second light receiving signal.

[0022] In addition, the above summary of the invention does not list all the necessary features of the present invention. In addition, sub-combinations of these feature groups can also constitute inventions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a diagram showing a gas sensor 10 for detecting a detection target gas.

[0024] Figure 2 This is a diagram showing changes in signal values ​​when condensation occurs in the light emitting unit 16 or the first light receiving unit 18 .

[0025] Figure 3 is a diagram showing the calculation of the baseline.

[0026] Figure 4A is a graph showing the results obtained using a fixed first cutoff frequency in the baseline calculation.

[0027] Figure 4B It shows that according to Figure 4A A graph showing the result of taking the ratio of the first light receiving signal to the second light receiving signal and the difference between the baseline calculated value.

[0028] Figure 5A This is a diagram showing the result obtained by changing the first cutoff frequency in a magnitude relationship with the immediately preceding signal value in the baseline calculation.

[0029] Figure 5B It shows that according to Figure 5A A graph showing the light reception signal ratio and the judgment signal calculated from the baseline is shown.

[0030] Fig. 6A It is a diagram showing the baseline calculation when condensation occurs.

[0031] Figure 6B It shows that Fig. 6A A diagram showing an example of a determination signal obtained by the difference between the light receiving signal ratio and the baseline calculated value.

[0032] Fig. 7AThis is a diagram showing the results obtained by changing the first cutoff frequency in the baseline calculation when condensation occurs.

[0033] Figure 7B It shows that according to Fig. 7A A diagram showing an example of a judgment signal calculated from a light receiving signal ratio and a baseline calculation value.

[0034] Figure 8 It is a diagram showing another embodiment of the gas sensor 10 .

[0035] Fig. 9 1 is a diagram showing a configuration example of the light emitting unit 16 .

[0036] Fig.10 1 is a diagram showing an example of a block diagram of the gas sensor 10 in the embodiment.

[0037] Fig.11 This is a diagram showing an example of a flowchart of a detection method. DETAILED DESCRIPTION

[0038] The present invention is described below by the embodiments of the invention, but the following embodiments do not limit the invention involved in the claims. In addition, the combination of features described in the embodiments may not all be necessary for the solution of the invention. In this specification, the same parts in each figure are marked with the same figure numbers, and the description is sometimes omitted. In addition, for the convenience of description, a part of the structure is sometimes not illustrated.

[0039] In this specification, sometimes the orthogonal coordinate system of the X-axis, Y-axis and Z-axis is used to explain technical matters. The orthogonal coordinate system only determines the relative position of the components and does not limit the specific direction. For example, the Z-axis direction is not limited to the height direction relative to the ground.

[0040] Figure 1 1 is a diagram showing a gas sensor 10 for detecting a detection target gas. The gas sensor 10 includes a light emitting unit 16, a first light receiving unit 18, and a computing unit 20. The light emitting unit 16, the first light receiving unit 18, and the computing unit 20 can be mounted on a supporting member 30. In this example, the light emitting unit 16 is mounted on one supporting member 30 of the supporting members 30 facing each other, and the first light receiving unit 18 and the computing unit 20 are mounted on the other supporting member 30. In this example, the plane parallel to the main surface of the supporting member 30 is set as the XY plane, and the direction perpendicular to the main surface of the supporting member 30 is set as the Z-axis direction for description.

[0041] The gas sensor 10 is an optical gas sensor that utilizes the unique absorption wavelength of the components contained in the detection target gas. The light emitting unit 16 irradiates the light 14 toward the path 12 through which the detection target gas passes. As an example, the light emitting unit 16 is an LED. The wavelength of the light 14 can be appropriately selected in accordance with the absorption wavelength of the detection target gas. A portion of the light 14 passes through the path 12 and is incident on the first light receiving unit 18. A portion of the light 14 is incident on the second light receiving unit 22 described later.

[0042] The first light receiving unit 18 receives at least a portion of the light 14 that has passed through the detection target gas, and outputs a first light receiving signal corresponding to the light receiving result to the calculation unit 20. As an example, the first light receiving unit 18 is a photodiode.

[0043] The calculation unit 20 calculates the first light receiving signal. As an example, the calculation unit 20 is an IC. Since the detection target gas absorbs the light 14 and the amount of light received at the absorption wavelength of the detection target gas decreases, the calculation unit 20 can calculate the concentration of the detection target gas or a value corresponding to the concentration based on the value of the first light receiving signal.

[0044] Here, as an example of the operation performed on the first light receiving signal, a specific example of the operation of the first light quantity information Φ1 related to the light quantity information absorbed by the gas as the detection object is shown. Let λ be the wavelength (um), let the intensity of the light 14 emitted from the light emitting unit 16 that reaches the first light receiving unit 18 in the absence of the detection gas be represented by Φ1(λ), ​​and let the sensitivity of the first light receiving unit 18 be Ri1(λ). Let the optical path length of the optical path from the light emitting unit 16 to the first light receiving unit 18 be L. In addition, let the absorption coefficient of the detection gas be μ(λ), and let the concentration of the detection object gas be c. Here, Φ(λ) is set to the value in the absence of the detection gas, but it can also be the value in the case where a certain reference concentration of the target gas is present.

[0045] [Number 1]

[0046] Φ1∝∫Φ1(λ)Ri1(λ)(1-e -cμ(λ)L )dλ…(1)

[0047] The first light quantity information Φ1 changes according to the concentration c of the detection gas. The higher the concentration of the detection gas, the larger Φ1 becomes.

[0048] Here, Φ1 may be corrected based on temperature information. In this case, the gas sensor 10 may further include a thermometer, and the computing unit 20 may receive a temperature signal from the thermometer. When the term based on temperature is considered, the equation 1 becomes the equation 2.

[0049] [Number 2]

[0050] Φ1∝∫Φ1(λ, Temp)Ri1(λ, Temp)(1-e -cμ(λ，Temp)L )dλ…(2)

[0051] Here, when the temperature correction formula is f1 and the value after temperature correction of Formula 2 is Φ1comp, it can be expressed as in Formula 3.

[0052] [Number 3]

[0053] Φ1comp∝f1(Temp)∫Φ1(λ, Temp)Ri1(λ, Temp)(1-e -cμ(λ，Temp)L )dλ···(3)

[0054] In the detection of condensation described later, the first light quantity information Φ1 of any of Formulas 1 to 3 can be used. Condensation can be detected by comparing the first light quantity information Φ1 with the first set value A1. Regarding the first set value A1, the threshold is determined by utilizing the fact that a further signal change will occur relative to the amount of absorbed light that can be expected by gas detection when condensation usually occurs. For example, in the case of a carbon dioxide sensor used as a breath detection sensor, the first set value A1 is determined based on the amount of absorbed light at a carbon dioxide concentration of 40,000 ppm contained in the breath. Normally, the concentration of carbon dioxide contained in the breath does not exceed about 40,000 ppm. On the other hand, when condensation occurs, a signal change greater than the change in the amount of absorbed light at 40,000 ppm of carbon dioxide may occur.

[0055] The gas sensor 10 may include a second light receiving unit 22. The second light receiving unit 22 may be built into the light emitting unit 16. The structure of the light emitting unit 16 and the second light receiving unit 22 will be described later. The second light receiving unit 22 receives the light 14 emitted by the light emitting unit 16 that does not pass through the path 12 through which the detection target gas passes, and outputs a second light receiving signal corresponding to the light receiving result. The second light receiving unit 22 may receive at least a portion of the light 14 that does not pass through the detection target gas. The second light receiving signal may be output to the operation unit 20. The operation unit 20 may use the signal value of the second light receiving signal to correct the first 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 unit 22 and performing the correction, the output variation caused by the change of the light amount of the light emitting unit 16 and the temperature can be corrected.

[0056] The operation unit 20 can correct the first light quantity information using the second light receiving signal. Here, as an example of correction, a specific example of the operation of the second light quantity information Φ2 related to the light quantity information absorbed by the gas as the detection object is shown. Let λ be the wavelength (μm), let the intensity of the light 14 emitted from the light emitting unit 16 that reaches the first light receiving unit 18 in the absence of the detection gas be represented by Φ1(λ), ​​let the intensity of the light that reaches the second light receiving unit be represented by Φ2(λ), let the sensitivity of the first light receiving unit 18 be Ri1(λ), ​​and let the sensitivity of the second light receiving unit 22 be Ri2(λ). Let the optical path length of the optical path from the light emitting unit 16 to the first light receiving unit 18 be L. In addition, let the absorption coefficient of the detection gas be μ(λ), and let the concentration of the detection object gas be c. Here, Φ1(λ) is set to a value in the absence of the detection gas, but it may be a value in the case where a certain reference concentration of the target gas is present. The second light quantity information Φ2 is obtained by Formula 4.

[0057] [Number 4]

[0058]

[0059] Here, the second light quantity information Φ2 may be corrected based on temperature information. In this case, the gas sensor 10 may further include a thermometer, and the computing unit 20 may receive a temperature signal from the thermometer. When the term based on temperature is considered, the equation 4 becomes the equation 5.

[0060] [Number 5]

[0061]

[0062] Here, when the temperature correction formula of the signal of the light receiving sensor is f1, the temperature correction formula of the signal of the second light receiving unit is f2, and the value after temperature correction of Formula 5 is Φ2comp, it can be expressed as Formula 6.

[0063] [Number 6]

[0064]

[0065] In addition, it is assumed that Ri2 corrects Ri1 and the temperature correction equation can be applied to the quotient of each sensor signal.

[0066] [Number 7]

[0067]

[0068] The gas sensor 10 may further include an optical filter 24 disposed between the light emitting unit 16 and the first light receiving unit 18. The optical filter 24 in this example is disposed on the surface of the first light receiving unit 18. The optical filter 24 is used to limit the wavelength of the light 14 incident on the first light receiving unit 18. As an example, the optical filter 24 is a bandpass filter. When the transmittance of the bandpass filter is set to T BPF When (λ), Formula 1 becomes Formula 8.

[0069] [Number 8]

[0070] Φ1∝∫Φ1(λ)Ri1(λ)T BPF (λ)(1-e -cμ(λ)L )dλ…(8)

[0071] Generally speaking, the sensitivity of the first light receiving unit 18 changes due to the influence of temperature. In a sensitivity curve in which the horizontal axis is the wavelength of light and the vertical axis is the sensitivity of the first light receiving unit 18, the influence of temperature is manifested as the sensitivity curve shifting in the horizontal axis direction. On the other hand, the sensitivity curve has a wavelength region in which the sensitivity value is almost flat. By using the optical filter 24 to allow only light of the wavelength region to be incident on the first light receiving unit 18, even if the temperature of the first light receiving unit 18 changes, the influence on the sensitivity can be suppressed.

[0072] There is no particular limitation on the type of gas to be detected. In this specification, as an example, the gas to be detected is set to be exhaled air for explanation. In this specification, when the gas to be detected is exhaled air, it is set to be carbon dioxide contained in exhaled air for explanation, but ethanol or the like may also absorb light 14. The gas sensor 10 for detecting 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 the earphone.

[0073] Figure 2 2 is a diagram showing changes in signal values ​​when condensation occurs on the light emitting unit 16 or the first light receiving unit 18. Figure 2 In the following figures, the first light receiving signal is represented by IR1 and the second light receiving signal is represented by IR2. Figure 2The horizontal axis represents time, the vertical axis on the left represents the signal intensity (%) of the value of the first light receiving signal and the signal intensity (%) of the value of the second light receiving signal, and the vertical axis on the right represents temperature. The reference of the signal intensity can be the signal value when there is no exhalation. The signal intensity in this example is the value obtained by expressing the value of each signal as a percentage when the value of each signal when there is no exhalation is standardized as 100% (reference value). The difference between the reference value and the signal intensity is set as the rate of change. In the case of this example, it is expressed by the rate of change (%) = reference value (100%) - signal intensity (%). The more the signal intensity deviates from 100%, the greater the rate of change, indicating a greater change relative to the reference value. However, the reference value may also be a value other than 100%. The solid line in the figure represents the first light receiving signal, the single-point 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. In addition, the figure shows the rate of change ΔIR1 of the first light receiving signal and the rate of change ΔIR2 of the second light receiving signal. The calculation unit 20 can calculate the rate of change ΔIR1 of the first light receiving signal and the rate of change ΔIR2 of the second light receiving signal. In this specification, the value of the first light receiving signal is sometimes referred to as the first light receiving signal, and the value of the second light receiving signal is sometimes referred to as the second light receiving signal. In addition, the calculation unit 20 can use the signal value directly for calculation, or can use the value obtained by converting the signal value into a rate of change for calculation. The expression of "signal value" and the expression of "rate of change" can be replaced with each other.

[0074] exist Figure 2 In the process, exhaled air is blown toward the gas sensor 10 which is cooled to about 0°C. Breathing is performed from 40 seconds to 2 minutes and 20 seconds in the figure, and the gas sensor 10 detects exhalation during the above period. The above period is shown in the figure as a breathing period. Since the amount of light received by the first light receiving unit 18 decreases due to the absorption of carbon dioxide, the first light receiving signal decreases when exhalation is detected. In addition, since the exhaled air diffuses rapidly in the air, the first light receiving signal increases (recovers) immediately after it decreases. The slight increase and decrease in the first light receiving signal from 40 seconds to 2 minutes and 20 seconds in the figure corresponds to breathing. A valley-shaped portion in the first light receiving signal corresponds to one breath. In Figure 2 During the breathing period, about 40 breaths were taken.

[0075] The second light receiving signal indicates the light receiving result of the light 14 that has not passed through the path 12 through which the detection target gas passes. Therefore, the change in the value of the second light receiving signal due to breathing is not observed. The temperature of the gas sensor 10 rises from around 0°C due to the temperature of the exhaled breath after the start of breathing, repeatedly increases and decreases while breathing continues, and gradually decreases when breathing ends.

[0076] When detecting exhaled breath, moisture contained in the exhaled breath may cause condensation on the gas sensor 10. Figure 2In the example, breath is blown toward the gas sensor 10 at 0°C to intentionally cause condensation on the gas sensor 10. When condensation occurs on the light emitting portion 16 or the first light receiving portion 18 of the gas sensor 10, part of the light 14 is absorbed, reflected, or refracted by the condensation, thereby bending in an unexpected direction, and affecting the first light receiving signal. Figure 2 The first light receiving signal drops significantly around 40 seconds, and then continues to drop during the breathing period. It is believed that the drop in the first light receiving signal is due to the influence of condensation caused by exhalation.

[0077] When condensation occurs, the S / N ratio of the first light receiving signal decreases, so the false detection rate increases. In addition, the case where condensation occurs on the light emitting unit 16 or the first light receiving unit 18 may also include the case where condensation occurs on the optical path through which the light 14 between the light emitting unit 16 and the first light receiving unit 18 passes. As an example, it may also include the case where condensation occurs on the optical filter 24. In addition, the condensation in this example is not limited to condensation caused by exhalation, and may also include condensation caused by other factors, and may also include dirt generated on the light emitting unit 16 or the first light receiving unit 18.

[0078] The operation unit 20 can detect 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 optical path may include the light emitting unit 16, the first light receiving unit 18, and the optical filter 24. The operation unit 20 can detect the condensation occurring in the light emitting unit 16 or the first light receiving unit 18 based on the rate of change ΔIR1 of the first light receiving signal and the rate of change ΔIR2 of the second light receiving signal. The operation unit 20 can calculate the first light quantity information described above based on the first light receiving signal, and obtain the condensation determination evaluation value based on the first light quantity information. The condensation determination evaluation value may be the first light quantity information itself, or may be the second light quantity information obtained by correcting the first light quantity information using the second light receiving signal. The condensation determination evaluation value may be any value obtained by using equations 1 to 8. The condensation determination evaluation value may be a value obtained using the rate of change ΔIR1 of the first light receiving signal and the rate of change ΔIR2 of the second light receiving signal. The condensation determination evaluation value may be a ratio of the rate of change of the first light receiving signal to the rate of change of the second light receiving signal (ΔIR1 / ΔIR2). The operation unit 20 may detect the occurrence of condensation in the optical path from the light emitting unit 16 to the first light receiving unit 18 based on the condensation determination evaluation value. In this way, it is possible to know whether the gas sensor 10 is in a state with a high false detection rate. The operation unit 20 may determine that condensation has occurred when the condensation determination evaluation value is greater than 2. The above value may be greater than 3 or greater than 4. The operation unit 20 may notify the detection result to the outside. The operation unit 20 uses the rates of change ΔIR1 and ΔIR2 at the same time to calculate the ratio of the rates of change (ΔIR1 / ΔIR2). The operation unit 20 may calculate the ratio of the rates of change (ΔIR1 / ΔIR2) in a time series.

[0079] The operation unit 20 can determine that condensation has occurred when the rate of change of the first light receiving signal is less than the first set value. The operation unit 20 can also determine that condensation has occurred when the condensation determination evaluation value is greater than the first set value. As an example, the first set value can be the rate of change of the first light receiving signal or the value of the condensation determination evaluation value when a carbon dioxide concentration of 40,000 ppm is detected. The carbon dioxide concentration in the human lung is about 40,000 ppm. When exhaled air is discharged from the lungs to the atmosphere, the exhaled air diffuses into the atmosphere, so a carbon dioxide concentration of more than 40,000 ppm will not be detected by the exhaled air. Therefore, it can be determined that condensation has occurred based on the above-mentioned first set value.

[0080] The operation unit 20 may also determine that condensation has occurred when the rate of change of the second light receiving signal is fixed and only the rate of change of the first light receiving signal decreases, and the rate of change of the first light receiving signal is less than the first set value or the condensation determination evaluation value is greater than the first set value. A fixed rate of change may mean that the change in the signal value is within 5% during a specified period. The above-mentioned specified period may be 30 seconds, 60 seconds, or a period that is 10 times the breathing cycle. The operation unit 20 may also 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 greater than a specified value. The above-mentioned specified 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).

[0081] Figure 3 is a diagram showing the calculation of the baseline. Figure 3 The horizontal axis represents time, and the vertical axis represents the value of the ratio of the intensity of the first light receiving signal to the second light receiving signal. In this specification, the ratio of the intensity of the first light receiving signal to the second light receiving signal is sometimes referred to as the light receiving signal ratio. As mentioned above, by dividing the first light receiving signal by the second light receiving signal, the output fluctuation caused by the change in the light amount of the light emitting unit 16 and the temperature can be corrected. Figure 3 In the above diagram, the change in the light receiving signal ratio from 10 seconds to 20 seconds corresponds to breathing. A valley in the light receiving signal ratio corresponds to one breath. Figure 3 In FIG. 1 , five valley-shaped portions appear in the waveform of the light reception signal ratio, thus showing the light reception signal ratios of five breaths.

[0082] In the subsequent figures, the light receiving signal ratio of the first light receiving signal and the second light receiving signal is also used to illustrate the implementation method, but the use of the second light receiving signal is not necessary. The signal value of the first light receiving signal can also be used instead of the light receiving signal ratio. In this case, the expression "light receiving signal ratio" can be replaced by "first light receiving signal". In this specification, even if the light receiving signal ratio is processed, the first light receiving signal can be processed in the same way, and even if the first light receiving signal is processed, the light receiving signal ratio can be processed in the same way.

[0083] The solid line in the figure represents the light receiving signal ratio. The single-dot chain line in the figure represents a determination threshold value described later. The calculation unit 20 calculates the baseline of the waveform of the first light receiving signal based on the light receiving signal ratio. The dotted line in the figure represents the calculated baseline.

[0084] The baseline is a signal waveform based on factors other than the detection target gas (interference). When the detection target gas is exhaled air, the baseline is a signal waveform based on factors other than carbon dioxide contained in the exhaled air. Figure 3The waveform is obtained by reducing or removing the component based on the concentration of carbon dioxide from the waveform shown by the solid line. The baseline may include a component of the intensity of the light 14 emitted by the light emitting unit 16 and a variable component caused by factors other than the change in the concentration of carbon dioxide.

[0085] When the gas sensor 10 detects exhalation, the temperature of the light emitting unit 16 and the first light receiving unit 18 changes according to the temperature of the exhaled breath, and the characteristics sometimes change. The baseline can be a signal waveform that includes the influence of such characteristic changes and does not include the influence of carbon dioxide. The baseline based on the interference of the frequency deviation from the breathing cycle can also include the influence of humidity, component degradation, etc., but in this specification, it is assumed that it mainly includes changes caused by the temperature of the exhaled breath or changes caused by 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 subsequent description, the changes caused by the temperature of the exhaled breath are processed first, and then the changes caused by temperature and condensation are processed.

[0086] The calculation unit 20 can calculate the baseline based on the light receiving signal ratio. In this way, the influence of exhalation on temperature can be appropriately reflected. Even when detecting other detection target gases, as long as the interference is correlated with the detection target gas, the influence of the interference can be appropriately reflected by calculating the baseline based on the signal value of the detection target gas.

[0087] Figure 3 The baseline calculation value is calculated based on the light receiving signal ratio, so it changes according to the breathing cycle, which shows the influence of temperature caused by exhalation. The parameters in the baseline calculation can be determined by experiments in a way that shows the change of the light receiving signal ratio caused by factors other than carbon dioxide. As an example, the parameter is the coefficient b0 described later.

[0088] The calculation unit 20 can calculate the baseline by removing the frequency component of the interference whose frequency deviates from the breathing cycle from the time waveform of the light receiving signal ratio. As an example, the calculation unit 20 calculates the baseline by filtering represented by infinite impulse response (IIR). Table 1 shows an example of the process of baseline calculation in IIR filtering.

[0089] [Table 1]

[0090] x0 y0=x0 x1 y1=x1×b0+y0×(1-b0) x2 y2=x2×b0+y1×(1-b0) x3 y3=x3×b0+y2×(1-b0)

[0091] In the table, x represents the signal value of the light receiving signal ratio, and y represents the calculated value of the baseline. b0 is a filter coefficient. The numbers after x and y represent the sampling point n. Table 1 shows that n=3.

[0092] The calculation unit 20 calculates the value yn of the baseline for each signal value xn of the light receiving signal ratio. As shown in Table 1, the calculated value yn of the baseline is calculated by summing the value obtained by multiplying the corresponding signal value xn by the coefficient b0 and the value obtained by multiplying the calculated value yn-1 of the previous baseline by (1-b0). In other words, the coefficient b0 determines the proportion in which the value of the corresponding signal value is reflected relative to the calculated value of the previous baseline. The coefficient b0 takes a value greater than 0 and less than 1. When the coefficient b0 is increased, the value of the corresponding signal value is further reflected, and the baseline easily follows the changes in the signal value. In the example of Table 1, the calculated value yn of the baseline reflects the value of the previous baseline yn-1, but in other examples, the calculated value yn of the baseline may also reflect the values ​​of the previous multiple baselines.

[0093] In the baseline calculation, the following method can be used instead of the IIR filter. As an example, the baseline can be calculated by the moving average filter (MA: Moving Average) shown in equations (9) and (10).

[0094] [Number 9]

[0095]

[0096] [Number 10]

[0097]

[0098] Among them, Y n represents the calculated value of the baseline, X n represents the signal value, M represents the number of intervals, and F s represents the sampling frequency, f c Indicates the cutoff frequency.

[0099] As another example, it is also possible to calculate by a weighted moving average filter (WMA: Weighted Moving Average) shown in equation (11).

[0100] [Number 11]

[0101]

[0102] Among them, W i Indicates weight. Other symbols are the same as above.

[0103] As another example, it is also possible to calculate by using finite impulse response filtering (FIR: Finite Impulse Response) shown in equations (12) and (13).

[0104] [Number 12]

[0105]

[0106] [Number 13]

[0107]

[0108] Among them, b i Represents the filter coefficient. Other symbols are the same as above.

[0109] As another example, calculation may be performed using a Butterworth filter as shown in equation (14).

[0110] [Number 14]

[0111]

[0112] Wherein, N represents the filter order, s represents the complex frequency, and other notations are the same as above.

[0113] In addition, the baseline may be determined based on a value when the signal changes less, such as data of the time when no breathing is performed in the baseline calculation. In addition, at least one of an upper limit and a lower limit may be set for the baseline. In addition, multiple baseline calculation methods may be changed according to the signal value and the environmental value.

[0114] Here, the calculation of the immediately preceding baseline is not limited to calculating the baseline of xn through xn-1. Any baseline calculation method that is difficult to track the breathing signal will suffice. For example, for xn, m can be set to a natural number, and the baseline calculation is performed using all signals from xn-1 to the earlier data xn-m. For example, if data is acquired every 0.1 seconds, m=3 can be set, and the baseline calculation of the signal xn is performed using the data of the signals xn-1, xn-2, and xn-3. The immediately preceding range can be determined in a manner that makes it difficult to track the breathing signal but can track slower temperature changes. The baseline calculation can be based on the ratio of the light-receiving signals before Tn, or it can be based on the ratio of the light-receiving signals in a specific period before Tn that is shorter than the breathing cycle.

[0115] The calculation unit 20 removes the baseline from the light receiving signal ratio. Removing the baseline may be a process of subtracting the baseline value at each moment from the signal value at that moment. By calculating and removing the baseline, changes in the signal value caused by factors other than carbon dioxide contained in the exhaled breath can be corrected, thereby enabling more accurate measurements including the above-mentioned condensation detection. The calculation unit 20 may use the first light receiving signal after removing the baseline to detect the occurrence of condensation, or may calculate a condensation determination evaluation value. In this specification, the signal after removing the baseline from the light receiving signal ratio is sometimes referred to as a determination signal.

[0116] The operation unit 20 can calculate at least one of the cycle and length of breathing. The operation unit 20 can use the determination signal to calculate at least one of the cycle and length of breathing. When the value of the determination signal is lower than the determination threshold, the operation unit 20 can determine that exhalation is detected. The operation unit 20 can calculate the cycle or length of breathing based on the period during which the value of the determination signal is lower than the determination threshold. The operation unit 20 can set a continuous period during which the value of the determination signal is lower than the determination threshold as the length of breathing. The operation unit 20 can calculate the sum of a continuous period during which the value of the determination signal is higher than the determination threshold and a continuous period during which the value of the determination signal is lower than the determination threshold as the cycle of breathing. The operation unit 20 can calculate the average value within a specified measurement period as the cycle or length of breathing. By calculating the cycle or length of breathing, it is possible to determine whether the emotion of the person who is breathing is excited or relaxed, etc. In the case of measuring the cycle or length of breathing, as long as the value of the determination signal can be compared with the determination threshold, the amplitude of the determination signal does not need to be calculated, and the measurement accuracy of the value of the determination signal may not be high.

[0117] Here, setting the coefficient b0 in the infinite impulse response is equivalent to removing frequency components above a predetermined frequency from the signal value in the calculation of the baseline. When the predetermined frequency is set as the first cutoff frequency, the relationship between the first cutoff frequency and the coefficient b0 is expressed by the equation shown in equation 15. In equation 15, a1=b0-1.

[0118] [Number 15]

[0119]

[0120] The calculation unit 20 can calculate the baseline based on the frequency component of the time waveform of the light receiving signal ratio that is lower than the set first cutoff frequency. By setting the coefficient b0 in the infinite impulse response, the baseline can be calculated based on the frequency component of the light receiving signal ratio that is lower than the first cutoff frequency. A specific example of the coefficient b0 and the first cutoff frequency will be described later.

[0121] Figure 4A is a graph showing the results obtained using a fixed first cutoff frequency in the baseline calculation. Figure 4A The axis and the solid and dashed lines in the figure Figure 3 In this example, the baseline calculation is performed so that the first cutoff frequency is fixed for the value yn of the baseline at each time. For example, in the example of Table 1, b0 is a fixed value for all n. Figure 4A The baseline has poor tracking performance when the light receiving signal ratio increases. Therefore, during the period of continuous breathing, the baseline does not return to the original level (IR1 / IR2=1 to 1.01), but becomes a relatively low level. In addition, there is a part where the baseline is lower than the light receiving signal ratio just after the period of continuous breathing ends.

[0122] Figure 4B This is a diagram showing an example of a determination signal obtained by taking the difference between the received light signal ratio and the calculated baseline value. Since the determination signal represents the signal component based on exhalation, ideally, the determination signal in the absence of exhalation coincides with the reference point (IR1 / IR2 = 0). Additionally, ideally, the determination signal in the presence of exhalation is smaller than the reference point. In Figure 4A , a part of the determination signal is located at a position above (positive side) the reference point (IR1 / IR2 = 0). In other words, the determination signal is shifted upward. This is considered to be because the followability of the baseline when the received light signal ratio increases is poor, causing the baseline to be evaluated as smaller than the actual value. Figure 4B In the figure, the dashed-dotted line represents the determination threshold. As an example, when the signal value is lower than the determination threshold, it is determined that exhalation has been detected. In

[0123] , since only a part of the signal value variation caused by exhalation is lower than the determination threshold, sometimes a part of the breath cannot be detected. Therefore, it is preferable to calculate the respiratory cycle, etc., more accurately. Figure 4B This is a diagram showing the result obtained by changing the first cut-off frequency according to the magnitude relationship of the immediately preceding signal value in the baseline calculation. The operation unit 20 can 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 can be set according to the change in the signal value of the received light signal ratio. In this example, the operation unit 20 sets the first cut-off frequency when the signal value of the received light signal ratio that is the object of calculating the baseline increases with respect to the signal value at the immediately preceding moment in the time waveform of the received light signal ratio to be higher than the first cut-off frequency when the signal value of the object of calculating the baseline decreases with respect to the immediately preceding signal value.

[0124] Figure 5A When using the notations in Table 1, the first cut-off frequency when xn > xn-1 is set to be higher than the first cut-off frequency when xn < xn-1. The operation unit 20 can set the first cut-off frequency to be high 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, even the 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

[0125] , the baseline follows the increase in the signal value of the first light emission signal well. Therefore, during the period when breathing is continuous and the period immediately after it, compared with the example of Figure 5A , the baseline returns to the vicinity of the original value (1 to 1.01). Figure 4A

[0126] In addition, 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. Therefore, it is considered that the influence of the temperature characteristics of the element appears in the time waveform of the baseline. The temperature of the element changes synchronously with the breathing, so the time waveform of the baseline appears as follows. Figure 5A The valley portion synchronized with breathing as shown in FIG. 1 is considered to be affected by the temperature of the exhaled breath 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 decreases, the baseline calculation value is difficult to follow the change of the signal value caused by the detection of carbon dioxide, so the baseline calculation value is not easy to include the influence caused by carbon dioxide, so that the influence of the temperature of the exhaled breath is appropriately reflected.

[0127] The operation unit 20 can set the first cutoff frequency when the signal value of the object serving as the calculation baseline of the light receiving signal ratio increases relative to the past signal value in the time waveform of the light receiving signal ratio to be higher than the first cutoff frequency when the signal value of the object serving as the calculation baseline value decreases relative to the past signal value. The above-mentioned past signal value can be the average value of the light receiving signal ratio in a period shorter than the breathing cycle of the period in which the light receiving signal ratio immediately before is set as the end of the period, or it can be the signal value of any light receiving signal ratio in the period, or it can be the signal value of all light receiving signal ratios in the period. When using the notation of Table 1, as an example, the first cutoff frequency when xn is higher than the average value of xn-1, xn-2, and xn-3 can be set to be higher than the first cutoff frequency when xn is lower than the average value.

[0128] Figure 5B It shows that according to Figure 5A The figure shows the ratio of the received light signal and the judgment signal calculated from the baseline. Figure 5B In the figure, the tiny noise component is removed, and the judgment signal is located below the reference point (IR1 / IR2=0) at all times. Figure 4B The determination threshold is shown in the same manner. According to this example, the deviation of the determination signal can be suppressed, and the breathing can be detected more accurately and the cycle and length of the breathing can be calculated.

[0129] The operation unit 20 can set the first cut-off frequency when the signal value of the object serving as the calculation baseline of the received light signal ratio increases with respect to the signal value at the immediately preceding moment in the time waveform of the received light signal ratio to be more than 10 times higher than the first cut-off frequency when the signal value of the object serving as the calculation baseline decreases with respect to the immediately preceding signal value. As an example, the first cut-off frequency when xn > xn-1 can be set to 1 Hz or more (for example, about 1.8 Hz (coefficient b0 = 0.24)), and the first cut-off frequency when xn < xn-1 can be set to 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 above magnification can be 2 times or more, can be 5 times or more, and can also be 20 times or more. The first cut-off frequency can be 3 Hz or less. In addition, the signal value at the immediately preceding moment can be the above-mentioned past signal value.

[0130] Fig. 6A It is a diagram showing baseline calculation in the case of dew condensation. Fig. 6A The horizontal axis represents time, the left vertical axis represents the received light signal ratio, and the right vertical axis represents temperature. The solid line in the figure represents the received light signal ratio, the dash-dot line in the figure represents the baseline, and the dotted line in the figure represents the temperature of the gas sensor 10.

[0131] In Fig. 6A it is the same as Figure 2 and exhaled breath is blown onto the gas sensor 10 at about 0°C. Breathing is performed from 40 seconds to 2 minutes and 20 seconds in the figure, and the gas sensor 10 detects the exhaled breath during the above period. The above period is set as the breathing period and shown in the figure. The minute fluctuations in the received light signal ratio during the breathing period correspond to breathing. One valley portion in the received light signal ratio corresponds to one breath. In Fig. 6A about 40 breaths are performed during the breathing period.

[0132] In this example, exhaled breath is also blown onto the gas sensor 10 at about 0°C to intentionally cause dew condensation. In Fig. 6A the received light signal ratio drops significantly near 40 seconds and then continues to drop until about 2 minutes and 20 seconds when the breathing ends. It is considered that the decrease in the received light signal ratio is due to the influence of dew condensation caused by exhaled breath.

[0133] In Fig. 6A the operation unit 20 calculates the baseline. The calculation method is the above IIR filter. In this example, for each moment value yn of the baseline, the baseline calculation is performed in such a way that the first cut-off frequency is fixed.

[0134] In Fig. 6ACondensation occurs during the breathing period, so the light receiving signal ratio continues to decrease during the breathing period. Therefore, it is found that the baseline cannot track the portion where the light receiving signal ratio decreases during the breathing period. In particular, it cannot track the initial stage (40 seconds to 1 minute) when the light receiving signal ratio decreases greatly due to condensation during the breathing period.

[0135] Figure 6B It shows that Fig. 6A An example of a judgment signal obtained by calculating the difference between the light receiving signal ratio and the baseline calculated value. The judgment signal represents a signal component based on exhalation, so the judgment signal in the absence of exhalation is ideally consistent with the reference point (IR1 / IR2=0). In addition, in the presence of exhalation, since carbon dioxide diffuses between breaths (peaks between valleys), it is also ideally consistent with the reference point (IR1 / IR2=0). However, in Figure 6B Many peaks are located below (negatively) the reference point. This is believed to be because the change in signal value due to condensation cannot be properly reflected in the baseline. The number of peaks located below (negatively) is particularly high in the early stage of the breathing period (40 seconds to 1 minute).

[0136] The dashed line in the figure indicates the determination threshold. As an example, when the signal value is lower than the determination threshold, it is determined that exhalation is detected. Figure 6B In the above example, only a part of the change of the light receiving signal ratio due to exhalation crosses the determination threshold, and the other changes are located at the lower side (negative side) than the determination threshold. In this case, since the period when the light receiving signal ratio is determined to be located at the lower side (negative side) than the determination threshold is the middle period of one breath, it may cause false detection of the cycle and length of the breath. Therefore, it is preferable to calculate the baseline more accurately.

[0137] Fig. 7A This is a diagram showing the results obtained by changing the first cutoff frequency in the baseline calculation when condensation occurs. Fig. 7A The axes and lines of 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 to be higher than the first cutoff frequency when condensation is not detected. As a result, the baseline can easily follow the change of the light receiving signal ratio caused by condensation. In other words, the influence of condensation can be appropriately included in the baseline. The detection of condensation can be performed by Figure 2 In addition to the cutoff frequency, the attenuation tendency, the filter order, and the type of low-pass filter may also be changed.

[0138] Figure 7B It shows that according to Fig. 7AAn example of a judgment signal calculated from the light receiving signal ratio and the baseline calculation value. Figure 7B In the case of , the peaks between the breaths (the peaks between the valleys) are roughly consistent with the reference point (IR1 / IR2=0). That is, the influence of condensation can be properly corrected. Figure 7B The determination threshold is omitted in the figure.

[0139] The decrease in the light receiving signal ratio due to condensation occurs at the beginning of the breathing period ( Fig. 6A and Fig. 7A The calculation unit 20 may set the first cutoff frequency to a value higher than the first cutoff frequency when condensation is detected, when the signal value of the light receiving signal ratio as the object of the baseline calculation value in the time waveform of the light receiving signal ratio decreases by more than the second set value relative to the signal value at the moment immediately before. Thereby, the tracking performance of the baseline can be improved, especially in the early stage of large changes in the breathing period.

[0140] As described above, the concentration of carbon dioxide in the lungs is about 40,000 ppm. When carbon dioxide flows from the lungs into the gas sensor 10 as exhaled air, it is considered that carbon dioxide diffuses in the atmosphere and the concentration detected by the gas sensor 10 is about 10,000 ppm. As an example, the second set value may be a signal value when a carbon dioxide concentration of 20,000 ppm or 30,000 ppm is detected.

[0141] The operation unit 20 can determine whether condensation is caused by exhalation based on the change in the signal value of the light receiving signal ratio or the baseline. In the case of condensation caused by exhalation, the decrease in the light receiving signal ratio in the initial stage of the breathing period is greater than that in the case of condensation caused by other factors. Therefore, when the decrease in the light receiving signal ratio or the baseline within a specified time from the beginning of the breathing period is greater than a specified value, the operation unit 20 can determine that condensation has occurred due to exhalation. The specified time can be an average value of the breathing cycle, which can be 10 seconds, 20 seconds, or 30 seconds. The specified value can be the change in the signal value when a carbon dioxide concentration of 20,000 ppm, 30,000 ppm, or 40,000 ppm is detected.

[0142] The calculation unit 20 can determine whether the condensation is caused by exhalation based on the ratio of the absolute value of the slope of the baseline from the start of the breathing period to the elapse of the prescribed time to the absolute value of the slope of the baseline from the end of the breathing period to the elapse of the prescribed time. As described above, in the case where the condensation is caused by exhalation, the absolute value of the slope of the baseline immediately after the start of the breathing period is relatively large. The calculation unit 20 can determine that condensation is caused by exhalation when the value obtained by dividing the absolute value of the slope of the baseline in the prescribed period after the start of the breathing period by the absolute value of the slope of the baseline in the prescribed period after the end of the breathing period is greater than the prescribed value.

[0143] Figure 8 1 is a diagram showing another embodiment of the gas sensor 10. The light emitting unit 16, the first light receiving unit 18 and the computing unit 20 of the gas sensor 10 of this embodiment are mounted on the same supporting member 30. The gas sensor 10 of this embodiment has a reflector 32, and the path 12 through which the detection target gas passes is formed between the supporting member 30 and the reflector 32. In the gas sensor 10 of this embodiment, a part of the light 14 irradiated by the light emitting unit 16 is reflected by the reflector 32, and the first light receiving unit 18 receives the reflected light 14. The other parts may be connected to the same Figure 1 The same as the gas sensor 10. By setting such a structure, the gas sensor 10 can be miniaturized.

[0144] Fig. 9 is a diagram showing a structural example of the light emitting unit 16. The light emitting unit 16 of this example includes 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. In the case of detecting exhaled breath, the substrate 40 is a GaAs substrate as an example.

[0145] 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 constituting 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 gas to be detected passes.

[0146] The light emitting element 44 and the second light receiving unit 22 can be arranged on the same substrate. The light emitting element 44 and the second light receiving unit 22 of this example are arranged on the second main surface 42 of the substrate 40. The light emitting element 44 has a stacked structure portion of a PN junction or a PIN junction. By supplying power to the stacked structure portion, the light emitting element 44 acts as an LED and emits light 14 of a wavelength corresponding to the band gap of the material of the stacked structure portion. In the case of detecting exhalation, the light emitting element 44 can use InAlSb near the absorption wavelength that can output carbon dioxide as the stacked structure portion. The above-mentioned light emitting element 44 is called a quantum infrared light emitting element.

[0147] A part of the light 14 travels through the substrate 40 and is emitted toward the path 12 through the first principal surface 41 . On the other hand, another part of the light 14 travels through the substrate 40 and is reflected by the first principal surface 41 to enter the second light receiving unit 22 .

[0148] The second light receiving unit 22 receives the light 14 traveling through the substrate 40. In other words, the second light receiving unit 22 receives the light 14 that has not passed through the path 12 (space where the detection target gas exists) through which the detection target gas passes. Thus, the output variation caused by the change in the light amount and temperature of the light emitting element 44 can be corrected. The second light receiving unit 22 can receive only the light 14 that has not passed through the space where the detection target gas exists.

[0149] The second light receiving unit 22 may also have a stacked structure. The stacked structure of the second light receiving unit 22 may be a diode structure of a PN junction or a PIN junction. The stacked structure and material of the second light receiving unit 22 may be the same as the stacked structure and material of the light emitting element 44. Thus, the temperature characteristics of the second light receiving unit 22 can be consistent with the temperature characteristics of the light emitting element 44. The above-mentioned second light receiving unit 22 is called a quantum infrared light receiving element.

[0150] Fig.10 FIG. 1 is a diagram showing an example of a block diagram of the gas sensor 10 in the embodiment. Fig.10 Schematic diagram of the gas sensor 10 shows the light emitting unit 16 , the first light receiving unit 18 , the second light receiving unit 22 , and the computing unit 20 .

[0151] As described above, the first light receiving unit 18 receives at least a portion of the light 14 emitted from the light emitting unit 16 and passing through the detection target gas. The first light receiving unit 18 outputs a first light receiving signal corresponding to the light receiving result to the calculation unit 20.

[0152] As described above, the second light receiving unit 22 receives at least a portion of the light 14 emitted from the light emitting unit 16 and not passing through the detection target gas. The second light receiving unit 22 outputs a second light receiving signal corresponding to the light receiving result to the calculation unit 20.

[0153] The operation unit 20 obtains the first light receiving signal from the first light receiving unit 18 and obtains the second light receiving signal from the second light receiving unit 22. As described above, the operation 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 operation unit 20 can detect condensation by the various methods described above. In addition, the operation unit 20 can calculate and remove the above-mentioned baseline. The operation unit 20 can also calculate the cycle or length of the above-mentioned breathing.

[0154] Fig.111 is a diagram showing an example of a flow chart of a detection method. The detection method of this example includes a first light receiving stage S102, a second light receiving stage S104, and a condensation detection stage S106. In the first light receiving stage S102, at least a portion of the light 14 that is irradiated to the path 12 through which the detection target gas passes and passes through the detection target gas is received, and a first light receiving signal corresponding to the light receiving result is output. The first light receiving stage S102 is performed by the first light receiving unit 18 described above.

[0155] In the second light receiving stage S104, at least a portion of the light 14 that has not passed through the detection target gas is received, and a second light receiving signal corresponding 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 stage S104 is performed by the second light receiving unit 22 described above. Fig.11 In the embodiment, the second light receiving stage S104 is performed after the first light receiving stage S102, but the order may be reversed or performed simultaneously.

[0156] In the condensation detection stage S106, the occurrence of condensation in the optical path through which the light 14 passes is detected based on the first light receiving signal and the second light receiving signal. The condensation detection stage S106 is performed by the above-mentioned operation unit 20. In the condensation detection stage S106, condensation can be detected by various methods including the above-mentioned condensation determination evaluation value. In addition, in the condensation detection stage S106, the above-mentioned baseline calculation and removal can be performed. In the condensation detection stage S106, the above-mentioned breathing cycle or length can also be calculated.

[0157] The present invention has been described above using the embodiments, but the protection scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various changes or improvements can be made to the above embodiments. According to the description of the claims, the mode in which such changes or improvements are made is also included in the protection scope of the present invention.

[0158] Description of Reference Numerals

[0159] 10: gas sensor; 12: path; 14: light; 16: light emitting unit; 18: first light receiving unit; 20: operation unit; 22: second light receiving unit; 24: optical filter; 30: supporting member; 32: reflector; 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, wherein the gas sensor is characterized in that: a light emitting portion that radiates light; a first light receiving unit that receives at least a portion of the light that has passed through the detection target gas and outputs a first light receiving signal corresponding to a light receiving result; a second light receiving unit that receives at least a portion of the light that has not passed through the detection target gas and outputs a second light receiving signal corresponding to the light receiving result; as well as A calculation unit detects, based on the first light receiving signal and the second light receiving signal, that condensation has occurred in an optical path from the light emitting unit to the first light receiving unit.

2. The gas sensor according to claim 1, characterized in that The calculation unit calculates the variation rate of the first light receiving signal and the variation rate of the second light receiving signal. The occurrence of the condensation is determined based on a condensation determination evaluation value obtained using a variation rate of the first light receiving signal and a variation rate of the second light receiving signal.

3. The gas sensor according to claim 2, characterized in that: The condensation determination evaluation value is a ratio of a change rate of the first light receiving signal to a change rate of the second light receiving signal.

4. The gas sensor according to claim 3, characterized in that: When the condensation determination evaluation value is 2 or more, it is determined that the condensation has occurred.

5. The gas sensor according to claim 1, characterized in that: The second light receiving unit receives the light that has not passed through the space where the detection target gas exists.

6. The gas sensor according to claim 1, characterized in that The gas sensor is arranged on the microphone device.

7. The gas sensor according to claim 1, characterized in that: The gas sensor is arranged on a device worn on the head.

8. The gas sensor according to any one of claims 1 to 7, characterized in that: The calculation unit calculates a base line of the waveform of the first light receiving signal based on a frequency component of the first light receiving signal lower than a set first cutoff frequency, and detects the occurrence of condensation based on a signal obtained by removing the base line from the first light receiving signal.

9. The gas sensor according to claim 8, characterized in that: The first cutoff frequency is set according to a change in a signal value of the first light receiving signal.

10. The gas sensor according to claim 9, characterized in that The calculation unit changes the first cutoff frequency when the condensation is detected.

11. The gas sensor according to claim 10, characterized in that: The calculation unit calculates the value of the baseline for each of the signal values ​​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 when the condensation is detected when the signal value of the first light receiving signal, which is the object of calculating the baseline value, is reduced by more than a second set value relative to the signal value at an immediately previous moment in the time waveform of the first light receiving signal.

12. The gas sensor according to claim 8, characterized in that The calculation unit calculates at least one of a cycle and a length of a breath containing the detection target gas using the first light receiving signal from which the baseline has been removed.

13. The gas sensor according to claim 1, characterized in that: The calculation unit determines whether the condensation is caused by exhalation based on a change in the signal value of the first light receiving signal.

14. A detection method for detecting a gas to be detected, wherein the detection method is characterized in that: receiving at least a portion of the light irradiated toward the path through which the detection target gas passes and passing through the detection target gas, and outputting a first light receiving signal corresponding to the light receiving result, receiving at least a portion of the light that has not passed through the detection target gas, and outputting a second light receiving signal corresponding to the light receiving result, The occurrence of condensation in the optical path through which the light passes is detected based on the first light reception signal and the second light reception signal.

Images