Gas concentration measuring device

Abstract

To perform a measurement of gas concentration simply and accurately.SOLUTION: A gas concentration measurement device 100 comprises: a concentration measurement space 22; a transmission unit 14 that transmits an ultrasonic wave to the concentration measurement space 22 in responce to a transmission signal; a reception unit 16 that receives the ultrasonic wave propagating through the concentration measurement space 22, and outputs a reception signal; and an analysis unit 18. The analysis unit 18 is configured to obtain a space propagation time in the concentration measurement space 22 on the basis of a timing when the transmission signal is input to the transmission unit 14 and a timing when the reception signal is output from the reception unit 16, and obtain concentration of gas of a measurement object on the basis of the space propagation time. The analysis unit 18 is configured to obtain a correction value relevant to a direct wave type propagation time on the basis of the direct wave type propagation time and a reflection wave type propagation time, and obtain a space propagation time on the basis of a post-correction propagation time having the direct wave type propagation time corrected based on the correction value, or one of the direct wave type propagation time of the reflection wave type propagation time and a propagation time corresponding to a value related to the direct wave type propagation time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas concentration measuring device, and more particularly to a device that measures gas concentration based on the propagation time of ultrasonic waves in a concentration measurement space. [Background technology]

[0002] Research and development is being conducted extensively on fuel cell vehicles, which run on electricity supplied from fuel cells. Fuel cells generate electricity through a chemical reaction between hydrogen and oxygen. Generally, hydrogen is supplied to the fuel cell as fuel, and oxygen is taken in from the surrounding air. Fuel cell vehicles are equipped with hydrogen tanks, which supply hydrogen to the fuel cell. When the hydrogen in the hydrogen tank runs low, hydrogen is supplied to the fuel cell vehicle's hydrogen tank from a hydrogen supply device installed at a service station.

[0003] Because hydrogen is a flammable gas, it is necessary to monitor hydrogen leaks from fuel cell vehicles and hydrogen supply systems. Therefore, hydrogen concentration measuring devices are widely used along with fuel cell vehicles and hydrogen supply systems. Hydrogen concentration measuring devices have the function of measuring the concentration of hydrogen in the air and sounding an alarm when the hydrogen concentration exceeds a predetermined value.

[0004] Patent Document 1 below describes a device for measuring the concentration of a specific gas. This device measures the concentration of a specific gas based on the propagation speed of ultrasonic waves in the air being measured. The device measures the propagation time from when ultrasonic waves are transmitted from a transmitter until the ultrasonic waves propagate through a measurement section in a concentration measurement space and are received by a receiver, and the propagation speed is calculated from this propagation time, which in turn determines the concentration of the gas.

[0005] Patent Document 2 describes a gas concentration sensor that detects the concentration of a gas to be measured by transmitting ultrasonic waves into a measurement chamber, receiving the waves reflected by the wall of the measurement chamber, calculating the propagation time for the ultrasonic waves to propagate through the measurement chamber, and further calculating the propagation velocity. It describes that the propagation time is calculated from the difference between the time when a first reflected wave, which is received first by an ultrasonic element, is received and the time when a second reflected wave, which is received later by the ultrasonic element, is received. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-100916 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-249691 Summary of the Invention [Problem to be solved by the invention]

[0007] In this specification, the direct wave method is a method of measuring the propagation time from when an ultrasonic wave is transmitted from a transmitter to when the ultrasonic wave propagates through a measurement section in a concentration measurement space and is received by a receiver, as described in Patent Document 1. On the other hand, the reflected wave method is a method of transmitting an ultrasonic wave into a measurement chamber and determining the propagation time from the difference between the time when a first ultrasonic wave, which is received first by an ultrasonic element, is received and the time when a second ultrasonic wave, which is received later by an ultrasonic element, is received, as described in Patent Document 2.

[0008] The direct wave method requires processing to compensate for the signal delay time in the transmitter and receiver, which can increase the amount of processing required for measurement.The reflected wave method does not require delay time compensation, but when the ultrasonic wave propagation distance is short or the propagation speed is high, the first and second ultrasonic waves may overlap on the time axis, making it difficult to measure the propagation time.

[0009] An object of the present invention is to measure the concentration of a gas simply and accurately. [Means for solving the problem]

[0010] The present invention includes a concentration measurement space in which a gas concentration is measured, a transmitting unit that transmits ultrasonic waves into the concentration measurement space in response to a transmission signal, a receiving unit that receives the ultrasonic waves that have propagated through the concentration measurement space and outputs a reception signal, and an analyzing unit that calculates a spatial propagation time for the ultrasonic waves to propagate through the concentration measurement space based on a timing at which the transmission signal is input to the transmitting unit and a timing at which the reception signal is output from the receiving unit, and calculates the concentration of the gas to be measured based on the spatial propagation time, and the analyzing unit calculates a correction value for the direct wave propagation time based on a direct wave propagation time calculated by a direct wave method and a reflected wave propagation time calculated by a reflected wave method, and corrects the direct wave propagation time based on the correction value. The spatial propagation time is calculated based on either the corrected propagation time or the reflected wave propagation time, which is the direct wave propagation time or a value related thereto, and the direct wave method is a measurement method for calculating the direct wave propagation time based on the difference between a transmission timing at which the transmission signal is input to the transmitter and a first reception timing at which the reception signal is first output from the receiver after the transmission signal is input to the transmitter, and the reflected wave method is a measurement method for calculating the reflected wave propagation time based on the difference between the first reception timing and a second reception timing at which the reception signal is secondly output from the receiver after the transmission signal is input to the transmitter.

[0011] Preferably, in the gas concentration measuring device described in claim 1, the analysis unit determines the correction value based on the direct wave propagation time and the reflected wave propagation time when the condition that the direct wave propagation time is equal to or greater than a predetermined background processing threshold is met.

[0012] Preferably, when the condition that the direct wave mode propagation time is less than a predetermined mode switching threshold that exceeds the background processing threshold is met, the analysis unit calculates the spatial propagation time based on the corrected propagation time.

[0013] Preferably, when the condition that the direct wave propagation time is equal to or greater than a predetermined method switching threshold that exceeds the background processing threshold is met, the analysis unit calculates the spatial propagation time based on the reflected wave propagation time.

[0014] The present invention also provides a concentration measurement space for measuring a gas concentration, a transmitting unit that transmits ultrasonic waves into the concentration measurement space in response to a transmission signal, a receiving unit that receives the ultrasonic waves that have propagated through the concentration measurement space and outputs a reception signal, and an analyzing unit that calculates a spatial propagation time for the ultrasonic waves to propagate through the concentration measurement space based on a timing at which the transmission signal is input to the transmitting unit and a timing at which the reception signal is output from the receiving unit, and calculates the concentration of the gas to be measured based on the spatial propagation time, and the analyzing unit calculates a correction value for the direct wave method propagation time based on a direct wave method propagation time calculated by a direct wave method and a reflected wave method propagation time calculated by a reflected wave method, and repeatedly measures the propagation time by the direct wave method and the reflected wave method, and calculates a time change of the direct wave method propagation time and In accordance with a change over time in the reflected wave system propagation time, either a corrected propagation time obtained by correcting the direct wave system propagation time based on the correction value or the reflected wave system propagation time is selected, and the spatial propagation time is calculated based on the selected one, wherein the direct wave system is a measurement system that calculates the direct wave system propagation time based on the difference between a transmission timing at which the transmission signal is input to the transmitter and a first reception timing at which the reception signal is first output from the receiver after the transmission signal is input to the transmitter, and the reflected wave system is a measurement system that calculates the reflected wave system propagation time based on the difference between the first reception timing and a second reception timing at which the reception signal is secondly output from the receiver after the transmission signal is input to the transmitter.

[0015] Preferably, the analysis unit recognizes one of the direct wave propagation time and the reflected wave propagation time as a main propagation time and the other as a secondary propagation time depending on the direct wave propagation time or a value related thereto, and if the absolute value of the time change of the main propagation time is equal to or greater than a predetermined change threshold and the absolute value of the time change of the secondary propagation time is less than a predetermined change threshold, calculates the spatial propagation time based on the secondary propagation time.

[0016] Preferably, the analysis unit recognizes one of the direct wave propagation time and the reflected wave propagation time as a main propagation time and the other as a secondary propagation time depending on the direct wave propagation time or a value related thereto, and when the absolute value of the time change of the main propagation time is equal to or greater than a predetermined change threshold and the absolute value of the time change of the secondary propagation time is equal to or greater than a predetermined change threshold, calculates the spatial propagation time based on the main propagation time.

[0017] Preferably, when a condition is met that the direct wave propagation time is equal to or greater than a predetermined method switching threshold, the analysis unit selects the reflected wave propagation time as the main propagation time.

[0018] Preferably, when a condition is met that the direct wave propagation time is less than a predetermined method switching threshold, the analysis unit selects the direct wave propagation time as the main propagation time. [Effects of the Invention]

[0019] According to the present invention, the concentration of a gas can be measured simply and accurately. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a configuration of a gas concentration measuring device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating a time waveform of a received signal. [Figure 3]10 is a diagram conceptually showing a direct wave propagation time Tβ relative to an actual spatial propagation time T0, and a reflected wave propagation time Tα relative to an actual spatial propagation time T0. FIG. [Figure 4] FIG. 10 is a diagram showing the relationship between hydrogen concentration and propagation velocity. [Figure 5] FIG. 10 is a diagram showing whether gas concentration measurement is performed by the direct wave method or the reflected wave method with respect to the direct wave method propagation time Tβ. DETAILED DESCRIPTION OF THE INVENTION

[0021] (1) Configuration of a gas concentration measuring device and basic processing performed by the gas concentration measuring device 1 shows the configuration of a gas concentration measuring device 100 according to an embodiment of the present invention. The gas concentration measuring device 100 comprises a housing 10, a transmitter 14, a receiver 16, and an analyzer 18. The housing 10 forms an analyzer housing space 20 and a concentration measurement space 22. The concentration measurement space 22 is a cylindrical space with both ends closed. The transmitter 14 is disposed at one end of the concentration measurement space 22, and the receiver 16 is disposed at the other end.

[0022] The analysis unit accommodating space 20 accommodates the analysis unit 18. The analysis unit 18 may be configured with a processor that executes a pre-loaded program. The processor may be fixed to the analysis unit accommodating space 20 while being fixed to a substrate.

[0023] The transmitting unit 14 and the receiving unit 16 are equipped with ultrasonic vibrators. The transmitting unit 14 and the receiving unit 16 are connected to the analyzing unit 18. The transmitting unit 14 transmits ultrasonic waves to the concentration measurement space 22 under the control of the analyzing unit 18. That is, the analyzing unit 18 outputs a transmission signal, which is an electrical signal, to the transmitting unit 14. The transmitting unit 14 converts the transmission signal into ultrasonic waves and transmits them. The receiving unit 16 receives the ultrasonic waves that have propagated through the concentration measurement space 22. The receiving unit 16 converts the received ultrasonic waves into a reception signal, which is an electrical signal, and outputs it to the analyzing unit 18.

[0024] The analysis unit 18 calculates the spatial propagation time for the ultrasonic waves to propagate through the concentration measurement space 22 based on the timing at which the transmission signal is input to the transmission unit 14 and the timing at which the reception signal is output from the reception unit 16, and calculates the concentration of the gas to be measured based on the spatial propagation time.

[0025] The analysis unit 18 determines the spatial propagation time required for an ultrasonic wave to propagate from one end of the concentration measurement space 22 to the other end using either a direct wave method or a reflected wave method. The method used to determine the spatial propagation time will be described later. The direct wave method determines the propagation time (direct wave method propagation time T ) based on the difference between the transmission timing at which the transmission signal is output from the analysis unit 18 to the transmitter 14 and the first reception timing at which the reception signal is first output from the receiver 16 after the transmission signal is output. β ) is a measurement method for determining the difference (time difference) between the transmission timing and the first reception timing. The difference (time difference) between the transmission timing and the first reception timing may be determined by subtracting the time indicating the transmission timing from the time indicating the first reception timing. The first reception signal output from the receiving unit 16 corresponds to the direct ultrasonic wave first received by the receiving unit 16. The direct ultrasonic wave is an ultrasonic wave that is transmitted from the transmitting unit 14, propagates through the concentration measurement space 22 from one end to the other, and is received by the receiving unit 16.

[0026] The reflected wave method calculates the propagation time (reflected wave method propagation time T α ) is a measurement method for determining the difference (time difference) between the first reception timing and the second reception timing. The difference (time difference) between the first reception timing and the second reception timing may be determined by subtracting the time indicating the first reception timing from the time indicating the second reception timing. The reception signal outputted the second time from the receiving unit 16 corresponds to the reflected ultrasound wave that is transmitted from the transmitting unit 14, propagates through the concentration measurement space 22 for one and a half round trips, and is received by the receiving unit 16. In other words, the reflected ultrasound wave is an ultrasound wave that is transmitted from the transmitting unit 14, propagates from one end to the other end of the concentration measurement space 22, is reflected at the other end, propagates through the concentration measurement space 22 from the other end to one end, is further reflected at the one end, propagates through the concentration measurement space 22, and is received by the receiving unit 16.

[0027] 2 shows a schematic diagram of the time waveform of the received signal output from the receiving unit 16. At time t=0, the analysis unit 18 outputs a transmission signal to the transmitting unit 14. Each received signal output from the receiving unit 16 to the analysis unit 18 has a sinusoidal time waveform that has been amplitude-modulated into a pulse shape. The first received signal output from the receiving unit 16 (direct wave received signal 24) reaches a maximum in absolute value of its peak value at time t=t1. The second received signal output from the receiving unit 16 (reflected wave received signal 26) reaches a maximum in absolute value of its peak value at time t=t2, which is later than time t=t1.

[0028] (2) Reflected wave method Measurement of gas concentration using the reflected wave method will be described with reference to Fig. 1. The analysis unit 18 outputs a transmission signal to the transmission unit 14. The analysis unit 18 stores the time waveform of the direct wave reception signal 24 output from the reception unit 16 and the time waveform of the reflected wave reception signal 26 output from the reception unit 16. The analysis unit 18 calculates the correlation value between the direct wave reception signal 24 and a shift signal obtained by temporarily advancing the reflected wave reception signal 26 by a shift time τ. The analysis unit 18 calculates the shift time τ when the correlation value is maximized by multiplying the reflected wave method propagation time T α is required.

[0029] In addition, the reflected wave propagation time T α When calculating the correlation coefficient, the Euclidean distance may be used instead of the correlation value. The Euclidean distance is defined as the square root of the time integral of the square of the difference between two signals. When calculating the Euclidean distance, for example, the magnitude of one or both of the two signals may be adjusted so that the maximum values ​​of the two signals are the same. The smaller the Euclidean distance, the greater the degree of similarity between the two signals.

[0030] The analysis unit 18 calculates the propagation time T αThe spatial propagation time T is calculated as half the value of T. The spatial propagation time T is the time required for an ultrasonic wave to propagate from one end of the concentration measurement space 22 to the other end. A concentration calculation formula (Formula 1) that expresses the relationship between the propagation speed of an ultrasonic wave and the concentration of a specific gas contained in the gas through which the ultrasonic wave propagates is widely known. The analysis unit 18 calculates the concentration of the gas from the spatial propagation time T and the length L of the concentration measurement space 22 using the concentration calculation formula (Formula 1) or a formula having the same meaning.

[0031]

number

[0032] where k is the specific heat ratio of the gas, R is the gas constant, and T mp is the temperature of the concentration measurement space 22. h is the molecular weight of the gas to be measured, and M a is the molecular weight of air that does not contain the gas to be measured. If we assume that the composition of air is 80% nitrogen and 20% oxygen, the specific heat ratio k can be set to 1.4. Also, the gas constant R is 8.31, and the molecular weight M of air is a When the gas to be measured is hydrogen, the molecular weight M h is 2.0. In (Equation 1), L / T represents the propagation speed of ultrasonic waves.

[0033] (3) Direct wave method Next, measurement of gas concentration using the direct wave method will be described with reference to Fig. 1. The analysis unit 18 outputs a transmission signal to the transmission unit 14. The analysis unit 18 stores the time waveform of the transmission signal and the time waveform of the direct wave reception signal 24 output from the reception unit 16. The analysis unit 18 calculates the correlation value between the transmission signal and a shifted signal obtained by temporarily advancing the direct wave reception signal 24 by a shift time τ. The correlation value indicates the degree to which the time waveforms of the two signals are similar. The analysis unit 18 calculates the shift time τ when the correlation value is maximum by multiplying it by the direct wave method propagation time T β The direct wave propagation time T β When calculating the correlation coefficient, the Euclidean distance may be used instead of the correlation value.

[0034] The analysis unit 18 calculates the direct wave propagation time T based on the time from when a zero cross point immediately after the peak of the positive or negative crest value of the transmission signal appears to when a zero cross point immediately after the peak of the positive or negative crest value of the received signal first output from the receiving unit 16 appears. β Here, the zero crossing point refers to the point where the time waveform of the signal intersects with the time axis.

[0035] 2, the time from when the analysis unit 18 outputs a transmission signal to the transmission unit 14 to when the reception unit 16 outputs each reception signal to the analysis unit 18 includes a delay time Td that is a combination of a transmission delay time and a reception delay time. Here, the transmission delay time is the time from when the analysis unit 18 outputs a transmission signal to when the transmission unit 14 transmits an ultrasonic wave, and the reception delay time is the time from when the reception unit 16 receives an ultrasonic wave to when the reception unit 16 outputs a reception signal to the analysis unit 18.

[0036] Therefore, the analysis unit 18 calculates the correction value Δβ=−Td, which is a value obtained by inverting the polarity of the delay time Td, by subtracting the correction value Δβ from the direct wave propagation time T β A corrected propagation time is calculated by adding the above to the propagation time Δβ, and this corrected propagation time is set as the spatial propagation time T. The correction value Δβ may be repeatedly calculated at predetermined time intervals based on background processing described below.

[0037] The background processing may be performed together with or separately from the measurement of the gas concentration. α0 and direct wave propagation time T β0 This is a process to calculate the correction value Δβ based on the reflected wave propagation time T α0 is obtained, and the direct wave propagation time T β0 is calculated, and the target correction value Δβ0 is calculated based on the following (Equation 2): Furthermore, the correction value Δβ is corrected so as to approach or match the target correction value Δβ0.

[0038]

number

[0039] The physical meaning of (Equation 2) will be explained. Figure 3 shows the direct wave propagation time T β , and the reflected wave propagation time T for the actual spatial propagation time T α is shown conceptually. Reflected wave propagation time T α is the direct wave propagation time T β is equal to twice the delay time Td, α =(T β -Td) × 2. Solve this equation for the correction value -Td, replace -Td with Δβ0, and T β and T α T β0 and T α0 The result is (Number 2).

[0040] The analysis unit 18 may calculate an error by subtracting the target correction value Δβ0 from the previously calculated correction value Δβ, and may calculate a new correction value Δβ by proportional-integral control based on this error. Alternatively, the analysis unit 18 may calculate a new correction value Δβ by using the target correction value Δβ0 as the correction value Δβ itself. The analysis unit 18 stores the newly calculated correction value Δβ until the next time the correction value Δβ is calculated.

[0041] The analysis unit 18 calculates the direct wave propagation time T β A corrected propagation time is calculated by adding a correction value Δβ to the above, and this corrected propagation time is set as the spatial propagation time T. Furthermore, the analysis unit 18 calculates the gas concentration using (Equation 1).

[0042] (4) Switching the measurement method In gas concentration measurement using the direct wave method, it is necessary to calculate the correction value Δβ in advance in order to calculate the spatial propagation time T. In contrast, in gas concentration measurement using the reflected wave method, it is not necessary to calculate the correction value Δβ in advance. The reason for this is that in gas concentration measurement using the reflected wave method, the spatial propagation time T from when the receiving unit 16 outputs the first received signal to when the receiving unit 16 outputs the second received signal is calculated. αThis is because the delay time Td is not included in the time difference between the first reception timing and the second reception timing. That is, the delay time Td is cancelled out in the process of determining the time difference between the first reception timing and the second reception timing.

[0043] However, measuring gas concentration using the reflected wave method has the following problem. Generally, as the gas concentration increases, the propagation speed of the ultrasonic waves increases. Figure 4 shows the relationship between hydrogen concentration and propagation speed at a temperature of 25°C. The horizontal axis represents hydrogen concentration (%), and the vertical axis represents propagation speed (m / sec). As shown in Figure 4, the propagation speed also increases with increasing hydrogen concentration. Furthermore, the change (slope) in the propagation speed relative to changes in hydrogen concentration tends to increase as the hydrogen concentration increases. This property is similar for other gases.

[0044] Therefore, as the gas concentration increases, the time it takes for the gas to propagate through the concentration measurement space 22 becomes shorter, and the reflected wave propagation time T α In other words, the time from when the direct wave reception signal is output from the receiving unit 16 until when the reflected wave reception signal 26 is output is shortened. As a result, the time waveform of the direct wave reception signal 24 and the time waveform of the reflected wave reception signal 26 overlap on the time axis, and the reflected wave propagation time T α On the other hand, in the measurement of gas concentration by the direct wave method, the reflected wave reception signal 26 does not overlap with the leading portion of the time waveform of the direct wave reception signal 24, so the direct wave method propagation time T β The measurement is relatively accurate.

[0045] Therefore, the gas concentration measuring device 100 according to this embodiment uses the direct wave propagation time T β and the reflected wave propagation time T α is repeatedly measured at predetermined time intervals, and the analysis unit 18 executes the following process in each measurement. β is equal to or greater than a predetermined method switching threshold tc, the gas concentration is measured by the reflected wave method. βWhen tc is less than the method switching threshold tc, the analysis unit 18 measures the gas concentration by the direct wave method.

[0046] In addition, when measuring gas concentration using the direct wave method, the direct wave propagation time T β The analysis unit 18 calculates the direct wave propagation time T β is equal to or greater than a predetermined background processing threshold tb, the correction value Δβ is updated. That is, the analysis unit 18 executes background processing at predetermined time intervals to obtain the correction value Δβ, and replaces the previously stored correction value Δβ with the new correction value Δβ and stores it. The background processing threshold tb may be a value less than the method switching threshold tc.

[0047] The analysis unit 18 calculates the direct wave propagation time T β is less than the background processing threshold tb, the background processing is not performed, and the correction value Δβ is maintained at the current value. If background processing has never been performed in the past, the analysis unit 18 may store an initial correction value Δβ obtained by experiment or simulation.

[0048] (5) Direct wave propagation time T β Judgment based on Figure 5 shows the direct wave propagation time T β 5 shows whether the gas concentration is measured by the direct wave method or the reflected wave method. FIG. 5 also shows the direct wave propagation time T β The range of the direct wave propagation time T β This is based on the following:

[0049] Direct wave propagation time T β is less than the background processing threshold tb, the analysis unit 18 calculates the direct wave propagation time T β Only the reflected wave propagation time T αThe analysis unit 18 maintains the state in which the previously calculated correction value Δβ is stored.

[0050] Direct wave propagation time T β is equal to or greater than the background processing threshold tb, the analysis unit 18 calculates the direct wave propagation time T β In addition, the reflected wave propagation time T α The analysis unit 18 calculates the direct wave propagation time T β T β0 The currently calculated reflected wave propagation time T α T α0 The target correction value Δβ0 is calculated based on Equation 2. The analysis unit 18 updates and stores the correction value Δβ so that the correction value Δβ coincides with or approaches the target correction value Δβ0.

[0051] The analysis unit 18 calculates the direct wave propagation time T β is less than the method switching threshold tc, the gas concentration is measured by the direct wave method. β The spatial propagation time T (corrected propagation time) is calculated by adding the correction value Δβ to the direct wave propagation time T, and the gas concentration is calculated based on the spatial propagation time T. β is equal to or greater than the method switching threshold tc, the gas concentration is measured using the reflected wave method. α is the spatial propagation time T, and the gas concentration is calculated based on that spatial propagation time T.

[0052] In this way, the analysis unit 18 calculates the direct wave propagation time T β The corrected propagation time, or the reflected wave propagation time T α Direct wave propagation time T β According to the process executed by the analysis unit 18, the spatial propagation time T is calculated based on one of the two. α When the propagation time T β When the method switching threshold tc is equal to or greater than the reflected wave propagation time T αThe gas concentration is calculated based on the reflected wave propagation time T α When it is difficult to calculate with high accuracy, that is, when the direct wave propagation time T β When is less than the system switching threshold tc, the direct wave system propagation time T β The gas concentration is calculated based on the

[0053] Direct wave propagation time T β When the propagation time T is less than the threshold value tc, the gas concentration is higher than when the propagation time T is equal to or greater than the threshold value tc, and the change in the propagation speed with respect to the change in the gas concentration is large. β Compared to when the propagation time T β When the system switching threshold tc is equal to or greater than the direct wave system propagation time T β is less than the method switching threshold tc, a higher measurement accuracy is required for the gas concentration, and the gas concentration may be measured by the reflected wave method. β The gas concentration can be measured easily and with high accuracy over a wide range of gas concentrations.

[0054] In addition, in the gas concentration measuring device 100 according to the present invention, the direct wave propagation time T β Even if the method switching threshold tc is less than the background processing threshold tb, background processing is executed if the background processing threshold tb is equal to or greater than the method switching threshold tc. α The correction value Δβ is calculated in the range of Δβ, and the correction value Δβ is calculated in a wide range.

[0055] (6) Processing to suppress accidental errors In the gas concentration measuring device 100, the direct wave propagation time T β or reflected wave propagation time T αTherefore, the analysis unit 18 calculates the direct wave propagation time T β When is greater than or equal to the background processing threshold tb, the direct wave propagation time T β or reflected wave propagation time T α may be selectively used to determine the spatial propagation time T and measure the gas concentration.

[0056] In this case, the analysis unit 18 calculates the direct wave propagation time T β and the reflected wave propagation time T α In other words, the analysis unit 18 selects the propagation time T β The corrected propagation time, or the reflected wave propagation time T α and calculates the spatial propagation time T based on the selected one.

[0057] (6-1) Direct wave propagation time T β When is less than the method switching threshold tc First, the direct wave propagation time T β The first process when the direct wave propagation time T β is recognized as the main propagation time, and the reflected wave propagation time T α is recognized as a secondary propagation time.

[0058] When the absolute value of the time change of the main propagation time is less than a predetermined change threshold, the analysis unit 18 calculates the spatial propagation time T based on the main propagation time.

[0059] When the absolute value of the time change of the main propagation time is equal to or greater than a predetermined change threshold and the absolute value of the time change of the secondary propagation time is equal to or greater than a predetermined change threshold, the analysis unit 18 calculates the spatial propagation time T based on the main propagation time.

[0060] Furthermore, when the absolute value of the time change of the main propagation time is equal to or greater than a predetermined change threshold and the absolute value of the time change of the secondary propagation time is less than a predetermined change threshold, the analysis unit 18 calculates the spatial propagation time T based on the secondary propagation time.

[0061] That is, the analysis unit 18 calculates the direct wave propagation time T β and the reflected wave propagation time T α The analysis unit 18 calculates the direct wave propagation time T β Each time the direct wave propagation time T β The direct wave propagation time T obtained earlier β Subtract the direct wave propagation time T β The analysis unit 18 also calculates the time change β of the reflected wave propagation time T α The reflected wave propagation time T obtained from α Subtract the reflected wave propagation time T α Calculate the time change α.

[0062] When the absolute value of the time change β is less than a predetermined change threshold, the analysis unit 18 calculates the direct wave propagation time T β The spatial propagation time T is calculated based on the above equation, and the gas concentration is measured using the direct wave method.

[0063] When the absolute value of the time change β is equal to or greater than a predetermined change threshold and the absolute value of the time change α is equal to or greater than a predetermined change threshold, the analysis unit 18 determines that the direct wave propagation time T β The spatial propagation time T is calculated based on the above equation, and the gas concentration is measured using the direct wave method.

[0064] When the absolute value of the time change β is equal to or greater than a predetermined change threshold and the absolute value of the time change α is less than the predetermined change threshold, the analysis unit 18 calculates the reflected wave propagation time T α The spatial propagation time T is calculated based on the above, and the gas concentration is measured using the reflected wave method.

[0065] (6-2) Direct wave propagation time T β When is equal to or greater than the method switching threshold tc Next, the direct wave propagation time T β is equal to or greater than the method switching threshold tc. In the second processing, the analysis unit 18 calculates the reflected wave method propagation time T α is recognized as the main propagation time, and the direct wave propagation time T β The analysis unit 18 measures the gas concentration by a process similar to the first process.

[0066] When the absolute value of the time change α is less than a predetermined change threshold, the analysis unit 18 calculates the reflected wave propagation time T α The spatial propagation time T is calculated based on the above, and the gas concentration is measured using the reflected wave method.

[0067] When the absolute value of the time change α is equal to or greater than a predetermined change threshold and the absolute value of the time change β is equal to or greater than a predetermined change threshold, the analysis unit 18 calculates the reflected wave propagation time T α The spatial propagation time T is calculated based on the above, and the gas concentration is measured using the reflected wave method.

[0068] When the absolute value of the time change α is equal to or greater than a predetermined change threshold and the absolute value of the time change β is less than the predetermined change threshold, the analysis unit 18 determines that the direct wave propagation time T β The spatial propagation time T is calculated based on the above equation, and the gas concentration is measured using the direct wave method.

[0069] (6-3) Effects According to this processing, even if the main propagation time changes suddenly, if the secondary propagation time does not change suddenly, the spatial propagation time T is calculated based on the secondary propagation time. When both the main propagation time and the secondary propagation time change suddenly, the spatial propagation time T is calculated based on the main propagation time. As a result, if an error accidentally occurs in the main propagation time, the gas concentration is measured based on the secondary propagation time. Therefore, errors that occur in the measured gas concentration due to an error accidentally occurring in the main propagation time are suppressed.

[0070] (7) Other In the above, the direct wave method or the reflected wave method is used to measure the gas concentration, and the direct wave propagation time T β In the embodiment shown, the determination as to whether to perform background processing is based on a comparison between the direct wave propagation time T β In the illustrated embodiment, the determination is based on a comparison of the direct wave propagation time T β In addition, direct wave propagation time T β For example, the direct wave propagation time T β These determinations may be made based on the determination gas concentration obtained by applying the above equation to (Equation 1). That is, the determination of whether to measure the gas concentration using the direct wave method or the reflected wave method, and the determination of whether to perform background processing, are made based on the direct wave method propagation time T β This may be done based on values ​​related to

[0071] In this case, the threshold value for each judgment is the direct wave propagation time T β For example, when each determination is made based on the determination gas concentration, a method switching threshold hc corresponding to the method switching threshold tc is determined, and a background processing threshold hb corresponding to the background processing threshold tb is determined.

[0072] When the gas concentration for determination is equal to or less than the method switching threshold hc, the direct wave method propagation time T β When the condition that the determination gas concentration is equal to or greater than the method switching threshold value tc is met and the determination gas concentration exceeds the method switching threshold value hc, the direct wave method propagation time T β is less than the method switching threshold tc. Similarly, when the determination gas concentration is equal to or less than the background processing threshold hb, the direct wave method propagation time T β is equal to or greater than the background processing threshold tb, and when the determination gas concentration exceeds the background processing threshold hb, the direct wave method propagation time T β is less than the background processing threshold tb.

[0073] The analysis unit 18 measures the gas concentration by the direct wave method when the determination gas concentration exceeds the method switching threshold hc, and measures the gas concentration by the reflected wave method when the determination gas concentration is equal to or less than the method switching threshold hc. The analysis unit 18 also performs background processing when the determination gas concentration is equal to or less than the background processing threshold hb, and does not perform background processing when the determination gas concentration exceeds the background processing threshold hb. [Explanation of symbols]

[0074] 10 Housing, 14 Transmitting unit, 16 Receiving unit, 18 Analyzing unit, 20 Analyzing unit accommodating space, 22 Concentration measurement space, 24 Direct wave receiving signal, 26 Reflected wave receiving signal, 100 Gas concentration measuring device.

Claims

1. a concentration measurement space for measuring a gas concentration; a transmitter that transmits ultrasonic waves to the concentration measurement space in response to a transmission signal; a receiver that receives the ultrasonic waves propagated through the concentration measurement space and outputs a reception signal; an analysis unit that obtains a spatial propagation time for the ultrasonic waves to propagate through the concentration measurement space based on the timing when the transmission signal is input to the transmitter and the timing when the reception signal is output from the receiver, and obtains the concentration of the gas to be measured based on the spatial propagation time; the analysis unit: obtains a correction value for the direct wave method propagation time based on the direct wave method propagation time obtained by the direct wave method and the reflected wave method propagation time obtained by the reflected wave method; obtains the spatial propagation time based on either the corrected propagation time obtained by correcting the direct wave method propagation time based on the correction value or the reflected wave method propagation time, based on one of the direct wave method propagation time or a value related thereto; the direct wave method is a measurement method for obtaining the direct wave method propagation time based on the difference between the transmission timing when the transmission signal is input to the transmitter and the first reception timing when the reception signal is first output from the receiver after the transmission signal is input to the transmitter; the reflected wave method is a measurement method for obtaining the reflected wave method propagation time based on the difference between the first reception timing and the second reception timing when the reception signal is output from the receiver for the second time after the transmission signal is input to the transmitter, and a gas concentration measurement device characterized by this.

2. In the gas concentration measurement device according to Claim 1, the analysis unit: obtains the correction value based on the direct wave method propagation time and the reflected wave method propagation time when the condition that the direct wave method propagation time is equal to or greater than a predetermined background processing threshold value is satisfied, and a gas concentration measurement device characterized by this.

3. In the gas concentration measurement device according to Claim 2, the analysis unit: obtains the spatial propagation time based on the corrected propagation time when the condition that the direct wave method propagation time is less than a predetermined method switching threshold value that exceeds the background processing threshold value is satisfied, and a gas concentration measurement device characterized by this.

4. In the gas concentration measurement device according to Claim 2, the analysis unit: When the condition that the direct wave mode propagation time is equal to or greater than a predetermined mode switching threshold exceeding the background processing threshold is satisfied, the gas concentration measuring device is characterized in that the space propagation time is obtained based on the reflected wave mode propagation time. **Claim 5** A concentration measurement space for measuring the gas concentration, A transmitter that transmits ultrasonic waves to the concentration measurement space in response to a transmission signal, A receiver that receives the ultrasonic wave propagated through the concentration measurement space and outputs a reception signal, Based on the timing when the transmission signal is input to the transmitter and the timing when the reception signal is output from the receiver, a space propagation time for the ultrasonic wave to propagate through the concentration measurement space is obtained, and an analysis unit that obtains the concentration of the gas to be measured based on the space propagation time, The analysis unit Based on the direct wave mode propagation time obtained by the direct wave mode and the reflected wave mode propagation time obtained by the reflected wave mode, a correction value for the direct wave mode propagation time is obtained, The measurement of the propagation time by the direct wave mode and the reflected wave mode is repeatedly executed, According to the time change of the direct wave mode propagation time and the time change of the reflected wave mode propagation time, a corrected propagation time obtained by correcting the direct wave mode propagation time based on the correction value, or one of the reflected wave mode propagation times is selected, and the space propagation time is obtained based on the selected one, The direct wave mode is a measurement mode for obtaining the direct wave mode propagation time based on the difference between the transmission timing when the transmission signal is input to the transmitter and the first reception timing when the reception signal is first output from the receiver after the transmission signal is input to the transmitter, The reflected wave mode is a measurement mode for obtaining the reflected wave mode propagation time based on the difference between the first reception timing and the second reception timing when the reception signal is output from the receiver for the second time after the transmission signal is input to the transmitter, and the gas concentration measuring device is characterized by this. **Claim 6** In the gas concentration measuring device according to claim 5, The analysis unit According to the direct wave mode propagation time or a value related thereto, one of the direct wave mode propagation time and the reflected wave mode propagation time is recognized as the main propagation time, and the other is recognized as the sub propagation time. When the absolute value of the time change of the main propagation time is greater than or equal to a predetermined change threshold and the absolute value of the time change of the sub-propagation time is less than the predetermined change threshold, the spatial propagation time is obtained based on the sub-propagation time. A gas concentration measuring device characterized by this.

7. In the gas concentration measuring device according to claim 5, The analysis unit, According to the direct wave mode propagation time or a value related thereto, one of the direct wave mode propagation time and the reflected wave mode propagation time is recognized as the main propagation time, and the other is recognized as the sub-propagation time. When the absolute value of the time change of the main propagation time is greater than or equal to a predetermined change threshold and the absolute value of the time change of the sub-propagation time is greater than or equal to the predetermined change threshold, the spatial propagation time is obtained based on the main propagation time. A gas concentration measuring device characterized by this.

8. In the gas concentration measuring device according to claim 6 or claim 7, The analysis unit, When the condition that the direct wave mode propagation time is greater than or equal to a predetermined mode switching threshold is satisfied, the reflected wave mode propagation time is selected as the main propagation time. A gas concentration measuring device characterized by this.

9. In the gas concentration measuring device according to claim 6 or claim 7, The analysis unit, When the condition that the direct wave mode propagation time is less than a predetermined mode switching threshold is satisfied, the direct wave mode propagation time is selected as the main propagation time. A gas concentration measuring device characterized by this.

Images