Patent Application
20250035594
The present disclosure relates to a gas concentration measurement apparatus, and in particular to an apparatus which measures a gas concentration based on a propagation time of ultrasound in a concentration measurement space.
Research and development are widely carried out for fuel cell vehicles which travel with electric power supplied from a fuel cell. A fuel cell generates electric power utilizing a chemical reaction between hydrogen and oxygen. In general, hydrogen is supplied to the fuel cell as a fuel, and oxygen is taken into the fuel cell from surrounding air. The fuel cell vehicle is equipped with a hydrogen tank, and hydrogen is supplied from the hydrogen tank to the fuel cell. When an amount of hydrogen in the hydrogen tank becomes low, hydrogen is supplied from a hydrogen supply apparatus provided in a service station to the hydrogen tank of the fuel cell vehicle.
Because hydrogen is a combustible gas, it is necessary to monitor for leakage of hydrogen from the fuel cell vehicle and the hydrogen supply apparatus. For this purpose, a hydrogen concentration measurement apparatus is widely in use in fuel cell vehicles and hydrogen supply apparatuses. The hydrogen concentration measurement apparatus has functions such as measuring concentration of hydrogen contained in air, or sending an alert when the hydrogen concentration becomes greater than a predetermined value.
Patent Literature 1 discloses an apparatus which measures concentration of a particular gas. This apparatus measures the concentration of the particular gas based on a propagation velocity of ultrasound in air which is the measurement target. A propagation time from transmission of the ultrasound from a transmitter to reception, by a receiver, of the ultrasound that has propagated through a measurement section within the concentration measurement space is measured, a propagation velocity is measured based on the propagation time, and the concentration of the gas is then measured.
Patent Literature 2 discloses a gas concentration sensor which transmits ultrasound to a measurement chamber, receives a reflected wave that has been reflected by a wall surface of the measurement chamber, determines a propagation time, which is a time of propagation of the ultrasound through the measurement chamber, and determines a propagation velocity, to thereby detect a concentration of gas to be measured. Patent Literature 2 discloses that the propagation time is determined based on a difference between a time of reception of a first reflected wave which is received by an ultrasound element at an earlier time, and a time of reception of a second reflected wave which is received by the ultrasound element at a later time.
Patent Literature 1: JP 2018-100916 A
Patent Literature 2: JP 2000-249691 A
In the present disclosure, the method as described in Patent Literature 1, in which the propagation time from transmission of the ultrasound from the transmitter to the reception, by the receiver, of the ultrasound that has propagated through the measurement section in the concentration measurement space is measured, will be referred to as a direct wave method. On the other hand, the method as described in Patent Literature 2, in which the ultrasound is transmitted to the measurement chamber, and the propagation time is determined based on the difference between the time of reception of the first ultrasound received by the ultrasound element at an earlier time and the time of reception of the second ultrasound received by the ultrasound element at a later time, will be referred to as a reflected wave method.
In the direct wave method, a process for compensating for delay times of signals at the transmitter and the receiver is required, and the number of processes necessary for the measurement may become large. In the reflected wave method, although it is not necessary to compensate for the delay times, when the distance of propagation of the ultrasound is short or when the propagation velocity is large, the first ultrasound and the second ultrasound may overlap on the time axis, making it difficult to measure the propagation time.
An advantage of the present disclosure lies in simply and accurately performing measurement of gas concentration.
According to one aspect of the present disclosure, there is provided a gas concentration measurement apparatus comprising: a concentration measurement space in which a concentration of a gas is measured; a transmitter that transmits ultrasound to the concentration measurement space in response to a transmission signal; a receiver that receives ultrasound that has propagated through the concentration measurement space, and that outputs a reception signal; and an analyzer that determines a space propagation time, which is time of propagation of the ultrasound through the concentration measurement space, based on a point in time at which the transmission signal is input to the transmitter, and a point in time at which the reception signal is output from the receiver, and that determines a concentration of a gas which is a measurement target based on the space propagation time, wherein the analyzer: determines, based on a direct wave method propagation time determined using a direct wave method and a reflected wave method propagation time determined using a reflected wave method, a correction value for the direct wave method propagation time; and determines the space propagation time based on one of a corrected propagation time obtained by correcting the direct wave method propagation time based on the correction value, or the reflected wave method propagation time, according to the direct wave method propagation time or a value related thereto, the direct wave method being a measurement method in which the direct wave method propagation time is determined based on a difference between a point in time of transmission at which the transmission signal is input to the transmitter, and a first point in time of reception at which the reception signal is output from the receiver a first time after the transmission signal is input to the transmitter, and the reflected wave method being a measurement method in which the reflected wave method propagation time is determined based on a difference between the first point in time of reception and a second point in time of reception at which the reception signal is output from the receiver a second time after the transmission signal is input to the transmitter.
Desirably, in the gas concentration measurement apparatus of claim 1, the analyzer determines the correction value based on the direct wave method propagation time and the reflected wave method propagation time when a condition of the direct wave method propagation time being greater than or equal to a predetermined background process threshold is satisfied.
Desirably, the analyzer determines the space propagation time based on the corrected propagation time when a condition of the direct wave method propagation time being less than a predetermined method switching threshold, which is greater than the background process threshold, is satisfied.
Desirably, the analyzer determines the space propagation time based on the reflected wave method propagation time when a condition of the direct wave method propagation time being greater than or equal to a predetermined method switching threshold, which is greater than the background process threshold, is satisfied.
According to another aspect of the present disclosure, there is provided a gas concentration measurement apparatus comprising: a concentration measurement space in which a concentration of a gas is measured; a transmitter that transmits ultrasound to the concentration measurement space in response to a transmission signal; a receiver that receives ultrasound that has propagated through the concentration measurement space, and that outputs a reception signal; and an analyzer that determines a space propagation time, which is a time of propagation of the ultrasound through the concentration measurement space, based on a point in time at which the transmission signal is input to the transmitter, and a point in time at which the reception signal is output from the receiver, and that determines a concentration of a gas which is a measurement target based on the space propagation time, wherein the analyzer: determines, based on a direct wave method propagation time determined through a direct wave method and a reflected wave method propagation time determined through a reflected wave method, a correction value for the direct wave method propagation time; repeatedly executes measurement of propagation time through the direct wave method and the reflected wave method; and selects one of a corrected propagation time obtained by correcting the direct wave method propagation time based on the correction value, or the reflected wave method propagation time, according to a change over time of the direct wave method propagation time and a change over time of the reflected wave method propagation time, and determines the space propagation time based on the selected one of the corrected propagation time or the reflected wave method propagation time, the direct wave method being a measurement method in which the direct wave method propagation time is determined based on a difference between a point in time of transmission at which the transmission signal is input to the transmitter, and a first point in time of reception at which the reception signal is output from the receiver a first time after the transmission signal is input to the transmitter, and the reflected wave method being a measurement method in which the reflected wave method propagation time is determined based on a difference between the first point in time of reception and a second point in time of reception at which the reception signal is output from the receiver a second time after the transmission signal is input to the transmitter.
Desirably, the analyzer: recognizes one of the direct wave method propagation time and the reflected wave method propagation time as a primary propagation time, and the other of the direct wave method propagation time and the reflected wave method propagation time as a secondary propagation time, according to the direct wave method propagation time or a value related thereto; and determines the space propagation time based on the secondary propagation time when an absolute value of a change over time of the primary propagation time is greater than or equal to a predetermined change threshold, and an absolute value of a change over time of the secondary propagation time is less than the predetermined change threshold.
Desirably, the analyzer: recognizes one of the direct wave method propagation time and the reflected wave method propagation time as a primary propagation time, and the other of the direct wave method propagation time and the reflected wave method propagation time as a secondary propagation time, according to the direct wave method propagation time or a value related thereto; and determines the space propagation time based on the primary propagation time when an absolute value of a change over time of the primary propagation time is greater than or equal to a predetermined change threshold, and an absolute value of a change over time of the secondary propagation time is greater than or equal to the predetermined change threshold.
Desirably, the analyzer selects the reflected wave method propagation time as the primary propagation time when a condition of the direct wave method propagation time being greater than or equal to a predetermined method switching threshold is satisfied.
Desirably, the analyzer selects the direct wave method propagation time as the primary propagation time when a condition of the direct wave method propagation time being less than a predetermined method switching threshold is satisfied.
According to an aspect of the present disclosure, measurement of the gas concentration can be performed simply and accurately.
The analyzer 18 is housed in the analyzer housing space 20. The analyzer 18 may be formed from a processor that executes a program which is read in advance. The processor may be fixed in the analyzer housing space 20, in a state of being fixed on a substrate.
Each of the transmitter 14 and the receiver 16 has an ultrasound transducer. The transmitter 14 and the receiver 16 are connected to the analyzer 18. The transmitter 14 transmits ultrasound to the concentration measurement space 22 according to control by the analyzer 18. That is, the analyzer 18 outputs a transmission signal which is an electric signal to the transmitter 14. The transmitter 14 converts the transmission signal to ultrasound, and transmits the ultrasound. The receiver 16 receives ultrasound that has propagated through the concentration measurement space 22. The receiver 16 converts the received ultrasound to a reception signal which is an electric signal, and outputs the reception signal to the analyzer 18.
The analyzer 18 determines a space propagation time, which is a time of propagation of the ultrasound through the concentration measurement space 22, based on a point in time of input of the transmission signal to the transmitter 14, and a point in time of output of the reception signal from the receiver 16, and determines a concentration of a gas which is a measurement target, based on the space propagation time.
The analyzer 18 determines the space propagation time required for the ultrasound to propagate from the one end to the other end of the concentration measurement space 22 using one measurement method of either a direct wave method or a reflected wave method. The selection of which measurement method is to be used for determining the space propagation time will be described later. The direct wave method is a measurement method in which the propagation time (a direct wave method propagation time Tβ) is determined based on a difference between a point in time of transmission at which the transmission signal is output from the analyzer 18 to the transmitter 14 and a first point in time of reception at which the reception signal is output from the receiver 16 a first time after the transmission signal is output. The difference between the point in time of transmission and the first point in time of reception (time difference) may be determined by subtracting time indicating the point in time of transmission from time indicating the first point in time of reception. The reception signal which is output from the receiver 16 for the first time corresponds to direct ultrasound which is received by the receiver 16 a first time. The direct ultrasound is ultrasound which is transmitted from the transmitter 14, propagates from the one end to the other end through the concentration measurement space 22, and is received by the receiver 16.
The reflected wave method is a measurement method in which the propagation time (a reflected wave method propagation time Tα) is determined based on a difference between the first point in time of reception and a second point in time of reception at which the reception signal is output from the receiver 16 a second time after the transmission signal is output. The difference between the first point in time of reception and the second point in time of reception (time difference) may be determined by subtracting the time indicating the first point in time of reception from time indicating the second point in time of reception. The reception signal which is output from the receiver 16 the second time corresponds to reflected ultrasound which propagates through the concentration measurement space 22 for one and a half round trips after being transmitted from the transmitter 14, and is received by the receiver 16. That is, the reflected ultrasound is ultrasound which is transmitted from the transmitter 14, propagates from the one end to the other end through the concentration measurement space 22, is reflected at the other end, propagates from the other end to the one end through the concentration measurement space 22, is reflected at the one end, propagates through the concentration measurement space 22, and is received by the receiver 16.
Measurement of the gas concentration through the reflected wave method will now be described with reference to
Alternatively, when the reflected wave method propagation time Tα is determined, Euclid distance may be employed in place of the correlation value. The Euclid distance is defined as a square root of a value obtained by time-integrating a square of a difference of two signals. When the Euclid distance is determined, for example, the magnitude(s) of one or both signals may be adjusted so that the maximum values of the two signals become equal to each other. A smaller Euclid distance means a higher degree of similarity between the two signals.
The analyzer 18 determines a value of a half of the reflected wave method propagation time Tα as a space propagation time T. The space propagation time T is time required for the ultrasound to propagate from the one end to the other end through the concentration measurement space 22. A concentration calculation formula (Formula (1)) is widely known, which represents a relationship between a propagation velocity of the ultrasound and the concentration of a particular gas contained in the gas through which the ultrasound propagates. The analyzer 18 uses the concentration calculation formula (Formula (1)) or a formula having the same meaning, to determine the concentration of the gas from the space propagation time T and a length L of the concentration measurement space 22.
Here, k represents a specific-heat ratio of the gas, R represents the gas constant, and Tmp represents a temperature of the concentration measurement space 22. Mh represents a molecular weight of the gas which is the measurement target, and Ma represents a molecular weight of air excluding the measurement target gas. When the composition of the air is assumed to be only 80% nitrogen and 20% oxygen, the specific-heat ratio k may be taken to be 1.4. The gas constant R is 8.31, and the molecular weight Ma of the air is 28.8. When the measurement target gas is hydrogen, the molecular weight Mh is 2.0. The term L/T in (Formula (1)) represents the propagation velocity of the ultrasound.
Next, measurement of the gas concentration using the direct wave method will be described with reference to
The analyzer 18 may determine the direct wave method propagation time Tβ based on a time from appearance of a zero-cross point immediately after a peak of a positive or negative wave height of the transmission signal to appearance of a zero-cross point immediately after a peak of a positive or negative wave height of the reception signal which is output from the receiver 16 the first time. Here, the zero-cross point refers to an intersection between the time waveform of the signal and the time axis.
As shown in
The analyzer 18 determines a corrected propagation time obtained by adding a correction value Δβ=−Td, which is the delay time Td with the polarity inverted, to the direct wave method propagation time Tβ, and sets the corrected propagation time as the space propagation time T. The correction value Δβ may be repeatedly determined at a predetermined time interval based on a background process to be described below.
The background process may be performed along with or separately from the measurement of the gas concentration. The background process is a process for determining the correction value Δβ based on a reflected wave method propagation time Tα0 and a direct wave method propagation time Tβ0. The reflected wave method propagation time Tα0 is determined, the direct wave method propagation time Tβ0 is determined, and a correction target value Δβ0 is determined based on the following Formula (2). Further, the correction value Δβ is modified so that the correction value Δβ becomes close to or coincides with the correction target value Δβ0.
Physical implication of Formula (2) will now be described.
The analyzer 18 may determine an error which is a value obtained by subtracting the correction target value Δβ0 from the correction value Δβ which is already determined, and may determine a new correction value Δβ through proportional integral control based on this error. Alternatively, the analyzer 18 may determine a new correction value Δβ by setting the correction target value Δβ0 as the correction value Δβ. The analyzer 18 stores the newly determined correction value Δβ, until the correction value Δβ is next determined.
The analyzer 18 determines the corrected propagation time obtained by adding the correction value Δβ to the direct wave method propagation time Tβ determined for the measurement of the gas concentration, and sets the corrected propagation time as the space propagation time T. The analyzer 18 further determines the gas concentration using Formula (1).
In the measurement of the gas concentration through the direct wave method, it is necessary to determine the correction value Δβ in advance, in order to determine the space propagation time T. On the other hand, in the measurement of the gas concentration through the reflected wave method, the in-advance determination of the correction value Δβ is not necessary. The reason for this is that, in the measurement of the gas concentration through the reflected wave method, the reflected wave method propagation time Tα from the output of the reception signal from the receiver 16 the first time to the output of the reception signal the second time does not include the delay time Td. In other words, the delay time Td is cancelled out in the process of determining the time difference between the first point in time of reception and the second point in time of reception.
However, in the measurement of the gas concentration through the reflected wave method, the following problem exists. In general, when the gas concentration becomes large, the propagation velocity of the ultrasound becomes larger.
Therefore, as the gas concentration becomes larger, the time of propagation through the concentration measurement space 22 becomes shorter, and the reflected wave method propagation time Tα becomes smaller. That is, the time from the output of the direct wave reception signal from the receiver 16 to the output of the reflected wave reception signal 26 becomes shorter. As a consequence, the time waveform of the direct wave reception signal 24 and the time waveform of the reflected wave reception signal 26 may overlap each other on the time axis, resulting in possible degradation of the measurement precision of the reflected wave method propagation time Tα. On the other hand, in the measurement of the gas concentration through the direct wave method, because the reflected wave reception signal 26 does not overlap a head portion of the time waveform of the direct wave reception signal 24, the measurement of the direct wave method propagation time Tβ is performed relatively accurately.
In consideration of the above, in the gas concentration measurement apparatus 100 of the present embodiment, the direct wave method propagation time Tβ and the reflected wave method propagation time Tα are repeatedly measured at a predetermined time interval, and the analyzer 18 performs the following process each time measurement is performed. Specifically, the analyzer 18 measures the gas concentration through the reflected wave method when the direct wave method propagation time Tβ is greater than or equal to a method switching threshold tc which is determined in advance. On the other hand, when the direct wave method propagation time Tβ is less than the method switching threshold tc, the analyzer 18 measures the gas concentration through the direct wave method.
For the measurement of the gas concentration through the direct wave method, the correction value Δβ for the direct wave method propagation time Tβ is necessary. The analyzer 18 updates the correction value Δβ when the direct wave method propagation time Tβ is greater than or equal to a background process threshold tb which is determined in advance. That is, the analyzer 18 performs the background process at a predetermined time interval to determine the correction value Δβ, replaces the correction value Δβ which has been stored with the new correction value Δβ, and stores the new correction value Δβ. The background process threshold tb may be less than the method switching threshold tc.
When the direct wave method propagation time Tβ is less than the background process threshold tb, the analyzer 18 does not perform the background process, and maintains the value of the correction value Δβ at the current value. When the background process has not been performed even once in the past, the analyzer 18 may store an initial correction value Δβ determined through experiments or a simulation.
When the direct wave method propagation time Tβ is less than the background process threshold tb, the analyzer 18 may only determine the direct wave method propagation time Tβ, and may avoid the determination of the reflected wave method propagation time Tα. The analyzer 18 maintains the state in which the value of the correction value Δβ which has been determined previously is stored.
When the direct wave method propagation time Tβ is greater than or equal to the background process threshold tb, the analyzer 18 determines not only the direct wave method propagation time Tβ, but also the reflected wave method propagation time Tα. The analyzer 18 determines the correction target value Δβ0 based on Formula (2) by setting the direct wave method propagation time Tβ determined at the current time as Tβ0, and the reflected wave method propagation time Tα determined at the current time as Tα0. The analyzer 18 updates the correction value Δβ such that the correction value Δβ coincides with or becomes close to the correction target value Δβ0, and stores the updated correction value Δβ.
When the direct wave method propagation time Tβ is less than the method switching threshold tc, the analyzer 18 measures the gas concentration through the direct wave method. That is, the analyzer 18 adds the correction value Δβ to the direct wave method propagation time Tβ, to determine the space propagation time T (corrected propagation time), and determines the gas concentration based on the space propagation time T. When the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc, the analyzer 18 measures the gas concentration through the reflected wave method. That is, the analyzer 18 sets the reflected wave method propagation time Tα as the space propagation time T, and determines the gas concentration based on the space propagation time T.
In this manner, the analyzer 18 determines the space propagation time T based on one of the corrected propagation time obtained by correcting the direct wave method propagation time Tβ based on the correction value Δβ, or the reflected wave method propagation time Tα, according to the direct wave method propagation time Tβ. According to the process performed by the analyzer 18, when the reflected wave method propagation time Tα is determined with high precision, that is, when the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc, the gas concentration is determined based on the reflected wave method propagation time Tα. When the reflected wave method propagation time Tα cannot be determined with high precision, that is, when the direct wave method propagation time Tβ is less than the method switching threshold tc, the gas concentration is determined based on the direct wave method propagation time Tβ.
When the direct wave method propagation time Tβ is less than the method switching threshold tc, the gas concentration is higher compared to the case where the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc, and the change of the propagation velocity with respect to the change of the gas concentration is large. Therefore, high measurement precision (small error ratio) for the gas concentration is not required compared to the case where the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc, and the gas concentration may be measured through the direct wave method, in which the measurement is simple. On the other hand, when the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc, high measurement precision for the gas concentration is required compared to the case where the direct wave method propagation time Tβ is less than the method switching threshold tc, and the gas concentration may be measured through the reflected wave method. In this manner, according to the gas concentration measurement apparatus 100 of the present embodiment, the gas concentration can be measured simply and with high precision for a wide range of direct wave method propagation time Tβ, that is, for a wide range of the gas concentration.
In addition, in the gas concentration measurement apparatus 100 of the present disclosure, even when the direct wave method propagation time Tβ is less than the method switching threshold tc, the background process is performed if the direct wave method propagation time Tβ is greater than or equal to the background process threshold tb. With this configuration, the correction value Δβ is determined for a range of the reflected wave method propagation time Tα in which sufficient precision can be ensured, and the correction value Δβ is determined for a wide range.
In the gas concentration measurement apparatus 100, random errors may be caused in the direct wave method propagation time Tβ or in the reflected wave method propagation time Tα due to vibration of the housing 10 or the like. In consideration of this, the analyzer 18 may determine the space propagation time T by selectively using the direct wave method propagation time Tβ or the reflected wave method propagation time Tα when the direct wave method propagation time Tβ is greater than or equal to the background process threshold tb, and may measure the gas concentration.
In this case, the analyzer 18 selects the propagation time according to a change over time of the direct wave method propagation time Tβ and a change over time of the reflected wave method propagation time Tα. That is, the analyzer 18 selects one of the corrected propagation time obtained by correcting the direct wave method propagation time Tβ based on the correction value Δβ, or the reflected wave method propagation time Tα, and determines the space propagation time T based on the selected one of the propagation times.
A first process will be described, which is executed when the direct wave method propagation time Tβ is less than the method switching threshold tc. In the first process, the analyzer 18 recognizes the direct wave method propagation time Tβ as a primary propagation time, and recognizes the reflected wave method propagation time Tα as a secondary propagation time.
When an absolute value of a change over time of the primary propagation time is less than a predetermined change threshold, the analyzer 18 determines the space propagation time T based on the primary propagation time.
When the absolute value of the change over time of the primary propagation time is greater than or equal to the predetermined change threshold and an absolute value of a change over time of the secondary propagation time is greater than or equal to the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the primary propagation time.
When the absolute value of the change over time of the primary propagation time is greater than or equal to the predetermined change threshold and the absolute value of the change over time of the secondary propagation time is less than the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the secondary propagation time.
That is, the analyzer 18 determines the direct wave method propagation time Tβ and the reflected wave method propagation time Tα at a predetermined time interval. Every time the direct wave method propagation time Tβ is determined, the analyzer 18 subtracts the direct wave method propagation time Tβ which is previously determined from the direct wave method propagation time T which is currently determined, to determine a change over time β of the direct wave method propagation time Tβ. In addition, the analyzer 18 subtracts the reflected wave method propagation time Tα which is previously determined from the reflected wave method propagation time Tα which is currently determined, to determine a change over time α of the reflected wave method propagation time Tα.
When an absolute value of the change over time β is less than a predetermined change threshold, the analyzer 18 determines the space propagation time T based on the direct wave method propagation time Tβ, and measures the gas concentration through the direct wave method.
When the absolute value of the change over time β is greater than or equal to the predetermined change threshold and an absolute value of the change over time α is greater than or equal to the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the direct wave method propagation time Tβ, and measures the gas concentration through the direct wave method.
When the absolute value of the change over time β is greater than or equal to the predetermined change threshold and the absolute value of the change over time α is less than the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the reflected wave method propagation time Tα, and measures the gas concentration through the reflected wave method.
A second process will now be described, which is executed when the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc.
In the second process, the analyzer 18 recognizes the reflected wave method propagation time Tα as the primary propagation time, and recognizes the direct wave method propagation time Tβ as the secondary propagation time. The analyzer 18 measures the gas concentration through a process similar to the first process.
When the absolute value of the change over time α is less than a predetermined change threshold, the analyzer 18 determines the space propagation time T based on the reflected wave method propagation time Tα, and measures the gas concentration through the reflected wave method.
When the absolute value of the change over time α is greater than or equal to the predetermined change threshold and the absolute value of the change over time β is greater than or equal to the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the reflected wave method propagation time Tα, and measures the gas concentration through the reflected wave method.
When the absolute value of the change over time α is greater than or equal to the predetermined change threshold and the absolute value of the change over time β is less than the predetermined change threshold, the analyzer 18 determines the space propagation time T based on the direct wave method propagation time Tβ, and measures the gas concentration through the direct wave method.
According to the process described above, even when the primary propagation time changes rapidly, if the secondary propagation time does not change rapidly, the space propagation time T is determined based on the secondary propagation time. In addition, when both the primary propagation time and the secondary propagation time change rapidly, the space propagation time T is determined based on the primary propagation time. With this configuration, when an error randomly occurs in the primary propagation time, the gas concentration is measured based on the secondary propagation time. Therefore, the errors which occur in the measurement value of the gas concentration due to random occurrence of errors in the primary propagation time can be suppressed.
In the above, an embodiment has been described in which whether the measurement of the gas concentration is to be performed through the direct wave method or the reflected wave method is judged based on comparison between the direct wave method propagation time Tβ and the method switching threshold tc. Further, in the embodiment described above, whether or not the background process is to be performed is judged based on comparison between the direct wave method propagation time Tβ and the background process threshold tb. Alternatively, these judgments may be executed based on a value related to the direct wave method propagation time Tβ, in place of the direct wave method propagation time Tβ. For example, these judgments may be executed based on a gas concentration for judgment determined by substituting the direct wave method propagation time Tβ into Formula (1). That is, the judgment of which of the direct wave method or the reflected wave method is to be used for the measurement of the gas concentration, and the judgment as to whether or not the background process is to be performed, may be executed based on a value related to the direct wave method propagation time Tβ.
In this case, as the thresholds in the judgments, values may be employed which correspond to the value related to the direct wave method propagation time Tβ. For example, when the judgments are to be executed based on the gas concentration for judgment, a method switching threshold hc corresponding to the method switching threshold tc is determined, and a background process threshold hb corresponding to the back ground process threshold tb is determined.
When the gas concentration for judgment is less than or equal to the method switching threshold hc, a condition where the direct wave method propagation time Tβ is greater than or equal to the method switching threshold tc is satisfied, and, when the gas concentration for judgment is greater than the method switching threshold hc, a condition where the direct wave method propagation time Tβ is less than the method switching threshold tc is satisfied. Similarly, when the gas concentration for judgment is less than or equal to the background process threshold hb, a condition where the direct wave method propagation time Tβ is greater than or equal to the background process threshold hb is satisfied, and, when the gas concentration for judgment is greater than the background process threshold hb, a condition where the direct wave method propagation time Tβ is less than the background process threshold tb is satisfied.
The analyzer 18 measures the gas concentration through the direct wave method when the gas concentration for judgment is greater than the method switching threshold hc, and measures the gas concentration through the reflected wave method when the gas concentration for judgment is less than or equal to the method switching threshold hc. In addition, the analyzer 18 performs the background process when the gas concentration for judgment is less than or equal to the background process threshold hb, and does not perform the background process when the gas concentration for judgment is greater than the background process threshold hb.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-184737 | Nov 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/040654 | 10/31/2022 | WO |
