Gas concentration measurement method and gas concentration measurement device

Abstract

To provide a gas concentration measurement method that measures concentration of gas at a shorter time by a gas sensor.SOLUTION: A gas concentration measurement method, which measures concentration of a measurement object gas by a gas sensor outputting an output value corresponding to the concentration of the measurement object gas, comprises: an exposure step of exposing the gas sensor to the measurement object gas; an acquisition step of acquiring an output value of the gas sensor for a period of time until a first time shorter than a time arriving at the output value corresponding to the concentration of the measurement object gas goes by since the exposure step starts; a step of obtaining concentration of the measurement object gas on the basis of a time rate of change in the output value acquired by the acquisition step.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a gas concentration measurement method and a gas concentration measurement device for measuring the concentration of a gas to be measured using a gas sensor that outputs an output value corresponding to the concentration of the gas to be measured. [Background technology]

[0002] In gas detection sensors, a method of increasing the specific surface area of ​​the gas detection section by using a porous material has been adopted to improve the detection sensitivity and other performance of the sensor. As prior art of this method, the following Non-Patent Document 1 proposes a hydrogen gas sensor that uses titanium dioxide nanotubes (pores) in the gas detection section.

[0003] In addition, Patent Document 1 below proposes a gas sensor that uses a semiconductor or metal porous body in the gas detection section to increase the adsorption area (surface area) and improve sensitivity and response characteristics. Furthermore, it proposes a means of achieving high sensitivity by supporting a catalyst such as platinum or palladium in the porous gas detection section to promote adsorption and desorption of the detected gas.

[0004] Furthermore, Patent Document 2 below proposes a gas sensor having a structure in which a porous titanium oxide layer, which serves as a gas detection section, is formed on titanium metal.

[0005] Furthermore, Patent Document 3 listed below discloses a hydrogen gas sensor in which a sensor element with a micro-tubular structure made mainly of titanium oxide is formed on the surface of an insulating substrate.

[0006] Furthermore, the following Patent Document 4 discloses a gas sensor proposed by the present inventor, which has a structure in which the pores in the porous body penetrate from the front side to the back side of the porous body and are not blocked on either side. This allows the gas to be measured to pass through the porous body, which is the gas detection unit, from the front side to the back side, and easily enter the pores of the porous body, making it possible to detect gas with high sensitivity and a fast response speed. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Oomman K. Varghese et al., “Hydrogen sensing using titania nanotubes”, Sensors and Actuators B 93 (2003) 338-344 [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-213851 [Patent Document 2] Japanese Patent Application Publication No. 8-145925 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-40961 [Patent Document 4] Japanese Patent Application Publication No. 2018-77152 Summary of the Invention [Problem to be solved by the invention]

[0009] In the gas sensors described in Non-Patent Document 1 and Patent Documents 1 to 4, gas is detected by adsorbing the gas to be detected onto the inner walls of the pores of the porous body. However, since the concentration is measured based on the output value of the gas sensor, it takes time for the output value of the gas sensor to reach an equilibrium state, and therefore the measurement time for the gas concentration takes a relatively long time, for example, several tens of seconds to several minutes.

[0010] Furthermore, Non-Patent Document 1 shows the change in resistance of a sensor when only nitrogen gas is passed after a certain concentration of hydrogen is passed through it, but the time it takes to return to the resistance value in the absence of hydrogen gas is extremely long, at about 2000 seconds, and there is an issue that the recovery speed of the sensor is slow. It is presumed that the gas sensors shown in Patent Documents 1 and 2, which have a similar sensor structure, also have the same issue.

[0011] As described above, conventional gas concentration measurement methods require a relatively long time to measure the gas concentration, and if the recovery speed is slow, the interval until the next measurement becomes long, resulting in a long time required for the entire gas concentration measurement operation.

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas concentration measurement method and a gas concentration measurement device that can measure gas concentrations in a shorter time. [Means for solving the problem]

[0013] A first aspect of the gas concentration measurement method of the present invention for solving the above problems is a gas concentration measurement method for measuring the concentration of a gas to be measured by a gas sensor that outputs an output value corresponding to the concentration of the gas to be measured, the method comprising: an exposure step of exposing the gas sensor to the gas to be measured; and a time period from the start of the exposure step that is shorter than the time required for the output value corresponding to the concentration of the gas to be measured to be reached. , the time from the start of the exposure step until the time when the rate of change of the output value of the gas sensor, which is increasing, changes from an increase to a decrease. The method comprises an acquisition step of acquiring an output value of the gas sensor until a first time period has elapsed, an exposure termination step of terminating the exposure of the gas sensor to the gas to be measured when the first time period has elapsed, and a step of determining the concentration of the gas to be measured based on the rate of change of the output value acquired in the acquisition step, and is characterized in that each of the steps is performed only once.

[0017] The above item one The present invention is characterized in that the gas sensor is exposed to the measurement target gas by being sprayed thereon in the exposing step.

[0018] The above item one In the aspect of the present invention, the first time period is a time period from the start of the exposure step until the time rate of change of the output value of the gas sensor, which increases from the start of the exposure step, changes from an increase to a decrease.

[0019] The gas concentration measurement device of the present invention for measuring the concentration of a measurement target gas comprises: a gas sensor that outputs an output value corresponding to the concentration of the measurement target gas; In the exposing step of exposing the gas sensor to the measurement target gas, shorter than the time it takes to reach an output value corresponding to the concentration of the gas to be measured , the time from the start of the exposure step until the time when the rate of change of the output value of the gas sensor, which is increasing, changes from an increase to a decrease. an exposure control means for controlling the time for exposing the gas sensor to the measurement target gas so as to expose the gas sensor to the measurement target gas for a first time period and stop the exposure when the first time period has elapsed; and an exposure control means for acquiring an output value of the gas sensor and determining whether the time for the gas sensor to reach an output value corresponding to the concentration of the measurement target gas is shorter than the time required for the gas sensor to reach the output value corresponding to the concentration of the measurement target gas after being exposed to the measurement target gas. The aforementioned and a calculation means for calculating the concentration of the gas to be measured based on the rate of change over time of the output value of the gas sensor acquired until a first time period has elapsed, and each of the means is performed only once. [Effects of the Invention]

[0021] According to the gas concentration measurement method and gas concentration measurement device of the present invention, the gas concentration can be measured accurately in a shorter time before the output value of the gas sensor measuring the gas concentration reaches an equilibrium state at which the output value is maximized. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram showing a first example of the configuration of a gas concentration measurement device for carrying out a gas concentration measurement method in an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a second example of the configuration of a gas concentration measurement device for carrying out a gas concentration measurement method in an embodiment of the present invention. [Figure 3] 1 is a diagram illustrating a configuration example of a gas sensor according to an embodiment of the present invention. [Figure 4] 1 is a diagram illustrating an outline of a gas concentration measurement method according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating an outline of a gas concentration measurement method according to an embodiment of the present invention. [Figure 6] 4 is a flowchart showing a first measurement process of the gas concentration measurement method according to the embodiment of the present invention. [Figure 7] 5 is a flowchart showing a second measurement process of the gas concentration measurement method according to the embodiment of the present invention. [Figure 8]6 is a flowchart showing a third measurement process of the gas concentration measurement method according to the embodiment of the present invention. [Figure 9] FIG. 2 is a graph showing a first measurement example in which the gas concentration measurement method according to the embodiment of the present invention is carried out. [Figure 10] FIG. 2 is a graph showing a first measurement example in which the gas concentration measurement method according to the embodiment of the present invention is carried out. [Figure 11] FIG. 4 is a graph showing a second measurement example in which the gas concentration measurement method according to the embodiment of the present invention is carried out. [Figure 12] 10 is data showing the relationship between the time rate of change of the gas sensor output value and the gas concentration in the second measurement example. [Figure 13] FIG. 4 is a diagram illustrating the rate of change of a gas sensor output value over time. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments are provided for the purpose of understanding the present invention, and the technical scope of the present invention is not limited to these.

[0024] FIG. 1 is a diagram showing a first example configuration of a gas concentration measurement device for carrying out a gas concentration measurement method according to an embodiment of the present invention. The gas concentration measurement device 100 according to the first example configuration includes a gas sensor 10, a gas supply pipe 20, a gas supply electromagnetic valve 30, and a control device 40. The gas sensor 10 is a sensor that detects a specific gas present in the surrounding area and outputs an electrical characteristic value (current value, voltage value, etc.) corresponding to the concentration of the gas. For example, the gas sensor 10 may be a so-called semiconductor sensor, a catalytic combustion sensor, or an electrochemical sensor that utilizes a gas oxidation-reduction reaction. The gas sensor 10 is appropriately selected depending on the type of gas to be measured (sample gas). As an example, the configuration of a gas sensor that detects hydrogen gas will be described below.

[0025] The gas sensor 10 is placed in a container 70 having a predetermined volume, and the gas supply pipe 20 is arranged to pass through the container 70 and introduce gas to the gas detection surface of the gas sensor 10 inside the container 70. The container 70 is also provided with an exhaust port 70a for gas or air.

[0026] The gas supply pipe 20 is a pipe that supplies sample gas to the gas detection surface of the gas sensor 10, and the sample gas is sprayed onto the detection surface of the gas sensor 10 from a sample gas supply source (not shown) at a predetermined pressure and flow rate.

[0027] The gas supply electromagnetic valve 30 is a valve that electromagnetically opens and closes the gas supply pipe 20. When the electromagnetic valve 30 is open, the sample gas is sprayed onto the gas sensor 10, and when the electromagnetic valve 30 is closed, the supply of the sample gas to the gas sensor 10 is stopped.

[0028] The control device 40 is a control device (exposure control means and calculation means) that acquires the output value of the gas sensor 10, performs predetermined calculation processing, and controls the opening and closing of the electromagnetic valve 30. The control device 40 is a control unit that includes, for example, a computer device such as a personal computer that controls the entire measurement, an analog or digital calculation circuit that calculates the output value of the gas sensor 10, and a drive device that drives the electromagnetic valve. The computer device functions as a calculation processing device that calculates the gas concentration based on the time rate of change of the output value of the gas sensor 10 (described later), and executes a calculation processing program that calculates the gas concentration based on the time rate of change of the gas concentration. The calculation processing program is a computer program for calculating the gas concentration based on the time rate of change of the gas concentration. Table data used to execute the calculation processing program is stored in a predetermined storage means of the computer device. This table data is data showing the correlation between the time rate of change of the output value of the gas sensor 10 and the gas concentration for the gas sensor 10 used in the gas concentration measurement method, and data showing this correlation is obtained in advance by experiment.

[0029] Fig. 2 is a diagram showing a second configuration example of a gas concentration measurement device for carrying out a gas concentration measurement method according to an embodiment of the present invention. Similar to the gas concentration measurement device 100 according to the first configuration example shown in Figs. 1 and 2, the gas concentration measurement device 200 according to the second configuration example is configured to include a gas sensor 10, a gas supply pipe 20, a gas supply electromagnetic valve 30, and a control device 40, and further includes an air supply pipe 50 and an air supply electromagnetic valve 60 for supplying air to the gas sensor 10, unlike the gas concentration measurement device 100 according to the first configuration example.

[0030] The air supply pipe 50 is a pipe that supplies air to the gas detection surface of the gas sensor 10, and the air is blown at a predetermined pressure and flow rate onto the gas detection surface of the gas sensor 10. An air supply electromagnetic valve 60 is provided in the air supply pipe 50.

[0031] The air supply electromagnetic valve 60 is a valve that electromagnetically opens and closes the air supply pipe 50. When the electromagnetic valve 60 is open, air is blown onto the gas sensor 10, and when the electromagnetic valve 60 is closed, the supply of air to the gas sensor 10 is stopped.

[0032] In the second configuration example as well, the gas sensor 10 is disposed in a container 70 having a predetermined volume, and the gas supply pipe 20 and the air supply pipe 50 are disposed so as to penetrate the container 70 and introduce gas or air to the gas detection surface of the gas sensor 10 in the container 70. The container 70 is also provided with an exhaust port 70a for gas or air.

[0033] 3A and 3B are diagrams showing an example of the configuration of a gas sensor used in a gas concentration measurement method according to an embodiment of the present invention, in which FIG. 3A is a perspective view, FIG. 3B is a top view, and FIG. 3C is a cross-sectional view taken along line AA in FIG. 3B.

[0034] The gas sensor 10 is a gas sensor in which a portion of a metal or semiconductor thin plate member 12 is formed into a porous body 14, and the thin plate portions on both sides of the porous body 14 serve as a pair of electrodes 18a, 18b. The porous body 14 serves as a gas detection unit that detects gas. Specifically, the gas sensor 10 is a single piece of metal or semiconductor thin plate member 12, and a portion of the surface of the thin plate 12 is anodized to form the porous body 14 having a large number of cylindrical pores 15 oriented in a direction approximately perpendicular to the thin plate surface and penetrating from one side to the other.

[0035] The porous body 14 is formed across the thin plate by anodizing a region from one end of the approximate center of the thin plate member 12 to the opposite end. The pores 15 that penetrate from one side of the thin plate member 12 to the opposite side are anodized until the bottom of the pores 15 just reaches the opposite side, and then the opposite side is polished using a technique such as polishing until the pores 15 are completely penetrated, thereby forming pores 15 that are open on both ends. Because one end of the pores 15 is not blocked by a substrate or the like, gas that flows in through the opening on one end of the pores 15 can pass through the opening on the other end. Since gas can permeate from one side of the porous body 14 to the opposite side, gas can easily enter the inside of the pores 15, improving the sensitivity and responsiveness of gas detection.

[0036] The thin plate portions on both sides of the porous body 14 having the pores 15 serve as a pair of electrodes 18a, 18b. The electrodes 18a, 18b are separated by the porous body 14. This has the advantage that the portions of the thin plate other than the porous body portion can be used as electrodes, eliminating the need for a process for forming electrodes. Further details of the configuration and manufacturing method of this gas sensor are disclosed in JP 2018-77152 A.

[0037] 4 and 5 are diagrams illustrating an outline of a gas concentration measurement method according to an embodiment of the present invention. As shown in FIG. 4, when a gas sensor is exposed to a sample gas at the start of measurement, its output value increases over a predetermined measurement time according to the concentration of the detected gas. When the output value reaches approximately its maximum, the output value stabilizes and reaches equilibrium, and the measurement ends at this timing. Because this maximum output value corresponds to the gas concentration, conventional gas concentration measurements require time for the gas sensor's output value to reach its maximum. The inventors have found and focused on the fact that the change in the gas sensor's output value from the start of measurement varies depending on the concentration of the sample gas to be measured. Specifically, they have obtained the technical insight that the rate of change of the output value over time from the start of measurement varies depending on the concentration of the sample gas to be measured. When the concentration is relatively high, the rate of change of the output value over time from the start of exposure of the sample gas to the gas sensor is large, and when the concentration is relatively low, the rate of change of the output value over time from the start of exposure of the sample gas to the gas sensor is small. This makes it possible to determine the gas concentration from the output value obtained in a very short time during the rise of the gas sensor's output value, which is before the gas sensor's output value reaches its maximum and reaches equilibrium.

[0038] The inventors also noticed that the recovery time of a gas sensor after exposing the gas sensor to the sample gas is shorter the lower the gas concentration is, and by stopping the exposure of the gas sensor to the sample gas while obtaining a relatively low output value before the output value reaches its maximum, the recovery time of the gas sensor can be shortened and the interval to the next measurement can be shortened.

[0039] In this way, in the gas concentration measurement method according to the embodiment of the present invention, the time rate of change is calculated from the output value of the gas sensor after a very short time has elapsed since the start of exposure of the sample gas to the gas sensor, and the gas concentration corresponding to this time rate of change is determined.

[0040] Furthermore, as shown in Figure 5, by acquiring the output value of the gas sensor a very short time after the start of exposure to the sample gas, the exposure to the sample gas can be stopped at a point when the gas sensor output value is relatively low, thereby shortening the recovery time of the gas sensor and enabling the next gas concentration measurement to be performed at short intervals. This makes it possible to repeat gas concentration measurements multiple times in a short cycle, and to determine the gas concentration with higher accuracy from the rate of change of the output value obtained from multiple gas concentration measurements.

[0041] 6 is a flowchart showing a first measurement process of the gas concentration measurement method according to the embodiment of the present invention. The gas concentration measurement device that performs the first measurement process may be either the gas concentration measurement device 100 of the first configuration example or the gas concentration measurement device 200 of the second configuration example, and performs a gas concentration measurement operation using the gas sensor 10 only once. In the case of the gas concentration measurement device 200, the air supply electromagnetic valve 50 is closed, and no air is supplied.

[0042] In addition, in the first, second and third measurement processes of the gas concentration measurement method in the embodiment of the present invention described below, the opening and closing operations of the electromagnetic valve, time measurement, acquisition of the output value of the gas sensor, calculation processing, etc. are performed under the control of the measurement device 40.

[0043] In step S100, the gas supply electromagnetic valve 30 of the gas supply pipe 20 is opened to start spraying the sample gas onto the gas sensor 10, thereby exposing the gas sensor 10 to the sample gas.

[0044] In step S102, the measuring device 40 starts acquiring the output value of the gas sensor 10, and in step S104, the measuring device 40 measures the time from the start of exposure to the sample gas, and acquires the output value of the gas sensor 10 until a first time period has elapsed that is shorter than the time it takes for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas.

[0045] The time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas is the time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas and reach an approximately equilibrium state if the gas sensor 10 is continuously exposed to the sample gas, and the first time, which is the time required for the gas sensor 10 to be exposed to the sample gas, is shorter than this time, and preferably is a very short time before the rate of change of the output value of the gas sensor 10, which increases from the start of exposure, changes from increasing to decreasing.

[0046] The gas sensor 10 outputs output values ​​multiple times during a first time period during which the gas sensor 10 is exposed to the sample gas. That is, the output interval of the gas sensor 10 is shorter than the first time period, and the control device 40 acquires multiple output values ​​from the gas sensor 10 during the first time period.

[0047] In step S106, the measuring device 40 calculates the time rate of change of the acquired output value, and then in step S108, the measuring device 40 calculates the concentration of the sample gas based on the calculated time rate of change. Specifically, the measuring device 40 calculates the time rate of change of the acquired output value of the gas sensor 10, and calculates the actual concentration of the sample gas from the time rate of change. The measuring device 40 stores table data indicating the relationship between the time rate of change of the output value of the gas sensor 10 and the gas concentration of the sample gas, and the measuring device 40 calculates the gas concentration corresponding to the time rate of change calculated in step S106 based on the data in the table data.

[0048] 7 is a flowchart showing a second measurement process of the gas concentration measurement method according to the embodiment of the present invention. The gas concentration measurement device that performs the second measurement process may be either the gas concentration measurement device 100 of the first configuration example or the gas concentration measurement device 200 of the second configuration example, and performs the gas concentration measurement operation using the gas sensor 10 multiple times. In the case of the gas concentration measurement device 200, the air supply electromagnetic valve 50 is closed, and no air is supplied.

[0049] In step S200, the gas supply electromagnetic valve 30 of the gas supply pipe 20 is opened to start spraying the sample gas onto the gas sensor 10, thereby exposing the gas sensor 10 to the sample gas.

[0050] In step S202, the measuring device 40 starts acquiring the output value of the gas sensor 10, and in step S204, measures the time from the start of exposure to the sample gas. In step S206, the measuring device 40 closes the gas supply electromagnetic valve 30 to stop the supply of the sample gas to the gas sensor 10 when a first time period has elapsed that is shorter than the time it takes for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas, and acquires the output value of the gas sensor 10 when the first time period has elapsed. Closing the gas supply electromagnetic valve 30 puts the gas sensor 10 in a state where it is not exposed to the sample gas.

[0051] The time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas is the time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas and reach an approximately equilibrium state if the gas sensor 10 is continuously exposed to the sample gas, and the first time, which is the time required for the gas sensor to be exposed to the sample gas, is shorter than this time, and preferably is a very short time before the rate of change of the output value of the gas sensor, which increases from the start of exposure, changes from increasing to decreasing.

[0052] The gas sensor 10 outputs output values ​​multiple times during a first time period during which the gas sensor 10 is exposed to the sample gas. That is, the output interval of the gas sensor 10 is shorter than the first time period, and the control device 40 acquires multiple output values ​​from the gas sensor 10 during the first time period.

[0053] In step S208, it is determined whether the measurement process of steps S200 to S206 has been performed N times (multiple times). If the number of times is less than N, in step S210, time is measured and the passage of a preset second time period corresponding to the recovery time of the gas sensor 10 is counted. After the second time period has elapsed, the process returns to step S200, and the gas supply electromagnetic valve 30 is opened again to expose the gas sensor 10 to the sample gas. In this manner, the measurement process of steps S200 to S206 is repeated N times to intermittently expose the gas sensor 10 to the sample gas multiple times, and an output value of the gas sensor 10 is obtained for each measurement process. Note that the control device 40 may also obtain the output value that continues to be output from the gas sensor 10 during the second time period, but this output value is not used in the calculation of the gas concentration.

[0054] If the measurement process of steps S200 to S206 has been repeated N times in step S208, the measurement device 40 calculates the time rate of change of each output value acquired each time in step S212. Furthermore, in step S214, the measurement device 40 calculates the concentration of the sample gas based on the calculated multiple time rate of change. For example, the concentration of the sample gas may be calculated using the average value of all the calculated multiple time rate of change. Alternatively, the concentration of the sample gas may be calculated using a value excluding the minimum and maximum values ​​from the calculated multiple time rate of change. The method for calculating the multiple time rate of change may be selected as appropriate. Table data showing the relationship between the time rate of change of the output value of the gas sensor 10 and the gas concentration of the sample gas is stored in the measurement device 40. The measurement device 40 calculates the gas concentration corresponding to the time rate of change calculated in step S212 (including a value obtained by calculating the multiple time rate of change) based on the data in the table data.

[0055] 8 is a flowchart showing a third measurement process of the gas concentration measurement method according to the embodiment of the present invention. The gas concentration measurement device that performs the third measurement process uses the gas concentration measurement device 200 according to the second exemplary configuration described above to repeatedly perform gas concentration measurement operations using the gas sensor 10.

[0056] In step S300, the gas supply electromagnetic valve 30 of the gas supply pipe 20 is opened to start spraying the sample gas onto the gas sensor 10, thereby exposing the gas sensor 10 to the sample gas.

[0057] In step S302, the measuring device 40 starts acquiring the output value of the gas sensor 10. In step S104, the measuring device 40 measures the time from the start of exposure to the sample gas. In step S306, when a first time period has elapsed that is shorter than the time it takes for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas, the measuring device 40 closes the gas supply electromagnetic valve 30 to stop the supply of the sample gas to the gas sensor 10, acquires the output value of the gas sensor 10 until the first time period has elapsed, and further opens the air supply electromagnetic valve 50 to supply air to the gas sensor 10. This supplies air to the gas sensor 10, forcibly removing the sample gas and shortening the recovery time of the gas sensor 10.

[0058] The time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas is the time required for the gas sensor 10 to reach an output value corresponding to the actual concentration of the sample gas and reach an approximately equilibrium state if the gas sensor 10 is continuously exposed to the sample gas, and the first time, which is the time required for the gas sensor to be exposed to the sample gas, is shorter than this time, and preferably is a very short time before the rate of change of the output value of the gas sensor, which increases from the start of exposure, changes from increasing to decreasing.

[0059] The gas sensor 10 outputs output values ​​multiple times during a first time period during which the gas sensor 10 is exposed to the sample gas. That is, the output interval of the gas sensor 10 is shorter than the first time period, and the control device 40 acquires multiple output values ​​from the gas sensor 10 during the first time period.

[0060] In step S308, it is determined whether the measurement process of steps S300 to S306 has been performed N times (multiple times). If the number of times is less than N, in step S310, time is measured and a preset second time period corresponding to the recovery time of the gas sensor 10 is counted. After the second time period has elapsed, in step S312, the air supply electromagnetic valve 50 is closed to stop the air supply, and the process returns to step S300. Then, in step S300, the gas supply electromagnetic valve 30 is opened again to expose the gas sensor 10 to the sample gas. In this way, the measurement process of steps S300 to S306 is repeated N times to intermittently expose the gas sensor to the sample gas multiple times, and an output value of the gas sensor 10 is obtained for each measurement process. Note that the control device 40 may also obtain the output value that continues to be output from the gas sensor 10 during the second time period, but this output value is not used in the calculation of the gas concentration.

[0061] By blowing air over the gas sensor 10 for a second period of time after the exposure has stopped, the recovery time of the gas sensor 10 can be accelerated, and this second period of time can be shortened, resulting in a shorter measurement cycle.

[0062] If the measurement process of steps S300 to S306 has been repeated N times in step S308, the measurement device 40 calculates the time rate of change of each output value acquired each time in step S314, and then calculates the concentration of the sample gas based on the calculated multiple time rate of change in step S316. Table data indicating the relationship between the time rate of change of the output value of the gas sensor 10 and the gas concentration of the sample gas is stored in the measurement device 40, and the measurement device 40 calculates the gas concentration corresponding to the time rate of change calculated in step S316 (including a value obtained by calculating the multiple time rate of change) based on the data in the table data.

[0063] 9 and 10 are graphs showing a first measurement example using the gas concentration measurement method according to the embodiment of the present invention. FIG. 10 is an enlarged view of the area enclosed by the dotted line in FIG. 9. In the first measurement example, hydrogen gas concentrations were measured using the gas sensor 10 shown in FIG. 3 according to the third measurement process of FIG. 8 using the second configuration example of the gas concentration measurement device shown in FIG. 2. Measurements were performed on four types of sample gas (hydrogen gas) with hydrogen gas concentrations of 10 ppm, 20 ppm, 50 ppm, and 100 ppm using a conventional gas concentration measurement method (FIGS. 9(a) and 10(a)), in which measurements were performed until the output value of the gas sensor 10 reached equilibrium. Measurements were also performed using the gas concentration measurement method of the present invention (FIGS. 9(b) and 10(b)). The opening time (first time) of the gas supply electromagnetic valve 30 was 1 second, and the opening time (second time) of the air supply electromagnetic valve 50 was 10 seconds. The output interval (unit measurement interval) of the gas sensor 10 was 300 msec. The higher the hydrogen gas concentration of the sample gas shown in Figures 9(a) and 10(a), the larger the time rate of change during the rise from the start of exposure in each of the multiple measurement steps at predetermined time intervals in Figures 9(b) and 10(b), confirming that the time rate of change of the output value corresponds to the gas concentration. Note that in Figures 9(b) and 10(b), the output values ​​(output currents) of the gas sensor corresponding to each concentration are shifted along the vertical axis to avoid overlapping on the graph. Therefore, the output values ​​of the gas sensor are in arbitrary units, and their magnitude represents a relative difference.

[0064] FIG. 11 is a graph illustrating a second measurement example performed using the gas concentration measurement method according to the embodiment of the present invention. In this second measurement example, hydrogen gas concentrations were measured using the gas sensor 10 illustrated in FIG. 3 according to the third measurement process of FIG. 8 using the second configuration example of the gas concentration measurement device shown in FIG. 2. Measurements were performed using the gas concentration measurement method according to the present invention for four types of sample gas (hydrogen gas) with hydrogen gas concentrations of 10 ppm, 20 ppm, 50 ppm, and 100 ppm. The opening time (first time) of the gas supply electromagnetic valve 30 was 2 seconds, and the opening time (second time) of the air supply electromagnetic valve 50 was 1 second. The output interval (unit measurement interval) of the gas sensor 10 was 300 msec. Note that in FIG. 11, similar to FIGS. 9(b) and 10(b), the output values ​​(output currents) of the gas sensor corresponding to each concentration are displayed with their coordinates shifted along the vertical axis to avoid overlapping on the graph. Therefore, the gas sensor output values ​​are in arbitrary units, and their magnitudes represent relative differences.

[0065] In the second measurement example, it was also confirmed that the higher the gas concentration of the sample gas, the larger the time change rate at the rise from the start of exposure in each of the multiple measurement steps per predetermined cycle, and that the time change rate of the gas sensor output value corresponds to the gas concentration.

[0066] Figure 12 shows data showing the relationship between the time rate of change of the gas sensor output value and the gas concentration in the second measurement example. A correlation is obtained in which the gas concentration increases as the calculated time rate of change increases. A calibration curve (calibration curve) showing the correlation can be derived using known statistical methods. It is also possible to estimate the concentration by machine learning using correlation data previously obtained through experiments.

[0067] Fig. 13 is a diagram illustrating the time rate of change of the gas sensor output value, and shows, as an example, the waveform of the gas sensor output value in the area enclosed by the dotted line in Fig. 11. The time rate of change of the gas sensor output value obtained by calculation can be calculated, for example, as the time rate of change (ΔI / Δt) of the amount of change (ΔI) in the sensor output value over a predetermined period (Δt: measurement interval of the gas sensor × n) during the first time period, which is the time during which the gas sensor is exposed to the sample gas. The data shown in Fig. 12 is a numerical value obtained by calculating the time rate of change of the gas sensor output value as the rate of change (ΔI / Δt) of the difference between the first and last sensor output values ​​within the first time period.

[0068] As another method for calculating the time rate of change of the gas sensor output value, for example, the maximum change (dI) among the changes of the gas sensor output value at adjacent (consecutive) unit measurement intervals during the first time period, which is the time period during which the gas sensor is exposed to the sample gas, may be calculated, and the time rate of change (dI / dt) may be used as the time rate of change of the gas sensor output value to be associated with the gas concentration.

[0069] The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention also includes design changes within the scope of the gist, including various modifications and alterations that would be conceivable to a person having ordinary knowledge in the field of the present invention. [Explanation of symbols]

[0070] 10: Gas sensor 12: Thin plate material 14: Porous material 18a, 18b: Electrode 20: Gas supply pipe 30: Gas supply electromagnetic valve 40: Control device 50: Air supply pipe 60: Air supply solenoid valve 70: Container

Claims

1. A gas concentration measurement method for measuring the concentration of a gas to be measured using a gas sensor that outputs an output value corresponding to the concentration of the gas to be measured, an exposing step of exposing the gas sensor to the measurement target gas; an acquisition process for acquiring an output value of the gas sensor during a first time period from the start of the exposure process until the time when a rate of change of the output value of the gas sensor, which increases from the start of the exposure process, changes from an increase to a decrease, the first time period being shorter than the time required for the output value to reach a value corresponding to the concentration of the target gas; an exposure stopping step of stopping exposure of the gas sensor to the measurement target gas when the first time period has elapsed; and a step of determining the concentration of the gas to be measured based on the rate of change of the output value acquired in the acquisition step, wherein each of the steps is performed only once.

2. 2. The gas concentration measuring method according to claim 1, wherein the gas sensor is exposed to the measurement target gas by being sprayed with the measurement target gas in the exposing step.

3. A gas concentration measurement device for measuring the concentration of a measurement target gas, a gas sensor that outputs an output value corresponding to the concentration of a gas to be measured; an exposure control means for exposing the gas sensor to the measurement target gas for a first time period, the first time period being a time period from the start of the exposure step until a rate of change in the output value of the gas sensor, which increases from an increase in the first time period to a decrease in the second time period, during an exposure step of exposing the gas sensor to the measurement target gas; and and a calculation means for acquiring an output value of the gas sensor, and calculating the concentration of the target gas based on a time rate of change of the output value of the gas sensor acquired during a first time period that is shorter than the time required for the gas sensor to reach an output value corresponding to the concentration of the target gas after being exposed to the target gas, wherein each of the means is performed only once.

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