JP7829855B2 - Gas detection device, gas detection method, and gas detection program - Google Patents

Description

This invention relates to a gas detection device, a gas detection method, and a gas detection program.

Gas sensors that utilize Micro Electro Mechanical Systems (MEMS) to detect specific gases such as hydrogen are known (see, for example, Non-Patent Documents 1-3). Non-Patent Document 1 describes a technique for detecting gases with high sensitivity while suppressing power consumption using a gas sensor formed using MEMS. Non-Patent Document 2 describes a technique for estimating the elemental content of a gas by measuring a gas containing multiple elements under constant power, constant resistance, and constant energy conditions using a gas sensor. Furthermore, Non-Patent Document 3 describes a technique for detecting hydrogen contained in an atmosphere in the range of 0% to 4% using a gas sensor in a high-humidity atmosphere within the temperature range of -15°C to 84°C.

Transient thermal response of micro-thermal conductivity detector (μTCD) for the identification of gas mixtures: An ultra-fast and low power method, Allireza Mahodafar et al., Microsystems &Nanoengineering 1 (2015) 15025 Investigating time-resolved response of micro thermal conductivity sensor under various modes of operation, Daniel Struka et al., Sensors and Actuators B 254 (2018) 771-777 MEMS-based thermal conductivity sensor for hydrogen gas detectionin automotive applications, Dominik Berndt et al., Sensors and Actuators A 305 (2020) 111670

The technologies described in Non-Patent Documents 1-3 detect hydrogen based on changes in the resistance value of a gas sensor caused by supplying a pulsed current to the sensor. However, when supplying a pulsed current to a gas sensor, the amount of current supplied to the sensor is limited to only two points: a minimum and a maximum value. The signal indicating the resistance value of the gas sensor, calculated from the supplied pulsed current, is affected by the surrounding environment, resulting in a low signal-to-noise ratio and potentially leading to misjudgment of the presence or absence of gas.

This invention aims to solve these problems and provide a gas detection device capable of accurately estimating the presence and concentration of gases.

The gas detection device according to the present invention comprises a conductor whose resistance changes in response to temperature changes, a power supply that supplies electricity to the conductor, an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor, and an estimation device that estimates the concentration of a predetermined gas present around the conductor. The estimation device gradually changes the amount of electricity supplied to the conductor, acquires multiple physical quantities detected by the electrical sensor while changing the amount of electricity supplied to the conductor, estimates the concentration of the gas present around the conductor based on the amount of electricity supplied to the conductor and the acquired multiple physical quantities, and outputs a concentration signal indicating the estimated gas concentration.

Furthermore, in the gas detection device according to the present invention, the power supply is a current source that supplies current to the conductor, the electrical sensor is a voltmeter that detects the voltage output from the conductor, and the estimation device preferably acquires multiple voltage values detected by the voltmeter while changing the amount of current supplied to the conductor, and estimates the amount of gas present around the conductor based on the amount of current supplied to the conductor and the resistance value and power calculated from the acquired multiple voltage values.

Furthermore, in the gas detection device according to the present invention, the power supply is a voltage source that applies voltage to the conductor, the electrical sensor is an ammeter that detects the current flowing through the conductor, and the estimation device preferably acquires multiple current amounts detected by the ammeter while changing the voltage value supplied to the conductor, and estimates the amount of gas present around the conductor based on the voltage value supplied to the conductor and the resistance value and power calculated from the acquired multiple current amounts.

Furthermore, in the gas detection device according to the present invention, the conductor is preferably placed in the atmosphere, and the gas is preferably hydrogen.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device repeatedly performs a supply process that gradually increases the amount of electricity supplied to the conductor from a first amount to a second amount higher than the first amount.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device calculates the power supplied to the conductor when the acquired physical quantities are output from the conductor, based on the amount of electricity supplied to the conductor and the acquired physical quantities; calculates the resistance value of the conductor when the acquired physical quantities are output from the conductor, based on the amount of electricity supplied to the conductor and the acquired physical quantities; calculates a correlation coefficient showing the correlation between power and resistance from the calculated power and resistance; and estimates the concentration of gas present around the conductor based on the correlation coefficient.

Furthermore, in the gas detection device according to the present invention, the correlation coefficient is preferably the ratio between the calculated change in power and the calculated change in resistance.

Furthermore, in the gas detection device according to the present invention, in the supply process, it is preferable that the estimation device increases the amount of electricity supplied to the conductor from a first amount to a second amount, and then gradually decreases the amount of electricity supplied to the conductor from the second amount back to the first amount.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device calculates the correlation coefficient by using the area of the region enclosed by the plots corresponding to each of the acquired physical quantities in a Cartesian coordinate system where the calculated power is the first axis and the calculated resistance value is the second axis.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device corrects the correlation coefficient based on the physical quantity obtained when supplying an amount of electricity closer to the first amount than the second amount.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device corrects the correlation coefficient based on the initially acquired physical quantity.

Furthermore, in the gas detection device according to the present invention, it is preferable that the estimation device estimates the resistance value when no electricity is supplied to the conductor from the calculated power and resistance values, determines whether the difference between the estimated resistance value and the reference resistance value is greater than or equal to a predetermined threshold difference, and outputs an alarm signal indicating that the conductor has deteriorated when it is determined that the difference between the estimated resistance value and the reference resistance value is greater than or equal to the predetermined threshold difference.

The gas detection method according to the present invention gradually changes the amount of electricity supplied to a conductor whose resistance changes in response to temperature changes. While the amount of electricity supplied to the conductor is changing, multiple physical quantities are acquired by an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor. Based on the amount of electricity supplied to the conductor and the acquired multiple physical quantities, the concentration of the gas present around the conductor is estimated, and a concentration signal indicating the estimated gas concentration is output.

The gas detection program according to the present invention causes a computer to perform the following processing: gradually changing the amount of electricity supplied to a conductor whose resistance changes in response to temperature changes; acquiring multiple physical quantities detected by an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor while the amount of electricity supplied to the conductor is changing; estimating the concentration of the gas present around the conductor based on the amount of electricity supplied to the conductor and the acquired multiple physical quantities; and outputting a concentration signal indicating the estimated gas concentration.

Furthermore, the gas detection device according to the invention comprises a conductor whose resistance changes in response to temperature changes, a power supply that supplies electricity to the conductor, an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor, and a determination device that determines whether or not a predetermined gas is present around the conductor. The determination device gradually changes the amount of electricity supplied to the conductor, acquires multiple physical quantities detected by the electrical sensor while changing the amount of electricity supplied to the conductor, and determines whether or not a gas is present around the conductor based on the amount of electricity supplied to the conductor and the acquired multiple physical quantities. When it determines that a gas is present around the conductor, it outputs a detection signal indicating that a gas has been detected.

The gas detection device according to the present invention can estimate the presence and concentration of gas with high accuracy.

This figure illustrates the outline of a hydrogen detection device according to an embodiment, where (a) shows the amount of current supplied to the hydrogen sensor of the hydrogen detection device according to the embodiment, (b) shows the voltage value output from the hydrogen sensor in response to the amount of current supplied to the hydrogen sensor as shown in (a), (c) shows the correlation between the amount of current supplied to the hydrogen sensor and the voltage value output from the hydrogen sensor, and (d) shows the correlation between the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor. This is a diagram showing a hydrogen detection device according to the first embodiment. This figure shows the current transition information as shown in Figure 2. This is a flowchart relating to the first aspect of the estimation process performed by the estimation device shown in Figure 2. This is a diagram showing a hydrogen detection device according to the second embodiment. Figure 5 shows the resistance compensation table. This is a flowchart relating to the first aspect of the estimation process performed by the estimation device shown in Figure 5. This is a diagram showing a hydrogen detection device according to the third embodiment. This is a flowchart relating to the first aspect of the estimation process performed by the estimation device shown in Figure 8. Figure 9 is a diagram illustrating the overview of the resistance value estimation process in S312. This figure shows a hydrogen detection device according to the first modified example. This is a flowchart relating to the first aspect of the estimation process performed by the estimation device shown in Figure 11. This figure shows a hydrogen detection device according to a second modified example. This is a flowchart relating to the first aspect of the determination process performed by the determination device shown in Figure 13. (a) is a diagram showing a first modified example of the sweep period according to the embodiment, (b) is a diagram showing a second modified example of the sweep period according to the embodiment, (c) is a diagram showing a third modified example of the sweep period according to the embodiment, and (d) is a diagram showing a fourth modified example of the sweep period according to the embodiment. (a) is a figure showing the simulation results and measured values when the amount of current corresponding to the increasing period, decreasing period, and pause period corresponding to the sweep period in the embodiment shown in Figure 1(a) is supplied to the platinum, and (b) is a figure showing the amount of current supplied to the platinum. This figure shows the appearance of the experimental apparatus used in Example 2. (a) is a diagram (1) showing the relationship between the hydrogen content and ratio (dR/dP) of the mixed gas, (b) is a diagram (2) showing the relationship between the hydrogen content and ratio (dR/dP) of the mixed gas, (c) is a diagram (1) showing the relationship between the hydrogen content and area _APR of the mixed gas, and (d) is a diagram (2) showing the relationship between the hydrogen content and area _APR of the mixed gas. (a) is a diagram (part 3) showing the relationship between the hydrogen content and ratio (dR/dP) of the mixed gas, and (b) is a diagram (part 3) showing the relationship between the hydrogen content and area _APR of the mixed gas. (a) is a figure showing the change in the ratio (dR/dP) when the hydrogen concentration is changed, (b) is a figure showing the change in area _APR when the hydrogen concentration is changed, and (c) is a figure showing the change in the thermal resistivity of the mixed gas when the hydrogen concentration is changed. Figure (4) shows the relationship between the hydrogen content and ratio (dR/dP) in the mixed gas, where (a) shows the change in the ratio (dR/dP) over time, and (b) shows the change in the amount of hydrogen introduced over time. (a) is a diagram showing the change in temperature over time of the atmosphere in which the experimental apparatus is placed, and (b) is a diagram showing the change in the resistance of platinum over time when a current of 10 mA is supplied during the increasing period. (a) is a figure showing the change over time of the ratio (dR/dP) before correction, (b) is a figure showing the change over time of the ratio (dR/dP) after correction, (c) is a figure showing the change over time of the area _APR before correction, and (d) is a figure showing the change over time of the area _APR after correction. This figure shows the characteristics of an experimental apparatus that uses tungsten instead of platinum as a hydrogen sensor. (a) shows the amount of current supplied to the hydrogen sensor, (b) shows the voltage value output from the hydrogen sensor in response to the amount of current supplied to the hydrogen sensor as shown in (a), (c) shows the simulation results and measured values when the amount of current supplied to the hydrogen sensor as shown in (a) is supplied to the hydrogen sensor, (d) shows the correlation between the amount of current supplied to the hydrogen sensor and the voltage value output from the hydrogen sensor, and (e) shows the correlation between the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor. This figure shows the characteristics of an experimental apparatus that uses cobalt instead of platinum as a hydrogen sensor. (a) shows the amount of current supplied to the hydrogen sensor, (b) shows the voltage value output from the hydrogen sensor in response to the amount of current supplied to the hydrogen sensor as shown in (a), (c) shows the simulation results and measured values when the amount of current supplied to the hydrogen sensor as shown in (a) is supplied to the hydrogen sensor, (d) shows the correlation between the amount of current supplied to the hydrogen sensor and the voltage value output from the hydrogen sensor, and (e) shows the correlation between the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor.

The following describes a hydrogen detection device, an example of a gas detection device according to the present invention, with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and its equivalents.

(Overview of the hydrogen detection device according to the embodiment)
The inventors of the present invention have found that by gradually increasing the amount of current supplied to the hydrogen sensor and then gradually decreasing the amount of current supplied to the hydrogen sensor, hydrogen can be detected without arranging a compensation element in addition to the detection element, as is done in conventional thermal conduction type hydrogen sensors. The hydrogen detection device according to the embodiment acquires a plurality of voltage values detected by a voltmeter while gradually changing the amount of current supplied to the hydrogen sensor, which is a conductor. Based on the amount of current supplied to the hydrogen sensor and the plurality of voltage values acquired from the hydrogen sensor, the hydrogen detection device according to the embodiment estimates the concentration of hydrogen present around the hydrogen sensor and outputs a concentration signal indicating the estimated concentration. The hydrogen detection device according to the embodiment can estimate the concentration of hydrogen present around the hydrogen sensor with high accuracy by estimating the hydrogen concentration based on the amount of current supplied to the hydrogen sensor and the plurality of voltage values acquired from the hydrogen sensor while changing the amount of current supplied to the hydrogen sensor.

Figure 1 is a diagram illustrating the overview of a hydrogen detection device according to an embodiment. Figure 1(a) shows the amount of current supplied to the hydrogen sensor of the hydrogen detection device according to the embodiment, and Figure 1(b) shows the voltage value output from the hydrogen sensor in response to the amount of current supplied to the hydrogen sensor as shown in Figure 1(a). Figure 1(c) shows the correlation between the amount of current supplied to the hydrogen sensor and the voltage value output from the hydrogen sensor, and Figure 1(d) shows the correlation between the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor. In the example shown in Figure 1, the hydrogen sensor is a platinum (Pt) wire with a diameter of 0.05 mm and a length of 88 mm. In Figure 1(a), the horizontal axis is time and the vertical axis is the amount of current supplied to the hydrogen sensor. In Figure 1(b), the horizontal axis is time and the vertical axis is the voltage value output from the hydrogen sensor. In Figure 1(c), the horizontal axis is the amount of current supplied to the hydrogen sensor and the vertical axis is the voltage value output from the hydrogen sensor. In Figure 1(d), the horizontal axis represents the power supplied to the hydrogen sensor, the left vertical axis represents the resistance of the hydrogen sensor, and the right vertical axis represents the temperature change of the hydrogen sensor. The temperature change of the hydrogen sensor was calculated from the change in the resistance of the hydrogen sensor using the temperature coefficient of resistance (TCR). In Figures 1(b) to 1(d), the solid line shows the case where the atmosphere surrounding the hydrogen sensor is nitrogen ( _N2 ) at one atmosphere, and the dashed line shows the case where the atmosphere surrounding the hydrogen sensor is hydrogen ( _H2 ) at one atmosphere. In Figures 1(a) and 1(d), the numbers "1" to "21" represent the number of steps when the amount of current supplied to the hydrogen sensor is changed in a stepwise manner. In Figure 1(d), the square marks indicate the characteristics in an atmosphere of 100% nitrogen, and the circles indicate the characteristics in an atmosphere of 100% hydrogen.

As shown in Figure 1(a), the current supplied to the hydrogen sensor is gradually increased in steps of 10 mA from 0.0 s to 1.0 s, then gradually decreased in steps of 10 mA from 1.0 s to 2.0 s, followed by a pause period of approximately 0.7 s. This pause period allows the hydrogen sensor's temperature to drop to an equilibrium temperature slightly above room temperature.

As shown in Figures 1(b) and 1(c), the correlation between the amount of current supplied to the hydrogen sensor and the voltage output from the hydrogen sensor differs depending on whether the surrounding atmosphere is nitrogen or hydrogen. When the surrounding atmosphere is hydrogen, the voltage output from the hydrogen sensor is lower than when the surrounding atmosphere is nitrogen. This is because hydrogen has a higher thermal conductivity than nitrogen, so the ratio of temperature decrease due to heat loss through the surrounding gas to temperature rise due to self-heating is larger. Therefore, when the surrounding atmosphere is hydrogen, the temperature rise of the hydrogen sensor is suppressed, and the voltage output from the hydrogen sensor is lower than when the surrounding atmosphere is nitrogen.

The hydrogen detection device according to this embodiment estimates the concentration of hydrogen present around the hydrogen sensor from the change in the correlation between the amount of current supplied to the hydrogen sensor and the voltage value output from the hydrogen sensor, which are caused by the presence of hydrogen in the surrounding area.

As shown in Figure 1(d), the hydrogen detection device according to the embodiment estimates the hydrogen concentration present around the hydrogen sensor based on a correlation coefficient calculated from the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor. In one example, the hydrogen detection device according to the embodiment estimates the hydrogen concentration present around the hydrogen sensor based on the slope indicated by arrow A in Figure 1(d), i.e., the ratio between the change in power P and the change in resistance R. In another example, the hydrogen detection device according to the embodiment estimates the hydrogen concentration present around the hydrogen sensor based on the area of region B indicated by the shaded area in Figure 1(d), i.e., the area enclosed by the plots corresponding to each of the acquired voltage values.

The hydrogen detection device according to this embodiment estimates the hydrogen concentration based on the change in the correlation between multiple current values and voltage values when the amount of current supplied to the hydrogen sensor is gradually changed, thereby enabling highly accurate estimation of the gas concentration.

(Configuration and function of the hydrogen detection device according to the first embodiment)
Figure 2 shows a hydrogen detection device according to the first embodiment.

The hydrogen detection device 1 comprises a hydrogen sensor 10, a current source 11, a voltmeter 12, a first control line 13, a second control line 14, and an estimation device 20. While gradually changing the amount of current supplied from the current source 11 to the hydrogen sensor 10, the hydrogen detection device 1 estimates the concentration of hydrogen present around the hydrogen sensor 10 based on the amount of current supplied to the hydrogen sensor 10 and multiple voltage values obtained from the voltmeter 12.

The hydrogen sensor 10 is a wire made of platinum with a diameter of approximately 0.01 to 0.1 mm. It self-heats when current is supplied from the current source 11, and its resistance increases as the temperature rises. The hydrogen sensor 10 is housed inside a container made of glass, ceramics, or synthetic resin, which has one or more openings for air to flow in. The openings in the container housing the hydrogen sensor 10 are covered with sponge metal and a fine metal mesh. Note that the hydrogen sensor 10 does not need to be housed inside a container if the influence of atmospheric convection is not significant. Also, if the convection flow rate is constant, it does not need to be housed inside a container by taking into account heat dissipation due to convection. Although the hydrogen sensor 10 is made of platinum, in the hydrogen detection device according to this embodiment, the hydrogen sensor may be any conductor containing metals such as tungsten (W) and cobalt (Co) whose resistance changes according to the temperature of the hydrogen sensor 10 itself, and the wire diameter may be 0.01 mm or less, or 0.1 mm or more. The hydrogen detection device according to this embodiment can improve detection sensitivity by shortening the wire diameter. Furthermore, although the hydrogen sensor 10 is wire-shaped, in the hydrogen detection device according to this embodiment, the hydrogen sensor may be formed as a thin film.

The current source 11 includes a step-down circuit that generates a DC voltage stepped down from a commercial power source or battery, a voltage control circuit that controls the step-down circuit, and an interface unit. The current source 11 supplies a voltage corresponding to the amount of current corresponding to a setting signal input to the interface unit from the estimation device 20 via the first control line 13 to the hydrogen sensor 10. In response to the setting signal input from the estimation device 20, the current source 11 repeats a sweep period having an increasing period, a decreasing period following the increasing period, and a pause period following the decreasing period. In the example shown in Figure 1(a), the increasing period is the period between 0.0 s and 1.0 s, and during the increasing period, the current source 11 gradually increases the amount of current supplied to the hydrogen sensor 10 in a stepwise manner of 10 mA from 0 mA, also called the first current amount, to 100 mA, also called the second current amount. The reduction period is from 1.0 s to 2.0 s. During this period, the current source 11 gradually reduces the amount of current supplied to the hydrogen sensor 10 in a stepwise manner, from 100 mA (also called the second current) to 0 mA (also called the first current), in increments of 10 mA. The pause period is from 2.0 s to 2.7 s. During this pause period, the current source 11 does not supply current to the hydrogen sensor 10.

The voltmeter 12 is a known voltmeter, and may be either an analog or digital voltmeter. The voltmeter 12 detects the voltage value output from the hydrogen sensor 10 when current is supplied from the current source 11 to the hydrogen sensor 10, and outputs a voltage signal indicating the detected voltage value to the estimation device 20 via the second control line 14. While the hydrogen detection device 1 has the current source 11 and voltmeter 12 as separate components, the hydrogen detection device according to this embodiment may have a source measure unit (SMU) integrating the current source and voltmeter instead of the current source 11 and voltmeter 12. Furthermore, the hydrogen detection device according to this embodiment may have an analog front-end (AFE) IC with a built-in current source and voltmeter instead of the current source 11 and voltmeter 12.

The estimation device 20 comprises a communication unit 21, a storage unit 22, an input unit 23, an output unit 24, and a processing unit 30. The communication unit 21, storage unit 22, input unit 23, output unit 24, and processing unit 30 are connected to each other via a bus 25. The estimation device 20 acquires multiple voltage values detected by a voltmeter while gradually changing the amount of current supplied to the hydrogen sensor, which is a conductor. Based on the amount of current supplied to the hydrogen sensor 10 and the multiple voltage values acquired from the hydrogen sensor 10, the estimation device 20 estimates the concentration of hydrogen present around the hydrogen sensor 10 and outputs a concentration signal indicating the estimated concentration.

The communication unit 21 has a communication interface circuit such as I2C. The communication unit 21 transmits a setting signal to the current source 11 via the first control line 13 and receives a voltage signal from the voltmeter 12 via the second control line 14.

The storage unit 22 includes, for example, at least one of a semiconductor memory device, a magnetic tape device, a magnetic disk device, or an optical disk device. The storage unit 22 stores operating system programs, driver programs, application programs, data, etc., used in processing by the processing unit 30. For example, the storage unit 22 stores an estimation program as an application program, which causes the processing unit 30 to execute an estimation process to estimate the concentration of hydrogen present around the hydrogen sensor 10. The estimation program may be installed in the storage unit 22 using a known setup program, etc., from a computer-readable portable recording medium such as a CD-ROM or DVD-ROM. The storage unit 22 also stores various data used in the estimation process. The storage unit 22 temporarily stores temporary data related to a predetermined process and stores a database for accumulating data. For example, the storage unit 22 stores current transition information 220 and a concentration estimation table 225 used when executing the estimation process.

The current transition information 220 is a table that stores information indicating the current supply pattern during the sweep period, which is the basic pattern of the current supplied from the current source 11. An example of a current supply pattern corresponding to the information stored in the current transition information 220 is the current supply pattern shown in Figure 1(a).

Figure 3 shows the current transition information 220.

The current transition information 220 includes a step column 221, a supplied current amount column 222, and a current supply time column 223. The step column 221 is indicated by the numbers "1" through "21" as identifiers.

The supply current amount column 222 stores the amount of current supplied from the current source 11 to the hydrogen sensor 10 in association with the step number shown in the step column. In the supply current amount column 222, a supply current amount of "10 mA" is stored in association with steps "1" and "20", a supply current amount of "20 mA" is stored in association with steps "2" and "19", a supply current amount of "30 mA" is stored in association with steps "3" and "18", a supply current amount of "40 mA" is stored in association with steps "4" and "17", a supply current amount of "50 mA" is stored in association with steps "5" and "16", and a supply current amount of "60 mA" is stored in association with steps "6" and "15". The supplied current of "70 mA" is stored in association with steps "7" and "14," the supplied current of "80 mA" is stored in association with steps "8" and "13," the supplied current of "90 mA" is stored in association with steps "9" and "12," and the supplied current of "100 mA" is stored in association with steps "10" and "11."

The current supply time column 223 stores the current supply time for each step, associated with the step number indicated in the step column. In the current supply time column 223, a current supply time of "0.1 seconds" is stored associated with steps "1" through "20," and a current supply time of "0.7 seconds" is stored associated with step "21."

In the current transition information 220, steps "1" to "10" represent an increasing period in which the amount of current supplied to the hydrogen sensor 10 gradually increases in a stepwise manner by 10 mA. Steps "11" to "20" represent a decreasing period in which the amount of current supplied to the hydrogen sensor 10 gradually decreases in a stepwise manner by 10 mA, and step "21" represents a pause period in which no current is supplied to the hydrogen sensor 10.

The concentration estimation table 225 is a table that stores the relationship between the correlation coefficient, which shows the correlation between the power P supplied to the hydrogen sensor 10 and the resistance value R of the hydrogen sensor 10, and the concentration of hydrogen present around the hydrogen sensor 10. The concentration estimation table 225 stores the relationship between the correlation coefficient, which is the ratio (dR/dP) between the change in power P dP and the change in resistance value R dR, and the hydrogen concentration. Furthermore, the concentration estimation table 225 stores the relationship between the correlation coefficient, which is the area APR of the region enclosed by plots corresponding to each of steps "1" to "20" of the current transition information 220 in a Cartesian coordinate system with power _P as the first axis and the calculated resistance value R as the second axis, and the hydrogen concentration.

The input unit 23 can be any device capable of data input, such as a touch panel or keyboard. The operator can use the input unit 23 to input characters, numbers, symbols, etc. When the input unit 23 is operated by the operator, it generates a signal corresponding to that operation. The generated signal is then supplied to the processing unit 30 as an instruction from the operator.

The output unit 24 can be any device capable of displaying video or images, including, for example, a liquid crystal display or an organic EL (Electro-Luminescence) display and a speaker. The output unit 24 displays video corresponding to video data supplied from the processing unit 30, or images corresponding to image data. The output unit 24 may also output audio, analog electrical signals, or digital electrical signals.

The processing unit 30 comprises one or more processors and their peripheral circuits. The processing unit 30 comprehensively controls the overall operation of the estimation device 20, and is, for example, a CPU. The processing unit 30 executes processing based on programs (driver programs, operating system programs, application programs, etc.) stored in the memory unit 22. Furthermore, the processing unit 30 can execute multiple programs (application programs, etc.) in parallel.

The processing unit 30 includes a current supply unit 31, a voltage acquisition unit 32, an estimation processing unit 33, and a density signal output unit 34. Each of these units is a functional module implemented by a program executed on the processor of the processing unit 30. Alternatively, each of these units may be implemented in the processing unit 30 as firmware.

(First aspect of estimation processing by the estimation device according to the first embodiment)
Figure 4 is a flowchart relating to a first mode of estimation processing performed by the estimation device 20. The estimation processing shown in Figure 4 is performed mainly by the processing unit 30 in cooperation with each element of the estimation device 20, based on a program stored in the storage unit 22 beforehand. Furthermore, the estimation processing shown in Figure 4 is repeatedly performed at a predetermined cycle.

First, the current supply unit 31 refers to the current transition information 220 stored in the memory unit 22 to determine the amount of current supplied from the current source 11 to the hydrogen sensor 10 (S101). The current supply unit 31 determines the amount of supplied current "10mA," which is stored in association with the "1" shown in the step column of the current transition information 220, as the amount of current supplied from the current source 11 to the hydrogen sensor 10.

Next, the current supply unit 31 outputs a setting signal to the communication unit 21 of the current source 11, indicating the supply current amount "10 mA" determined in the process of S101 (S102). The communication unit 21 transmits the setting signal received from the current supply unit 31 to the current source 11 via the first control line 13. The current source 11 supplies current to the hydrogen sensor 10 so that the supply current amount corresponds to the setting signal. The current source 11 supplies current to the hydrogen sensor 10 so that the supply current amount is 10 mA.

Next, the voltage acquisition unit 32 acquires the voltage value detected by the voltmeter 12 (S103). The voltage acquisition unit 32 transmits a voltage request signal to the voltmeter 12 via the communication unit 21. Upon receiving the voltage request signal, the voltmeter 12 transmits a voltage signal indicating the detected voltage value to the communication unit 21 via the second control line 14. The voltage acquisition unit 32 acquires the voltage value corresponding to the voltage signal transmitted from the voltmeter 12 and stores the voltage information indicating the acquired voltage value in the storage unit 22, associating it with the "1" shown in the step column of the current transition information 220.

Next, the current supply unit 31 increments the step count by one (S104), making the step count "2". Then, the current supply unit 31 determines whether the current step count is the final step, step "20" (S105). If the current supply unit 31 determines that the current step count is not the final step (S105-NO), it waits for a current supply time of "0.1 seconds," which is associated with the current step count of "1." The process then returns to S101.

From this point onward, the processes S101 to S105 are repeated until the current supply unit 31 determines that the current step number is the final step (S105-YES). As the processes S101 to S105 are repeated until the current step number is determined to be the final step (S105-YES), the current supply unit 31 repeatedly performs the current supply process, supplying current corresponding to the increasing and decreasing periods shown in Figure 1(a). As the current supply unit 31 repeats the current supply process, the current source 11 supplies current corresponding to the increasing and decreasing periods shown in Figure 1(a) to the hydrogen sensor 10. The voltage acquisition unit 32 sequentially acquires the voltage values output from the hydrogen sensor 10 while the current corresponding to each step of the increasing and decreasing periods shown in Figure 1(a) is supplied.

When it is determined that the current step is the final step (S105-YES), the estimation processing unit 33 calculates the power supplied to the hydrogen sensor 10 at each step from the supplied current and the voltage value obtained in the processing of S103 (S106). The estimation processing unit 33 calculates the power supplied to the hydrogen sensor 10 at each step by multiplying the current I at each step "1" to "20" by the voltage value V obtained at each step "1" to "20". The estimation processing unit 33 stores the calculated power P in the storage unit 22, associating it with the corresponding step number.

Next, the estimation processing unit 33 calculates the resistance value R of the hydrogen sensor 10 at each step from the amount of current supplied to the hydrogen sensor 10 and the multiple voltage values obtained in the processing of S103 (S107). The resistance value R of the hydrogen sensor 10 at each step is calculated by dividing the voltage value V obtained in each step "1" to "20" by the amount of current I in each step "1" to "20". The estimation processing unit 33 stores the calculated resistance value R in the storage unit 22, associating it with the corresponding step number.

Next, the estimation processing unit 33 calculates a correlation coefficient showing the correlation between power P and resistance R from the power P and resistance R calculated in S106 and S107, respectively (S108). The estimation processing unit 33 calculates the correlation coefficient as the ratio (dR/dP) between the calculated change in power P dP and the change in resistance R dR. The estimation processing unit 33 calculates a correlation coefficient corresponding to the slope shown by arrow A in Figure 1(d) from the power P and resistance R stored in the storage unit 22 in association with each of steps "7" to "10". The current supplied to the hydrogen sensor 10 in steps "7" to "10" is 70mA, 80mA, 90mA, and 100mA. As shown in Figure 1(d), from step "7" to step "10", the change in power P and the change in resistance R are in an almost linear relationship. The estimation processing unit 33 calculates the ratio (dR/dP) between the change in power P (dP) and the change in resistance R (dR) from the power P and resistance R in steps 7 to 10, for example, by the least squares method. In nitrogen, the ratio (dR/dP) is 4.242 Ω/W, while in hydrogen, the ratio (dR/dP) is 0.858 Ω/W. The ratio (dR/dP) in nitrogen differs significantly from that in hydrogen.

Next, the estimation processing unit 33 estimates the hydrogen concentration present around the hydrogen sensor 10 based on the current supplied to the hydrogen sensor 10 and the voltage value obtained in processing S103, using the correlation coefficient calculated in processing S106 to S108 (S109). The estimation processing unit 33 refers to the concentration conversion table 225 stored in the storage unit 225 and estimates the concentration corresponding to the ratio (dR/dP), which is the correlation coefficient calculated in processing S108, as the hydrogen concentration present around the hydrogen sensor 10.

The concentration signal output unit 34 then outputs a concentration signal indicating the detected hydrogen concentration to the output unit 24 (S110). The output unit 24 displays an image indicating the detected hydrogen concentration in response to the input concentration signal.

(Second aspect of estimation processing by the estimation device according to the first embodiment)
The second aspect of the estimation process differs from the first aspect of the estimation process in that process S108 calculates a correlation coefficient showing the correlation between power P and resistance R from the power P and resistance R. The processes of the second aspect of the estimation process other than process S108 are the same as those of the first aspect of the estimation process, so a detailed explanation is omitted here.

The estimation processing unit 33 calculates the area APR of the region enclosed by plots corresponding to each of the multiple voltage values obtained in the S103 process, in a Cartesian coordinate system with the calculated power _P as the first axis and the calculated resistance R as the second axis, as the correlation coefficient. The estimation processing unit 33 calculates the correlation coefficient corresponding to the area B of the region shown by the shaded area in Figure 1(d) from the power P and resistance R stored in the storage unit 22 in association with each of steps "1" to "20". The estimation processing unit 33 calculates the area APR of the region enclosed by plots corresponding to each of the multiple voltage values obtained in the S103 process, for example by the coordinate method, from the power P and resistance _R of each of steps "1" to "20". Note that in nitrogen, the area _APR is 0.00484 Ω·W, and in hydrogen, the area _APR is 0.00016 Ω·W, and the area _APR in nitrogen is significantly different from the area _APR in hydrogen.

(Effects and effects of the hydrogen detection device according to the first embodiment)
In the hydrogen detection device 1, the hydrogen concentration present around the hydrogen sensor 10 can be estimated without using a compensation sensor for comparison, by estimating the hydrogen concentration based on the voltage value acquired while gradually changing the current supplied to the hydrogen sensor 10. Furthermore, since the hydrogen detection device 1 does not constantly supply current to the hydrogen sensor 10, it is possible to reduce power consumption compared to hydrogen detection devices that use a compensation sensor.

Furthermore, the hydrogen detection device 1 estimates the hydrogen concentration using the amount of current supplied to the hydrogen sensor 10 and a ratio (dR/dP) or area _APR calculated based on multiple voltage values acquired while the amount of current supplied to the hydrogen sensor 10 is changed. Since the hydrogen detection device 1 uses the ratio (dR/dP) or area _APR calculated based on multiple current amounts and voltage values as parameters, it can generate a signal with a larger signal-to-noise ratio than when the hydrogen concentration is estimated using only two points, the minimum and maximum values. In addition, by using the ratio (dR/dP) or area _APR as parameters, the hydrogen detection device 1 can estimate the concentration of hydrogen present around the hydrogen sensor 10 with high accuracy.

Furthermore, in the hydrogen detection device 1, the estimation device 20 gradually changes the current supplied to the hydrogen sensor 10 in a stepwise manner rather than in a pulsed manner, thus allowing for a higher current to be supplied to the hydrogen sensor 10. When the temperature of the atmosphere containing hydrogen rises rapidly, there is a risk of explosion due to the oxidation reaction of hydrogen. Therefore, when supplying current to the hydrogen sensor 10 in a pulsed manner, the amplitude of the pulse cannot be increased, and a signal with a high signal-to-noise ratio cannot be generated. On the other hand, in the hydrogen detection device 1, because the current supplied to the hydrogen sensor 10 is gradually increased in a stepwise manner, the current supply can be stopped if an explosion is imminent. This reduces the risk of explosion due to the oxidation reaction of hydrogen, and allows for the generation of a signal with a high signal-to-noise ratio.

Furthermore, since the hydrogen detection device 1 uses a platinum wire with a diameter of approximately 0.01 to 0.1 mm as the hydrogen sensor 10, there is no need to form the hydrogen sensor using MEMS, resulting in lower manufacturing costs compared to hydrogen detection devices that use MEMS-formed hydrogen sensors.

Furthermore, in the first mode of the estimation process by the estimation device 20, the correlation coefficient is calculated using steps "7" to "10," where the change in power P and the change in resistance R are linearly related. Therefore, the ratio between the change in power P and the change in resistance R is calculated as the correlation coefficient. Because the first mode of the estimation process by the estimation device 20 uses steps where the change in power P and the change in resistance R are linearly related, the correlation coefficient can be calculated with high accuracy.

(Configuration and function of the hydrogen detection device according to the second embodiment)
Figure 5 shows a hydrogen detection device according to the second embodiment.

The hydrogen detection device 2 differs from the hydrogen detection device 1 in that it has an estimation device 40 instead of the estimation device 20. The estimation device 40 differs from the estimation device 20 in that it has a storage unit 42 and a processing unit 50 instead of the storage unit 22 and processing unit 30. The configuration and function of the components of the hydrogen detection device 2, other than the storage unit 42 and processing unit 50, are the same as those of the components of the hydrogen detection device 1, which are given the same reference numerals; therefore, a detailed explanation is omitted here.

The memory unit 42 differs from the memory unit 22 in that it has a resistance correction table 420. The configuration and functions of the memory unit 42, other than the resistance correction table 420, are the same as those of the memory unit 22, so a detailed explanation is omitted here. The resistance correction table 420 is a table that stores correction coefficients used to correct the power supplied to the hydrogen sensor 10 and the resistance value of the hydrogen sensor 10, associated with temperature.

Figure 6 shows the resistance compensation table 420.

The resistance correction table 420 has a temperature column 421, a resistance value column 422 at 10 mA, and a correction coefficient column 423. The temperature column 421 shows temperatures from -40°C to 40°C. The temperature intervals shown in the temperature column 421 are appropriately set according to the accuracy required for correction; for example, it may be 1°C, 0.5°C, or 0.1°C.

The resistance value column 422 at 10 mA displays the resistance value stored in association with each of the temperatures shown in the temperature column 421. The resistance value shown in the resistance value column 422 at 10 mA is the resistance value of the hydrogen sensor 10 at each temperature when the supply current supplied to the hydrogen sensor 10 is 10 mA. The resistance value shown in the resistance value column 422 at 10 mA is measured by setting the ambient temperature of the hydrogen sensor 10, which is placed in the atmosphere, to the corresponding temperature shown in the temperature column 421, and supplying a current of 10 mA to the hydrogen sensor 10.

The correction coefficient column 423 shows the correction coefficients stored in association with each of the temperatures shown in the temperature column 421. In the first embodiment, where the correlation coefficient corresponds to the slope indicated by arrow A in Figure 1(d), the correction coefficient is the ratio between the change in power P and the change in resistance R at each temperature, based on the ratio between the change in power P and the change in resistance R when the temperature is 25°C. In the second embodiment, where the correlation coefficient corresponds to the area of region B in Figure 1(d), the correction coefficient is the area of the region enclosed by the plots at each temperature, based on the area of the region enclosed by the plots when the temperature is 25°C. The correction coefficient is calculated, for example, based on the change in room temperature and the ratio (dR/dP) and the change in area _APR in a nitrogen atmosphere. Note that when the change in temperature is small, such as near room temperature, the correction coefficient may be calculated to change in proportion to the change in room temperature.

The processing unit 50 differs from the processing unit 30 in that it has a correction unit 55. The configuration and functions of the processing unit 50, other than the correction unit 55, are the same as those of the processing unit 30, so a detailed explanation is omitted here.

(Estimation processing by the estimation device according to the second embodiment)
Figure 7 is a flowchart relating to a first mode of estimation processing performed by the estimation device 40. The estimation processing shown in Figure 7 is performed mainly by the processing unit 50 in cooperation with each element of the estimation device 40, based on a program stored in the storage unit 42 beforehand. Furthermore, the estimation processing shown in Figure 7 is performed repeatedly at a predetermined cycle. The processing in S201 to S208 is the same as the processing in S101 to S108, so a detailed explanation is omitted here.

When the process in S208 is completed, the correction unit 55 determines the correction coefficient to be used when correcting the correlation coefficient calculated in the process in S208 (S209). The correction unit 55 refers to the correction coefficient column 423 and determines the correction coefficient stored in association with the resistance value R in step "1" calculated in the process in S207 to be the correction coefficient to be used when correcting the correlation coefficient calculated in the process in S208.

Next, the correction unit 55 corrects the correlation coefficient calculated in process S208 using the correction coefficient determined in process S209 (S210). The correction unit 55 corrects the correlation coefficient by multiplying the correlation coefficient calculated in process S208 by the correction coefficient determined in process S209. The correction unit 55 stores the corrected correlation coefficient in the storage unit 42.

Next, the estimation processing unit 33 estimates the hydrogen concentration present around the hydrogen sensor 10 based on the correlation coefficient corrected in the processing of S210 (S211). Then, the concentration signal output unit 34 outputs the concentration signal to the output unit 24, similar to the processing in S110 (S212).

(Effects and effects of the hydrogen detection device according to the second embodiment)
In the hydrogen detection device 2, the estimation device 40 corrects the correlation coefficient used to estimate the hydrogen concentration using a correction coefficient defined according to the temperature. Therefore, it is possible to determine the presence or absence of hydrogen with high accuracy regardless of temperature changes in the hydrogen sensor 10 itself.

Furthermore, in the hydrogen detection device 2, the correction coefficient for correcting the correlation coefficient is determined based on the voltage value acquired in step "1," which is the first step in the sweep period. Therefore, since the temperature of the hydrogen sensor 10 is close to room temperature, the correlation coefficient can be corrected with high accuracy.

(Configuration and function of the hydrogen detection device according to the third embodiment)
Figure 8 shows a hydrogen detection device according to the third embodiment.

The hydrogen detection device 3 differs from the hydrogen detection device 1 in that it has an estimation device 60 instead of an estimation device 20. The estimation device 60 differs from the estimation device 20 in that it has a storage unit 62 and a processing unit 70 instead of a storage unit 22 and a processing unit 30. The configuration and function of the components of the hydrogen detection device 2, other than the storage unit 62 and the processing unit 70, are the same as those of the components of the hydrogen detection device 1, which are given the same reference numerals; therefore, a detailed explanation is omitted here.

The memory unit 62 differs from the memory unit 22 in that it has reference resistance information 620. The configuration and function of the memory unit 62, other than the reference resistance information 620, are the same as those of the memory unit 22, so a detailed explanation is omitted here. The reference resistance information 620 indicates the resistance value of the hydrogen sensor 10 when the temperature is 25°C. The resistance value of the hydrogen sensor 10 when the temperature is 25°C is also called the reference resistance value.

The processing unit 70 differs from the processing unit 30 in that it includes a deterioration determination unit 75, an alarm signal output unit 76, and a detection signal output unit 77. The configuration and functions of the processing unit 70, other than the deterioration determination unit 75, alarm signal output unit 76, and detection signal output unit 77, are the same as those of the processing unit 30, so a detailed explanation is omitted here.

(Estimation processing by the estimation device according to the third embodiment)
Figure 9 is a flowchart relating to a first mode of estimation processing performed by the estimation device 60. The estimation processing shown in Figure 9 is performed mainly by the processing unit 70 in cooperation with each element of the estimation device 60, based on a program stored in the storage unit 22 beforehand. The processing in S301 to S310 is the same as the processing in S101 to S110, so a detailed explanation is omitted here.

When the process in S310 is completed, the degradation determination unit 75 determines whether or not hydrogen is present around the hydrogen sensor 10 based on the current supplied to the hydrogen sensor 10 and the voltage value obtained in the process in S303, using the correlation coefficient calculated in processes S306 to S308 (S311). The degradation determination unit 75 determines that hydrogen is not present around the hydrogen sensor 10 when the ratio (dR/dP), which is the correlation coefficient calculated in the process in S308, is greater than or equal to a predetermined threshold (S311-NO). Alternatively, the degradation determination unit 75 determines that hydrogen is present around the hydrogen sensor 10 when the ratio (dR/dP), which is the correlation coefficient calculated in the process in S108, is less than a predetermined threshold (S311-YES). The threshold used in the process in S109 is the value obtained by subtracting a coefficient corresponding to the error from the ratio (dR/dP) when hydrogen is not present in the atmosphere.

The degradation determination unit 75, upon determining that hydrogen is not present (S311-NO), estimates the resistance value of the hydrogen sensor 10 when no current is supplied to it, based on the power P and resistance value R calculated in processes S306 and S307 (S312).

Figure 10 is a diagram illustrating the overview of the resistance value estimation process in S312. In Figure 10, the horizontal axis represents the power supplied to the hydrogen sensor, the left vertical axis represents the resistance value of the hydrogen sensor, the right vertical axis represents the temperature change of the hydrogen sensor, and the square marks indicate the characteristics in an atmosphere of 100% nitrogen. The numbers "1" to "20" represent the number of steps when the amount of current supplied to the hydrogen sensor is changed in a stepwise manner.

In Figure 10, the relationship between the change in power P and the change in resistance R is linear from step "7" to step "10," which is enclosed by a dashed line. On the other hand, the relationship between the change in power P and the change in resistance R is nonlinear from step "1" to step "5," which is enclosed by a dashed line in Figure 10. In the resistance estimation process of S312, the degradation determination unit 75 estimates the resistance of the hydrogen sensor 10 when no current is supplied to it, using exponential or power approximation from the plots corresponding to steps "1" to "5."

Next, the degradation determination unit 75 determines whether the difference between the resistance value estimated in S312 and the reference resistance value is greater than or equal to a predetermined threshold difference (S313). The degradation determination unit 75 calculates the absolute value of the difference between the resistance value estimated in S311 and the reference resistance value corresponding to the reference resistance information 620. Then, the degradation determination unit 75 determines whether the absolute value of the difference between the estimated resistance value and the reference resistance value is greater than or equal to a predetermined threshold difference.

If it is determined that the absolute value of the difference between the estimated resistance value and the reference resistance value is less than a predetermined threshold difference (S313-NO), the process returns to S301.

If the absolute value of the difference between the estimated resistance value and the reference resistance value is determined to be greater than or equal to a predetermined threshold difference (S313-YES), the alarm signal output unit 76 outputs an alarm signal to the output unit 24 indicating that the hydrogen sensor 10 has deteriorated (S314). The output unit 24 displays an image indicating that the hydrogen sensor 10 has deteriorated, in response to the alarm signal input. The process then returns to S301. Subsequently, the processes S301 to S314 are repeated until the determination processing unit 33 determines that hydrogen is present around the hydrogen sensor 10 (S311-YES).

When the determination processing unit 33 determines that hydrogen is present around the hydrogen sensor 10 (S311-YES), the detection signal output unit 77 outputs a detection signal to the output unit 24 indicating that hydrogen has been detected (S315). In response to the input detection signal, the output unit 24 displays an image indicating hydrogen detection and outputs an audio alert sound indicating hydrogen detection.

(Effects and effects of the hydrogen detection device according to the third embodiment)
In the hydrogen detection device 3, the estimation device 60 outputs an alarm signal when the absolute value of the difference between the resistance value of the hydrogen sensor 10 and the reference resistance value when no current is supplied to the hydrogen sensor 10 exceeds a predetermined threshold difference, thereby allowing the operator to recognize the deterioration of the hydrogen sensor 10 over time.

Furthermore, in the hydrogen detection device 3, the estimation device 60 acquires multiple voltage values while increasing the current, enabling it to calculate a nonlinear relationship plot between the change in power P and the change in resistance R, and a linear relationship plot between the change in power P and the change in resistance R. In the hydrogen detection device 3, the estimation device 60 uses the nonlinear relationship plot between the change in power P and the change in resistance R to accurately estimate the resistance value of the hydrogen sensor 10 when no current is supplied to it.

(Modified example of a gas detection device according to an embodiment)
Hydrogen detection devices 1 to 3 are detection devices that estimate the concentration of hydrogen in the atmosphere and detect hydrogen. However, the gas detection device according to the embodiment may be a detection device that estimates the concentration of hydrogen and detects hydrogen in an atmosphere other than the atmosphere, such as nitrogen. Furthermore, the gas detection device according to the embodiment may be a detection device that detects elements other than hydrogen, such as helium (He) and carbon monoxide (CO), in the atmosphere.

Furthermore, while hydrogen detection devices 1 to 3 determine the presence or absence of hydrogen using the ratio (dR/dP) and area _APR as parameters, the hydrogen detection device according to the embodiment may determine the presence or absence of hydrogen using parameters other than the ratio (dR/dP) and area _APR . For example, the hydrogen detection device according to the embodiment may determine the presence or absence of hydrogen using the delay amount from the peak of the current supplied to the platinum at the peak of the temperature rise of the hydrogen sensor 10 as a parameter.

Furthermore, hydrogen detection devices 1 to 3 acquire multiple voltage values detected by the voltmeter 11 while varying the amount of current supplied to the hydrogen sensor 10. However, the hydrogen detection device according to this embodiment may also acquire multiple current amounts detected by the ammeter while varying the voltage value applied to the hydrogen sensor 10.

Figure 11 shows a hydrogen detection device according to the first modified example.

The hydrogen detection device 4 differs from the hydrogen detection device in that it has a voltage source 16, an ammeter 17, and an estimation device 20a instead of a current source 11, a voltmeter 12, and an estimation device 20. The configuration and function of the components of the hydrogen detection device 4, other than the voltage source 16, ammeter 17, and estimation device 20a, are the same as those of the components of the hydrogen detection device 1, which are given the same reference numerals; therefore, a detailed explanation is omitted here.

The voltage source 16 includes a step-down circuit that generates a DC voltage stepped down from a commercial power source or battery, a voltage control circuit that controls the step-down circuit, and an interface unit. The voltage source 16 supplies a voltage value corresponding to a setting signal input to the interface unit from the estimation device 20a via the first control line 13 to the hydrogen sensor 10.

The ammeter 17 is a known ammeter, and may be either an analog or digital ammeter. Furthermore, the hydrogen detection device according to this embodiment may have an SMU integrating the voltage source and ammeter instead of the voltage source 16 and ammeter 17, or it may have an AFE IC with a built-in voltage source and ammeter instead of the voltage source 16 and ammeter 17. The ammeter 17 detects the amount of current flowing through the hydrogen sensor 10 when voltage is applied from the voltage source 16 to the hydrogen sensor 10, and outputs a current signal indicating the detected amount of current to the estimation device 20a via the second control line 14.

The estimation device 20a differs from the estimation device 20 in that it has a storage unit 27 and a processing unit 30a instead of the storage unit 22 and processing unit 30. The configuration and function of the components of the estimation device 20a other than the storage unit 27 and processing unit 30a are the same as those of the components of the estimation device 20, which are given the same reference numerals; therefore, a detailed explanation is omitted here.

The memory unit 27 differs from the memory unit 22 in that it stores voltage transition information 270 instead of current transition information 220. The voltage transition information 270 is a table that stores information indicating the voltage application pattern during the sweep period, which is the basic pattern of the voltage output from the voltage source 16. Similar to the current transition information 220 described with reference to Figure 3, the voltage transition information 270 has a step column, an applied voltage value column, and a voltage application time column. The applied voltage value column and the voltage application time column store the applied voltage value and application time in relation to the number of steps indicated in the step column. The voltage transition information 270 stores the voltage application pattern so that voltage values are applied to the hydrogen sensor 10 to form a sweep period having an increasing period where the voltage value rises in a stepwise manner, a decreasing period where the voltage value falls in a stepwise manner, and a pause period.

The processing unit 30a differs from the processing unit 30 in that it has a voltage application unit 36, a current acquisition unit 37, and an estimation processing unit 38 instead of a current supply unit 31, a voltage acquisition unit 32, and an estimation processing unit 33. The configuration and function of the components of the processing unit 30a other than the voltage application unit 36, the current acquisition unit 37, and the estimation processing unit 38 are the same as those of the components of the processing unit 30 that are given the same reference numerals, so a detailed explanation is omitted here.

(First aspect of estimation processing by the estimation device relating to the first modified example)
Figure 12 is a flowchart relating to a first mode of estimation processing performed by the estimation device 20a. The estimation processing shown in Figure 12 is performed mainly by the processing unit 30a in cooperation with each element of the estimation device 20a, based on a program stored in the storage unit 27 beforehand. Furthermore, the estimation processing shown in Figure 12 is repeatedly performed at a predetermined cycle.

First, the voltage application unit 36 refers to the voltage transition information 270 stored in the memory unit 27 to determine the voltage value to be applied from the voltage source 16 to the hydrogen sensor 10 (S401). The voltage application unit 36 determines the applied voltage value stored in association with "1" in the step column of the voltage transition information 270 as the voltage value to be applied from the voltage source 16 to the hydrogen sensor 10.

Next, the voltage application unit 36 outputs a setting signal indicating the voltage value determined in the process of S401 to the communication unit 21 of the voltage source 16 (S402). The communication unit 21 transmits the setting signal received from the voltage application unit 36 to the voltage source 16 via the first control line 13. The voltage source 16 supplies the applied voltage value corresponding to the setting signal to the hydrogen sensor 10 in response to the input of the setting signal.

Next, the current acquisition unit 37 acquires the amount of current detected by the ammeter 17 (S403). The current acquisition unit 37 transmits a current request signal to the ammeter 17 via the communication unit 21. Upon receiving the current request signal, the ammeter 17 transmits a current signal indicating the detected amount of current to the communication unit 21 via the second control line 14. The current acquisition unit 37 acquires the amount of current corresponding to the current signal transmitted from the ammeter 17 and stores the current information indicating the acquired amount in the storage unit 22, associating it with the "1" shown in the step column of the voltage transition information 270.

Next, the voltage application unit 36 increments the step count by one (S404), making the step count "2". Then, the voltage application unit 36 determines whether the current step count is the final step (S405). If the voltage application unit 36 determines that the current step count is not the final step (S405-NO), it waits for the voltage application time stored in association with the current step count, "1". Then, the process returns to S401.

From this point onward, the processes S401 to S405 are repeated until the voltage application unit 36 determines that the current step number is the final step (S405-YES). As the processes S401 to S405 are repeated until the current step number is determined to be the final step (S405-YES), the voltage application unit 36 repeatedly performs the voltage application process, applying the voltage corresponding to the voltage transition information 270. As the voltage application unit 36 repeatedly performs the voltage application process, the voltage source 16 applies the voltage corresponding to the voltage transition information 270 to the hydrogen sensor 10. The current acquisition unit 37 sequentially acquires the amount of current flowing through the hydrogen sensor 10 while the voltage value corresponding to the voltage transition information 270 is applied.

When it is determined that the current step is the final step (S405-YES), the estimation processing unit 38 calculates the power supplied to the hydrogen sensor 10 at each step from the applied voltage value and the amount of current obtained in the processing of S403 (S406). The estimation processing unit 33 calculates the power supplied to the hydrogen sensor 10 at each step by multiplying the voltage value V at each step by the amount of current I obtained at each step. The estimation processing unit 38 stores the calculated power P in the storage unit 22, associating it with the corresponding step number.

Next, the estimation processing unit 38 calculates the resistance value R of the hydrogen sensor 10 at each step from the voltage value applied to the hydrogen sensor 10 and the multiple current amounts obtained in the processing of S403 (S407). The resistance value R of the hydrogen sensor 10 at each step is calculated by dividing the voltage value V at each step by the current amount I obtained at each step. The estimation processing unit 33 stores the calculated resistance value R in the storage unit 22, associating it with the corresponding step number. The processing of S408 to S410 is the same as the processing of S108 to S110, so a detailed explanation is omitted here.

Furthermore, the hydrogen detection device according to the embodiment may estimate the hydrogen concentration by acquiring physical quantities indicating electrical characteristics detected by electrical sensors other than the voltmeter 11 and ammeter 16 while changing the amount of electricity supplied to the hydrogen sensor 10 by supplying current or applying voltage. The physical quantities indicating electrical characteristics acquired by the hydrogen detection device according to the embodiment may be any physical quantities that can be calculated, including the power and resistance of the hydrogen sensor 10, along with the physical quantity indicating the electricity supplied to the hydrogen sensor 10. The electrical sensors may be resistance meters that detect the resistance value of the hydrogen sensor 10, or power meters that detect the power of the hydrogen sensor 10. The hydrogen detection device according to the embodiment may also include resistance meters and power meters as electrical sensors.

Furthermore, while hydrogen detection devices 1 to 3 estimate the concentration of hydrogen present around the hydrogen sensor 10, the hydrogen detection device according to this embodiment may determine whether or not hydrogen is present around the hydrogen sensor 10.

Figure 13 shows a hydrogen detection device according to a second modified example.

The hydrogen detection device 5 differs from the hydrogen detection device 1 in that it has a determination device 80 instead of an estimation device 20. The determination device 80 differs from the estimation device 20 in that it has a processing unit 90 instead of a processing unit 30. The configuration and function of the components of the hydrogen detection device 5, other than the processing unit 90, are the same as those of the components of the hydrogen detection device 1, which are assigned the same reference numerals; therefore, a detailed explanation is omitted here.

The processing unit 90 differs from the processing unit 30 in that it has a determination processing unit 93 and a detection signal output unit 94 instead of the estimation processing unit 33 and the concentration signal output unit 34. The configuration and functions of the processing unit 90, other than the determination processing unit 93 and the detection signal output unit 94, are the same as those of the processing unit 30, so a detailed explanation is omitted here.

(Determination process by the determination device relating to the second modified example)
Figure 14 is a flowchart relating to a first mode of the determination process performed by the determination device 80. The determination process shown in Figure 14 is performed mainly by the processing unit 90 in cooperation with each element of the determination device 80, based on a program stored in the storage unit 22 beforehand. The processes from S501 to S508 are the same as the processes from S101 to S108, so a detailed explanation is omitted here.

When the process in S508 is completed, the determination processing unit 93 determines whether or not hydrogen is present around the hydrogen sensor 10 based on the correlation coefficient calculated in processes S506 to S508 from the amount of current supplied to the hydrogen sensor 10 and the voltage value obtained in process S503 (S509). The determination processing unit 93 determines that hydrogen is not present around the hydrogen sensor 10 if the ratio (dR/dP), which is the correlation coefficient calculated in process S508, is greater than or equal to a predetermined threshold (S509-NO). Alternatively, the determination processing unit 93 determines that hydrogen is present around the hydrogen sensor 10 if the ratio (dR/dP), which is the correlation coefficient calculated in process S508, is less than a predetermined threshold (S509-YES). The threshold used in process S509 is the value obtained by subtracting a coefficient corresponding to the error from the ratio (dR/dP) when hydrogen is not present in the atmosphere.

If the determination processing unit 93 determines that hydrogen is not present (S509-NO), the process returns to S501. Thereafter, the process from S501 to S509 is repeated until the determination processing unit 93 determines that hydrogen is present (S509-YES).

When the determination processing unit 93 determines that hydrogen is present (S509-YES), the detection signal output unit 94 outputs a detection signal to the output unit 24 indicating that hydrogen has been detected (S510). In response to the input detection signal, the output unit 24 displays an image indicating that hydrogen has been detected and outputs an audio alert sound indicating that hydrogen has been detected.

Furthermore, in hydrogen detection devices 1 to 3, a sweep period is repeated, consisting of an increasing period in which the current increases in a stepwise manner, a decreasing period in which the current decreases in a stepwise manner, and a pause period. However, in the gas detection device according to this embodiment, the sweep period may be in other forms.

Figure 15(a) shows a first modified example of the sweep period according to the embodiment, and Figure 15(b) shows a second modified example of the sweep period according to the embodiment. Figure 15(c) shows a third modified example of the sweep period according to the embodiment, and Figure 15(d) shows a fourth modified example of the sweep period according to the embodiment. In Figures 15(a) to 15(d), the horizontal axis represents time, and the vertical axis represents the amount of current supplied to the hydrogen sensor.

The first modified sweep period differs from the sweep period in the embodiment shown in Figure 1(a) in that it has an increasing period in which the current increases in a stepwise manner, a pause period following the increasing period, and no decreasing period. The first modified sweep period may be used when the hydrogen detection device according to the embodiment performs the first aspect of the estimation process. The second modified sweep period differs from the sweep period in the embodiment shown in Figure 1(a) in that the current increases monotonically without a stepwise increase during the increasing period, and decreases monotonically without a stepwise decrease during the decreasing period. In the second modified sweep period, the increasing and decreasing periods are triangular waves. The third modified sweep period differs from the sweep period in the embodiment shown in Figure 1(a) in that the current does not change in a stepwise manner during the increasing and decreasing periods, and the increasing and decreasing periods are sine waves.

The fourth variation of the sweep period differs from the sweep period in the embodiment shown in Figure 1(a) in that, in addition to the increase period, decrease period, and pause period, it includes a pulse period in which the current quantity is changed in a pulsed manner before the increase period. The voltage value acquired during the pulse period may be used, for example, when correcting the correlation coefficient by the estimation device 40 according to the second embodiment.

Furthermore, while the hydrogen detection device 2 corrects the correlation coefficient based on the voltage value obtained in step "1," the hydrogen detection device according to the embodiment may correct the correlation coefficient based on the voltage value obtained in a step closer to step "1" than step "10." That is, the hydrogen detection device according to the embodiment may correct the correlation coefficient based on the voltage value obtained when a current amount closer to 10 mA supplied in step "1" is supplied than the 100 mA supplied in step "10."

The temperature change of platinum when current amounts corresponding to the increasing, decreasing, and pausing periods corresponding to the sweep period in the embodiment shown in Figure 1(a) was supplied to the platinum was simulated using the finite element method (FEM) on the supercomputer "TSUBAME".

Figure 16(a) shows the simulation results and measured values when current amounts corresponding to the increasing period, decreasing period, and pause period corresponding to the sweep period in the embodiment shown in Figure 1(a) are supplied to the platinum, and Figure 16(b) shows the amount of current supplied to the platinum. In Figure 16(a), the horizontal axis is time and the vertical axis is the temperature change of the platinum, and in Figure 16(b), the horizontal axis is time and the vertical axis is the amount of current supplied to the hydrogen sensor. In Figure 16(a), the square marks indicate measured values in an atmosphere of 100% nitrogen, and the circles indicate measured values in an atmosphere of 100% hydrogen. Waveform W101 shows the simulation results in an atmosphere of 100% nitrogen, and the square marks indicate the simulation results in an atmosphere of 100% nitrogen. Waveform W102 shows the simulation results in an atmosphere of 100% hydrogen, and the circles indicate the simulation results in an atmosphere of 100% hydrogen. The platinum material is in the form of a wire with a diameter of 0.05 mm and a length of 88 mm. In the simulation, only thermal conduction is considered in heat transport; convection and radiation are not taken into account. Furthermore, the temperature of the platinum is set to room temperature, and the temperature rise from that temperature is calculated.

As shown in Figure 16(a), the simulation results for both a 100% nitrogen atmosphere and a 100% hydrogen atmosphere closely match the measured values, including the fact that the peak of the platinum temperature rise due to heat accumulation appears with a delay from the peak of the current supplied to the platinum. Since the simulation results considering only heat conduction closely match the measured values, it can be inferred that, at room temperature, when supplying the current corresponding to the sweep period shown in Figure 1(a) to a wire-shaped platinum, heat conduction contributes significantly more to heat transport than convection and radiation.

Figure 17 shows the external appearance of the experimental apparatus used in Example 2.

In the experimental setup shown in Figure 17, a wire-shaped platinum strip was placed in a test tube filled with a mixture of nitrogen and hydrogen gas. The voltage output from the platinum strip was measured when a current corresponding to the sweep period shown in the embodiment in Figure 1(a) was supplied to the platinum strip in the atmospheric environment. The platinum strip had a wire-like shape with a diameter of 0.05 mm and a length of 88 mm.

(Regarding the response characteristics when the hydrogen concentration is changed)
Using the experimental apparatus shown in Figure 17, the voltage output from platinum was measured when a current corresponding to the sweep period shown in the embodiment in Figure 1(a) was supplied to the platinum while varying the hydrogen content in the mixed gas introduced into the test tube. From the current supplied to the platinum and the measured voltage, the ratio (dR/dP) between the change in power P supplied to the platinum (dP) and the change in resistance R (dR) was calculated. In addition, the area APR of the region enclosed by the plots corresponding to each of the multiple measured voltage values was calculated in a Cartesian coordinate system with power P as the first axis and the calculated resistance _R as the second axis.

Figure 18(a) is a diagram (part 1) showing the relationship between the hydrogen content and ratio (dR/dP) of the mixed gas, and Figure 18(b) is a diagram (part 2) showing the relationship between the hydrogen content and ratio (dR/dP) of the mixed gas. Figure 18(c) is a diagram (part 1) showing the relationship between the hydrogen content and area _APR of the mixed gas, and Figure 18(d) is a diagram (part 2) showing the relationship between the hydrogen content and area _APR of the mixed gas. In Figures 18(a) and 18(b), the horizontal axis represents time, the left vertical axis represents the ratio (dR/dP), and the right vertical axis represents the hydrogen concentration of the mixed gas. In Figures 18(c) and 18(d), the horizontal axis represents time, the left vertical axis represents area _APR , and the right vertical axis represents the hydrogen concentration of the mixed gas. The hydrogen content was changed in 1% increments from 1% to 10%, and in 20% increments from 20% to 100%. The graphs shown in Figures 18(a) to 18(d) plot the ratio (dR/dP) and area _APR calculated when the sweep period shown in Figure 1(a), which is repeated every 2.7 seconds, is repeated over a predetermined period of time.

The ratio (dR/dP) and area _APR both change in accordance with the change in the hydrogen concentration contained in the mixed gas, and it was confirmed that the hydrogen concentration can be estimated in both the first and second modes of estimation processing by the estimation device in the hydrogen detection devices 1 to 3 according to the embodiment.

(Regarding the repeatability characteristics when the hydrogen concentration is changed)
Using the experimental apparatus shown in Figure 17, nitrogen gas without hydrogen and a mixed gas with a hydrogen content of 10% were alternately introduced into a test tube, and the voltage value output from the platinum was measured when the amount of current corresponding to the sweep period according to the embodiment shown in Figure 1(a) was supplied to the platinum. From the amount of current supplied to the platinum and the measured voltage value, the ratio (dR/dP) between the change in power P supplied to the platinum (dP) and the change in resistance R (dR) was calculated. In addition, the area APR of the region enclosed by the plots corresponding to each of the multiple measured voltage values was calculated in a Cartesian coordinate system with power _P as the first axis and the calculated resistance R as the second axis.

Figure 19(a) is a diagram (part 3) showing the relationship between the hydrogen content and ratio (dR/dP) in the mixed gas, and Figure 19(b) is a diagram (part 3) showing the relationship between the hydrogen content and area _APR in the mixed gas. In Figure 19(a), the horizontal axis represents time, the left vertical axis represents the ratio (dR/dP), and the right vertical axis represents the hydrogen concentration in the mixed gas. In Figure 19(b), the horizontal axis represents time, the left vertical axis represents the area _APR , and the right vertical axis represents the hydrogen concentration in the mixed gas. The graphs shown in Figures 19(a) and 19(b) plot the ratio (dR/dP) and area _APR calculated when the sweep period shown in Figure 1(a), which is repeated every 2.7 seconds, is repeated over a predetermined time.

It was confirmed that both the ratio (dR/dP) and the area _APR remained the same with each repetition, both in a nitrogen gas atmosphere and in a mixed gas atmosphere with a hydrogen content of 10%.

(Regarding the correlation coefficient (dR/dP) and the relationship between area _APR and hydrogen concentration)
Figure 20(a) shows the change in the ratio (dR/dP) when the hydrogen concentration is changed, Figure 20(b) shows the change in area _APR when the hydrogen concentration is changed, and Figure 20(c) shows the change in the thermal resistivity of the mixed gas when the hydrogen concentration is changed.

It was confirmed that the ratio (dR/dP) shown in Figure 20(a) and the area _APR shown in Figure 20(b) both decrease exponentially with respect to hydrogen concentration. Furthermore, it was confirmed that the hydrogen concentration characteristics of both the ratio (dR/dP) shown in Figure 20(a) and the area _APR shown in Figure 20(b) substantially coincide with the hydrogen concentration characteristics of the thermal resistivity of the mixed gas when the concentration is changed. Thermal resistivity is the reciprocal of thermal conductivity, and this supports the fact that heat conduction contributes far more to heat transport than convection and radiation.

In the experimental apparatus shown in Figure 17, the possibility of detecting lower concentrations of hydrogen was verified using an apparatus in which the diameter of the platinum was changed from 0.05 mm to 0.03 mm, and the practicality of the correction process in the hydrogen detection apparatus according to the second embodiment was also verified. By changing the diameter of the platinum from 0.05 mm to 0.03 mm, the resistance of the platinum increases by approximately three times. Therefore, the amount of platinum heated becomes approximately three times that of the experimental apparatus shown in Figure 17, and the measured voltage also increases by approximately three times. Consequently, the detection accuracy of the experimental apparatus becomes approximately ten times that of the experimental apparatus shown in Figure 17.

(Regarding the detectability of low concentrations of hydrogen)
Figure 21 is the fourth figure showing the relationship between the hydrogen content and ratio (dR/dP) in the mixed gas. Figure 21(a) shows the change in ratio (dR/dP) over time, and Figure 21(b) shows the change in the amount of hydrogen introduced over time. In Figure 21(a), the horizontal axis represents time, and the vertical axis represents the ratio (dR/dP). In Figure 21(b), the horizontal axis represents time, and the vertical axis represents the hydrogen content. The hydrogen content was changed in 0.4% increments from 0.4% to 4%. The graph shown in Figure 21(a) plots the ratio (dR/dP) calculated when the sweep period shown in Figure 1(a), which is repeated every 2.7 seconds, is repeated over a predetermined period of time.

The ratio (dR/dP) changes even at 0.4% in accordance with the change in hydrogen concentration contained in the mixed gas. It was confirmed that a hydrogen concentration of approximately 0.4% can be detected in the first embodiment of the estimation process by the estimation device in the hydrogen detection devices 1 to 3 according to the embodiment.

(Regarding the practicality of the correction process)
Figure 22(a) shows the change in ambient temperature over time in which the experimental apparatus is placed, and Figure 22(b) shows the change in the resistance of platinum over time when a current of 10 mA is supplied during the increasing period. In Figure 22(a), the horizontal axis represents time, and the vertical axis represents the ambient temperature in which the experimental apparatus is placed. In Figure 22(b), the horizontal axis represents time, and the vertical axis represents the resistance of platinum when a current of 10 mA is supplied.

The change in the resistance of platinum over time when a current of 10 mA is supplied closely matches the change in the ambient temperature of the experimental setup. Since the change in resistance over time when a current of 10 mA is supplied closely matches the change in ambient temperature of the experimental setup, it was confirmed that the correction factor calculated from the resistance of platinum when a current of 10 mA is supplied reflects fluctuations in room temperature.

Figure 23(a) shows the change over time of the ratio (dR/dP) before correction, and Figure 23(b) shows the change over time of the ratio (dR/dP) after correction. Figure 23(c) shows the change over time of the area _APR before correction, and Figure 23(d) shows the change over time of the area _APR after correction. In Figures 23(a) and 23(b), the horizontal axis represents time and the vertical axis represents the ratio (dR/dP), and in Figures 23(c) and 23(d), the horizontal axis represents time and the vertical axis represents the area _APR . The graphs shown in Figures 23(a) to 23(d) plot the ratio (dR/dP) and area _APR calculated when the sweep period shown in Figure 1(a), which is repeated every 2.7 seconds, is repeated over a predetermined period of time.

In Figure 23(a), the displacement of the ratio (dR/dP) that is presumed to be due to the temperature change of the atmosphere in which the experimental apparatus indicated by arrows A, B, C, and D is placed is not observed in the corrected ratio (dR/dP). Similarly, in Figure 23(c), the displacement of area _APR that is presumed to be due to the temperature change of the atmosphere in which the experimental apparatus indicated by arrows E, F, G, and H is placed is not observed in the corrected area _APR . It has been confirmed that the correction process in the hydrogen detection device according to the second embodiment eliminates the effect of temperature changes in the atmosphere in which the hydrogen detection device is placed.

In the experimental setup shown in Figure 17, we investigated whether tungsten and cobalt could be used as hydrogen sensors instead of platinum, which is typically used as a hydrogen sensor. Platinum has a face-centered cubic lattice structure. On the other hand, tungsten has a body-centered cubic lattice structure, and cobalt has a hexagonal close-packed structure; therefore, the crystal structures of tungsten and cobalt differ from those of platinum.

Figure 24 shows the characteristics of an experimental apparatus using tungsten instead of platinum as a hydrogen sensor, and Figure 25 shows the characteristics of an experimental apparatus using cobalt instead of platinum as a hydrogen sensor. The experimental apparatus used to obtain the characteristics shown in Figures 24 and 25 has the same configuration and function as the experimental apparatus shown in Figure 13, except for the hydrogen sensor material.

Figures 24(a) and 25(a) show the amount of current supplied to the hydrogen sensor, and Figures 24(b) and 25(b) show the voltage values output from the hydrogen sensor in response to the current amounts shown in Figures 24(a) and 25(a). Figures 24(c) and 25(c) show the simulation results and measured values when the current amounts shown in Figures 24(a) and 25(a) are supplied to the hydrogen sensor. Figures 24(d) and 25(d) show the correlation between the amount of current supplied to the hydrogen sensor and the voltage values output from the hydrogen sensor, and Figures 24(e) and 25(e) show the correlation between the power supplied to the hydrogen sensor and the resistance value of the hydrogen sensor.

In Figures 24(a) and 25(a), the horizontal axis represents time, and the vertical axis represents the amount of current supplied to the hydrogen sensor. In Figures 24(b) and 25(b), the horizontal axis represents time, and the vertical axis represents the voltage output from the hydrogen sensor. In Figures 24(c) and 25(c), the horizontal axis represents time, the left vertical axis represents the resistance of the hydrogen sensor, and the right vertical axis represents the temperature change of the hydrogen sensor. In Figures 24(d) and 25(d), the horizontal axis represents the amount of current supplied to the hydrogen sensor, and the vertical axis represents the voltage output from the hydrogen sensor. In Figures 24(e) and 25(e), the horizontal axis represents the power supplied to the hydrogen sensor, the left vertical axis represents the resistance of the hydrogen sensor, and the right vertical axis represents the temperature change of the hydrogen sensor.

It was confirmed that even when tungsten and cobalt are used as hydrogen sensors instead of platinum, the ratio (dR/dP) and area _APR can be calculated in the hydrogen detection device according to the embodiment, just as when platinum is used as the hydrogen sensor.

1-3 Hydrogen detection device (gas detection device)
10. Hydrogen sensor (conductive material)
11 Current source 12 Voltmeter 16 Voltage source 17 Ammeter 20, 20a, 40, 60, 80 Estimation device 31 Current supply unit 32 Voltage acquisition unit 33, 38 Estimation processing unit 34 Concentration signal output unit 36 Voltage application unit 37 Current acquisition unit 55 Correction unit 75 Degradation determination unit 76 Alarm signal output unit 93 Determination processing unit 94 Detection signal output unit

Claims (15)

A conductor whose resistance changes in response to temperature changes,
A power supply that supplies electricity to the conductor,
An electrical sensor that detects a physical quantity indicating the electrical properties of the conductor,
The device includes an estimation device for estimating the concentration of a predetermined gas present around the conductor,
The estimation device is,
The amount of electricity supplied to the conductor is gradually changed.
While changing the amount of electricity supplied to the conductor, a plurality of physical quantities detected by the electrical sensor are acquired.
Based on the amount of electricity supplied to the conductor and the correlation between the power input to the conductor and the resistance value of the conductor, calculated from the acquired multiple physical quantities, the concentration of the gas present around the conductor is estimated.
Outputs a concentration signal indicating the estimated concentration of the gas.
A gas detection device characterized by the following features. The power supply is a current source that supplies current to the conductor,
The electrical sensor is a voltmeter that detects the voltage output from the conductor,
The estimation device is,
While changing the amount of current supplied to the conductor, multiple voltage values detected by the voltmeter are acquired.
Based on the amount of current supplied to the conductor and the resistance and power calculated from the acquired plurality of voltage values, the amount of gas present around the conductor is estimated.
The gas detection device according to claim 1. The power supply is a voltage source that applies a voltage to the conductor,
The aforementioned electrical sensor is an ammeter that detects the current flowing through the conductor,
The estimation device is,
While changing the voltage value supplied to the conductor, multiple current amounts detected by the ammeter are acquired.
Based on the voltage value supplied to the conductor and the resistance value and power calculated from the acquired multiple current amounts, the amount of gas present around the conductor is estimated.
The gas detection device according to claim 1. The aforementioned conductor is placed in the atmosphere,
The gas detection device according to claim 2 or 3 , wherein the gas is hydrogen. The estimation device is a gas detection device according to any one of claims 2 to 4, wherein the estimation device repeats a supply process that gradually increases the amount of electricity supplied to the conductor from a first amount to a second amount higher than the first amount. The estimation device is,
From the amount of electricity supplied to the conductor and the acquired physical quantities representing the plurality of electrical characteristics, the power supplied to the conductor is calculated when the acquired physical quantities are output from the conductor.
From the amount of electricity supplied to the conductor and the acquired multiple physical quantities, the resistance value of the conductor is calculated when the acquired multiple physical quantities are output from the conductor.
From the calculated power and resistance values, a correlation coefficient showing the correlation between the power and the resistance value is calculated.
Based on the correlation coefficient, the amount of gas present around the conductor is estimated.
The gas detection device according to claim 5. The gas detection device according to claim 6, wherein the correlation coefficient is the ratio between the calculated change in power and the calculated change in resistance. The gas detection device according to claim 6, wherein, in the supply process, the estimation device increases the amount of electricity supplied to the conductor from the first amount to the second amount, and then gradually decreases the amount of electricity supplied to the conductor from the second amount to the first amount. The gas detection device according to claim 8, wherein the estimation device calculates the area of the region enclosed by plots corresponding to each of the acquired plurality of voltages or currents as the correlation coefficient in a Cartesian coordinate system in which the calculated power is the first axis and the calculated resistance value is the second axis. The gas detection device according to any one of claims 6 to 9, wherein the estimation device corrects the correlation coefficient based on a physical quantity obtained when supplying an amount of electricity closer to the first amount than the second amount. The gas detection device according to claim 10, wherein the estimation device corrects the correlation coefficient based on the initially acquired physical quantity. The estimation device estimates the resistance value when no electricity is supplied to the conductor from the calculated power and resistance value.
Determine whether the difference between the estimated resistance value and the reference resistance value is greater than or equal to a predetermined threshold difference.
A gas detection device according to any one of claims 6 to 11, which outputs an alarm signal indicating that the conductor has deteriorated when it is determined that the difference between the estimated resistance value and the reference resistance value is greater than or equal to a predetermined threshold difference. The amount of electricity supplied to a conductor whose resistance changes in response to temperature changes is gradually altered.
While changing the amount of electricity supplied to the conductor, multiple physical quantities are obtained by an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor.
Based on the amount of electricity supplied to the conductor and the correlation between the power input to the conductor and the resistance value of the conductor, calculated from the acquired plurality of physical quantities, the concentration of a predetermined gas present around the conductor is estimated.
Outputs a concentration signal indicating the estimated concentration of the gas.
A method for detecting a gas, characterized by including the following. The amount of electricity supplied to a conductor whose resistance changes in response to temperature changes is gradually altered.
While changing the amount of electricity supplied to the conductor, multiple physical quantities are obtained by an electrical sensor that detects physical quantities indicating the electrical characteristics output from the conductor.
Based on the amount of electricity supplied to the conductor and the correlation between the power input to the conductor and the resistance value of the conductor, calculated from the acquired multiple physical quantities, the concentration of a predetermined gas present around the conductor is estimated.
Outputs a concentration signal indicating the estimated concentration of the gas.
A gas detection program characterized by having a computer perform the processing. A conductor whose resistance changes in response to temperature changes,
A power supply that supplies electricity to the conductor,
An electrical sensor for detecting a physical quantity that indicates the electrical characteristics output from the conductor,
The device includes a determination device for determining whether or not a predetermined gas is present around the conductor,
The determination device is
The amount of electricity supplied to the conductor is gradually changed.
While changing the amount of electricity supplied to the conductor, a plurality of physical quantities detected by the electrical sensor are acquired.
Based on the amount of electricity supplied to the conductor and the correlation between the power input to the conductor and the resistance value of the conductor, calculated from the acquired multiple physical quantities, it is determined whether or not the gas is present around the conductor.
When it is determined that the gas is present around the conductor, a detection signal indicating that the gas has been detected is output.
A gas detection device characterized by the following features.