Temperature control method for gas detection device and temperature control device for gas detection device

Abstract

To enable more accurate detection of a target gas by suppressing the influence of conditions of environmental gas.SOLUTION: A method of controlling temperature of a gas detection device is provided in which detection heating control is performed in a given cycle, the detection heating control including steps of: performing first pulse heating for a predetermined first period at a purge temperature for reducing adsorbed substances in a gas diction unit (#1); performing preheating for a predetermined second period at a preheat temperature higher than the ambient environment temperature after the first pulse heating (#3); and performing second pulse heating for a predetermined third period at a measurement temperature after the preheating (#5), where the measurement temperature is in a range of 150-450°C, inclusive.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a temperature control method and a temperature control device in a gas detection device that utilizes the fact that an electrical characteristic value of a gas detection section changes upon contact with a target gas under specific conditions. [Background technology]

[0002] As disclosed in Patent Document 1, there is a gas detection device that detects the presence and concentration of a target gas in an environmental gas environment based on changes in the characteristics of a gas detection section when the gas detection section is heated.

[0003] Furthermore, there are gas detection devices that perform a predetermined temperature control before and after heating when detecting a target gas, as shown in Patent Documents 2 and 3. This configuration eliminates the influence of interference gases and improves the detection sensitivity of the target gas. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-167954 A [Patent Document 2] JP 2017-90188 A [Patent Document 3] JP 2018-194434 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in reality, when an interference gas is contained in the environmental gas, it is difficult to detect the target gas, and it is necessary to provide multiple gas detection units in order to detect the target gas with high accuracy. This is thought to be due in part to factors other than the presence of interference gas, such as differences in humidity (relative humidity; the same applies below) of the environmental gas, which reduces the selectivity of the target gas.

[0006] An object of the present invention is to suppress the effect of interference gases on the sensitivity of a target gas and to detect the target gas with higher accuracy. [Means for solving the problem]

[0007] In order to achieve the above object, a characteristic configuration of a temperature control method for a gas detection device according to one embodiment of the present invention is a temperature control method for a gas detection device that detects acetone present in an environmental gas by measuring electrical characteristics of a gas detection section heated to a predetermined measurement temperature, wherein detection heating control is performed at a predetermined cycle, and the detection heating control comprises the steps of: performing first pulse heating for a predetermined first time at a purge temperature for reducing adsorbates in the gas detection section; performing pre-heating for a predetermined second time at a predetermined pre-heating temperature higher than the ambient environmental temperature after the first pulse heating; and performing second pulse heating for a predetermined third time at the measurement temperature after the pre-heating, wherein the measurement temperature is 150° C. or higher and 450° C. or lower, the environmental gas contains ethanol, and the environmental gas is exhaled breath. The acetone detection includes calculating a ratio of a value of the electrical property within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone to the measurement temperature to a value of the electrical property within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone to the measurement temperature, and calculating the concentration of the acetone present in the environmental gas based on a graph showing the relationship between the ratio and the concentration of the acetone. The point is that

[0008] Furthermore, a characteristic configuration of a temperature control device for a gas detection device according to one embodiment of the present invention is a temperature control device for a gas detection device that detects acetone present in an environmental gas by measuring an electrical characteristic of a gas detection section heated to a predetermined measurement temperature, a detection control unit that measures an electrical characteristic value of the gas detection unit to detect the acetone present in the environmental gas; The gas detector includes a heater section for heating the gas detection section, and a temperature control section for controlling a heating operation of the heater section, and the temperature control section performs detection heating control at a predetermined cycle, and the detection heating control includes a first pulse heating for a predetermined first time at a purge temperature for reducing adsorbates in the gas detection section, a preheating for a predetermined second time at a preheating temperature higher than an ambient temperature after the first pulse heating, and a second pulse heating for a predetermined third time at the measurement temperature after the preheating, the measurement temperature being 150° C. or higher and 450° C. or lower, the environmental gas includes ethanol, and the environmental gas is exhaled breath. the detection control unit calculates a ratio of a value of the electrical characteristic within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone to the measurement temperature to a value of the electrical characteristic within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone to the measurement temperature, and calculates the concentration of the acetone present in the environmental gas based on a graph showing a relationship between the ratio and the concentration of the acetone. The point is that

[0009] With the above configuration, even in the case of an environmental gas containing a mixture of acetone and ethanol, it is possible to suppress deterioration of the detection sensitivity of acetone due to the influence of humidity in the environmental gas while increasing selectivity with respect to ethanol, which is an interference gas contained in the environmental gas, and to detect acetone with high accuracy by suppressing the influence of the state of the environmental gas. In addition, there are cases where acetone in breath is detected for medical or health purposes. Furthermore, the detection control unit can measure an electrical characteristic value of the gas detection unit and calculate the acetone concentration from the electrical characteristic value or a change in the electrical characteristic value. According to the above configuration, acetone can be appropriately detected in breath.

[0010] It is also preferable that the purge temperature is 350° C. or more and 450° C. or less, and the second time period is 5 seconds or more and 45 seconds or less.

[0011] With this configuration, deterioration of acetone detection sensitivity due to the influence of humidity and adsorbed substances can be more appropriately suppressed, and acetone can be detected with greater accuracy. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing an overview of a gas detection device. [Diagram 2] FIG. 4 is a diagram showing a heating pattern in detection heating control according to the embodiment. [Diagram 3] FIG. 13 is a diagram showing a flow of detection heating control. [Figure 4] FIG. 13 is a diagram showing a heating pattern in detection heating control of a comparative example. [Diagram 5] 11 is a double logarithmic graph illustrating the relationship between humidity and sensitivity in a comparative example. [Figure 6] 4 is a double logarithmic graph illustrating the relationship between humidity and sensitivity in an embodiment. [Figure 7] 1 is a graph illustrating the relationship between the preheating temperature and the amount of change IRH in acetone concentration due to humidity fluctuation in an embodiment. [Figure 8] 1 is a graph illustrating the relationship between the preheating time and the amount of change IRH in acetone concentration due to humidity fluctuation in an embodiment. [Figure 9]1 is a double logarithmic graph illustrating the selectivity between acetone and ethanol at a measurement temperature of 300° C. [Figure 10] 1 is a double logarithmic graph illustrating the selectivity between acetone and ethanol at a measurement temperature of 400° C. [Figure 11] 1 is a double logarithmic graph illustrating the selectivity between acetone and ethanol at a measurement temperature of 200° C. [Figure 12] 1 is a graph illustrating the relationship between the measurement temperature and the ratio IET of the acetone concentration to the ethanol concentration in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] [Gas detection device] The configuration of gas detection device 100 according to this embodiment will be described with reference to FIG. 1. Gas detection device 100 detects the presence of acetone (C3H6O) in breath, which is an environmental gas, and derives the concentration of acetone in the breath (hereinafter simply referred to as "detecting acetone"). Gas detection device 100 has a sensor element 20, a heating control section 12 (an example of a "temperature control section"), a detection control section 13, and a temperature detection section 14. Sensor element 20 has at least a gas detection layer 10 (an example of a "gas detection section"), a catalyst layer 11, and a heater layer 6 (an example of a "heater section"). A configuration including at least heating control section 12 and heater layer 6 of sensor element 20 is referred to as a temperature control device.

[0018] The gas detection device 100 heats the gas detection layer 10 to an appropriate temperature depending on the type of target gas by passing electricity through the heater layer 6 using the heating control unit 12, and detects the target gas based on the electrical characteristic values ​​(electrical resistance value, voltage value, etc.) of the gas detection layer 10.

[0019] [Sensor element] The sensor element 20 is supported by the silicon substrate 1 to form a diaphragm. The sensor element 20 has a support layer 5, an insulating layer 7, a gas detection layer 10, and a catalyst layer 11. The support layer 5 is formed on the silicon substrate 1, and a heater layer 6 is formed on the support layer 5. The insulating layer 7 is formed on the support layer 5 to cover the entire heater layer 6. A pair of bonding layers 8 is formed on the insulating layer 7, and an electrode layer 9 is formed on the bonding layer 8. The gas detection layer 10 is formed between the pair of electrode layers 9 on the insulating layer 7. The catalyst layer 11 is formed on the insulating layer 7 in a form covering the gas detection layer 10. The sensor element 20 may have a bridge structure, and the heater layer 6 may also serve as an electrode.

[0020] The support layer 5 is formed by sequentially laminating a thermal oxide film 2, a Si3N4 film 3, and a SiO2 film 4. The heater layer 6 generates heat when energized, thereby heating the gas detection layer 10 and the catalyst layer 11.

[0021] The gas sensing layer 10 is a semiconductor layer mainly composed of metal oxide. For example, the gas sensing layer 10 is a mixture mainly composed of tin oxide (SnO2). The electrical resistance value of the gas sensing layer 10 changes upon contact with the target gas. The gas sensing layer 10 may be a thin film having a thickness of about 0.2 to 1.6 μm, or may be a film (thick film) having a thickness exceeding 1.6 μm.

[0022] The catalyst layer 11 is heated by the heater layer 6 to a high temperature, and burns gases that are active (combustible) at that temperature. Furthermore, at that temperature, the target gas, acetone, is transmitted and diffused and reaches the gas sensing layer 10. In this way, the accuracy of acetone detection is improved by appropriately controlling the heating temperature. In other words, when detecting acetone as the target gas, the catalyst layer 11 has the function of burning non-target gases other than acetone, such as hydrogen gas, so that they do not reach the gas sensing layer 10, thereby providing gas selectivity to the gas detector 100. Therefore, the gas sensing layer 10 can efficiently detect acetone that has transmitted and diffused through the catalyst layer 11.

[0023] The catalyst layer 11 is formed by supporting a catalyst metal on a support mainly composed of a metal oxide. Specifically, the catalyst layer 11 is formed by bonding metal oxides supporting the catalyst metal to each other via a binder.

[0024] [Heating control section] The heating control unit 12 controls the current supply to the heater layer 6, and heats the gas sensing layer 10 by supplying current to the heater layer 6. The heating control unit 12 can also heat the heater layer 6 to a desired set temperature by controlling the voltage or current supplied to the heater layer 6.

[0025] Specifically, the heating control unit 12 receives power from a power source such as a battery (not shown) and energizes the heater layer 6 of the sensor element 20 to heat the sensor element 20. The heating temperature, i.e., the temperature reached by the gas detection layer 10 and the catalyst layer 11, is controlled, for example, by changing the voltage applied to the heater layer 6. In the following description, heating to a certain temperature means applying a voltage corresponding to that temperature, and the heating time is the time for which the voltage is applied.

[0026] [Detection control section] The detection control unit 13 detects the target gas by measuring an electrical characteristic value of the gas detection layer 10. For example, the detection control unit 13 measures the resistance value of the gas detection layer 10 by measuring the electrical resistance value (electrical characteristic value) between the pair of electrode layers 9, and detects the target gas from the resistance value or a change in the resistance value.

[0027] The temperature detection unit 14 detects the temperature of the gas detection layer 10 or the temperature of the gas detection layer 10 and its surroundings (hereinafter collectively referred to as the ambient temperature). Specifically, the temperature detection unit 14 is a temperature sensor such as a thermistor. In addition, the temperature detection unit 14 can detect the temperature of the heater layer 6 (which is substantially equivalent to the temperature of the gas detection layer 10) by measuring the resistance value of the heater layer 6. The temperature detected by the temperature detection unit 14 is sent to the heating control unit 12.

[0028] [Heating operation] In the acetone detection operation, the heating control unit 12 heats the detection control unit 13 of the sensor element 20 by pulse heating. Pulse heating is a heating operation in which the temperature is repeatedly raised to a measurement temperature suitable for detecting acetone, which is a target gas, for a predetermined time at a predetermined interval. In addition, a predetermined time before heating to the measurement temperature and detecting acetone, purge heating is performed to raise the temperature to a predetermined purge temperature for a predetermined time. By performing purge heating, the adsorbed matter of the gas detection layer 10 is removed or reduced, and the surface of the gas detection layer 10 is cleaned. Specifically, hydrogen, carbon monoxide, etc. attached to the surface of the gas detection layer 10 are burned by pulse heating, and the adsorbed matter of the gas detection layer 10, such as moisture, is removed or reduced. This prevents the detection sensitivity of acetone from being deteriorated due to dirt on the surface of the gas detection layer 10 caused by the surrounding environment.

[0029] When detecting acetone in breath, the detection sensitivity of acetone is sufficiently achieved by setting the measurement temperature to 100°C or higher and 500°C or lower. However, when ethanol is present in breath as an interfering gas, the selectivity with respect to ethanol decreases. Therefore, when detecting acetone in breath, the measurement temperature is preferably set to 150°C or higher and 400°C or lower.

[0030] Furthermore, the detection sensitivity of acetone may decrease depending on the humidity in the breath. In other words, when the humidity in the breath exceeds a certain level, the detection sensitivity of acetone decreases significantly. This is thought to be because, when the humidity in the breath is high, the moisture in the breath is adsorbed onto the surface of the gas detection layer 10 by the time the breath is heated to the measurement temperature, even if the breath is purged and heated.

[0031] Therefore, in this embodiment, during the period from after purge heating until heating to the measurement temperature, the gas sensing layer 10 is heated to a preheating temperature that is higher than the temperature of the breath or the ambient temperature, which is the temperature around the gas sensing layer 10, but lower than the measurement temperature. By heating the gas sensing layer 10 to the preheating temperature after purge heating and before detecting acetone at the measurement temperature, the temperature of the gas sensing layer 10 is prevented from dropping too much, and moisture in the breath is prevented from being adsorbed onto the surface of the gas sensing layer 10. As a result, it is possible to prevent a decrease in the detection sensitivity for acetone due to humidity in the breath.

[0032] 1 and 2, in the temperature control device according to this embodiment, as the detection heating control, the heating control unit 12, which is a temperature control unit, controls the heater layer 6 to first perform purge heating (first pulse heating) to a purge temperature tp for a predetermined first pulse time Wp (one example of "first time"), then hold the heating temperature at a preheating temperature tr for a predetermined preheating time Wr ​​(one example of "second time") (preheating), and then heat to a measurement temperature td for a predetermined second pulse time wd (one example of "third time") (second pulse heating), and measure an electrical characteristic value of the gas sensing layer 10 when it is heated to the measurement temperature td. Then, this detection heating control is repeated for each period T, and the electrical characteristic value of the gas sensing layer 10 is measured while it is heated to the measurement temperature td, thereby detecting acetone.

[0033] Similarly, in the temperature control method according to this embodiment, detection heating control is performed in the following steps as shown in FIG.

[0034] First, heating to the purge temperature tp is started as purge heating (step #1). Then, it is determined whether the first pulse time Wp has elapsed since heating to the purge temperature tp was started (step #2). If the first pulse time Wp has not elapsed, purge heating is continued to maintain the purge temperature tp, and a purge pulse to the purge temperature tp is performed for the first pulse time Wp (No in step #2).

[0035] When the first pulse time Wp has elapsed (Yes in step #2), heating to preheating temperature tr is started (step #3). Then, it is determined whether the preheating time Wr ​​has elapsed since heating to the preheating temperature tr was started (step #4). If the preheating time Wr ​​has not elapsed, preheating continues and the preheating temperature tr is maintained (No in step #4).

[0036] When the pre-heating time Wr ​​has elapsed (Yes in step #4), heating to the measurement temperature td is started (step #5). While the measurement temperature td is maintained, it is determined whether a predetermined measurement time has elapsed since heating to the measurement temperature td was started (step #6). When the predetermined measurement time has elapsed, the electrical resistance of the gas detection layer 10 is measured to detect acetone (step #7). Specifically, for acetone detection, the electrical resistance value Rs(Air) of the gas detection layer 10 measured by performing the above-mentioned detection heating control in an environmental gas that does not contain acetone is stored, and the ratio (hereinafter referred to as the "resistance ratio") between the electrical resistance value Rs(Air) of the gas detection layer 10 measured by performing the above-mentioned detection heating control in an environmental gas (breath) in which acetone is to be detected is calculated. Then, the concentration of acetone corresponding to the measured resistance ratio is derived from a graph or table showing the relationship between the resistance ratio calculated in advance and the concentration of acetone.

[0037] Then, it is determined whether the second pulse time Wd has elapsed since the heating to the measurement temperature td was started (step #8). If the second pulse time Wd has not elapsed, heating to the measurement temperature td continues, the measurement temperature td is maintained, and a detection pulse for the measurement temperature td is performed at the second pulse time Wd (No in step #8).

[0038] When the second pulse time Wd has elapsed (Yes in step #8), heating to the measurement temperature td is terminated (step #9). Then, it is determined whether or not time T has elapsed since purge heating was started (step #10). Heating is stopped until time T has elapsed, and when time T has elapsed, the process from purge heating is repeated. This causes the above-mentioned detection heating control to be repeated every time (cycle) T.

[0039] As described above, the purge pulse and the detection pulse are performed during the period T with the preheating sandwiched between them. In the above-mentioned detection heating control, the period T is 10 seconds or more and 300 seconds or less, more preferably 30 seconds or more and 150 seconds or less, for example, 60 seconds. The first pulse time Wp of the purge pulse is 0.05 seconds or more and 0.5 seconds or less, for example, 0.20 seconds. The second pulse time Wd of the detection pulse is 0.05 seconds or more and 0.5 seconds or less, for example, 0.20 seconds. The preheating time Wr ​​in the preheating is 5 seconds or more and 45 seconds or less, for example, 5 seconds. The measurement time from the start of heating to the measurement temperature td to the measurement of the electrical resistance is any time between 0.05 seconds or more and 0.20 seconds or less, for example, the measurement time is 0.10 seconds.

[0040] The purge temperature tp can be 350° C. or higher, preferably 350° C. or higher and 450° C. or lower, for example 400° C. The preheating temperature tr is preferably 30° C. or higher and 70° C. or lower, more preferably 40° C. or higher and 60° C. or lower. Under these conditions, the measurement temperature td is 150° C. or higher and 450° C. or lower, more preferably 240° C. or higher and 400° C. or lower.

[0041] The detection heating control according to this embodiment will be compared with the conventional detection heating control with reference to Figs. 1 to 11 below. As shown in Fig. 4, the conventional detection heating control performs a purge pulse for 0.2 seconds at a purge temperature tp of 400°C, stops heating for 5 seconds, and then performs a detection pulse for 0.2 seconds at a measurement temperature td of 300°C with a period T of 30 seconds. Note that the detection heating control according to this embodiment adds preheating for 5.0 seconds at various temperatures with a preheating temperature tr of 30 to 70°C between the purge pulse and the detection pulse to the conventional detection heating control. The measurement time was set to 0.10 seconds.

[0042] Figures 5 and 6 compare the effect of humidity on the detection sensitivity of acetone between conventional detection heating control and detection heating control with additional preheating at a preheating temperature tr of 50°C for 5.0 seconds.

[0043] The detection sensitivity of acetone when conventional heating control for detection is performed varies greatly depending on the humidity of the environmental gas (exhaled breath). As shown in Figure 5, when the humidity is 50% or 65%, the change in the resistance ratio with respect to the gas concentration of acetone, the target gas, is sufficiently large (the slope of the graph is large), and it can be seen that the detection sensitivity of acetone is sufficiently ensured. When the humidity becomes 80%, the change in the resistance ratio with respect to the gas concentration of acetone decreases significantly (the slope of the graph becomes smaller) compared to when the humidity is 50% or 65%, and it can be seen that the detection sensitivity of acetone is greatly reduced. Here, the change in acetone concentration due to humidity fluctuations (ratio of maximum value to minimum value) at a resistance ratio of 0.5 is defined as I RH (The smaller the value, the more the humidity fluctuation is suppressed.) The acetone concentration at the resistance ratio of 0.5 is the minimum at 0.04 ppm when the humidity is 50%, and the maximum at 0.37 ppm when the humidity is 80%. Therefore, I RH would be 9.25.

[0044] In contrast, the detection sensitivity of acetone when the detection heating control according to this embodiment is performed does not change significantly even if the humidity of the environmental gas (breath) changes. As shown in FIG. 6, the change in the resistance ratio to the acetone gas concentration at humidity levels of 50%, 65%, and 80% is sufficiently large (the slope of the graph is large). RH is 1.8, which shows that the resistance fluctuation due to humidity fluctuation is significantly suppressed and the detection sensitivity of acetone is sufficiently secured. This shows that the effect of humidity on the detection sensitivity of acetone is suppressed by performing pre-heating between the purge pulse and the detection pulse.

[0045] In Fig. 7, the preheating temperature tr and I RH Here, as a comparative example, the relationship between I and I RH The measurement result was 9.2. The measurement results of conventional detection heating control without preheating are plotted in the figure assuming a preheating temperature of 20°C. It can be seen that when the preheating temperature tr is 30 to 70°C, humidity fluctuation is suppressed more than in the comparative example. Also, when the preheating temperature tr is 40 to 60°C, I RH is below 3.0, and humidity fluctuations are significantly suppressed.

[0046] From the above results, it is clear that the influence of humidity fluctuations on acetone detection sensitivity can be suppressed by setting the preheating temperature tr to 30° C. or higher and 70° C. or lower, and that even greater effects can be obtained by setting it to 40° C. or higher and 60° C. or lower. The preheating temperature tr can be set appropriately depending on the measurement environment, such as the measurement temperature.

[0047] In addition, Fig. 8 shows the relationship between the preheating time and I when the preheating temperature tr is set to 50°C and the preheating time is changed from 5.0 to 50.0 seconds. RH The relationship between I and the preheat time is summarized. By setting the preheat time to 5.0 seconds or more and 45.0 seconds or less, the I RH Furthermore, when the preheating time is between 5.0 and 30.0 seconds, I RHFrom this, it can be seen that the preheating time is preferably 5.0 seconds or more and 45.0 seconds or less, and more preferably 5.0 seconds or more and 30.0 seconds or less.

[0048] Next, it will be shown that even when the environmental gas (breath) contains ethanol as an interference gas, when the detection heating control according to this embodiment is performed, selectivity between acetone and ethanol is ensured.

[0049] As shown in Figures 9 to 11, when the temperature control according to this embodiment is performed using an environmental gas with a relative humidity of 65%, graph A showing the change in resistance ratio versus acetone gas concentration is sufficiently separated from graph E showing the change in resistance ratio versus ethanol gas concentration, and it is seen that the selectivity between acetone and ethanol is ensured. Here, the ratio of the acetone concentration to the ethanol concentration at which the resistance ratio is 0.5 (the ethanol concentration divided by the acetone concentration) is defined as I ET (the higher the value, the greater the selectivity), the values ​​are 1.8 at 200°C (Figure 11), 7.5 at 300°C (Figure 9), and 3.7 at 400°C (Figure 10).

[0050] In Fig. 12, a purge pulse is performed for 0.2 seconds at a purge temperature tp of 400°C, preheating is performed for 5.0 seconds at a preheating temperature tr of 50°C, and then the measurement temperature td is set to various temperatures from 150°C to 450°C. The relationship between the measurement temperature and I ET Here, as a comparative example, the conventional detection heating control without preheating is used. ET As a result of measuring I ET was 1.1. ET =1.3) to 450°C (I ET = 1.3), the I ET It was also found that the measurement temperature td is preferably 240°C or higher and 400°C or lower, and that a selectivity three times higher than that of conventional methods can be obtained.

[0051] From the above results, it can be seen that when the measurement temperature td is 150°C or higher and 450°C or lower, higher selectivity than conventional methods is obtained, and when the measurement temperature td is 240°C or higher and 400°C or lower, the selectivity of acetone to ethanol is better.

[0052] [Another embodiment] <1> In the above embodiment, an example has been described in which pre-heating is performed consecutively with purge heating and heating to the measurement temperature td, but pre-heating may be performed a predetermined time after purge heating, or heating to the measurement temperature td may be performed a predetermined time after pre-heating. In other words, pre-heating may be performed with an interval between at least one of purge heating and heating to the measurement temperature td.

[0053] <2> In each of the above-described embodiments, the preheating is not limited to a continuous heating configuration, but may be performed intermittently with a predetermined heating stop period therebetween. In this case, multiple pulse heating to the preheating temperature may be performed.

[0054] <3> In each of the above embodiments, the interference gas is not limited to ethanol and may be any gas. Furthermore, the environmental gas is not limited to breath and may be any gas that is required to be detected as containing a target gas or not.

[0055] <4> In each of the above embodiments, the configuration is not limited to measuring the resistance ratio, and other electrical characteristics may be measured. The electrical characteristics may be, for example, an electrical resistance value at a predetermined time after heating to the measurement temperature td is started, an electrical resistance value at the end of the detection pulse, or a change or rate of change in the electrical resistance value at two predetermined points in the detection pulse. Moreover, the measurement of the electrical characteristics is not limited to a configuration in which the measurement is performed while heating to the measurement temperature td is being performed, and may be performed after heating to the measurement temperature td is completed.

[0056] <5> In each of the above embodiments, the configuration of the sensor element 20 is not limited to the configuration of the sensor element 20 including the gas detection layer 10 that is a thin-film semiconductor, and any gas sensor configuration can be used. For example, the sensor element 20 of the above embodiments may be a two-layer gas sensor in which the gas detection layer 10 is made of a semiconductor with a relatively large thickness. In addition, for example, the sensor element 20 of the above embodiments may be a substrate-type gas sensor without the catalyst layer 11 that covers the gas detection layer 10. In addition, a sensor element 20 may be used that includes a coil of an electrode wire that serves as both an electrode as the gas detection layer 10 and a heater as the heater portion, and has an oxide semiconductor around the coil.

[0057] In addition, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, provided that no contradiction arises. Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0058] The present invention can be applied to gas detection for detecting a predetermined target gas contained in an environmental gas. [Explanation of symbols]

[0059] 6 Heater layer (heater part) 10 Gas detection layer (gas detection part) 12 Heating control section (temperature control section)

Claims

1. 1. A temperature control method for a gas detection device that detects acetone present in an environmental gas by measuring an electrical characteristic of a gas detection unit heated to a predetermined measurement temperature, comprising: Heating control for detection is performed at a predetermined cycle. The sensing heating control includes: performing a first pulse heating for a first predetermined time at a purge temperature for reducing adsorbates in the gas detection unit; performing a preheating step after the first pulse of heating at a preheating temperature higher than the ambient temperature for a second preheating time; and performing a second pulse heating at the measurement temperature for a third predetermined time period after the pre-heating. The measurement temperature is 150° C. or higher and 450° C. or lower, the environmental gas includes ethanol; the environmental gas is exhaled air; The acetone detection method includes calculating a ratio of a value of the electrical characteristic after a predetermined measurement time has elapsed and within the third hour after heating of the environmental gas not containing acetone to the measurement temperature to a value of the electrical characteristic after the third hour after heating of the environmental gas containing acetone to the measurement temperature, to a value of the electrical characteristic after a predetermined measurement time has elapsed and within the third hour after heating of the environmental gas not containing acetone to the measurement temperature, and calculating the concentration of acetone present in the environmental gas based on a graph showing the relationship between the ratio and the concentration of acetone.

2. The purge temperature is 350° C. or more and 450° C. or less, 2. The method for controlling the temperature of a gas detection device according to claim 1, wherein the second time period is greater than or equal to 5 seconds and less than or equal to 45 seconds.

3. 1. A temperature control device for a gas detection device that detects acetone present in an environmental gas by measuring an electrical characteristic of a gas detection unit heated to a predetermined measurement temperature, comprising: a detection control unit that measures an electrical characteristic value of the gas detection unit to detect the acetone present in the environmental gas; A heater unit for heating the gas detection unit; a temperature control unit for controlling a heating operation of the heater unit, The temperature control unit performs detection heating control at a predetermined cycle, The sensing heating control includes: a first pulse heating step for a first predetermined time period at a purge temperature for reducing adsorbates in the gas sensing portion; preheating the substrate after the first pulse at a preheat temperature higher than the ambient temperature for a second preheat time; a second pulse heating at the measurement temperature after the preheating for a third predetermined time period; The measurement temperature is 150° C. or higher and 450° C. or lower, the environmental gas includes ethanol; the environmental gas is exhaled air; the detection control unit calculates a ratio of a value of the electrical characteristic within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone to the measurement temperature to a value of the electrical characteristic within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas containing the acetone to the measurement temperature, to a value of the electrical characteristic within the third hour and after a predetermined measurement time has elapsed since heating of the environmental gas not containing acetone was started, and calculates the concentration of acetone present in the environmental gas based on a graph showing the relationship between the ratio and the concentration of acetone.

4. The purge temperature is 350° C. or more and 450° C. or less, 4. The temperature control apparatus for a gas detection apparatus according to claim 3, wherein said second time period is between 5 seconds and 45 seconds.

Images