JP5749537B2 - Gas detection device and gas detection method - Google Patents

Description

  In the present invention, a gas detection layer whose electrical characteristics change due to contact with a detection target gas, and a sensor element in which a heater layer for heating the gas detection layer is formed, and the heater layer is energized at a predetermined normal cycle, A gas detection apparatus comprising: an energization driving unit that changes a temperature of the gas detection layer; and a gas detection unit that detects a detection target gas based on an electrical characteristic of the gas detection layer at a detection timing when the heater layer is energized; The present invention relates to a gas detection method executed in the gas detection device.

In such a gas detection device, the sensor element is constituted by a thin film gas sensor, and by starting energization to the heater layer, the gas detection layer is set to an appropriate temperature (for example, 400 to 500) according to the type of gas to be detected. The presence / absence and concentration of the detection target gas are detected based on the electrical characteristics (electric resistance value, voltage value, etc.) of the gas detection layer in a state where the temperature is maintained. In this case, since the energization driving means for energizing the heater layer is driven by, for example, battery driving, it is possible to detect the detection target gas without changing the battery for a long time by reducing power consumption as much as possible. Is needed. For this reason, the thin film gas sensor has a high heat insulation and low heat capacity structure such as a diaphragm structure manufactured by using a microfabrication process, and the energization driving means intermittently energizes the heater layer at a predetermined cycle to consume power. Is employed (see, for example, Patent Document 1).
Here, for example, when detecting a detection target gas that is a combustible gas such as methane gas or propane gas, the energization period of the heater layer is set to 30 s, and the energization of the heater layer is performed for a relatively short time of 50 to 500 ms. The heater layer is kept at a high temperature (for example, about 400 to 500 ° C.), and the electric resistance value of the gas detection layer is measured (detection timing). The stop state is maintained until 30 s has elapsed from the start (between 29.95 and 29.995 s from the stop of energization). And it is set as the structure which repeats starting electricity supply again, measuring an electrical resistance value, and stopping electricity supply. Thereby, it is said that it is possible to reduce the power consumption while reducing the energization time as much as possible and reliably detecting the detection target gas.

JP 2000-292395 A

In the installation environment of the gas detector as described above, methane gas, which is a detection target gas, and oxygen gas, nitrogen gas, hydrogen gas, carbon monoxide gas, water vapor, etc., which are non-detection target gases, coexist. In addition, as a non-detection target gas, although it is a trace amount, harmful gas harmful to the sensor element of the gas detection device (causes deterioration of characteristics) and interference gas that interferes with the sensor element (the gas detection layer changes its resistance, as if the detection target gas In some cases, various gas components may coexist temporarily, such as gas that induces false detection that behaves as if there is.
Therefore, various measures are taken in the gas detection device in order to prevent the influence of harmful gas, interference gas and the like. For example, with respect to interference gases such as low-boiling hydrocarbon gases (ethanol, VOC), hydrogen gas, carbon monoxide gas, etc., they are selectively burned in the selective combustion layer coated with the gas detection layer. Measures are taken so as not to affect the output. Furthermore, for harmful gases such as silicon, measures are taken such that an activated carbon adsorption layer (filter means) is provided at the gas inlet through which the detection target gas can flow into the gas detection layer in the gas detection device. .
Various measures such as those mentioned above have prevented the effects of harmful gases that are non-detection target gases, interference gases, etc., but if the gas detector is used in an environment where those gases coexist for a long period of time, the characteristics gradually increase. May change. Specifically, when the electric resistance value in the air is remarkably reduced, or when the detection target gas is methane gas, the selectivity to the interference gas such as carbon monoxide gas or hydrogen gas in the gas detection layer may deteriorate. (Even if carbon monoxide gas and hydrogen gas coexist, the electric resistance value of the gas detection layer decreases, and it behaves as if methane gas exists, that is, it may be erroneously detected). Furthermore, the gas detection layer becomes sensitized, that is, the electrical resistance value indicated by the methane concentration determined in advance from the concentration characteristics of the gas detection layer decreases, and a false alarm as if methane gas leakage has occurred may be issued. is there.

  In order to prevent such characteristic deterioration, the package of the sensor element is being strengthened so that the non-detection target gas can be prevented from reaching the sensor element including the gas detection layer in the gas detection device. As an example, in order to prevent interference gas and harmful gas, which are non-detection target gases, from entering the inside of the housing provided with the sensor element from outside the gas inlet provided in the housing. , Improved airtightness of the package (inspection gas for direct flow into the sensor element in the housing without passing through the activated carbon adsorption layer provided near the gas inlet during periodic inspections, and the housing structure is fitted Etc.) and functional enhancement of activated carbon adsorption layer provided at gas inlet (increased amount of activated carbon, improvement of particle size distribution, change of packing density, lamination of activated carbon with different functions, etc.) Yes.

However, the enhancement of the sensor element package is in a trade-off relationship with the detection response of the detection target gas. That is, due to the improvement in the airtightness of the above-described package, the detection target gas is basically not allowed to enter from other than the gas inlet, similarly to the harmful gas and the interference gas. In addition, due to the improved function of the activated carbon adsorption layer, the time constant for the detection target gas in the atmosphere to pass through the activated carbon and reach the surface of the gas detection layer increases, leading to a decrease in detection response. Here, this detection responsiveness is obtained when the detection target gas is present inside the casing when the sensor element is provided inside the casing and the detection target gas having a predetermined concentration exists outside the casing. Time required to enter and contact the gas detection layer of the sensor element and reduce the electric resistance value of the gas detection layer to a predetermined electric resistance value (detection response time, that is, a detection target gas existing outside the housing) Reaches the sensor element provided inside the casing and is determined by the lower limit time during which it is possible to detect in the gas detection layer that the detection target gas is present above the concentration to be alarmed. For example, in Table 1, for a plurality of gas detection devices in which sensor elements are packaged, the time until the heater layer is energized is set to 5 s and an alarm is issued at an atmospheric methane concentration of 1.25% (12500 ppm). Shows the survey results. As can be seen from Table 1, the response at an atmospheric methane concentration of 1.25% is 15 to 25 s in the detection response time in the package having the conventional structure, whereas the detection response time is 45 when the package is strengthened. It can be seen that it has doubled to ~ 50s.
Therefore, if the sensor element package is strengthened, the influence of the non-detection target gas can be reduced, but the detection responsiveness of the detection target gas is lowered.

On the other hand, the criteria to be satisfied for the detection responsiveness are separately defined. For example, in the case of flammable methane gas as the detection target gas, the methane concentration in the atmosphere is 1.25%. It is said that it is necessary to be able to issue an alarm within 60 seconds (within the detection response regulation time) from the gas leak.
In such a situation, in addition to the relationship between the detection timing for detecting the electric resistance value of the gas detection layer corresponding to the cycle of energization to the heater layer and the timing of the occurrence of gas leakage, the detection response time is also taken into account. The time from the leak until the alarm is issued needs to be within the detection response regulation time. Therefore, if the detection responsiveness decreases (detection response time increases) due to the enhancement of the sensor element package, it may take a long time to issue an alarm, and the alarm cannot be issued within the specified detection response time. There's a problem.

  For example, as shown in FIG. 15, when the energization cycle of the gas detection device of the reinforced package with the detection response time 45 s is driven at 45 s (the detection timing comes every 45 s), the first detection timing (0 s) If a gas leak occurs simultaneously (Case 1), an alarm is issued 45 seconds after the second detection timing, and an alarm can be given within the detection response regulation time (60 s from the occurrence of the gas leak). If a gas leak occurs after 5 s after the detection timing (0 s) (Case 2), the detection response time has not elapsed at the second detection timing (45 s) after 40 s from the gas leakage. The detection target gas above the concentration that should be alarmed has not been detected, the alarm is not issued, and an alarm is issued at the third detection timing (90 s) after 85 s from the gas leakage. Which may not satisfy the response specified time. That is, in case 2, the time of 85 s has elapsed from the gas leak until an alarm is issued. Similarly, when a gas leak occurs after 25 s after the first detection timing (0 s) (case 3), the detection response time at the second detection timing (45 s) 20 s after the gas leakage. Therefore, the detection target gas above the concentration that should be alarmed is not detected, the alarm is not issued, and an alarm is issued at the third detection timing (90 s) 65s after the gas leakage. The response time may not be met. That is, in case 3, the time of 65 s has elapsed from the gas leak until the alarm is issued.

  For this reason, in the conventional gas detection device with battery driving in mind, the cycle in which the energization driving means energizes the heater layer includes a decrease in detection response (increase in detection response time) and a detection response regulation time due to package reinforcement. Considering, for example, when the specified detection response time is 60 s, the detection response time must be set to a relatively short time interval such as within 20 s when the detection response time is 40 s and within 10 s when the detection response time is 50 s. There is a problem that the energization cycle cannot be lengthened and hinders low power consumption.

  Therefore, in view of the above-described problems, the present invention eliminates the influence of non-detection target gas and detects power leakage while eliminating the influence of non-detection target gas. The purpose is to provide a technology capable of shortening the time from occurrence to issuing an alarm and issuing an alarm within the specified detection response time.

[Configuration 1]
The gas detection device according to the present invention for achieving the above object is
A sensor element in which a gas detection layer whose electrical characteristics are changed by contact with the detection target gas, and a heater layer for heating the gas detection layer;
The sensor element is provided inside a casing having a gas inlet through which the detection target gas can flow from the outside, and a non-detection target gas is provided in a flow path from the gas inlet to the inside of the casing. Filter means to which
Energization driving means for energizing the heater layer at a predetermined normal cycle to change the temperature of the gas detection layer;
Electrical resistance as the electrical characteristic of the gas sensing layer at the detection timing for the heater layer energized, a first determination for determining whether or not being lower than the first threshold value, use the first determination The detection target gas is detected by a second determination that determines whether or not the electric resistance value after the electric resistance value is lower than a second threshold value that is less than the first threshold value. a gas detecting means for,
Gas type determination means for determining a gas type present in the atmosphere of the gas detection layer based on the electrical characteristics of the gas detection layer when the heater layer is energized ;
An energization cycle changing unit that changes the normal cycle based on a detection result of the gas detection unit and a determination result by the gas type determination unit ,
The energization cycle changing means continues energization of the normal cycle when the electrical resistance value in the first determination is equal to or greater than the first threshold value,
When the electrical resistance value in the second determination exceeds the second threshold and the determination result of the gas type determination unit is the detection target gas, the normal period is less than the first threshold. To a shorter shortening cycle,
In the second determination, the gas detection unit is configured to issue an alarm when the electrical resistance value is equal to or less than the second threshold value .

Moreover, the gas detection method according to the present invention for achieving the above object is preferably executed by the gas detection device having the above-described characteristic configuration,
Using a sensor element in which a gas detection layer whose electrical characteristics change by contact with a detection target gas and a heater layer for heating the gas detection layer are formed,
The sensor element is provided inside a casing having a gas inlet through which the detection target gas can flow from the outside, and a non-detection target gas is provided in a flow path from the gas inlet to the inside of the casing. Is provided with filter means to which
The energization drive means energizes the heater layer at a predetermined normal cycle, changes the temperature of the gas detection layer,
Gas detection means, the electric resistance value as the electrical characteristic of the gas sensing layer at the detection timing for the heater layer energized, a first determination for determining whether or not being lower than the first threshold value, the A second determination is made as to whether or not the electric resistance value detected after the electric resistance value used for the first determination is lower than a second threshold value that is less than the first threshold value at a detection timing. The detection target gas is detected by the determination,
The gas type determination means determines the gas type present in the atmosphere of the gas detection layer based on the electrical characteristics of the gas detection layer when the heater layer is energized,
An energization cycle changing means is a gas detection method for changing the normal cycle based on a detection result of the gas detection means and a determination result by the gas type determination means ,
The energization cycle changing means continues energization of the normal cycle when the electrical resistance value in the first determination is equal to or greater than the first threshold value,
When the electrical resistance value in the second determination exceeds the second threshold and the determination result of the gas type determination unit is the detection target gas, the normal period is less than the first threshold. To a shorter shortening cycle,
In the second determination, the gas detection unit is configured to issue an alarm when the electrical resistance value is equal to or less than the second threshold value .

According to the gas detection device and the gas detection method of the above-described configuration 1, the gas detection unit performs the electrical resistance value based on the electrical resistance value of the gas detection layer at the detection timing before the gas type determination unit determines the gas type. Since the first determination of whether or not is lower than the first threshold value, the determination of the gas type by the gas type determination unit and the change of the energization cycle by the energization cycle change unit are the electrical resistances at the detection timing by the first determination. Based on the result of whether or not the value is lower than the first threshold value, for example, when the electric resistance value is lower than the first threshold value, there is a possibility that gas leakage has occurred Therefore, it is possible to detect the detection target gas in the normal cycle on the assumption that gas leakage does not occur when the detection is higher than the first threshold value.
Thereby, when a simple determination is performed by the first determination and it is considered that no gas leakage occurs, the determination with higher accuracy is omitted, thereby simplifying the configuration and reducing power consumption. be able to.
Furthermore, according to the gas detection device and the gas detection method of the first configuration, when the electric resistance value is lower than the first threshold value in the first determination, the gas detection unit is further used in the first determination. Using the electric resistance value as the electric characteristic at the detection timing detected after the electric resistance value, a second value indicating whether the electric resistance value is equal to or smaller than a second threshold value (alarm threshold value) that is smaller than the first threshold value. Since the determination is performed, when it is determined in the first determination that there is a possibility of gas leakage, the second determination is performed based on the second threshold with higher accuracy, and it is possible to determine more accurately whether or not there is gas leakage. It becomes possible. In this second determination, among the electric resistance values at the detection timing, an electric resistance value in a stable state that is detected after the electric resistance value used in the first determination is used, and more severe than the first threshold value. Since the reference second threshold value is used, a determination with higher accuracy than the first determination can be performed. For example, in the second determination, if the electrical resistance value is less than or equal to the second threshold value, a gas leak alarm is issued assuming that a gas leak has occurred, and if it exceeds the second threshold value, has a gas leak occurred? Since it is not possible to determine whether or not, in order to make a more accurate determination, the gas type determination unit can determine the gas type.

[Configuration 2]
In addition to the configuration of the gas detection device of the above configuration 1, the gas detection device according to the present invention is characterized in that the detection target gas existing outside the casing is provided inside the casing. Reaching the sensor element, the lower limit of the time during which it is possible to detect that the gas to be detected is present in a concentration that should be alarmed in the gas detection layer is the detection response time,
The time required to detect the detection target gas existing outside the casing in the gas detection layer of the sensor element provided inside the casing is set as a detection response regulation time,
Before Symbol detection timing, the detection response time or more, the probe response defined as the time becomes shorter set within the time band than on the basis of the determination result by the gas type determination means, the energizing cycle changing means Is that the normal period is changed to the shortened period.

Further, gas detection method according to the present invention, which is preferably performed by gas detecting device having the above construction, in addition to the means of gas detection method having the aforementioned configuration 1, its features means conductible period Based on the determination result by the gas type determination unit, the change unit reaches the sensor element in which the detection target gas existing outside the casing reaches the sensor element, The detection target that exists in the outside of the casing and has a detection response time that is a lower limit of the time during which it is possible to detect that the detection target gas is present in a concentration that should be alarmed in the gas detection layer. gas, so that the casing the time required to detect in the sensor element provided inside a probe response defined time shorter than has been the time zone, the normal cycle It lies in the fact that changes to the serial shortening cycle.

According to the gas detection device and the gas detection method of the above configuration 2, the sensor element (gas detection layer) is provided inside the casing, and the detection target gas flows from the outside via the inlet and the filter means of the casing.
When the detection target gas is detected in the gas detection device whose package is reinforced to enter, the detection timing for detecting the detection target gas is determined after detecting the gas type present in the atmosphere of the gas detection layer. Since the normal period is changed so that it is within the time zone set for more than the time and shorter than the detection response regulation time, the detection timing can be changed only when necessary according to the gas type, and it has been changed. At the detection timing, it is possible to detect the detection target gas so as not to exceed the detection response regulation time.
Here, the detection response time is greater than the concentration at which the detection target gas existing outside the casing reaches the sensor element provided inside the casing and the detection target gas should alarm in the gas detection layer. The gas detection device with the package strengthened as described above tends to have a longer time than a gas detection device with no package reinforcement. is there. Further, the detection response regulation time is a time required to detect the detection target gas existing outside the casing in the gas detection layer of the sensor element provided inside the casing. In addition, the detection response time can use what was measured beforehand about each gas detection apparatus, and detection response regulation time is predetermined by the law etc.
For example, as shown in FIG. 5, when the energization cycle of the gas detection device of the reinforced package with a detection response time of 45 s is driven at a normal cycle of 45 s (a cycle in which detection timing comes every 45 s), the first detection timing (0 s) When a gas leak occurs (case 1) at the same time, a warning is given within the detection response regulation time 45 seconds after the second detection timing (within 60 seconds from the occurrence of the gas leak). On the other hand, if a gas leak occurs after 5 s after the first detection timing (0 s) (case 2), the detection response time at the second detection timing (45 s) after 40 s from the gas leakage. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is issued, the gas type determination means determines the gas type as necessary (for example, the detection target gas exists) In this case, by shortening the energization to the heater layer from the normal cycle 45 s to the shortened cycle 10 s, it is possible to warn at the third detection timing (55 s) after 50 s from the gas leak, and from the gas leak Since only 50 s has elapsed until the is issued, the detection response regulation time can be satisfied. Similarly, if a gas leak occurs after 25 s after the first detection timing (0 s) (case 3), the detection response time elapses at the second detection timing (45 s) 20 s after the gas leak. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is issued, the gas type determination means determines the gas type as necessary (for example, when the detection target gas exists) In addition, by shortening the energization to the heater layer from the normal period 45 s to the shortened period 10 s, it is possible to give an alarm at the fifth detection timing (75 s) after 50 s from the gas leak, and issue an alarm from the gas leak. Since only the time of 50 s has passed, the specified detection response time can be satisfied. In case 3, since the detection response time has not elapsed at the third and fourth detection timings, the detection target gas having a concentration higher than the alarm level is not detected, and no alarm is issued.
Therefore, it is possible to detect the presence and concentration of the detection target gas more accurately by eliminating the influence of the non-detection target gas using the gas detection device with an enhanced package, and it is necessary depending on the gas type. Only in such a case, the normal cycle is changed (the detection timing is changed) to prevent the change from being made unnecessarily, and the power consumption can be reduced. In addition, the alarm can be issued within the specified detection response time by minimizing the time from the occurrence of gas leakage until the alarm is issued.
Furthermore, according to the gas detection device and the gas detection method of the above-described configuration 2, the energization cycle changing means includes a normal cycle within a time period in which the detection timing is set to be longer than the detection response time and shorter than the detection response regulation time. If the determination result by the gas type determination means is the detection target gas, the normal cycle for energizing the heater layer is changed to a shortened cycle shorter than this normal cycle, so there is a detection target gas. Thus, only when it is necessary to perform detection with higher accuracy, detection can be performed by changing the energization of the heater layer to a shortened cycle. On the other hand, when there is no detection target gas, the normal cycle is maintained. Detection can be performed to reduce power consumption. In addition, even when the detection response time is long in the gas detection device with an enhanced package, the detection target gas can be detected earlier by detecting the detection timing gas by reducing the detection timing cycle. It is possible to reliably shorten the time until the detection response specified time.
Therefore, in detecting the presence and concentration of the detection target gas, it is possible to eliminate the influence of the non-detection target gas and reduce the power consumption more reliably, but the time from the occurrence of the gas leak until the alarm is issued. The alarm can be issued more reliably within the specified detection response time.

[Configuration 3]
  The gas detection device according to the present invention is characterized in that, in addition to the configuration of the gas detection device according to the first or second configuration, the gas detection device is configured such that after the energization cycle changing unit changes the normal cycle to the shortened cycle, The means is that the second determination is made based on the electric resistance value at the detection timing in the shortening period.

  The gas detection method according to the present invention is preferably executed by the gas detection device having the above-described characteristic configuration. In addition to the means for the gas detection method of the above-described configuration 1 or 2, the characteristic means includes The gas detection unit is configured to perform the second determination based on the electrical resistance value at the detection timing in the shortening cycle after the energization cycle changing unit changes the normal cycle to the shortening cycle. It is in.

  According to the gas detection device and the gas detection method of the configuration 3, after the energization cycle changing unit changes the normal cycle to the shortened cycle, the gas detection unit performs the electrical resistance value at the detection timing in the shortened cycle. Based on the above, the second determination can be performed.

[Configuration 4 ]
Gas detecting apparatus according to the present invention, in addition to the gas detecting device having the above structure 1 or 2, its characteristic configuration, after the previous SL energization cycle changing means to change the normal cycle the shortening period, the the gas detection unit in the detection timing in the shortened cycle based on electrical resistance, have a row the first determination of whether the electric resistance value is lower than the first threshold value, then the second The point is that the determination is made .

Further, gas detection method according to the present invention, which is preferably performed by gas detecting device having the above construction, in addition to the means of gas detection method having the aforementioned configuration 1 or 2, its features means, before after serial energization cycle changing means changes the said normal cycle the shortening period, on the basis of the electric resistance the gas detection unit in the detection timing in the shortened period, the electric resistance than the first threshold value there line the first determination of whether or not reduced, then there is in that is configured to perform the second determination.

According to the gas detection device and the gas detection method of the above configuration 4 , when the electric resistance value exceeds the second threshold value in the second determination, the gas type is determined, and when the determination result is the detection target gas, change the normal period shorter period, have first row determines whether the electrical resistance value detected is lower than the first threshold value in detection timing on Speed cycle after the change, then, the first 2 determines the line Unode, or to continue the detection remains shorter period, or to continue the detection back to the normal cycle can be determined based on the first determination result. For example, if the electrical resistance value is not lower than the first threshold value in the first determination, the first determination and the second determination are repeated by returning to the normal cycle, and if it is equal to or lower than the first threshold value, It is possible to continue the detection of the detection target gas by keeping the shortened period and further performing the second determination.
Therefore, power consumption can be reduced by continuing energization with a shortened period only when necessary, and returning to energization with a normal period if not necessary.

[Configuration 5 ]
The gas detection device according to the present invention is characterized in that, in addition to the configuration of the gas detection device according to any one of the above configurations 1 to 4 , the gas type determination unit is configured to detect the gas detection layer when the heater layer is energized. It is the point which determines the gas kind which exists in the said atmosphere using the change state of an electrical resistance value as an electrical property.

According to the gas detection device of the above configuration 5 , since the gas type existing in the atmosphere is determined using the change state of the electric resistance value of the gas detection layer when the heater layer is energized, it is methane gas that is the detection target gas. Or whether the gas is other than methane gas (carbon monoxide, hydrogen, etc.).
Here, when the gas type is methane gas, for example, as shown in FIG. 3, the relationship between the energization time and the electric resistance value during energization of the heater layer is such that the electric resistance value gradually decreases as time passes. It draws a trajectory that stabilizes toward a predetermined value.
On the other hand, when the gas type is a gas other than methane gas, for example, as shown in FIG. 3, the relationship between the energization time and the electric resistance value when the heater layer is energized decreases asymptotically as time elapses. Then, a trajectory that turns asymptotically increasing after a predetermined minimum value is drawn. This asymptotic decrease is caused by gas such as carbon monoxide and hydrogen adsorbed on the gas detection layer of the sensor element being burned when the heater layer is energized and the temperature of the gas detection layer rises. It is what.
Therefore, in determining the gas type in the atmosphere of the gas detection layer, the gas type can be accurately and easily determined by examining what path the energization time and electrical resistance value at the time of energizing the heater layer draw. Can be determined.

[Configuration 6 ]
In addition to the configuration of the gas detection device of Configuration 5 , the gas detection device according to the present invention is characterized in that a plurality of the electrical resistance values are used to determine a gas type using the change state of the electrical resistance value. The difference is that the difference between the two is used.

According to the gas detection device having the above configuration 6, the gas type can be determined by a change in the electric resistance value in a short time, and therefore the gas type can be determined more easily.
That is, since the relationship (trajectory) between the energization time of the gas other than methane gas and the electrical resistance value has a portion that increases asymptotically from the minimum value as described above, a plurality of electrical resistance values are extracted and the difference (energization time). If the difference is positive, it can be immediately determined that the gas is other than methane gas.

[Configuration 7 ]
In addition to the configuration of the gas detection device of the above configuration 5 , the gas detection device according to the present invention is characterized in that the electrical resistance value is minimized when the gas type is determined using the change state of the electrical resistance value. The point is to use the occurrence of the value.

According to the gas detector of the said structure 7 , since a gas type can be determined by the change of the electrical resistance value in a short time, a gas type can be determined more simply.
That is, since the relationship (trajectory) between the energization time and the electrical resistance value of gases other than methane gas has a minimum value as described above, this minimum value appears by extracting the appearance (existence) of this minimum value. In the case of (present), it is possible to immediately determine the gas type as a gas other than methane gas. Since this minimum value appears relatively early in time when the heater layer is energized, the gas type can be determined in a short time. In the case of methane gas, there is no minimum value because the electric resistance value is stabilized at a predetermined value.

[Configuration 8 ]
The gas detector according to the present invention is characterized in that, in addition to the configuration of the gas detector of configuration 5 described above, the characteristic configuration is that when the gas type is determined using the change state of the electrical resistance value, The difference is that the second-order differential value and the second-order differential value are used.

According to the gas detection device having the above-described configuration 8, the gas type can be determined based on the change in the electric resistance value in a short time, and therefore the gas type can be determined more easily.
In other words, the relationship (trajectory) between the energization time of the gas other than methane gas and the electric resistance value increases so as to draw an asymptotic line that gradually rises from the minimum value and asymptotically approaches a constant value. The trajectory. On the other hand, in the case of methane gas, which is a detection target gas, the electric resistance value decreases so as to draw an asymptotic line that asymptotically approaches a constant value. Thus, since the electric resistance value of methane gas shows a different locus from the electric resistance values of other gases, the gas type can be determined by obtaining the first-order differential value and the second-order differential value.
That is, the relationship (trajectory) between the energization time of the gas other than methane gas and the electric resistance value becomes a locus having a shape that increases while drawing an asymptotic line after the appearance of the minimum value, and therefore, 1 after the appearance of the minimum value. The second order differential value is a positive value, and the second order differential value is a negative value. On the other hand, in the case of methane gas, which is the detection target gas, the trajectory decreases so as to draw an asymptotic line after the appearance of the minimum value while descending, and therefore the first-order differential value is 0 or less without the appearance of the minimum value. The value is maintained and the second-order differential value is 0 or more. Therefore, the gas type can be determined by confirming the positive / negative relationship between the first-order differential value and the second-order differential value.

[Configuration 9 ]
In addition to the configuration of the gas detection device of the above configuration 5 , the gas detection device according to the present invention is characterized in that the gas type is determined using the change state of the electrical resistance value at a plurality of detection timings. The electrical resistance value is used.

According to the gas detector of the above configuration 9, the gas type can be determined based on the change in the electric resistance value in a short time, and therefore the gas type can be determined more easily.
In other words, the relationship (trajectory) between the energizing time of the gas other than methane gas and the electrical resistance value is a trajectory that increases so as to draw an asymptotic line that gradually rises from the minimum value and gradually approaches a certain value after the appearance of the minimum value. It becomes. On the other hand, in the case of methane gas, which is the detection target gas, it becomes a trajectory that draws an asymptote that ascends to a constant value while descending. Therefore, the first-order differential value of a gas other than methane gas becomes a positive value after the appearance of the minimum value, whereas the first-order differential value of methane gas is a value of 0 or less. Thereby, the gas type can be determined by the first-order differential value of the electrical resistance value. Further, by determining the gas type based on the first-order differential values at a plurality of detection timings rather than the first-order differential value at one detection timing of the electrical resistance value, it is possible to eliminate erroneous determination due to measurement errors, noises, etc. Can be accurately determined.

[Configuration 10 ]
The gas detection device according to the present invention is characterized in that, in addition to the configuration of the gas detection device according to any one of the configurations 1 to 9 , the gas detection device includes the sensor element including an electrical insulating layer and an oxide semiconductor. It is a thin film sensor element provided with the layer and a pair of electrode layer which detects the electrical resistance value as the said electrical characteristic of the said gas detection layer.

According to the gas detection device having the above configuration 10 , since the sensor element is formed of a thin film sensor element, the heat capacity of the gas detection layer constituting the thin film sensor element is very small, and heat input from the heater layer In contrast, it can be configured to be very responsive.

[Configuration 11 ]
The gas detector according to the present invention is characterized in that, in addition to the configuration of any of the gas detectors 1 to 10 described above, the characteristic configuration is driven by power supply from a built-in battery.

According to the gas detection device having the above-described configuration 11 , the gas detection device is driven by power supply from a built-in battery, so that it is not necessary to install the gas detection device in the vicinity of a fixed power source, and the installation property is improved.
In the gas detection device, the heater layer is energized in a cycle in which the energization time is as short as possible, the energization cycle is shortened only when necessary, and a normal cycle having the longest period is employed when not necessary. Therefore, power consumption is reduced, and even when a built-in battery is used, it is possible to configure a gas detection device that can continue to operate sufficiently for a predetermined period.

The figure which shows the schematic structure of the detection system of a gas detector Diagram showing the specific structure of the gas detector The graph which shows the relationship between the energization time to a heater layer, and an electrical resistance value The flowchart which shows the 1st determination which concerns on 1st Embodiment, 2nd determination, gas kind determination, and the change of a normal period The conceptual diagram which shows time from shortening of the normal period which concerns on 1st Embodiment, and issuing a warning after gas leak generation | occurrence | production The graph which shows the relationship between the time from the gas leak occurrence to the alarm and the delay time from the detection timing to the gas leak occurrence when the normal cycle is changed or not The conceptual diagram which shows time from shortening of the normal period which concerns on 2nd Embodiment, and issuing a warning after gas leak generation | occurrence | production Flow chart showing first determination, second determination, gas type determination and change of normal period according to the third embodiment The figure which shows the detection range of the electrical resistance value for the gas type determination which concerns on 4th Embodiment The figure which shows an example of the detection point of two electrical resistance values for the gas type determination which concerns on 5th Embodiment The figure which shows an example of the detection point of the electrical resistance value of 3 points | pieces for gas type determination which concerns on 5th Embodiment The figure which shows an example of the detection point of four electrical resistance values for the gas type determination which concerns on 5th Embodiment Flow chart showing second determination, gas type determination and change of normal cycle according to another embodiment The flowchart which shows the 1st determination which concerns on another embodiment, the change of energization time, the 2nd determination, gas type determination, and the change of a normal period Conceptual diagram showing time from conventional gas leak occurrence to alarm

[First Embodiment]
Hereinafter, the first embodiment of the gas detection device 100 according to the present invention will be described in detail.
As shown in FIG. 1, the gas detection device 100 includes a thin film sensor element (sensor element) in which a gas detection layer 10 whose electrical characteristics are changed by contact with a detection target gas and a heater layer 6 that heats the gas detection layer 10 are formed. Example) 20, energization driving means 12 for energizing the heater layer 6 in a predetermined normal cycle to change the temperature of the gas detection layer 10, and the gas detection layer when the heater layer 6 is energized (detection timing) The gas detection means 13 for detecting the detection target gas based on the electrical resistance value 10 (an example of electrical characteristics) and the electrical resistance value of the gas detection layer 10 when the heater layer 6 is energized (an example of electrical characteristics) The gas type determination means 14 for determining the gas type present in the atmosphere of the gas detection layer 10 based on the above, and the predetermined normal period is shortened from the normal period according to the determination result of the gas type by the gas type determination means 14 Shortening cycle Energization cycle changing means 15 for changing, constituted by a these power supplies lithium battery (not shown).
Moreover, in the gas detection apparatus 100, as shown in FIG. 2, the thin film sensor element 20 is provided in the inside of the housing | casing 31 provided with the inflow port 30 which can flow in detection object gas. An activated carbon adsorbing layer (an example of a filter unit) 32 to which a non-detection target gas adheres is provided in the flow path to the inside of the thin film sensor element. Therefore, the thin film sensor element 20 is connected to the thin film sensor element 20 from the outside through the inlet 30. The gas detection device 100 is packaged in a state where portions other than the inlet 30 are sealed.
As will be described later, in the gas detection device 100, the detection target gas is, for example, methane gas. Basically, the heater layer 6 is energized intermittently at a predetermined cycle, and the heater is heated. It is configured to detect methane gas in a state where the electric resistance value of the gas detection layer 10 is relatively stable (in FIG. 3, when 200 ms has elapsed since the start of energization) in a high temperature state just before the end of energization of the layer 6. ing.

  1 and 2 are diagrams showing a schematic configuration of the gas detection device 100, and FIG. 3 is a diagram illustrating the methane gas contained in the air at a concentration of 1000 ppm and 4000 ppm in the air when the heater layer 6 is energized. FIG. 4 shows the relationship between the energization time and the electrical resistance value of methane gas contained at a concentration of 500 ppm, hydrogen gas contained at a concentration of 4000 ppm in air, and carbon monoxide gas contained at a concentration of 500 ppm in air. The flow which shows the change of gas detection (1st determination and 2nd determination), gas type determination, and an electricity supply period is shown.

[Thin film sensor element]
FIG. 1 shows the structure of a thin film sensor element 20 used in the embodiment of the present invention.
The thin film sensor element 20 has electrical characteristics as a result of at least one of the presence and concentration of the detection target gas on the support substrate having a diaphragm structure in which the outer peripheral part or both ends of the thin support layer 5 are supported by the Si substrate 1. The gas detection layer 10 in which the electrical resistance value changes and the heater layer 6 for heating the gas detection layer 10 are formed.

Next, the detailed structure and manufacturing method of the thin film sensor element 20 will be described.
The thin film sensor element 20 is configured by providing a support layer 5 in which a thermal oxide film 2, a Si ₃ N ₄ film 3 and a SiO ₂ film 4 are sequentially laminated on a Si substrate 1 by a semiconductor process. A heater layer 6 is provided on the insulating layer 7, and an insulating layer (an example of an electrical insulating layer) 7 made of a SiO ₂ film is provided on the upper side of the heater layer 6, and a pair of electrodes is provided on the insulating layer 7. A layer 9 is provided, and a gas detection layer 10 is provided on the pair of electrode layers 9 and across the electrode layers 9. Further, in the case of the example shown in FIG. 1, the selective combustion layer 11 is provided in a form covering the entire pair of electrode layers 9 and the gas detection layer 10. The thickness of each layer is about 0.1 to 50 μm. The power consumption during a period required for one gas detection by the thin film sensor element 20 is less than 8.0 mJ until the temperature of the gas detection layer 10 reaches a predetermined high temperature state after energization is started. The response time of the thin film sensor element 20 is 50 to 100 ms.
The gas detection layer 10 is formed by forming, for example, an n-type semiconductor of tin oxide (SnO ₂ ) by a sputtering method or the like.

The selective combustion layer 11 is configured by supporting a catalyst on a carrier made of a metal oxide, and is configured in a layered manner by bonding metal oxides supporting the catalyst to each other via a binder.
As the catalyst, palladium (Pd), platinum (Pt), rhodium (Rh), or the like that can oxidize and remove a reducing gas that also serves as an interference gas with respect to the detection target gas is used.
Examples of the metal oxide constituting the support include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), tungsten oxide (WO ₃ ), and zinc oxide. (ZnO), titanium oxide (TiO ₂ ), iron oxide (Fe ₂ O ₃ ), copper oxide (CuO), or a mixture thereof can be used.
Moreover, as a binder which couple | bonds said metal oxide (metal oxide which carry | supports a catalyst), an alumina fine powder, an alumina sol, a silica fine powder, a silica sol, and magnesia can be used, for example.
Here, any of the above catalysts, metal oxides, and binders may be used alone or in combination of two or more.

The thin film sensor element 20 is manufactured as follows.
As shown in FIG. 1, a Si ₃ N ₄ film 3 and a SiO ₂ film 4 are sequentially formed by plasma CVD on a Si substrate 1 having a thermal oxide film 2 on both sides as a support layer 5 having a diaphragm structure. To do. Next, the heater layer 6 is formed in the center portion of the diaphragm structure, and the SiO ₂ insulating layer 7 is formed in this order so as to cover the heater layer 6 by sputtering. A pair of bonding layers 8 is formed thereon, and a pair of electrode layers 9 is formed on the bonding layer 8. Film formation is performed by an ordinary sputtering method using an RF magnetron sputtering apparatus. The film formation conditions are the same for both the bonding layer (Ta or Ti) 8 and the electrode layer (Pt or Au) 9. The Ar gas pressure is 1 Pa, the substrate temperature is 300 ° C., the RF power is 2 W / cm ² , and the film thickness is, for example, the bonding layer 8. / Electrode layer 9 = 500 cm / 2000 mm.

Next, an SnO ₂ film, which is the gas detection layer 10, is formed on the pair of electrode layers 9 and over the electrode layers 9. The film formation is performed by a reactive sputtering method using an RF magnetron sputtering apparatus. SnO ₂ having 0.5% by mass of Sb is used for the target. The film formation conditions are Ar gas pressure of 2 Pa, substrate temperature of 150 to 300 ° C., and RF power of 2 W / cm ² . The size of the gas detection layer 10 is preferably about 50 to 200 μm square, and the thickness is preferably about 0.2 to 1.6 μm, for example.

On the gas detection layer 10, a support made of a porous metal oxide such as Al ₂ O ₃ or Cr ₂ O ₃ is loaded with a noble metal oxidation catalyst such as Pd or Pt, and selected in a paste form with an inorganic binder and a solvent. The selective combustion layer 11 is formed so as to cover the entire gas detection layer 10 by applying the combustion layer material by screen printing and baking at 500 ° C. for 1 hour or longer. The selective combustion layer 11 needs to be formed in a size that sufficiently covers the entire gas detection layer 10. Finally, Si (silicon) is removed from the back surface of the Si substrate 1 by etching to form a diaphragm structure.
The role of the selective combustion layer 11 is to burn a reducing gas (non-detection target gas) such as hydrogen gas, carbon monoxide gas, and alcohol gas other than methane gas, which is the detection target gas, so as not to reach the gas detection layer 10. The thin film sensor element 20 has gas selectivity. Further, it is considered that oxygen is supplied to the surface of the gas detection layer 10 to play a role of improving sensitivity.
The supported amount of the noble metal oxidation catalyst such as Pd or Pt contained in the selective combustion layer 11 is 5 to 9% by mass (catalyst mass / (catalyst + support) mass × 100).

[Case, activated carbon adsorption layer]
As shown in FIG. 2, the housing 31 accommodates therein a disk-like base 31 a on which the thin film sensor element 20 can be mounted and fixed, and the thin film sensor element 20 mounted and fixed on the base 31 a. And a cylindrical cap 31b that can be used. The casing 31 has a gas flow in which one end of a cap 31b is welded to a base 31a in which the thin film sensor element 20 is provided, and a gas to be detected can flow into the other end of the cap 31b from the outside. An inlet 30 is formed and configured. The gas inflow port 30 is stretched with a metal mesh such as stainless steel so that the detection target gas can flow in. Therefore, the casing 31 is packaged in a sealed state so that it is difficult for the detection target gas and the non-detection target gas to enter and exit from other than the gas inlet 30. The cap 31b may be a metal cap made of stainless steel or the like to enhance the packaging of the thin film sensor element 20, but may be fixed by a plug-in type as a cap made of resin or the like. The base 31a is supported by a plurality of stems penetrating the front and back of the base 31a.
Further, an activated carbon adsorbing layer 32 for adsorbing and removing the non-detection target gas is supported and fixed by a metal net 33 for activated carbon such as stainless steel at a location inside the casing 31 that has passed through the metal mesh as the gas inlet 30 from the outside. It is provided in the state that was done.
The activated carbon adsorbing layer 32 is formed of, for example, activated carbon, silica gel, or a material combining these activated carbon and silica gel.
A configuration in which non-detection target gas (for example, gas of organic solvent such as alcohol, silicon vapor, NOx) or the like contained in the gas flowing into the cap 31b from the gas inlet 30 is adsorbed and removed by the activated carbon adsorption layer 32. It has become. The activated carbon adsorption layer 32 can be configured to strengthen the package of the thin film sensor element 20 by adjusting the amount of activated carbon, improving the particle size distribution, changing the packing density, stacking activated carbons having different functions, and the like. . For example, it can be configured as various packages as shown in Table 1. As described above, when the package of the thin film sensor element 20 is strengthened, the influence of the non-detection target gas can be reduced, but the detection responsiveness of the detection target gas is reduced. The detection response time is that the detection target gas existing outside the casing 31 reaches the thin film sensor element 20 provided inside the casing 31 and the gas detection layer 10 should alarm the detection target gas. This is the lower limit time during which it is possible to detect the presence of the concentration or higher, and the gas detection device 100 with the package strengthened as described above has a longer time than the gas detection device 100 with no package reinforcement. Tend to be.
Here, in the example shown in FIG. 5 and FIG. 7 in the present embodiment, as the package of the thin film sensor element 20, standard activated carbon having a reinforced structure shown in Table 1 is doubled in thickness (twice the normal thickness), A metal cap welding type configuration is adopted, and a detection response time of 45 s is adopted.

[Energization drive means]
Next, the energization driving means 12 intermittently performs pulsed energization to the heater layer 6 at a predetermined normal cycle, and repeatedly changes the temperature of the gas detection layer 10 between a high temperature state and a low temperature state. It is configured to be able to. In this pulse energization, for example, an interval from the pulse energization to the next pulse energization is set to a period of 45 s, and among the 45 s, the heater layer energization is performed for 200 ms and not performed for 44.80 s. It can be performed intermittently (repetitively). That is, the detection timing in FIG. 5 exists at an interval (a period of 45 s) from the pulse energization to the next pulse energization.
Further, when the energization driving unit 12 receives an energization cycle change signal for changing the energization cycle from the energization cycle changing unit 15 described later, the normal cycle can be set to a shortened cycle shorter than the normal cycle. It is configured. The pulse energization at this time is, for example, an interval from the pulse energization to the next pulse energization being a 10 s period, of which the heater layer energization is performed for 200 ms and not performed for 9.80 s. In addition, it can be performed intermittently (repeatedly) (see FIGS. 3 and 5).
Here, the said high temperature state which can detect methane gas favorably can be set according to detection object gas, for example, in the case of methane gas, it is set as 350 to 450 degreeC (high temperature state). It can be detected with high accuracy.
Further, when the energization driving unit 12 heats the heater layer 6 to a high temperature state, the ambient temperature of the thin film sensor element 20 is detected and corrected according to the ambient temperature, and then the heater layer 6 is moved to. It is preferable to control energization. Thereby, the temperature of the heater layer 6 can be accurately heated to a high temperature state by appropriate energization.

[Gas detection means]
The gas detection means 13 detects the detection target gas based on the electric resistance value of the gas detection layer 10 in a state (high temperature state) where the temperature of the gas detection layer 10 has reached a temperature at which the detection target gas can be detected with high accuracy. It is configured so that presence or absence and concentration can be detected. That is, as the gas detection layer 10 is heated to a high temperature in the presence of methane gas when the heater layer 6 is energized, the electric resistance value of the gas detection layer 10 decreases and approaches a predetermined electric resistance value and stabilizes. By using this stabilized electrical resistance value, the presence or concentration of methane gas and the concentration can be detected accurately and accurately. The electric resistance value means an electric resistance value of a variable resistor among a fixed resistor and a variable resistor provided in series in the thin film sensor element 20.
Specifically, as shown in FIG. 3, in the present embodiment, within the time period from the start of energization by the energization driving means 12 until the elapse of 200 ms when the energization to the heater layer 6 ends, Since the stabilized electric resistance value is obtained when 200 ms has passed, just before the energization of the heater layer 6 is completed, methane gas is set to be detected when this 200 ms has passed (upper part of FIG. 3). And described as second determination). Therefore, the electric resistance value when methane gas is present or absent in the atmosphere of the gas detection layer 10 and the electric resistance value when methane gas of a specific concentration is present in the atmosphere (for example, in the air) are previously gasified. By setting for each detection device (thin film sensor element) and comparing this setting result with the electric resistance value detected when 200 ms elapses from the start of energization, the presence or concentration of methane gas can be detected. For example, the electrical resistance value detected when 200 ms elapses from the start of energization is lower than the alarm threshold for methane gas leakage (electric resistance value when methane gas is present in the air at a concentration of about 2000 ppm: an example of the second threshold value). If it is present (such as when methane gas is present in the air at a concentration of 4000 ppm), gas leakage can be detected as methane gas leaking.
On the other hand, the gas detection unit 13 uses the electric resistance value at the time of 200 ms, which is just before the energization by the energization driving unit 12 is started and the energization to the heater layer 6 is finished, that is, before performing the second determination, that is, After energization is started, the first determination can be performed using the electrical resistance value detected before the second determination is performed. In this case, in the second determination described above, the first determination is performed using the first threshold value of the electrical resistance value that is larger than the alarm threshold value as the second threshold value. Can be performed prior to the second determination. As a result, when it is considered that a simple determination is made based on the first determination and no gas leakage has occurred, a more accurate determination (second determination or the like) is omitted, thereby simplifying the configuration and consuming. Electric power can be reduced.
Specifically, as shown in FIG. 3, in the first determination, when the electrical resistance value detected when 100 ms has elapsed from the start of energization is lower than the first threshold value, it is necessary to perform the second determination. Judge as a thing. Here, the first threshold value is, for example, a case where methane gas having a relatively low concentration (for example, about 1000 ppm) is present in the air, and hydrogen gas (for example, about 4000 ppm) or carbon monoxide gas (for example, about 1000 ppm) in the air. The electric resistance value is set so that it can be discriminated to some extent from the case where a gas other than methane gas such as about 500 ppm) is present, and the timing at which the first determination is performed is such that the first threshold value is as described above. Is set to an elapsed time from the start of energization of the heater layer 6 (about 100 ms in FIG. 3). As a result, when the electrical resistance value is not lower than the first threshold value, although the accuracy is low, it is determined that air or a relatively low concentration of methane gas is present, and no alarm is required. 2 can be omitted. On the other hand, if the electrical resistance value is low, it is determined that there is a high possibility that a gas other than methane gas or a relatively high concentration of methane gas is present, and a higher accuracy is obtained. 2 determinations can be made.
Therefore, in this embodiment, the gas detection means 13 is comprised so that 1st determination by a 1st threshold value may be performed and 2nd determination may be performed as needed. Note that, according to the result of the second determination, the gas type determination unit 14 described later determines the gas type.

[Gas type determination means]
The gas type determination means 14 changes the electrical resistance value just after the start of energization to the heater layer 6 (for example, about 20 to 200 ms, preferably about 20 to 100 ms, more preferably about 20 to 80 ms). Based on a state, it is comprised so that the kind of gas which exists in the atmosphere of the gas detection layer 10 can be detected. Here, as shown in FIG. 3, the relationship (change state) between the energization time and the electrical resistance value when the heater layer is energized is as follows: when the gas type contained in the air is methane gas, the electrical resistance value increases with time. Asymptotically decreases and stabilizes to a predetermined value. On the other hand, when the gas species contained in the air is other than methane gas, the electrical resistance value decreases asymptotically as time passes, resulting in a predetermined minimum. It draws a trajectory that turns to an asymptotic increase through a value. Therefore, when the gas type determination means 14 determines the gas type in the atmosphere of the gas detection layer 10, it is examined what kind of locus the locus of the energization time and the electric resistance value at the time of energizing the heater layer is drawn. Thus, it is possible to accurately and simply determine the gas type (methane gas as a detection target gas, carbon monoxide gas other than methane gas, hydrogen gas, or the like).

Specifically, the gas type contained in the air is determined based on the difference between a plurality of electrical resistance values when the heater layer is energized.
That is, as shown in FIG. 3, when the time from the start of energization to the heater layer 6 to the end of energization is 200 ms, the electric resistance value is a gas other than methane gas (carbon monoxide, hydrogen). Since, for example, asymptotically increases after about 40 ms from the start of energization until about 100 ms elapses, there are two points of electrical resistance values between 40 ms and 100 ms (for example, 40 ms and 60 ms). When the value (difference) obtained by subtracting the shorter electrical resistance value from the electrical resistance value with the longer energization time is positive, there is a gas other than methane gas. Then it can be determined. On the other hand, since the electric resistance value in the case of methane gas decreases and stabilizes asymptotically between 40 ms and 100 ms, it can be determined that methane gas exists when the difference is negative. In FIG. 3, the electrical resistance value when methane gas is contained in the air at a concentration of 1000 ppm is stabilizing near the first threshold value. In the above, the difference was taken using the two electrical resistance values, but the difference between the three or more electrical resistance values may be taken, and the gas type is determined by detecting the slope from the differential value of the electrical resistance value. May be.

Moreover, the gas type contained in the air can also be determined based on the presence of the minimum value when the heater layer is energized.
That is, when the time from the start of energization to the heater layer 6 to the end of energization is 200 ms as shown in FIG. 3, the electrical resistance value in the case of a gas other than methane gas (carbon monoxide, hydrogen) is Asymptotically decreases from the start of energization, for example, reaches a minimum value until about 40 ms elapses after about 20 ms elapses, and increases asymptotically until about 100 ms elapses after about 40 ms elapses. Therefore, the electrical resistance value at three points (for example, at 20 ms, 40 ms, 60 ms, etc.) is detected, and among these electrical resistance values, the electrical resistance value at 40 ms is the smallest value, and so on. When the electric resistance value has a minimum value between the hour and 60 ms, it can be determined that a gas other than methane gas exists. On the other hand, the electrical resistance value in the case of methane gas decreases asymptotically and stabilizes within 100 ms from the start of energization, so there is no minimum value, and the above three points (for example, 20 ms, 40 ms, 60 ms) )) Does not have a minimum value, it can be determined that methane gas is present. In this case, four or more electrical resistance values may be taken, and the gas type may be determined by detecting the slope from the differential value of the electrical resistance value.

[Energization cycle changing means]
The energization cycle changing means 15 is configured to change a predetermined normal cycle to a shortened cycle shorter than the normal cycle. That is, when the determination result is methane gas as the detection target gas, the energization cycle changing unit 15 changes the normal cycle to the shortened cycle according to the determination result of the gas type by the gas type determination unit 14, while the determination result When the gas is a gas other than methane gas, the normal period is maintained as it is. As a result, it is possible to determine whether or not to shorten the energization period according to the gas type present in the atmosphere of the gas detection layer 10, and therefore the normal period is shortened only when shortening is necessary according to the gas type. Thus, methane gas can be detected. For example, FIG. 5 shows an example in which the energization cycle changing means 15 is configured to shorten the normal cycle 45 s to the shortened cycle 10 s, and maintain the shortened cycle 10 s after the change, and at a plurality of detection timings, An example of performing detection is also shown.
And the energization cycle changing means 15 can shorten the normal cycle to the shortened cycle so that the detection timing in the shortened cycle is within the time zone that is equal to or longer than the detection response time and shorter than the specified detection response time. It is configured. The detection response regulation time is a time required to detect the detection target gas existing outside the casing 31 by the gas detection layer 10 of the thin film sensor element 20 provided inside the casing 31. . In addition, the detection response time can use what was measured beforehand about each gas detection apparatus, and detection response regulation time is predetermined by the law etc., These are the memory (not shown) provided in the gas detection apparatus 100 ) Etc.

〔battery〕
The battery is arranged inside the gas detection device 100 and configured to supply power to each of the above means. For example, a lithium battery having a relatively long service life is used.

[Methane gas presence and concentration detection, gas type determination, energization cycle change]
Hereinafter, the presence / absence / concentration of methane gas present in the atmosphere (air) of the gas detection layer 10 in the gas detection device 100 having the above-described configuration will be described with reference to FIGS. 3 to 6 (first determination and second determination). ), Determination of the gas type, and change of the normal cycle will be described below.

First, the first determination by the gas detection means 13 will be described. As shown in FIG. 4, when energization of the heater layer 6 is started by the energization driving means 12 (step # 1), 200 ms elapses from the start of energization. Then, the energization is stopped until the energization is stopped, and then the energization is stopped and the heating is resumed after 45 seconds from the start of energization. That is, as shown in FIG. 3, the first determination and the second determination are performed by the gas detection means 13 during the energization time until 200 ms elapses from the start of energization, and the timing at which the first determination and the second determination are performed. Is the detection timing.
And the gas detection means 13 detects the electrical resistance value of the gas detection layer 10 when 100 ms elapses from the start of energization, and performs a first determination as to whether or not this electrical resistance value is lower than the first threshold value ( Step # 3). When the electrical resistance value is not lower than the first threshold (step # 3: No), the atmosphere of the gas detection layer 10 is air or a relatively low concentration (for example, about 1000 ppm) in the air. Assuming that methane gas is present (see FIG. 3), the process returns to step # 2 to perform detection by the first determination in the normal cycle. On the other hand, when the electrical resistance value is lower than the first threshold (step # 3: Yes), hydrogen gas (for example, about 4000 ppm), carbon monoxide gas (for example, about 500 ppm), etc. in the air. Assuming that a gas other than methane gas or methane gas may exist at a high concentration (for example, about 4000 ppm) (see FIG. 3), the process proceeds to step # 4 in order to perform the second determination with higher accuracy. Thereby, before performing the second determination, by performing a simple determination by the first determination, when it is considered that methane gas leakage of a predetermined concentration or more has not occurred, by omitting a more accurate determination, It is possible to achieve a simple configuration and reduce power consumption.

Next, the gas detection means 13 detects the electric resistance value of the gas detection layer 10 when 200 ms elapses from the start of energization, and determines whether or not the electric resistance value is equal to or less than an alarm threshold value (second threshold value). (Step # 4). If the electrical resistance value is less than or equal to the alarm threshold (step # 4: Yes), a gas leak alarm is issued assuming that a relatively high concentration of methane gas (for example, about 4000 ppm in the air) exists (step # 4). # 6). Thereby, it can be determined that the methane gas concentration in the atmosphere has become higher than a predetermined concentration when the electric resistance value is equal to or lower than the alarm threshold value. In this case, a speaker or the like is provided to a person around the gas detection device 100. The occurrence of an abnormal state of methane gas leakage can be notified by the generation of an alarm from, an alarm display on a liquid crystal display, or the like.
On the other hand, when the electrical resistance value exceeds the alarm threshold value (step # 4: No), the cause that the electrical resistance value in the first determination is lower than the first threshold value is due to a gas other than methane gas. Therefore, the gas type determination means 14 determines the gas type (step # 5).

  The gas type determination unit 14 determines the gas type in the atmosphere of the gas detection layer 10 based on the change state of the electric resistance value after 200 ms has elapsed since the start of energization of the heater layer 6 detected by the gas detection unit 13. To do. That is, as described in the gas type determination means 14, for example, if the electrical resistance value at two points (at 40 ms and 60 ms) is detected and the difference between the electrical resistance values is positive, methane gas is included in the air. If not (step # 7: No), if negative, methane gas is contained in the air (step # 7: Yes), and the gas type is determined. When methane gas is not included, that is, when there is a gas other than methane gas (step # 7: No), it is determined that no methane gas leaks and the process returns to step # 2, and the detection by the first determination is performed in the normal cycle. Do. If methane gas is included (step # 7: Yes), the process returns to step # 4 to determine again whether or not high-concentration methane gas exists (second determination).

Here, when performing the second determination again in step # 4, the energization cycle changing means 15 changes the normal cycle to the shortened cycle (step # 8), and the electrical resistance value at the detection timing in the shortened cycle is set. The second determination to be compared with the second threshold is performed (step # 4).
That is, the energization cycle changing unit 15 changes the energization to the heater layer 6 from the normal cycle to the shortened cycle when methane gas is present in the atmosphere of the gas detection layer 10 by the gas type determination unit 14 (step # 8). ).
As described above, the second determination is performed by changing the normal cycle to the shortened cycle, in addition to detecting methane gas with higher accuracy, as described with reference to FIG. 15 in the background art. In order to detect the detection target gas in a state where the time from the gas leakage to issuing an alarm does not exceed the detection response specified time even when the detection responsiveness decreases (detection response time increases) with the package strengthening of the device 100 It is. In this case, the energization cycle changing means 15 performs the normal cycle so that any one of the periodically repeated detection timings is within a time zone set longer than the detection response time and shorter than the specified detection response time. Is a shortened cycle.

  In this step # 8, for example, as shown in FIG. 5, when the energizing cycle of the gas detector 100 of the reinforced package with the detection response time 45s is driven at the normal cycle 45s (the cycle at which the detection timing comes every 45s), If a gas leak occurs simultaneously with the first detection timing (0 s) (Case 1), an alarm is given within the detection response regulation time after 45 s, which is the second detection timing (within 60 s from the occurrence of the gas leak). On the other hand, if a gas leak occurs after 5 s after the first detection timing (0 s) (case 2), the detection response time at the second detection timing (45 s) after 40 s from the gas leakage. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is issued, the gas type determination means 15 detects the detection target gas below the concentration to be alarmed and determines the gas type. Then, if necessary (for example, when the detection target gas exists), the third detection after 50 s from the gas leakage by shortening the energization to the heater layer 6 from the normal period 45 s to the shortening period 10 s. An alarm can be made at the timing (55 s), and since only 50 s has passed from the gas leak until the alarm is issued, the detection response regulation time can be satisfied. Similarly, if a gas leak occurs after 25 s after the first detection timing (0 s) (case 3), the detection response time elapses at the second detection timing (45 s) 20 s after the gas leak. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is given, the gas type determination means 15 detects the detection target gas below the concentration to be alarmed to determine the gas type. If necessary (for example, when a detection target gas exists), the energization of the heater layer 6 is shortened from the normal period 45 s to the shortening period 10 s, so that the fifth detection timing 50 s after gas leakage ( 75 s), and since only 50 s has elapsed from the gas leak until the alarm is issued, the detection response regulation time can be satisfied. In case 3 of FIG. 5, at the third and fourth detection timings, since the detection response time has not elapsed, the detection target gas above the concentration to be alarmed is not detected, and no alarm is given.

Here, in FIG. 6, for a plurality of gas detection devices 100, gas leakage occurs when the energization cycle changing means 15 changes the normal cycle to the shortened cycle as described above and when the normal cycle is not changed to the shortened cycle. The relationship between the time from the start to the alarm (vertical axis) and the delay time from the detection timing to the occurrence of gas leakage (horizontal axis) is shown. In FIG. 6, the normal period is set to 45 s, the shortening period is set to 10 s, and the detection response regulation time is set to 60 s. Further, the detection response times of the gas detection devices were those having the detection response times shown in Table 1 of 25 s, 45 s, and 50 s. Specifically, Examples 1 and 2 are examples of the present application in which the normal cycle is changed to a shortened cycle in each gas detection device 100 having the detection response times of 45 s and 50 s in Table 1. On the other hand, Comparative Examples 1, 2, and 3 are conventional examples in which the detection response times in Table 1 are 25 s, 45 s, and 50 s, respectively, and the normal period is not changed to the shortened period.
As can be seen from FIG. 6, in Examples 1 and 2 according to the present application, the detection response time is 45 s and 50 s, which are relatively long (the package is strengthened and hardly affected by the non-detection target gas). Regardless of the value of the delay time of the occurrence of gas leak, the time until the alarm is shorter than the detection response regulation time of 60 s, and does not exceed the detection response regulation time, so that it is surely and early. An alarm can be issued.
On the other hand, in Comparative Example 1, no matter what value the delay time of the occurrence of gas leakage takes, the time until the alarm is shorter than the detection response regulation time of 60 s, but the detection response time is short. That is, the gas tightness of the gas detection device and the function of the activated carbon adsorption layer are low, which is easily influenced by the non-detection target gas, and it may be difficult to accurately detect methane gas.
On the other hand, in Comparative Examples 2 and 3, although the detection response time is relatively long as 45 s and 50 s (the package is strengthened and hardly affected by the non-detection target gas), the delay time of the occurrence of gas leakage takes a predetermined value. In this case, the time until the alarm becomes longer than the detection response prescribed time of 60 s, and the detection response prescribed time cannot be satisfied.
Therefore, as in the present application, the normal cycle in which the heater layer 6 is energized by the energization cycle changing means 15 is shortened to a shortened cycle, thereby eliminating the influence of the non-detection target gas using the gas detection device 100 with an enhanced package. Thus, the presence / absence and concentration of the detection target gas can be detected more accurately, and the normal cycle is changed (detection timing is changed) only when necessary according to the gas type, and the change is made wastefully. This can be prevented and power consumption can be reduced. In addition, the alarm can be issued within the specified detection response time by minimizing the time from the occurrence of gas leakage until the alarm is issued.

[Second Embodiment]
In the first embodiment, the energization driving unit 12 and the energization cycle changing unit 15 set the normal cycle to 45 s, the shortening cycle to 10 s, and the detection response time corresponding to the gas detection device 100 to 45 s, 50 s, and the like. Although the detection response specified time is set to 60 s, the detection timing is not limited to these specific numerical values as long as the detection timing is equal to or longer than the detection response time and within a time zone shorter than the detection response specified time. For example, as shown in FIG. 7, the normal cycle may be 100 s, the shortening cycle may be 30 s, the detection response time may be 80 s, and the detection response specified time may be 120 s.
In this case, as shown in FIG. 7, when the energization cycle of the gas detection device 100 of the reinforced package with a detection response time of 80 s is driven at a normal cycle of 100 s (a cycle in which the detection timing comes every 100 s), the first detection timing When gas leakage occurs after 20 seconds after (0 s) (case 1), within the detection response regulation time after 80 s (within 120 s from the occurrence of gas leakage), which is the second detection timing (100 s). Alarm. On the other hand, if a gas leak occurs after 30 s after the first detection timing (0 s) (case 2), the detection response time at the second detection timing (100 s) after 70 s from the gas leak. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is issued, the gas type determination means 14 detects the detection target gas below the concentration to be alarmed and determines the gas type. Then, if necessary (for example, when a detection target gas is present), the third detection after 100 s from the gas leakage by shortening the energization to the heater layer 6 from the normal period 100 s to the shortened period 30 s. An alarm can be issued at the timing (130 s), and since only 100 s has elapsed from the gas leak until the alarm is issued, the detection response regulation time can be satisfied. Similarly, when a gas leak occurs after 50 s after the first detection timing (0 s) (case 3), the detection response time is obtained at the second detection timing (100 s) after 50 s from the gas leak. Since the detection target gas above the concentration to be alarmed is not detected and no alarm is issued, the gas type determination means 14 detects the detection target gas below the concentration to be alarmed and determines the gas type. Then, if necessary (for example, when a detection target gas exists), the energization to the heater layer 6 is shortened from the normal cycle 100 s to the shortened cycle 30 s, so that the fourth ( 160 s), and since only 110 s has elapsed from the gas leak until the alarm is issued, the detection response regulation time can be satisfied. In case 3, since the detection response time has not elapsed at the third detection timing, the detection target gas having a concentration higher than the alarm level is not detected, and no alarm is issued.

[Third Embodiment]
In the first and second embodiments, after changing the normal cycle to the shortened cycle in step # 8 of FIG. 4, the process returns to step # 4, and the electric resistance value at the time when 200 ms elapses from the start of energization at the detection timing is displayed as an alarm. Although it is configured to perform the second determination as to whether it is equal to or less than the threshold (second threshold), as illustrated in FIG. 8, the first determination may be performed before the second determination is performed. With respect to the electrical resistance value in the shortened cycle, by performing a simple first determination before performing a highly accurate determination by the second determination (step # 9), the electrical resistance value decreases below the first threshold value by the first determination. If it is determined that it is not (step # 9: No), the second determination is omitted and the normal cycle is resumed (step # 2). On the other hand, when it is determined in the first determination that the electrical resistance value is lower than the first threshold (step # 9: Yes), the electrical resistance value in the shortened period is maintained while maintaining the shortened period. The second determination can be made by using (step # 4). Thereby, the methane gas is detected in a state where the energization to the heater layer 6 is maintained in a shortened cycle only when necessary, and the power consumption can be reduced by returning to the energization in the normal cycle if not necessary. . Steps # 1 to # 8 are the same as in FIG.

[Fourth Embodiment]
In the first embodiment, the gas type contained in the air is determined based on the difference between the plurality of electrical resistance values or the presence of the minimum value when the heater layer is energized, but the determination of the gas type is limited to these. is not. For example, as shown in FIG. 9, the first-order differential value and the second-order differential value of the electrical resistance value are calculated, the first-order differential value is 0 or less, and the second-order differential value is 0 or more. In some cases, it may be determined that the gas is a detection target gas.
That is, as shown in FIG. 9, when the time from the start of energization to the heater layer 6 to the end of energization is 200 ms, the electric resistance value is a gas other than methane gas (carbon monoxide, hydrogen). For example, from about 50 ms after the start of energization to 200 ms until the end of energization, it increases so as to draw an asymptotic line that asymptotically rises to a constant value. When the resistance value is detected and the first-order differential value and the second-order differential value are obtained, the first-order differential value becomes a positive value and the second-order differential value becomes a negative value. Thereby, it can be determined that gas other than methane gas exists.
On the other hand, the electrical resistance value in the case of methane gas, which is the detection target gas, decreases so as to draw an asymptotic line that ascends to a constant value during the period from 50 ms to 200 ms. The value is 0 or less, and the second-order differential value is 0 or more. Therefore, if the first-order differential value and the second-order differential value thus obtained are the values where the first-order differential value is 0 or less and the second-order differential value is 0 or more, it is determined that methane gas exists. Can do.
In the above description, the gas type is determined using the electric resistance value at one point, but the gas type may be determined using electric resistance values at two or more points for more reliable determination.
Further, for more reliable determination, the point at which the differential value is calculated is the electrical resistance value at the point not affected by noise, and further processing such as moving average of the data to remove instantaneous changes is performed. You can also.

[Fifth Embodiment]
In the first embodiment, the gas type contained in the air is determined based on the difference between the plurality of electrical resistance values or the presence of the minimum value when the heater layer is energized, but the determination of the gas type is limited to these. is not. For example, as shown in FIGS. 10 to 12, when all the first-order differential values of the electrical resistance values at a plurality of detection timings are 0 or less, it can be determined that the gas is a detection target gas (methane gas).
That is, as shown in FIGS. 10 to 12, when the time from the start of energization to the heater layer 6 to the end of energization is 200 ms, the gas is a gas other than methane gas (carbon monoxide, hydrogen). For example, the electrical resistance value increases from about 50 ms after the start of energization to 200 ms from the end of energization to 200 ms until the end of energization. When the electrical resistance values at any of a plurality of detection timings are detected and their first-order differential values are obtained, the first-order differential values of the electrical resistance values at these detection timings are all positive values. Thereby, it can be determined that gas other than methane gas exists.
On the other hand, in the case of methane gas, which is a detection target gas, since it decreases so as to draw an asymptotic line that ascends to a constant value during the period from 50 ms to 200 ms, a plurality of electric powers at arbitrary detection timings. The first-order differential values of resistance values are all 0 or less. Therefore, when all the values of the first-order differential values of the plurality of electrical resistance values are 0 or less, it can be determined that methane gas is present.
In addition, FIG. 10 is a figure which shows an example in the case of determining a gas type by detecting an electrical resistance value by 2 points | pieces. In this case, electrical resistance values at two points where the energization elapsed time is 50 ms (T1) and 150 ms (T2) are detected. FIG. 11 is a diagram illustrating an example in the case where the gas type is determined by detecting the electrical resistance value at three points. In this case, electrical resistance values at three points where energization elapsed time is 50 ms (T1), 100 ms (T2), and 150 ms (T3) are detected.
And FIG. 12 is a figure which shows an example in the case of determining a gas type by detecting an electrical resistance value by 4 points | pieces. In this example, electrical resistance values at four points with energized elapsed times of around 15 ms (T1), around 30 ms (T2), 100 ms (T3), and 150 ms (T4) are detected. In this case, the first-order differential value of the electric resistance value of the gas other than methane detected in the vicinity of 15 ms (T1) and in the vicinity of 30 ms (T2) is a value of 0 or less as in the case of methane gas.
Further, in the above, the gas type is determined using the electric resistance values of 2 to 4, but the gas type may be determined using the electric resistance values at five or more detection points for more reliable determination. Good.
For more reliable determination, the points where the differential value is calculated are spaced from each other so as not to be affected by noise, and the moving average of the data is used to eliminate instantaneous changes. Processing can also be performed.

[Another embodiment]
(1) In the above embodiment, the gas detection means 13 performs the second determination after performing the first determination .

(2) In the above embodiment, the presence of the gas species and methane gas is detected using the electric resistance value of the variable resistance as the electric characteristics of the gas detection layer 10 (thin film sensor element 20), but the present invention is particularly limited to this. Instead, the presence of the gas species and the methane gas can be detected using the output voltage of the fixed resistance of the gas detection layer 10 (thin film sensor element 20).

(3) In the above embodiment, the gas detection layer 10 is made of a material mainly composed of tin oxide (SnO ₂ ). However, the present invention is not particularly limited to such a material. Depending on the gas to be detected, indium oxide (In ₂ O ₃ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), titanium oxide (TiO ₂ ), iron oxide (Fe ₂ O ₃ ), etc. can also be employed.

(4) In the said embodiment, although it comprised so that it might drive by the electric power supply from the built-in battery, it is not limited to this in particular, A fixed power supply exists in the vicinity of the installation location of a gas detection apparatus. In this case, the power supply may be received from the fixed power source.

(5) In the above embodiment, as shown in FIG. 1, the insulating layer 7 made of the SiO ₂ film is provided so as to cover the entire heater layer 6 provided on the support layer 5, and the insulating layer A configuration in which a pair of electrode layers 9 is provided on 7 is illustrated. However, the electrode layer may be provided on the heater layer without providing the insulating layer 7. Further, the electrode layer and the heater layer may not be provided independently but may be configured to be used together.

(6) In the above embodiment, the detection target gas has been described as methane gas. However, any gas can be used as the detection target gas as long as it has a change state in electrical characteristics similar to that of methane gas.

(7) In the above embodiment, the energization time to the heater layer is set to a certain time (for example, 200 ms). However, for example, the energization time to the heater layer can be changed based on the determination result of the first determination. . That is, as shown in FIG. 14, a first determination is made to determine whether or not the electrical resistance value is lower than the first threshold value. If the electrical resistance value is not lower than the first threshold value, The energization time is set as a normal energization time (for example, 100 ms) (step # 09). If the electrical resistance value is lower than the first threshold value, the energization time to the heater layer is set to an extended energization time (for example, 200 ms) longer than the normal energization time (step # 10). As described above, based on the determination result of the first determination, if the electric resistance value is not lower than the first threshold value, the energization time to the heater layer is set to the normal energization time (for example, 100 ms), thereby reducing the power consumption. If the electrical resistance value is lower than the first threshold value while being able to be reduced, the energization time to the heater layer is set to an extended energization time (for example, 200 ms) longer than the normal energization time (for example, 200 ms), and thereafter The second determination and the gas type determination can be performed with high accuracy. Incidentally, in FIG. 14, operations other than step # 09 and step # 10 are the same as those in FIG.

  The present invention eliminates the influence of the non-detection target gas in detecting the presence / absence and concentration of the detection target gas, and can reduce the power consumption while reducing the time from the occurrence of the gas leak to the alarm. The present invention can be applied to a gas detection device and a gas detection method that can be shortened and issue an alarm within a predetermined detection response time.

6: Heater layer 7: Insulating layer (electrical insulating layer)
9: Electrode layer 10: Gas detection layer 12: Energization drive means 13: Gas detection means 14: Gas type determination means 15: Energization cycle change means 20: Thin film sensor element (sensor element)
30: Gas inlet 31: Housing 32: Activated carbon adsorption layer (filter means)
100: Gas detector

Claims (15)

A sensor element in which a gas detection layer whose electrical characteristics are changed by contact with the detection target gas, and a heater layer for heating the gas detection layer;
The sensor element is provided inside a casing having a gas inlet through which the detection target gas can flow from the outside, and a non-detection target gas is provided in a flow path from the gas inlet to the inside of the casing. Filter means to which
Energization driving means for energizing the heater layer at a predetermined normal cycle to change the temperature of the gas detection layer;
Electrical resistance as the electrical characteristic of the gas sensing layer at the detection timing for the heater layer energized, a first determination for determining whether or not being lower than the first threshold value, use the first determination The detection target gas is detected by a second determination that determines whether or not the electric resistance value after the electric resistance value is lower than a second threshold value that is less than the first threshold value. a gas detecting means for,
Gas type determination means for determining a gas type present in the atmosphere of the gas detection layer based on the electrical characteristics of the gas detection layer when the heater layer is energized ;
An energization cycle changing unit that changes the normal cycle based on a detection result of the gas detection unit and a determination result by the gas type determination unit ,
The energization cycle changing means continues energization of the normal cycle when the electrical resistance value in the first determination is equal to or greater than the first threshold value,
When the electrical resistance value in the second determination exceeds the second threshold and the determination result of the gas type determination unit is the detection target gas, the normal period is less than the first threshold. To a shorter shortening cycle,
The gas detector is a gas detector that issues an alarm when the electrical resistance value is equal to or lower than the second threshold value in the second determination . The detection target gas existing outside the casing reaches the sensor element provided inside the casing, and the detection target gas is present in a concentration that should be alarmed in the gas detection layer. The lower limit of the time that can be detected is the detection response time,
The time required to detect the detection target gas existing outside the casing in the gas detection layer of the sensor element provided inside the casing is set as a detection response regulation time,
Before Symbol detection timing, the detection response time or more, the probe response defined as the time becomes shorter set within the time band than on the basis of the determination result by the gas type determination means, the energizing cycle changing means There gas detecting device according to claim 1 for changing the normal cycle the shortening period.   The gas detection unit is configured to perform the second determination based on the electric resistance value at the detection timing in the shortening period after the energization period changing unit has changed the normal period to the shortening period. The gas detection device according to claim 1 or 2. After the energization cycle changing unit changes the normal cycle to the shortened cycle, the gas detection unit lowers the electrical resistance value below the first threshold based on the electrical resistance value at the detection timing in the shortened cycle. The gas detection device according to claim 1 or 2, wherein the first determination as to whether or not the operation is performed is performed, and then the second determination is performed . The gas type determination means, by using a state of change of the electric resistance value as electric characteristics of the gas sensing layer at the heater layer energization, any of judges claims 1 to 4 the gas species present in the atmosphere The gas detection device according to claim 1. The gas detection device according to claim 5 , wherein a difference between the plurality of electric resistance values is used to determine a gas type using the change state of the electric resistance value. The gas detection device according to claim 5 , wherein the appearance of the minimum value of the electric resistance value is used to determine the gas type using the change state of the electric resistance value. The gas detection device according to claim 5 , wherein a first-order differential value and a second-order differential value of the electric resistance value are used to determine a gas type using the change state of the electric resistance value. The gas detection device according to claim 5 , wherein the electric resistance value at a plurality of the detection timings is used to determine the gas type using the change state of the electric resistance value. The sensor element is a thin film sensor element including an electrical insulating layer, the gas detection layer made of an oxide semiconductor, and a pair of electrode layers that detect an electrical resistance value as the electrical characteristic of the gas detection layer. The gas detection device according to any one of claims 1 to 9 . The gas detection device according to any one of claims 1 to 10 , which is driven by power supply from a built-in battery. Using a sensor element in which a gas detection layer whose electrical characteristics change by contact with a detection target gas and a heater layer for heating the gas detection layer are formed,
The sensor element is provided inside a casing having a gas inlet through which the detection target gas can flow from the outside, and a non-detection target gas is provided in a flow path from the gas inlet to the inside of the casing. Is provided with filter means to which
The energization drive means energizes the heater layer at a predetermined normal cycle, changes the temperature of the gas detection layer,
Gas detection means, the electric resistance value as the electrical characteristic of the gas sensing layer at the detection timing for the heater layer energized, a first determination for determining whether or not being lower than the first threshold value, the A second determination is made as to whether or not the electric resistance value detected after the electric resistance value used for the first determination is lower than a second threshold value that is less than the first threshold value at a detection timing. The detection target gas is detected by the determination,
The gas type determination means determines the gas type present in the atmosphere of the gas detection layer based on the electrical characteristics of the gas detection layer when the heater layer is energized,
An energization cycle changing means is a gas detection method for changing the normal cycle based on a detection result of the gas detection means and a determination result by the gas type determination means ,
The energization cycle changing means continues energization of the normal cycle when the electrical resistance value in the first determination is equal to or greater than the first threshold value,
When the electrical resistance value in the second determination exceeds the second threshold and the determination result of the gas type determination unit is the detection target gas, the normal period is less than the first threshold. To a shorter shortening cycle,
The gas detection method, wherein the gas detection means notifies an alarm when the electrical resistance value is not more than the second threshold value in the second determination . And is conductible cycle changing means based on a determination result by the gas type determining unit, wherein the detection timing is reached to the sensor element provided on the inside of the detection target gas is the housing that exists outside of the housing In addition, the gas detection layer has a detection response time that is a lower limit of the time during which it is possible to detect that the detection target gas is present at a concentration that should be alarmed or more, and exists outside the housing. The normal gas so that the detection target gas is within a time zone set shorter than a detection response regulation time, which is a time required to be detected by the sensor element provided in the housing. The gas detection method according to claim 12, wherein a cycle is changed to the shortened cycle . The gas detection unit is configured to perform the second determination based on the electric resistance value at the detection timing in the shortening period after the energization period changing unit has changed the normal period to the shortening period. The gas detection method according to claim 12 or 13 . After the energization cycle changing unit changes the normal cycle to the shortened cycle, the gas detection unit lowers the electrical resistance value below the first threshold based on the electrical resistance value at the detection timing in the shortened cycle. The gas detection method according to claim 12 or 13 , wherein the first determination is made as to whether or not the second determination is made, and then the second determination is made .

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