JP5517963B2 - Gas detector - Google Patents

Description

  The present invention relates to a low power consumption type gas detection device with battery driving in mind.

Generally, a gas sensor is used for applications such as a gas leak alarm, and is a device that is selectively sensitive to a specific gas, for example, a reducing gas such as CO, CH ₄ , C ₃ H ₈ , and C ₂ H ₅ OH. Therefore, high sensitivity, high selectivity, high response, high reliability, and low power consumption are indispensable.
By the way, gas leak alarms that are widely used for household use are intended for detection of flammable gas for city gas and propane gas, for detection of incomplete combustion gas in combustion equipment, Alternatively, there are those having both of these functions, but the spread rate is not so high due to cost and installation problems.
Therefore, from the viewpoint of improving the diffusion rate of the gas leak alarm device, it is desired to improve the installation property, specifically, to make the gas leak alarm device cordless by driving the battery.

Low power consumption is the most important for realizing battery drive, but when detecting CH ₄ and C ₃ H ₈ with a catalytic combustion type or semiconductor type gas sensor, it is heated to a high temperature of 400 ° C to 500 ° C. Need to be detected. For this reason, in the conventional method of sintering powder such as SnO ₂ as a gas sensing film, there is a limit to reducing the thickness even if a method such as screen printing is used, and the heat capacity is large for use in battery driving. There was a problem of passing. Therefore, a gas sensor having an ultra-low heat capacity structure using a microfabrication process and a diaphragm structure has been developed.

As a prior art of such a gas sensor, for example, there is a gas sensor having a diaphragm structure described in Patent Document 1 (Japanese Patent Laid-Open No. 2005-164666).
Here, FIG. 7 is a cross-sectional view of a gas sensor having a general diaphragm structure, which is substantially the same as the gas sensor described in FIG.

As shown in the cross-sectional view of FIG. 7, the gas sensor 100 has a diaphragm structure thermally insulating support by a thermally oxidized SiO ₂ layer 21, a CVD-Si ₃ N ₄ layer 22 and a CVD-SiO ₂ layer 23 on the upper side of the Si substrate 1. Layer 2 is formed. The heater layer 3 is made of Ni—Cr and is provided on the upper side of the heat insulating support layer 2. The heat insulating support layer 2 and the heater layer 3 are covered with an electric insulating layer 4 made of a sputtered SiO ₂ layer. On the lower side of the pair of sensing electrode layers 52 made of Pt, a bonding layer 51 made of Ta is also formed as an intermediate layer with respect to the electrical insulating layer 4 which is a base oxide film. The pair of sensing electrode layers 52 is provided with a gas sensing layer 53 made of Sb-doped SnO ₂ layer passed. A part of the electrical insulating layer 4, the pair of sensing electrode layers 52 and the gas sensing layer 53 are covered with a gas selective combustion layer 54 which is a Pd-supported Al ₂ O ₃ sintered material. Instead of the Pd-supported Al ₂ O ₃ sintered material, a Pt-supported Al ₂ O ₃ sintered material or a Pd / Pt alloy-supported Al ₂ O ₃ sintered material may be used.

  In addition, the gas sensor 100 drives the heater by inputting a driving signal from a heater driving unit (not shown) to the heater layer 3 through a conducting wire. The gas sensing layer 53 comes into contact with the gas while being heated to a high temperature of 400 ° C. to 500 ° C. by the heater layer 3, and functions as a sensor by outputting a sensor resistance value that changes in the gas sensing layer 53 as a detection signal. To do.

Such a gas sensor 100 detects flammable gases such as CH ₄ and C ₃ H ₈ . In this case, the heater layer 3 is energized for a fixed time of 50 to 500 ms, and the temperature of the gas sensing layer 53 is maintained at a high temperature (High 400 to 500 ° C.). The sensor resistance value of the gas sensing layer 53 is measured by the sensing electrode layer 52 in such a high temperature state, and the presence or absence of CH ₄ , C ₃ H _8, etc. and the combustible gas concentration are detected from the change. Such detection is performed periodically (for example, every 30 seconds). (High-Off method).

Here, the gas selective combustion layer 54 at a high temperature burns reducing gases such as CO and H _{2 and} other miscellaneous gases, but inactive combustible gases such as CH ₄ and C ₃ H ₈ are gas selective combustion layers. 54 is transmitted. The combustible gas diffuses in the gas selective combustion layer 54 and reacts with SnO ₂ in the gas sensing layer 53, thereby changing the sensor resistance value of SnO ₂ . By detecting this change in the sensor resistance value, the presence or concentration of a combustible gas such as CH ₄ or C ₃ H ₈ generated when a gas leak occurs in a gas device or the like is detected.

  When incomplete combustion (CO) is detected, the temperature of the heater layer 3 is once increased to a high temperature (High 400 to 500 ° C.) for a certain period of 50 to 500 ms, and the gas sensing layer 53 is cleaned. Then, the temperature is lowered to a low temperature (Low about 100 ° C.) and incomplete combustion (CO) is detected. This is known to increase CO sensitivity and gas selectivity (High-Low-Off method).

Also, in the High state, not only cleaning but also detection of flammable gases such as CH ₄ and C ₃ H ₈ is performed, and in combination with detection of incomplete combustion gases such as CO in the Low state, flammable gases and incompleteness with one sensor. There are also gas sensors that can detect both combustion gases.

As described above, the heater driving method of these gas sensors is intermittent driving in which (1) driving by the high-off method or (2) driving by the high-low-off method is repeated at a predetermined cycle (for example, a cycle of 150 seconds). Therefore, low power consumption is achieved.
The gas sensor disclosed in Patent Document 1 performs sensing based on the same principle. The prior art is like this.

Japanese Patent Laying-Open No. 2005-164666 (paragraphs [0049], [0050], FIG. 1, etc.)

  In general, in the atmosphere of the installation environment of the gas detection device on which the gas sensor is mounted, other miscellaneous gases coexist in addition to the detection target gas. The miscellaneous gas is a gas type such as combustible gas, oxygen, nitrogen, carbon dioxide gas, and water vapor that is not detected. Some of these gases become interference gases for the gas sensor, the resistance value of the gas sensor changes temporarily, and it may behave as if there is a gas to be detected, leading to false detection.

  In order to eliminate the influence of such interference gas and accurately detect the presence and concentration of the detection target gas, the interference gas is removed by the gas selective combustion layer, and the detection target gas can be detected at a sufficiently high temperature. It is necessary to energize for hours. However, there is a problem that such heating hinders low power consumption.

  Accordingly, the present invention is to solve the above-described problems, and an object thereof is to provide a gas detection device that improves gas type determination logic and realizes low power consumption while maintaining detection performance. There is to do.

In order to solve the above problem, the invention described in claim 1
A gas sensor having a gas sensing layer whose electrical resistance characteristics change by contact with a gas to be detected, and a heater layer for heating the gas sensing layer;
A heater layer driving section for driving the heater layer;
A signal processing / driving unit to which the gas sensing layer and the heater layer driving unit are connected;
With
The signal processing / driving unit is
In the normal state, a first mode drive means for controlling said heater layer driver so that the gas sensing layer by heating from the heater layer is a temperature for detecting the presence or absence of interference gas or detection target gas,
First mode determination means for determining that an interference gas or a detection target gas is present when an electric resistance value of the gas sensing layer is lower than an electric resistance value with respect to air ;
If it is determined that the interference gas or detection target gas is present the first mode determining means, the gas sensing layer a temperature for burning the interference gas by heating from the heater layer and the temperature detected only detection target gas a second mode drive means and said controlling the heater layer driver Ru switches the heating temperature of the heater layer such that,
It functions as second mode determination means for determining the presence or concentration of the detection target gas based on the fact that the electric resistance value of the gas sensing layer decreases as the energization time elapses and approaches a certain value. This is a gas detection device.

The invention described in claim 2
A gas sensor having a gas sensing layer whose electrical resistance characteristics change by contact with a gas to be detected, and a heater layer for heating the gas sensing layer;
A heater layer driving section for driving the heater layer;
A signal processing / driving unit to which the gas sensing layer and the heater layer driving unit are connected;
With
The signal processing / driving unit is
In a normal time, the heater layer driving unit is controlled so that the gas sensing layer has a temperature that makes the electric resistance characteristic of the detection target gas different from the electric resistance characteristic of the interference gas by heating from the heater layer. Mode driving means;
First mode determination means for determining whether or not a gas to be detected is included based on the electrical resistance characteristics of the gas sensing layer;
Second mode driving means for controlling the heater layer driving unit so that the gas sensing layer detects only the detection target gas by heating from the heater layer only when the gas is the detection target gas;
The gas detection device functions as second mode determination means for determining the presence or concentration of a detection target gas based on the electric resistance characteristic of the gas detection layer.

The invention described in claim 3
The gas detection device according to claim 2,
The first mode determination means acquires a plurality of difference values using sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode driving means, and these difference values are zero. The gas detection device is characterized in that it is determined that the detection target gas is included when the value is equal to or less than a predetermined value, and that the interference gas is included when the detection target gas is greater than the predetermined value.

The invention described in claim 4
The gas detection device according to claim 2,
The first mode determination means acquires a plurality of differential values using sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode driving means, and these differential values are 0. The gas detection device is characterized in that it is determined that the detection target gas is included when the value is equal to or less than a predetermined value, and that the interference gas is included when the detection target gas is greater than the predetermined value.

Moreover, the invention described in claim 5 is
The gas detection device according to claim 2,
The first mode determination means acquires time state change characteristics according to sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode drive means. The gas detection device is characterized in that when a minimum value appears, it is determined that an interference gas is included, and when a minimum value does not appear among the time-varying state characteristics, it is determined that a detection target gas is included.

The invention described in claim 6
In the gas detection device according to any one of claims 1 to 5,
Output control means for outputting gas information related to the detection target gas based on the determination content by the first mode determination means or the second mode determination means;
It is provided with this.

The invention described in claim 7
In the gas detection device according to any one of claims 1 to 6,
The gas detection device is driven by power supplied from a power supply circuit using a built-in battery.

The invention described in claim 8
In the gas detection device according to any one of claims 1 to 7,
The signal processing / driving unit is driven by energizing the heater layer at a predetermined cycle,
The gas detection layer may be heated at a predetermined cycle.

The invention described in claim 9 is
In the gas detection device according to any one of claims 1 to 8,
The gas sensor
A Si substrate having a through hole;
A diaphragm-like heat insulating support layer stretched over the opening of the through hole;
The heater layer provided on the thermal insulating support layer;
An electrical insulation layer provided to cover the thermal insulation support layer and the heater layer;
A pair of sensing electrode layers provided on the electrically insulating layer;
The gas sensing layer made of an oxide semiconductor, which is provided on the electrical insulating layer and the pair of sensing electrode layers and in the vicinity of the heater layer, and whose sensor resistance value is changed by the gas in contact with the gas sensing layer;
It is a sensor provided with this.

Moreover, the invention described in claim 10 is
The gas detection device according to claim 9, wherein
The gas sensor is further provided so as to cover the surface of the gas sensing layer, and is made of an Al ₂ O ₃ sintered material that supports Pd (palladium), Pt (platinum), or an alloy containing Pd and Pt as a catalyst. A gas detection device comprising a gas selective combustion layer.

  ADVANTAGE OF THE INVENTION According to this invention, the gas detection apparatus which improves the determination logic of a gas type and tries to implement | achieve low power consumption, maintaining detection performance can be provided.

It is a block block diagram of the gas detection apparatus which shows embodiment of this invention. It is a characteristic view which shows the response waveform of the gas sensor heated to 250 degreeC. It is a characteristic view which shows the response waveform of the gas sensor heated to 450 degreeC. It is a characteristic view which shows the response waveform of the gas sensor heated to 300 degreeC. It is explanatory drawing of interference gas determination logic. It is explanatory drawing of interference gas determination logic. It is sectional drawing of a gas sensor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the gas detection apparatus 1000 of this embodiment includes a gas sensor 100, a heater layer driving unit 200, an alarm display circuit 300, an alarm sound output circuit 400, an external output circuit 500, a storage circuit 600, a signal processing / driving unit. 700 and a power supply circuit 800.

  The gas sensor 100 is the sensor described above with reference to FIG. 7, and is given the same reference numerals and redundant description is omitted. Further, instead of the gas sensor 100, a gas detection circuit in which a peripheral circuit is added to the gas sensor 100 may be used. The heater layer 3 of the gas sensor 100 (or gas detection circuit) is connected so that the heater layer driving unit 200 can be electrically energized, and the heater layer driving unit 200 is energized and heated to the heater layer 3. Has been made. In addition, a signal processing / driving unit 700 is connected to the pair of sensing electrode layers 52 of the gas sensor 100 (or the gas detection circuit), and changes in sensor resistance due to gas detection of the gas detection layer 53 are detected. Details of this detection will be described later in the detection process.

  The heater layer driving unit 200 is a circuit unit that is supplied with power from the power supply circuit 800 and drives the heater layer 3 by energization in the first mode driving or the second mode driving as will be described later. The heater layer driving unit 200 is connected to the signal processing / driving unit 700 to perform various controls. Details of these driving operations will be described later in the detection process.

  The alarm display circuit 300 includes a display unit such as an LED, a lamp, and an LCD display and its driver, and can be displayed on the display unit as an alarm display when an abnormality is detected. The alarm display circuit 300 is connected to the signal processing / driving unit 700 to perform various controls. Although not shown, the alarm display circuit 300 is supplied with power from the power supply circuit 800.

  The alarm sound output circuit 400 includes, for example, a speaker and a driver thereof, and can output an alarm sound from the speaker when an abnormality is detected. The alarm sound output circuit 400 is connected to the signal processing / driving unit 700 to perform various controls. Although not shown, the alarm sound output circuit 400 is supplied with power from the power supply circuit 800.

  The external output circuit 500 is, for example, a contact circuit or a communication circuit, and can output the detected contents to the outside as an output signal such as a voltage when an abnormality is detected by the gas detector 1000. The external output circuit 500 is connected to the signal processing / driving unit 700 to perform various controls. Although not shown, the external output circuit 500 is supplied with power from the power supply circuit 800.

  The memory circuit 600 is connected to the signal processing / driving unit 700 to read and write various data. The memory circuit 600 stores setting data such as threshold values for generating various alarms, determination conditions for first mode driving and second mode driving described later, and history data such as state data when the gas detection device issues an alarm. Is remembered. Although not illustrated, the memory circuit 600 is supplied with power from the power supply circuit 800.

  The signal processing / driving unit 700 is constituted by a CPU such as a microcomputer and its peripheral circuits, and controls and drives the above-described units. Since the output by the sensor resistance value from the gas sensing layer 53 of the gas sensor 100 is an analog signal, the signal processing / driving unit 700 includes an A / D conversion circuit that converts these analog signals into digital signals. The signal processing / driving unit 700 is supplied with power from the power supply circuit 800.

  The power supply circuit 800 supplies power. As this power supply circuit, a consumable battery such as a built-in dry battery or a rechargeable battery is assumed, but it may be constituted by a commercial power supply such as AC 100 V and a constant voltage circuit.

Next, gas detection performed by the program processing of the signal processing / driving unit 700 will be described below.
First, the signal processing / driving unit 700 normally has a temperature (250 ° C.) at which the gas sensing layer 53 detects the presence or absence of an interference gas or a detection target gas by heating from the heater layer 3 of the gas sensor 100. It functions as a means for controlling the heater layer driving section 200 (first mode driving means 701). Specifically, a pulse is applied so that the temperature of the heater layer 3 becomes 250 ° C. over 200 ms.

  Subsequently, the signal processing / driving unit 700 functions as a unit that determines whether or not the interference gas or the detection target gas is included based on the electric resistance characteristic of the gas sensing layer 53 (first mode determination unit 702).

  FIG. 2 shows changes in sensor resistance when the gas sensing layer 53 is heated at 250 ° C. for 200 ms in each atmospheric gas by such first mode driving. As is clear from FIG. 2, the electrical resistance characteristic representing the relationship between the energization time and the sensor resistance value is the sensor resistance value for all gases (air, methane gas, carbon monoxide, hydrogen) as time passes. The decreasing characteristic is shown. Such a tendency occurs when the heating temperature of the heater layer 3 is as low as 250 ° C. In particular, the gas characteristics of methane gas, carbon monoxide, and hydrogen have similar trends and cannot be distinguished. On the other hand, since the resistance of methane gas, carbon monoxide, and hydrogen is low with respect to the resistance of air, there is sufficient sensitivity. That is, it is possible to detect the presence or absence of interference gas or detection target gas.

  Therefore, an electrical resistance characteristic (or a simplified sensor resistance value at a lapse of a predetermined time of 150 ms, for example, for air) that represents the relationship between the energization time and the sensor resistance value for air is registered in the storage circuit 600 and compared. It is determined by. For example, assuming that the sensor resistance value when a predetermined time has elapsed is registered, the sensor resistance value when the registered air has elapsed for a predetermined time (for example, 150 ms) and the sensor detected when the predetermined time (for example, 150 ms) has elapsed since energization The resistance value is compared, and the sensor resistance value sufficiently lower than the sensor resistance value when the registered air has passed for a predetermined time (for example, 150 ms) (for example, the resistance value at which the methane reaches 1000 ppm level (approximately 80% or less of the resistance value in the air) )) Is detected, it can be determined that there is an interference gas or a detection target gas. And it becomes possible to change to the 2nd mode drive. In addition, when the sensor resistance value when the registered air has passed for a predetermined time (for example, 150 ms) and the detected sensor resistance value are substantially the same (for example, when the resistance value is more than about 80% of the air resistance value), interference gas or detection The detection is terminated as air that does not contain the target gas. Normally, the first drive mode and the first determination mode at a relatively low temperature of 250 ° C. are often ended, which contributes to lower power consumption.

Subsequently, the signal processing / driving unit 700 has a temperature at which the interference gas is combusted by heating from the heater layer 3 of the gas sensor 100 when the interference gas or the detection target gas is included, and the gas detection layer 53 has only the detection target gas. It functions as a means for controlling the heater layer driving unit 200 so that the temperature is detected (second mode driving means 703).
Specifically, the pulse is applied so that the temperature is higher than that of the first mode driving unit 701 and the temperature of the heater layer 3 is 450 ° C. over 200 ms.
The pulse for the second mode drive may be energized continuously after the pulse for the first drive mode, or may be energized with an interval from the pulse for the first drive mode.

  Subsequently, the signal processing / driving unit 700 functions as a unit that determines the presence or concentration of the detection target gas based on the resistance characteristic of the gas sensing layer 53 (second mode determination unit 704).

FIG. 3 shows changes in the sensor resistance value of the gas sensing layer 53 when the gas sensing layer 53 in each atmospheric gas reaches 450 ° C. by such second mode driving. As is apparent from FIG. 3, the electrical resistance characteristic representing the relationship between the energizing time and the sensor resistance value, in accordance with the energizing time has elapsed, the detection target gas (methane), the sensor resistance of the gas sensing layer 53, Although approaches a constant value after the reduction as the energization time has passed, the other interference gases (carbon monoxide, hydrogen), shows a characteristic that the sensor resistance increases as the energization time has elapsed.
For the detection target gas, the sensor resistance value of the gas sensing layer 53 tends to decrease as the concentration increases as compared to the sensor resistance value at 250 ° C. in FIG.

For example, in the case of the detection target gas (methane gas), the relationship between the energization time and the sensor resistance value decreases as the time elapses, and becomes stable at a predetermined value after about 100 ms. There is sensitivity because the sensor resistance value of methane gas (1000 ppm) is lower than the sensor resistance value of air, and the sensor resistance value of methane gas (4000 ppm) is lower than the sensor resistance value of methane gas (1000 ppm). Therefore, the presence or absence of the detection target gas (methane gas) is easy to detect, and for methane gas, the sensor resistance value and the concentration are approximately proportional to each other, and the calculation for calculating the concentration at the sensor resistance value in the memory circuit 600 is performed. If the equation is registered, it is possible to detect the concentration.
On the other hand, the relationship between the energization time and the sensor resistance value in the case of other interference gases (carbon monoxide, hydrogen) is as follows. The sensor resistance value once decreases as time elapses, and then increases around 50 ms. It approaches the sensor resistance value. This is because the interference gas disappears by combustion. Therefore, if this tendency is detected, the presence or absence of interference gas (carbon monoxide, hydrogen) can be detected. Therefore, the determination result for the interference gas may be output.

  Therefore, the first mode determination unit and the second mode determination unit determine whether the gas type is air, detection target gas (methane gas), or interference gas (carbon monoxide, hydrogen). The concentration of the detection target gas (methane gas) is also determined.

  Subsequently, the signal processing / driving unit 700 notifies gas information related to the detection target gas (for example, that there is a detection target gas) based on the determination content by the first mode determination unit 702 or the second mode determination unit 704. Functions as a means for outputting (information) (output control means 705). When the detection target gas is detected, the signal processing / driving unit 700 causes the alarm display circuit 300 to display an alarm, causes the alarm sound output circuit 400 to output an alarm sound, or causes the external output circuit 500 to perform an external output. To function. It should be noted that such an output may also be performed when detecting the interference gas. A series of driving operations including the first mode driving unit 701, the first mode determining unit 702, the second mode driving unit 703, the second mode determining unit 704, and the output control unit 705 are performed at a predetermined cycle (30 s, 120 s, etc.). ) Is repeated every time.

  According to such a gas detection apparatus 1000 of this embodiment, normally, the first mode drive that heats the temperature to about 250 ° C. is set to a mode with low power consumption, and the temperature is not detected until the detection target gas or the interference gas is detected. By using the second mode drive that heats to about 450 ° C., it is possible to significantly reduce power consumption during normal operation. Normally, only the first mode with low power consumption continues to be detected, which contributes to reduction of power consumption in the long run.

  Next, another embodiment will be described. In this embodiment, the determination logic of gas detection by the signal processing / driving unit 700 is improved without changing the configuration described above with reference to FIG. In this embodiment, air and interference gas can be detected particularly in the first mode driving, and the driving in the second mode driving is further suppressed to realize more effective low power consumption.

Next, gas detection performed by the program processing of the signal processing / driving unit 700 will be described below.
First, the signal processing / driving unit 700 is configured so that the gas sensing layer 53 differs from the electrical resistance characteristic of the detection target gas and the electrical resistance characteristic of the interference gas by heating from the heater layer 3 of the gas sensor 100 in a normal time ( It functions as a means for controlling the heater layer driving section 200 so as to be 300 ° C. (first mode driving means 701). In detail, it supplies with electricity so that the temperature of the heater layer 3 may be 300 degreeC over 200 ms.

  Subsequently, the signal processing / driving unit 700 functions as means for determining whether or not the detection target gas is included based on the electric resistance characteristic of the gas sensing layer 53 (first mode determination means 702).

  FIG. 4 shows changes in the sensor resistance value when the gas sensing layer 53 in each atmospheric gas reaches 300 ° C. by such first mode driving. As is clear from FIG. 4, the electrical resistance characteristic representing the relationship between the energization time and the sensor resistance value is once the sensor resistance value for the air and the detection target gas (methane gas) is temporarily increased as the energization time elapses. It is a trace that stabilizes to a predetermined value after decreasing, but for other interference gases (carbon monoxide, hydrogen), the sensor resistance value once decreases as the energization time elapses, and increases after a predetermined minimum value It draws a turning trajectory. Moreover, since the sensor resistance value about methane gas, carbon monoxide, and hydrogen is low with respect to the sensor resistance value in air, it has sensitivity. Therefore, it is possible to accurately and easily determine the gas type by examining what kind of locus the energization time and the sensor resistance value draw.

  That is, it can be determined whether it is air, interference gas, or detection target gas. Therefore, an electrical resistance characteristic (or a simplified sensor resistance value at a lapse of a predetermined time of 150 ms, for example, for air) that represents the relationship between the energization time and the sensor resistance value for air is registered in the storage circuit 600 and compared. It is determined by. For example, assuming that the sensor resistance value when a predetermined time has elapsed for air is registered, the sensor resistance value when the registered air has elapsed for a predetermined time (for example, 150 ms) and when the predetermined time (for example, 150 ms) has elapsed since energization. The detected sensor resistance value is compared, and the resistance value sufficiently lower than the sensor resistance value when the registered air has passed for a predetermined time (for example, 150 ms) (for example, the resistance value at which the methane reaches 1000 ppm level (about 80% of the air resistance value)). % Or less)) is detected, it is determined that there is an interference gas or a detection target gas, and whether it is a predetermined interference gas or a detection target gas based on the following determination method is a detection target gas It is possible to change to the second mode drive. In addition, when the sensor resistance value when the registered air has passed for a predetermined time (for example, 150 ms) and the detected sensor resistance value are substantially the same (for example, when the resistance value is more than about 80% of the air resistance value), interference gas or detection The detection is terminated as air that does not contain the target gas. As will be described later, the detection is also terminated when the interference gas is used. In the previous embodiment, the transition to the second mode driving is performed even with the interference gas. However, in this embodiment, the process is completed even with the air or the interference gas, which further contributes to lower power consumption.

  The first mode determination unit 702 acquires a plurality of difference values using sensor resistance values of the gas sensing layer 53 at a plurality of points in time after the heater layer 3 is driven by the first mode driving unit 701, and these difference values are obtained. Is less than a predetermined value close to 0 (for example, 10% or less, more preferably 5% or less of the resistance value at a short time), it is determined that the detection target gas is included, and a predetermined value (for example, a resistance value at a short time) 10%, more preferably 5% or less), it is determined that the interference gas is contained.

Specifically, in FIG. 4, in the case of interference gas (CO, H ₂ ), the sensor resistance value decreases to about 40 ms as the energization time elapses, and then starts increasing and increases to 200 ms. For example, as shown in FIG. 5A, the sensor resistance values at two arbitrary points between 40 ms and 200 ms are compared, and the sensor resistance value at the time when the energization time is long (for example, the B point of the black dot of 150 ms) is short. Interference gas when the difference value obtained by subtracting the sensor resistance value at the time (for example, point A of the black circle of 100 ms) is larger than a predetermined value close to 0 (for example, 10% of the resistance value at the short time, more preferably 5% or less) Can be determined to exist. If the gas is a gas to be detected, the sensor resistance value is stable after the decrease, and the sensor resistance value at a short time (for example, a white circle of 100 ms) from the sensor resistance value at a long time of energization (for example, point B of a white circle of 150 ms). When the difference value obtained by subtracting the point A) is almost close to 0, and the difference is less than or equal to a predetermined value close to 0 (for example, 10% or less, more preferably 5% or less of the resistance value at a short time) It can be determined that the detection target gas (methane gas) is present. Therefore, discrimination between the interference gas and the detection target gas is easy.

  In the above description, sensor resistance values at two points are used, but a difference between point C and point B and a difference between point B and point A may be taken at three points as shown in FIG. In this case, in the interference gas, both the difference value between the point C and the point B (black circle) and the difference value between the point B and the point A (black circle) are positive, and the upward tendency is reliably captured. It can be determined that there is. In addition, in the detection target gas, the difference value between the point B and the point A (white circle) is negative, but the difference value between the point C and the point B (white circle) is a value close to 0 and there is no inclination. It can be determined that the gas is a detection target gas.

  Further, as shown in FIG. 5C, the difference between D point and C point, the difference between C point and B point, and the difference between B point and A point may be taken at 4 points, respectively. In this case, in the interference gas, the difference value between point B and point A (black circle) is negative, but the difference value between point D and point C (black circle) and the difference value between point C and point B (black circle) In both cases, the polarity is positive, and the rising tendency is reliably captured, so that it can be determined that the gas is an interference gas. Further, in the detection target gas, the difference value between point B and point A (white circle) is negative, but the difference value between point D and point C (white circle) and the difference value between point C and point B (white circle) Both of these values are close to 0, and the tendency of no inclination is reliably captured, and it can be determined that the gas is a detection target gas.

  The first mode determination unit 702 acquires a plurality of differential values using the sensor resistance values of the gas sensing layer 53 at a plurality of time points after the heater layer 3 is driven by the first mode driving unit 701. When the differential value difference value is larger than a predetermined value close to 0, it is determined that the interference gas is included, and when the differential value is equal to or less than the predetermined value close to 0, it is determined that the detection target gas is included.

Specifically, in FIG. 4, in the case of interference gas (CO, H ₂ ), the sensor resistance value decreases to about 40 ms and then increases until it increases to 200 ms. As shown in (a), the sensor resistance values at any two points between 40 ms and 200 ms are compared, and the sensor resistance value at a short time from the sensor resistance value at a long energization time (for example, point B of a black dot of 150 ms). A differential value is obtained by dividing a difference value obtained by subtracting a value (for example, a black dot A of 100 ms) by time (t2−t1 = 50 ms), and interference occurs when the differential value difference value is larger than a predetermined value close to 0. It can be determined that gas is present. If it is a gas to be detected, the sensor resistance value is stable after the decrease, and the sensor resistance value at a short time (for example, the B point of a white circle of 150 ms) from the sensor resistance value at the time of a long energization time (for example, a white circle of 100 ms). The differential value obtained by dividing the difference value obtained by subtracting (A point) by time (t2−t1 = 50 ms) is also almost 0, and when the differential value is less than a predetermined value close to 0, the detection target gas ( It can be determined that methane gas is present. Therefore, discrimination between the interference gas and the detection target gas is easy.
The predetermined value is appropriately determined by experiments or the like. For example, when the sensor resistance value of 10 kΩ is defined to be within 10% between 100 ms and 150 ms, the predetermined value is 20 Ω / ms.

  In the above description, sensor resistance values at two points are used. However, as shown in FIG. 5B, the differentiation between point C and point B and the differentiation between point B and point A may be taken at three points. In this case, in the interference gas, both the differential value between point C and point B (black circle) and the differential value between point B and point A (black circle) are positive, and the upward trend is reliably captured. It can be determined that there is. Further, in the gas to be detected, the differential value between the point B and the point A (white circle) is negative, but the differential value between the point C and the point B (white circle) is a value close to 0 and there is no inclination. It can be determined that the gas is a detection target gas.

  Further, as shown in FIG. 5C, the differentiation between the D point and the C point, the differentiation between the C point and the B point, and the differentiation between the B point and the A point may be taken at four points, respectively. In this case, in the interference gas, the differential value between point B and point A (black circle) is negative, but the differential value between point D and point C (black circle) and the differential value between point C and point B (black circle) In both cases, the polarity is positive, and the rising tendency is reliably captured, so that it can be determined that the gas is an interference gas. Further, in the detection target gas, the differential value between point B and point A (white circle) is negative, but the differential value between point D and point C (white circle) and the differential value between point C and point B (white circle) Both of these values are close to 0, and the tendency of no inclination is reliably captured, and it can be determined that the gas is a detection target gas. Needless to say, the point at which the differential value is calculated is set with a sufficient interval so as not to be affected by noise during measurement. Further, the influence of noise may be removed by moving average of data during processing and using data from which an instantaneous change is removed.

  In more detail, the first mode determination unit 702 acquires time state change characteristics based on sensor resistance values of the gas sensing layer 53 at a plurality of time points after the heater layer 3 is driven by the first mode driving unit 701. When the minimum value appears in the change state characteristic, it is determined that the interference gas is included, and when the minimum value does not appear in the time change state characteristic, it is determined that the detection target gas is included.

Specifically, as shown in FIG. 6, since the minimum value appears between 0 ms and 200 ms from the start of energization, the interference gas exists when the minimum value appears, and the minimum value appears. If the value does not appear, it can be determined that the detection target gas (methane gas) exists. Even with such a detection method, the electric resistance characteristic of the interference gas can be reliably captured, and the interference gas can be determined. The first mode determination is performed in this way.
In addition, in the first mode determination, in addition to the case where it is determined that the air is detected, the processing is also terminated when it is determined that the gas is not the detection target gas but the interference gas.

Subsequently, the signal processing / driving unit 700 controls the heater layer driving unit so that the gas sensing layer 53 reaches a temperature at which only the sensing target gas is detected by heating from the heater layer 3 only when the gas is the sensing target gas. It functions as a means (second mode driving means 703).
Specifically, a pulse that is higher in temperature than the first mode driving unit 701 and has a heater temperature of 450 ° C. is applied for 200 ms.

  Subsequently, the signal processing / driving unit 700 functions as a unit that determines the presence or concentration of the detection target gas based on the resistance characteristic of the gas sensing layer 53 (second mode determination unit 704).

  FIG. 3 shows changes in the sensor resistance value of the gas sensing layer 53 in each atmospheric gas when the gas sensing layer 53 reaches 450 ° C. by such second mode driving. As is clear from FIG. 3, the electrical resistance characteristic representing the relationship between the energization time and the sensor resistance value indicates that the sensor resistance value decreases for the detection target gas (methane gas) as time elapses. .

  For example, in the case of the detection target gas (methane gas), the relationship between the energization time and the sensor resistance value decreases as the time elapses, and becomes stable at a predetermined value after about 100 ms. There is sensitivity because the sensor resistance value of methane gas (1000 ppm) is lower than the sensor resistance value of air, and the sensor resistance value of methane gas (4000 ppm) is lower than the sensor resistance value of methane gas (1000 ppm). Therefore, the presence or absence of the detection target gas (methane gas) is easy to detect, and for methane gas, the sensor resistance value and the concentration are approximately proportional to each other, and the calculation for calculating the concentration at the sensor resistance value in the memory circuit 600 is performed. If the equation is registered, it is possible to detect the concentration.

  Therefore, the first mode determination unit and the second mode determination unit determine whether the gas type is air, detection target gas (methane gas), or interference gas (carbon monoxide, hydrogen). The concentration of the detection target gas (methane gas) is also determined.

Subsequently, the signal processing / driving unit 700 notifies gas information related to the detection target gas (for example, that there is a detection target gas) based on the determination content by the first mode determination unit 702 or the second mode determination unit 704. Functions as a means for outputting (information) (output control means 705). The signal processing / driving unit 700 functions to cause the alarm display circuit 300 to display an alarm, to cause the alarm sound output circuit 400 to output an alarm sound, and to cause the external output circuit 500 to perform an external output.
A series of driving operations including the first mode driving unit 701, the first mode determining unit 702, the second mode driving unit 703, the second mode determining unit 704, and the output control unit 705 as described above are performed in a predetermined cycle (here, 30 s or It is repeated every 120 s).

According to such a gas detection apparatus 1000 of the present embodiment, the detection target gas is detected by detecting the presence or absence of the detection target gas by setting the power consumption mode as a first mode drive that normally heats the temperature to about 300 ° C. By performing the second mode driving in which the temperature is heated to about 450 ° C. for the first time only when it is detected, it becomes possible to significantly reduce power consumption during normal operation. In particular, when only the interference gas is used, the second mode drive is not performed, which contributes to low power consumption.
Note that the heater temperature and cycle shown in this embodiment are due to the characteristics of the sensor used, and even if different heater temperatures and cycles are used, the contents of the present invention are not departed. Moreover, although embodiment mentioned above demonstrated the case where a thin film gas sensor was used as a gas sensor, this invention is not limited to a thin film gas sensor.

  The gas detection device of this embodiment has been described above with reference to the drawings. According to these embodiments, if the combustion is performed only when it is determined that the target gas or the interference gas exists without being burned at a high temperature (450 ° C.) as in the prior art, it contributes to the reduction in power consumption.

  The gas detection device of the present invention is particularly applicable to uses such as a gas leak alarm.

1000: Gas detector 100: Gas sensor 1: Si substrate 2: Thermal insulating support layer 21: Thermally oxidized SiO ₂ layer 22: CVD-Si ₃ N ₄ layer 23: CVD-SiO ₂ layer 3: Heater layer 4: Electrical insulating layer 5: Gas detection unit 51: Bonding layer 52: Sensing electrode layer 53: Gas sensing layer 54: Selective combustion layer 200: Heater layer driving unit 300: Alarm display circuit 400: Alarm sound output circuit 500: External output circuit 600: Storage circuit 700: signal processing / driving unit 701: first mode driving unit 702: first mode determining unit 703: second mode driving unit 704: second mode determining unit 705: output control unit 800: power supply circuit

Claims (10)

A gas sensor having a gas sensing layer whose electrical resistance characteristics change by contact with a gas to be detected, and a heater layer for heating the gas sensing layer;
A heater layer driving section for driving the heater layer;
A signal processing / driving unit to which the gas sensing layer and the heater layer driving unit are connected;
With
The signal processing / driving unit is
In the normal state, a first mode drive means for controlling said heater layer driver so that the gas sensing layer by heating from the heater layer is a temperature for detecting the presence or absence of interference gas or detection target gas,
First mode determination means for determining that an interference gas or a detection target gas is present when an electric resistance value of the gas sensing layer is lower than an electric resistance value with respect to air ;
If it is determined that the interference gas or detection target gas is present the first mode determining means, the gas sensing layer a temperature for burning the interference gas by heating from the heater layer and the temperature detected only detection target gas a second mode drive means and said controlling the heater layer driver Ru switches the heating temperature of the heater layer such that,
Second mode determination means for determining the presence or concentration of the detection target gas based on the fact that the electrical resistance value of the gas sensing layer approaches a constant value after decreasing as the energization time elapses ;
Gas detecting apparatus characterized by that function. A gas sensor having a gas sensing layer whose electrical resistance characteristics change by contact with a gas to be detected, and a heater layer for heating the gas sensing layer;
A heater layer driving section for driving the heater layer;
A signal processing / driving unit to which the gas sensing layer and the heater layer driving unit are connected;
With
The signal processing / driving unit is
In a normal time, the heater layer driving unit is controlled so that the gas sensing layer has a temperature that makes the electric resistance characteristic of the detection target gas different from the electric resistance characteristic of the interference gas by heating from the heater layer. Mode driving means;
First mode determination means for determining whether or not a gas to be detected is included based on the electrical resistance characteristics of the gas sensing layer;
Second mode driving means for controlling the heater layer driving unit so that the gas sensing layer detects only the detection target gas by heating from the heater layer only when the gas is the detection target gas;
Second mode determination means for determining the presence or concentration of the detection target gas based on the electric resistance characteristics of the gas sensing layer;
Gas detecting apparatus characterized by that function. The gas detection device according to claim 2,
The first mode determination means acquires a plurality of difference values using sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode driving means, and these difference values are zero. A gas detection device that determines that a detection target gas is included when the value is less than or equal to a predetermined value, and determines that interference gas is included when the detection target gas is greater than a predetermined value. The gas detection device according to claim 2,
The first mode determination means acquires a plurality of differential values using sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode driving means, and these differential values are 0. A gas detection device that determines that a detection target gas is included when the value is less than or equal to a predetermined value, and determines that interference gas is included when the detection target gas is greater than a predetermined value. The gas detection device according to claim 2,
The first mode determination means acquires time state change characteristics according to sensor resistance values of the gas sensing layer at a plurality of time points after the heater layer is driven by the first mode drive means. A gas detection device that determines that an interference gas is included when a minimum value appears, and determines that a detection target gas is included when a minimum value does not appear among time-varying state characteristics. In the gas detection device according to any one of claims 1 to 5,
Output control means for outputting gas information related to the detection target gas based on the determination content by the first mode determination means or the second mode determination means;
A gas detection device comprising: In the gas detection device according to any one of claims 1 to 6,
A gas detection device driven by power supplied from a power supply circuit by a built-in battery. In the gas detection device according to any one of claims 1 to 7,
The signal processing / driving unit is driven by energizing the heater layer at a predetermined cycle,
The gas detection device, wherein the gas detection layer is heated at a predetermined cycle. In the gas detection device according to any one of claims 1 to 8,
The gas sensor
A Si substrate having a through hole;
A diaphragm-like heat insulating support layer stretched over the opening of the through hole;
The heater layer provided on the thermal insulating support layer;
An electrical insulation layer provided to cover the thermal insulation support layer and the heater layer;
A pair of sensing electrode layers provided on the electrically insulating layer;
The gas sensing layer made of an oxide semiconductor, which is provided on the electrical insulating layer and the pair of sensing electrode layers and in the vicinity of the heater layer, and whose sensor resistance value is changed by the gas in contact with the gas sensing layer;
It is a sensor provided with, The gas detection apparatus characterized by the above-mentioned. The gas detection device according to claim 9, wherein
The gas sensor is further provided so as to cover the surface of the gas sensing layer, and is made of an Al ₂ O ₃ sintered material that supports Pd (palladium), Pt (platinum), or an alloy containing Pd and Pt as a catalyst. A gas detection device comprising a gas selective combustion layer.

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