JP4210758B2 - Gas alarm - Google Patents

Description

  The present invention relates to a gas alarm device that detects gas based on a change in electrical resistance value of a semiconductor, and relates to a gas alarm device provided with an inspection mode for performing an inspection by a simple method.

  In general homes and the like, gas alarms that generate warnings by detecting leakage of methane, which is a component of city gas, are widely used. When such a gas alarm device is normally installed, the operation of the alarm device is checked by applying a detection target gas. For example, the operation check of the city gas alarm function is performed by collecting city gas collected by a gas stove or the like into a dropper-shaped container and applying it to a gas alarm device. However, there are cases where city gas is not opened in the residence where the gas alarm is installed. For this reason, workers carry a lighter, and when checking the operation of the gas alarm, the lighter Volatile gas (butane) generated when the gas is not ignited is collected with a dropper-shaped collector and used as a substitute for city gas.

  In the conventional gas alarm device, the gas sensor unit that detects city gas, especially methane, has an activated carbon filter layer to suppress false alarms on gases such as alcohol. This layer suppresses lighter gas (butane) sensitivity. Has an effect. Therefore, a hole called an inspection hole is provided so that the lighter gas reaches the gas sensor element without going through the activated carbon filter layer.

  FIG. 6 shows the structure of such a conventional gas sensor unit. In a case 102 having an opening 101 on the upper surface, an activated carbon filter unit 103 is provided so as to cover the opening 101, and below that. A gas sensor element 104 is arranged, and an inspection hole 105 is provided on the wall surface of the case 102 so that lighter gas can reach the gas sensor element 104 without passing through the activated carbon filter portion 103.

  The conventional gas sensor element used in such a gas sensor structure is large in size and resistant to poisoning, so even if the inspection hole as described above is provided, the influence on the sensor performance is small and can be used without any problem. It was.

  However, recently, in order to save the power of the sensor portion for the purpose of saving the power of the gas alarm device, the development of miniaturizing the gas sensor element using a tin oxide thin film as the gas sensitive portion has been advanced. For example, in Patent Documents 1 and 2 below, as a gas sensor element for power saving, the outer periphery or both ends of a thin film-like support film are supported by a Si substrate, the outer periphery or both ends are thick, and the central portion is A thin film heater is formed on a thin diaphragm-like support substrate, the thin film heater is covered with an electrical insulating layer, and a film-like gas-sensitive layer made of an oxide semiconductor is formed on the thin film heater. There has been proposed a small sensor structure provided with a catalyst filter layer carrying a noble metal catalyst.

However, in general, when the size of the gas sensor element is reduced, the gas sensor element is easily affected by poisonous substances from the environment. Therefore, in such a fine sensor structure, there is a problem that there is a path to reach the gas sensor element without passing through an activated carbon filter such as an inspection hole, and it is difficult to maintain stability over time. Therefore, in the case of using a fine gas sensor element, it is not possible to provide an inspection hole, and a measure is taken to strengthen the function of the filter as compared with the prior art. As this strengthening method, an attempt is made to increase the amount of filter material such as activated carbon or make the opening provided in the case smaller.
JP 2003-262598 A JP 2003-262599 A

  The enhancement of the filter function as described above does not greatly change the detection performance of methane having low adsorptivity to the filter, but the sensitivity to butane gas, which is a gas having stronger adsorptivity, is lowered. This becomes an obstacle when the operation check of the above-mentioned city gas detection function is carried out with lighter gas.

  This invention is made in view of the above-mentioned situation, and it aims at providing the gas alarm which can perform the operation | movement check of a city gas detection function by a simple method even if the city gas is not opened. To do. In particular, an object of the present invention is to provide a gas alarm device that can easily check the operation of an alarm function even in a case where a gas sensor unit having an advanced filter function is mounted.

  For the fine gas sensor element using a tin oxide thin film, the present inventors have measured the electric resistance value of the film gas sensitive layer when the film gas sensitive layer temperature is periodically switched between a high temperature and a low temperature by a heater. As a result of intensive analysis of the thermal response characteristics, the gas alarm installation site at a time different from the time to detect the detection target gas in the movement of the electrical resistance value at the temperature set to detect the detection target gas Thus, the present inventors have found that there is a sensitivity in the easily available gas species, and have completed the present invention.

  That is, the gas alarm device according to the present invention includes a gas sensor portion having a film-like gas sensitive layer made of an oxide semiconductor material, and the temperature of the film-like gas sensitive layer is set to a first temperature and a second temperature higher than that. A temperature control means for periodically switching and setting to at least two different temperatures, a resistance detection means for detecting the electrical resistance value of the film-like gas sensitive layer, and an alarm generated by the electrical resistance value detected by the resistance detection means A gas alarm device comprising: determining means for determining the electrical resistance value of the film-like gas sensitive layer when the temperature control means holds the second temperature by the resistance detecting means. A normal detection mode for detecting hydrogen gas, and an inspection mode for checking the operation of the alarm function, wherein the inspection mode is an electric resistance of the film-like gas sensitive layer when held at the second temperature. The detection timing of the electrical resistance value after the second temperature switching in the inspection mode is set shorter than the detection timing of the electrical resistance value after the second temperature switching in the normal detection mode. It is characterized by that.

  According to the gas alarm device of the present invention, in addition to the normal detection mode for detecting hydrocarbon gas such as methane, ethane, propane, etc., it has a different inspection mode. When the membranous gas sensitive layer is set to the same temperature as the detection temperature in the normal detection mode (the second temperature), the resistance detection time in the normal detection mode (from the temperature switching to the detection of the electrical resistance value) The electrical resistance value at a time set shorter than (time) is detected, and the judgment is made by the judgment means based on the value, and an alarm operation is performed. By doing in this way, it is an alarm device for detecting hydrocarbon gas such as city gas, but it is a gas type other than hydrocarbon gas and can be easily collected at the site, for example, alarm function by carbon monoxide gas It is possible to perform inspections.

  In the gas alarm device of the present invention, the gas sensor unit is a diaphragm-like support substrate in which the outer peripheral part or both end parts of the thin film-like support film are supported by the Si substrate, and the outer peripheral part or both end parts are thick and the central part is thin. There may be provided a gas sensor element in which a heater is formed on the heater and the film-like gas sensitive layer is formed on the heater via an electric insulating layer. By adopting such a structure, the thermal stabilization time of the film-like gas sensitive layer becomes extremely short, and the difference between the gas types can be clearly captured in the change in the electric resistance value after the second temperature switching. The range of choice of time that can be done will be expanded. That is, it can be set as a preferable form in that the selection range of the electric resistance value detection timing after the second temperature switching in the inspection mode becomes larger.

  In the gas alarm device of the present invention, the detection time of the electrical resistance value in the inspection mode may be set within a range of 5 to 150 msec after the second temperature switching. This is preferable because sensitivity to gases such as carbon monoxide and hydrogen that can be obtained in the field because it is included in the inner flame of a portable lighter can be particularly increased.

  In the gas alarm device of the present invention, Pt and / or Pd may be added to the inside or the surface of the film-like gas sensitive layer. That is, Pt and Pd may be contained inside the film-like gas sensitive layer, or a coating layer containing Pt and Pd may be provided on the surface of the film-like gas sensitive layer. By doing so, the city gas and other flammable gases in general detection mode are stable over time and have high sensitivity characteristics.

  According to the present invention, although it is an alarm device for detecting hydrocarbon gas, the alarm function is inspected with a gas other than hydrocarbon gas that can be easily collected on site, for example, carbon monoxide gas. Is possible. Therefore, even if the city gas is not opened, the operation of the alarm function can be checked by a simple method. Moreover, since carbon monoxide gas and hydrogen can permeate | transmit an activated carbon filter, the said operation | movement check can be performed also in the case of the gas sensor part with a high filter function.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a gas sensor element 10 mounted on a gas alarm device according to an embodiment of the present invention. This gas sensor element 10 has a diaphragm-like support substrate 16 in which the outer peripheral portion or both end portions of a thin film-like support layer (support film) 12 are supported by an Si substrate 14 and the outer peripheral portion or both end portions are thick and the central portion is thin. A thin-film heater layer 18 is formed thereon, the heater layer 18 is covered with an electrical insulating layer 20, and a film-like gas sensitive layer electrode (sensitive layer electrode) 24 is formed thereon via a bonding layer 22. Further, after forming a film-like gas sensitive layer 26 composed of a film-like body containing at least tin oxide (SnO ₂ ), a noble metal catalyst formed so as to completely cover the film-like gas sensitive layer 26 on the outermost surface ( A selective combustion layer (catalyst filter layer) 28 carrying Pt, Pd, etc.) is provided.

  In addition, in order to implement | achieve the above inspection modes in this invention, it is not limited to such a gas sensor element structure. However, with such a configuration, the temperature of the film-like gas sensitive layer 26 can be made to respond very quickly to changes in the energization voltage by the heater layer 18 that is a temperature control means, and in terms of power consumption. This is very practically advantageous.

  FIG. 2 shows an example of the gas sensor unit 30 on which the gas sensor element 10 described above is mounted. The gas sensor unit 30 covers a cylindrical or rectangular case 34 having an opening 32 on the upper surface, the gas sensor element 10 housed in the bottom of the case 34, and the lower surface of the opening 32 in the case 34. And an activated carbon filter part 36 filled. Gas that has entered through the opening 32 reaches the gas sensor element 10 after passing through the activated carbon filter 36 and does not pass through the activated carbon filter 36 such as the inspection hole 105 shown in FIG. A route to the gas sensor element 10 is not intentionally provided. When such a path is generated, the gas sensor element is changed with time due to long-term poisoning, which is disadvantageous for practical use. However, in this invention, it does not limit to the thing without the path | route which reaches | attains a gas sensor element without passing through an activated carbon filter part.

  A plurality of pins 38 serving as connection terminals to the electric wiring board are projected from the lower surface of the case 34, and a wiring (not shown) connected to the heater layer 18 and the sensitive layer electrode 24 is formed by these pins 38. Are respectively connected to each other to enable voltage application to the heater layer 18 and to detect the electric resistance value of the film-like gas sensitive layer 26.

  FIG. 5 is a cross-sectional view of the gas alarm device 50 according to the embodiment in which the gas sensor unit 30 described above is mounted. The gas alarm device 50 includes a rectangular housing 56 having an inspection gas injection hole 54 together with an opening 52 on the front surface, an electric wiring board 60 including a control unit 58 provided in the housing 56, and the electric wiring board 60. And a gas sensor unit 30 incorporated in the circuit. Then, the control unit 58 controls the voltage application to the heater layer 18 described above, controls the detection and timing of the electric resistance value of the film-like gas sensitive layer 26, and based on the detected electric resistance value. It is determined whether or not to issue an alarm. Alarms include lighting of warning lights such as LEDs, and warning sounds such as buzzers, etc. Usually, these gas alarm devices 50 are also equipped with warning lights and speakers (not shown). Has been. Furthermore, although not shown, a power supply unit such as a battery is also provided.

  The gas alarm device 50 according to the present embodiment includes a normal detection mode for detecting city gas and an inspection mode for checking the operation of an alarm function including the gas sensor unit 30, which will be described in detail below. To do.

  FIG. 3 shows a pattern of voltage application to the heater layer 18 provided in the gas sensor element 10 and resistance detection timing (timing) in the normal detection mode and the inspection mode. As shown in the figure, a pulsed voltage is applied to the heater layer 18, whereby the temperature of the film-like gas sensitive layer 26 periodically changes between a low temperature range (first temperature) and a high temperature range (second temperature). Switching is set to repeat. It is set for the purpose of detecting city gas in the high temperature range and detecting gas other than city gas in the low temperature range or for power saving. The temperature in the high temperature region is set so that the temperature is in the range of 420 to 530 ° C., for example. Further, the low temperature range can be set, for example, from room temperature to 150 ° C., and no voltage is applied so as to reach room temperature in the figure.

  In this gas alarm device 50, after switching from a low temperature region to a high temperature region which is a detection temperature, the gas concentration is determined or an alarm is generated based on an electric resistance value when a predetermined time has passed. As shown in FIG. 3, in the normal detection mode, the electric resistance value of the film-like gas sensitive layer 26 is measured when 200 msec has elapsed since the energization of the heater layer 18 is turned on, and the energization of the heater layer 18 is turned off simultaneously with the measurement You are in control. In the inspection mode, control is performed so that the electrical resistance value of the film-like gas sensitive layer 26 is measured at a predetermined timing shorter than 200 msec.

  The principle that enables normal detection of city gas and operation check of alarm function by such control will be described. FIG. 4 shows the responsiveness in various gases when the temperature of the electric resistance value of the film-like gas sensitive layer 26 in the gas sensor element 10 is changed with the voltage pattern of FIG. At that time, the voltage applied to the heater layer 18 was set to 2.8 V, and the film-like gas sensitive layer 26 was set to 450 ° C. In the gas sensor element 10 having this structure, the thermal stabilization time of the film-like gas sensitive layer 26 is extremely short and reaches a set temperature of 450 ° C. in about 5 msec. Therefore, the behavior of the change of the electric resistance value within 200 msec after the heater voltage application shown in FIG. 4 is caused by the temporal change of the adsorbed species on the surface of the film-like gas sensitive layer 26.

As shown in FIG. 4, the electric resistance value in methane (CH ₄ ), which is a component of city gas, stabilizes after decreasing to 30 msec, whereas in carbon monoxide, it decreases to around 30 msec and then starts to increase. I understand that. From this result, in this gas sensor element 10, the normal detection mode and the inspection mode may be set as follows.

That is, in the normal detection mode, in order to selectively detect methane and suppress the sensitivity to CO and H ₂ that are miscellaneous gases, the time when the electrical resistance value is detected (elapsed time since turning on the heater layer 18) The time) is preferably selected from the time when the resistance value of the miscellaneous gas rises to some extent, specifically from an arbitrary time after 150 msec, for example, a point of 200 msec is set.

  On the other hand, in the inspection mode time setting, if it is less than 5 msec, it does not reach a level lower than the electrical resistance value (about 4.6 kΩ) in 500 ppm of methane set as the lower limit of the methane alarm level. It becomes difficult to give a high gas sensitivity. In addition, if it exceeds 150 msec, the electrical resistance value in CO rises above the level (about 4.6 kΩ) in 500 ppm of methane, which is considered to be the lower limit of the methane alarm level, so that sufficient gas sensitivity is provided after 150 msec. It becomes difficult. From the above, in the inspection mode, it is desirable to detect and judge the electrical resistance value at a certain point selected from the range of 5 msec to 150 msec. As described above, the range of temporal selection of the detection timing of the electrical resistance value used in the inspection mode can be selected from a shorter time as the thermal stabilization time of the film-like gas sensitive layer 26 is shorter. Therefore, also in this respect, the gas sensor element structure shown in FIG. 1 is preferable.

  The switching method between the inspection mode and the normal detection mode is not particularly limited. For example, the inspection mode is set until the predetermined time elapses after the power is turned on, and the mode is automatically shifted to the normal detection mode after the predetermined time elapses. It may be configured. Further, the inspection mode and the detection mode may be manually switched by a switch or the like provided outside the gas alarm.

  With the above configuration, in the normal detection mode, carbon monoxide gas or the like does not reach the warning level for methane, but in the inspection mode, the carbon monoxide gas reaches the warning level for methane. It becomes possible to make it. Here, the carbon monoxide gas can be easily collected at the installation site of the gas alarm as the internal flame gas of the lighter. Therefore, with the configuration as described above, it is possible to check the operation of the alarm function by a simple method without adversely affecting the gas detection in the normal detection mode.

  Examples will be described below, but the present invention is not limited to such examples.

  A gas sensor element having the configuration shown in FIG. 1 was produced by the following procedure.

First, Si ₃ N ₄ and SiO ₂ films are sequentially formed by plasma CVD on one surface of the Si substrate on which both sides of the SiO ₂ film are formed by thermal oxidation, and a film that becomes the support layer 12 of the diaphragm structure is formed. Formed. Next, a heater layer 18 made of NiCr or PtW was formed thereon. Further, after the SiO ₂ insulating film 20 was formed by the sputtering method, a Pt / Ta bilayer film was formed as the sensitive layer electrode 24 as an electrode of the film-like gas sensitive layer. Here, the Ta film serves as a bonding layer 22 between the SiO ₂ and Pt films. Further, an SnO ₂ film having a thickness of 0.1 to 10 μm was formed thereon as a film-like gas sensitive layer 26 by sputtering. Next, a powder in which 0.1 to 7.5% by weight of Pd catalyst is supported on alumina particles is used as a paste together with a binder, and is applied to the surface of the film-like gas sensitive layer (SnO ₂ ) 26 by screen printing, followed by firing. A selective combustion layer (catalyst filter layer) 28 having a thickness of about 30 μm was formed. Finally, Si was completely removed from the back surface of the Si substrate by a dry etching method with a diameter of 400 μm to obtain a support substrate 16 having a diaphragm structure including the Si substrate 14 and the support layer 12 as shown in FIG.

  The obtained gas sensor element 10 was accommodated in the case 34 shown in FIG. 2, and the activated carbon filter part 36 was provided below the opening 32 to constitute the gas sensor part 30. And this gas sensor part 30 was integrated in the housing 56 shown in FIG. 5, and the gas alarm device 50 was produced.

  The control method of the gas alarm device 50 was as follows. That is, as shown in FIG. 3, the applied voltage to the heater layer 18 is set to 0V for the energizing voltage except that the gas sensor is held at 450 ° C. for 200 msec for detection of methane, and 2.8V is set to 450 ° C. The pulse energization was performed for 200 msec, and the energization was repeated every 30 seconds. In the normal detection mode, an electric resistance value near the last point maintained at 450 ° C., that is, when 200 msec has elapsed is detected, and an alarm is determined based on the magnitude of this value. In this case, both the heater energization and electrical resistance value detection cycle in the inspection mode and the heater energization and electrical resistance value detection cycle in the normal detection mode are both 30 seconds, but this cycle is different. It may be. For example, the inspection work time can be shortened by making the heater energization and electrical resistance detection cycle in the inspection mode shorter than the heater energization and electrical resistance detection cycle in the normal detection mode. Is also possible.

  At that time, the electric resistance values in the normal detection mode of 1000 ppm of methane and 3000 ppm of methane (see FIG. 4) are set as the first and second alarm levels, respectively, and the first alarm level (3.0 kΩ) is set. ), That is, when the value of the first stage alarm level is below the value (3.0 kΩ), it is indicated by the LED lighting as a warning light, and the second level alarm level (1.6 kΩ) When the change exceeds the value, that is, when it falls below the value of the second-stage alarm level (1.6 kΩ), a buzzer sound is generated in addition to the lighting of the LED.

  In addition, as an inspection mode, an electrical resistance value is detected when 40 msec has passed since the temperature is maintained at 450 ° C., and an alarm is issued based on whether this value exceeds the first-stage alarm level or the second-stage alarm level described above. Configured to emit.

  Note that the alarm judgment value and type of alarm in the inspection mode need not match the alarm judgment value and type of alarm in the normal detection mode. For example, when the inspection level changes beyond the first-stage alarm level, an alarm equivalent to the alarm issued when the second-stage alarm level in the normal detection mode is exceeded may be issued.

  In addition, switching between the normal detection mode and the inspection mode is configured to be switchable by an external switch for the convenience of the test.

  Hereinafter, a verification method and result of the gas alarm device manufactured with the above-described configuration will be described.

  Gas was supplied from the inspection gas injection hole 54 of the gas alarm device 50 using a dropper-shaped gas supply device. Gas species subjected to gas injection were 1000 ppm methane air diluted gas, 100% methane gas, 500 ppm carbon monoxide diluted gas, and lighter flame gas (gas containing carbon monoxide).

The types of alarms for the normal detection mode and the inspection mode were confirmed. The results are shown in Table 1 below.

  As can be seen from Table 1, in the normal detection mode, the first and second stage alarms are issued for 100% methane gas, and the first stage alarm is issued for 1000 ppm methane air diluted gas, whereas 500 ppmCO No warning was given for the / air dilution gas and the lighter flame gas.

  On the other hand, in the inspection mode, for 100% methane gas and 1000 ppm methane air diluted gas, an alarm similar to that in the normal detection mode was issued, whereas for the 500 ppm CO / air diluted gas, a first-stage alarm was issued. For the lighter flame gas, the first and second warnings were issued.

  As described above, by adopting the inspection mode of the present invention, it is possible to realize the operation inspection of the gas sensor unit for detecting city gas by the lighter flame gas even in a place where the gas is not opened. It was.

It is sectional drawing which shows the structure of the gas sensor element used with the gas alarm which concerns on one Embodiment of this invention. It is sectional drawing which shows the internal structure of the gas sensor part carrying the same gas sensor element. It is a graph which shows the pattern of the voltage application to the heater layer of the gas sensor part, and the resistance detection time of normal detection mode and inspection mode. It is a graph which shows the responsiveness in various gas when changing the temperature about the electrical resistance value of the film-like gas sensitive layer in the gas sensor part. It is sectional drawing which shows the internal structure of the gas alarm device carrying the said gas sensor part. It is sectional drawing which shows the internal structure of the conventional gas sensor part.

Explanation of symbols

10 ... Gas sensor element 12 ... Support layer (support film)
14 ... Si substrate 16 ... Support substrate 18 ... Heater layer 20 ... Electrical insulation layer 26 ... Film-like gas sensitive layer 30 ... Gas sensor unit 50 ... Gas alarm

Claims (5)

A gas sensor portion having a film-like gas-sensitive layer made of an oxide semiconductor material;
Temperature control means for periodically switching and setting the temperature of the film-like gas sensitive layer to at least two different temperatures of a first temperature and a second temperature higher than the first temperature;
Resistance detection means for detecting an electrical resistance value of the film-like gas sensitive layer;
In a gas alarm device comprising: determination means for determining the occurrence of an alarm based on the electrical resistance value detected by the resistance detection means,
A normal detection mode for detecting hydrocarbon gas by detecting an electric resistance value of the film-like gas sensitive layer when the temperature control means is held at the second temperature by the resistance detection means; and an alarm function. It has an inspection mode to check the operation,
The inspection mode is to detect the electrical resistance value of the film-like gas sensitive layer when the second temperature is maintained, and the detection timing of the electrical resistance value after the second temperature switching in the inspection mode is detected. The gas alarm device is set shorter than the detection time of the electric resistance value after the second temperature switching in the normal detection mode.   The gas sensor unit supports an outer peripheral part or both ends of a thin film-like support film by a Si substrate, and forms a heater on a diaphragm-like support substrate in which the outer peripheral part or both ends are thick and the central part is thin, 2. The gas alarm device according to claim 1, further comprising a gas sensor element in which the film-like gas sensitive layer is formed on the heater via an electric insulating layer.   The gas alarm device according to claim 1 or 2, wherein the detection time of the electric resistance value in the inspection mode is set within a range of 5 to 150 msec after the second temperature switching.   The gas alarm device according to any one of claims 1 to 3, wherein Pt and / or Pd is added to the inside or the surface of the film-like gas sensitive layer.   The gas alarm device according to any one of claims 1 to 4, wherein carbon monoxide gas is detected in the inspection mode.

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