JPH11283147A - Gas alarm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain stable detection accuracy for a long time by correcting a discrimination level corresponding to the change characteristics or fluctuation characteristics of a gas sensor with the passage of time or corresponding to seasons concerning a gas leak alarm. SOLUTION: This concerns a gas alarm provided with a gas sensor 2 to change its electric characteristics by detecting gas, a heater 3 for heating this gas sensor 2 to a prescribed temperature, a temperature sensor 4 for measuring the temperature of the gas sensor 2 and a control means for controlling the heater 3 based on the temperature of the gas sensor 2 measured by this temperature sensor 4, for processing the output signal of the gas sensor 2 and performing warning operation when that output signal exceeds a discrimination level, wherein the detection accuracy of the gas sensor 2 is corrected corresponding to cumulative operating time from the time point of operation start as an alarm or the fluctuation corresponding to seasons.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor which detects dangerous situations such as gas leaks and fires by using a gas sensor, and issues an alarm to people around for safety and a communication signal to the outside or a distant place. The present invention relates to a gas alarm device that generates an alarm and notifies the occurrence of a dangerous state. In particular, the invention relates to gas alarms operable by battery power.

[0002]

2. Description of the Related Art Conventionally, fire alarms and gas leak alarms installed in homes, buildings and the like generally use a commercial power supply or a rechargeable battery. As another alarm device, a portable alarm device for detecting contamination of air in a tunnel is also known. These alarms have a sensor for detecting a phenomenon to be detected, and a judgment level (detection level) to be compared with a measured value such as a gas concentration according to the danger is predetermined. Generally, an alarm operation is performed upon detecting an abnormal state. And the temperature,
When the detection sensitivity of the sensor is affected by humidity, pressure, and the like, it is common practice to correct the determination level and the like to improve the performance.

Further, since the performance of the sensor is affected by dirt on the surface, a function such as heat cleaning may be provided to remove dirt components. Further, in a sensor whose characteristics change with use over time, replacement and correction of the determination level are performed at regular intervals, in which case measures are simply taken in accordance with the accumulated operation time and the like. Not just. In particular, the accumulated operating time information is reset at the same time as the power is turned off, and in that case, there is a problem that information serving as a guide for replacement or correction is lost.

[0004]

SUMMARY OF THE INVENTION Among various types of alarms,
As a gas leak alarm that has been widely used in ordinary households, a gas leak alarm using a semiconductor-type gas sensor is widely known.
Many of these semiconductor gas sensors use an electronic circuit to detect a decrease in the resistance value of the sensor due to adsorption of the gas to be detected. It is known that the detection sensitivity of this type of semiconductor gas sensor fluctuates due to aging or seasonal fluctuation. Therefore, if the set value for detection is corrected in consideration of the influence of the aging characteristics and seasonal fluctuation, the detection accuracy can be improved, and a more accurate alarm can be realized. Therefore, it is an issue to appropriately correct the detection sensitivity according to the aging characteristics and seasonal fluctuation characteristics of the gas sensor, and to realize a gas alarm device with stable characteristics.

[0005] In addition, although a general alarm uses an AC power supply, elimination of the power supply line is important for the spread of alarms because there is no outlet nearby or the power supply line is conspicuous even if it is present. It has become a challenge. That is, the problem is to make the gas alarm device usable with a battery power supply.

Accordingly, the present invention seeks to maintain and improve the detection accuracy by appropriately correcting the detection sensitivity in accordance with aging and seasonal fluctuations, and to provide a gas alarm which can be driven by a battery power supply. Things.

[0007]

According to a first aspect of the present invention, there is provided a gas sensor which detects gas and changes its electrical characteristics, a heater for heating the gas sensor to a predetermined temperature, and a gas sensor. A temperature sensor for measuring the temperature of the gas sensor, and control means for controlling heating of the heater based on the temperature of the gas sensor measured by the temperature sensor, and performing an alarm operation when an output signal of the gas sensor exceeds a determination level. The gas alarm device includes means for correcting the detection sensitivity of the gas sensor according to the cumulative operation time from the start of operation as the alarm device.

According to a second aspect of the present invention, in the gas alarm according to the first aspect, the use environment temperature is measured by using the temperature sensor or another temperature sensor, and a function of a season estimated from the use environment temperature is used. Means are provided for correcting the detection sensitivity of the gas sensor according to the seasonal variation characteristic of a certain gas sensor and the aging characteristic of the gas sensor which is a function of the cumulative operation time.

According to a third aspect of the present invention, in the gas alarm device according to the second aspect, as the element for estimating a season,
The lowest temperature of the use environment measured by the temperature sensor is used.

According to a fourth aspect of the present invention, in the gas alarm according to the first, second or third aspect, the temperature sensor for measuring the temperature of the gas sensor is commonly used for measuring the ambient temperature.

The invention according to claim 5 is the invention according to claims 1, 2, 3
Or in the gas alarm according to 4, wherein the control means comprises:
A nonvolatile storage means such as an EEPROM is provided, and the detection sensitivity of the gas sensor is corrected using information stored in the storage means.

[0012] The invention according to claim 6 is the invention according to claims 1, 2, and 3.
The gas alarm described in 3, 4, or 5, wherein a battery is used for power supply and a means for intermittently heating the heater is provided.

In the invention described in each of the above claims,
As a specific content of correcting the detection sensitivity of the gas sensor, it is conceivable that the control means corrects the determination level to be compared with the output signal of the gas sensor.

Further embodying the present invention as described above,
For example, by reducing the size of the gas sensor using silicon microfabrication technology, the heat capacity of the sensor itself is reduced, and the gas sensor is intermittently heated by a heater to greatly reduce the energy required for its operation. In addition, a nonvolatile memory is built in the control circuit constituting the gas alarm,
By storing elapsed time information (calendar information), accumulated operation time information, seasonal information, and the like from the time of manufacture, reliable control data is supplied to the CPU.

Further, a heater for heating and a temperature sensor are provided near the gas sensor, and the heater is intermittently heated under a constant heating condition so that the gas sensor is heated to a predetermined temperature by energy supplied from the battery. It is desirable to do. The temperature sensor is originally used to monitor the heating state so that the sensor temperature falls within a predetermined range. At the same time, this temperature sensor is also used as an environmental temperature sensor for measuring the operating temperature of the gas sensor when the gas sensor is not heated. If necessary, use environment conditions, especially temperature and humidity,
If various sensors such as pressure are separately provided, information from these sensors can be used for correcting the detection sensitivity of the gas sensor.

As described above, according to the present invention, the cumulative operating time information and seasonal information are estimated from the time information from the time of manufacture and the temperature information of the use environment, and the detection sensitivity is adjusted in accordance with the aging characteristic and seasonal variation characteristic of the gas sensor. Is to maintain stable detection sensitivity over a long period of time. In addition, even if a power supply interruption or battery replacement such as a commercial power supply interruption occurs, various information and the like already stored in the non-volatile storage means are continuously retained and can be used for correction of detection sensitivity and the like. A gas alarm is provided.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration diagram of an embodiment in which the present invention is applied to a battery-operated gas leak alarm. This gas leak alarm is installed in the home and has the function of detecting methane gas or CO gas generated during fuel gas leak or incomplete combustion, and reporting a dangerous situation by buzzer or sound. I have. Conventional gas leak alarms include
As described above, there is a device that operates with a commercial power supply or a DC power supply supplied from outside, but in the present embodiment, a battery power supply is used.

In FIG. 1, the gas leak alarm is a C
It is intensively controlled by a PU (microcomputer) 1. Reference numeral 100 denotes a methane sensor circuit for detecting methane gas, which is a main component of fuel gas, and reference numeral 200 denotes a CO sensor circuit. Here, the methane sensor circuit 100 will be mainly described. The gas sensor 2 in the methane sensor circuit 100 is an extremely small sensor having a small heat capacity manufactured using a film forming technique that is a silicon microfabrication technique. In the gas sensor 2, a resistor such as tungsten is formed on silicon by a thin film technique, and a SnO ₂ thin film is formed in the vicinity thereof or in an insulated upper layer portion. Catalytic technology is also used to make it more responsive to gases.

FIG. 2 shows a gas sensor (SnO)._TwoThin film gassen
(2) and the sensor 2 and the sensor 2
Of Heater 3 and Temperature Sensor (Platinum Temperature Sensor) 4
And gs₁, gs_TwoIs a terminal of the gas sensor 2,
h₁, h_TwoIs the terminal of heater 3, t₁, t _TwoIs the end of the temperature sensor 4
I am a child.

When detecting gas, the heater 3 is applied for several tens of milliseconds.
, The gas sensor 2 is heated by a predetermined temperature. Since it is sufficient that the gas leak can be normally detected within 20 seconds, the heater 3 may be heated for several tens of milliseconds once every 10 seconds. For this reason, since the heater 3 does not need to be energized during a normal period, the actual energy consumption is extremely small, and the configuration is suitable for battery driving.

The gas sensor 2 has a temperature at which the gas sensor 2 easily reacts depending on the type of gas to be detected. Therefore, a thin-film temperature sensor 4 is disposed near the gas sensor 2. Since the temperature sensor 4 is made of platinum, stable temperature measurement is possible. Heater 3
Is a diode D _{1 under} the control of the CPU 1 shown in FIG.
For a certain period of time through the heating.
The temperature of the gas sensor 2 heated by the heater 3 is detected as a change in resistance value by a bridge circuit including the temperature sensor 4 and the resistors R _{2 to} R ₄ , amplified by the amplifier Amp ₁ , and input to one input of the comparator CP _1. Input to the terminal.
An analog judgment level output from the CPU 1 is input to the other input terminal of the comparator CP ₁ , the output signal level of the amplifier Amp 1 is compared with the judgment level, and the result is subjected to A / D conversion by the CPU 1. The signal processing is performed to determine whether the gas sensor 2 has reached a predetermined temperature. Since such a level detection function is well known,
Here, the details are omitted.

The gas sensor 2 is supplied with a voltage of 1 V by a constant voltage circuit 5 via a resistor R ₁ , and the temperature sensor 4 is connected to the constant voltage circuit 5 via resistors R ₂ and Rs. The constant voltage circuit 5 is connected to the battery 7. When the gas concentration is low, the resistance value of the gas sensor 2 keeps a high value, but the resistance value gradually decreases as the gas concentration increases. The terminal voltage of the gas sensor 2 is inputted to one input terminal of the comparator CP ₂ for detecting a gas concentration, to the other input terminal is input analog determination level from CPU 1. Then, the output signal of the comparator CP ₂ is inputted to the CPU 1, the alarm operation or the like described later with signal processing after A / D conversion is performed.

Although the methane sensor circuit 100 has been described here, the CO sensor circuit 200 for detecting CO gas is used.
Has almost the same configuration, and the description is omitted. In FIG. 1, a control signal for absorbing the variation of the gas sensor is input to the CO sensor circuit 200. This signal is also input to the methane sensor circuit 100 (not shown). In other words, if there is a large difference in the ability to react to gas due to manufacturing variations of the gas sensor 2, C
The PU ₁ corrects the terminal voltage of the gas sensor 2 by equivalently changing and controlling the value of the resistor R ₁ , for example.

When the methane sensor circuit 100 or the CO sensor circuit 200 detects a gas having a concentration equal to or higher than the set concentration, C
The PU 1 instructs the audio LSI 13 to generate audio. Since the audio LSI 13 is a commercially available LSI and is used in many electronic devices, a detailed description of its functions will be omitted. Note that 12 is a power supply circuit for audio, 14 is an amplifier, 1
5 is a speaker. The voice LSI 13 generates different voice content depending on which of the methane sensor circuit 100 and the CO sensor circuit 200 detects the gas. The reason is that the corresponding measures are different depending on the type of the generated gas.

Further, even if the detection level of gas does not reach the alarm level, if it is desired to take an initial measure without generating a sound as a pre-alarm if possible, it is not shown in the figure. May be lit. In this case, the current supplied to the LED may be about 2 to 10 mA. Usually, even if a part of the current of the voice alarm requiring about 100 mA is used for the pre-alarm, it does not affect much of the battery life.

The audio power supply circuit 12 has a voltage stabilizing function for absorbing voltage fluctuations of the battery 7. Further, a battery voltage detection circuit 8 is connected to the CPU 1 and detects the voltage of the battery 7. This function is because when the battery voltage falls below a predetermined value, there is a concern that the detection capability of the gas sensor 2 becomes insufficient or the level of the generated voice alarm decreases.

Furthermore, at both ends of the battery 7 series circuit of the electromagnetic latch 9, 11 and the transistor T _2, T ₁ is connected to a CO and for methane, the transistors T _2, T ₁ denotes a CPU
1 is turned on by a control signal from the control unit 1. R
₁₀ is a resistor on the input side of the transistor T2. The electromagnetic latches 9 and 11 are for driving the display panel 10 when a gas leak is detected. In the figure, the electromagnetic latch 11
The illustration of the display panel driven by the above is omitted for convenience. For this display, for example, the display plate 10 may be configured by a well-known means so that green or blue is displayed in a state where there is no gas leakage, and red or orange close to a dangerous image is displayed when gas leakage is detected.

The CPU 1 has a nonvolatile memory (EE)
PROM) 16 is connected. The memory 16 is an electrically rewritable memory, and stores a heating control condition of the heater 3 for heating the gas sensor 2, a determination level for detecting gas leakage, and the like. These information are stored in the CPU 1
Is used to control the sensor circuits 100 and 200. The non-volatile memory 16 also stores various information such as accumulated operation time information of the sensor and seasonal variation information as described later.

Here, the nonvolatile memory 16 is stored in the CPU 1
However, in the battery-operated gas leak alarm, once the battery 7 is inserted, the CPU 7 is used until the life of the battery 7 expires.
Since the memory in 1 is also non-volatile, the non-volatile memory 16 can be omitted in this type of alarm. However, when the battery life expires, the operation is different from that of the non-volatile memory 16, so that there are functional restrictions. When the RAM in the CPU 1 is used, it is necessary to set data by communication using an external setting unit described later.

Note that, in FIG.₁Is inspection tie
Light emitting diode, SW for indicating₁Is voice
Switch for switching, T_ThreeIs a transistor for external output
Ta, R ₁₁Is the input resistance.

FIG. 3 is a diagram showing the aging characteristics of the gas sensor 2 in this embodiment, and shows the relationship between the number of years of use and the sensor resistance. For several months from the start of use, the sensor resistance in the state of detecting gas tends to increase,
After that period, the sensor resistance gradually decreases, and the change decreases after about two years. Although this characteristic slightly differs depending on the individual sensor, it is well known that the sensor has an aging characteristic as shown schematically.

FIG. 4 is a diagram showing the seasonal variation characteristics of the gas sensor 2 in this embodiment, and shows the relationship of the change in the sensor resistance with the passage of the month. Since the gas sensor 2 is of a semiconductor type, it is affected by the ambient temperature. For this reason, a temperature compensation circuit is generally provided, and the influence of the ambient temperature is reduced by a temperature correction function. However, even with a sensor having such a correction function, it is known that the resistance value of the gas sensor throughout the year varies as shown in FIG. Further, the actual secular variation of the resistance value of the gas sensor is measured as a composite value of FIGS.
Since the value of the seasonal variation is smaller than the width of the secular variation, it is shown in FIG. 4 as a change in the sensor resistance. It is said that the seasonal variation as shown in FIG. 4 depends on the cumulative result of the temperature characteristic and the humidity characteristic, and is considered to have not only a temperature change but also a time delay element.

Considering the actual situation of the installation location of the alarm, the gas leak alarm for city gas is often installed near the ceiling of the place where the gas equipment is used. For example,
It will most often be installed near the ceiling of the kitchen. In such an installation environment, when gas equipment is used for cooking, the temperature near the ceiling starts to rise rapidly. Also, considering the actual environment of the dwelling, the use of air conditioning greatly affects the situation. The use of air conditioning is generally thought to reduce humidity. In addition, although low and high temperature conditions are improved by air conditioning, there are few homes that always operate air conditioning. Usually, air conditioning is stopped at night or used only during the daytime, such as 24 hours a day. Considering that, the effect of air conditioning is considerably reduced.

FIG. 5 shows the relationship between the minimum temperature and the passage of the month. When air conditioning is not used (characteristic line a), the average monthly minimum temperature is stably changing throughout the year. In addition, even when air conditioning is used, air conditioning is often stopped at midnight or the like, so focusing on the lowest temperature should clearly show the effect of seasonal fluctuations. However, when air conditioning is constantly performed throughout the year (characteristic line c), for example, the minimum temperature can be maintained at 15 degrees.

On the other hand, there is a case where air conditioning is used only in the summer and winter (characteristic line b). In this case, the minimum temperature changes due to the influence of air conditioning only in the season. However, as mentioned earlier, air conditioning often does not function during the time when the lowest temperature is recorded, such as late at night, so if the average value of the lowest temperature is created by a moving average, the effect of air conditioning will often be affected. , And it is possible to detect gas leakage and the like. The purpose of measuring the minimum temperature in this manner is to correct the detection sensitivity according to the seasonal variation characteristics shown in FIG. This minimum temperature can be measured using the temperature sensor 4 in a state where the temperature of the gas sensor 2 is not detected.

Although a certain amount of seasonal information can be obtained by measuring the minimum temperature as described above, a more direct method of obtaining the seasonal information is to store the date of manufacture in the nonvolatile memory 16 shown in FIG. There is a method of writing day information. Season information can be easily obtained by reading this information and adding the subsequent cumulative operation time. This method is based on the assumption that the period difference between the time when the manufacturing date information is written to the nonvolatile memory 16 and the time when the alarm device is turned on and actually started to be used can be largely ignored. .

In the case of an alarm using an AC power supply, the power supply is turned on for the first time after installation at the place of use. In this case, the sensitivity correction according to the seasonal variation characteristic can be performed using the lowest temperature. But,
In the battery-type alarm device of the present embodiment, when the battery is set, the power supply is started, that is, when the battery is used.For example, when the battery is set at the factory, it can be regarded that the battery has been used. If the date of manufacture is written in the non-volatile memory 16, it is possible to substantially eliminate the difference in the period. In this regard, the writing of seasonal information in the nonvolatile memory is particularly effective for a battery-operated alarm device.

The accumulated operation time from the start of use of the gas sensor can be easily obtained by the CPU 1 accumulating the time at regular time intervals. When the power supply is cut off, the CPU 1
Becomes impossible to calculate and memorize. However, by writing the accumulated information to the nonvolatile memory 16 at regular time intervals or when the power is turned off, when the power can be used again, the contents of the nonvolatile memory 16 are read out and accumulated. The calculation of the operation time and the like can be restarted. Needless to say, the interruption period cannot be accumulated. Considering the operation of the alarm, it is considered that the influence of the interruption period is not so large. If an error occurs in the seasonal information, the seasonal variation can be estimated from the lowest temperature information in FIG.

In the case where the effect of air conditioning is greater as an actual use environment classification of the alarm device, that is, in an application in which the influence of air conditioning is greater than the seasonal influence, as shown in FIG. If the determination level is corrected based on the situation of the lowest temperature of the moving average in units of days, more accurate gas leak detection becomes possible.

FIG. 6 is a flowchart showing the operation of the CPU 1. When the power is turned on and the CPU 1 starts operating, the software is started. In step S1, season information previously written in the non-volatile memory 16 is read out as an initial set, and the use start month is set in the RAM. As another method, use start month information may be sent to the CPU 1 from an external circuit not shown in FIG. C
The I / O port of the PU 1 can be prepared for exclusive use, and the use start month information can be transmitted to the CPU 1 by various methods.

The gas sensor 2 desirably cleans foreign substances and dust adhered to the surface before starting use, and the cleaning can stabilize the operation of the sensor. In addition, a memory set and a function set necessary for the operation of the CPU 1 are required. These processes are executed according to the design conditions of each CPU.

When the initial setting is completed, the alarm of the gas sensor 2 is monitored in step S2. Specifically, the state of the gas is measured from the state of the gas sensor 2,
When there is an abnormality, an alarm action is performed, and when no gas is detected, no special action is performed. This step is performed at regular intervals,
For example, since it is executed every 10 seconds (S4No, S5Ye
s) The cumulative operation time is counted in the time unit.

When step S2 is completed, step S3 is executed, for example, every 10 seconds. In this step, the ambient temperature is measured by the temperature sensor 4, and seasonal variation correction calculation and aging correction calculation are performed. These calculation methods and usage methods will be described later. Also, the calculation result and important information (cumulative operation time information, year / month / day information, etc.) are set as calculation parameters in the non-volatile memory 16 so as to be prepared in case of power-off.

When step S3 is completed, for example, 1
Time adjustment is performed so that step S2 is performed every 0 seconds (step S5). As an example, if an interrupt process is used, the CPU 1 can automatically execute the process after step S2 after 10 seconds. Since various kinds of software are realized, a method suitable for the system may be selected.

FIG. 7 shows a calculation example of aging correction. As for the aging characteristics, there is a method in which a calculation formula is created by using the date from the start of use as a coefficient and the correction amount is obtained by calculation.However, since there are variations in sensors, the cumulative operation time is divided in FIG. The decision level is multiplied by a constant coefficient. Since various methods can be used for the correction calculation, an executable calculation method may be selected in consideration of the aging characteristics of the sensor and the processing function of the CPU 1.

FIG. 8 shows a calculation example of the seasonal variation correction. There is a seasonal division method according to the four seasons, and a monthly division method. In FIG. 8, as shown in FIG. 8A, the seasonal variation is divided into monthly units. Based on the seasonal information set when the power is turned on, the CPU 1 creates a calendar by adding the elapsed time, so that it is possible to determine what month the current time is. The correction numbers n _{1 to} n _{12 at} that time may be determined according to the seasonal variation characteristics of the sensor, for example, the characteristic changes as shown in FIG.

In addition to setting the correction number for each month, that is, for each season, it is also conceivable to set the correction number by taking a moving average of the lowest temperature as shown in FIG. If the moving average is calculated for a slightly longer period such as the past 15 days, 30 days, and 60 days, it matches the long-term fluctuation characteristics of the sensor. If the moving average period is selected in accordance with the characteristics determined by the configuration, structure, and the like of the sensor itself, it is possible to select a correction number more suited to the actual situation. It should be noted that correction of short-term fluctuations in gas detection sensitivity with respect to changes in ambient temperature has been conventionally performed. It has become.

FIG. 9 shows a method for selecting a long-term correction factor for the gas detection sensitivity. We have already incorporated a time delay element into the moving average, but as an actual software function, it is better to incorporate not only the delay element but also the time advance element separately, and match the actual sensor characteristics with the software function. In some cases, implementation is easy, and creation of calculation formulas is simplified. For this reason, a method is also conceivable in which, after determining a reference condition, a time delay element and an advance element are separately added. In this way, various means are used to automatically adjust and set the gas leak determination level that matches the actual characteristics.

[0049]

As described above, according to the present invention, the control circuit of the gas sensor is provided with a function of measuring the cumulative operating time of the sensor and the operating environment temperature, and the detection of the gas sensor is performed according to the aging characteristic and the seasonal variation characteristic. Since the sensitivity is corrected, the detection sensitivity can always be maintained high regardless of long-term use or season. In particular, by setting the date of manufacture and the like in the non-volatile memory, measurement of the accumulated operation time is facilitated, and correction according to the seasonal variation characteristic is also facilitated. Further, there is no possibility that data such as the accumulated operation time is lost due to an unexpected power failure or the like, and stable and accurate gas detection can be always performed. The present invention can be applied not only to gas leak alarms but also to various gas alarms, fire alarms, and the like in which long-term fluctuation factors of sensor characteristics are known.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a battery-operated gas leak alarm according to an embodiment.

FIG. 2 is a configuration diagram of a gas sensor, a heater, and a temperature sensor in the embodiment.

FIG. 3 is a diagram showing aging characteristics of the gas sensor in the embodiment.

FIG. 4 is a diagram showing seasonal variation characteristics of the gas sensor according to the embodiment.

FIG. 5 is a diagram showing the relationship between the passage of the month and the minimum temperature.

FIG. 6 is a flowchart illustrating an operation of a CPU according to the embodiment.

FIG. 7 is a diagram illustrating a calculation example of aging correction in the embodiment.

FIG. 8 is a diagram illustrating a calculation example of seasonal variation correction in the embodiment.

FIG. 9 is a diagram illustrating a method for selecting a correction element for gas detection sensitivity in the embodiment.

[Description of Signs] 1 CPU 2 Gas sensor 3 Heater 4 Temperature sensor 5 Constant voltage circuit 7 Battery 8 Battery voltage detection circuit 9, 11 Electromagnetic latch 10 Display panel 12 Audio power supply circuit 13 Audio LSI 14 Amplifier 15 Speaker 16 Non-volatile memory ( EEPROM) 100 Methane sensor circuit 200 CO sensor circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Katsumi Onodera 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Fuji Electric Co., Ltd.

Claims (7)

[Claims] 1. A gas sensor that changes its electrical characteristics by detecting a gas, a heater that heats the gas sensor to a predetermined temperature, a temperature sensor that measures the temperature of the gas sensor, and a temperature sensor that measures the temperature of the gas sensor. Control means for controlling the heating of the heater based on the above, processing an output signal of the gas sensor, and performing an alarm operation when the output signal exceeds a determination level. A gas alarm device comprising means for correcting the detection sensitivity of a gas sensor in accordance with the cumulative operation time from a point in time. 2. The gas alarm according to claim 1, wherein a temperature of a use environment is measured using the temperature sensor or another temperature sensor, and a seasonal variation characteristic of the gas sensor is a function of a season estimated from the environment temperature. And a means for correcting the detection sensitivity of the gas sensor according to the aging characteristic of the gas sensor which is a function of the cumulative operation time. 3. The gas alarm according to claim 2, wherein the lowest temperature of the use environment measured by the temperature sensor is used as an element for estimating the season. 4. The gas alarm device according to claim 1, wherein the temperature sensor for measuring the temperature of the gas sensor is used for measuring the ambient temperature. 5. The gas alarm according to claim 1, 2, 3, or 4, wherein the control means includes a non-volatile storage means, and the detection sensitivity of the gas sensor is determined by using information stored in the storage means. A gas alarm characterized by correction. 6. The gas alarm according to claim 1, wherein a battery is used for power supply, and a means for intermittently heating the heater is provided. Alarm. 7. The gas alarm device according to claim 1, wherein the control means corrects a determination level compared with an output signal of the gas sensor to reduce the detection sensitivity of the gas sensor. A gas alarm characterized by correction.