JP5330067B2 - Gas alarm - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas alarm that prevents an alarm concentration from being changed even if a drive voltage supplied to a gas sensor changes. <P>SOLUTION: The gas sensor 1 outputs a sensor output Vs corresponding to a gas concentration of a gas to be detected. The drive voltage Vd is supplied to the gas sensor 1 from a voltage source 2. A CPU 31 generates an alarm by use of an alarm buzzer 41 and an alarm lamp 42 when the sensor output Vs from the gas sensor 1 becomes an alarm value or above. A drive voltage detection circuit 20 detects the drive voltage Vd supplied to the gas sensor 1. The CPU 31 sets the alarm value based on the drive voltage Vd detected by the drive voltage detection circuit 20. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a gas alarm device, and in particular, a gas sensor for detecting a gas concentration of a detection target gas, a power supply means for supplying a driving voltage to the gas sensor to drive the gas sensor, and a gas concentration detected by the gas sensor The present invention relates to a gas alarm device comprising: an alarm generation means for generating an alarm when is equal to or greater than an alarm value.

As an example of the gas sensor described above, a contact combustion type is known (for example, Patent Documents 1 and 2). As shown in FIG. 12, the catalytic combustion type gas sensor 1 has a sensor element Rs and a reference element Rr. The sensor element Rs includes a catalyst carrier 11 made of a carrier (for example, alumina (Al ₂ O ₃ )) that supports a catalyst (for example, palladium (Pd)) that promotes combustion with the detection target gas, and a catalyst carrier 11 that covers the catalyst carrier 11. The platinum heater 12 is broken. The reference element Rr is composed of a carrier 13 that is insensitive to the detection target gas and a platinum heater 14 covered with the carrier 13.

  The platinum heater 12 of the sensor element Rs and the platinum heater 14 of the reference element Rr are provided so as to have the same resistance value in the air (air base) without the detection target gas. The sensor element Rs and the reference element Rr described above constitute a bridge circuit B together with the fixed resistors R1 and R2. A driving voltage (for example, 2.0 V) is supplied to the bridge circuit B from a voltage source 2 as a power supply means. When the drive voltage is supplied, the sensor element Rs is heated and the detection target gas burns.

  According to the above configuration, the bridge circuit B is in an equilibrium state on the air base, and the midpoint potential difference V0 becomes zero. On the other hand, in the air containing the detection target gas, the temperature of the sensor element Rs rises due to combustion heat with the detection target gas, and the resistance value of the platinum heater 12 of the sensor element Rs increases accordingly. On the other hand, since the reference element Rr does not combust with the detection target gas, it becomes lower than the temperature of the sensor element Rs. For this reason, the bridge circuit B is in an unbalanced state, and a midpoint potential difference V0 is generated. The voltmeter 3 detects the midpoint potential difference V0 and outputs it as a sensor output Vs corresponding to the concentration of the detection target gas. The gas alarm is configured to generate an alarm when the sensor output Vs becomes an alarm value (for example, 0.25 V) or more.

  By the way, the drive voltage supplied by the voltage source 2 described above may fluctuate. Now, it is assumed that the driving voltage varies within a range of ± 0.5V with respect to 2.0V. If the resistance values of the sensor element Rs and the reference element Rr in the air base described above are, for example, 10Ω and the same, as shown in FIGS. 13A and 14A, the drive voltage is in the range of ± 0.5V. The sensor output does not fluctuate even if it fluctuates. Therefore, as shown in FIG. 15A, the alarm concentration (%), which is the gas concentration when an alarm is generated from the gas alarm device, is constant even when the drive voltage varies.

  However, the resistance values of the sensor element Rs and the reference element Rr are difficult to be exactly the same, and are often slightly different. When the resistance values of the sensor element Rs and the reference element Rr are thus different, as shown in FIGS. 13B and 13C, 14B and 14C, the sensor output at the time of air base is 0. The sensor output also fluctuates greatly due to fluctuations in the driving voltage.

  Therefore, when the alarm value is constant at, for example, 0.25 V as in the prior art, as shown in FIGS. 15B and 15C, the alarm concentration (%) varies depending on the variation of the drive voltage. . That is, as shown in FIG. 15B, when the sensor element Rs = 10Ω and the reference element Rr = 7Ω, the alarm concentration (%) increases as the drive voltage increases. As shown in FIG. 15C, when the sensor element Rs = 7Ω and the reference element Rr = 10Ω, the alarm concentration (%) decreases as the drive voltage increases. For this reason, there was a problem that a highly accurate alarm could not be performed.

  As the above-described contact combustion type gas sensor 1, a configuration as shown in FIG. 16 is also known. In FIG. 16, the same reference numerals are given to the same parts as those of the gas sensor 1 already described with reference to FIG. 12, and the detailed description thereof will be omitted. As shown in the figure, the bridge circuit B of the gas sensor 1 includes a variable resistor VR in addition to the sensor element Rs, the reference element Rr, and the fixed resistors R1 and R2. By providing the variable resistor VR, even if the resistance values of the sensor element Rs and the reference element Rr are not the same, for example, the sensor output Vs when the drive voltage of 2V is supplied is adjusted to zero. be able to.

  In this case, as shown in FIGS. 17 and 18, the variation in the sensor output Vs with respect to the drive voltage of 2V is suppressed, but the variation in the sensor output Vs with respect to the variation in the drive voltage is not improved. Therefore, similarly to the gas alarm using the gas sensor 1 shown in FIG. 12, as shown in FIG. 19, the alarm concentration (%) fluctuates according to the fluctuation of the drive voltage, so that a highly accurate alarm can be performed. There was a problem that it was not possible. In addition, the gas sensor 1 is not limited to the contact combustion type, and it is known that the sensor output Vs fluctuates according to the fluctuation of the drive voltage even if it is a semiconductor type or a limit current type.

JP 2005-84787 A Japanese Patent Laid-Open No. 7-301612

  Therefore, an object of the present invention is to provide a gas alarm device in which the alarm concentration does not vary even when the drive voltage supplied to the gas sensor varies.

The invention according to claim 1, which has been made in order to solve the above-described problem, includes a gas sensor that outputs a sensor output corresponding to the gas concentration of a detection target gas, and a power source that drives the gas sensor by supplying a driving voltage to the gas sensor. And an alarm generating means for generating an alarm when a sensor output output from the gas sensor is equal to or higher than an alarm value, wherein the gas sensor includes a sensor element and a reference element connected in series with each other. Drive voltage detection for detecting the drive voltage supplied from the power supply means by outputting the sensor output based on a midpoint potential difference generated in the bridge circuit. And alarm value setting means for setting the alarm value according to the drive voltage detected by the drive voltage detection means. , A plurality of premeasured further comprising a storage means for the sensor output of the gas sensor during the air base is stored on the size of the drive voltage, based on a plurality of sensor outputs stored in said storage means, to said driving voltage Relational expression calculation means for calculating a linear function expression indicating an alarm value obtained by adding a reference alarm value to the sensor output at the time of air base, and the alarm value setting means is a drive detected by the drive voltage detection means The gas alarm device is characterized in that a value obtained by substituting the voltage into the linear function equation calculated by the relational expression calculating means is set as an alarm value .

2. The gas alarm according to claim 1 , further comprising abnormality detection means for detecting an abnormality of the power supply means based on the drive voltage detected by the drive voltage detection means. It exists in the vessel.

As described above, according to the first aspect of the present invention, the alarm value setting means sets the alarm value according to the drive voltage detected by the drive voltage detection means, so that the drive voltage supplied to the gas sensor varies. Even if the alarm concentration does not change.

According to the second aspect of the present invention, it is possible to detect an abnormality of the power supply means by using the drive voltage detected by the drive voltage detection means.

It is a circuit diagram which shows one Embodiment of the gas alarm device of this invention. It is a table | surface which shows an example of the data of the sensor output Vs with respect to the drive voltage Vd = 1.5V, 2.0V, and 2.5V stored in RAM. It is a table | surface which shows an example of the alarm value with respect to the drive voltage Vd = 1.5V, 2.0V, and 2.5V stored in RAM. It is a graph which shows the sensor output and alarm value with respect to the drive voltage in 1st Embodiment. It is a flowchart which shows the process sequence of CPU which comprises the gas alarm device of FIG. It is a graph which shows the alarm concentration with respect to the drive voltage in the gas alarm device of this invention. 2 is a table showing the sensor output of the gas sensor shown in FIG. 1 with respect to the driving voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. 2 is a graph showing the sensor output of the gas sensor shown in FIG. 1 with respect to the drive voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. It is a graph which shows the relationship between the sensor output Vs with respect to the drive voltage 2.0V, and the inclination A of the linear function type | formula which shows the sensor output with respect to a drive voltage. It is a graph which shows the sensor output and alarm value with respect to the drive voltage in 2nd Embodiment. It is a circuit diagram which shows a gas sensor when a power supply transformer is used as a voltage source. It is a figure which shows an example of the gas sensor of a contact combustion type. 13 is a table showing the sensor output of the gas sensor shown in FIG. 12 with respect to the drive voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. 13 is a graph showing the sensor output of the gas sensor shown in FIG. 12 with respect to the drive voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. It is a graph which shows the alarm concentration of the conventional gas alarm device with respect to the drive voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. It is a figure which shows an example of the contact combustion type gas sensor which provided the variable resistance. (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Sensor output of the gas sensor shown in FIG. 16 with respect to the drive voltage when Rs = 7Ω, Rr = 10Ω. . 17 is a graph showing the sensor output of the gas sensor shown in FIG. 16 with respect to the drive voltage when (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω. (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω with respect to the driving voltage when the conventional gas alarm using the gas sensor shown in FIG. It is a graph which shows alarm density | concentration.

First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the gas alarm device 10 includes a gas sensor 1, a drive voltage detection circuit 20 as drive voltage detection means, a microcomputer (hereinafter referred to as μCOM) 30, an alarm buzzer 41, and an alarm lamp 42. I have. The gas sensor 1 includes a sensor element Rs and a reference element Rr, fixed resistors R1 and R2, a voltage source 2 as a power supply means, and a voltmeter 3. The sensor element Rs includes a catalyst carrier 11 and a platinum heater 12. The catalyst carrier 11 is made of a carrier (alumina (Al ₂ O ₃ )) supporting a catalyst (for example, palladium (Pd)) that promotes combustion with the detection target gas. The platinum heater 12 is a resistance temperature detector whose resistance value changes according to temperature, and is covered with the catalyst carrier 11.

  The reference element Rr includes a carrier 13 and a platinum heater 14. The carrier 13 is composed of only the carrier that is insensitive to the detection target gas. The platinum heater 14 is a resistance temperature detector whose resistance value changes according to temperature, and is covered with the carrier 13. The sensor element Rs and the reference element Rr constitute a bridge circuit B together with the fixed resistors R1 and R2. The voltage source 2 drives the gas sensor 1 by supplying a drive voltage Vd between the connection point of the reference element Rr and the fixed resistor R1 and the connection point of the sensor element Rs and the fixed resistor R2. A midpoint potential difference V 0 generated between the connection point of the fixed resistors R 1 and R 2 and the connection point of the reference element Rr and the sensor element Rs is connected to the voltmeter 3. The voltmeter 3 detects the connected midpoint potential difference V0 and outputs it as a sensor output Vs. The analog value of the sensor output Vs from the voltmeter 3 is converted into a digital value by an A / D converter (not shown) and then supplied to the μCOM 30 described later.

  The drive voltage detection circuit 20 is composed of an OP amplifier 21. The OP amplifier 21 is a voltage follower whose -input end is connected to the output end. The driving voltage Vd supplied from the voltage source 2 is input to the + input terminal of the OP amplifier 21. Then, the OP amplifier 21 amplifies the drive voltage Vd input to the + input terminal with an amplification factor of 1 and outputs it. The analog value of the drive voltage Vd output from the OP amplifier 21 is converted into a digital value by an A / D converter (not shown) and then supplied to the μCOM 30 described later.

  The μCOM 30 is a computer that controls the entire gas alarm device 10, and generates an alarm by controlling an alarm buzzer 41 and an alarm lamp 42, which will be described later, when the sensor output Vs from the gas sensor 1 exceeds an alarm value Vw. To do. Further, the μCOM 30 resets the alarm value Vw according to the drive voltage Vd detected by the drive voltage detection circuit 20.

  The μCOM 30 includes a central processing unit (CPU) 31 that performs various processes in accordance with a program, a ROM 32 that is a read-only memory that stores a program for processing performed by the CPU 31, and a work that is used in various processes in the CPU 31. And a RAM 33 which is a readable / writable memory having an area, a data storage area for storing various data, and the like. The alarm buzzer 41 is a device that generates a buzzer sound (alarm sound) according to the control of the μCOM 30. The alarm lamp 42 is a light emitting element that emits light according to the control of the μCOM 30.

  Next, operation | movement of the gas alarm device 10 of the structure mentioned above is demonstrated. First, in the manufacturing process of the gas alarm device 10, the manufacturer changes the drive voltage Vd supplied to the gas sensor 1 to, for example, 1.5V, 2.0V, and 2.5V. The manufacturer measures the data of the sensor output Vs in the air base at that time, and stores it in the RAM 33 or the like as storage means using a setting device or the like. Thereby, the RAM 33 stores the data of the sensor output Vs at the time of the air base with respect to the driving voltages Vd of three magnitudes (1.5 V, 2.0 V, 2.5 V). For example, when the sensor element Rs = 10Ω and the reference element Rr = 7Ω, the sensor output Vs as shown in FIG. 2 is measured and stored in the RAM 33.

  When the sensor output Vs data as shown in FIG. 2 is stored, the CPU 31 adds 0.25 V as a reference alarm value to each stored sensor output Vs, and uses the added value as an alarm value Vw. Is stored in the RAM 33. For example, when the sensor output Vs data as shown in FIG. 2 is stored, as shown in FIG. 3, 0.25V is applied to these sensor outputs Vs = −0.131V, −0.176V, −0.221V. The added values 0.119V (−0.131V + 0.25V), 0.074V (−0.176V + 0.25V), and 0.029V (−0.221V + 0.25V) are used as the alarm value Vw corresponding to each drive voltage Vd. Stored.

  Thereafter, the CPU 31 functions as a relational expression calculating means, and displays an alarm value line L1 (FIG. 4) which is a linear function expression indicating an alarm value Vw for an arbitrary drive voltage Vd from the alarm value Vw data stored in the RAM 33. Ask. Specifically, as shown in FIG. 3, (drive voltage Vd, alarm value Vw) = (1.5 V, 0.119 V), (2.0 V, 0.074 V), (2. A linear function formula (Vw = 0.088 × Vd + 0.25) passing through three points of 5V and 0.029V) is defined as an alarm value line L1. As apparent from FIG. 4, this alarm value line L1 is drawn in parallel to the sensor output line L2 for an arbitrary drive voltage Vd, and the difference between the alarm value line L1 and the sensor output L2 is always the reference alarm value = It becomes 0.25V.

  When the gas alarm device 10 described above is shipped and the power is turned on after installation in the home, the CPU 31 starts an operation as shown in FIG. First, the CPU 31 controls the gas sensor 1 to detect the gas concentration of the detection target gas, and takes in the sensor output Vs corresponding to the gas concentration (step S1). Further, the CPU 31 takes in the drive voltage Vd output from the drive voltage detection circuit 20 (step S2). Next, the CPU 31 functions as an alarm value setting means, and substitutes the drive voltage Vd acquired in step S2 for the linear function equation (Vw = 0.088 × Vd + 0.25) of the alarm value line L1 obtained as described above. The alarm value Vw is set for the obtained value (step S3). Thereafter, the CPU 31 determines whether or not the sensor output Vs captured in step S1 is equal to or higher than the alarm value Vw set in step S3 (step S4).

  If the sensor output Vs is lower than the alarm value (N in step S4), the CPU 31 returns to step S1 again. On the other hand, if the sensor output Vs is greater than or equal to the alarm value Vw (Y in step S4), the CPU 31 determines that a gas leak has occurred and acts as an alarm generating means to generate an alarm by the alarm buzzer 41 and the alarm lamp 42. Start (step S5). Thereafter, the CPU 31 takes in the sensor output Vs again (step S6), takes in the drive voltage Vd (step S7), and sets the alarm value Vw (step S8), and the sensor output Vs taken in step S6 becomes the step S8. When the value falls below the alarm value Vw set in (N in Step S9), the alarm by the alarm buzzer 41 and the alarm lamp 42 is stopped (Step S10), and the process returns to Step S1.

  According to the gas alarm device 10 described above, since the CPU 31 sets the alarm value Vw according to the drive voltage Vd detected by the drive voltage detection circuit 20, the resistance values of the sensor element Rs and the reference element Rr are different. Even if the drive voltage Vd supplied to the gas sensor 1 fluctuates during the operation, the alarm concentration (%) does not fluctuate as shown in FIG.

  In the first embodiment described above, the sensor output Vs for the three drive voltages is measured in advance and stored in the RAM 33 in order to obtain the alarm value line L1, but the present invention is not limited to this. . In order to obtain a linear function indicating the alarm value line L1, sensor outputs Vs for at least two drive voltages may be measured in advance and stored in the RAM 33.

  In the first embodiment described above, the alarm value line L1 is obtained and the alarm value is set according to the drive voltage Vd detected by the drive voltage detection circuit 20 from the alarm value line L1. Is not limited to this. For example, the alarm value Vw corresponding to the drive voltage Vd may be set from a table of the drive voltage Vd and the alarm value Vw as shown in FIG.

Second Embodiment Next, the gas alarm device 10 of the present invention in the second embodiment will be described. In addition, since the structure of the gas alarm device 10 in 2nd Embodiment is the same as that of 1st Embodiment, detailed description is abbreviate | omitted here. Next, operation | movement of the gas alarm device 10 of 2nd Embodiment is demonstrated.

The sensor output Vs with respect to the drive voltage Vd can be expressed by the following equation (1).
Vs = Vd × Rr / (Rs + Rr) −Vd / 2 (1)
Therefore, for example, when the resistance values of the sensor element Rs and the reference element Rr are (A) Rs = Rr = 10Ω, (B) Rs = 10Ω, Rr = 7Ω, (C) Rs = 7Ω, Rr = 10Ω, each drive voltage When the sensor output Vs with respect to Vd = 1.5V, 2.0V, and 2.5V is obtained using the above equation (1), it is as shown in FIGS.

  Therefore, as shown in FIG. 8, the linear function equations of the sensor output line L2 in (A) to (C) are (A) Vs = 0 × Vd, (B) Vs = −0.088 × Vd, ( C) Vs = 0.088 × Vd. That is, the slope A of the linear function equation of the sensor output line L2 is 0 for (A), -0.088 for (B), and 0.088 for (C).

As described above, the sensor output Vs with respect to the drive voltage Vd can be expressed by a linear function of Vs = A × Vd. Therefore, if the sensor output Vs for one drive voltage Vd is measured, the slope A of the sensor output line L2 of the gas sensor 1 can be obtained from the following equation (2).
A = 1 / Vd × Vs (2)

For example, the relationship of the slope A with respect to the sensor output Vs when the drive voltage Vd = 2.0 V can be expressed by the following equation (3) as shown in FIG.
A = 1 / 2.0 × Vs = 0.5 × Vs (3)

  Therefore, in the manufacturing process of the gas alarm device 10, the manufacturer sets the drive voltage Vd supplied to the gas sensor 1 to, for example, 2.0 V, and measures and sets data of the sensor output Vs in the air base at that time. It stores in RAM33 etc. as a storage means using a container. Thereby, the data of the sensor output Vs of the gas sensor 1 at the time of air base with respect to the predetermined drive voltage Vd = 2.0 V is stored in the RAM 33. For example, when the sensor element Rs = 10Ω and the reference element Rr = 7Ω, −0.176 V is measured as the sensor output Vs.

  When the data of the sensor output Vs is stored, the CPU 31 functions as a relational expression calculation means, and a value obtained by dividing the stored sensor output Vs = −0.176V by the corresponding drive voltage V = 2.0V (−0 .176V / 2.0V) = − 0.088 is obtained as the slope of the sensor output line L2, which is a linear function expression indicating the sensor output Vs with respect to the drive voltage Vd. Further, a value obtained by adding 0.25 V, which is the reference alarm value, to the obtained linear function expression Vs = −0.088 × Vd of the sensor output line L2 is a linear function expression Vw = −0.088 of the alarm value line L1. Set as xVd + 0.25.

  When the gas alarm device 10 described above is shipped and turned on after being installed in the home, the CPU 31 starts an operation substantially equivalent to that of the first embodiment. In step S3, the CPU 31 substitutes the driving voltage Vd acquired in step S2 into the above-described first-order function equation Vw = −0.088 × Vd + 0.25 of the alarm value line L1 to obtain the alarm value Vk. Set as.

  According to the gas alarm device 10 described above, since the CPU 31 sets the alarm value Vw according to the drive voltage Vd detected by the drive voltage detection circuit 20, the resistance values of the sensor element Rs and the reference element Rr are different. Even if the drive voltage Vd supplied to the gas sensor 1 fluctuates during the operation, the alarm concentration (%) does not fluctuate as shown in FIG.

  Further, according to the gas alarm device 10 described above, it is only necessary to measure the sensor output Vs with respect to the drive voltage Vd = 2.0 V at the time of manufacture, and the drive voltage Vd is changed as in the first embodiment to perform a plurality of drives. Since it is not necessary to measure the sensor output Vs of the gas sensor 1 at the time of air base with respect to the voltage Vd, the manufacturing cost can be suppressed.

  In the above-described embodiment, the bridge circuit B is configured by the sensor element Rs, the reference element Rr, and the fixed resistors R1 and R2. However, the present invention is not limited to this. For example, a variable resistor VR may be used as shown in FIG.

  In the embodiment described above, a contact combustion type gas sensor 1 is used, but the present invention is not limited to this. The gas sensor 1 can be applied to either a semiconductor type or a limit current type as long as the sensor output Vs changes with respect to the change of the driving voltage Vd.

  In the first and second embodiments described above, the drive voltage Vd is detected only for setting the alarm value Vw, but the present invention is not limited to this. For example, when the drive voltage Vd is provided with an upper limit threshold value and a lower limit threshold value, and the CPU 31 functions as an abnormality detection means and the drive voltage Vd exceeds the lower limit threshold value or falls below the lower limit threshold value, A failure (abnormality) of the voltage source 2 may be detected. For example, as shown in FIG. 1, in the gas alarm device 10 of the type that directly transforms the primary voltage of the power transformer T and applies an AC voltage to the gas sensor 1, the transformer T is broken (for example, the transformer winding is broken or short-circuited). Anomalies such as can be detected. Further, when used in an AC90V or less or AC110V abnormality (for example, when used outside of Japan by mistake), it can be detected as an abnormality in the drive voltage Vd and detected.

  Further, the above-described embodiments are merely representative forms of the present invention, and the present invention is not limited to the embodiments. That is, various modifications can be made without departing from the scope of the present invention.

1 Gas sensor 2 Voltage source (power supply means)
20 Drive voltage detection circuit (drive voltage detection means)
31 CPU (alarm generating means, alarm value setting means, relational expression calculating means)
33 RAM (storage means)

Claims (2)

A gas sensor that outputs a sensor output corresponding to the gas concentration of the gas to be detected; power supply means for driving the gas sensor by supplying a driving voltage to the gas sensor; and when the sensor output output from the gas sensor is greater than or equal to an alarm value In a gas alarm device comprising an alarm generating means for generating an alarm,
The gas sensor includes a bridge circuit including a sensor element and a reference element connected in series with each other, and outputs the sensor output based on a midpoint potential difference generated in the bridge circuit.
Drive voltage detection means for detecting the drive voltage supplied by the power supply means;
Alarm value setting means for setting the alarm value according to the drive voltage detected by the drive voltage detection means;
Further comprising a,
It further comprises storage means for storing the sensor output of the gas sensor at the time of air base for a plurality of driving voltages measured in advance.
Relational expression calculating means for calculating a linear function expression indicating an alarm value obtained by adding a reference alarm value to a sensor output at the time of air base with respect to the driving voltage based on a plurality of sensor outputs stored in the storage means; Prepared,
The alarm value setting means sets a value obtained by substituting the drive voltage detected by the drive voltage detection means into a linear function equation calculated by the relational expression calculation means as an alarm value. . 2. The gas alarm device according to claim 1, further comprising an abnormality detection means for detecting an abnormality of the power supply means based on the drive voltage detected by the drive voltage detection means.

Images