JPH06341969A - Composite gas detector - Google Patents

Abstract

PURPOSE:To provide a composite gas detector which can be reduced in consumed electric power and is suitable for portable use. CONSTITUTION:A gas sensor S1 and a compensating element S2 mutually connected in series and resistances R1 to R3 mutually connected in series compose a bridge circuit 16a, and in addition, a gas sensor S3 and a compensating element S4 mutually connected in series and resistances R1 to R6 mutually connected in series compose a bridge circuit 16b. Fixed voltage is applied through a fixed voltage circuit to the bridge circuits 16a, 16b mutually connected in series, and a connecting point P5 between the bridge circuits 16a, 16b is set up to have the fixed voltage, and the output voltages of the bridge circuits 16a, 16b are severally supplied to operational amplifiers ICa, ICb to detect gas. The composite gas detector has such a formation as mentioned above.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a composite gas detector having a gas sensor capable of detecting a plurality of gases, and more particularly,
The present invention relates to a composite gas detector suitable for carrying, which includes a gas detection circuit with reduced power consumption.

[0002]

BACKGROUND OF THE INVENTION Composite gas detectors are gas detectors that include a plurality of gas sensors that are selective to their respective flammable gases. 300 to 400 mA at all times for gas sensor
When the air containing the combustible gas comes into contact with the gas sensor, the reaction heat is generated by reacting with the air and the temperature of the gas sensor rises. The heat of reaction increases the temperature of the gas sensor, which increases the electrical resistance of the metal wire of the gas sensor. The gas detector detects flammable gas by detecting a change in the resistance value of the metal wire as an electric signal.

A conventional composite gas detector is shown in FIG.
S based on an example of the scan detection circuit, S₁, S
₃Is a catalytic combustion type with selectivity for combustible gas
Gas sensor, compensating element S₂, S_FourAnd each directly
Column connected. These series circuits are connected in series.
Resistance R₁~ R₃And resistance R_Four~ R₆(R₂，
R _FiveAre variable type resistors) connected in parallel.
The gate circuits 6a and 6b are configured. Gas sensor S₁
And compensator S₂Connection point P with₁And variable resistance R₂Tap
To P₂Then, the connection point P₁Is the normal rotation of the operational amplifier ICa
Connected to the input terminal, tap P₂Is the operational amplifier ICa
Output terminal of operational amplifier ICa connected to non-inverting input terminal
The child is connected to the sensor detection circuit 4. Bridge circuit
Connection point P of 6b₃And tap P_FourIs the operational amplifier
It is connected to the non-inverting input terminal and the inverting input terminal of ICb,
The output terminal of is connected to the sensor detection circuit 4.

Power supply voltage is supplied from the power supply 1 to the constant voltage circuits 2 and 3, and bridge circuits 6a and 6 are supplied via the constant voltage circuit 2.
A constant voltage is applied to each b, and a constant voltage is applied to each of the operational amplifiers ICa and ICb, the sensor detection circuit 4, and the external detection circuit 5 via the constant voltage circuit 3. While the sensor detection circuit 4 and the external output circuit 5 require an applied voltage of 3 to 4 volts, the gas sensors S ₁ , S ₃
It is said that a voltage of 1 to 2 V is optimum as the applied voltage. A constant current is applied to each of the gas sensors S ₁ and S ₃ . Therefore, it is necessary to equip each circuit of the gas detection circuit with the constant voltage circuits 2 and 3 capable of applying a predetermined voltage. Further, as the power source 1, a commercial power source (AC100V) is usually used, but when the composite gas detector is used for portable use, a battery suitable for those circuits is selected and used.

[0005]

The conventional composite gas detector has no problem in power consumption when a commercial power source (100 VAC) is used as the power source. However, when it is used as a portable device, it is necessary to use a battery, and each gas sensor always has 300
The gas sensor must be heated by supplying a constant current of approximately 400 mA. Therefore, the composite gas detector in which the bridge circuit incorporating the gas sensor is provided in parallel has a drawback that power consumption increases and battery life is shortened.

Further, the voltage applied to the gas sensor is
In the case of a contact combustion type sensor having a wire diameter of about 50 μm, 1-2 V is said to be optimal, and therefore,
The voltage applied to the bridge circuit must be set to about 2-3 volts. In addition, operational amplifiers ICa, IC
In order to stably drive b, the sensor detection circuit 4, and the external output circuit 5, it is necessary to apply a constant voltage of usually 3 to 4 V as the applied voltage. In addition, each gas
It is necessary to constantly supply a constant current of about 300 to 400 mA to the sensor, and from the relationship with the maximum load current of the constant voltage circuit, as shown in FIG. 2, the bridge circuits 6a and 6b and the sensor detection circuit 4 are respectively supplied. It is necessary to provide the constant voltage circuits 2 and 3. Further, it is necessary to supply current to each of the constant voltage circuits, which increases power consumption and shortens the life of the battery. The present invention has been made in view of the above problems, and an object of the present invention is to provide a composite gas detector capable of reducing power consumption.

[0007]

In order to solve the above problems, a composite gas detector of the present invention comprises at least two or more gas sensors, and a plurality of gas sensors corresponding to each of the gas sensors. Is connected in series, and the voltage due to the potential difference obtained from the bridge circuit is amplified to detect the gas. Further, the composite gas detector of the present invention includes at least two or more gas sensors, a plurality of bridge circuits corresponding to each of the gas sensors are connected in series, and the voltage applied to each of the bridge circuits is constant. The gas is detected by amplifying the voltage due to the potential difference obtained from the bridge circuit.

[0008]

By the means as described above, in the composite gas detector of the present invention, the bridge circuits each having the gas sensor having the selectivity for each gas are connected in series, and the constant voltage is applied to the bridge circuits connected in series. Is applied to reduce the power consumption and extend the life of the battery.
In addition, the bridge circuits are connected in series, and the applied voltage is applied to the bridge circuits connected in series so that a constant current consumption flows through the bridge circuits connected in series, and at the same time, the sensor detection circuit and the external output circuit are connected. Also, by applying a constant voltage, the battery life is extended by reducing the power consumption.

[0009]

EXAMPLE An example of the composite sensor detector of the present invention will be described below.
Will be described based on the sensor detection circuit of FIG. same
In the figure, catalytic combustion with selectivity for each gas
Type gas sensor S ₁, S₂Bridge circuit 16 including
a and 16b are the bridge circuits 6a and 6b shown in FIG.
The circuit configuration is the same, but the bridge circuits 16a and 16b
Are connected in series. In the bridge circuit 16a,
Sensor S₁And compensator S₂Connection point P with₁Is an increase in calculation
Connected to the non-inverting input terminal of the width ICa, tap P₂But
It is connected to the inverting input terminal of the operational amplifier ICa. Bu
The ridge circuit 16b includes a gas sensor S₃And compensator S_Four
Connection point P with₃To the non-inverting input terminal of the operational amplifier ICb
Connected, tap P_FourIs an inverting input terminal of the operational amplifier ICb
Connected to the child. That of operational amplifiers ICa and ICb
Each output terminal is connected to the sensor detection circuit 14,
The output terminal of the sensor detection circuit 14 is connected to the external output circuit 15.
Has been.

[0010] The reference voltage circuit 12 includes a resistor R ₇ to R ₉ which are connected in series (R ₈ is variable resistor) consists, resistors R ₈
The tap P ₆ is connected to the input terminal of the buffer circuit 13 composed of the feedback type amplifier ICc, and its output terminal is connected to the connection point P ₅ of the bridge circuits 16a and 16b. Capacitor C ₁ -C ₃ input and output stage of the amplifier ICc are capacitors for high frequency bypassing. A constant voltage is applied from the constant voltage circuit 11 to the bridge circuits 16a and 16b connected in series, and a predetermined reference voltage is applied to the connection point P ₅ thereof via the buffer circuit 13. A constant voltage is applied to 16a and 16b. Of course, in the embodiment of FIG. 2, two bridge circuits each having a gas sensor are connected in series, but the present invention is not limited to this embodiment, and two or more bridge circuits may be connected in series. .

Next, the operation of the gas detection circuit of FIG. 2 will be described. Bridge circuit 16 connected in series
A constant voltage of 3 to 6 volts is applied to a and 16b via the constant voltage circuit 11, and _{1 to} each of the gas sensors S ₁ and S ₃ .
A voltage of 2 volts is applied. At the same time, a constant voltage of 3 to 6 volts is applied from the constant voltage circuit 11 to the reference voltage circuit 12, the sensor detection circuit 14, and the external output circuit 15.
Is being applied to. Each gas sensor S _1, S ₃ is supplied a constant current, in the steady state voltage between the terminals of the gas sensor S _1, S ₃ is coercive constant. Assuming that the combustible gas is in contact with the gas sensor S ₁ with air, combustible gas reacts with the air increases the temperature of the gas sensor S ₁ is the resistance of the gas sensor S ₁ rises . Since the potential at the connection point P ₅ between the bridge circuits 16a and 16b is kept constant, the voltage across the gas sensor S ₁ increases.

In the operational amplifier ICa, a reference voltage V _ra is applied to its inverting input terminal, and a connection point P ₁ is applied to its non-inverting input terminal.
Voltage V _P1 is applied, the voltage due to the potential difference between the voltage V _P1 and the reference voltage V _ra is amplified by the operational amplifier ICa, the output voltage is input to the sensor detection circuit 14 and amplified, and the output is further displayed by the display meter. Is supplied to the external output circuit 15 for driving the. Similarly, when the gas sensor S ₃ reacts to a predetermined combustible gas, the voltage due to the potential difference between the reference voltage V _rb and the voltage V _p4 at the connection point P ₄ is input to the operational amplifier IC _b and amplified. Then, the combustible gas can be detected by being input to the sensor detection circuit 14.

Of course, in the composite gas detection circuit of the present invention, the connection point P ₅ of the bridge circuits connected in series is kept constant even if the respective gas sensors simultaneously detect combustible gas. Since the terminal voltage of each gas sensor rises and the potential difference between each terminal voltage and the reference voltage is supplied to the operational amplifiers ICa and ICb,
Flammable gases can be detected. If the voltage drop across the gas sensors S ₁ and S ₃ and the compensating elements S ₂ and S ₄ is about 1 volt, the constant voltage of the constant voltage circuit 11 is 4V.
It suffices to set the voltage to the voltage, and at the same time, it is possible to set the applied voltage to the sensor detection circuit 14 and the external output circuit 15, so that it is not necessary to provide each constant voltage circuit. Although the output terminals of the operational amplifiers ICa and ICb are common in the embodiment, they may be connected to the sensor detection circuit 14 in parallel. Further, the sensor detection circuit 14 may be provided with a changeover switch to detect each combustible gas. Incidentally, in the embodiment, the description has been given on the detection circuit of the combustible gas, but the composite gas detector of the present invention can be applied to the composite gas detector by the detection circuit configured by the gas sensor in the bridge circuit. Is clear.

[0014]

As described above, in the composite gas detector of the present invention, the bridge circuit including the gas sensor is connected in series,
A measurable state can be set by supplying a predetermined constant current to the bridge circuit connected in series. Therefore, there is an advantage that the power consumption can be reduced as compared with the composite gas detector in which the bridge circuits are connected in parallel. Furthermore, by setting a constant voltage so that a voltage of 1 to 2 volts is applied to each gas sensor of the bridge circuit connected in series, the constant voltage is set to 3 to 4 volts, and at the same time, the sensor detection circuit. Since it can be used as a power supply voltage for the above, there is an advantage that power consumption can be reduced. According to the composite gas detector of the present invention, it is possible to reduce power consumption and extend the life of the battery, and therefore it is extremely effective as a portable composite gas detector.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a composite gas detection device according to the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional composite gas detection device.

[Explanation of symbols]

10 Battery 11 Constant Voltage Circuit 12 Reference Voltage Circuit 13 Buffer Circuit 14 Sensor Detection Circuit 15 External Output Circuit 16a, 16b Bridge Circuit ICa, ICb, ICc Operational Amplifier S ₁ , S ₃ Gas Sensor S ₂ , S ₄ Compensation Element

Claims (2)

[Claims] 1. A composite gas detector comprising at least two gas detectors.
A composite comprising one or more gas sensors, a plurality of bridge circuits corresponding to each of the gas sensors being connected in series, and amplifying a voltage due to a potential difference obtained from the bridge circuits to detect a gas. Gas detector. 2. A composite gas detector comprising at least 2
A voltage provided by one or more gas sensors, a plurality of bridge circuits corresponding to each of the gas sensors are connected in series, the applied voltage of each of the bridge circuits is kept constant, and a voltage due to a potential difference obtained from the bridge circuit. A compound gas detector characterized by amplifying and detecting gas.