JP3809898B2 - Combustible gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for detecting the concentration of a combustible gas such as methane using a contact combustion type gas sensor.
[0002]
[Prior art]
The catalytic combustion type gas sensor is configured such that a heater coil that generates heat when energized is surrounded by an oxidation catalyst so as to form a heat conduction relationship. This sensor measures the concentration of combustible gas by detecting the electrical resistance of the heater coil because the oxidation catalyst generates heat when it comes into contact with the combustible gas to be detected and the temperature of the heater coil rises due to heat conduction. Can do.
[0003]
[Problems to be solved by the invention]
However, due to the use of the combustion heat generated by the oxidation catalyst, there is a risk of misjudgment that there is no heat generation in a high concentration where combustion of combustible gas is impossible, that is, in an oxygen-deficient state, and that there is sometimes zero gas.
The present invention has been made in view of such problems, and an object of the present invention is to make it possible to determine whether or not the environment is a high-concentration environment even when the concentration indication value is extremely low. It is to provide a sex gas detection device.
[0004]
[Means for Solving the Problems]
In order to solve such a problem, in the present invention, a heater that generates heat by Joule heat when energized, an electrical insulating layer formed on the surface of the heater, and a combustible gas formed on the surface of the electrical insulating layer A catalytic combustion type gas sensor that is heated by the heater by forming a heat conduction relationship while maintaining electrical insulation with the heater by the electrical insulating layer. In the flammable gas detection device for detecting the flammable gas having a higher thermal conductivity than air using the gas, the concentration of the flammable gas is increased so that the oxidation catalyst layer cannot maintain the oxidation reaction. things, that the thermal conductivity of the combustible gas becomes lower than the case where resistance values of the heater caused by the higher than the thermal conductivity of the air is in contact with the air To detect Ri.
[0005]
[Action]
At normal concentrations, the resistance increases due to heat from contact combustion, and in high concentration regions, the Joule heat of the sensor is dissipated in proportion to the gas concentration, and the resistance value is shorter than when exposed to air. Detection is performed by decreasing the output with time and changing the output.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Therefore, details of the present invention will be described below based on the illustrated embodiment.
FIG. 1 shows an embodiment of the combustible gas detection device of the present invention, in which a catalytic combustion gas sensor 1 and a sensor current detection resistor 2 for detecting a current flowing through the sensor 1 are connected in series. A constant voltage maintaining circuit 4 is connected to both ends of the catalytic combustion gas sensor 1.
As shown in FIG. 2, the contact combustion type gas sensor 1 is formed with an electrically insulating material 11 such as alumina on a heater coil 10 that generates heat when energized so as to form a heat conduction relationship. Further, an oxidation catalyst layer 12 that generates heat by promoting combustion of combustible gas is formed.
[0007]
The measurement circuit 5 calculates the gas concentration based on the voltage of the sensor current detection resistor 2 and the calibration curve data stored in the data storage means 6 in the low concentration region, and does not cause catalytic combustion due to lack of oxygen. When high flammable gas flows in, the determination is made based on the form of the current change detected based on the voltage of the sensor current detection resistor 2, that is, the state in which the current increases with time after the current decreases. It is configured.
[0008]
The data storage means 6 stores calibration curve data for a gas concentration combustible by atmospheric oxygen and an oxidation catalyst, for example, 0 to 80%.
[0009]
In this embodiment, in the environment where methane is present at a combustible concentration, that is, in the range of region I, the oxidation catalyst layer 12 generates heat with a calorific value corresponding to the concentration. As the temperature rises, the resistance value rises corresponding to the methane concentration (region I in FIG. 3). Therefore, the measurement circuit 5 outputs the methane concentration based on the calibration curve data stored in the data storage means 6.
[0010]
On the other hand, when a high concentration of methane gas that makes contact combustion in the catalytic combustion gas sensor 1 incapable of flowing in, methane burns in the oxidation catalyst layer 12 due to the remaining oxygen at the beginning of the inflow, and the concentration becomes high in a short time. Although the value is output, oxygen disappears over time, the catalytic combustion of methane stops, and the heat generation by combustion stops. In addition, the heat of the heater coil 10 is deprived by methane, which has a higher thermal conductivity than air, and the resistance value is lower than when pure air is in contact (region II in FIG. 3).
[0011]
As a result, the measurement circuit 5 determines that the methane concentration has risen above the combustible concentration based on a large current change that has occurred in a short period of time, and in this embodiment, has rapidly increased to 80% or more, and outputs an alarm signal as necessary. To do.
[0012]
In the above-described embodiment, the driving is performed by the DC voltage. However, it is clear that the same effect can be obtained even if the pulse voltage is supplied as shown in FIG. Power consumption at the heater of the gas sensor can be reduced.
[0013]
In the above embodiment, the heater is formed in a coil shape. However, a catalytic combustion type gas sensor in which an oxidation catalyst is formed on the surface of the plate heater through an insulating layer may be used. It is clear that the same effect is achieved.
[0014]
Furthermore, although the present invention has been described for methane that has a significantly different thermal conductivity from air, other combustible gases having a higher thermal conductivity than air, such as hydrogen (thermal conductivity 6.28), ethane (thermal conductivity). It can also be applied to the detection of 1.26).
[0015]
【The invention's effect】
As described above, according to the present invention, according to the present invention, the resistance value is increased due to heat in catalytic combustion at a normal concentration, and the Joule heat of the sensor is dissipated in proportion to the gas concentration in the high concentration region, and is released to the air. It is possible to determine whether or not the environment is a high-concentration environment by reducing the resistance value in a short time and changing the output as compared with the case of being exposed .
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a hydrogen concentration measuring apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing an embodiment of a catalytic combustion type gas sensor.
FIGS. 3A and 3B are explanatory diagrams showing the operation of the apparatus. FIG.
FIGS. 4A to 4C are explanatory diagrams showing operations when driven by pulse voltages, respectively.
[Explanation of symbols]
1 Contact combustion type gas sensor 2 Sensor current detection resistance

Claims (1)

A heater that generates heat due to Joule heat by energization, an electrical insulating layer formed on the surface of the heater, and an oxidation catalyst layer that generates heat by oxidizing a combustible gas formed on the surface of the electrical insulating layer , A flammable gas having a thermal conductivity higher than that of air using a contact combustion gas sensor in which the oxidation catalyst layer is electrically insulated from the heater by the electrical insulation layer and forms a heat conduction relationship and is heated by the heater. In the combustible gas detection device that detects
Said oxidation catalyst layer is the concentration of the combustible gas as is impossible to maintain the oxidation reaction was rose, the thermal conductivity of the combustible gas due to higher than the thermal conductivity of air If resistance values of the heater generated Te is in contact with the air combustible gas detector for detecting by lower than.

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