JP3809897B2 - Combustible gas concentration measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring the concentration of a combustible gas such as hydrogen using a catalytic combustion type gas sensor.
[0002]
[Prior art]
The catalytic combustion type gas sensor is configured by enclosing a heater coil that generates heat when energized with an oxidation catalyst so as to form a heat conduction relationship. When contacted with a combustible gas to be detected, the oxidation catalyst generates heat and conducts heat. As a result, the temperature of the heater coil rises. Therefore, the concentration of the combustible gas can be measured by detecting the electric resistance of the heater coil.
[0003]
[Problems to be solved by the invention]
However, because of the use of temperature changes due to combustion heat from the oxidation catalyst, there is no heat generation in a high concentration where combustion of combustible gas is impossible, that is, in an oxygen deficient environment, and the concentration of combustible gas is extremely low, There is an inconvenience that it cannot be distinguished from an extremely high state.
The present invention has been made in view of such problems, and an object of the present invention is to provide a gas measuring device that can detect the concentration of a combustible gas from a low concentration to a high concentration that cannot be combusted. Is to provide.
[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 a combustible gas concentration measuring device for detecting a combustible gas having a thermal conductivity higher than that of air , the heat conductive gas sensor is connected to a bridge circuit so as to apportion a constant operating voltage with the catalytic combustion gas sensor. , Detecting the output of the bridge circuit and the current flowing through the contact combustion gas sensor and the heat conduction gas sensor, and detecting the combustible gas detected in advance. And degrees, for detecting the concentration of combustible gas on the basis of the relationship between the currents flowing through the output and the catalytic combustion type gas sensor and the heat conductive gas sensor of the bridge circuit.
[0005]
[Action]
The low-concentration region and the high-concentration region are distinguished by utilizing the relationship between the concentration of the combustible gas detected in advance, the output of the bridge circuit, and the current flowing through the contact combustion gas sensor and the heat conduction gas sensor. Separately, the concentration of combustible gas is detected .
[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 hydrogen concentration measuring apparatus according to the present invention. The catalytic combustion type gas sensor 1 forms a heat conduction relationship in the heater coil 2 that generates heat when energized as shown in FIG. In this way, an electrical insulating layer 3 made of an electrically insulating material, such as alumina, is formed, and an oxidation catalyst layer 4 that promotes an oxidation reaction between combustible gas and oxygen is formed on the outer periphery thereof.
The heat conduction type gas sensor 5 is arranged so that a material having a large temperature resistance coefficient and having no catalytic action on the test gas, for example, a material in which platinum is plated with gold is formed in a heat conduction relationship with the test gas. Configured.
[0007]
The contact combustion type gas sensor 1 and the heat conduction type gas sensor 5 are balanced and bridge-connected so as to have zero output in the atmosphere together with the reference resistors 8 and 7 and are operated from the power source 9 via the current detection resistor 8. Electric power is supplied, and a constant voltage maintaining circuit 11 is connected to the bridge unit 10.
[0008]
The measurement circuit 12 receives the sensor current flowing through the sensors 1 and 5, that is, the voltage of the current detection resistor 8, and the unbalanced voltage resulting from the gas sensitivity of the sensors 1 and 5, that is, the bridge output, and stores data. The gas concentration is calculated from the calibration curve data stored in the means 13.
[0009]
In this embodiment, when the concentration of the combustible gas in the atmosphere, for example, hydrogen gas, rises from zero%, the combustion heat in the oxidation catalyst is proportional to the gas concentration in the state where oxygen is sufficiently present. The resistance value of the heat conduction type gas sensor 5 decreases and the output of the bridge portion 10 increases as shown in the region I of the curve A in FIG. Since the rate of increase in the resistance value of the heater coil 2 is larger than the rate of decrease in the resistance value of the heat conduction type gas sensor 5, the current increases as the concentration of hydrogen gas increases as shown in region I of curve B in FIG. Decrease.
[0010]
When the gas concentration further rises to a predetermined concentration, the contact combustion type gas sensor 1 has a lower resistance because the degree of combustion in the oxidation catalyst layer 4 becomes lower, and the heat of hydrogen gas compared to air. Cooling due to high conductivity also reduces the temperature.
On the other hand, in the heat conduction type gas sensor 5, since the heat dissipation by the hydrogen gas having a higher heat conductivity than air becomes large, the temperature is lowered and the resistance value is also lowered. The reduction ratio of the resistance values of the catalytic combustion type gas sensor 1 and the thermally conductive gas sensor 5, towards the catalytic combustion type gas sensor 1 it is heat only the amount that the combustion stopped Takoiru 2 large Kikunaru.
Therefore, contrary to the case where the concentration of hydrogen gas is low (region I), the resistance change rate of the heat conduction type gas sensor 5 is greatly affected by the change in gas concentration, and the maximum value is shown in region II of FIG. As the hydrogen gas concentration increases, the output of the sensor circuit 10 decreases.
On the other hand, in the region where the concentration of hydrogen gas is high, the resistance values of the two sensors 1 and 5 both decrease, so that the sensor current flowing through the resistor 8 increases.
[0011]
That is, the resistance value of the catalytic combustion type gas sensor 1 is
RHW + ΔRa−ΔRb
(However, RHW is a resistance value in contact with air, ΔRa is a resistance change caused by temperature rise due to combustion heat of combustible gas, and ΔRb is a thermal conductivity of combustible gas higher than air. Resistance change due to temperature drop)
In addition, the resistance value of the heat conduction type gas sensor 5 is
RTE-ΔRc
(However, RTH is the resistance value in contact with air, and ΔRc is the resistance change caused by the temperature drop due to the thermal conductivity of combustible gas higher than air)
Can be expressed as
Also usually
ΔRb ≒ ΔRc
It can be said.
For this reason, in the concentration of the region I, since oxygen that can sufficiently burn the combustible gas exists, ΔRa increases and the bridge output also increases. On the other hand, since ΔRb≈ΔRc << ΔRa, the current value decreases. .
At the concentration in region II, since there is no oxygen that can sufficiently burn the combustible gas, ΔRa decreases and the bridge output also decreases. On the other hand, since ΔRb≈ΔRc << ΔRa, the current value increases.
[0012]
On the other hand, two types of gas concentration values (region I and region II in FIG. 3) exist for the same sensor output, but the sensor current, that is, the voltage of the resistor 8 is detected by the measurement circuit 12. Thus, either region I or region II can be specified.
[0013]
Therefore, the sensor current is detected by the measurement circuit 12, and either the region I or the region II is determined from the value, while the data storage means 13 causes the curve A shown in FIG. 3, that is, the relationship between the bridge output and the hydrogen concentration. Can be detected as a standard curve using a single calibration curve data from a low concentration to a high concentration using the current value of the sensor unit 10 as a criterion.
[0014]
Incidentally, the relationship between the bridge output and the sensor current described above, taking the hydrogen gas concentration in the parameter, and stores in the memory means the relation between the sensor voltage and the sensor current relationship, or as the dictionary data, and the bridge output It is clear that the gas concentration can be detected by accessing with the sensor current.
[0015]
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.
[0016]
Furthermore, the present invention is particularly effective for measuring the concentration of hydrogen gas having a thermal conductivity significantly different from that of air, but other combustible gases having a thermal conductivity higher than that of air, such as methane (thermal conductivity 1.64). It can be applied to the detection of the above.
[0017]
【The invention's effect】
As described above, according to the present invention, the relationship between the concentration of the combustible gas detected in advance, the output of the bridge circuit, and the current flowing through the catalytic combustion gas sensor and the heat conduction gas sensor is used. Thus, since the concentration of the combustible gas is detected by distinguishing the low concentration region from the high concentration region, it is possible to detect a wide range of concentrations by selectively using the characteristics of the catalytic combustion type gas sensor and the heat conduction type gas sensor .
[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.
FIG. 3 is a diagram showing the relationship between the bridge output and sensor current and the gas concentration in the apparatus.
[Explanation of symbols]
1 Contact Combustion Gas Sensor 5 Thermal Conduction Gas Sensor 8 Sensor Current Detection Resistance

Claims (1)

A heater that generates heat by Joule heat when energized, 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 concentration measuring device that detects
A heat conduction gas sensor is connected to a bridge circuit so as to apportion a constant operating voltage to the contact combustion gas sensor, and the output of the bridge circuit and the current flowing through the contact combustion gas sensor and the heat conduction gas sensor are detected. The combustible gas concentration is detected based on the relationship between the concentration of the combustible gas detected in advance, the output of the bridge circuit and the current flowing through the contact combustion gas sensor and the heat conduction gas sensor. Sex gas concentration measuring device.

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