JP3929845B2 - Combustible gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustible gas detection device that detects high-concentration and low-concentration combustible gases using different types of sensors.
[0002]
[Prior art]
A contact combustion type gas sensor with an oxidation catalyst layer formed on the heater is used to detect low-concentration combustible gases at the lower explosion limit, and a non-oxidized layer is used to detect high-concentration combustible gases. In a flammable gas detection device that detects a flammable gas in a wide range from low concentration to high concentration, one switch is used depending on the concentration of the flammable gas to be detected. The sensor is selected, or the point in time when the detection signal of the catalytic combustion type gas sensor becomes scale over is detected and switched to the conduction type gas sensor.
[0003]
[Problems to be solved by the invention]
However, since the contact combustion type gas sensor detects heat generation due to the oxidation reaction between oxygen in the atmosphere and the combustible gas as a change in resistance of the heater, if the concentration of the combustible gas is extremely high, causing oxygen deficiency, Oxidation reaction does not occur, and there are no combustible gases, but the result is as follows.
The present invention has been made in view of such a problem, and an object of the present invention is to automatically set a sensor corresponding to the concentration of the combustible gas to be measured regardless of the concentration of the combustible gas. It is providing the combustible gas detection apparatus which can be selected.
[0004]
[Means for Solving the Problems]
In order to solve such a problem, in the present invention, the switching means switches between the low concentration region detection unit provided with the catalytic combustion type gas sensor and the high concentration region detection unit provided with the heat conduction type gas sensor while always operating. Te in combustible gas detecting device for measuring the concentration of a combustible gas, the low when the detected output of the density region detection unit detects that exceeds a predetermined value, and pulse-shaped signal from the low-density region detection unit When the output is detected, the switching means selects the high density region detection unit.
[0005]
[Action]
If the flammable gas is present in a high concentration in an environment where the oxygen concentration is sufficient for combustion, the detection output of the low concentration region detection unit consisting of a catalytic combustion type gas sensor exceeds the specified value. Switch to the department.
In addition, if the oxygen concentration is not sufficient to burn the combustible gas on the catalyst, combustion for a very short time due to oxygen adsorbed on the surface of the catalyst occurs. A signal is output. The specific signal waveform is detected and switched to the high concentration region detection unit.
[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 the figure, reference numerals 1 and 2 denote a high concentration region gas detection unit and a low concentration region gas detection unit, respectively. The detection unit 1 is configured by bridging a thermally conductive gas detection sensor S1, a compensation element C1, and fixed resistors R1 and R2, and the low concentration region gas detection unit 2 includes a catalytic combustion type gas sensor S2, a compensation element C2, The resistors R3 and R4 are configured by bridge connection, and a power source 3 is connected to each operating voltage supply point.
[0007]
The heat conduction type gas sensor S1 is arranged such 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.
[0008]
As shown in FIG. 2, the contact combustion type gas sensor S2 has an electrically insulating material, for example, an electrically insulating layer 11 such as alumina formed on the heater coil 10 that generates heat when energized so as to form a heat conduction relationship. Further, an oxidation catalyst layer 12 that promotes an oxidation reaction between the combustible gas and oxygen is formed.
[0009]
The compensation element C1 is configured so that the temperature coefficient of resistance is substantially equal, and is configured to be accommodated in a container or the like so as not to contact the combustible gas.
The compensation element C2 is configured so that the temperature coefficient of resistance is substantially equal, does not generate oxidation heat due to the combustible gas, forms the same heat conduction relationship as the gas in the environment, and has a test gas. On the other hand, it is configured to have the same heat conduction characteristics as the contact combustion type gas sensor S2.
[0010]
Returning again to FIG. 1, the detection signal switching means 5 of the high density region the gas detection section 1, also the detection signal of the low-concentration region the gas detection section 2 outputs respectively to the judging means 4 and the switching means 5 to be described later ing.
[0011]
The determination unit 4 detects that the detection output of the low concentration region gas detection unit 2 has exceeded a specified value, or that a pulsed signal has been output from the low concentration region gas detection unit 2, and switches the switching unit 5 to a switching signal. Is output.
[0012]
The switching unit 5 normally outputs a signal from the low concentration region gas detection unit 2 to the measurement unit 6 , while outputting a signal from the high concentration region gas detection unit 1 to the measurement unit 6 in response to the input of the switching signal. It is configured.
[0013]
In this embodiment, in the state where the concentration of the combustible gas is within the low concentration region, no signal is output from the determination unit 4, so the switching unit 5 uses the detection signal from the low concentration region gas detection unit 2 as the measurement unit 6. Output to. Thereby, combustible gas with a low concentration can be detected with high sensitivity by the catalytic combustion type gas sensor S2.
[0014]
In such a state, when the concentration of the combustible gas increases with time, the level of the detection signal from the low concentration region gas detection unit 2 increases, and exceeds a preset reference value. As a result, since the signal is output from the determination means 4 , the switching means 5 outputs the detection signal from the high concentration region gas detection unit 1 to the measurement means 6 , and based on the calibration data stored in the data storage means 7. Continue to measure the increased gas concentration.
[0015]
On the other hand, when the concentration of the combustible gas rapidly increases as shown in FIG. 3 (a), the oxygen concentration decreases relatively rapidly. Therefore, the catalytic combustion type gas sensor S2 is adsorbed on the surface of the catalyst. After burning for a very short time with oxygen, the sensor does not function as a sensor. Therefore, after a predetermined level signal is output from the low-concentration region gas detection unit 2 for a short time, the level drops rapidly, as shown in FIG. A pulse-like signal as shown is output, and thereafter, the catalytic combustion gas sensor S2 and the compensation element C2 are thermally balanced to output a signal equal to zero concentration.
[0016]
Since the determination means 4 detects this pulse signal and outputs the signal, the switching means 5 outputs the detection signal from the high concentration region gas detection unit 1 to the measurement means 6 , and increases the concentration of the gas. It can be measured based on the signal of the high concentration region gas detector 1.
[0017]
When the concentration of the combustible gas decreases with time and the level of the detection signal of the low concentration region gas detection unit 2 falls below the reference value, the signal from the determination means 4 stops. As a result, the switching means 5 outputs a detection signal from the low concentration region gas detection unit 2 to the measurement means 6 , and the combustible gas having a low concentration is detected with high sensitivity based on the calibration data stored in the data storage means 7. To detect.
[0018]
【The invention's effect】
As described above, according to the present invention, the sensor corresponding to the concentration of the combustible gas to be measured can be automatically selected regardless of the concentration of the combustible gas.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a combustible gas detection device of 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 diagrams showing a pulse-like output of a low concentration region gas detection unit when contacting a high concentration gas.
[Explanation of symbols]
1 High concentration region gas detector 2 Low concentration region gas detector
4 judgment means
5 switching means
6 the measuring means 10 a heater coil 11 electrical insulating layer C1, C2 compensating element S1 thermal conductivity type gas sensor S2 catalytic combustion type gas sensor

Claims (2)

A combustible gas detection device that measures the concentration of combustible gas by switching by a switching means while always operating a low concentration region detection unit equipped with a catalytic combustion type gas sensor and a high concentration region detection unit equipped with a heat conduction type gas sensor In
When it is detected that the detection output of the low concentration region detection unit exceeds a predetermined value, and when it is detected that a pulsed signal is output from the low concentration region detection unit, the high concentration region is detected by the switching means. A combustible gas detector that selects a detector. The low-concentration area detection unit has a resistance temperature coefficient substantially equal to that of the catalytic combustion type gas sensor, does not generate heat of oxidation due to the combustible gas, and forms a heat conduction relationship that is the same as the gas in the environment. 2. The combustible gas detection device according to claim 1, wherein the high-concentration region gas detection unit is connected with a compensation element having a resistance temperature coefficient substantially equal and configured so as not to contact the combustible gas.

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