JP2004177150A - Gas detector and gas detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a gas sensor from being poisoned or a false report from being sent by gas being generated by a space for a supplementary circuit. <P>SOLUTION: In a gas detector, a middle space 32 is provided between a small chamber 14 for accommodating a gas sensor 6 and the space 26 for a supplementary circuit. An air vent 34 is provided at the middle space 32 so that a surrounding atmosphere blows through, thus preventing gas from the space 26 for a supplementary circuit from reaching the small chamber 14, and hence preventing the gas sensor 6 from being poisoned or a false report from being sent by gas being generated from a printed circuit board 20. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
Field of application of the invention
The present invention relates to prevention of gas sensor poisoning and false alarms in a gas detection device, and more particularly to isolation of poisoning gas and false alarm gas from a circuit board of a gas sensor and a housing containing the circuit board from the gas sensor.
[0002]
[Prior art]
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 7-65276
[Patent Document 2] Japanese Patent Application Laid-Open No. H8-233664
Patent Literatures 1 and 2 disclose that a small room is provided in a housing of a gas detection device to house a gas sensor, and a circuit board in another part of the housing is isolated from the gas sensor. Also disclosed is that a gas vent is provided in a small room containing a gas sensor, and a filter such as activated carbon, silica gel, or zeolite is further stacked on the vent to remove poisoning substances and prevent false reports. ing.
[0006]
The gas detection devices of Patent Documents 1 and 2 have basically the structure of FIG. 2 is a housing base, 4 is a cover, 6 is a metal oxide semiconductor gas sensor, 8 and 9 are gas vents, 10 and 11 are filters, and 14 is a small room for accommodating the gas sensor 6. 20 is a printed circuit board, 21 is a battery as a power supply, 22 is a power supply circuit, 23 is a buzzer for alarm, and 24 is a gas detection circuit such as a microcomputer. Reference numeral 26 denotes a space for an auxiliary circuit, which is separated from the small room 14 by a partition wall 28.
[0007]
A toxic gas such as silicon gas is generated from the printed circuit board 20 or the like. In addition, from an insulating coating film or the like applied to the surface of the printed circuit board 20, an organic solvent-based gas that reduces the resistance value of the gas sensor and causes a false report is generated. The filter provided around the gas sensor adsorbs and removes the poisoning gas and the false alarm gas. However, in the high temperature and high humidity season, the adsorbed gas is desorbed and the gas sensor is affected. On the other hand, since the gas sensor is driven by a battery, sufficient heat cleaning cannot be performed. This causes the poisoning gas or miscellaneous gas to be hardly desorbed while adsorbed on the gas sensor. For these reasons, the gas generated from the auxiliary circuit side may poison the gas sensor or cause a false alarm. According to the experience of the inventors, it is difficult to sufficiently separate the small room 14 and the space 26 by the partition wall 28, and gas enters the small room 14 from the gap between the printed circuit board 20 and the base 2 or the cover 4. There were many.
[0008]
[Problems of the Invention]
An object of the present invention is to prevent a gas sensor from being poisoned or misreported by a gas generated in a space for an auxiliary circuit (claims 1 to 5).
[0009]
Configuration of the Invention
The present invention provides a gas detection device, in which a space for a gas sensor and a space for an ancillary circuit are separately provided in a housing of the gas detection device, wherein the space for the ancillary circuit is located between the space for the gas sensor and the space for the ancillary circuit. An intermediate space provided with a vent hole for diluting gas generated in the space and discharging the diluted gas to the surroundings.
[0010]
Preferably, partition walls are provided between the space for the auxiliary circuit and the intermediate space, and between the intermediate space and the space for the gas sensor.
Preferably, the ventilation holes are provided on both the left and right sides or both the front and rear sides of the housing in the intermediate space so that the surrounding atmosphere can freely flow between them.
[0011]
Preferably, the gas sensor provided in the space for the gas sensor is a gas sensor which is always kept at around room temperature and is heated in a pulsed manner.
[0012]
The present invention also provides a method for detecting a gas by separately providing a space for a gas sensor and a space for an auxiliary circuit in a housing of a gas detection device, wherein the space for a gas sensor and the space for an auxiliary circuit are provided. The gas sensor is provided with an intermediate space having a vent hole for diluting gas generated in the space for the auxiliary circuit and discharging the diluted gas to the surroundings, thereby preventing the gas from entering the space for the gas sensor. The gas detection method is characterized in that poisoning and misinformation are prevented.
[0013]
Function and Effect of the Invention
In the present invention, an intermediate space is provided between the space for the auxiliary circuit and the space for the gas sensor, and the gas generated in the space for the auxiliary circuit is exhausted to the surroundings from the ventilation hole of the intermediate space. The poisoning gas and the false alarm gas do not flow into the space, so that the gas sensor can be prevented from poisoning and false alarms.
[0014]
By providing a partition formed by a part of the housing or the like between the intermediate space and the space for the auxiliary circuit, and between the intermediate space and the space for the gas sensor, the space for the gas sensor and the space for the auxiliary circuit are provided. Can be separated sufficiently. For this reason, the gas sensor is completely prevented from being poisoned or misreported.
[0015]
Further, when the ventilation holes in the intermediate space are provided on both the left and right sides or the front and rear sides of the housing in this portion, the surrounding air flows so as to blow through the intermediate space, so that the gas sensor is more completely prevented from being poisoned or erroneously notified.
[0016]
If the gas sensor is a metal oxide semiconductor or contact-combustion gas sensor of the type that is constantly kept at room temperature and is heated in a pulsed manner, the heating tends to be insufficient, so that prevention of poisoning and false alarms is particularly important. Becomes important. Therefore, the present invention is particularly effective for a gas detection device using such a gas sensor. For example, the gas detection device is operated by using a battery power supply, a shared security line such as 24 V, a fire detection monitoring line, or the like as a power supply. Especially suitable for the case.
[0017]
【Example】
1 to 3 show examples and their characteristics. In these figures, reference numeral 2 denotes a base and reference numeral 4 denotes a cover, both of which are made of a synthetic resin such as ABS. The cover 4 is attached to the base 2 by screwing or fitting. Reference numeral 6 denotes a gas sensor, which is a gas sensor of a contact combustion type using the combustion heat of a metal oxide semiconductor or a combustible gas. In this case, the gas sensor is a pulse-driven gas sensor which is always kept at room temperature and heated in a pulsed manner. In the case of the embodiment, the gas sensor 6 is a SnO 2 -based metal oxide semiconductor gas sensor, and is pulse-heated at a cycle of 60 seconds for 14 msec. The duty ratio of the pulse heating is preferably 1/30 or less, more preferably 1/100 or less. Reference numerals 8 and 9 denote gas vents, which are provided in the cover 4 and filters 10 and 11 made of, for example, activated carbon, silica gel, or zeolite are superposed on the gas vents 8 and 9 so as to adsorb and remove poisoning gas and interfering gas. I do. Reference numeral 14 denotes a small room containing the gas sensor 6.
[0018]
Reference numeral 20 denotes a printed board on which a battery 21, a power supply circuit 22, a buzzer 23 for notification, and a gas detection circuit 24 such as a microcomputer and a load resistor are mounted. Reference numeral 26 denotes an additional circuit space for accommodating a portion of the printed circuit board 20 on which main circuit components are mounted. Reference numerals 28 and 30 denote partitions provided by extending the cover 4 toward the printed circuit board 20. Numeral 32 is an intermediate space between the auxiliary circuit space 26 and the small room 14.
[0019]
A vent hole 34 is provided in the intermediate space 32. As shown in FIG. 2, the ventilation holes 34 are provided, for example, on both the left and right sides of the cover 4 so that the surrounding air blows through the intermediate space 32 from the ventilation holes 34. The gas entering through 30 is not trapped. The ventilation holes 34 are not limited to being provided on the left and right sides of the cover 4, and may be provided, for example, in front of the cover 4 (upper surface in FIG. 2) and on the base 2. The printed circuit board 20 extends through the intermediate space 32 to the small room 14, and the intermediate space 32 may contain no additional circuit components or only auxiliary circuit components that do not generate gas. preferable. In the embodiment, the three-color LEDs 36 for display attached to the LED board 38 are housed to prevent the intermediate space 32 from increasing the size of the gas detection device.
[0020]
The application of the gas detection device of the embodiment is arbitrary, and may be used as a gas alarm device used for detecting a gas such as CO, methane, or LPG, or may be used as a portable gas detection device. Also, poisoning or false alarm of the gas sensor 6 causes a problem in many cases because the power of the power supply is insufficient. Therefore, it is particularly suitable when the battery 21 is used as a power supply. In addition to this, the power supply may be a shared security line for crime prevention, door lock, fire, etc., or a monitoring line for fire detection. Further, in the embodiment, the filters 10 and 11 are provided so as to overlap the gas vents 8 and 9, but these may be provided inside the gas sensor 6 or the like.
[0021]
FIG. 3 shows the behavior of the resistance value of the gas sensor in about four months from April to August, 2002. As an example, a gas detector provided with the intermediate space 32 as shown in FIG. 1 was used, and as a comparative example, a gas detector not provided with the intermediate space 32 was used as shown in FIG. The structure of these gas detectors is shown in FIGS. 1 and 4. A sponge-like activated carbon filter is used for the filters 10 and 11, and the gas sensor 6 has a heater film and a SnO2 film laminated on an insulating substrate. Then, one heated to about 300 ° C. for 14 msec at a cycle of 60 sec was used. The gas detection device is used for detecting CO in a kitchen or the like. The characteristics in FIG. 3 are the average values of the data of the five gas detectors in each of the example and the comparative example. In FIG. 3, the resistance of the metal oxide semiconductor one second after the pulse heating is measured, and the ratio between the resistance in air during use and the resistance in air during manufacture is shown. Although not shown in FIG. 1, a thermistor is mounted on the printed circuit board 20 to correct the temperature dependency of the gas sensor.
[0022]
In the example, the behavior of the resistance value in the air is relatively stable, but in the comparative example, after about 70 days, the resistance value in the air decreases to about 1/3 of the initial value. If even a small amount of CO is added here, an alarm is issued at a CO concentration lower than the detection target concentration and a false report is made. As a cause of such a false report, a high boiling organic solvent vapor or the like generated from the printed circuit board 20 or each mounted component may enter the small room 14 and accumulate in the filters 10 and 11 in the comparative example. Was to do. Next, when these gases accumulated in the filters 10 and 11 reached the rainy season and became hot and humid, they were desorbed from the filters 10 and 11 and confined in the small room 14 to cause a false alarm. In addition, the fact that the filters 10 and 11 were the cause of the false alarm could be confirmed by removing the filters 10 and 11 from the gas detection device of the comparative example and analyzing the gas generated from the filters due to the desorption by heating. On the other hand, in the embodiment, since the gas generated from the auxiliary circuit side can be discharged to the surroundings in the intermediate space, the resistance level in the air does not decrease.
[0023]
As described above, in the embodiment, it is possible to prevent gas generated from the auxiliary circuit, the housing, and the like from entering the small room accommodating the gas sensor 6 and causing poisoning and false alarm.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a gas detection device according to an embodiment. FIG. 2 is an enlarged cross-sectional view in the II-II direction of FIG. 1. FIG. 3 is a characteristic diagram of the gas detection device of the embodiment. Cross-sectional view of [Description of symbols]
2 Base 4 Cover 6 Gas sensors 8, 9 Gas vents 10, 11 Filter 14 Small room 20 Printed circuit board 21 Battery 22 Power supply circuit 23 Buzzer 24 Gas detection circuit 26 Auxiliary circuit space 28, 30 Partition wall 32 Intermediate space 34 Vent hole 36 LED
38 LED board

Claims (5)

In the case where the space for the gas sensor and the space for the auxiliary circuit are separately provided in the housing of the gas detection device,
An intermediate space having a vent hole for diluting gas generated in the space for the auxiliary circuit and discharging the gas to the surroundings is provided between the space for the gas sensor and the space for the auxiliary circuit. Gas detector. 2. The gas detection device according to claim 1, wherein partitions are provided between the space for the auxiliary circuit and the intermediate space, and between the intermediate space and the space for the gas sensor. The gas detection device according to claim 1, wherein the ventilation holes are provided on both left and right sides or both front and rear sides of the housing in the intermediate space so that an ambient atmosphere can freely flow between them. The gas detection device according to any one of claims 1 to 3, wherein the gas sensor provided in the space for the gas sensor is a gas sensor which is always kept at around room temperature and is heated in a pulsed manner. In a method in which a space for a gas sensor and a space for an ancillary circuit are separately provided in a housing of a gas detection device so as to detect a gas, By providing an intermediate space with a ventilation hole for diluting gas generated in the space for the incidental circuit and discharging the gas to the surroundings, the gas sensor is prevented from entering the space for the gas sensor. A gas detection method characterized in that the gas detection is prevented.

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