JPS6146455Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas detection element, and more specifically to a gas sensor that prevents malfunctions due to ambient temperature changes, ambient air currents, etc. as much as possible.

[Prior Art] Conventionally, gas leak detectors have been provided to detect gas leaks, and such gas leak detectors have been equipped with a gas sensor.

These conventional gas sensors are capable of detecting specific gases depending on the purpose.

For example, to detect flammable gases, catalytic combustion gas detection elements using catalysts such as Pt and Pd, and
Semiconductor gas sensing elements using metal oxide semiconductors such as SnO ₂ and ZnO were used.

In addition, such a gas sensor was developed in Japanese Patent Application Laid-open No.
As shown in Japanese Patent No. 130299, a filter was generally provided for the purpose of improving gas selectivity.

Regardless of the type of sensing element used in such gas sensors, the gas sensitive material used as the sensing element must be heated to 200 to 400°C due to gas adsorption/desorption or reaction temperature. It was something to do.

[Problems to be solved by the invention] However, since these conventional gas sensors use heating, they are easily affected by the surrounding environmental temperature, especially when there is a sudden temperature change. During this time, the output changed so much that it became undetectable.

Furthermore, because conventional gas sensors are heated, they cannot prevent temperature drop due to air currents, and if installed in a place where there is particularly strong wind, they may be affected by surrounding air currents. As a result, the output changed and became undetectable.

Although filters are used in conventional gas sensors, these filters can hardly be expected to have heat retention properties or airflow resistance.

Therefore, in the present invention, by surrounding the gas sensitive body itself as a sensing element with a thermally insulating member,
It is an object of the present invention to provide a gas sensor that is not easily affected by external temperature changes and can always stably detect gas without being affected by air currents or the like.

[Means for solving the problems] In order to solve the above-mentioned problems, the present invention has the following features:
It is characterized in that the gas sensitive body is surrounded by a skeleton-like heat insulating member provided at a position away from the gas sensitive body.

[Embodiment] An embodiment of the present invention will now be described with reference to the accompanying drawings.

Fig. 1 is a partially cutaway front view of a gas detection element related to the present invention, Fig. 2 is a perspective view thereof, Fig. 3 is a wiring diagram, and Fig. 4 is a graph showing the dependence of gas sensor sensitivity on ambient temperature. FIG. 5 is a graph showing the influence of gas sensor sensitivity on airflow velocity.

In each figure, the gas sensor related to the present invention has two electrodes 3, 3 made of Ni pins etc. erected on the top of a base 5, and a coiled platinum wire heater is installed between these two electrodes 3, 3. A gas sensitive body 4 around which an oxidation catalyst is coated and baked is fixed. Furthermore, such electrodes 3, 3 and gas sensitive body 4 are surrounded by a skeleton-like heat insulating member 2 fixed to a base 5 and having air permeability. Furthermore, in order to make the entire electrodes 3, 3, gas sensitive body 4, and thermally insulating member 2 explosion-proof,
It is covered with filter 1.

In addition, as the skeleton-like heat insulating member 2 having air permeability, low-density (high porosity) porcelain, asbestos, glass wool, etc. can be used.

When this gas sensor is wired as shown in FIG. 3 and operated in flammable gas, the thermally insulating member 2 is formed in a skeleton shape with air permeability. External combustible gas comes into contact with the gas sensitive body 4 through the holes in the sensor, and the presence of combustible gas is detected based on the change in output caused by the temperature rise due to combustion of the gas in contact. be.

In such a gas sensor, combustible gas is detected while the gas sensitive body 4 is heated to a constant temperature by a coiled platinum wire heater. Therefore, it is desirable that the temperature of the gas sensitive body 4 at this time is always constant without being influenced by external temperature or air flow.

In this regard, in the gas sensor according to the present invention, since the gas sensitive body 4 is surrounded by the thermally insulating member 2,
Since less heat is released from the gas sensitive body 4 to the outside,
It is extremely unaffected by outside temperature. This point is particularly important, as shown in Figure 4, when the outside temperature is low, the sensitivity of conventional gas sensors decreases significantly, whereas the gas sensor related to the present invention shows almost no decrease in sensitivity. It is. Therefore, the gas sensor related to the present invention is
It can be used without being affected by outside temperature.

Furthermore, when there is an airflow outside the gas sensor, the temperature of the gas sensitive body 4 of the conventional gas sensor decreases due to the airflow, as shown in FIG.
As a result, the sensitivity is significantly reduced, but in the gas sensor according to the present invention, since the gas sensitive body 4 is surrounded by the heat insulating member 2, it is relatively unaffected by air currents. In particular, as the air velocity increases, conventional gas sensors cannot detect it, but the gas sensor according to the present invention can detect it.

Furthermore, even when combustible gas comes into contact with the gas sensing element 4 and burns, and the temperature of the gas sensing element 4 rises, in conventional gas sensors, the heat is immediately released to the outside. Although the presence of a toxic gas could not be detected, the gas sensor according to the present invention can sufficiently detect the presence of the gas because its temperature is maintained by the heat insulating member 2.

Furthermore, even when the power supply voltage is momentarily cut off, the gas sensor according to the present invention retains heat in the thermally insulating member 2, so as soon as the power is turned on again, the combustible gas is removed. Detection can now be performed.

Further, once the temperature of the gas sensitive body 4 is set to a predetermined temperature, heat emission is extremely small, so that the subsequent supply voltage can be reduced, which also contributes to power saving.

[Effects of the invention] As explained above, the present invention is less susceptible to external temperature changes and is less affected by external temperature changes by surrounding the gas sensitive body itself as a sensing element with a thermally insulating member. Gas detection can always be performed stably without being affected by

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention,
Figure 1 is a partially cutaway front view of a gas detection element related to the present invention, Figure 2 is a perspective view of the same, Figure 3 is a wiring diagram,
FIG. 4 is a graph showing the dependence of gas sensor sensitivity on ambient temperature, and FIG. 5 is a graph showing the influence of air flow velocity on gas sensor sensitivity. 1... Filter, 2... Heat insulating member, 3...
...electrode, 4...gas sensitive body, 5...base.

Claims (1)

[Scope of utility model registration request] A gas sensor characterized in that a gas sensitive body is surrounded by a skeleton-like heat insulating member provided at a position away from the gas sensitive body.