1. Field of the Invention
The present invention relates to a gas detector, and more particularly to a gas detector capable of giving a driving signal to an alarm for the leak of fuel gases, such as hydrogen gas, methane gas, butane gas, with high reliability, by eliminating the noise induced by steam, ethanol gas, or smoke, etc. present concurrently with said fuel gases.
2. Prior Art
Generally, metallic oxides, such as SnO.sub.2, ZnO, Fe.sub.2 O.sub.3, In.sub.2 O.sub.3, WO.sub.2, CeO.sub.2, have the property of showing a resistance change when they come into contact with hydrogen gas, methane gas, butane gas, etc., while they are heated to high temperature, and by using such a property, they are applied to actual use as gas sensing elements for detecting the leak of fuel gases, including LPG and natural gas. However, said gas sensing elements are defective in selectivity to gases. That is, they show the resistance change not only to target gases for detection, such as hydrogen gas, methane gas, butane gas, contained in LPG, natural gas, etc. consumed domestically, but also to steam formed during cooking as well as ethanol gas from various seasonings. Therefore, said gas sensing elements detect these other than the leaked fuel gases to be detected, thereby reducing the reliability of detection.
The prior art relating to the present invention has been disclosed in U.S. Pat. Nos. 3,644,795, 3,835,529 and 3,732,519 That is, U.S. Pat. No. 3,644,795 discloses a structure, wherein highly strong gas detection elements are used which are obtained by adding silicon compound into gas sensor components including semiconductors of metallic oxide such as SnO.sub.2, ZnO, Fe.sub.2 O.sub.3, or NiO, Cr.sub.2 O.sub.3, and the output induced by change in resistance of said elements is inputted to a buzzer. U.S. Pat. No. 3,835,529 discloses a method for preparing a gas sensing element composed of metallic oxide semiconductors, such as SnO.sub.2, ZnO, Fe.sub.2 O.sub.3, TiO.sub.2, Cr.sub.2 O.sub.3, NiO, CoO, through processes of mixing, forming, baking and installation of electrode. And in U.S. Pat. No. 3,732,519, a gas sensing element including a pair of electrodes and porous metallic oxides containing semiconductor wherein the metallic oxides contain the particles of Al.sub.2 O.sub.3 and SiO.sub.2, was disclosed. All of them are inventions depending on the selectivity of gas sensing elements.