The catalytic combustion type gas sensor detecting the principles of the combustible gas (H2, CO, CH4, etc.) in contact with oxygen in the air, oxidation reaction, reaction heat is generated (flameless catalytic combustion heat), such that the platinum wire as the temperature sensitive material is increased , the resistance value increased accordingly. In general, the combustible gas concentration in the air is not too high (less than 10%), combustible gas can be completely burned calorific value related to the concentration of the combustible gas. The greater the concentration of combustible gas in air, heat of reaction (heat of combustion) oxidation reaction (combustion) produced the more the platinum wire temperature change (increase) the larger, the more the resistance value is increased. Thus, as long as the measured value of the variable resistance element sensitive to a platinum wire ([Delta] R), the combustible gas concentration in the air can be detected. However, simply using a platinum wire coil as the detection element, its life is short, therefore, the practical application of the detection element, are coated with a platinum oxide catalyst outside the wire ring. This is to extend its life, but also can improve the response characteristics of the detection element.
Bridge circuit catalytic combustion type gas sensors shown in FIG. FIG detection element F1; F2 of a compensation element, the effect is the deviation ambient temperature compensation other than the combustible gas catalytic combustion, supply voltage variations caused by other factors. In operation, the holding current required by 100mA ~ 200mA in F1 and F2 of, for the oxidation reaction heat of the flammable gas generation (combustion of the contact) on the detector element F1 required. When the detecting element F1 in contact with a combustible gas, since the effect of intense oxidized (burned), releasing heat, so that the temperature rise detecting element, the resistance value is increased accordingly, no balancing bridge circuit, is generated between the A, B potential difference E.
Thus, the resistance detection element and the compensating element F1 F2 ratio RF2 / RF1 is close to the range of 1, A, E the potential difference between points A and B, is approximately proportional to the ΔRF. Here, ΔRF due to temperature changes (heat of combustion) of combustible gas is produced by catalytic combustion caused with combustion heat (heat of oxidation reaction combustible gas) is proportional to the contact. I.e. ΔRF represented by the formula
Ρ- temperature coefficient of resistance of the detection element; ΔT- combustible gas catalytic combustion due to the temperature increase caused by the detecting element; ΔH- calorific combustible gas is combusted in contact; C- heat capacity detecting element; a Q-combustible gas combustion heat; m- combustible gas concentrations [% (Vol)]; α- constant determined by the catalyst coated on the detector element. For [rho], C material and values of the detection element α, the shape, structure, surface treatment and other factors. Q is determined by the kind of combustible gas. Thus, under certain conditions, it is determined constants. but
I.e., A, m is proportional to the concentration of the combustible gas and the potential difference between points A and B. If the ammeter or voltmeter connected between the A, B points, can be measured by A, B between the potential difference E, and thereby obtain the combustible gas concentration in the air. If, when the combustible gas can reach a certain concentration in the air and with the corresponding circuit, the automatic alarm signal, which induces a characteristic curve shown in FIG.
E is the potential difference between A, B, and thereby obtain the combustible gas concentration in the air. If, when the combustible gas can reach a certain concentration in the air and with the corresponding circuit, the automatic alarm signal, which induces a characteristic curve shown in FIG. Technology area
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