Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample
Patent
1994-01-28
1996-11-12
Warden, Jill
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing gas sample
73 2321, 73 2331, 73 3106, 422 94, 422 98, G01N 2704, G01N 2714, G01N 2716
Patent
active
055737285
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for selectively detecting a gas present in ambient air, and it is mainly intended for safety applications, particularly detecting leaks from networks and from assemblies that implement such a gas.
BACKGROUND OF THE INVENTION
Conventionally, when using solid state sensors, in particular semiconductors, gas detection is based on variation in the resistance of a semiconductor metal oxide such as SnO.sub.2 in the presence of a reducing gas, which variation can be related to the concentration of the gas.
However, such a method suffers from the drawback of not discriminating properly between reducing gases.
In order to improve the selectivity of such sensors, it is known to associate a catalyst with the semiconductor element constituting the sensor, the catalyst being constituted by a noble metal such as platinum or palladium, and being present at a concentration that does not exceed 1% of the weight of the oxide.
It is also known that the response of such sensors can be improved by varying the temperature to which they are raised by means of a platinum resistance element integrated in the sensor and serving to heat it.
Nevertheless, neither of those improvements to the preceding method provides a solution that is completely satisfactory, which is why suggestions have been made to use the variation in the temperature of the sensor due to the heat given off by combustion of the gas in addition to measuring conductance.
Unfortunately, implementing such a method turns out to be particularly difficult since the temperature of the sensor depends not only on the heat from the reaction, but also on variations in ambient temperature or on gas flow conditions relating to speed and direction which can give rise to temperature variations in the sensor that are of the same order of magnitude as those associated with the combustion of the gas.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to provide a gas detection device that is both simple and reliable, that enables variations in ambient temperature to be compensated, and that amplifies the variation in the temperature of the sensor that is due to the combustion of the gas.
Another object of the invention is to implement a device that is not sensitive to the flow conditions of the gas acting on the solid state sensor constituting an element of the device, or at any rate that is relatively insensitive thereto.
These objects are achieved by a device for selective detection of gas, enabling a first gas to be detected relative to a second gas, the device comprising a solid state sensor provided with an insulating substrate having a first face and a second face, a heater element deposited on the first face of said substrate, metal electrodes deposited on the second face of said substrate, and a semiconductor layer formed on said electrode and over the second face of said substrate, wherein detection is performed by simultaneously determining a voltage U representative of the resistance of the semiconductor element of the solid state sensor and the voltage difference S between a voltage representative of the temperature of the heater element of said solid state sensor and a voltage representative of the temperature of a heater element of a reference sensor, said voltage U and said voltage difference S each being compared with a different and predetermined threshold voltage in order to enable selective detection of gas.
The temperature difference between the solid state sensor and the reference sensor due to the combustion of the gas gives a simple image of the concentration of the gas that needs subsequently merely to be combined with the variation in the resistance of the solid state sensor in order to make it possible to perform said selection between the two gases that may interact with said sensors.
Advantageously, the semiconductor layer of the solid state sensor is provided with a catalyst constituting more than 1% but not more than 20% by weight thereof.
This considerable increase in the quantity of cata
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Patent Abstracts of Japan, vol. 13, No. 32 (P-817) 25 Janvier 1989.
Patent Abstracts of Japan, vol. 9, No. 129 (P-361) Juin (1985).
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Dutronc Pascale
Loesch Muriel
Lucat Claude
Marteau V eronique
Menil Francis
Gaz de France
Ludlow Jan M.
Warden Jill
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