Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample
Reexamination Certificate
1992-08-12
2001-05-22
Smith, Lynette R. F. (Department: 1645)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing gas sample
C422S098000, C073S025050, C073S031050, C073S031060, C429S111000
Reexamination Certificate
active
06235243
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a gas sensor array for detecting individual gas constituents in a gas mixture. The array is composed of a plurality of individual sensor elements, which include semiconductive oxides, wherein the individual sensor elements are respectively applied on an electrically non-conductive substrate and wherein the array is provided with a contact electrode arrangement for measuring the electrical conductivity. In addition, the array includes a heating arrangement for heating to a given predetermined operational temperature, a protective sheath, which will protect the array against external mechanical influences, and a fastening base are also provided. The individual sensor elements have prescribed, individual operating temperatures allocated to them and the combinations between the respective sensor signals are formed for detecting the individual gas constituents, and these combinations are supplied to a processing unit.
Two proposals have been disclosed for selectively detecting and quantifying individual constituents in a gas mixture of chemically different gases. One of these proposals is directed to what is referred to as analysis equipment, wherein, for example, the employment are provided for quadripole mass spectroscopy or “FTIR”. These relatively involved apparatus have the required suitability for measuring jobs at testing stands, such as, for example, motor testing stands and gas measuring stations. In the field of what is referred to as a low-cost apparatus that can be employed for monitoring jobs, it has also been proposed to employ gas sensors on the basis of heated tubes of semiconductive SiO
2
, which is provided with different precious metal dopings in order to obtain the selectivity of the sensor for a specific gas by projection. See, for example, an article by J. Watson and A. Price,
Proc. IEEE,
Vol. 66, 1978, p. 1670, which article is directed to an investigation of the selectivity of such sensors with respect to CO and to CH
4
.
These latter sensors have high transverse sensitivities, for example they are generally sensitive not only for the gas to be detected but also other gases. Given such sensors for reducing gases on the basis of SnO
2
, for example, the sensor with the basic material SnO
2
is also O
2
-sensitive, for example, these sensors for reducing gases also react to O
2
. Evaluation methods based on the principle of a pattern recognition can only be conditionally implemented with these sensors, since the individual sensors of an appertaining array do not generally comprise the stability required for this purpose. The problems that occur are based on the drift of the sensor signal and on unit scatter. In this respect, see a portion of a book by S. R. Morrison,
Chemical Sensing with Solid State Devices,
Academic Press, New York, 1989, Chapter 13.1.2.
Similarly constituted problems also occur given other standard sensor materials, such as, for example, Fe
2
O
3
, TiO
2
and, in particular, ZnO.
SUMMARY OF THE INVENTION
An object of the present invention is to create a gas sensor array for detecting individual gas constituents in a gas mixture that, with high reliability and low transverse sensitivity, enables detecting and quantifying of the individual constituents in the gas mixture of chemically different gases, and the gas sensor array should have a cost-beneficial structure.
These objects are obtained in an improvement in a gas sensor array for detecting individual gas constituents in a gas mixture, said array being composed of a plurality of individual sensor elements which are based on semiconductor metal oxides, said sensor elements being respectively applied on electrically non-conductive substrates, the array being provided with a contact electrode arrangement for measuring the electrical conductivity and being provided with a heating arrangement for heating at a predetermined operating temperature, with a protective sheath that protects the array against external mechanical influences and with a fastening base wherein the individual sensor elements have prescribed individual operating temperatures allocated to them and wherein differences between respective sensor signals are formed for detecting individual gas constituents, with these differences being supplied to a processing unit. The improvements are that at least one part of the individual sensor element is based on a &bgr;-Ga
2
O
3
thin film and that all individual sensor elements are provided on a common substrate in a planar arrangement.
The invention allows the employment of arrays that contain individual sensor elements on the basis of catalytically non-active, stable semiconductive thin layers or films, for example Ga
2
O
3
, wherein, in the case of the individual sensor elements, the following is present:
a selection between oxygen sensitivity and sensitivity for reducing gases is made by selecting the operating temperature;
individual sensor elements are lent a specific sensitivity for individual, non-reducing gases on the basis of designational, catalytic activation of the Ga
2
O
3
, which, itself, is not catalytically active and by selecting a suitable operating temperature; and
a setting of the sensitivity for oxidizing gases (NO
x
, Cl
2
and Br
2
) is possible by varying the type of semiconduction by doping the material (for example changing to a p-type).
Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims.
REFERENCES:
patent: Re. 33980 (1992-06-01), Matsuura et al.
patent: 4045729 (1977-08-01), Loh
patent: 4057996 (1977-11-01), Firth et al.
patent: 4347732 (1982-09-01), Leary
patent: 4453397 (1984-06-01), Ohta et al.
patent: 4457161 (1984-07-01), Iwanaga et al.
patent: 4533608 (1985-08-01), Somorjai et al.
patent: 4542640 (1985-09-01), Clifford
patent: 4574264 (1986-03-01), Takahashi et al.
patent: 4584867 (1986-04-01), Forster
patent: 4792433 (1988-12-01), Katsura et al.
patent: 4991424 (1991-02-01), Lehto
patent: 0 141 090 (1985-05-01), None
patent: 2 331 016 (1977-06-01), None
patent: 1 527 406 (1978-10-01), None
patent: 1 562 623 (1980-03-01), None
Morrison, “Chemical Sensing with Solid State Devices”, Academic Press, Inc. 1989, pp. 520-523.
Michel:, Adolph L., et al., Ceramic Engineering Science Proceedings, 8[9-10] pp. 1095-1105, (1987).
Fleischer Maximilian
Meixner Hans
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
Smith Lynette R. F.
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