Measuring and testing – Gas analysis – With compensation detail
Patent
1996-02-05
1998-08-04
Williams, Hezron E.
Measuring and testing
Gas analysis
With compensation detail
73 3106, 73 2901, 7333505, 204411, 204412, 340632, 364498, 364553, G01N 2712, G01N 3100, G08B 1710
Patent
active
057896593
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to methods of monitoring multiple electrode resistive gas sensors comprising a gas-sensitive resistor, preferably but not exclusively comprising a semi-conductive oxide material, and having an active surface and a plurality of pairs of electrodes for the purpose of measuring the resistance, with the electrode pairs being different from each other as regards the spacing between the electrodes of the pair or the disposition of the pair within the body of the resistor relative to the active surface, i.e. the external surface in contact with the gaseous atmosphere.
The term "monitoring" is used here in a broad sense to mean making use of the signals from the sensor for any desired purpose, including determination of one or more target gases in a gaseous mixture; making corrections to compensate for factors that would otherwise tend to give rise to errors in the information received by the user; and testing the sensor itself for correct operation. Determination of target gases in a gaseous medium containing more than one target gas comprises detection and/or measurement of those gases. In general, the target gas is a gas capable of causing the electrical resistance of the sensor to vary in response to gas concentration.
A multiple electrode resistive gas sensor is disclosed in the document GB 2 218 523B, which describes a method of detecting and/or measuring at least one gas by exposing an active surface of a gas sensor to the gas or gases, allowing the latter to diffuse through a porous body of the sensor on which the active surface is formed, the body being of a suitable electrically conductive material, and measuring resultant changes in the electrical. conductance of the body material in at least one region of the latter remote from the active surface. For this purpose, electrodes are arranged at suitable positions remote from the active surface.
The document W092/21018 discloses a multiple electrode sensing device of the above type, which has a plurality of electrodes arranged in pairs, with the electrodes of one pair being spaced apart by a different distance from that by which the electrodes of another pair are spaced apart. The same document discloses that, alternatively, some aspect (such as relative position) of the relationship between the electrodes of a pair and the active surface, is different from one pair of electrodes to the next. Gas composition is determined from the relationship between the resistances across the respective pairs of electrodes.
It is often required that the presence of any one or more of a number of specified gases (commonly referred to as "target" gases) should be determined in a gaseous mixture. Conventional practice is to construct for this purpose an array of discrete gas sensing devices, with each sensor being normally one that is sensitive to a respective one of the target gases. A conventional array of this kind suffers from the fact that each sensor is a separate device, subject to its own manufacturing tolerances and imperfections. As a result, such an array has the serious disadvantage that drift effects occur in practice. Results obtained from the array as a whole tend to be seriously affected by cumulative errors arising in the various devices. This also has the effect that repeatability between arrays tends to be virtually impossible.
An object of the invention is to overcome these drawbacks of sensor arrays.
A further object is to enable a plurality of target gases to be determined (detected, measured) in a mixture of gases, without the disadvantages of conventional sensor arrays.
According to the invention in a first aspect, a method of analysing a gaseous medium using a multiple-electrode resistive gas sensor comprising a resistor having an active surface and a plurality of pairs of electrodes, the electrode pairs being different from each other as regards the spacing between the electrodes of the pair or the disposition of the pair within the resistor relative to the active surface, the gaseous medium containing at least one tar
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Capteur Sensors & Analysers Ltd.
Middleton James B.
Wiggins J. David
Williams Hezron E.
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