Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1999-05-03
2001-11-13
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S012000, C702S076000, C702S100000, C702S104000, C073S001020, C073S053010
Reexamination Certificate
active
06317696
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for detecting fluids, and relates particularly to an apparatus and method for detecting fluids by observing the change in electrical behaviour of a sensor in the presence of such fluids. By “fluids” is meant samples of liquid and/or gas and/or vapour and combinations and/or mixtures of the same.
DESCRIPTION OF THE RELATED ART
Many materials are known to undergo changes in electrical behaviour in the presence of gases, primarily as a result of surface phenomena at the fluid/material interface, and which can be used to provide characteristic information to identify the gas causing the electrical change.
UK patent GB 2203553 discloses a gas sensor in which a layer of semi-conducting organic polymer such as polypyrrole is subjected to an alternating electrical signal in the frequency range 1 MHz to 500 MHz, and the frequency of which is then varied, and the variation in impedance characteristics of the organic polymer layer is obtained as a function of frequency in the presence of a gas to be detected. This variation in electrical behaviour as a function of frequency can then be used to identify the presence of a particular gas.
The above arrangement suffers from a number of drawbacks, including that the frequency scanning technique involved is time consuming, and the necessary hardware is expensive. In addition, although the exact mechanism by which the changes in electrical behaviour of the sensor are not fully understood, it is believed to result from many complex and interrelated factors which may vary throughout the course of the frequency scanning process, thus limiting the reproducibility of measurements, and which in turn may limit the accuracy with which gases may be detected.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided an apparatus for detecting one or more fluids, the apparatus comprising: sensor means having electrical properties dependent upon the presence and/or concentration of one or more fluids, excitation means for applying one or more excitation pulses to the sensor means, detector means for detecting the behaviour of the sensor means in response to the excitation means, and transforming means for transforming an output of the detector means from the time domain to the frequency domain to determine the electrical properties of the sensor means as a function of frequency over a pre-determined frequency range.
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patent: 5034192 (1991-07-01), Wrighton et al.
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patent: 0 332 935 A1 (1989-03-01), None
patent: 0 358 249 A2 (1990-03-01), None
patent: 2203553B (1988-10-01), None
patent: WO 94/29263 (1994-12-01), None
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Nakata et al., New strategy for the development of a gas sensor based on the dynamic characteristics: principle and preliminary experiment, May 1992, Sensors and Actuators B. pp. 187-189.
Chandler Robert
Clements Jonathan
Beyer Weaver & Thomas LLP
Bloodhound Sensors Limited
Hoff Marc S.
Vo Hien
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