Data processing: measuring – calibrating – or testing – Testing system – Of sensing device
Reexamination Certificate
1998-05-13
2001-05-22
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of sensing device
C702S027000, C702S077000, C708S200000, C708S813000, C422S098000
Reexamination Certificate
active
06236951
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for the interrogation of sensors, with particular—but by no means exclusive—reference to semiconducting organic polymer based gas sensors.
There is a great deal of current interest in the use of semiconducting organic polymers in gas sensing applications, since such polymers display rapid gas adsorption/desorption kinetics, relatively high sensitivities and responses which broadly mimic the response of the human olfactory system (see, for example, Persaud K C, Bartlett J G and Pelosi P, in ‘Robots and Biological Systems: Towards a new bionics?’, Eds. Dario P, Sandini G and Aebisher P, NATO ASI Series F: Computer and Systems Sciences 102 (1993) 579). A typical sensor comprises a pair of electrodes bridged by at least one layer of semiconducting organic polymer; transduction is usually accomplished by measuring changes in the dc resistance of the sensors, these changes being induced by adsorption of gaseous species onto the polymer.
SUMMARY OF THE INVENTION
British Patent GB 2 203 553 discloses an improved interrogation method whereby an ac electric signal is applied to the sensor, and changes in an ac impedance quantity, such as resistance, reactance, or capacitance, are measured as a function of ac frequency. One advantage of this approach is the increase in the information derived from a single sensor: in contrast to the single measurement made with the dc transduction technique, a plurality of measurements are made (at a variety of ac frequencies). However, sweeping the ac frequency is a relatively cumbersome process, requiring an expensive Impedance Analyser.
The present invention provides an improved means of performing multifrequency measurements of sensors in which time domain measurement techniques are accompanied by an appropriate transformation to the frequency domain.
According to one aspect of the invention there is provided a method for interrogating a sensor comprising the steps of:
applying a periodic electrical signal to the sensor;
obtaining a signal therefrom; and
performing an operation on the obtained signal to obtain the sensor response at a plurality of frequencies, said operation including a transformation to the frequency domain of said signal or a quantity related to said signal.
The sensor may be a gas sensor and may comprise semiconducting organic polymer.
Alternatively, the gas sensor may be a metal oxide, bulk acoustic wave or surface acoustic wave device.
The periodic electrical signal may be a pseudo random binary signal (PRBS), which may be in the form of a m-sequence.
The periodic electrical signal may be a Golay code, a Walsh function or any related periodic code.
The operation may comprise a Fourier transformation.
Cross correlation may be employed in order to obtain the multifrequency sensor response function.
The sensor response may be obtained by coherent demodulation of said signal.
Alternatively, co-variance may be employed in order to obtain the multifrequency sensor response function.
According to a second aspect of the invention there is provided a sensor interrogation apparatus comprising:
periodic electrical signal generator means for applying a periodic electrical signal to said sensor;
signal collection means for obtaining an electrical signal from said sensor; and
time to frequency domain transformation means arranged to transform the obtained electrical signal to the frequency domain.
The sensor may be a gas sensor, which may comprise semiconducting organic polymer.
Alternatively, the gas sensor may be a metal oxide, bulk acoustic wave or surface acoustic wave device.
The signal collection means may comprise a load resistor.
The time to frequency domain transformation means may comprise coherent demodulation means.
The time to frequency domain transformation may comprise computing means adapted to perform Fourier transformations.
The periodic electrical signal generator means may comprise a PRBS generator, which may itself comprise shift registers.
The periodic electrical signal generator means may comprise a Golay code, a Walsh function generator, or a generator generating any related periodic code.
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Z X Ding and P A Payne, “A New Golay Code System for Ultrasonic Pulse Echo Measurements”, Meas. Sci. Technol. 1 (1990), pp. 158-165, 1990.*
Persaud et al., “Design Strategies for Gas and Odour Sensors Which Mimic the Olfactory System”, Robots and Biological Systems: vol. 102, 1993, pp 579-602.
Ding et al. “A New Golay Code System for Ultrasonic Pulse Echo Measurements”, Meas. Sci. Technol. 1, 1990, pp 158-165.
Amrani Mohammed El Hassan
Payne Peter Alfred
Persaud Krishna Chandra
Bui Bryan
Christie Parker & Hale LLP
Hoff Marc S.
Osmetech PLC
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