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SEWING Informe resumido

Project ID: IST-2000-28084
Financiado con arreglo a: FP5-IST
País: Poland

Software for acquisition of data obtained from sensors sensitive for different ions in presence of interferences (three versions)

One of the key results of the project is software for processing of raw measurement data from several CHEMFET sensors and a temperature sensor. Usage of such software is a must, as real CHEMFET sensors are not sufficiently specific (i.e. they respond not only to their "main ion" but also to some interfering ions), their response curve is non-linear and temperature dependent.

There were 3 approaches to design of data processing algorithms.

The PW group assumed availability of steady state (current or voltage) readouts from CHEMFETs and a temperature sensor - all located in the reactor of the probe. Initially sensor calibration - water sample measurement cycle was investigated. Finally, an original multistep standard addition type measurement technique was developed, that combines calibration and measurement phases. For NO3, NH4, K and Na sensors (as used in the final demonstrator probe) the first of four steps consists of complete readout from CHEMFETs and a temperature sensor, after water sample (pre-treated with Ionic Strength Adjuster) was placed in the reactor of the probe. Next measurement set is performed after injecting low level of standard liquid (with all the main ions). Then follows injection of high level of the main (most troublesome) interfering ion, i.e. K, and measurement. Finally, injection of high level of the remaining main ions and measurement -complete the cycle.

A special purpose optimisation based algorithm has been developed that uses measurement from all sensors in all steps of the measurement cycle and sensor models (also new ones - developed in this project) to perform estimation of main ion concentration in the sample. The algorithm and the software that implements it is data driven, and so it can accept arbitrary number of main ions, sensors (can be redundant if available) if requested via configuration files. The software library has been integrated with the dedicated measurement unit control firmware made by Systea, to provide on-line estimates of ion concentration. Stand-alone off-line processing program has been also provided.

The TUL group assumed availability of time responses from the sensors, and used inverse problem solution algorithms to estimate of ion mixture composition. The approach aimed at reducing estimation uncertainty due to CHEMFET measurement inaccuracy. The work ended at the research state, with some publication documenting the results.

The UPC group also considered a time evolution of responses from a redundant array of sensors. Using ideas from signal processing (multiple interference cancellation) the group aimed at decreasing of ion content estimation inaccuracy due to sensor non-specifity and measurement error, making some assumptions about statistics of the two sources of inaccuracy. The work ended at the research state with numerous publications documenting acheivements.

More information on the Sewing project can be found at:

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Leszek OPALSKI, (Head of Circuits and Systems Division in the Institute of El)
Tel.: +48-22-6607989
Fax: +48-22-8252300
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