Schlüsselwörter
(Englisch)
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Breath-alcohol concentration; traceability; SI; OIML; Dubowski
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Kurzbeschreibung
(Englisch)
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Since January 1st 2005 the police use breath-alcohol-test-instruments during traffic control. These instruments are increasingly used in restaurants, discotheques, the medical prevention and occupational security. In all domains the guarantee of the measurement stability can not be solely left to the manufacturer or his representative.
The ordinance of the FDJP on breath-alcohol devices is in vigour since January 1st 2012. Breath-alcohol-test-instruments for official controls have to be yearly verified by METAS and new instruments can only put onto the market with a valid conformity assessment.
For the verification and type approval tests of breath alcohol devices wet breath is generated with a commercial system. The system is expensive in operation and the traceability is given via a recommendation of the international organisation on legal metrology (OIML). This recommendation is heavily disputed and partly modified nationally. The "Physikalisch-Technische Bundesanstalt" in Germany has recently shown that this generation method exhibits systematic bias.
The traceability of the breath-alcohol concentration is effected on the one hand with gravimetrically prepared gas mixtures in pressure cylinders, and otherwise by a wet generation with bubble trains according to the convention of Dubowski.
The introduction of the evidential-breath-alcohol-test was controversially discussed and the national assembly accepted it only in the second reading. As a confidence-building measure the traceability of the breath-alcohol-tests-results has to be ensured to the international system of units (SI) without the OIML-convention.
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Projektziele
(Englisch)
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A traceable generator for wet breath alcohol with carbon dioxide is developed. The relative uncertainty of the breath alcohol concentration shall be less than 0.5 %.
Rationale for the targeted uncertainty: For the verification of breath-alcohol-measuring-instruments a relative uncertainty of 1 % is sufficient. For the evaluation of a bias of approx-mately 1 % to 2 % between the saturation method according to Duboswki and an SI-traceable method a relative uncertainty of 1 % is simply not sufficient. Taking into account the new calibration possibilities in the area of micro-/nanoflow the targeted uncertainty is technically feasible.
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Abstract
(Englisch)
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The aim of the project has been achieved. A traceable generator for wet breath-alcohol has been built and successfully validated. The liquid components water and ethanol are regulated by electromechanical pumps and mixed or a gravimetrically produced water-ethanol-mixture is directly regulated. The water-ethanol-mixture is subsequently nebulized, mixed with hot synthetic air and vaporized. The ethanol concentration of the produced wet ethanol/air-mixture is traceable via calibrated mass-flow meter to the international system of units (SI). The expanded uncertainty in the breath-alcohol-concentration-range 100 µg/l to 400 µg/l is 3 % to 0.3 % relative, respectively. For breath-alcohol-concentrations > 200 µg/l the targeted uncertainty of < 0.5 % has been achieved. With a calibration of the liquid mass-flow meters by the laboratory of flow and hydrometry (project microflow) lower uncertainties should be feasible in the future.
The traceability to the SI was successfully demonstrated by comparative measurements of two water-ethanol-mixtures. Within the uncertainties the calculated and measured ethanol concentrations in air agree. The flame-ionization-detector JUM FID VE7 (FID) was used as a comparator, which has been adjusted by the humidified ethanol-reference-gas-standard NPL A-392.The achievable uncertainties of the FID measurements are currently not sufficient to confirm the discovered deviations of the wet generation method according to OIML R126 to the SI. In collaboration with the EMPA a metrological breath-alcohol-measurement-instrument shall be developed for this purpose.
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Umsetzung und Anwendungen
(Englisch)
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The project results are on the one hand utilized in the project EviTEst (P-5232.40019). The developed base is directly used for the evaluation and validation of a commercial automated breath-alcohol-generator. The generator is intended to be used for type testing and verification of evidential breath analyzers.
On the other hand the project results justify the development of a metrological breath-alcohol-measurement-instrument in collaboration with the EMPA on the basis of the quantum-cascade laser spectrometry. With this measurement system, an independent confirmation of the discovered deviations of the wet breath-alcohol generation according to OIML R126 by PTB will be feasible. Today’s complex and obscure correction after adjustment of breath-alcohol-measurement-instrument would become obsolete. Together with EMPA third party money for interested manufactures shall be acquired.
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Publikationen / Ergebnisse
(Englisch)
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Martin Stalder, Daniel Schwaller, Bernhard Niederhauser, Hanspeter Andres, and Samuel Wunderli; New Calibration System for Breath-Alcohol Analysers Based on SI ; CHIMIA, 2013, 67, Nr. 12.
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