Abstract: The invention relates to a calibrating gas generator for generating a calibrating gas with a pregiven concentration of a calibrating gas component. The calibrating gas generator includes two vessels through which gas can flow. These two vessels contain the calibrating gas component in a calibrating solution and are connected in series. The temperature of the calibrating solution is controlled to a constant value by a temperature control apparatus. In order to improve the constancy of temperature, one of the vessels is arranged at least partially within the other vessel and this other vessel is configured, at least in part, as a heat insulating jacket for the one vessel.

Abstract: A device for generating a test gas e.g., ethanol has at least two series-connected containers, which are filled with a calibration solution. A carrier gas, which is enriched with the calibration substance present in the solution corresponding to the vapor pressure of the calibration substance at the given temperature, is passed through these calibration containers. To prevent or to reduce the depletion of the components necessary for the gaseous calibration substance in the calibration solution, a defined amount of a stock solution is fed through the calibration containers in counterflow to the direction of delivery of the carrier gas.

Abstract: A method for assuring valid measured values of breath alcohol concentration for the determination of the alcohol concentration in human blood by means of a gas analyzer operating on the principle of infrared absorption. Values of the rise of expiration concentration S(t) independent of the vital capacity of the subject, that is, the maximum expiration volume after deep inhalation, are calculated from the measured values of the breath alcohol concentration and expiration volume and subjected to a criterion comprising positive and negative threshold values (trigger levels) before they are released for further processing.The giving out of invalid measured values, which are attributable to too low an expiration volume, too short an expiration time, residual alcohol in the mouth or insufficient sample volume, is avoided.