Abstract: This invention relates to a measuring head which comprises an intake, an outlet, a mouthpiece and an electrically controlled proportional valve. The intake may be connected to a pressurized gas reservoir. The outlet releases exhaled gas and excess gas into the ambient. A mouthpiece provides gas to a subject and accepts exhaled gas from the subject. The electrically controlled, proportional valve is pneumatically connected between said intake and said mouthpiece for controlling the gas flow from said intake to said mouthpiece and said outlet. The invention further relates to a method for controlling a gas flow from the intake to the outlet.

Abstract: The invention relates to an actuation and evaluation circuit for a laser diode (1) and a photodiode (3) for determining the concentration of a gas. The laser diode can generate light in the range of an absorption line of the gas. The circuit comprises a driver (10, 11, 12, 13) for generating a driving signal (17) for the laser diode (1), an assembly (8, 9) for generating a reference signal (20), and a subtractor (5) for subtracting the reference signal (20) from the signal (21) supplied by the photodiode. The invention further relates to a measuring device for determining the concentration of a gas by means of such an actuation and evaluation circuit. Finally, the invention relates to a corresponding method.

Abstract: The invention relates to a method for determining the temporal position of a wave packet (31) in a flow measuring apparatus, and to a flow measuring apparatus. The method includes the sampling of the wave packet at a plurality of points in time, wherein a measured value is created at each point in time. Subsequently, a sum of products (43, 54, 55, 63, 64) is calculated, wherein each product is calculated for a determined point in time from a plurality of points in time and each product is the product of a value of a compare function (44, 53, 56, 61, 62) at the determined point in time and the measured value at the determined point in time. Finally, the temporal position of the wave packet is calculated from the sum of products.