Abstract: In the optical measurement of the flow vectors in gas flows, two substantially parallel light beams (11a, 11b) are focussed at separate focussing spots. The particles passing the focussing spots light up and thereby generate a start pulse and a stop pulse, respectively. Therewith, the component of the flow vector extending in the normal plane to the optical axis (OA) is detected by transit time measurement. The flow component pointing in the direction of the optical axis (OA) is detected independent thereof according to the Doppler principle by supplying the scattered light generated by the particles to an optical frequency/amplitude converter (22).

Abstract: An optical head, to which laser light is supplied, produces, in a measuring volume, at least two focusing points at which particles flowing through the measuring volume are illuminated and cause scattered radiation which is collected by the optical head. The laser beam is directed, via at least one first light guide, to the optical head. From the optical head, the radiation received from the measuring volume is supplied, via at least one second light guide, to a light receiving means. The optical head is small-sized and may be rotated about its optical axis by means of a rotating device.

Abstract: The apparatus contains a dispersion means (DP) decomposing the incident laser beam into a number of colors (C1-C5) spacially separated from each other. The focusing points of said colors are subsequently traversed by particles contained in the flow. The light from the measuring volume (MV) is conducted via the dispersion means to a light receiving means (AV) in which the light is decomposed again into the individual colors. Due to a switching means (SE), the colors used for the measurment are selectible. Thus, the space of the focusing points used for the measurement may be varied.

Abstract: For the optical measurement of flow vectors in gas currents, two substantly parallel light beams are focused at separate focusing points. The particles traversing the one focusing point are illuminated and thus generate start pulses, while particles traversing the other focusing point produce, as they flash up, stop pulses. By means of such a process, it is possible to determine the component of the flow vector (v) extending in the normal plane to the vertical axis (OA). It is an object of the invention to detect by simple means also the flow vector component extending in parallel to the optical axis (OA). According to the invention, focusing points (FG1, FB2; FB1, FG2) of beams (S1, S2) with different focal distances are produced. In a first measurement (A), the straight line traversing the focusing points (FG1) and (FB2) is formed at an angle (.gamma..sub.A) to the normal plane of the optical axis.

Abstract: This disclosure relates to an apparatus for measuring flow rates in gas sams and includes an optic component and an electronic component. The optic component starts with a focussed laser beam which is passed through a beam splitting prism so as to define two partial beams which, in turn, pass through a lens system so as to have two adjacent remote focal points. Particles in the gas stream passing through the focal points, which are located therein, reflect light in the form of reflected light beams which pass through a further lens system to pulse generators which, when actuated, generate a start pulse and a stop pulse with these pulses controlling the formation of a saw toothed wave controlling the amplitude of the generated wave, and the generated wave being directed to binary converter means and collector means which, in conjunction with an oscilliscope provides a visual wave having an amplitude indicative of a flow rate.