Abstract: A device for measuring a level of a fluid in a container by measuring the transit time of an emitted acoustic pulse to the fluid surface and of its return echo through a guide conduit. The transit time of the emitted acoustic pulse is prolonged so that the transit time is long enough to reliably separate the emitted decaying acoustic pulse from its echo. An approach region with a subsequent bend is provided in the acoustic guide conduit.

Abstract: A measuring device includes means for converting a physical quantity to be measured into a corresponding magnetic field. A magnetooptic element is aligned with a polarizer which passes incident light in one plane only. The part of the magnetooptic element which intercepts the transmitted magnetic field rotates the throughgoing light and the position of rotation is indicated on an optical indicator.

Abstract: A refractometer for measuring the index of refraction of a sample medium comprises a sample medium sensor and a reference medium sensor. Both sensors are combined into a single measuring probe which is connected by a flexible cable to a housing unit which accommodates the source of light, photodetectors, the test data processor and the indicator. The refractometer with the single probe is portable and easy to handle.

Abstract: For measuring the speed of movement of one phase in another, and particularly the rate of sedimentation of corpuscles in blood plasma, a container is filled with a blood sample, a light beam is directed through the container and an image of a vertical plane in the container traversed by the beam is formed in a measuring plane, the light intensity at two vertically spaced regions of the measuring plane is measured, the container is moved until a certain light intensity relationship exists between the two regions, indicating that the image of the boundary of the one phase in the other phase is located between the regions, and after a selected time interval the container is raised until the same light intensity relationship is established between the two regions and the distance through which the container has been raised is indicated.