Abstract: A device for determining the spatial position of a sensor element (3) which is spatially displaceable relative to a reference element (1), includes three coils (4, 5, 6) which are arranged in the sensor element (3), consist of at least one wire turn, and are wound about a common center (7), at least three coils (2) which are arranged in the reference element (1) in spatially remote positions and consist of at least one wire turn, a current generator (11) for exciting the sensor element coils (4, 5 6) or the reference element coils (2) by means of a presettable excitation alternating current, and a processing circuit (15) for the voltages induced in the reference element coils (2) or in the sensor element coils (4, 5, 6). The processing circuit includes an arithmetic circuit which calculates, on the basis of the induced voltages, the distance coordinates x.sub.m, y.sub.m and z.sub.

Abstract: Heterodyne optical time domain reflectometer (OTDR) for determining the attenuation behavior of a monomode waveguide (test waveguide) by measurement of the backscattered parts of light pulses transmitted in said waveguide. An acousto-optic modulator (AOM) which deflects the transmission beam from a laser into the waveguide to be tested at a light frequency which is modulated with the acoustic frequency when the AOM is acoustically energized in a pulse mode. The light pulses backscattered from the test waveguide are superimposed on a local oscillator beam (LO) constituted by the laser beam which traverses the AOM when the AOM is not energized. The optical system losses are reduced in that the superposition is realized in a passive coupler, particularly a fibre coupler (10, 26).