Abstract: A rpm-measuring device including a closed light path comprising a coil formed of a plurality of winding layers of an optical fiber having first and second ends; a beam splitter connected to the first and second ends; an arrangement for passing two light beams in opposite directions through the coil by applying the two light beams to the first and second ends, respectively, and an arrangement for superposing the two light beams subsequent to their passage through the coil and for evaluating a phase-shift based on the Sagnac-effect. The distance of the light path between the first end and any selected first location of the optical fiber is identical to the distance of the light path between the second end and a second location of the optical fiber.

Abstract: A fiber-optic rotation sensor (fiber gyro) includes an optical transmission system into which a light signal is fed by means of a laser diode. The modulation is effected by means of a piezomodulator. The coupled-out signal is fed to a receiver diode and the amplified output signal of the latter is fed to a phase sensitive rectifier and to a peak-to-peak value measuring device. The measured peak-to-peak value represents the proportionality factor K through which the output signal of rectifier is divided. Therefore it is possible with this method to constantly measure the proportionality factor K, which changes under various influences and to thus eliminate errors in the determination of the Sagnac phase.