Abstract: In an interferometric fiberoptic sensor with homodyne detection for measuring electrical fields or voltages, the measurement signal is compensated separately from operating point control. The measurement signal originating from the electrical field is compensated in a piezoelectric modulator (5) which consists of modulator elements which are identical with the at least one sensor element (3) with respect to material, geometric shape and crystal orientation. Additional separate apparatus (4) with a sufficiently large phase swing are provided for operating point control. Modulator element and sensor element (3) are essentially at the same temperature so that the temperature-dependence of the matter constants of the sensor element and the temperature-dependence of the fiber interferometer are eliminated. The sensor preferably operates in accordance with the principle of a fiberoptic two-mode interferometer.

Abstract: A method and apparatus for monitoring the state of the surface of a moving body wherein a four-terminal eddy-current coil circuit is connected in a feedback loop of an RC resonator. The eddy-current coil circuit is placed in proximity to the monitored surface of the moving body and connected in the feedback loop of an RC resonator such that a change in the state of the surface of the moving body results in a change in the conductivity thereof, which conductivity change produces a phase displacement changing the output frequency of the RC resonator. During operation, a first data set is obtained from the coil circuit and RC resonator presenting a first runout profile of the body when the monitored state is in an initial state. The first data set is stored in a memory, and a subsequent profile is derived to obtain a second data set indicative of the operational state of the surface of the moving body.

Abstract: A monitoring device for semiconductor rectifiers which are located in a three-phase current bridge circuit, in which the bridge circuit is provided with two semiconductor rectifiers per rectifier branch, including a current-sensitive detector circuit connected to each pair of semiconductor rectifiers of each branch through a resistor, wherein when the semiconductor rectifiers are intact, the sum of all current flowing through the resistors is zero, as detected by the current-sensitive detector circuit.

Abstract: The invention concerns a measuring instrument for measuring phase shifts in four terminal electrical networks, where the network whose phase shift is to be measured is connected into the feedback circuit of an R-C phase shifter oscillator, and where the generated frequency depends on the phase shift of the four terminal network and of the RC-phase shifter, and where the circuit is so dimensioned that the following oscillation conditions are satisfied:.phi.(.omega.) + .phi. = 0 (or integral multiples of 2 .pi.)(1).vertline.F (.omega.).vertline..multidot..vertline.H.vertline..multidot.A = 1 (2)where .phi. = phase shift of the network whose phase shift is to be measured.phi.(.omega.) = phase shift of the R-C phase shifterF (.omega.