A high resolution positioning sensor having a magnetic field generator, a device connected to the magnetic field generator for concentrating lines of magnetic flux produced by the magnetic field generator, and a magneto resistive element connected to the concentrating device. The magneto resistive element is adapted to change resistive properties as a function of magnetic flux density. A reference position scale is also provided, having a transducer grid with a number of protuberances. Two flux couplers are connected to the magneto resistive element and are arranged out of phase with one another with respect to the protuberances of the transducer grid. These flux couplers modulate flux distribution between the concentrating device and the transducer grid.

The rotor of an electric rotary machine is provided with two identical transmitting devices each including an amplitude modulator and a transmitting antenna. One of the modulators modulates a carrier with clock pulses while the other modulator modulates the same carrier with a data signal from the rotor expressed by a binary digital code including pulses identical in both shape and phase to the clock pulses. The transmitting antennas are disposed symmetrically with respect to a receiving antenna located externally of the rotor to induce the two modulated carriers substantially in phase across the receiving antenna.

A shaft monitoring system for sensing axial movement of a shaft, especially in a gas turbine engine, comprises a toothed wheel attached to and rotatable with the shaft, and a pair of inductive sensors disposed radially of the toothed wheel for sensing the passage of the teeth as the shaft rotates. In one embodiment, the toothed wheel has two axially-spaced sets of teeth, one set straight cut and the other set diagonal cut, so that the phase difference between the respective outputs of the sensors varies with axial movement of the shaft. In another embodiment, the sensors are positioned at opposite axial ends of the toothed wheel, so that axial movement of the shaft causes one sensor output to increase in amplitude while the other decreases.

Detector circuitry for detecting magnetic field disturbances resulting from the movement of equipment through a pipe of magnetic material, the detector circuitry comprising a difference circuit fed with the outputs of two longitudinally spaced sensor means via respective DC blocking means, a saturating difference amplifier feeding an integrator and fed with the outputs of the difference circuit and the integrator, and indicating means fed from the integrator. The detector circuitry may also including level setting means and a comparator fed with the outputs of the integrator and the level setting means and feeding the indicating means. A second comparator may be connected in parallel with the first comparator and fed with the inverse of the output of the level setting means and the output of the integrator.

The invention makes it possible to detect and measure the movement of a moving member (50) through an amagnetic or low permeability metal wall. The installation requires ferromagnetic material targets placed at regular intervals over the moving member. The transducer is positioned facing the moving member by its detection face (16). It comprises two ferromagnetic cores (2, 8) surrounded both by an exciting coil (4) and a measuring coil (10), at whose terminals the measuring signal is taken. The latter is proportional to the variable reluctance of the magnetic circuit, which varies as a function of the position of the ferromagnetic targets (48). The transducer is completed by a balancing core (34). Application to the measurement of the displacement of control rods in the vessel of a pressurized water reactor.