Abstract: A planar magnetic current sensor is described, incorporating a number of features designed to improve the efficiency and reliability of the basic sensor. The improvements comprise providing inner and outer conductive shields, an increased number of sensor elements for a given circuit board area, and distributing the resistance of the sensor circuitry.

Abstract: A device for measuring alternating voltage in a conductor under test using a first set of capacitive voltage sensors 32a-f mounted on an electrically insulating support member. The sensors are disposed on the support member at spaced intervals along a first notional circle and are connected in parallel between an inner signal conductor 33 and a zero voltage reference conductor 37. A second set of capacitive voltage sensors 34a-f are mounted on the support member at spaced intervals along a second notional circle and are connected in parallel between an outer signal conductor 35 and the reference conductor 37. The support member is configured to allow a conductor under test 38 to be introduced into the interior of the device so that the sensors surround the axis of the conductor. Each sensor has a signal electrode 48 connected to the signal conductor and a reference electrode 50 connected to the reference conductor and is orientated with the signal electrode facing the conductor under test.

Abstract: An electrical energy meter comprises an electrically insulating housing (10) for securing relative to least two mains cables (22,24) each having a conductive core surrounded by a sheath of insulating material. The housing includes respective electrical contacts for piercing the insulating sheath of each cable, a current probe for measuring current flowing in at least one of the cables, and circuit means for calculating and displaying electrical energy as a function of the voltage across the contacts and the output of the current probe. An improved current probe is employed comprising a series of Rogowski coils equally spaced around the circumference of a circle, with the gap between two adjacent coils permitting the current-carrying conductor to be introduced into the loop. An alternative current probe employs two such concentric loops of coils, enabling compensation for the effects of external current source pickup.

Abstract: An apparatus for remotely sensing the currents flowing in a set of substantially parallel conductors carrying N independent AC currents comprises N magnetic field sensors M1, M2 positioned to take mutually independent measurements of the magnetic field generated by the conductors and provide corresponding signals. Processing means 12′ or 12″ derive further signals, respectively corresponding to the conductor currents, based upon the sensor signals and the location and angular orientation of each sensor relative to each conductor.

Abstract: A device for measuring alternating current in a conductor comprising an even number of identical coils (C1) to (C14) mounted on an electrically insulating coil support member (10). Half the coils (C1) to (C7) are equally spaced around a first notional circle and are connected in series by a first conductive track (12) and the other half of the coils (C) to (C14) are equally spaced around a second notional circle, concentric with the first, and are connected in series by a second conductive track (14). The support member (10) has a recess (16) to allow a conductor under test to be introduced into the centre of the concentric circles. The device further includes means (R1, R2, 20) for deriving the alternating current in the conductor as a function of the voltages induced in the first and second sets of series-connected coils. The coils (C1) to (C14) and the support member are manufactured by printed circuit or thick film technology.

Abstract: An ultrasonic transducer includes a film of piezoelectric material mounted on the support column. Two overlapping metal foil electrodes are in intimate contact with the two opposite surfaces of the film respectively, and a respective electrical lead is connected to each electrode.

Abstract: An apparatus for measuring the speed of an air flow comprises an ultrasonic transmitter and an ultrasonic detector mounted spaced apart on a housing for insertion in the air flow. A circuit inside the housing derives the speed of the air flow as a function of the time taken for the burst to reach the detector.

Abstract: An ultrasonic measuring apparatus comprising a master unit and a slave unit each having a respective transmitter circuit for transmitting towards the other unit a burst of ultrasound and each having a respective receiver circuit to detect the burst of ultrasound transmitted by the other unit. The slave unit is responsive to the detection of a burst transmitted by the master unit to transmit a return burst back to the master unit. The master unit includes control means for disabling its receiver circuit during transmission of the said burst to the slave unit and thereafter until the end of a first period of time which is sufficiently long to permit all echoes from the said burst to decay to a level where the master unit receiver circuit is not sensitive enough to detect them.