Abstract: A compass includes a magnetic sensing element in the form of a coil surrounding magnetic material. Electric current is supplied to the coil in opposite directions, depending on the state of switches operated at times T0, for a first direction, and T5, for a reverse current direction. A voltmeter measures voltages across the coil, namely at least V1 at time T1, after T0, and V2 at time T2, after T5, with T1?T0=T2?T5=predetermined ?T. A processor indicates V1?V2, the magnitude and sign of which indicate the strength and direction of the earth's magnetic field respectively.

Abstract: A measurement device (10) comprising a sensing circuit (30) which is electrically floating and fully isolated. The sensing circuit (30) has a first (134) and a second (148) transformer across which is connected a measurement circuit (110). The device is so constructed that any signal generated in the coil (132) of the said first transformer (134) that is connected to the measurement circuit (110) caused by a change in any external magnetic field relative to the measurement circuit (110) is in anti-phase with the corresponding signal generated in the coil (164) of the said second transformer (148) that is connected to the measurement circuit (110).

Abstract: A telescopic arrangement (10) having a hollow cylinder (12) and a part (14) which is telescopically engaged with the cylinder. The arrangement is provided with at least one coil (22) constituting a first form of pulse-induction device, and at least one target (28) constituting a second form of pulse-induction device, to monitor the position of the said part (14) relative to the cylinder (12). A plurality of devices (22) each of one of the said first and second forms of device are positioned on the outside of the cylinder (12), at different respective positions therealong. At least one (28) of the other of the said first and second forms of device is fixed relative to the said part (14) of the arrangement (10) in a position such that it is moved over the said plurality of devices (22) in succession as the said part (14) is telescopically moved relative to the cylinder (12) of the arrangement (10).

Abstract: A pulse-induction displacement transducer comprising at least one coil component (100,150), at least one target (112,174), and pulse induction circuitry (102,152} constructed and arranged to cause a pulse of electrical current to pass through the said at least one coil component (100,150). The pulse ends abruptly. Subsequently, the electrical current passing through the said at least one coil component (100,150), or the voltage across it, is measured at a time when any electrical current through or voltage across the said at least one coil component (100, 150) would have died away in. the absence of a target. This provides an indication of the relative position between the target (112,174) and the said at least one coil component (100, 150). The said at least one coil component (100,150) comprises a first terminal portion (108,158), a first coil part (104,152) connected directly or indirectly to the said first terminal portion (108,158) and wound in one sense.

Abstract: A depth gauge includes an upright elongate support (1) and several spaced emitters (2) and spaced detectors (3) mounted on the elongate support. The emitters (2) and detectors are electrically connected to a processor that sends signals to the emitters and receives signals from the detectors. In a first aspect, at least two sets of emitters or at least two sets of detectors are mounted on the elongate support. The sets may be directed in different respective directions. In a second aspect, each emitter may emit radiation, and/or each detector may detect radiation, selectively only within a selected range of frequencies, or emit/detect radiation outside the selected range only at a comparatively reduced level. Different emitters may emit radiation, and/or different detectors may detect radiation, only within different ranges of frequencies, or emit/detect radiation outside those ranges only at comparatively reduced levels.

Abstract: An ultrasonic flowmeter comprising an elongate duct through which fluid flows when the flowmeter is in use. Ultrasonic transducers are arranged respectively to transmit and receive ultrasonic pulses propagated through such fluid when the flowmeter is in use. Electronic circuitry is connected to the transducers to provide a measure of the time delay between emission of an electronic pulse from one of the transducers and reception of the pulse by the other of the transducers. The circuitry is constructed to enable an output to be provided which is dependent upon that delay and which is indicative of the rate of flow of fluid through the duct. The transducers are located respectively at opposite ends of the duct and are arranged to transmit and receive ultrasonic pulses propagated through the fluid substantially parallel to the duct from one end thereof to the other.

Abstract: A position indicator device (10) comprising a first array (12) of uniformly spaced-apart pulse induction affecting targets fixed in position relative to a second array of uniformly spaced-apart pulse induction affecting targets (14). The spacing between the centres of adjacent targets of the first array (12) differs from that of the second (14). The device further comprises a first set (18) of pulse-induction coils comprising a plurality of such coils and a second set (20) of pulse-induction coils comprising a plurality of such coils. The coils of the first set (18) are fixed relative to those of the second set (20). Those of the first set (18) are located adjacent to the first array (12) of targets. Those of the second set (20) are located adjacent to the second array (14) of targets. The targets (the said first and second arrays together) and the coils (the said first and second sets together) are movable relative to one another.

Abstract: An ultrasonic flowmeter comprising an elongate duct through which fluid flows when the flowmeter is in use. Ultrasonic transducers are arranged respectively to transmit and receive ultrasonic pulses propagated through such fluid when the flowmeter is in use. Electronic circuitry is connected to the transducers to provide a measure of the time delay between emission of an electronic pulse from one of the transducers and reception of the pulse by the other of the transducers. The circuitry is constructed to enable an output to be provided which is dependent upon that delay and which is indicative of the rate of flow of fluid through the duct. The transducers are located respectively at opposite ends of the duct and are arranged to transmit and receive ultrasonic pulses propagated through the fluid substantially parallel to the duct from one end thereof to the other.