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An electrical current measuring device, for measuring the current in an electrical conductor (11), includes first and second measurement channels. Each of these channels includes a sensor (12) adapted to be located adjacent the conductor (11) and coupled via optical fibers (14,16) to source circuitr

An electrical current measuring device, for measuring the current in an electrical conductor (11), includes first and second measurement channels. Each of these channels includes a sensor (12) adapted to be located adjacent the conductor (11) and coupled via optical fibers (14,16) to source circuitry (18) and detector circuitry (20). The sensor (12) incorporates a material (22) which exhibits the Faraday magneto-optic effect and the source circuitry (18) is arranged to deliver an unpolarized light signal which is subsequently polarized by a first polarizer (23) to enable a linearly polarized light signal to be incident to the material (22). The quantum of rotation in the plane of polarization imposed on the signal emerging from the material (22) is monitored via a second polarizer (24) by the detector circuitry (20) as a measure of the electrical current flowing in the conductor (11). The sensor material (22) of the first channel has a Verdet constant which is more temperature sensitive than that of the sensor material of the second channel. In addition, each measurement channel is arranged to maintain a constant light intensity incident on its detector circuitry (20), and gain-control circuitry (17,19) is provided at the outputs of the two measurement channels to deliver to an output terminal a modified measure of the sensed electrical current which is compensated against temperature variations.

대표청구항 ▼

An electrical current measuring device, for measuring the current in an electrical conductor (11), comprises first and second measurement channels, each channel comprising a sensor (12) adapted to be located adjacent the conductor (11) and coupled via optical fibres (14,16) to source circuitry (18)

An electrical current measuring device, for measuring the current in an electrical conductor (11), comprises first and second measurement channels, each channel comprising a sensor (12) adapted to be located adjacent the conductor (11) and coupled via optical fibres (14,16) to source circuitry (18) and detector circuitry (20), the sensor (12), incorporating a material (22) which exhibits the Faraday magneto-optic effect and the source circuitry (18) being arranged to deliver an unpolarised light signal which is subsequently polarised by a first polariser (23) to enable a linearly polarised light signal to be incident to the material (22) and the quantum of rotation in the plane of polarisation imposed on the signal emerging from the material (22) being monitored via a second polariser (24) by the detector circuitry (20) as a measure of the electrical current flowing in the conductor (11), wherein the sensor material (22) of the first channel is different from the sensor material (22) of the second channel, having a Verdet constant which is more temperature sensitive than that of the second channel; each measurement channel is arranged to maintain a constant light intensity incident on its detector circuitry (20), and gain-control circuitry (17,19) is provided at the outputs of the two measurement channels to deliver to an output terminal a modified measure of the sensed electrical current which is compensated against temperature variations, the gain control circuitry (17,19) comprising a gain-controllable amplifier connected to the output of the detector circuitry (20) of the first channel, a divider (17) connected to the outputs of the respective detector circuitry (20) of the first and second channels for computing the ratio of said signals, means for comparing the computed ratio with pre-stored data (FIG. 3) representative of known signal ratios achieved under known constant currents but varying temperatures whereby to evaluate a proportionality measure with respect to temperature, and means for applying said proportionality measure to gain control the gain-controllable amplifier to provide the modified measure of the sensed electrical current from the detector circuitry (20) of the first channel.