US3621390A
Expired / Lapsed
US
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Arrangement for measuring a time variable magnetic field using the faraday effect
Assignee: BBC Brown Boveri AG Germany
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Filing: 1969-04-22
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Granted: 1971-11-16
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Expires: 1989-04-22
Abstract
Abstract An arrangement for measuring a time-variable magnetic field in order to measure, for example, the current flowing in a highvoltage line, utilizes a measuring head subjected to a magnetic field proportional to the line current which encloses a magnetooptical element in the form of a Faraday cell that functions in conjunction with an optical divider in the form of a Koesters prism to form a two-beam interferometer. A laser produced monochromatic light beam fed to the measuring head over an optical fiber bundle passes through a polarizing filter onto the divider plane of the Koesters prism where it is split into two partial beams. One beam passes through a first quarter-wave plate in which it is circularly polarized in a dextrorotary sense, thence through the Faraday cell where it undergoes multiple reflection in the magnetic field and thence through a second quarter-wave plate back to the divider plane of the Koesters prism. The other beam passes through the same path but in the opposite direction, passing first through the second quarter-wave plate where it is polarized in a levorotary sense, and ultimately arriving back at the divider plane. The two returning beams combine in the divider plane of the Koesters prism to form an outgoing beam consisting of two 90* phase-displaced components modulated in intensity as a function of the variation in the magnetic field. The two phase-shifted beam components are passed respectively through optical fiber bundles to a processing circuit where they are converted into correspondingly modulated electrical signal components which are then demodulated to a final output electrical signal constituting a measure of the current in the high-voltage line.
Inventors
- 👤 Friedrick K Von Willisen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-22 18:01
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/01; G02F1/09; G01; G01R; G01R15/00; G01R15/14; G01R15/24; G01R15/245; G01R15/246
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
192 words
In an arrangement for measuring a time-varied magnetic field, the combination comprising an optical beam divider, means directing a monochromatic light beam into said divider to produce first and second outgoing beam components, first and second circular polarizers initially traversed by said first and second beam components respectively, said polarizers being oriented such that the beam components issuing initially therefrom are circularly polarized in opposite directions respectively, a magneto-optical element exhibiting a Faraday effect and which is located in and subjected to the magnetic field to be measured, said magneto-optical element being transversed by said circularly polarized beam components along the same path but in opposite directions whereby due to the Faraday effect a difference in the optical path length between said beam components proportional to said time variable magnetic field is produced, said first and second beam components being then passed through said second and first circular polarizers respectively and brought to interference in said divider thereby to produce an intensitymodulated light beam, and means including photodetector means deriving from said intensity modulated light beam sinusoidal electric signals the arguments of which are proportional to the magnetic field to be measured.
Claim 2
Dependent Claim
192 words
In an arrangement for measuring a time-varied magnetic field, the combination comprising an optical beam divider, means directing a monochromatic light beam into said divider to produce first and second outgoing beam components, first and second circular polarizers initially traversed by said first and second beam components respectively, said polarizers being oriented such that the beam components issuing initially therefrom are circularly polarized in opposite directions respectively, a magneto-optical element exhibiting a Faraday effect and which is located in and subjected to the magnetic field to be measured, said magneto-optical element being transversed by said circularly polarized beam components along the same path but in opposite directions whereby due to the Faraday effect a difference in the optical path length between said beam components proportional to said time variable magnetic field is produced, said first and second beam components being then passed through said second and first circular polarizers respectively and brought to interference in said divider thereby to produce an intensitymodulated light beam, and means including photodetector means deriving from said intensity modulated light beam sinusoidal electric signals the arguments of which are proportional to the magnetic field to be measured.
Claim 3
Dependent Claim
244 words
In an arrangement for measuring the variation in a magnetic field in order to measure, for example, the current flowing in a high voltage line, the combination comprising a measuring head subjected to a magnetic field proportional to the line current, said measuring head enclosing a magneto-optical element constituted by a Faraday cell which in cooperation with an optical beam divider constituted by a Koesters prism forms a two-beam interferometer, means directing a monochromatic light beam into said prism to produce at the divider plane therein first and second outgoing beam components, first and second circular polarizers initially traversed by said first and second beams respectively, said polarizers being oriented such that the beam components issuing initially therefrom are circularly polarized in opposite directions respectively, said polarized beam components being directed into said Faraday cell for multiple reflection between the plane parallel end surfaces thereof along the same path but in opposite directions whereby due to the Faraday effect a difference in the optical path length between said beam components proportional to the variation in said magnetic field is produced, said first and second beam components after issuing from said Faraday cell being passed through said second and first circular polarizers respectively and brought to interference in said prism to produce an intensity-modulated light beam from which sinusoidal electRic signals are derived via means including photodetector means, the arguments of the sinusoidal signals being proportional to the magnitude of the field to be measured.
Claim 4
Dependent Claim
244 words
In an arrangement for measuring the variation in a magnetic field in order to measure, for example, the current flowing in a high voltage line, the combination comprising a measuring head subjected to a magnetic field proportional to the line current, said measuring head enclosing a magneto-optical element constituted by a Faraday cell which in cooperation with an optical beam divider constituted by a Koesters prism forms a two-beam interferometer, means directing a monochromatic light beam into said prism to produce at the divider plane therein first and second outgoing beam components, first and second circular polarizers initially traversed by said first and second beams respectively, said polarizers being oriented such that the beam components issuing initially therefrom are circularly polarized in opposite directions respectively, said polarized beam components being directed into said Faraday cell for multiple reflection between the plane parallel end surfaces thereof along the same path but in opposite directions whereby due to the Faraday effect a difference in the optical path length between said beam components proportional to the variation in said magnetic field is produced, said first and second beam components after issuing from said Faraday cell being passed through said second and first circular polarizers respectively and brought to interference in said prism to produce an intensity-modulated light beam from which sinusoidal electRic signals are derived via means including photodetector means, the arguments of the sinusoidal signals being proportional to the magnitude of the field to be measured.
Claim 5
Dependent Claim
63 words
An arrangement as defined in claim 2 for measuring a variable magnetic field wherein said circular polarizers are constituted by quarter-wave plates secured to one face of said Koesters prism in general parallel relation to the end faces of said Faraday cell, and wherein the incident light beam is plane polarized in a direction parallel to the divider plane of said Koesters prism.
Claim 6
Dependent Claim
67 words
An arrangement as defined in claim 2 for measuring a variable magnetic field produced by current flow on a high-voltage line wherein said measuring head is subjected to the potential of the line and wherein said means including said photodetector means for deriving sinusoidal electric signals from said intensity-modulated light beam have ground potential and are connected to said measuring head by way of light-transmitting fiber bundles.
Claim 7
Dependent Claim
63 words
An arrangement as defined in claim 2 for measuring a variable magnetic field wherein said circular polarizers are constituted by quarter-wave plates secured to one face of said Koesters prism in general parallel relation to the end faces of said Faraday cell, and wherein the incident light beam is plane polarized in a direction perpendicular to the divider plane of said Koesters prism.
Claim 8
Dependent Claim
285 words
An arrangement as defined in claim 2 for measuring a variable magnetic field wherein said circular polarizers are constituted by quarter-wave plates secured to one end face of said prism and wherein said Faraday cell is rotated by a small angle relative to said prism whereby the wave fronts of said first and second beam components interfering in said prism are sheared thus to produce a sinusoidal intensity distribution over the cross section of said intensity-modulated beam issuing therefrom, and which further includes two slit diaphragms disposed in the path of said intensity-modulated light beam issuing from said prism such that two light beams phase-shifted by 90* in modulation are separated, a pair of photodetectors, a pair of fiber bundles directing said phase-shifted light beams respectively to said photodetectors, a pair of amplifiers connected respectively to the outputs of said photodetectors, a pair of modulator stages correlated respectively to said amplifiers, an intermediate frequency oscillator, a phase shifter producing a phase shift of 90*, the two inputs to one of said modulator stages being constituted respectively by the output of the correlated amplifier and the output directly from said intermediate frequency oscillator, and the two inputs to the other modulator stage being constituted respectively by the output of the correlated amplifier and an output from said intermediate frequency oscillator following passage through said phase shifter, an additive network to which the outputs from said two modulator stages are connected, said additive network producing a carrier signal phase-modulated proportional to the magnetic field to be measured, and a frequency discriminator and integrator following said additive network for demodulating said phase-modulated carrier signal to determine the phase which is proportional to the magnetic field to be measured.
References Cited (Backward Citations)
US3495892A
Cited
US3502978A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-11-15 | 1975-05-17 | 1975-11-16 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-11-15 | 1979-05-17 | 1979-11-16 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-11-15 | 1983-05-17 | 1983-11-16 | $7700.00 | Window Closed / Lapsed |