Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1997-03-24
1998-07-14
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25022721, 250225, 385 11, 385 12, 356351, 324 7611, 324 96, G02F 105, G02F 109, G01R 1500
Patent
active
057808473
ABSTRACT:
A fiber optic, Faraday-effect current sensor (optical current transducer) which has improved temperature sensitivity due to compensation for temperature-induced variations of the Verdet constant. Fiber optic sensing coils can exhibit shifts in their bias angle due to a number of reasons, including physical rotation of the fibers, an apparent circular birefringence attributable to the sensing coil shape (Berry's phase), circular birefringence in the sensing fiber, or a DC magnetic field or current. The present invention takes advantage of the change in bias angle by identifying a preferred channel from the two sensing axes of the output fiber, based on the manner in which these axes respond to the change in bias angle. One of the axes will exhibit a change in sensitivity that exacerbates the change in sensitivity due to the Verdet constant, while the other channel will exhibit a change that complements, or compensates for, the change in sensitivity due to the Verdet constant. Once the preferred channel is identified, a polarizing fiber is attached to the output of the sensing coil, aligned to transmit the preferred channel to the optical detector.
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Dawson Jay W.
MacDougall Trevor W.
Chernivec Gerald F.
Lee John R.
Minnesota Mining and Manufacturing Company
Westin Edward P.
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