Faraday Current Sensor Birefringence Compensation
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Solution Overview
Problem
Existing electric current measuring apparatus using the Faraday effect face challenges in accurately compensating for temperature-dependent errors, particularly due to birefringence in optical fibers, which leads to significant fluctuations in measurement values, making it difficult to maintain a ratio error within ±0.5%.
Innovation Solution
The apparatus incorporates a light incident and emitting unit, an optical fiber sensor, a Faraday rotator, quarter-wave plates, and a polarization splitter, with the Faraday rotation angle adjusted to 22.5° + α° at 23°C, and the phase differences compensated between linearly polarized lights in the reciprocating optical path, using polarization maintaining fibers and birefringent elements to stabilize the measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Faraday rotation angle is adjusted to 22.5° + α° at 23°C to compensate for temperature characteristics, then the reliability of measurement is improved, but the device complexity increases due to additional quarter-wave plates and polarization maintaining fibers
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the Faraday rotation angle to 22.5° + α° at a reference temperature of 23°C. This preliminary adjustment compensates for temperature characteristics before actual measurement begins, allowing the system to maintain high reliability across varying temperatures without requiring real-time complex adjustments during operation.
Solution Approach 2:
The patent introduces quarter-wave plates and polarization maintaining fibers as intermediary elements that mediate between the light source and the measurement system. These intermediaries convert light polarization states and maintain polarization integrity, enabling temperature compensation while managing the inherent complexity through standardized optical components.
2Manufacturing precision
If birefringence compensation is implemented using polarization maintaining fibers, then the manufacturing precision is improved, but the ease of manufacture deteriorates due to alignment requirements
Solution Approach 1:
The patent applies local quality by implementing birefringence compensation specifically in the optical fiber sections where it is most critical, using polarization maintaining fibers only in necessary segments of the optical path. This localized approach achieves the required manufacturing precision without requiring the entire system to use complex polarization-maintaining components, thereby improving ease of manufacture.
3Measurement precision
If the fluctuation range of ratio error is reduced to within ±0.5%, then the measurement precision is improved, but the loss of time increases due to extended compensation procedures
Solution Approach 1:
The patent performs temperature compensation adjustments preliminarily at the reference temperature of 23°C before actual measurements begin. By completing the compensation setup in advance, the system achieves high measurement precision (ratio error within ±0.5%) without requiring time-consuming compensation procedures during the actual measurement process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces the fluctuation range of the ratio error to ±0.5%, enhances the reliability of the electric current measurement, and simplifies the assembly process by eliminating the need for fine adjustments of crystal axes, while maintaining stability across a wide temperature range.
Implementation Method 1
uses the Faraday effect, that is, uses rotation of a polarization plane of a light by action of a magnetic field
Implementation Method 2
an optical fiber for a sensor, a Faraday rotator, a first quarter-wave plate and a second quarter-wave plate
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Provided is a current measuring device such that it is possible to reliably keep the fluctuation range for the ratio error in output to within a range of ±0.5% and such that assembly thereof can be simplified. The current measuring device is configured to include at least a light entrance and exit, an optical fiber for a sensor, a Faraday rotator, a first 1/4 wavelength plate, a second 1/4 wavelength plate, a polarization separator, a light source, and a signal processing circuit comprising a photoelectric conversion element. The optical fiber for a sensor has birefringence and comprises one end into which two circularly polarized light beams having different directions of rotation enter and another end that reflects the circularly polarized light beams that have entered. In addition, the phase difference of two linearly polarized light beams in the round-trip light path between the two 1/4 wavelength plates is compensated, and the Faraday rotational angle when the Faraday rotator is magnetically saturated is set to 22.5°+α° so that the fluctuation range for the ratio error in the measured value of the current to be measured is set to be in the range of ±0.5%. In addition, the crystal axes on the optical faces of the two 1/4 wavelength plates are set to be perpendicular or are set to be in the same direction.