Optical Fiber Mode Filter for Molten Mass Temperature Measurement
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Solution Overview
Problem
Existing measuring devices for high-temperature melts, such as metal or cryolite melts above 500 °C, face significant measurement inaccuracies due to radiation mode absorption and signal attenuation in long optical fibers, leading to deviations of over 10°C in temperature readings, which are exacerbated by fiber length changes and instability.
Innovation Solution
The solution involves a compact design that filters out interfering modes using a quartz glass optical fiber with a metal sheath for mechanical stability, a mode filter arranged in a closed curve, and an optical fiber connection within the cable drum to improve measurement accuracy and constancy, with a distributor to manage length deviations and connect consumable and non-consumable fiber sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a long optical fiber is used for measuring in melts, then the measurement range is extended, but the measurement precision deteriorates due to radiation mode absorption and signal attenuation
Solution Approach 1:
The optical fiber is segmented into two distinct sections: a consumable section with a first diameter that is fed into the melt, and a non-consumable section with a second, smaller diameter that remains outside the melt. This segmentation allows the fiber to function effectively at different locations, with the thinner non-consumable section filtering out interfering radiation modes while the longer consumable section provides adequate length for measurement.
Solution Approach 2:
Different sections of the optical fiber are given different local qualities - the consumable section has a larger diameter suitable for withstanding melt conditions and feeding into the immersion lance, while the non-consumable section has a smaller diameter specifically optimized for filtering radiation modes. This local differentiation resolves the contradiction by applying the appropriate fiber property at the appropriate location.
2Measurement precision
If the optical fiber diameter is reduced to filter modes, then the measurement precision improves, but the mechanical stability deteriorates
Solution Approach 1:
The fiber is divided into two sections with different diameters and functions. The thinner non-consumable section (second diameter) provides mode filtering for precise measurements, while the thicker consumable section (first diameter) provides mechanical strength and stability. This segmentation allows each section to be optimized for its specific function without compromising the other.
Solution Approach 2:
The distributor acts as an intermediary component that connects the two fiber sections of different diameters. It manages the transition between the consumable and non-consumable sections, allowing the thin mode-filtering section to be effectively coupled with the robust consumable section, thereby maintaining both precision and mechanical stability.
3Measurement precision
If a mode filter is implemented, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The mode filtering function is merged directly into the non-consumable section of the optical fiber itself, rather than being implemented as a separate external filter component. This integration simplifies the overall device structure while maintaining the mode filtering capability needed for precise measurements.
Solution Approach 2:
The distributor serves as an intermediary that manages the complexity of connecting and managing the two different fiber sections. It provides a structured way to handle the transition between consumable and non-consumable sections, simplifying the overall fiber management system despite the presence of multiple fiber types.
4Productivity
If the optical fiber is fed according to consumption, then the productivity improves, but the measurement precision deteriorates due to length changes
Solution Approach 1:
The fiber system is segmented into a consumable portion that is fed according to usage and a permanent non-consumable portion with the critical mode-filtering diameter. As the consumable section is used up and fed through, the non-consumable section remains in place, maintaining consistent optical properties and measurement precision throughout the measurement process.
Solution Approach 2:
The system automatically maintains the correct fiber configuration through the distributor, which manages the transition between consumable and non-consumable sections. This self-managing system ensures that the precision-critical non-consumable section remains in place while the consumable section is replenished, maintaining both productivity and precision without manual intervention.
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 enhances measurement precision in high-temperature melts, reducing temperature measurement deviations to less than 10°C, while the metal sheath and mode filter suppress interfering modes, and the distributor ensures accurate signal transmission and fiber management.
Implementation Method 1
an optical fiber for receiving radiation from the melt
Implementation Method 2
the fiber absorbs the radiation at its immersion end with a large number of so-called modes, including vibration modes. The different modes are attenuated at different intensities over the long length of the fiber
Data Source
Figure 1
Figure 2
AI summary
The device comprises an optical fiber (6) for receiving radiation from a molten mass, a cable reel (8) having an external circumference for winding up the optical fiber and an internal space surrounded by the external circumference, and a distributor and a mode filter for the optical fiber, where the distributor and the mode filter are arranged in the internal space. The cable reel is arranged on a carrier to be rotatable in a detachable manner. The carrier comprises a feed facility for the optical fiber and/or an instrument panel. The internal space of the cable reel has a detector. The device comprises an optical fiber (6) for receiving radiation from a molten mass, a cable reel (8) having an external circumference for winding up the optical fiber and an internal space surrounded by the external circumference, and a distributor and a mode filter for the optical fiber, where the distributor and the mode filter are arranged in the internal space. The cable reel is arranged on a carrier to be rotatable in a detachable manner. The carrier comprises a feed facility for the optical fiber and/or an instrument panel. The internal space of the cable reel has a detector, a data storage unit, a signal transducer facility, and/or an electrical interface. The detector is arranged at an inside of a housing of a signal transducer facility, which connects the optical fiber to an electrical cable. The internal space contains a splicer for connecting optical fibers. Two optical fibers are connected by splicing in the internal space, where the splicing is a welded connection. The mode filter comprises an arrangement of a section of the optical fiber extending on a closed curve and/or a circular path. The optical fiber extends in 1-20 turns of a coil on the closed curve. A smallest diameter of the closed curve is 1-6 cm. The circumference of the mode filter is surrounded by the distributor. The internal space of the cable reel is mechanically and/or electromagnetically sealed. The detector, an end of an optical fiber connected to the detector, and a band-pass filter are: connected to each other in a non-detachable manner; and sealed against moisture and stray light. A core of the optical fiber connected to the detector on one side and to the optical fiber wound onto the cable reel on the other side has a diameter smaller than a diameter of the optical fiber wound onto the cable reel on its end connected to the detector. An antenna for wireless signal transmission is arranged on the measuring device. A molten metal or molten cryolite mass has a melting point of 500[deg] C. An independent claim is included for a cable reel.