Eddy Current Speed Sensor With Differential Magnet-Sensor Pairs
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Solution Overview
Problem
Existing devices, such as Ferraris sensors, face challenges in reliably determining the speed or acceleration of electrically conductive objects made from magnetizable materials due to interference from changes in magnetization and distance, which affect the measurement signal quality.
Innovation Solution
A device with multiple magnets and sensors arranged in a specific configuration to generate and detect external and internal magnetic fields, allowing for the compensation of pre-magnetization and distance changes by forming a difference between measurement signals from sensors with opposite polarizations, thereby isolating the object's movement-induced signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single magnet and sensor are used to detect movement of electrically conductive objects, then the device structure is simple, but measurement reliability deteriorates due to interference from magnetization changes and distance variations
Solution Approach 1:
The device is segmented into two identical subsystems: a first magnet with a first sensor, and a second magnet with a second sensor. Each subsystem independently measures the magnetic field, and the two measurements are subsequently combined through signal processing to eliminate interference. This segmentation allows the system to maintain structural simplicity while improving measurement reliability through differential measurement.
Solution Approach 2:
The interference signals from magnetization changes and distance variations, which were previously harmful to measurement accuracy, are converted into beneficial information. By using identical magnet-sensor pairs positioned symmetrically, the interference affects both sensors equally, allowing it to be eliminated through differential calculation. The harmful interference is thus transformed into a common-mode signal that can be rejected.
2Reliability
If magnets and sensors are arranged to compensate for external magnetic fields and distance changes, then measurement reliability improves, but device complexity increases
Solution Approach 1:
The two magnet-sensor subsystems are positioned at different locations relative to the object, with magnets arranged on opposite sides. This local differentiation in positioning, combined with identical local structures at each position, enables spatial compensation of interference signals while maintaining overall structural simplicity. Each local subsystem remains simple, but their combined effect achieves interference rejection.
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 the reliability of speed and acceleration measurements by eliminating external magnetic field and distance-related interference, providing a more accurate determination of the object's movement.
Implementation Method 1
The external magnetic field induces eddy currents in the moving electrically conductive object
Implementation Method 2
The external magnetic field induces eddy currents in the moving electrically conductive object, which create an internal magnetic field that opposes the external magnetic field
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a device (20) and a method for determining the speed or acceleration of an electrically conductive object (4, 4c) in a predefined movement direction (X), having at least four magnets (1, Ib) for producing an external magnetic field (Ia) each, each pair of first magnets (1) being spaced from each other with opposite polarity in the movement direction (X), and a first sensor (3) being arranged between the two first magnets with measurement axis (Y) perpendicular to the movement direction, each pair of second magnets (Ib) being spaced from each other with opposite polarity in the movement direction, and a second sensor (3a) being arranged between the two second magnets with measurement axis perpendicular to the movement direction, first and second magnets and first and second sensors each being arranged along an axis (Z) running perpendicularly to the movement direction (X) and measurement axis (Y). The speed or acceleration of the object (4, 4c) is calculated on the basis of the difference between the first and second measurement signals, which each detect the internal magnetic field produced by eddy currents in the object, whereby influences of external magnetic fields and changes in the distance between the sensors and the measurement object can be compensated.