Inductive Proximity Sensor With Phase-Shifted Detection Coils
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Solution Overview
Problem
Conventional inductive proximity sensors face challenges in accurately determining the instant of a target discontinuity and distinguishing between the presence and absence of a target due to variations in signal amplitude and distance, leading to unreliable detection.
Innovation Solution
The implementation of a method using two pairs of phase-shifted detection coils to generate differential inductive signals, with a stationary target creating an offset to differentiate between target presence and absence, allowing for precise transition detection and reducing false positives by ensuring signals are within a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inductive proximity sensors are used, then the structure is simple, but the measurement precision of target discontinuity instant is poor
Solution Approach 1:
The detection system is segmented into multiple detection coils arranged in specific spatial configurations, with each coil contributing to detecting different aspects of the target's position. This segmentation allows precise determination of target discontinuity instants by analyzing signals from multiple coils, while the segmented structure can be integrated into a single sensor device.
Solution Approach 2:
The patent transitions from single-coil or simple pair configurations to three-dimensional spatial arrangements of multiple detection coils. By adding spatial dimensionality to the coil configuration, the system achieves higher measurement precision for target position and discontinuity detection without simply increasing the number of components in a single plane.
2Reliability
If signal amplitude threshold is used for target detection, then the detection method is simple, but the reliability of target detection is poor due to distance variations
Solution Approach 1:
Instead of relying on absolute signal amplitude thresholds that vary with distance, the patent changes the detection parameter to the temporal relationship and phase difference between signals from multiple detection coils. This parameter transformation makes detection independent of amplitude variations caused by distance changes, thereby improving reliability without requiring complex amplitude normalization circuits.
Solution Approach 2:
The system uses feedback from multiple detection coils to cross-validate target presence. By comparing signals from different coils and using their temporal and phase relationships, the system creates a feedback mechanism that confirms target detection reliability, reducing false positives even when individual signal amplitudes vary due to distance.
3Measurement precision
If differential coils are used to detect target discontinuities, then the detection capability is improved, but the ability to distinguish target presence from absence is lost
Solution Approach 1:
The detection system is segmented into multiple detection coils with different spatial positions and orientations. This segmentation allows the system to maintain differential detection capability for discontinuities while also having specific coils that can detect the overall presence or absence of a target, as each coil's signal characteristics provide different information about target state.
Solution Approach 2:
The patent uses more detection coils than the minimum required for differential detection. This excessive action provides redundant information that enables both discontinuity detection and target presence/absence distinction. The additional coils provide extra signal sources that can indicate overall target presence even when differential signals are ambiguous.
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 approach enhances the reliability of target detection by minimizing the impact of signal amplitude and distance variations, enabling accurate determination of target transitions and distinguishing between target presence and absence with improved precision.
Implementation Method 1
inductive measuring and typically comprise one or several excitation coils generating an inductive field and one or several detection coils generating a current depending on the received inductive field
Implementation Method 2
detection coils generating a current depending on the received inductive field
Implementation Method 3
When a metallic object, called a target, is moved close to the sensor, the magnetic coupling between the excitation coil and the detection coil or coils is modified
Data Source
AI summary
An electronic circuit detecting proximity includes an excitation coil emitting an inductive excitation field toward a target. A first pair of detection coils obtains a first differential inductive signal that is modified by a transition of the target within the inductive field. An out-of phase second pair of detection coils obtains a second differential inductive signal that is modified by a transition of the target within the inductive field. A comparator generates a transition signal when the difference between the first and second differential signals reaches a threshold value. A stationary target, in a ferromagnetic or conductive material, creates an offset to the signals at the outlet of the coil pairs. The offset is decreased during the presence of a movable target within the same type of material or increased during the presence of a movable target within another type of material. A comparator detects the offset level.