Electromagnetic Proximity Sensing with Adaptive Threshold Drift Compensation
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Solution Overview
Problem
Conventional proximity sensors face issues with drifting due to harsh environments, mechanical stress, and changing installation conditions, leading to unstable switching distances and potential functional failures, as they fail to effectively compensate for temperature fluctuations and other environmental changes.
Innovation Solution
An electromagnetic proximity sensor that adapts its switching threshold based on measured presence and absence levels to compensate for drifts, using a sensor element with a transmitter and receiver coil or an oscillating circuit to derive a sensor signal, and an evaluation unit that adjusts the threshold to maintain a constant switching distance, employing auto-correction or auto-detection methods to ensure robust switching behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed switching distance is used in conventional proximity sensors, then the sensor structure remains simple, but the switching behavior becomes unstable due to drifts caused by temperature fluctuations, wear, aging, and contamination
Solution Approach 1:
The sensor performs self-calibration by automatically determining presence and absence levels during operation and adapting its own switching threshold without external intervention. The control unit monitors the sensor signal and adjusts the threshold to compensate for drifts, enabling the sensor to maintain accurate switching behavior autonomously throughout its service life
Solution Approach 2:
The system implements feedback by continuously monitoring the sensor signal and comparing it against dynamically determined presence and absence levels. Based on this feedback, the control unit adjusts the switching threshold to maintain stable switching behavior despite environmental changes, wear, or contamination
2Reliability
If temperature compensation is implemented using correction tables, then some temperature effects are addressed, but the solution remains error-prone because the measuring electronics temperature does not correspond to the sensor element temperature
Solution Approach 1:
The patent replaces the mechanical/physical approach of temperature sensing with an electrical signal processing approach. Instead of measuring temperature directly with separate sensors, the system uses the sensor signal itself to determine presence and absence levels, eliminating the need for separate temperature measurement and correction tables
Solution Approach 2:
The control unit acts as an intermediary that processes the sensor signal to extract presence and absence levels. This intermediary processing step allows the system to indirectly account for temperature effects without directly measuring temperature, bypassing the problem of temperature sensor inaccuracy
3Length of stationary object
If the switching distance is increased to improve detection range, then the sensitivity of the sensor increases, but the switching distance changes significantly more due to drifts and installation conditions
Solution Approach 1:
The switching threshold is made dynamic rather than fixed. The control unit continuously adapts the threshold based on the determined presence and absence levels, allowing the system to maintain stable switching distance even when the absolute signal levels change due to drifts or installation variations. This dynamic adaptation compensates for the increased sensitivity to environmental changes that comes with larger switching distances
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
The solution prevents unintentional shifting of switching distances and maintains reliable sensor operation in harsh environments, enhancing detection robustness and availability by compensating for wear, aging, contamination, and temperature fluctuations, reducing the need for frequent adjustments and minimizing sensor model variations.
Implementation Method 1
an inductive proximity sensor detects conductive, in practice mainly metallic, targets
Implementation Method 2
A method for continuously measuring a magnetic field using a sensor is known from FR 2 985 034 A1
Data Source
Figure 1a~1d
Figure 2~3
AI summary
An electromagnetic proximity sensor (10) for detecting a target object (20) is described. The sensor comprises a sensor element (12) for generating a sensor signal that changes with the distance of the target object (20) and an evaluation unit (14) in which the presence of the target object (20) at a switching distance (16) is detected by comparing the sensor signal with a switching threshold (22). The evaluation unit (14) is configured to detect an absence level (24a) of the sensor signal when no target object (20) is influencing the sensor signal, and/or a presence level (24c) of the sensor signal when a target object (20) is detected as present, and to adjust the switching threshold (22) based on the absence level (24a) and/or the presence level (24c).