Inductive Proximity Detector with Switched Windings for Temperature Compensation
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Solution Overview
Problem
Inductive proximity detectors are sensitive to coil positioning and temperature drifts, affecting their reliability in detecting metallic targets over time, regardless of the target's nature.
Innovation Solution
An inductive proximity detector design featuring a resonant oscillating circuit with a detection coil and a reference coil of lower mutual inductance, using common components and processing means to determine the presence of a metallic target by calculating frequency differences and comparing them to a learned threshold, with a switch to alternate coil connections and a common capacitor, minimizing sensitivity to coil positioning and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single detection coil is used in the oscillating circuit, then the detector can detect metallic targets, but the detector becomes highly sensitive to coil positioning and temperature drifts
Solution Approach 1:
The oscillating circuit is segmented into two separate coils: a detection coil for sensing metallic targets and a reference coil for temperature compensation. Each coil is independently connected to the oscillating circuit through a switch that alternates between positions, allowing separate measurement and compensation functions while maintaining detection reliability and reducing positioning sensitivity.
2Measurement precision
If coils are positioned precisely to achieve accurate detection, then detection accuracy improves, but the system becomes sensitive to temperature drifts and positioning faults
Solution Approach 1:
A reference coil is introduced as an intermediary element that experiences the same temperature drifts as the detection coil but does not detect metallic targets. By alternately measuring the oscillation frequency with both coils and comparing the differences, the system compensates for temperature effects while maintaining accurate metallic target detection.
3Reliability
If a reference coil with low mutual inductance is added to the circuit, then temperature drift compensation is achieved, but the device complexity increases
Solution Approach 1:
The oscillating circuit and processing means are designed to handle both detection coil and reference coil measurements universally. The switch alternates between connecting the detection coil and reference coil to the same oscillating circuit, allowing a single circuit design to perform both metallic target detection and temperature compensation functions without requiring separate dedicated circuits for each coil.
Data Source
Figure 1~3
AI summary
The detector has a parallel inductance-capacitance type oscillating circuit (1) including a reference coil (11) arranged to produce mutual inductance opposite to a metal target (4) to be detected, where the inductance is less than the inductance of a detection coil (10) opposite to the target. The circuit has a switch (13) i.e. analog electronic switch, adapted to take two positions for alternatively connecting the two coils. A processing unit (3) is connected to the coils, and permits to determine the presence or absence of the target at the proximity of the detector.