Inductive Proximity Sensing With ΣΔ Modulation at Longer Range
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Solution Overview
Problem
Inductive proximity sensors face challenges in detecting electrically conductive objects at large distances due to reduced magnetic field strength and limited resolution, requiring high-resolution signal techniques and significant effort to achieve extended operating distances.
Innovation Solution
The use of a ΣΔ modulator to evaluate the output signal of an LC resonant circuit, incorporating a filter and converters to produce a pulse frequency modulated data stream, which enhances resolution and robustness against electromagnetic interference, allowing for both binary and analog sensing applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the spacing of the target from the coil is increased to achieve larger operating distances, then the operating distance is improved, but the magnetic field strength reduces with the third power making detection increasingly difficult and resolution deteriorates
Solution Approach 1:
The patent changes the evaluation parameter from direct impedance measurement to phase-locked loop frequency detection. By measuring the frequency shift of a phase-locked oscillating signal instead of directly measuring impedance or damping, the system achieves higher resolution detection at extended operating distances where magnetic field strength is reduced.
2Measurement precision
If high-resolution signal techniques are used to detect small changes in coil impedance at large operating distances, then detection precision is improved, but the system becomes more complex and requires significant effort in production and alignment
Solution Approach 1:
The patent replaces complex mechanical signal processing (rectification, filtering, threshold comparison) with an electronic phase-locked loop system. The PLL automatically tracks the resonant frequency and provides high-resolution detection through frequency measurement, eliminating the need for precise mechanical alignment and complex signal processing circuits.
3Device complexity
If conventional rectification and comparator methods are used for signal evaluation, then the system remains simple, but the quality of rectification and comparator limits the achievable resolution and operating distance
Solution Approach 1:
The patent changes the measured parameter from amplitude (after rectification) to frequency (via phase-locked loop). By measuring the frequency of a phase-locked oscillating signal, the system achieves high resolution without the limitations of rectification quality and comparator thresholds, while maintaining relatively simple circuit implementation.
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 enables high-resolution detection and precise measurement of object spacing, achieving extended operating distances with improved robustness and dynamic range, suppressing noise and interference.
Implementation Method 1
An alternating magnetic field which is radiated into space in a directed manner is built up by means of an electric resonant circuit from a coil and a capacitor (LC resonant circuit)
Implementation Method 2
If an electrically conductive object (also called a 'target' in the following) moves into the range of the alternating field, eddy currents are induced in the target by the alternating field which in turn give rise to a magnetic field which is oppositely directed to the exciting magnetic field
Implementation Method 3
eddy currents are induced in the target by the alternating field
Implementation Method 4
The generation of the eddy currents removes energy from the exciting magnetic field and thus influences the impedance of the coil or damps the LC resonant circuit
Data Source
AI summary
The invention relates to an inductive proximity sensor with a sensor element which includes a resonant circuit which provides an output signal which depends on the damping by an electrically conductive object. In accordance with the invention, the inductive proximity sensor has a ΣΔ modulator for the evaluation of an output signal of the resonant circuit. The invention furthermore relates to a method for the determination of the presence and/or of the spacing of a metallic object with the help of an inductive proximity sensor.