Inductive Proximity Sensing with Early Digitization and Signal Mixing
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Solution Overview
Problem
Inductive proximity sensors face challenges in accurately determining the presence and distance of electrically conductive objects due to temperature variations and external electromagnetic interference, requiring complex and expensive compensation circuits, and typically only offer threshold-based detection rather than continuous measurement.
Innovation Solution
The integration of an A/D converter to digitize the analog output signal early in processing, followed by a mixer that multiplies the digital signal with a reference signal to extract amplitude information, allowing for robust digital processing and continuous distance measurement, while reducing electromagnetic interference and eliminating the need for complex analog circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If analog compensation circuits are used to compensate temperature influence on the LC resonant circuit, then temperature stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex analog compensation circuits with a digital signal processing approach. An A/D converter converts the analog output signal to digital, and a microprocessor digitally processes the signal to compensate for temperature effects. This substitution of digital electronics for analog compensation circuitry reduces device complexity while maintaining temperature stability.
Solution Approach 2:
The patent changes the state of the output signal from analog to digital through A/D conversion. This parameter change enables digital processing techniques that can compensate for temperature variations without requiring additional analog compensation components, thereby simplifying the overall circuit while improving reliability.
2Ease of operation
If threshold value detection with analog circuits is used, then simple detection is achieved, but continuous distance measurement capability is lost
Solution Approach 1:
The patent converts the output signal from analog to digital form through an A/D converter. This parameter change enables the use of digital signal processing techniques including Fourier transformation and autocorrelation, which can extract both threshold detection information and continuous amplitude information for precise distance measurement, simultaneously achieving simplicity and precision.
Solution Approach 2:
The digital signal processing approach provides multi-functionality: it can perform both simple threshold-based presence detection and continuous distance measurement by analyzing signal amplitude. The same digital processing circuitry handles both detection modes, eliminating the need for separate analog circuits for each function.
3Reliability
If the analog output signal is processed without early digitization, then external electromagnetic interference influences are not precluded, but processing flexibility is maintained
Solution Approach 1:
The patent performs preliminary digitization of the output signal as early as possible in the signal processing chain, before further processing steps. This preliminary conversion to digital form precludes external electromagnetic interference influences from affecting subsequent processing, while the use of standard A/D converter integrated circuits keeps the added complexity manageable.
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 simple, cost-effective, and robust operation of inductive proximity sensors by converting analog signals to digital form, allowing for precise detection of object presence and distance with improved resistance to electromagnetic interference and temperature variations, and enabling digital filtering and linearization.
Implementation Method 1
inductive proximity sensors detect electrically conductive metals on the basis of the eddy current principle. An alternating magnetic field which is radiated into space in a directed manner is built up e.g. by means of an electrical 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.
Data Source
AI summary
The invention relates to an inductive proximity sensor for determining the presence and/or the distance of an electrically conductive object which is designed to evaluate an oscillation in the form of an analog signal whose amplitude depends on the presence or absence and/or on the distance of an electrically conductive object. In accordance with the invention, the inductive proximity sensor includes at least one A/D converter which converts this analog signal into a digital input signal and includes at least one mixer which multiplies the digital input signal by a digital reference signal to form a digital output signal, wherein the digital reference signal is identical to the digital input signal or only differs from the digital input signal by a constant factor. The invention further relates to a method for determining the presence and/or the distance of an electrically conductive object with the aid of a proximity sensor.