Eddy Current Sensor Beat Frequency Signal Processing
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Solution Overview
Problem
Existing eddy current sensors for determining the position of metal bodies in motor vehicle steering devices face challenges with high-frequency operations, requiring expensive 'high-end' evaluation devices due to low inductance and high-frequency oscillating circuits, which are not easily handled by standard automotive computing units.
Innovation Solution
Incorporating a reference eddy current sensor that generates a 'beat' frequency from the impedance signals of both the eddy current sensor and the reference sensor, allowing simple computing units to evaluate the position of metal bodies by forming a lower frequency signal, which can be processed using a flip-flop module and oscillator devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the eddy current sensor uses high-frequency oscillating circuits to achieve accurate position determination, then measurement precision is improved, but device complexity and cost increase due to requiring high-end evaluation devices
Solution Approach 1:
The system divides the high-frequency signal processing into two parts: the reference eddy current sensor provides a stable high-frequency reference signal, while the measuring eddy current sensor processes the actual measurement. The evaluation device then processes the difference signal at a lower effective frequency, segmenting the complex high-frequency processing task into manageable parts that can be handled by standard microcontrollers.
Solution Approach 2:
The reference eddy current sensor acts as an intermediary that provides a stable reference signal. By comparing the measuring sensor's signal against this reference, the system converts high-frequency impedance changes into lower frequency beat signals that are easier to process, effectively using the reference sensor as a mediator to simplify the evaluation task.
2Volume of moving object
If the coil geometry is reduced to save installation space, then volume is reduced, but inductance decreases requiring even higher operating frequencies
Solution Approach 1:
The reference eddy current sensor creates a copy of the high-frequency oscillating field without the metal body interference. This reference copy allows the system to measure position changes by comparing against the known reference frequency, enabling accurate measurement even when the measuring coil operates at very high frequencies due to its small size.
3Ease of manufacture
If standard automotive microcontrollers are used instead of high-end evaluation devices, then manufacturing cost is reduced, but the ability to process high-frequency signals is insufficient
Solution Approach 1:
The system uses periodic modulation by forming beat signals from the interference between the reference high-frequency signal and the measuring signal. This periodic beat signal has a much lower frequency that standard microcontrollers can easily process, while still containing the position information from the original high-frequency measurement.
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
Enables the use of cost-effective and commonly available microcontrollers to evaluate high-frequency signals, reducing manufacturing costs and complexity while maintaining accurate position determination of metal bodies.
Implementation Method 1
When an electrically conductive object, in particular a metal body, approaches the eddy current sensor, the alternating field induces eddy currents in the metal body. These eddy currents themselves form their own electromagnetic field, which counteracts the coil field, which changes the impedance or inductance of the coil.
Implementation Method 2
Eddy current sensors have a coil which is fed with a high-frequency alternating current, as a result of which an electromagnetic alternating field is formed around the coil. The field lines of the high-frequency alternating field emerge from the sensor level. When an electrically conductive object, in particular a metal body, approaches the eddy current sensor, the alternating field induces eddy currents in the metal body.
Implementation Method 3
the evaluation device being designed for this purpose is to form a beat from impedances detected by the devices, which are output as signals with corresponding frequencies, and to determine the position of the metal body as a function of the beat. The device of the reference eddy current sensor thus determines a reference impedance according to the high-frequency feed of the coil. The evaluation device forms the so-called beat from the frequencies that are recorded by the measuring device of the reference eddy current sensor and the eddy current sensor.
Data Source
Figure 1
AI summary
The invention relates to a sensor device (5) for determining the position of a metal body (4), in particular an actuator (2) of a steering device of a motor vehicle, comprising at least one Eddy current sensor (6), which has a coil (6') for generating a high-frequency electromagnetic alternating field and a device (6") for operating the coil (6') and for detecting an impedance of the coil (6'), and comprising an analyzing device (7), which determines the position of the metal body (4) relative to the coil (6') using the detected impedance. A reference Eddy current sensor (8) is provided which has a reference coil (8') for generating a high-frequency electromagnetic alternating field and a reference device (8") for operating the reference coil (8') and for detecting an impedance of the reference coil (6') and which is oriented/designed such that the electromagnetic alternating field of the reference Eddy current sensor is free of metal bodies, wherein the analyzing device (7) is designed to form a beat from the detected impedance and to determine the position of the metal body (4) dependent on the beat.