Sensor Evaluation Circuit Using Alternating Oscillation Counting
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Solution Overview
Problem
Existing sensor evaluation circuits for inductive and capacitive sensors are complex, costly, and sensitive to temperature and supply voltage, making them unsuitable for low-cost applications, particularly in areas like motor vehicles.
Innovation Solution
A circuit arrangement with two complex impedances, where one is part of the sensor, forms oscillating circuits that alternate counting and excitation, using a counter and switching device to generate a pulse-width-modulated output signal, allowing for simple and cost-effective evaluation of sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PLL circuits or complex evaluation circuits are used for sensor evaluation, then measurement accuracy is improved, but device complexity and cost increase significantly
Solution Approach 1:
The evaluation circuit is divided into two separate oscillating circuits, each with its own sensor coil and capacitor. This segmentation allows independent operation of each circuit, simplifying the overall design while maintaining measurement accuracy through differential comparison of the two circuits' frequencies
Solution Approach 2:
The circuit uses changes in oscillation frequency as the measurement parameter instead of complex phase or amplitude demodulation. By detecting frequency shifts in the two oscillating circuits caused by sensor impedance changes, the system achieves accurate measurement with simpler circuitry
2Measurement precision
If PLL circuits are used for sensor evaluation, then measurement capability is improved, but temperature sensitivity increases
Solution Approach 1:
Each oscillating circuit is designed with locally optimized components (inductor and capacitor values) to achieve similar center frequencies. This local quality optimization ensures that both circuits respond similarly to temperature changes, allowing differential measurement to cancel out temperature effects while maintaining measurement capability
3Measurement precision
If complex stabilization measures are implemented for supply voltage, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The oscillating circuits are designed to be inherently stable against supply voltage variations through their resonant nature. The circuits self-regulate their oscillation frequency based on their component values rather than requiring external voltage regulation, eliminating the need for complex stabilization measures
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 the evaluation of inductive or capacitive sensors with simple circuitry, reducing costs and eliminating the need for expensive components, while providing high resolution and dynamic measurement results.
Implementation Method 1
two complex impedances, the complex impedances each being part of an oscillating circuit in which the complex impedances can be excited to oscillate
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
A circuit system for evaluating a sensor, wherein the circuit system comprises two complex impedances (2, 3, 13, 14), wherein the complex impedances (2, 3, 13, 14) are each part of a resonant circuit in which the complex impedances (2, 3, 13, 14) can be excited to perform oscillations, and wherein at least one of the two complex impedances (2, 3, 13, 14) are part of the sensor, is characterized with respect to a particularly cost-effective and as simple a circuit design as possible in that a counter (9, 18) and a switch apparatus (8, 16) are provided, wherein the counter (9, 18) can be used to alternately count the oscillations of one of the two resonant circuits, the switch apparatus (8, 16) can be switched when a specifiable counter reading has been reached, and the switch signal of the switch apparatus serves as a pulse width-modulated output signal (11, 21) for the circuit system.