Oscillation Sensor Calibration Using Frequency-Synced PWM
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Solution Overview
Problem
Oscillation sensors face challenges in calibration due to the introduction of low-frequency harmonics from pulse width modulation, which degrade the signal-to-noise ratio and are difficult to eliminate, especially when the duty cycle affects the calibration of the sensor.
Innovation Solution
The oscillation sensor employs a calibration unit that provides a modulated calibration control signal with a cycle frequency dependent on the oscillation frequency, minimizing modulation effects by synchronizing the cycle frequency with the oscillation frequency to reduce harmonic interference and enhance signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If pulse width modulation is used to control the calibration element, then electronic calibration is enabled, but low frequency harmonics are injected into the circuitry degrading the signal-to-noise ratio
Solution Approach 1:
A low-pass filter is introduced as an intermediary component between the pulse width modulated calibration element and the oscillator circuitry. This filter mediates the harmful high-frequency switching harmonics generated by PWM, allowing only the essential low-frequency calibration signal to pass through to the oscillator, thereby preserving electronic calibration functionality while eliminating noise degradation of the sensor signal.
2Adaptability or versatility
If different duty cycles are selected for calibration, then different harmonics are introduced into each oscillation sensor, but these harmonics are difficult to eliminate by filtering
Solution Approach 1:
The low-pass filter is designed with specific cutoff frequency parameters that remain constant regardless of the PWM duty cycle used for calibration. By properly selecting the filter's time constant (RC product) to be much larger than the PWM period, the filter effectively attenuates harmonics across the entire duty cycle range, providing universal harmonic rejection that maintains calibration flexibility without requiring complex adaptive filtering.
3Measurement precision
If laser calibration of the calibration element is used, then precise calibration is achieved, but it is expensive and does not allow recalibration
Solution Approach 1:
The patent replaces the mechanical/laser-based physical trimming method with an electronic pulse width modulation system. Instead of physically adjusting the calibration element's electrical properties using laser trimming, the invention uses PWM to dynamically control the effective resistance of the calibration element, achieving equivalent calibration precision through electronic means that are cheaper, more flexible, and allow for recalibration.
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 significantly improves the signal-to-noise ratio across a broad range of oscillation frequencies, allowing for better sensitivity and operating point adjustment, while also compensating for parasitic effects like temperature variations.
Implementation Method 1
an oscillator comprising: a resonance circuit for providing an oscillation signal
Implementation Method 2
a gain stage configured to provide a feedback to the resonance circuit to inject energy for excitation of the resonance circuit to maintain oscillation
Implementation Method 3
the sensing coil produces an alternating magnetic field which is substantially affected by the presence of conductive objects
Implementation Method 4
the presence of an object in the sensing range leads to a decrease of a quality factor of the resonance circuit caused by an energy loss due to the production of eddy currents in the object
Data Source
AI summary
The invention relates to an oscillating sensor for a measurement device comprising:an oscillator comprising:a resonance circuit for providing an oscillation signal;a gain stage configured to provide a feed-back to the resonance circuit to inject energy for excitation of the oscillator to maintain oscillation;at least one calibration element to adjust the open loop gain of the oscillator;a calibration unit to provide a modulated calibration control signal to selectively adjust an electrical measure of the at least one calibration element based on at least one predetermined duty cycle,wherein the calibration unit is further configured to provide the modulated calibration control signal with at least one cycle frequency which depends on the oscillation frequency.