Inductive Displacement Sensor Measurement Method Using Synchronous Demodulation
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Solution Overview
Problem
Inductive displacement sensors, such as LVDTs, face challenges in achieving fast and precise position measurement due to high response times and increased gain errors, particularly when using multiple acquisition chains or being sensitive to environmental noise.
Innovation Solution
A measurement method involving alternating excitation and digitization of voltages across secondary windings, with processing phases that include multiplication by reference sine and cosine, integration, and calculation of amplitudes to estimate core position, allowing for sliding synchronous demodulation and robust noise resistance using a single analog-digital converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If two distinct acquisition chains are used to acquire and digitize measurement voltages simultaneously, then the measurement response time is reduced to close to one excitation period, but the gain error is increased
Solution Approach 1:
The patent merges the acquisition of both measurement voltages into a single acquisition chain, using one analog-to-digital converter to sequentially sample both voltages during the same excitation period. This eliminates the gain error associated with using two separate converters while maintaining fast response time through efficient time-multiplexed sampling and processing
2Measurement precision
If a single analog-to-digital converter is used to acquire both measurement voltages, then the gain error is reduced, but the measurement response time increases to greater than two excitation periods
Solution Approach 1:
The patent performs preliminary processing of the sampled voltage data through synchronous demodulation and integration during the same excitation period in which the samples are acquired. By completing the calculation of both measurement voltages and their ratio within one excitation period, the system achieves fast response time while using a single converter
Solution Approach 2:
The patent uses periodic excitation of the transformer primary winding at a determined frequency, and performs synchronous demodulation of the secondary voltages at the same frequency. This periodic action allows efficient extraction of amplitude information from the sampled voltages, enabling fast processing with a single converter
3Device complexity
If asynchronous demodulation is used to process measurement voltages, then the acquisition can be simplified, but the system becomes more sensitive to environmental noises
Solution Approach 1:
The patent implements synchronous demodulation that uses the known excitation frequency as a reference to process the measurement voltages. This frequency-locked processing method provides inherent noise rejection by correlating the measurement signals with the excitation frequency, eliminating environmental noise at other frequencies while maintaining acquisition simplicity
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 method reduces response time, increases measurement refresh rate, and eliminates gain errors associated with multiple converters while being robust to environmental noise, simplifying the acquisition chain.
Implementation Method 1
The transformer comprises a primary winding 3, a first secondary winding 4 and a second secondary winding 5. An excitation voltage Ve is applied to the terminals of the primary winding 3... A first measurement voltage Va is measured across the terminals of the first secondary winding 4 and a second measurement voltage Vb across the terminals of the second secondary winding 5
Implementation Method 2
The magnetic core 2 slides axially in the cylindrical body and thus modifies the distribution of the magnetic field which prevails in said cylindrical body
Data Source
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AI summary
A measurement method using an inductive displacement sensor (1) that comprises a transformer and a magnetic core (2), the transformer comprising a primary winding (3) and two secondary windings (4, 5), the measurement method comprising: - an excitation phase; - an acquisition phase; - a first main processing phase implemented at two measurements voltages and comprising the steps, for each measurement voltage, of: multiplying the measurement voltage by a reference sine function and by a reference cosine function; carrying out a first integration of each resulting signal on a sliding window having a width equal to the excitation period; carrying out a second integration of each integrated signal on a sliding window having a width equal to an excitation half-period; producing an amplitude of the measurement voltage; - a first final processing phase comprising the step of producing an estimation of a position of the magnetic core.