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Design and Analysis of a Relaxation Oscillator-Based Interface Circuit for LVDT
Harikumar Ganesan, ,
Published in Institute of Electrical and Electronics Engineers Inc.
2019
Volume: 68
   
Issue: 5
Pages: 1261 - 1270
Abstract
This paper presents a simple, novel interfacing scheme for linear variable differential transformer (LVDT) that does not require a precise sine wave oscillator (with stable amplitude and frequency) for excitation or any phase matching circuit like traditional methods. The primary and the secondary coils of the LVDT are integral parts of a relaxation oscillator (RO). The RO injects a current waveform with a triangular shape through the primary coil which in turn induces a square-shaped voltage waveform in the secondary coils. The RO utilizes the amplitudes of those waveforms and generates a pulsewidth modulation (PWM) output signal whose duty cycle ratio is proportional to the measurand, core position. This quasi-digital PWM signal is passed through a low-pass filter to obtain an analog output. PWM time period measurement using a counter yields a digital output. This method guarantees good stability since the output is dependent only on a pair of dc reference voltages apart from the transformation constant of the sensor. A detailed analysis of the sources of error, their effect on the performance of the scheme and appropriate design choices for error mitigation are also presented. A prototype of the proposed circuit was built and tested in the laboratory. The nonlinearity error noted from the tests conducted was less than 0.16% for the analog output and 0.18% for the digital output. A resolution of up to 11 bits was achieved for the digital output. © 2018 IEEE.
About the journal
JournalData powered by TypesetIEEE Transactions on Instrumentation and Measurement
PublisherData powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
ISSN00189456
Open AccessNo
Concepts (12)
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    Errors
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    INDUCTIVE SENSORS
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    Low pass filters
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    Phase matching
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    Pulse width modulation
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    Timing circuits
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    Current excitation
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    Interface circuits
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    LINEAR POSITIONS
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    LINEAR VARIABLE DIFFERENTIAL TRANSFORMER
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    Ratiometric
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    RELAXATION OSCILLATORS