This paper presents a simple, new LVDT-to-digital converter that does not require a precise sine-wave excitation or a phase-matching circuit, like the traditional methods. The scheme relies on a triangular current excitation to the primary coil, derived from a couple of dc reference voltages. A dual-slope conversion of the secondary voltages in a ratiometric manner yields a digital output that is automatically de-sensitized to extraneous variations and directly proportional to the measurand (displacement). A detailed analysis of the effect of circuit parameters on the performance of the scheme is also presented. A prototype of the proposed circuit built and tested in the laboratory gave an effective number of bits of up to 12.7 bits and a speed of 10 conversions/s. The non-linearity error noted from the tests conducted was less than 0.15%. © 2001-2012 IEEE.

Boby George

Department of Electrical Engineering

Sankaran Aniruddhan

Harikumar Ganesan

INDUCTIVE SENSORS

Phase matching

Current excitation

DIGITAL CONVERTERS

DUAL SLOPE CONVERTER

LVDT

Ratiometric

Frequency converters

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IIT Madras

A Dual Slope LVDT-to-Digital Converter

IEEE Sensors Journal

This paper presents a simple relaxation oscillator based read-out circuit for Linear Variable Differential Transformer (LVDT). The new scheme does not require precise sine wave oscillator for excitation and the associated phase matching circuits like the traditional methods. The scheme is designed to perform ratiometric computation of the sensing variables and provides an output that is proportional to the measurand, displacement. The primary and the secondary coils are integral parts of a Relaxation Oscillator (RO). The RO injects a current waveform with triangular shape through the primary. This induces a square shape waveform in the secondary coils. The RO utilizes the amplitudes of those waveforms to derive the core position and represents it as a change in duty cycle of the output signal. The PWM output lends itself to easy digitization of the displacement using an up/down counter. Or, if analog output is required, the PWM output can be passed through a low pass filter and the same can be obtained. A prototype of the proposed read-out circuit has been built and tested (a) using standard variable inductors emulating the change in the value of the inductances of an LVDT and (b) a commercially available LVDT. The worst case non-linearity error noted from the tests conducted was less than 0.3 %. © 2018 IEEE.

I2MTC 2018 - 2018 IEEE International Instrumentation and Measurement Technology Conference: Discovering New Horizons in Instrumentation and Measurement, Proceedings

A relaxation oscillator based interface circuit for LVDT

A novel read-out circuitry for Linear Variable Differential Transformers (LVDT) is presented in this paper. The proposed method avoids the use of low distortion sine wave oscillators for primary excitation and the associated phase compensation circuitry. The read-out circuit uses the secondary coil of an LVDT as part of a Colpitts oscillator along with a frequency counter to derive the position information. The proposed method also utilizes ratiometric computation for better linearity. Results of the measurements carried out for the proposed oscillator based read-out circuit are comparable to those obtained from commercially available LVDT signal conditioners. The measurements provide an accuracy of 12 bits over a 26 mm range with an update rate in excess of 4 kS/s, and a linearity error of +/- 0.17% of the Full Scale (FS). © 2017 IEEE.

I2MTC 2017 - 2017 IEEE International Instrumentation and Measurement Technology Conference, Proceedings

A simple and efficient oscillator based read-out scheme for LVDT

This paper presents a simple digitizer suitable for differential variable inductive/reluctance sensors. The proposed scheme uses two digital I/O pins, a counter and a comparator of a microcontroller and obtains a digital output directly proportional to the measurand which is sensed using a differential variable inductive/reluctance sensor possessing either a linear or an inverse transfer characteristic. The scheme uses a ratio-metric approach in the computation and hence the output is less sensitive to variation in the parameters such as excitation voltage, reference voltage, offset of the comparator, etc. A prototype of the proposed system has been built and tested using standard variable inductors that emulated a differential inductive sensor following an inverse characteristic. The output recorded was linear across the full range and worst-case error noted was less than 0.3 %. For the prototype developed, the time taken to complete a measurement was 200 μs. The prototype digitizer has been interfaced with a commercially available LVDT and tested. The worst-case error observed in this test was 0.77%. Also, the same digitizer has been employed to get a digital readout from a differential variable reluctance based displacement sensor. The worst-case error was less than 0.83%. The test results establish the efficacy of, the simple and cost effective, scheme developed. © 2015 IEEE.

Conference Record - IEEE Instrumentation and Measurement Technology Conference

A simple microcontroller based digitizer for differential inductive sensors

A new, simple, and high accuracy dual slope inductance-to-digital converter (DSIDC) suitable for differential reluctance sensors is presented in this paper. Differential reluctance sensors have two inductors that vary in a push-pull manner with respect to measurand. In many such sensors, the relationship between inductance and measurand is nonlinear. It is known that a small linear range can be obtained by taking the difference between the values of the sensor inductances. The proposed DSIDC accepts the sensor inductances having nonlinear characteristics and provides a linear digital output directly proportional to the measurand [without employing a dedicated analog-to-digital converter (ADC)]. The output of the DSIDC is linear for the full range of the sensor. As the output is in digital form, it can be easily stored and processed in a digital system. The DSIDC is based on dual-slope ADC principle and possesses many advantages. The effect of various parameters on the performance of the DSIDC was analyzed, quantified, and presented in this paper. A prototype DSIDC has been built and tested with a differential variable reluctance based displacement transducer. Output from the DSIDC was linear for the full range of input. © 1963-2012 IEEE.

IEEE Transactions on Instrumentation and Measurement

Design and analysis of a dual-slope inductance-to-digital converter for differential reluctance sensors

Timer-Based Demodulator for AM Sensor Signals Applied to an Inductive Displacement Sensor

Journal	Data powered by TypesetIEEE Sensors Journal
Publisher	Data powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
ISSN	1530437X
Open Access	No