Modification of the Maxwell–Wien Bridge for Accurate Measurement of a Process Variable by an Inductive Transducer
01 Sep 2010-IEEE Transactions on Instrumentation and Measurement (IEEE)-Vol. 59, Iss: 9, pp 2445-2449
TL;DR: A modified operational-amplifier-based Maxwell-Wien bridge measurement technique has been proposed in which the effect of stray capacitance and inductance is minimized and linear characteristics over a wide range of displacement with good repeatability, linearity, and variable sensitivity have been described.
Abstract: The small inductance of an inductive transducer generally linearly changes with a process variable, but their measurement by the usual inductive bridge circuit like the Maxwell bridge, the Maxwell-Wien Bridge, the Hay bridge, etc., suffers from errors due to the effect of the stray capacitance between bridge nodal points and the ground and the stray inductance on the inductive coil, respectively. The conventional Wagner-Earth technique is not suitable for continuous measurement. In this paper, a modified operational-amplifier-based Maxwell-Wien bridge measurement technique has been proposed in which the effect of stray capacitance and inductance is minimized. In the first phase of the experiment, the bridge performance has been studied with a known variable inductor, and in the second phase, the same experimentation was done by replacing the variable inductor with an inductive coil having an adjustable core position for the measurement of displacement. The linear characteristics over a wide range of displacement with good repeatability, linearity, and variable sensitivity have been described.
Citations
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TL;DR: In this article, a microcontroller-based interface circuit for inductive sensors with a variable self-inductance was proposed and analyzed, where the circuit just requires an external resistor and a reference inductor so that two RL circuits are formed.
Abstract: This paper proposes and analyses a microcontroller-based interface circuit for inductive sensors with a variable self-inductance. Besides the microcontroller (μC) and the sensor, the circuit just requires an external resistor and a reference inductor so that two RL circuits are formed. The μC appropriately excites such RL circuits in order to measure the discharging time of the voltage across each inductor (i.e. sensing and reference) and then it uses such discharging times to estimate the sensor inductance. Experimental tests using different commercial μCs at different clock frequencies show the limitations (especially, due to parasitic resistances and quantisation) and the performance of the proposed circuit when measuring inductances in the millihenry range. A non-linearity error lower than 0.3% full-scale span (FSS) and a resolution of 10 bits are achieved, which are remarkable values considering the simplicity of the circuit.
43 citations
Cites background from "Modification of the Maxwell–Wien Br..."
...In the previous applications [3,4,6,7], the sensor inductance is in the range of units or tens of millihenry, but lower values (e....
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...The second type is an AC-excited bridge (such as the Maxwell bridge [6] or the Maxwell-Wien bridge [3]) providing an amplitude-modulated signal that needs to be demodulated and digitized before being read by the digital system....
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...of ±1 mm [2], ±5 mm [3] and ±6 mm [4]), position (e....
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...Furthermore, the sensor is expected to have an inductance of some units or tens of millihenry [3,4,6,7]; lower values of inductance would require a very high speed reference oscillator that is not feasible nowadays in common low-cost 8-bit microcontrollers....
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TL;DR: A new, simple, and high accuracy dual slope inductance-to-digital converter (DSIDC) suitable for differential reluctance sensors is presented and can be easily stored and processed in a digital system.
Abstract: 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.
29 citations
Cites background from "Modification of the Maxwell–Wien Br..."
...Some signal conditioning schemes suitable for inductive sensors have been presented in [8]–[11]....
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11 May 2015
TL;DR: This paper presents a simple digitizer suitable for differential variable inductive/reluctance sensors that uses a ratio-metric approach in the computation and hence the output is less sensitive to variation in the parameters.
Abstract: 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.
27 citations
Cites background from "Modification of the Maxwell–Wien Br..."
...The quazi-balanced [9] and modified Maxwell-Wien bridge [10] schemes are examples of such improvements....
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TL;DR: An optimal design method for the inductive angle sensor is proposed based on the response surface methodology and Maxwell finite element method and the optimal parameters of the sensor are determined by finding the minimum value of the responsesurface model.
27 citations
TL;DR: In this paper, an artificial neural network (ANN)-based improved inductive signal conditioning circuit for pressure transducers with a bellow as a sensor is presented, where the ANN modeling estimates and compensates the nonlinearity of OISCC.
Abstract: This paper presents the development of an artificial neural network (ANN)-based improved inductive signal conditioning circuit for pressure transducer with bellow as sensor. A bellow is an elastic-type mechanical pressure sensor. The deflection of the bellow due to applied pressure must be translated into an efficient electrical signal for continuous monitoring, wireless transmission, and digital readout. A ferromagnetic wire attached to the bellow as a part of an inductive coil arrangement, gets deflected due to applied pressure, thereby changing the self inductance of the coil. An op-amp inductive signal conditioning circuit (OISCC) is designed to produce voltage proportional to changes in self-inductance, but the OISCC voltage versus applied pressure exhibits a considerable nonlinearity error due to stray inductances and component drifts. The ANN modeling estimates and compensates the nonlinearity of OISCC. An embedded unit is used for implementation of ANN learning process. The pressure transducer with significant stability has exhibited high linearity and sensitivity of ±0.35% and 10 mH/psig, respectively, in the measuring range of 0–70 psig. The design and experimental aspects of the technique are reported.
16 citations
Cites methods from "Modification of the Maxwell–Wien Br..."
...A modified Maxwell-Wien bridge for measurement of displacement based on inductance change has been developed in which the effect of stray capacitance and inductance are minimized [10]....
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References
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133 citations
"Modification of the Maxwell–Wien Br..." refers methods in this paper
...To minimize these errors, different types of balancing techniques along with some special techniques like the Wagner–Earth technique [4], [5] have been proposed by various investigators....
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TL;DR: In this paper, the authors present a systematic, complete, and consistent presentation of the technological innovations, recent implementations and current trends regarding the analog distance and travel sensing offered by noncontacting inductive sensors for industrial applications.
Abstract: Noncontacting inductive sensors are applicable on a large scale for position detection or travel measurement in industrial applications. Reasons for such broad acceptance in many sectors of industry are noncontact and wear-free sensing of the target (any metal object), reliability and robustness, resistance to fouling, water tightness and compact size. The present work is intended to be a systematic, complete, and consistent presentation of the technological innovations, recent implementations and current trends regarding the analog distance and travel sensing offered by noncontacting inductive sensors for industrial applications. It starts with the fundamentals of inductive sensing and presents the physical basics gained by modern analytic and simulation methods, as well as high-level integrated circuits for inductive sensors. The following sections deal with present-day inductive analog proximity sensors and with the distinctive technological innovation offered by the new inductive linear displacement sensors and with miniaturization results achieved through consistent integration.
112 citations
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TL;DR: In this article, electrical measurements and measuring instruments, Electrical measurements and measurement instruments, electrical measurement and measuring instrument, Electrical measurement and measurement instrument, electrical measurements, measuring instruments and measuring devices.
Abstract: Electrical measurements and measuring instruments , Electrical measurements and measuring instruments , کتابخانه دیجیتالی دانشگاه علوم پزشکی و خدمات درمانی شهید بهشتی
96 citations
TL;DR: In this article, a new algorithm based on spatial Discrete Fourier Transform (DFT) capable of calculating the current to be measured is presented, which can be implemented by a DSP that processes output signals of solid state magnetic sensors forming a circular array centred in the current conductor.
Abstract: Solid state magnetic sensors can measure a current by sensing the field near the conductor. Means are required to distinguish between useful and interference fields and that are those of conductors near the current under measurement and environmental fields. Starting from analytical expressions of the magnetic field, spatial harmonic analysis is performed. It is then possible to separate the effects of the field generated by the current under measurement from those of interference fields. A new algorithm based on spatial Discrete Fourier Transform (DFT) capable of calculating the current to be measured is presented. The algorithm can be implemented by a DSP that processes output signals of solid state magnetic sensors forming a circular array centred in the current conductor.
69 citations
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...capacitance and resistance in the opposite arm, the crosstalk errors [13]‐[ 15 ] between the coil and the outside magnetic field may be assumed to be eliminated by the balancing capacitor....
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10 May 1994
TL;DR: In this paper, an automatic method for bridge circuit balancing, based on a digital control signal, is presented, which can be used in many situations, e.g. due to electrical interference between the bridge circuit and the human body or some mechanical part of the screwdriver used.
Abstract: Conventional bridge circuits are balanced by means of mechanical changes of trimming capacitances and resistances. It is a well known fact that this can be very difficult in many situations, e.g. due to electrical interference between the bridge circuit and the human body or some mechanical part of the screwdriver used. There may also be physical constraints prohibiting mechanical changes of some bridge elements. To avoid these problems, the balancing procedure should be automatized. In this article an automatic method for bridge circuit balancing, based on a digital control signal, is presented. Ordinary ac-bridge circuits are nonlinear with respect to changes of the capacitive sensor element. Using some standard operational amplifiers it is easy, however, to obtain a linear bridge circuit output. A theoretical model of the linear bridge circuit is derived. The excellent performance of the linear bridge circuit predicted by theory is verified by practical experiments. >
64 citations
"Modification of the Maxwell–Wien Br..." refers methods in this paper
...Takagishi [11] has reported modified approaches of the balancing technique of an ac Wheatstone bridge network, whereas Saxena and Saleem [10] and Holmberg [6] have proposed a self-balancing technique for achieving high accuracy in measurement....
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