A Linearizing Digitizer for Wheatstone Bridge Based Signal Conditioning of Resistive Sensors
TL;DR: A novel signal conditioning scheme, which provides a linear-digital output directly from the resistive sensor(s) that are connected in such bridge configurations, and drastically reduces the effect on the output due to the lead wires that connect the Wheatstone bridge and the DSADC.
Abstract: Output of a typical Wheatstone bridge, when it is connected to measure from a single or a dual resistive element, possesses non-linear characteristic. This paper presents a novel signal conditioning scheme, which provides a linear-digital output directly from the resistive sensor(s) that are connected in such bridge configurations. In the present scheme, the input stage of a dual-slope analog-to-digital converter (DSADC) is suitably augmented to incorporate the quarter-bridge and (or) half-bridge containing the resistive sensor as an integral part of the DSADC. A combination of the current mode excitation and wisely selected integration and de-integration operations of the DSADC enable to achieve linearization in the digitization process itself, leading to an overall reduction in the complexity level and number of blocks used keeping the high accuracy unaltered. A detailed analysis has been conducted to quantify the effect of various sources of errors in the output of the DSADC. The details are presented in the paper. The proposed method not only provides a linear digital output but also drastically reduces the effect on the output due to the lead wires that connect the Wheatstone bridge and the DSADC. Thus, the proposed scheme is well suited for the situations where the sensor(s) is (are) remotely located at a distance. Simulation studies as well as results from a prototype developed and tested establish the practicality of the proposed scheme. The inherent non-linearity of the Wheatstone bridge is reduced by nearly two orders of magnitude.
Citations
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TL;DR: This paper presents a review of different methods applied to linearize sensor characteristics reported in the literature and concludes that the digital methods combined with software techniques perform the job with better flexibility and efficiency.
Abstract: Today, the sensing devices play an important role for various system automation and monitoring of different physical and chemical parameters. Nonlinearity is an important long-time issue for most of the sensors, so to compensate nonlinearity, various linearization schemes are reported in the literature. The accuracy of linearization schemes depends on the type and the nonlinearity value of the sensor output. Since it is difficult to find an exact polynomial equation or other functions to represent the response curve; it gives more error when the measurement parameter is determined from the inverse approximation functions. As many sensors are used for different applications, the linearized characteristics will simplify the design, calibration, and accuracy of the measurement. This paper presents a review of different methods applied to linearize sensor characteristics reported in the literature. Due to availability of high-performance analog devices, analog methods are still popular among many researchers. However, due to the advancement of IC technologies, hardware implementation of the software methods can be done easily with reduced time, cost, and more accuracy, so the digital methods combined with software techniques perform the job with better flexibility and efficiency.
19 citations
Cites background or methods from "A Linearizing Digitizer for Wheatst..."
...…necessary signal conditioning circuits have been employed to linearize the response of thermistor, Hall effect sensor, and single or double resistive element Wheatstone bridge (Mohan et al., 2008; Mohan et al., 2011; Sreekantan and George, 2014; Ramadoss and George, 2015; Nagarajan et al., 2017)....
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...Recently, conventional dual slope analog to digital converter with necessary signal conditioning circuits have been employed to linearize the response of thermistor, Hall effect sensor, and single or double resistive element Wheatstone bridge (Mohan et al., 2008; Mohan et al., 2011; Sreekantan and George, 2014; Ramadoss and George, 2015; Nagarajan et al., 2017)....
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...(Nagarajan et al., 2017) Dual slope ADC for direct interface to μC (quarter/half bridge resistive sensors) <0....
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TL;DR: This article proposes simple relaxation-oscillator-based digital interfacing schemes for resistive sensors in single-element and quarter-bridge forms, equipped with novel compensation techniques, that render a direct-digital output proportional to sensor resistance.
Abstract: This article proposes simple relaxation-oscillator-based digital interfacing schemes for resistive sensors in single-element and quarter-bridge forms. The proposed interfaces, equipped with novel compensation techniques, render a direct-digital output proportional to sensor resistance. These interfaces offer many meritorious features, such as simplicity of design, nonrequirement of the reference voltage, lower execution time, and negligible influences from circuit nonidealities. The methodology of the interfaces and their design criteria and error analysis are described in this article. The first two interfaces are suitable for nonremote resistive sensors, while the third interface has been developed for remotely located resistive sensors. The functionality of the proposed interfaces has been verified using simulation as well as detailed experimental studies. The developed interfaces provide a linear direct-digital output, and the maximum experimental nonlinearity is merely 0.08%. Later, a representative sensor based on the giant magnetoresistance (GMR) phenomenon is selected, characterized, and tested with the developed interfaces. The complete instrumentation system is shown to act as a linear digital magnetometer. Finally, the performance of the developed interfaces is compared and shown to be better/comparable with respect to the existing works.
14 citations
Cites background from "A Linearizing Digitizer for Wheatst..."
...However, these schemes require precision (matched) reference voltages and works in [11] need an additional phase to start the conversion....
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...Alternatively, the work in [11] makes the output independent of wire resistance using instrumentation amplifier (IA) and an involved switching logic....
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...Simple dual-slope-based circuits for different types of resistive sensors are reported in [10] and [11]....
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...A number of digital techniques, such as pulsewidth conversion [7]–[9], dual slope [10], [11], direct microcontroller interfacing [12]–[15], sigma-delta [16], and relaxation oscillator [17]–[21], are prevalent for resistive sensors....
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TL;DR: Analog signal conditioning circuit based on dual differential subtractor for wide range resistive measurement of single element resistive sensor is presented in this paper, which helps to achieve high accuracy and wide dynamic range by generating a control voltage proportional to the sensor resistance.
Abstract: Analog signal conditioning circuit based on dual differential subtractor for wide range resistive measurement of single element resistive sensor is presented in this paper. The differential output from the sensor and a voltage-controlled reference resistor is followed by an auto-nulling technique, which helps to achieve high accuracy and wide dynamic range by generating a control voltage proportional to the sensor resistance. The presented automatic approach not only enhances the auto-nulling range but also ensures constant sensitivity. The interface design provides high accuracy, fast and linear response at the same time avoids drawbacks of lead wire variations. A prototype PCB of the proposed circuit is fabricated and tested. The experimental result shows that the circuit can measure a wide range of resistance (20 $\text{k}\Omega $ - 1.1 $\text{M}\Omega$ ) with relative error less than 0.78%, compared to other bridge-based circuits which are capable of measuring the maximum resistance of up-to 10 $\text{k}\Omega $ for the same accuracy. Multiple variations of the proposed circuit are designed and experimentally tested for verifying the tunability of the circuit in terms of the sensitivity and the range of resistance measurement. The prototype circuit is also interfaced with an in-house fabricated MEMS-based ammonia sensor, proving its efficacy in resistive sensor system development.
13 citations
Cites background from "A Linearizing Digitizer for Wheatst..."
...To handle these dynamic properties robust signal conditioning circuits are required [8], [9]....
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...However, the Wheatstone bridge is not preferable for single elements resistive sensors due to high non-linearity [1], [9]....
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TL;DR: A fully analog method has been introduced in order to implement a null measurement instrument for a resistive Wheatstone bridge with a single resistive sensor to evaluate the performance and usefulness of the proposed method.
Abstract: When high-speed measurements are not necessary, the Wheatstone bridge-based null measurement instruments surpass the Wheatstone Bridge-based instruments using deflection technique, due to the fact that the null method has some intrinsic advantages over the deflection method. In this particle, a fully analog method has been introduced in order to implement a null measurement instrument for a resistive Wheatstone bridge with a single resistive sensor. In order to implement the proposed circuit, only two operational amplifiers and some passive elements have been used. The proposed method can be constructed and implemented by discrete components without any special limitation. Since the suggested scheme has linear output, the required computation in order to measure and display the measurand is reduced dramatically. Finally, in order to evaluate the performance and usefulness of the proposed method, it has been tested experimentally as well as by using computer aided design software.
12 citations
TL;DR: In this work, excellent characteristics of LT199x selectable gain amplifiers are exploited to precisely divide an input current, and an excellent linearity is found with a relative error within ±0.1% after a preliminary calibration procedure.
Abstract: Highly accurate and stable current references are especially required for resistive-sensor conditioning. The solutions typically adopted in using resistors and op-amps/transistors display performance mainly limited by resistors accuracy and active components non-linearities. In this work, excellent characteristics of LT199x selectable gain amplifiers are exploited to precisely divide an input current. Supplied with a 100 µA reference IC, the divider is able to exactly source either a ~1 µA or a ~0.1 µA current. Moreover, the proposed solution allows to generate a different value for the output current by modifying only some connections without requiring the use of additional components. Experimental results show that the compliance voltage of the generator is close to the power supply limits, with an equivalent output resistance of about 100 GΩ, while the thermal coefficient is less than 10 ppm/°C between 10 and 40 °C. Circuit architecture also guarantees physical separation of current carrying electrodes from voltage sensing ones, thus simplifying front-end sensor-interface circuitry. Emulating a resistive-sensor in the 10 kΩ–100 MΩ range, an excellent linearity is found with a relative error within ±0.1% after a preliminary calibration procedure. Further advantage is that compliance voltage can be opposite in sign of that obtained with a passive component; therefore, the system is also suitable for conditioning active sensors.
12 citations
Cites methods from "A Linearizing Digitizer for Wheatst..."
...Several linearization techniques have been reported, as the Current Mode WB [11], switches driven integration/deintegration method [12], and the double differential potential subtractor [13]....
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References
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TL;DR: This paper presents a general concept for the linearization of impedance bridges with circuit components changing in only one polarity, and a feedback loop using a transadmittance amplifier reduces nonlinearity from 9% to 0.4% over plusmn20% of bridge imbalance.
Abstract: This paper presents a general concept for the linearization of impedance bridges with circuit components changing in only one polarity. A feedback loop using a transadmittance amplifier, which is properly designed and matched to the nominal value of the bridge components, reduces nonlinearity from 9% to 0.4% over plusmn20% of bridge imbalance. The method can be applied for dc or ac bridges, and the linearization can conveniently be integrated with the readout circuit, resulting in a highly linear sensor readout. In addition to the linearization of the bridge transfer function itself, the method can be applied for the linearization of a range of transducers with a hyperbolic transfer function
18 citations
"A Linearizing Digitizer for Wheatst..." refers background or methods in this paper
...Output of the methods presented in [7]–[9], [17], [18] and [33] suffer from lead wire resistance and its variation due to temperature....
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...In (1), VB is the excitation for the bridge and kB is the bridge constant (kB = 4; quarter-bridge and kB = 2; half-bridge) Equation (1) clearly shows that the bridge output VoB will be a non-linear function of the measurand [3]–[6], and the transfer function of these bridge configurations will be a hyperbolic function [7]....
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Journal Article•
20 Oct 2011-World Academy of Science, Engineering and Technology, International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering
TL;DR: In this paper, a new circuit arrangement for a current-mode Wheatstone bridge that is suitable for low-voltage integrated circuits implementation is presented, which features severe reduction of the elements number, low supply voltage (1V) and low power consumption (<350uW).
Abstract: This paper presents a new circuit arrangement for a current-mode Wheatstone bridge that is suitable for low-voltage integrated circuits implementation. Compared to the other proposed circuits, this circuit features severe reduction of the elements number, low supply voltage (1V) and low power consumption (<350uW). In addition, the circuit has favorable nonlinearity error (<0.35%), operate with multiple sensors and works by single supply voltage. The circuit employs MOSFET transistors, so it can be used for standard CMOS fabrication. Simulation results by HSPICE show high performance of the circuit and confirm the validity of the proposed design technique. Keywords—Wheatstone bridge, current-mode, low-voltage, MOS.
15 citations
"A Linearizing Digitizer for Wheatst..." refers methods in this paper
...of using current driven Wheatstone bridge and its variants are discussed in [10]–[13]....
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...source [11]–[13], leading to a complex configuration....
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01 Nov 2008
TL;DR: This article proposes a topology of current-mode improved Wheatstone bridge based on dual-output current differencing transconductance amplifier (DO-CDTA) that shows good agreement to theoretical anticipation and provide ability to measure small resistance changes at a wide range of frequency.
Abstract: This article proposes a topology of current-mode improved Wheatstone bridge based on dual-output current differencing transconductance amplifier (DO-CDTA). The features of the proposed configuration are that: magnitude of output signal can be controlled via the input bias currents; the proposed circuit is low temperature sensitive, the circuit description is very simple. The circuit performances are depicted through PSPICE simulations, they show good agreement to theoretical anticipation and provide ability to measure small resistance changes at a wide range of frequency (more than 60 MHz). The power consumption is approximately 4.55 mW at ~1.5 V supply voltages.
15 citations
TL;DR: In this article, a circuit for lead resistance compensation and complex balancing of the 1/4 and 1/2, AC or DC excited bridges is described, and it is possible to add this circuit in front of the instrumentation already in use.
Abstract: In some specific applications, the strain-gauge bridge branches are separated and remote. Lead resistances between bridge branches and the measuring instrument introduce significant measurement error. The well-known error compensating circuits do not suit all applications, or they cannot be added to the already existing instrumentation without modification of its internal circuits. A circuit for lead resistance compensation and complex balancing of the 1/4 and 1/2, AC or DC excited bridges is described. It is possible to add this circuit in front of the instrumentation already in use with no modification of the instrumentation itself. >
14 citations
TL;DR: Test results show that the output of the overall transducer is linear across a wide range of angles, and thus underline the efficacy of the proposed scheme for differential type sensors with third-order transfer characteristics.
Abstract: This paper presents a new linearizing digital converter (LDC) that accepts output from differential type sensors with third-order polynomial transfer characteristics and provides a linear digital output proportional to the measurand. The LDC is realized using a modified dual-slope converter. Detailed operation of the proposed LDC, design procedure, and analysis of the effect of various circuit parameters on performance of the LDC are presented in this paper. The proposed methodology of LDC is also extended for sensors with second-order polynomial characteristics. The functionality of the LDC has been verified with the help of simulation studies. A prototype LDC has been developed and interfaced with a novel reluctance-Hall effect-based angle sensor (having a third-order characteristic) and tested. Test results show that the output of the overall transducer is linear across a wide range of angles, and thus underline the efficacy of the proposed scheme for differential type sensors with third-order transfer characteristics.
14 citations
"A Linearizing Digitizer for Wheatst..." refers background or methods in this paper
...The output of the sensors needs to be push-pull in nature to apply the scheme in [22]....
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...A linearizing digitizer has been reported in [22], for obtaining a linear digital output from two sensing elements that follow a polynomial characteristic....
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...This approach [22] is not useful in the case of quarter-bridge as these criteria are not satisfied....
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