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.
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TL;DR: In this paper , a three-level pulse signal is used to excite the RTD via the long lead wire to compensate for the variation in the lead-wire resistance disturbed by the change in the ambient temperature.
Abstract: A procedure for the precise determination and compensation of the lead-wire resistance of a resistance transducer is presented. The proposed technique is suitable for a two-wire resistance transducer, especially the resistance temperature detector (RTD). The proposed procedure provides a technique to compensate for the lead-wire resistance using a three-level pulse signal to excite the RTD via the long lead wire. In addition, the variation in the lead-wire resistance disturbed by the change in the ambient temperature can also be compensated by using the proposed technique. The determination of the lead-wire resistance from the proposed procedure requires a simple computation method performed by a digital signal processing unit. Therefore, the calculation of the RTD resistance and the lead-wire resistance can be achieved without the requirement of a high-speed digital signal processing unit. The proposed procedure is implemented on two platforms to confirm its effectiveness: the LabVIEW computer program and the microcontroller board. Experimental results show that the RTD resistance was accurately acquired, where the measured temperature varied from 0 °C to 300 °C and the lead-wire resistance varied from 0.2 Ω to 20 Ω, corresponding to the length of the 26 American wire gauge (AWG) lead wire from 1.5 m to 150 m. The average power dissipation to the RTD was very low and the self-heating of the RTD was minimized. The measurement error of the RTD resistance observed for pt100 was within ±0.98 Ω or ±0.27 °C when the lead wire of 30 m was placed in an environment with the ambient temperature varying from 30 °C to 70 °C. It is evident that the proposed procedure provided a performance that agreed with the theoretical expectation.
3 citations
TL;DR: In this paper , two sigma-delta modulation-based direct-digital converters (DDCs) for single-element resistive sensors have been proposed, which produce linear digital output without using a separate analog-to-digital converter.
Abstract: This work proposes the design and performance studies of two sigma-delta modulation-based direct-digital converters (DDCs) for single-element resistive sensors. Both the interfaces produce linear digital output, without using a separate analog-to-digital converter. The first of the two designs is a simple direct-digital interface that can be used in all applications where the lead wires, connecting the sensor element to the modulator interface, possess negligible resistance. The second DDC circuit is an enhanced version of the first design and produces digital output, independent of error due to lead-wire resistance. Thus, this improved modulator interface can be efficiently used in remote measurement applications. Moreover, both interfaces possess further useful features, such as output-span enhancement facility, fast conversion rate, use of single regulated voltage source, and relatively low implementation cost. Performances of the proposed interfaces are studied comprehensively through simulation and experimental validation. The maximum experimental nonlinearities, in the two designs, are found to be around 0.25%. This proves the primary efficacy of the schemes in producing linear output characteristics. Moreover, the enhanced sigma-delta digitizer exhibits a maximum error of just 0.1% for variations in lead-wire resistance. A detailed comparison study brings out efficacies of the proposed interfaces.
3 citations
01 Jul 2022
TL;DR: In this paper , an improved resistance to digital converter (RDC) for low-value resistive sensors with lead resistance compensation is presented. But the proposed scheme is based on the dual-slope ADC with three switches and a diode.
Abstract: Improved resistance to digital converter (RDC) for a low-value resistive sensor with lead resistance compensation is presented. The proposed scheme is based on the dual-slope ADC with three switches and a diode. It completes measurement in one charging-discharging cycle only, hence it provides improvement to existing RDCs, where lead compensation is not available. Moreover, it is faster compared to existing direct microcontroller interfaces (DMI) where 2 or 3 charging-discharging cycles are required. The scheme works by connecting the resistive sensor to the input terminal of the integrator of the dual-slope ADC. In the charging path (or mode), sensor resistance is present along with lead resistance; and in discharging path, sensor resistance is bypassed, and only lead resistance is there. The difference between the RC time constant during these two modes is used to find the sensor resistance. The diode is used to turn on a switch for bypassing the resistive sensor. The diode voltage drop is not there in the charging and discharging path, which is another novelty. The scheme works with low-value resistive sensors (≈ 100 Ω), a feature not found in existing RDCs. The hardware prototype of the proposed scheme on the breadboard shows a maximum error of ±0.87 % in the range of 100 Ω to 180 Ω.
3 citations
TL;DR: In this paper , the authors reviewed various types of gas sensors and interface circuits implemented with different technologies, analyzes their research significance in various areas, and provides ideas for future gas sensor research directions.
Abstract: With the development of science and technology, gas sensors have gradually expanded to many vertical fields. However, each application requires different technical requirements for gas sensors, such as low cost, small size, high sensitivity, high precision, and low power consumption. To create gas sensors that meet the performance requirements, researchers worldwide are working on solutions in fields such as sensitive materials, sensor arrays, and interface circuits. However, there are bottlenecks in the research of interface circuits, which limits the volume, power consumption, and intelligent design development of gas sensors. Therefore, this article reviews various types of gas sensors and interface circuits implemented with different technologies, analyzes their research significance in various areas, and provides ideas for future gas sensor research directions.
3 citations
TL;DR: Various types of gas sensors and interface circuits implemented with different technologies are reviewed, their research significance in various areas is analyzed, and ideas for future gas sensor research directions are provided.
Abstract: With the development of science and technology, gas sensors have gradually expanded to many vertical fields. However, each application requires different technical requirements for gas sensors, such as low cost, small size, high sensitivity, high precision, and low power consumption. To create gas sensors that meet the performance requirements, researchers worldwide are working on solutions in fields such as sensitive materials, sensor arrays, and interface circuits. However, there are bottlenecks in the research of interface circuits, which limits the volume, power consumption, and intelligent design development of gas sensors. Therefore, this article reviews various types of gas sensors and interface circuits implemented with different technologies, analyzes their research significance in various areas, and provides ideas for future gas sensor research directions.
3 citations
References
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01 Jan 1999
105 citations
"A Linearizing Digitizer for Wheatst..." refers background in this paper
...1(b) is useful, when two sensing elements of same type are employed to achieve higher sensitivity [3]....
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...sensor may be located far from the measurement unit and the lead resistance of the wires will introduce appreciable errors in the measurement [3]....
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...Magneto Resistance (GMR) sensors, pressure sensors and flow meters [3]–[6]....
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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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...Various linearization techniques have been reported to obtain a final linear output, from the bridge [3], [8], [9]....
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TL;DR: A dual-slope capacitance-to-digital converter that operates on the elements of a differential capacitive sensor and provides a digital output that is linearly proportional to the physical quantity being sensed by the sensor is presented and analyzed in this paper.
Abstract: A dual-slope capacitance-to-digital converter (CDC) that operates on the elements of a differential capacitive sensor and provides a digital output that is linearly proportional to the physical quantity being sensed by the sensor is presented and analyzed in this paper. The converter topology is so chosen that a linear digital output is obtained for not only a sensor possessing linear input-output characteristics but also a sensor possessing inverse characteristics. The digital output in the proposed converter is dependent only on, apart from the sensitivity of the sensor, a dc reference voltage. Hence, high accuracy and linearity are easily obtained by employing a precision dc reference. Since the proposed CDC is based on the popular dual-slope analog-to-digital converter structure, it possesses all the advantages (resolution, accuracy, and immunity to noise and component parameter variations) and limitations (requirement of auto-zero and low conversion speed) applicable to the dual-slope technique. A prototype built and tested for a typical differential capacitive sensor with a nominal capacitance value of 250 pF gave a worst-case error of less than 0.05%.
58 citations
"A Linearizing Digitizer for Wheatst..." refers methods in this paper
...As in a typical dual slope technique, here too, to initiate a conversion, the digitizer has to invoke an auto-zero phase to set the output to zero [26]....
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TL;DR: In this article, the authors proposed a direct connection of different configurations of resistive sensor bridges to a microcontroller without any intermediate active component, which relies on measuring the discharging time of a RC network that includes the resistances of the sensor bridge.
Abstract: This paper proposes the direct connection of different configurations of resistive sensor bridges to a microcontroller without any intermediate active component. Such a direct interface circuit relies on measuring the discharging time of a RC network that includes the resistances of the sensor bridge. For quarter-, half-, and full-bridge circuits, we combine the discharging times to estimate the fractional resistance change x of the bridge arms. Experimental results for half- and full-bridge circuits emulated by resistors yield a nonlinearity error below 0.3%FSR (full-scale range) for x between 0 and 0.1 and an effective resolution of 11 bit. Measurements on two commercial magnetoresistive sensors yield higher nonlinearity errors: 1.8%FSR for an AMR (Anisotropic Magnetoresistive) sensor and 5.8%FSR for a GMR (Giant Magnetoresistive) sensor, which are mainly due to the nonlinearity of the sensors themselves. Therefore, the nonlinearity of the measurement is limited by the sensors, not by the proposed interface circuit and linearisation algorithm.
54 citations
"A Linearizing Digitizer for Wheatst..." refers methods in this paper
...Some of the methods proposed earlier for quarter-bridge configurations use an internal comparator and counter of a microcontroller and requires three charging and discharging periods [19], [20]....
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TL;DR: In this article, an easily implementable signal conditioning circuit for resistive humidity and temperature sensors is presented based on a relaxation oscillator in which both the frequency and the duty-cycle of the square-wave output signal simultaneously carry information from two different types of sensors.
Abstract: An easily implementable signal conditioning circuit for resistive humidity and temperature sensors is presented. It is based on a relaxation oscillator in which both the frequency and the duty-cycle of the square-wave output signal simultaneously carry information from two different types of sensors. The output frequency is linearly related to the resistive unbalance of an active bridge, whereas the duty-cycle is independently controlled by a thermal sensor for controlling temperature error of the humidity sensor (RH). The design, analysis, and experimental characterization of the circuit and its application to a sol-gel thin film porous γ-Al2O3-based humidity sensor and resistance temperature detector are reported. Experimental results confirm the theoretical value predicted. The circuit covering wide resistance measurement range has the potential for remotely monitoring measurement parameters accurately.
52 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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...A linear resistance to frequency converter, based on a relaxation oscillator has been developed and reported for single element in [17]....
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TL;DR: In this paper, a new circuit topology based on duality of the well known voltage-mode Wheatstone bridge is described, which can implement ratiometric current measurement which is a vital aspect of current-mode instrumentation and signal processing.
Abstract: This paper describes a new circuit topology based on duality of the well known voltage-mode Wheatstone bridge. This topology can implement ratiometric current measurement which is a vital aspect of current-mode instrumentation and signal processing. The theory of the proposed circuit is developed and its advantages and limitations are discussed. The new circuit (called AZKA cell) may be thought of as the current-mode alternative of traditional voltage-mode Wheatstone bridge. It presents the current-mode circuit designers and engineers their own relevant interface cell. The advantages of the new circuit are stated and some conditioning circuits for its output signal are proposed. Finally, a linearization circuit based on CCII+ is introduced.
50 citations