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
More filters
TL;DR: In this paper, the authors proposed a digital signal conditioning (DSC) scheme to interface resistive sensors with wide-span operation, which requires a single reference voltage and single operation cycle and provides a direct digital output proportional to the sensor-resistance.
Abstract: Resistive sensors, with wide-span of operation, are used in a number of industrial scenarios. In some of these cases, such resistive sensors may need to be located in a remote environment, away from the electronics unit. This article brings-forth new and efficient digital signal conditioning techniques to interface the aforementioned classes of resistive sensors. The first proposed technique employs a simple circuitry that requires a single reference voltage and single operation cycle and provides a direct-digital output proportional to the sensor-resistance. Next, this scheme is further enhanced, with the addition of few auxiliary components, to address the case of remotely-located resistive sensors. The novel circuit-designs also ensure other positive features like: 1) short execution time; 2) compatibility to resistive sensors in different configurations; and 3) negligible dependence on many nonideal parameters. The proposed schemes are systematically presented and thoroughly analyzed in this article. Elaborate simulation and emulation studies are used to evidence the performance. A maximum nonlinearity of 0.07% and 12-bit resolution is obtained for the first digitizer, during the hardware tests. The utility of the schemes to interface a temperature sensor with wide-span is also studied. Vital performance parameters of the schemes are derived and compared with the state-of-art works.
9 citations
TL;DR: In this article , the authors describe the design, analysis, and performance verification of simple digitizing interfaces for different types of three-wire resistive sensors, which is adaptable for various resistive sensor configurations and does not depend on the effect of connecting wire resistances and various other nonideal parameters (e.g., threshold voltage and pin resistance of microcontroller, offset voltage of comparator, etc.).
Abstract: This article describes the design, analysis, and performance verification of simple digitizing interfaces for different types of three-wire resistive sensors. The proposed interface uses an efficient resistance-to-time conversion technique that charges an internal capacitor, between two reference levels, through selected resistive-sensor paths. A simple analog circuit controlled using a digital timing unit realizes the aforementioned technique. This approach is adaptable for various resistive sensor configurations and does not depend on the effect of connecting wire resistances and various other non-ideal parameters (e.g., threshold voltage and pin resistance of microcontroller, offset voltage of comparator, etc.). In addition, the proposed schemes utilize its digital unit (e.g., microcontroller) only for control and timing operations, thus saving on power. The detailed working principle of the proposed interfaces and their error analysis are discussed in the article. Later, performance verification is carried out using simulation as well as emulation studies. These studies clearly show that the presented digitizing interfaces provide linear digital transfer characteristics with maximum nonlinearity of 0.17% and wire resistance compensation. Further, tests are conducted with various remotely located commercial sensors. The outcomes of these studies are reported and compared with the state-of-the-art works.
9 citations
TL;DR: In this paper, a simple digitizer circuit suitable for bridge-based resistive sensors is reported, which provides a linear transfer characteristic, for all common types of resistive bridges.
Abstract: A simple digitizer circuit suitable for bridge-based resistive sensors is reported in this article. The digitizer provides a linear transfer characteristic, for all common types of resistive bridges. Besides, the digitizer output is independent of the parasitic capacitance of the resistive sensors, connecting wire impedances, and mismatch among the bridge elements. The methodology of the digitizer is mathematically derived and analyzed. A number of experimental studies of the digitizer are carried out with various types of bridge configurations. Linear output characteristic, with all other expected meritorious features, is obtained during all these tests, and the maximum output nonlinearity is less than 0.06%. Tests are also conducted with an industrial magnetoresistance (MR) sensor bridge. The results demonstrate a magnetic sensing system with higher performance when compared with the conventional interface for MR sensors.
9 citations
TL;DR: In this article, a modified Maxwell's inductance bridge based on operational amplifier configuration for high lift-off testing is investigated. But the receiver coil self-impedance is removed to improve signal-to-noise ratio and to make output signal proportional to impedance change only.
Abstract: Pulsed eddy current testing is widely used because of its richness in spectral components. However, the degrading sensitivity as lift-off increases poses a challenge to its application in thick insulation or buried structures and weld areas. In the transmitter-receiver probe, self-impedance (offset) of receiver coil dominates the output signal, reducing the signal-to-noise ratio, especially at high lift-off. This limits the subsequent amplification of the output signal by the signal conditioning circuit. In practice, bridge-based measurements are used to mitigate this challenge but result in small linear range input-output characteristics. Electromagnetic interference and stray capacitance effects also cause measurement errors. This paper investigates a modified Maxwell’s inductance bridge based on operational amplifier configuration for high lift-off testing. The receiver coil self-impedance is removed to improve signal-to-noise ratio and to make output signal proportional to impedance change only. Experiments are performed to evaluate the performance of the circuit in crack detection. The results show improved signal-to-noise ratio with maximum linearity deviation of 0.30%, and a higher crack detection sensitivity at 30mm high lift-off, in comparison to the conventional bridge circuit with maximum linearity deviation of 0.53%.
8 citations
Additional excerpts
...linear range input-output characteristic [20], [21]....
[...]
TL;DR: A wide-dynamic-range multi-sensor readout interface for portable environmental monitoring systems with two-step self-optimization schemes of adaptive range detection and coarse self-cancelation and range-based path control and current DAC-based correlated double sampling (CDS) for resistive sensing interfaces is presented.
Abstract: This article presents a wide-dynamic-range multi-sensor readout interface for portable environmental monitoring systems with two-step self-optimization schemes. It proposes two-step self-optimization methods of adaptive range detection and coarse self-cancelation (CSC) for current-type sensor interfaces, and range-based path control and current DAC-based correlated double sampling (CDS) for resistive sensing interfaces. Their digital conversions are provided by two kinds of high-resolution ADCs, namely, an incremental $\Delta \Sigma $ current detector and a two-step SAR- $\Delta \Sigma $ ADC. The proposed ROIC prototype is fabricated in a 180-nm CMOS process, achieving a dynamic range (DR) of 136.5 dB and 160.9 dB, and a maximum SNR of 109.8 dB and 108.6 dB for current and resistance detection, respectively. For system-level feasibility, an environmental monitoring system prototype based on the ROIC is also manufactured and functionally verified by integrating two kinds of in-house micro-electro-mechanical systems (MEMS) sensor devices, the MCU, and the Bluetooth module, supporting wireless air quality and water pollution monitoring capabilities.
8 citations
References
More filters
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]....
[...]
...sensor may be located far from the measurement unit and the lead resistance of the wires will introduce appreciable errors in the measurement [3]....
[...]
...Magneto Resistance (GMR) sensors, pressure sensors and flow meters [3]–[6]....
[...]
...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]....
[...]
...Various linearization techniques have been reported to obtain a final linear output, from the bridge [3], [8], [9]....
[...]
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]....
[...]
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]....
[...]
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....
[...]
...A linear resistance to frequency converter, based on a relaxation oscillator has been developed and reported for single element in [17]....
[...]
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