A Dual-Differential Subtractor-Based Auto-Nulling Signal Conditioning Circuit for Wide-Range Resistive Sensors
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.
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TL;DR: An autonulling-based multimode impedance-to-voltage converter (AN-Z2V) signal conditioning circuit for resistive–capacitive (R-C) sensors that takes advantage of the reuse of the phase tracking and aut onulling modules to extract the in-phase and quadrature components of the sensors.
Abstract: In this article, we propose an autonulling-based multimode impedance-to-voltage converter (AN-Z2V) signal conditioning circuit for resistive–capacitive (R-C) sensors. The proposed technique takes advantage of the reuse of the phase tracking and autonulling modules to extract the in-phase and quadrature components of the sensors. The circuit is designed for three sensing modes: 1) Mode-C for capacitive sensors with leakage resistor; 2) Mode-R for resistive sensors with parasitic shunt capacitor; and 3) Mode-Z for impedance R-C sensor. A novel autotuning quadrature phase generator circuit is designed and implemented for the generation of reference 90° phase-shifted signal for the leaky capacitive sensors. A prototype of the proposed circuit is fabricated and tested. Measurement results show that AN-Z2V provides the measurement range with low relative error compared with the reported systems. The system is tested for a range of 10–760 pF and 56 $\text{k}\Omega $ –6.5 $\text{M}\Omega $ for mode-C and mode-R, respectively. The accuracy of the proposed circuit is found to be ±0.11% and ±0.07% for mode-C and mode-R, respectively. The capacitance and resistance of the impedance R-C sensor are simultaneously measured in mode-Z for a range of 33–528 pF and 100 $\text{k}\Omega $ –7.8 $\text{M}\Omega $ , respectively.
14 citations
Cites background from "A Dual-Differential Subtractor-Base..."
...The signal conditioning circuits for these sensors are generally based on bridge-based circuits, relaxation oscillator-based resistance/capacitance to frequency converters, and direct digital converters [4]–[7]....
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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
TL;DR: In this paper , a selective hydrogen sulfide gas sensor based on zinc ferrite film which is obtained by a microwave-assisted solvothermal deposition route is reported. And a dual-differential subtractor based auto balancing interface circuit is proposed to drive this sensor which is advantageous in terms of accuracy and particularly suitable for a device such as ours, which has a wide dynamic range.
Abstract: We report on a selective hydrogen sulfide gas sensor based on zinc ferrite film which is obtained by a microwave-assisted solvothermal deposition route. The response of the chemiresistive device is found to be in the range of 1872% - 90% for 5.6 ppm – 0.3 ppm of H2S gas at an operating temperature of 250°C. The density functional theory studies suggest physisorption of the H2S molecules at the partially-inverted ZnFe2O4 surface as the reason behind the fast rise (of the order of ~40 sec) and fall time (of the order of ~70 sec) with complete recovery of the device. Finally, a dual-differential subtractor based auto-balancing interface circuit is proposed to drive this sensor which is advantageous in terms of accuracy and particularly suitable for a device such as ours, which has a wide dynamic range.
11 citations
16 Aug 2020
TL;DR: In this article, a simple, low cost, screen-printed flexible capacitive sensor for moisture, and water level detection is presented, which is fabricated on the flexible polyamide substrate.
Abstract: A simple, low cost, screen-printed flexible capacitive sensor for moisture, and water level detection is presented in this paper. The sensor is fabricated on the flexible polyamide substrate. The interdigitated structure electrodes are screen printed on the substrate to form the capacitive fingers using carbon paste. The relative permittivity of the medium changes due to the water vapors on the sensor, which in turn changes the capacitance of the sensor due to the fringing field. A novel auto-nulling based signal conditioning circuit was utilized to measure the capacitance of the sensor. The flexible nature of the sensor enhances the use of the fabricated capacitive sensor in applications such as diaper wetness monitoring, soil moisture monitoring, body hydration monitoring.
11 citations
TL;DR: In this paper , a low-voltage low-power resistive sensor measurement system with high sensitivity is presented, where the sensitivity of the system is fully auto-calibrated for a wide range of base resistors.
Abstract: Objective: The objective of the paper is to present a novel systematic approach for the design and development of a portable, low-voltage low-power resistive sensor measurement system with high sensitivity. The goal of the proposed system is to be able to measure the $\Delta {R}/{R}_{s}$ for a wide range of baseline resistance of sensor ${R}_{s}$ ( $1 {k}\Omega $ to $1 {M}\Omega $ i.e. 3 orders of magnitude) with high resolution and programmable sensitivity. Method: An auto-calibrated resistive sensor interface using a novel half-bridge based circuit is presented. The square-wave excitation and square-wave demodulation technique are utilised to reduce the power consumption of the proposed technique. Moreover, the sensitivity of the system is fully auto-calibrated for a wide range of base resistors. Results: With a supply voltage of 3.3 V and bandwidth of 10 Hz, the developed system is able to measure a minimum $\Delta {R}/{R}_{s}$ of about 20 ppm for $100 {k}\Omega $ base resistance. Overall, the power consumption of the developed system is 36.3 mW (for four channels). Significance: The system is useful for low-voltage low-power sensor nodes as a highly sensitive readout for the resistive sensor arrays. In addition, the developed system is useful for the stain sensors in the development of flexible hybrid electronics for wearable applications.
6 citations
References
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TL;DR: In this paper, the accuracy and resolution of direct resistive sensor-to-microcontroller interfaces using theoretical and experimental methods are analyzed. But the experimental results were similar for both microcontrollers and agreed with theoretical predictions.
Abstract: This paper analyses the accuracy and resolution of direct resistive sensor-to-microcontroller interfaces using theoretical and experimental methods. Three calibration techniques are evaluated: single-point, two-point and three-signal. This last method is a two-point calibration technique that needs a single calibration resistor. For each calibration formula, we analyse both the effects of the internal resistances of the microcontroller pins on the accuracy and the resolution, which is evaluated by the combined standard uncertainty of the calculated resistance. The experimental analysis was performed by measuring resistors in the range of Pt1000-type temperature sensors with two commercial microcontrollers (AVR AT90S2313 and PIC16F873). The experimental results were similar for both microcontrollers and agreed with theoretical predictions. For the AVR, the three-signal measurement method yielded a 0.01% relative systematic error and a 0.10 Ω resolution when averaging 10 calculated resistances.
109 citations
"A Dual-Differential Subtractor-Base..." refers background in this paper
...The analytical derivation also suggests that the range of Rs is increased by an additional (Vc Iex ) over the previous reported works related to voltage-controlled resistance circuit architecture [23], [24]....
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TL;DR: A novel circuit to directly connect differential resistive sensors to microcontrollers without using either a signal conditioner or an analog-to-digital converter (ADC) in the signal path is introduced.
Abstract: This paper is a continuation of a previous work with regard to the direct connection of differential sensors to microcontrollers without using intermediate electronics between them. This paper focuses on the measurement of differential capacitive sensors, whereas the previous work dealt with the resistive counterparts. The proposed circuit is analyzed, and the main limitation seems to be the fact that the magnitude of the input parasitic capacitances of the microcontroller is similar to or even higher than the sensor capacitances. Methods to overcome this limitation are proposed, particularly when measuring low-value differential capacitive sensors such as microelectromechanical system (MEMS) sensors. Experimental tests of the circuit have been carried out by measuring a commercial capacitive accelerometer working as a tilt sensor. Although such a sensor has a low value (1.5 pF) and low sensitivity (0.105 pF/g), the measurement has shown a nonlinearity error of 1% full-scale span (FSS), which is a remarkable value considering the simplicity of the circuit.
91 citations
TL;DR: In this paper, a generalized form of Tellegen's theorem that allows the efficient derivation of new results is presented, and also capable of simple expression in terms of wave variables.
Abstract: Among the theorems of circuit theory, Tellegen's theorem is unusual in that it depends solely upon Kirchhoff's laws and the topology of the network. The theorem therefore applies to all electrical networks that obey Kirchhoff's laws, whether they be linear or nonlinear, time-invariant or time-variant, reciprocal or nonreciprocal, hysteretic or nonhysteretic; the excitation is arbitrary, and the initial conditions are also immaterial. When specific assumptions are made concerning the network elements, the excitation, and the initial conditions, Tellegen's theorem reduces to many useful network theorems. In this paper a generalized form of Tellegen's theorem that allows the efficient derivation of new results is presented. A special formthe "difference form"-of this theorem is shown to be of particular value, and also capable of simple expression in terms of wave variables. The application of the generalized form of Tellegen's theorem is illustrated by an example.
88 citations
"A Dual-Differential Subtractor-Base..." refers background in this paper
...For a given power, Pex = Vex Iex of the excitation current loop, the input power delivered by the source must be greater than or equal to the total power dissipated across the loop [31], [32] and is given as:...
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TL;DR: In this article, polynomial regression is used to demonstrate calculations, but the definition of nonlinearity also accommodates alternative nonlinear regression procedures.
Abstract: Quantitative measures of the nonlinearity of an analytical method are defined as follows: the "(dimensional) nonlinearity" of a method is the square root of the mean of the square of the deviation of the response curve from a straight line, where the straight line is chosen to minimize the nonlinearity. The "relative nonlinearity" is defined as the dimensional nonlinearity divided by the difference between the maximum and minimum assayed values. These definitions may be used to develop practical criteria for linearity that are still objective. Calculation of the nonlinearity requires a method of curve-fitting. In this article, we use polynomial regression to demonstrate calculations, but the definition of nonlinearity also accommodates alternative nonlinear regression procedures.
76 citations
"A Dual-Differential Subtractor-Base..." refers background in this paper
...Since nonlinearity is the measure of the average deviation of a function from an ideal straight line in a bounded domain [30], this deviation from the ideal curve, at any point along the curve is given by [ f (R) − g (R)] where g (R) is the linear best fit of the solution curve....
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Book•
29 Jun 2011TL;DR: In this article, the Analog Lock-in Amplifier (ALAM) was used to detect small and noisy signals in sensor interfaces, and the Second Generation Current-Conveyor (CCII) was proposed.
Abstract: Introduction.- 1. Physical and Chemical Sensors.- 2. Resistive, Capacitive and Temperature Sensor Interfacing Overview.- 3. The Voltage-mode Approach in Sensor Interfaces Design.- 4. The Current-mode Approach in Sensor Interfaces Design.- 5. Detection of Small and Noisy Signals in Sensor Interfacing: The Analog Lock-in Amplifier.- A1. The Second Generation Current-Conveyor (CCII).- A2. Noise and Offset Compensation Techniques.
69 citations
"A Dual-Differential Subtractor-Base..." refers background in this paper
...To handle these dynamic properties robust signal conditioning circuits are required [8], [9]....
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...Also, the oscillator-based circuits suffer from the gain-bandwidth product limitation for low resistance values (typically <50 k ) [8]....
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