A dual-slope resistance-to-digital (DSRDC) converter that accepts the resistance of a single-element resistive-type sensor as input and provides a direct digital output proportional to the parameter being sensed by the resistive-type sensor is presented in this paper. A high level of linearity and accuracy is achieved since the output of the DSRDC is dictated only by the magnitudes of a pair of dc reference voltages and the transformation constant of the sensor. Sensitivity analysis shows that the effect of circuit parameter variations on the output is minimal. Simulation studies and test results obtained on a prototype establish the efficacy of the proposed scheme. © 2006 IEEE.

Boby George

Department of Electrical Engineering

Varadarajan Jagadeesh Kumar

Analog to digital converters

CIRCUIT PARAMETER

DIGITAL CONVERTERS

DIGITAL OUTPUT

Reference voltages

RESISTANCE-TO- DIGITAL CONVERTER (RDC)

RESISTIVE TYPE

Simulation studies

Test results

TRANSFORMATION CONSTANT

Dielectric properties

Linear transformations

Multicarrier modulation

Sensitivity analysis

Sensors

Frequency converters

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

A Novel Dual-Slope Resistance-to-Digital Converter

IEEE Transactions on Instrumentation and Measurement

A noncontact (capacitive-coupled) probe for the measurement of the conductivity of liquids is presented. Insulation introduced between the measurement electrodes and the liquid intrudes a couple of coupling capacitances. Though the capacitive coupling overcomes the problems of electrode polarization and contamination associated with contacting electrodes, the large reactances of the coupling capacitors pose a problem in the measurement of comparatively very small resistance of the liquid. An auto-balancing signal conditioning scheme presented here overcomes the problem posed by the large capacitive reactances and provides directly a measurable output proportional only to the conductance of the liquid. Error analysis of the probe presented herein helps the optimal design of the probe. A worst case error of ± 0.9% was obtained from a prototype noncontact conductivity probe, developed and tested. © 2019 IEEE.

A Capacitive-Coupled Noncontact Probe for the Measurement of Conductivity of Liquids

A novel readout circuit for interfacing single element resistive sensors is presented in this paper. The proposed scheme is based on a new relaxation oscillator (RO). The RO, along with a timer counter provides a digital output proportional to the resistance of the sensor. The output characteristic of most of the existing readout circuits for resistive sensors suffers from gain, offset, and nonlinearity errors. The sources of errors include various nonideal circuit parameters and their drift. The output of the proposed readout circuit has a special feature that it is not a function of the circuit parameters such as: 1) offset voltages of the opamps and comparators; 2) bias currents of the opamps and comparators; 3) gain of various units employed; 4) ON-resistance of the switches; 5) value or mismatch in the magnitudes of the reference voltages employed; 6) delay of the switches and comparator; 7) leakage current of the switch; and 8) slew rate of the opamp. Such a scheme will be useful for high accuracy measurements, even when the parameters 1)-8) may vary or drift, due to variation in the measurement environment. A prototype of the proposed readout scheme has been developed in the laboratory and the performance has been evaluated under various conditions. The output was found to be linear with a worst-case nonlinearity of 0.05%. Test results from a prototype developed show that the proposed scheme possesses all the features, described above, as expected. © 2017 IEEE.

A resistive sensor readout circuit with intrinsic insensitivity to circuit parameters and its evaluation

In this paper, a new digitizer, which accurately provides the values of the change in the capacitor Cx and resistor Rx of a parallel R-C sensor, is presented. Conventional measurement schemes for parallel R-C sensors require a precision sinusoidal excitation, followed by a signal conditioner, a demodulator and an ADC. This increases the cost and complexity of the scheme. Hence, a dc excitation and an ADC modified to measure Rx and Cx directly is preferred, by the design engineers. But, such a scheme has not been reported. Another challenge is the low-modulation nature of such sensors, i.e., the change in resistance ΔR and capacitance ΔC can be very small compared with the nominal values R0 and C0 of the sensor. This introduces a large offset in the digital output, leading to an inefficient conversion. The proposed digitizer employs a dc excitation and provides accurate digital values of change ΔR in Rx and ΔC in Cx of the sensor. The digitizer employs a simple, but effective automatic calibration, with the help of an improved switched capacitor controlled voltage and obtains an output independent of the nominal values (R0 and C0) of the sensor leading to an efficient conversion compared with the existing schemes. A detailed analysis of the sources of errors affecting the output of the digitizer has been conducted. A prototype of the proposed digitizer has been developed and tested in the laboratory for a wide range of R0 and C0. The results show that the output of the proposed digitizer is independent of the R0 and C0 and can accurately measure the ΔR and ΔC without any cross-sensitivity. © 2017 IEEE.

IEEE Sensors Journal

A Switched-Capacitor Circuit-Based Digitizer for Efficient Interfacing of Parallel R-C Sensors

Direct resistive sensor interface to a microcontroller has several advantages but has one prominent disadvantage, namely, the measurement is affected by the resistances of: 1) wires that connect the sensor to the port pins and 2) the internal resistances of the port pins of the microcontroller. A direct sensor-to-microcontroller interface scheme that compensates the effect due not only to resistances of lead wires but also the effect of microcontroller port pin's internal resistance and any offset present in those pins is presented in this paper. Since the resistances of lead wires are compensated, automatic temperature compensation (temperature effect of lead wires) is also obtained. Simulation study and results obtained from a prototype built and tested establish the efficacy of the proposed method. A maximum error of 0.06% was observed from the prototype developed, when it was tested under room temperature, after interfacing it with the sensor Pt100, with a lead wire resistance RLD = 21Ω. The error increased to a maximum of 0.08%, when the RLD varied from 0 to 100Ω When the same prototype was tested under elevated room temperature of 30 °C to 100 °C, the maximum error observed was 0.18%. © 2017 IEEE.

Improved Single-Element Resistive Sensor-to-Microcontroller Interface

A novel resistance-to-digital converter (RDC), based on the integrating type analogue-to-digital converter principle, is presented in this study. The conversion time of the proposed scheme is not a function of the current value of the parameter being measured. Thus, by suitably setting this parameter, the converter can be made to reject the effects of interference at a particular frequency, such as, that due to power-line at 50/60 Hz. Error analysis was conducted to ascertain the effects of non-idealities of various components of the circuit, on its output. Simulation studies were carried out in LTSPICE to verify the linearity and the interference rejection capability of the converter. Further, a prototype RDC was developed in the laboratory and tested to confirm the results of the simulation. © The Institution of Engineering and Technology.

IET Circuits, Devices and Systems

Resistance-to-digital converter designed for high power-line interference rejection capability

A novel, simple and high accuracy dual slope direct digital converter suitable for differential capacitive sensors is presented in this work. The proposed technique provides a linear digital output proportional to the parameter being sensed by differential capacitive sensors irrespective of the fact that the sensor could possess either a linear or an inverse characteristic. In the proposed technique, the output is dependent only on, apart from the sensitivity of the sensor, a single dc reference voltage. Thus by employing a precision dc reference voltage, high accuracy is easily achieved. The proposed direct capacitance to digital converter is based on the popular dual-slope analog to digital converter structure and hence possesses all the advantages of the dual-slope technique, namely, high resolution, accuracy and immunity to noise and component parameter variations. A prototype built and tested for a typical differential capacitive sensor with a nominal value of 250 pF gave a worst-case error less than 0.05 %. © 2009 IEEE.

2009 IEEE Intrumentation and Measurement Technology Conference, I2MTC 2009

Novel switched-capacitor dual slope capacitance to digital converter for differential capacitive sensors

A high accuracy switched capacitor, triple slope digital converter suitable for differential capacitive sensors is presented. The proposed technique accepts differential capacitive sensors possessing either linear or inverse characteristics and provides a linear capacitance to digital conversion. The output is dependent only on a pair of d.c. reference voltages and the clock frequency. Detailed analysis of the proposed scheme establishes that the sensitivity of the scheme to parameter variations is minimal. A prototype implemented and tested for a typical differential capacitive transducer of full-scale ±250pF gave a worst-case error less than 0.05.

Journal	IEEE Transactions on Instrumentation and Measurement
ISSN	00189456
Open Access	No