Boby George

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.

A new, simple and high-accuracy impedance-to-digital converter (IDC) is proposed in this paper. Conventionally, the parameters of sensors that can be modeled using a parallel combination of a capacitor (C) and a resistor (R) are measured using ac bridges, excited from a sinusoidal source. Recently, with the widespread use of digital systems in instrumentation, capacitance-to-digital converters and resistance-to-digital converters gained a lot of importance. An IDC that accepts sensors having C and R in parallel and provides digital outputs directly proportional to the C and R values is presented in this paper. This can be used not only for sensors whose C and R values vary with the measurand but also when C or R of a sensor needs to be measured keeping the output not affected by parasitic R or C present in parallel with the sensing element. Another application of the IDC is in the measurement of the dissipation factor of dielectric materials. The proposed IDC is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference. A prototype of the proposed IDC has been developed and tested in the laboratory. Accuracy of the prototype IDC developed was 0.15% for the measurement of C and 0.04% for the measurement of R. The total conversion time of the prototype converter developed is 3 s, and its total power dissipation is 175.8 mW. The IDC was also interfaced with a polymer-based impedance humidity sensor, measured its C and R values for a range of humidity, computed the humidity, and compared its performance with another instrument, showing the practicality of the proposed IDC.

An efficient signal conditioning (SC) scheme that helps to obtain a linear output from a magnetoresistive (MR) angle sensor for 0\circ-360 \circ range is presented in this paper. Most of the existing MR angle sensors have a sine/cosine relationship between the output and sensing angle, but a linear characteristic will be very useful. The new SC circuit of the proposed transducer accepts and processes output signals from an MR sensor that is sine/cosine in nature and gives an output directly proportional to the sensing angle. The sensitivity of the transducer output to variations in different circuit and mechanical parameters has been analyzed in detail, and their effect has been quantified. The functionality of the SC has been studied using SPICE simulations. A prototype of the proposed SC circuit has been built and tested using emulated sensor output signals. The output of the prototype circuit was linear from 0\circ to 360 \circ, and worst case error was less than 0.08%. An angle sensor unit has been built using an MR sensor IC, interfaced to the SC circuit and tested. As expected, the output was found to be linear for a full-circle range. © 1963-2012 IEEE.

This paper presents a novel resistance-to-digital converter (RDC) suitable for differential resistive sensors. The proposed RDC provides a digital output linearly proportional to the parameter being sensed by a differential resistive sensor not only for differential resistive sensors possessing linear characteristic but also for sensors possessing inverse characteristic. The proposed RDC is based on the sigma-delta type analog-to-digital converter (Σ-Δ ADC) principle and hence possesses all the advantages and limitations of a Σ-Δ ADC. Experimental results on a prototype built and tested gave a worst case error < 0.15 %, establishing the efficacy of the proffered RDC. ©2008 IEEE.

Recently, a training mannequin suitable for ophthalmic blocks has been developed. It provides a new feature of visual feedback to the trainee. A validation of the efficacy of this training system with needle angle visualization, ocular structure proximity, and procedural warning features was conducted in an evaluative study with 41 participants; 21 post graduate trainees and 20 ophthalmic consultants from a tertiary ophthalmic care facility in Chennai, India. The participant's performance was evaluated and analyzed using an appropriate scoring scheme in two sessions with and without visual feedback. The participants were also requested to provide feedback on the anatomical likeness and usage. A two tailed signed rank Wilcoxon test verified the statistical significance of the visual feedback (Pz(4.55, 0.05)= 0.9999, P < 0.001). The mean score of the participants showed an increase 58.86% and 25.5% for graduate trainee and consultants respectively and a mean reduction of 85.41% in the warning indications provided was also substantiated the efficacy of the visual feedback.

Signal conditioning of inductive sensors so as to obtain an output proportional to just the change in the inductance alone is fraught with problems. The large value of self inductance that is present in a sensor coil and the change in the inductance being a small fraction of this large inductance coupled with the winding resistance of the sensor coil make signal conditioning of such inductive sensors a challenge. This paper presents a simple analog front-end suitable for signal conditioning of inductive sensors. The proposed signal conditioning circuit provides an output linearly related to the change in inductance due to the measurand alone, masking the large value of self (offset) inductance present in inductive sensors as well as the appreciable winding resistance. A prototype of the proposed signal conditioning circuit was developed and tested in the laboratory. Test results validate the efficacy of the technique presented herein. © 2013 IEEE.

Capacitance-to-Digital Converter (CDC) ICs available in the market use square wave excitation signals but a sinusoidal excitation is preferred in various applications, such as ice detection, liquid level measurement, humidity measurement, proximity sensing, etc. A dual slope technique based CDC that employs a sinusoidal excitation has been reported recently, but it requires a large number of excitation cycles, to complete an accurate conversion. This paper presents an improved CDC that employs a specially designed method to achieve high accuracy even when a much smaller number of excitation cycles, than the reported scheme, are employed to complete the conversion. A prototype CDC has been developed and tested. In comparison with an existing CDC, the new CDC achieved a substantial reduction (by a factor of 4000) in the number of excitation cycles during integration period, resulting in an improved update rate. Worst case error observed from the prototype CDC was less than 0.24%.

Most of the existing flow sensors are expensive and limited in their capabilities for sensing bidirectional flow. Low-cost and accurate flow sensors with bidirectional sensing capability have numerous applications in the residential and irrigation sectors. Evaluation of a low-cost, cantilever-based sensor, suitable for measuring flow rates under turbulent flow conditions is presented in this article. Such sensors are reported for micro-fluidic applications but its potential application in large diameter pipes under turbulent flow has not been studied yet. A cantilever formed using a thin stainless-steel strip is used as the sensing element in the proposed sensor. One of the ends of the cantilever is firmly fitted to the inner wall of the pipe, and it bends or deflects towards the direction of the flow as a function of the flow rate. To experimentally evaluate the sensor in detail, the mean deflection angle of the cantilever is measured using a camera, and an image processing algorithm. In practice, the angle can be sensed using simpler methods. The performance of the prototype sensor has been evaluated after building an appropriate regression model. The results are subsequently expressed in terms of the mean flow velocity, thereby providing its potential utility in pipes of other dimensions. The shape of the mean flow velocity with respect to the mean angle of deflection characteristic of the proposed sensor matched well with the theoretical deflection computed. The sensor developed has given an accuracy of 3 % of full scale, for flow rates in the range of 2-15.5 m3/hr. The proposed sensing mechanism can realize cost-effective, simple, and reliable flow sensors. Such sensors will find applications in residential and industrial domains.

A novel Dual-Slope Resistance-to-Digital Converter (DSRDC) suitable for single element resistive sensors is presented in this paper. The digital output of the converter is directly proportional to the measurand and is insensitive to the nominal value of resistance, Ro, of the sensor. The choice of fixed resistance employed in a typical DSRDC has been made to be independent of Ro and the constraints on its accuracy have been relaxed. This makes the Resistance-to-Digital Converter versatile, in a manner that it can be easily interfaced with a wide range of resistive sensors having different values of Ro. This task was accomplished by employing an automatic calibration technique, wherein, the reference voltage is digitally adjusted by a Switched Capacitor Controlled Voltage Source (SCCVS). A prototype DSRDC was developed and tested against various values of Ro, which were in-turn emulated using known resistances of values ranging from 25 kü to 200 kü. The worst case error in reading was observed to be less than 0.65 %.

Palpation is the process of using one's hand to perform a physical examination. Ophthalmic anaesthetists palpate the orbital bone around the eye, to locate anatomical markers to help them guide the needle safely for regional needle block into the orbital cavity. The anaesthetists are provided very little training on palpation procedure due to the lack of a suitable training system. Inadvisable palpation can cause damage to the soft tissue if the applied force is more than required. There is a necessity to provide ophthalmic anaesthetists with the relevant knowledge about palpation and the force exerted during this procedure. In this paper, a load cell based palpation sensor which can be integrated with recently developed ophthalmic anaesthesia training systems with a virtual instrument environment that is capable of mimicking the skin reaction to applied palpation with the variable warning threshold is proposed.