Nandagopal Ramadoss

Bio: Nandagopal Ramadoss is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Inductive sensor & Linear variable differential transformer. The author has an hindex of 1, co-authored 2 publications receiving 23 citations.

A simple microcontroller based digitizer for differential inductive sensors

Abstract: This paper presents a simple digitizer suitable for differential variable inductive/reluctance sensors. The proposed scheme uses two digital I/O pins, a counter and a comparator of a microcontroller and obtains a digital output directly proportional to the measurand which is sensed using a differential variable inductive/reluctance sensor possessing either a linear or an inverse transfer characteristic. The scheme uses a ratio-metric approach in the computation and hence the output is less sensitive to variation in the parameters such as excitation voltage, reference voltage, offset of the comparator, etc. A prototype of the proposed system has been built and tested using standard variable inductors that emulated a differential inductive sensor following an inverse characteristic. The output recorded was linear across the full range and worst-case error noted was less than 0.3 %. For the prototype developed, the time taken to complete a measurement was 200 µs. The prototype digitizer has been interfaced with a commercially available LVDT and tested. The worst-case error observed in this test was 0.77%. Also, the same digitizer has been employed to get a digital readout from a differential variable reluctance based displacement sensor. The worst-case error was less than 0.83%. The test results establish the efficacy of, the simple and cost effective, scheme developed.

A Simple Microcontroller Based Digitizer for

Abstract: This paper presents a simple digitizer suitable for differential variable inductive/reluctance sensors. The proposed scheme uses two digital I/O pins, a counter and a comparator of a microcontroller and obtains a digital output directly proportional to the measurand which is sensed using a differential variable inductive/reluctance sensor possessing either a linear or an inverse transfer characteristic. The scheme uses a ratio-metric approach in the computation and hence the output is less sensitive to variation in the parameters such as excitation voltage, reference voltage, offset of the comparator, etc. A prototype of the proposed system has been built and tested using standard variable inductors that emulated a differential inductive sensor following an inverse characteristic. The output recorded was linear across the full range and worst-case error noted was less than 0.3 %. For the prototype developed, the time taken to complete a measurement was 200 s. The prototype digitizer has been interfaced with a commercially available LVDT and tested. The worst-case error observed in this test was 0.77%. Also, the same digitizer has been employed to get a digital readout from a differential variable reluctance based displacement sensor. The worst-case error was less than 0.83%. The test results establish the efficacy of, the simple and cost effective, scheme developed. Keywords—Differential inductive sensor; Digitizer; microcontroller interface; linearization; timer-counter; DVRT; LVDT

Linearization of the sensors characteristics: a review

Abstract: Today, the sensing devices play an important role for various system automation and monitoring of different physical and chemical parameters. Nonlinearity is an important long-time issue for most of the sensors, so to compensate nonlinearity, various linearization schemes are reported in the literature. The accuracy of linearization schemes depends on the type and the nonlinearity value of the sensor output. Since it is difficult to find an exact polynomial equation or other functions to represent the response curve; it gives more error when the measurement parameter is determined from the inverse approximation functions. As many sensors are used for different applications, the linearized characteristics will simplify the design, calibration, and accuracy of the measurement. This paper presents a review of different methods applied to linearize sensor characteristics reported in the literature. Due to availability of high-performance analog devices, analog methods are still popular among many researchers. However, due to the advancement of IC technologies, hardware implementation of the software methods can be done easily with reduced time, cost, and more accuracy, so the digital methods combined with software techniques perform the job with better flexibility and efficiency.

Study of a Modified LVDT Type Displacement Transducer With Unlimited Range

Abstract: The conventional LVDT is generally used as displacement transducer but has some limitations such as small linear range, measurement errors due to stray capacitance effect, electromagnetic interference effect, and core loss effect. In this paper, a modified LVDT type displacement transducer has been proposed in order to overcome these limitations of conventional LVDT. The proposed LVDT will consist of only two identical coils instead of three coils of conventional LVDT. This design does not require any excitation coil. In this design, two identical coils wound on a former made of ferromagnetic material act as displacement sensing inductive coils with specially designed movable core. The design has been analyzed under three cases. It has been shown that the range of the displacement transducer is about 50% of the overall length of the sensor under two cases like conventional LVDT and is about 100% of the overall length of the sensor under the third case. So in this paper, a displacement transducer has been designed and tested experimentally considering only the third case with unlimited range equal to the entire length of the sensor. The transducer consists of an op-amp-based differential inductance measuring circuit and an output instrumentation amplifier. The performance equations of this sensor under three cases and of the transducer under third case are derived in the paper. The experimental results reported in the paper are found to follow the derived equations with very good linearity and repeatability.

Measuring Dynamic Signals with Direct Sensor-to-Microcontroller Interfaces Applied to a Magnetoresistive Sensor.

Abstract: This paper evaluates the performance of direct interface circuits (DIC), where the sensor is directly connected to a microcontroller, when a resistive sensor subjected to dynamic changes is measured The theoretical analysis provides guidelines for the selection of the components taking into account both the desired resolution and the bandwidth of the input signal Such an analysis reveals that there is a trade-off between the sampling frequency and the resolution of the measurement, and this depends on the selected value of the capacitor that forms the RC circuit together with the sensor resistance This performance is then experimentally proved with a DIC measuring a magnetoresistive sensor exposed to a magnetic field of different frequencies, amplitudes, and waveforms A sinusoidal magnetic field up to 1 kHz can be monitored with a resolution of eight bits and a sampling frequency of around 10 kSa/s If a higher resolution is desired, the sampling frequency has to be lower, thus limiting the bandwidth of the dynamic signal under measurement The DIC is also applied to measure an electrocardiogram-type signal and its QRS complex is well identified, which enables the estimation, for instance, of the heart rate

Seat Occupancy Detection Based on a Low-Power Microcontroller and a Single FSR

Abstract: This paper proposes a microcontroller-based measurement system to detect and confirm the presence of a subject in a chair. The system relies on a single Force Sensing Resistor (FSR), which is arranged in the seat of the chair, that undergoes a sudden resistance change when a subject/object is seated/placed over the chair. In order to distinguish between a subject and an inanimate object, the system also monitors small-signal variations of the FSR resistance caused by respiration. These resistance variations are then directly measured by a low-cost general-purpose microcontroller unit (MCU) without using either an analogue processing stage or an analogue-to-digital converter. Two versions of such a MCU-based circuit are presented: one to prove the concept of the measurement, and another with a smart wake-up (generated by the sudden resistance change) intended to reduce the energy consumption. The feasibility of the proposed measurement system is experimentally demonstrated with subjects of different weight sitting at different postures, and also with objects of different weight. The MCU-based circuit with a smart wake-up shows a standby current consumption of 800 nA, and requires an energy of 125 µJ to carry out the measurement after the wake-up.

Fast Calibration Methods for Resistive Sensor Readout Based on Direct Interface Circuits.

Abstract: A simple method to measure the resistance of a sensor and convert it into digital information in a programmable digital device is by using a direct interface circuit. This type of circuit deduces the value of the resistor based on the discharge time through it for a capacitor of a known value. Moreover, the discharge times of this capacitor should be measured through one or two resistors with known values in order to ensure that the estimate is not dependent on certain parameters that change with time, temperature, or aging. This can slow down the conversion speed, especially for high resistance values. To overcome this problem, we propose a modified process in which part of the discharge, which was previously performed through the resistive sensor only, is only conducted with the smallest calibration resistor. Two variants of this operation method, which differ in the reduction of the total time necessary for evaluation and in the uncertainty of the measurements, are presented. Experiments carried out with a field programmable gate array (FPGA); using these methodologies achieved reductions in the resistance conversion time of up to 55%. These reductions may imply an increase in the uncertainty of the measurements; however, the tests carried out show that with a suitable choice of parameters, the increases in uncertainty, and therefore errors, may be negligible compared to the direct interface circuits described in the literature.