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Abstract-This paper proposes and analyses a microcontroller-based interface circuit for inductive sensors with a variable self-inductance. Besides the microcontroller (µC) and the sensor, the circuit just requires an external resistor and a reference inductor so that two RL circuits are formed. The µC appropriately excites such RL circuits in order to measure the discharging time of the voltage across each inductor (i.e. sensing and reference) and then it uses such discharging times to estimate the sensor inductance. Experimental tests using different commercial µCs at different clock frequencies show the limitations (especially, due to parasitic resistances and quantisation) and the performance of the proposed circuit when measuring inductances in the millihenry range. A non-linearity error lower than 0.3% FullScale Span (FSS) and a resolution of 10 bits are achieved, which are remarkable values considering the simplicity of the circuit.

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Problems related to the so called "loss of life", or isolation aging of distribution transformers [7], have been interesting over a long period of time. Since the beginning of the last century various concepts have been used to explain the transformers loss of life and as usual those are interpreted incorrectly. In fact, "loss of life" has always been understood as "reducing the isolation's loss of life".There are existing therminological differencess in IEEE and IEC standards, that are used in the methods for determination of ageing in distribution transformers. This paper is comparative analysis between the variables, defined in those standards. The presented analysis relates to a transformer with the following parameters: 630 kVA, 10/0,4 kV, Dy5. Index Terms-hot spot temperature, loss of life, transformer1-4244-1298-6/07/$25.00 ©2007 IEEE.

Direct sensor-to-microcontroller is a simple approach for direct interface of passive modulating sensors to a microcontroller without any active components in between the sensor and the microcontroller and without an analog to digital converter. The metrological performances of such interface circuits are limited by certain microcontroller parameters which are predetermined by the manufacturing technology. These limitations can be improved by specific hardware-related techniques and can improve the accuracy, speed and resolution of the measurements. Such hardware solutions as well as proper selection of the electrical components are addressed in this paper. It has been shown that employment of only a few MOSFET transistors can reduce the maximal relative error of single point calibration more than fifteen times and can increase the measuring speed around 30 % in all calibration techniques in the measurement range of PT1000 resistive temperature sensors. Moreover, the effective number of resolution bits increases by more than 1.3 bits when using an external comparator.