Enhancing Accuracy in Actigraphic Measurements: A Lightweight Calibration Method for Triaxial Accelerometers

This paper presents a simple, lightweight, automatic calibration method for low-cost triaxial accelerometers, utilizing the Earth’s gravitational constant in various orientations. It can be easily implemented using only fixed-point arithmetic and can run on low-power microcontrollers for real-time measurements, making it practical for scenarios with limited data storage and computational power, such as actigraphy or IoT applications. The method offers ease of use by automatically detecting motionless intervals, eliminating the need for complex positioning techniques. The procedure detects resting states and calculates the corresponding three-dimensional mean acceleration values during the measurement. After appropriately selecting these mean values, a set of calibration points is formed and passed to a gradient-based optimization algorithm for iterative estimation of the calibration coefficients. Different metrics were used for verification and comparison with other methods, which were calculated through simulations and tests based on real measurements. The results show that, despite its lightweight nature, the method performs equally to more complex solutions. This article provides a thorough explanation of a novel method for collecting calibration points, the optimization algorithm, and the methods used for performance evaluation in a reproducible manner.

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Comparison of Measurement Methods for the Frequency Range 2–150 kHz (Supraharmonics) Based on the Present Standards Framework

Advances in power electronics, increasing share of renewables in the energy system and e-mobility cause an increase of disturbances in the frequency range 2-150 kHz, also known as supraharmonics. A rigorous, credible and agreed measurement framework is essential to evaluate electromagnetic compatibility (EMC) in this frequency range. While a normative method exists for measuring equipment emission in the laboratory, no normative method exists yet for the measurement of supraharmonic disturbance levels in the grid. The aim of this research is a detailed comparison of potential measurement methods derived from existing standards IEC 61000-4-7, IEC 61000-4-30, CISPR 16-1-1 and a critical assessment of their suitability for disturbance measurements in grid applications. Based on a comprehensive set of synthetic signals and real measurements from laboratory and field, this article studies the ability of the methods to assess the typical characteristics of supraharmonic emission with relevance to EMC coordination. It presents the benefits and drawbacks of the existing measurement methods and discusses the suitability of possible modifications for grid compliance assessment. The results and recommendations intend to be an input for the present activities of IEC SC 77A WG 9 to define a normative method for the measurement of supraharmonic disturbance levels to be included in the next edition of IEC 61000-4-30.

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