This work describes the design and testing of a power Voltage-Controlled Current Source (VCCS) based on the Howland Current Source (HCS) topology. This source is part of a system that contains a three-axial Helmholtz coil and is used to generate a controlled magnetic field environment for aerospace applications. Initially, the paper presents the HCS theory and practical limitations on the premise that the system must be built using low-cost off-the-shelf components. The paper also carefully address on how to design and plan the VCCS matching physical and electrical parameters/limitations of a specific Helmholtz coil. All project details as well as the built VCCS electronics and its results are shown. These include linearity and a first order calibration test, stability and low-frequency error measurement, step response and a frequency limitation analysis. The built source is capable of sourcing up to ±1.5 A at ±25 V, maintaining its linearity and achieving an error smaller than 0.5% with a first order calibration. The final HCS prototype together with the Helmholtz coil allows an excellent capability regarding magnetic field generation for both open and closed-loop applications.
ResumoNeste artigo é apresentada a descrição do algoritmo TRIAD para a determinação da atitude tridimensional de um corpo, por meio da observação de dois vetores. Esse algoritmo, apesar de não constituir a solução ótima para o problema, pode ser implementado eficientemente em computadores. Também é apresentada a matriz cartesiana de covariância da atitude para o algoritmo. Os pormenores do cálculo desta matriz são esmiuçados, resultando em uma equação analítica simples em função dos conjuntos de medidas tomados de tríades de dois diferentes sensores no sistema de coordenadas do corpo. As soluções apresentadas podem ser utilizadas para implementar sistemas de determinação da atitude altamente integrados, usando sensores inerciais e sensores de referência com tecnologia de micro-fabricação (Micro-Electro-Mechanical Systems -MEMS) e microcontroladores de baixo custo.
Palavras-chave: Determinação da atitude. Triad. Matriz de covariância
AbstractThis article presents a description of the TRIAD algorithm, which utilizes two vector observations for determining a body three-dimensional attitude. This algorithm describes a deterministic form to calculate the attitude and it does not constitute the optimal solution for the problem, but can be implemented efficiently on computers. The Cartesian covariance matrix for this algorithm is also presented. This matrix calculation are addressed in details, resulting in a simple analytical formula based on two different sensor sets measurements in the body frame. The solutions presented are suited to implement highly integrated attitude determination systems that employ MEMS (Micro-Electro-Mechanical Systems) technology sensors and low cost microcontrollers.
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