Control of a 3-axis Helmholtz Chamber

Abstract

Any sensor requires some calibration in order to produce accurate results. This is generally done by subjecting the sensor to a known stimulus and adjusting sensor parameters to obtain the correct output. This presents a problem when dealing with magnetic sensors since the earth’s magnetic field will affect the output. This can be solved using a set of Helmholtz coils to produce a specific field in a particular axis depending on the current supplied to the said coils. For a 3-axis sensor, three sets of coils are required in a setup known as a Helmholtz cage. This allows the magnetic field in all 3-axis to be set separately, to subject the sensor to a specific field vector. Such a setup can then be used to test the attitude control system of the pico-satellite being developed by the University of Malta. The Helmholtz cage would be used to supply the specific magnetic field vector, which together with the light received on each face of the satellite can be used to obtain the orientation of the satellite on its simulated orbital path. Coils inside the satellites can then be used to produce an opposing magnetic field to change the orientation of the satellite. This dissertation highlights the theoretical and practical aspects as well as the development steps undertaken in designing and building a controller for a 3-axis Helmholtz chamber, which interfaces to an orbital simulator in MATLAB to supply the required field.