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An efficient and productive joining technique to weld aluminium has become a priority challenge for promoting the use of aluminium in the electrical industry. One of the challenges is to obtain welds with superior mechanical properties with the consistent quality of weld surface as well as low electrical resistance. In this paper, the influence of rotational speed during the friction stir spot welding of AA 5754-H111 was studied to analyse the mechanical and electrical properties of the welds. The results from two rotational speeds (1000 rpm and 4500 rpm) are presented and compared to the base material. It was observed that the samples welded at 1000 rpm showed a higher average shear failure load (~ 1.1 kN) compared to the samples welded at 4500 rpm (~ 0.94 kN). The microhardness of the samples welded at 1000 rpm was higher than that of the base material, while the microhardness of samples welded at 4500 rpm was lower. It was also found that the friction welded sheets, regardless of the rotational speed used, showed increased electrical resistance compared to the base material, albeit this increase for the samples welded at 1000 rpm was about 42%, compared to samples welded at 4500 rpm where this increase was just 14%.

In this paper we present the model of digital stochastic DFT processor. Compared to the classical DFT/FFT processors, the proposed model has two advantages: first, it is much simpler and cheaper to implement, and second, it allows us to compute individual DFT components either in isolation or in parallel. In order to prove the validity of our model, we have simulated the measurement of reactive power and energy. In addition, we have conducted several experiments under field and laboratory conditions. The obtained results have shown that reactive power and energy can be measured with an accuracy of several ppm.