This thesis investigates the performance of some windows on the flow signals that are generated from the planar capacitance spatial filter (PCSF) according to the moving of the solid particle in the channel of the filter. The sensor that operates as non-invasive device for solid flow measurement utilizes the thin wall of a dielectric pipe section as a shielding layer to protect the sensor from erosion, rust and moisture, and to make it more versatile. The finite-difference model equations are solved using successive over relaxation (SOR) methods. The waveforms show that the response of the PCSF is spatially-biased towards particle flowing closer to the plane of sensing electrodes and that the resulting flow signal is non-sinusoidal. The SOR method that is used to compute the PCSF potential fields has been investigated using a mesh of 110 by 32 nodes, and the algorithm was programmed in MATLAB (Release 2013a) using an Intel core ™ i3 PC,CPU processor. To study the effect of the total harmonic distortion (THD) content on the flow signals that are calculated with respect to the fundamental frequency of the power spectrum density through a specific quantitative criterion, this work comprises a comparative study among three types of windows; Hanning, Hamming, and a subOptimal window called the Kaiser window. The effect of particle flying heights, relative permittivity and size on the THD of the flow signal were examined. It was found that the THD of flow signals at heights closer to the plane of sensing electrodes is high and decreasing gradualy when the particle flying height is far above the sensor. All the three windows used in this work have better suppression of harmonics distortion as compared with unwindowed (raw) flow signal.