Analysis of the performance of the capacitive displacement transducer

An output signal from the capacitive displacement transducer has been mathematically modeled. Interest is focused on the importance of the spectral content of the signal in determining transducer performance. It has been shown that the phase-error due to the space harmonics of the capacitance between the receiving and transmitting electrodes always exhibits a ripple with the spatial frequency equal to the number of the transmitting electrodes. An analysis of the mathematical model suggests general rules of mechanical and electrical design that are necessary in order to create effective and viable devices with reduced measurement errors. In particular, a variety of the staircase functions with rapidly decreasing Fourier components can be applied as the driving supply. Another alternative is to combine a specially formed driving supply with low-pass filtering in the time domain. Experimental results for three different (four-, six-, and eight-phase) transducer systems confirm the validity of the model.<
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