Abstract
The effects of non-parallelism and surface roughness on the linearity of a guard-ring, three-terminal capacitance displacement transducer have been observed using a Michelson interferometer technique. The results are referred to an established theoretical model, modified slightly to account for the particular geometry of the transducer. For small electrode separations the effect of non-parallelism could lead to calibration errors in capacitance transducers but the surface roughness of the electrodes is unlikely to present great practical problems.

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