The Hilbert transform as a quality control tool in capacitive pressure transmitters

The capacitive pressure transmitters consist of an isolating diaphragm connected to a sensing line through some inner tubes which contain silicone oil. The accuracy of the sensor is determined by the efficiency of the filling process with silicone oil in the transmitter inner chambers, so that the fact of not filling completely any of the transmitter chambers can affect the dynamic response of it. In fact, the oil loss syndrome is one of the most important breakdowns, since the sensor dynamic behaviour is no longer linear. In this work the Hilbert transform is applied to detect the non-linearity in the sensor response to a sinusoidal pressure wave. Such sensor suffers the oil loss syndrome at an incipient phase. The ill sensor is compared with a linear one and the efficiency of the analysis is proved for the detection of a non-linear behaviour as opposed to the traditional methods based on Fourier analysis. At last, a non-linear model taken from literature is validated with empirical data. & 2009 Elsevier Ltd. All rights reserved.