The finite element method has been used for modelling the electrostatic field and for calculation of the capacitance and deviations from ideal behaviour of displacement sensors on the basis of the potential linearity of the versus distance dependence. Various designs of sensors, the effects of electrode roughness, spherical deformation, rounding of edges and tilt have been analysed. The elimination of errors due to fringing of the electrostatic field is most effective with thick electrodes and the gap between the central electrode and the guard ring filled with a dielectric. Any deviation from planarity causes deterioration of the linearity. The most serious sources of error are the tilt and eventual rounding of the working electrode's edge, especially at small electrode separations. If the tilt may change with distance, then the electrodes should be preferentially aligned in their closest position.

http://iopscience.iop.org/article/10.1088/0957-0233/9/10/016/pdf

Analysis of linearity errors of inverse capacitance position sensors

In alternating current electrical metrology, the balancing procedure is the act of reduction to zero of a measured terminal-pair voltage (or current), accomplished via injection of a compensation voltage (current) in the circuit. An automatic compensation technique is described here: the terminal-pair voltage is continuously sensed, by means of vector synchronous detection, and the injected voltage is directly synthesized from the main circuit source. An implementation of the compensation technique, realized with analog electronics, permits compensation of audio frequency small voltages down to the nV range, with settling time in the order of milliseconds.

Automatic compensation technique for alternating current metrology based on synchronous filtering

Error analysis of a new cylindrical capacitive sensor (CCS) for measuring five-dimensional motions of a rotor

The invention relates to a method and device for acquiring a geometric form. The inventive method comprises the following steps consisting in: placing a set of sensors (4a) on the geometric form (a curve or surface), each sensor providing signals that are representative of the orientation of the curve or surface at the location of said sensor; selecting a model of the curve or surface; determining the parameters of the model from the signals; and determining the spatial distribution of the points of the form from said parameters. The invention is particularly suitable for use in the fields of machining, joinery, masonry and construction.

Method and device for acquiring a geometric form

A quadrature phase shifter for sinusoidal signals is presented. The circuit provides phase delay (within ) and unity gain (within 6%) in the frequency range 100 Hz to 10 kHz. It consists of a second-order lowpass current-controlled filter; the cutoff frequency is mantained equal to the input frequency with a frequency to current converter. In this way, the filter provides a phase delay between input and output. The main feature of the phase shifter is the absence of internal feedback; this avoids the introduction of long settling time constants when the phase shifter is part of control loops and gives almost instantaneous (within a period) resettling of the phase delay when amplitude or phase variations of the input signal occur.

https://iopscience.iop.org/article/10.1088/0957-0233/8/6/015/pdf

Gian Bartolo Picotto

Papers

A surface profile reconstruction method based on multisensor capacitive transducers