Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1980-11-12
1982-12-28
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
73728, 336 30, G01D 520, G01L 910
Patent
active
043655173
DESCRIPTION:
BRIEF SUMMARY
The invention relates to Foucault current detectors for displacements or approach.
These, generally intended for the measurement of dimensions or the counting of metallic elements, are constituted in the prior art by an oscillator of which the windings represent the sensitive face. The passage of a conductive metallic mass in the alternating magnetic field created by the oscillator has the effect of generating currents induced in the metallic mass. The oscillator is adjusted in such a manner that the supplementary charge which results stops its operation: the device is thus a proximity detector and not a detector providing a linear signal as a function of displacement.
The present invention proposes to provide a linear detector adapted to measure very small displacements (not exceeding a fe millimeters) with a high resolution (of the order of 1/10th of a micron for example), and a good insensibility to thermal variations and electrical parasitics. Such a detector, adapted to carry out industrial measurements (levels, outputs, pressures or others) must present great simplicity of manufacture and construction.
The detector according to the invention comprises two substantially identical windings one at least of which cooperates with a conductive element the displacements of which are to be measured, means for applying to these windings respectively, in series with two resistances, rectangular signals at low frequency, means for detecting the peak values of the voltages respectively received at the common points between the respective windings and the corresponding resistances, and means for determining the difference between these peak values, and is characterised, in combination, in that the said element is of non-ferromagnetic metal, that the two windings are directly coupled to a common point of application of the said signals, and that a free wheel diode couples the said common point to the common point of the resistances.
According to a preferring embodiment, the said rectangular signals are generated by a multivibrator and applied to the base of a transistor coupling the common point of the two windings to earth, a continuous reference voltage being applied to the common point of the resistances.
Other features, as well as the advantages of the invention will appear clearly in the light of the following description:
In the accompanying drawing:
FIG. 1 shows schematically a detector device in accordance with the invention;
FIG. 2 shows a first manner of construction of the detector member proper, with its two windings opposite to a single metallic element;
FIG. 3 shows a variant in which the two windings are disposed opposed to two separate metallic elements;
FIG. 4 is a diagram of a peak detector circuit adapted to be used in the device of FIG. 1;
FIG. 5 shows a preferred manner of construction of the detector device of FIG. 1;
FIG. 6 shows waveforms intended to illustrate the operation of the device;
FIG. 7 shows in part a first variant of the circuit of FIG. 5, in which supplementary diodes are intended to compensate for the influence of temperature; and
FIG. 8 shows, seen in section, a third manner of construction of the detector member proper, more particularly intended for the measurement of displacements of a pusher element.
In FIG. 1 there are shown two identical windings 1 and 2, disposed in two Ferrite half-pots 3 and 4 intended to concentrate the lines of force directed towards two identical conductive metallic elements 5 and 6, one of which is for example fixed and the other of which is that of which it is intended to measure the displacements. These elements have for example a thickness comprised between 2/10ths of a millimeter and 1 millimeter.
A pulse generator 9 provides rectangular signals of predetermined frequence and cyclic ratio which are applied to the windings through charging resistances 7 and 8 respectively.
The points A and B common to the respective resistances and to the corresponding windings are coupled to two inputs of a differential amplifier 12, by means of two peak dete
REFERENCES:
patent: 2959962 (1960-11-01), Epstein
patent: 3336525 (1967-08-01), Church
patent: 3995493 (1976-12-01), Nishihara
Ramel Francois
Rousseau Alain
Drucker William A.
Effa Etudes
Woodiel Donald O.
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