Measuring and testing – Volume or rate of flow – By measuring electrical or magnetic properties
Patent
1997-06-09
1998-12-29
Hoon, Max H.
Measuring and testing
Volume or rate of flow
By measuring electrical or magnetic properties
7386108, G01N 158
Patent
active
058544291
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for providing protection against an external magnetic filed to a system for conveying rotary drive about an axis between two mechanical members that are coupled together magnetically.
Systems are already known for conveying rotary drive about an axis between two mechanical members by magnetic coupling, such systems comprising at least two magnetized elements, each secured to a respective one of said mechanical member. One of the magnetic elements constitutes the driving portion of the system while the other magnetic constitutes the driven portion thereof. The magnetic elements are magnetized axially and they are designed to interact with each other so that rotation imparted to one of the mechanical members is transmitted to the other mechanical member via the above-described drive system.
The Applicant has observed that when such systems providing drive by magnetic coupling are in the presence of a magnetic field, and more particularly of a magnetic field gradient, such drive systems can be disturbed and, for example, loss of magnetic synchronization can be observed between the driving portion and the driven portion of the drive system.
For example, in the field of fluid metering and as shown in FIG. 1, it is known from Brazilian utility model 91BR-100684 to provide a magnetic protection device 1 which surrounds a drive system 2 making use of magnetic coupling in a water meter.
The drive system comprises two axially magnetized rings 3 and 5 disposed facing each other along a geometrical axis coinciding with the axis of a spinner 7 and of a shaft 9 connected to a totalizing counter. The protection device comprises two parts 11 and 13 of magnetic material that are symmetrical about the horizontal midplane P passing between the magnetized rings 3, 5. As shown in FIG. 2, each of the parts 11 and 13 has two cylindrical wall portions 11a & 11b or 13a & 13b extending parallel to the geometrical axis over the same axial extent or height, and the walls are connected together in pairs at their axially remote edges vial respective third web portions 11c and 13c that are annular and that extend radially, thereby causing each piece to be U-shaped in a section that contains the geometrical axis.
The protection device 1 is obtained by uniting the two pieces made of magnetic material, thereby giving said device the form of a torus of approximately rectangular section.
When the magnetic protection device 1 is installed in the water meter, it is placed around the two magnetized rings 3 and 5 and its axial extent or height corresponds to that of the magnetic drive system.
Such a protection device channels field lines from a magnetic field external to the water meter, and as a result the external magnetic field is greatly reduced in the zone inside the parts 11 and 13 made of magnetic material and within which the magnetized rings 3 and 5 are situated.
Nevertheless, the Applicant has observed that in the presence of an external magnetic field, a magnetic field gradient is set up in the vicinity of the axial ends of the zone inside the parts 11 and 13 in which the rings 3 and 5 are situated, and that this gradient can hinder operation of the drive system making use of magnetic coupling.
The Applicant has also observed that by increasing the inside diameter of the parts 11 and 13, the above-specified zone in which the magnetic field due to the external magnetic field is substantially zero is itself reduced. The effectiveness of such a protection device therefore relies on its proximity relative to the magnetized rings. In certain types of meter, such proximity can give rise to magnetic interactions between the magnetized rings and the parts made of magnetic material.
The present invention seeks to remedy the drawbacks of the prior art by means of a device for providing a system for conveying rotary drive about an axis between two mechanical members by magnetic coupling with protection against a magnetic field external thereto, which device is simple to implement and makes it possible to
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patent: 4253341 (1981-03-01), Ikeda et al.
patent: 5691586 (1997-11-01), Yonnet et al.
Freund Marcel
Haudebert Lionel
Hoon Max H.
Pojunas Leonard W.
Schlumberger Industries S.A.
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