Measuring and testing – Liquid level or depth gauge – Float
Reexamination Certificate
1998-11-05
2001-07-03
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Float
C073S322500
Reexamination Certificate
active
06253611
ABSTRACT:
This invention relates to a liquid level indicating gauge apparatus of the kind which includes, in combination, an upright cylindrical tube of non-magnetic material, a first permanent magnet which is movable axially within and along the tube and a second permanent magnet which is magnetically coupled to the first magnet and is movable along the outside of the tube, and wherein one of said magnets is incorporated in a float that is adapted and arranged to float at the surface of a liquid, so that as the floating magnet rises and falls, the second magnet follows, rising and falling in sympathy, and thereby indicates the level of the surface of the liquid supporting the floating magnet.
In such arrangements as have been hitherto proposed, either the tube is immersed in the liquid whose level is to be measured of DE-A-1 139 660, or U.S. Pat. No. 5,020,367, for example; or in a converse arrangement, of DE-A-1 034 877, for example, the tube will contain such liquid. Thus the float may be in the form of a ring or collar surrounding the tube within which is located the second magnet; or in the converse arrangement, the floating magnet will be arranged within the gauge tube and a second magnet will be arranged in a follower arranged externally of the gauge tube.
Thus it is known to provide a gauge system where a float rises and falls inside a sealed gauge tube of non-magnetic material, such as austenitic stainless steel, and which tube is connected, in sealed manner, to a tank or receiver the liquid level of whose content is to be measured or indicated. Such a tank and gauge may for example contain inflammable or toxic fluid, or it may be part of a pressurised system. The pressure resisting and integral construction of a gauge of this type renders it particularly safe and suitable for use in marine, process engineering and many other services.
Where magnetic forces are used to couple two magnets, one arranged within, and the other arranged without the gauge tube, the magnetic coupling forces needed for one magnet reliably to follow the second magnet are very strong; and this is particularly the case with systems designed to be secure and reliable, so that shock or vibration cannot readily dislodge the follower magnet from its correct position.
And it is known to employ in such gauges, internal and external magnets which are magnetically coupled, either using forces of magnetic attraction, or using forces of magnetic repulsion. However where, as in DE-A-23 42 735, strong magnetic forces are employed, there are generally present significant radial forces pulling the coupled magnets towards or away from one another. This gives rises to severe instability of the magnetic array; with the inner magnet being urged laterally towards the side wall of the gauge tube, while equally strong forces pull the outer magnet towards the outer side of the tube. These radial forces give rise to friction which can greatly impair the accuracy of the level gauge indication. Indeed, the prior art does not disclose a practical and commercially usable system which provides for a magnetically stable array such that one magnet reliably follows the movements of the other, with high frictional forces being avoided.
Accordingly, it is the main purpose of this invention to provide a liquid level gauge tube device of the general kind referred to, with the tube having inner and outer coupled magnets, but in which the magnets are arranged in a magnetically stable array, with frictional forces set up between the float magnet and the tube wall on the one hand, and between the follower magnet and the tube wall on the other hand, being minimised, and with the system being such as to provide for a reliable, rapid and sensitive response to liquid level change causing float movement.
A further preferred requirement of such a device is that the visual indication of level should not be restricted substantially to a front on view of the external follower system. And it is preferred that the device should be light, simple and economic and should also lend itself to remote signalling; and preferably it should be capable of being adapted to indicate high and low level alarm positions.
Broadly, this invention provides a liquid level indicator which comprises, in combination, an upright cylindrical tube of non-magnetic material, a first permanent magnet movable coaxially within the tube, and a second annular permanent magnet movable coaxially outside the tube, both magnets having magnetic polar axes which are in parallel with the axis of the tube, and both magnets having like poles uppermost, and with one said magnet being carried by a float resting at the surface of the liquid whose level is to be indicated, and the magnets being so spaced that the magnet carried by the float supports the other magnet by magnetic repulsion at a level above that adopted by the floating magnet.
Preferably, a third permanent magnet is provided, which third magnet is mechanically linked either to said first permanent magnet or to said second permanent magnet and is of similar form to that of the magnet to which it is linked, and whose magnetic field is aligned in the same direction as the first and second magnets.
The first magnet may be carried by the float and the float is slidable within the tube, and the second magnet is attached to a liquid level indicator sleeve slidable along the outside of the tube.
According to another aspect of this invention there is provided a liquid level indicating gauge apparatus which includes, in combination, an upright cylindrical tube of non-magnetic material, a first permanent magnet of cylindrical disc-like or ring like shape movable axially within and along the tube and a second permanent magnet of annular shape surrounding the tube and movable axially along the outside thereof; and wherein both said magnets are so magnetized and maintained in such orientation relative to each other and to the tube as to have the same polarities in the field directions with their magnetic poles being aligned along the tube axis or in parallel therewith, and wherein one of said magnets is incorporated in a float that it is adapted and arranged to float at the surface of a liquid, while the other of said magnets is supported by magnetic repulsion at a level just above that adopted by the floating magnet, with said magnetic repulsion having both axial and radial components. Due to these components, both axial and radial, of the forces of magnetic repulsion, it is possible to arrange the coupled magnets, one supported by the other, in a magnetically stable array, and with the radial force component providing what equates to a “self-centreing” effect; or an effect where the magnets, one inside and one outside the gauge tube, tend to find positions which are substantially coaxial with the tube axis.
Either the tube will be immersed in the liquid whose level is to be measured; or the tube will contain such liquid. The floating magnet may be carried by a float which is in the form of a collar surrounding the tube; or the floating magnet will be mounted in a float arranged within the gauge tube. In either case the second, follower magnet will be supported by magnetic repulsion at a higher level and on the opposite side of the tube wall from the floating magnet.
In the preferred arrangement, as so far described there have been two magnets, one being float mounted and the other being arranged to follow movements of the first. However in an alternative arrangement, there are three such permanent magnets arranged to be movable coaxially, back and forth, generally along said tube axis. All said magnets are magnetized so as to have the same polarities in the field directions along and in parallel with the tube axis; and two of said magnets are arranged paired along said axis at a fixed distance from one another, while the third magnet is maintained generally coaxial with the magnets of said pair, and by magnetic repulsion, at a level between them. In such an array, the third magnet is supported by magnetic repulsion by the lower of the other two m
Carter Jason
Varga Otto Herman
Nixon & Vanderhye P.C.
Seetru Limited
Williams Hezron
Wilson Katina
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