Measuring and testing – Liquid level or depth gauge – Float
Reexamination Certificate
1999-09-22
2001-03-13
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Float
C073S307000, C073S317000, C073S319000, C073S320000, C073S321000, C200S08400B
Reexamination Certificate
active
06199428
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
In many technical systems or apparatuses it is necessary to measure the fluid level of a container filled with a fluid.
It is already known to use for this purpose a measuring apparatus having a float and a mechanical-electrical movement pickup coupled to the latter. The movement pickup detects a change in the position of the float caused by the variable fluid level and, at its output, provides an electrical signal which is characteristic of the height of the fluid level.
In many applications, it is necessary to measure the fluid level of inflammable or explosive fluids. In these cases, generating an electrical signal in the container and passing it through the container wall often cannot be tolerated for safety reasons, which is why structurally complicated mechanical bushings are used.
A further disadvantage of known fluid level measuring devices consists in the use of complicated configurations that are cost-intensive and, in some instances, also maintenance-intensive. Fluid level measuring devices of this type are not appropriate for installation in commodity and/or disposable products, on account of their high costs.
Further difficulties arise in the case of measuring fluid filling levels in miniature containers, since known fluid level measuring devices frequently have a physical volume that is too large for such applications.
European Patent EP 680 614 B1 discloses an apparatus for detecting an angular position of an object by a giant magneto resistor (GMR) sensor.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a fluid level measuring device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is constructed in a simple manner, can be produced in a cost-effective manner and can be employed advantageously in particular in the case of measuring the fluid level of inflammable or explosive fluids or else in case of use in disposable products having, if appropriate, a small physical size.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a container containing a fluid, a fluid level measuring device for measuring a fluid filling level in the container, the fluid level measuring device including:
a float disposed in the container and having a given relative density less than a relative density of the fluid;
a magnet generating a magnetic field disposed in the container and coupled to the float in terms of movement and, in an event of a change in the fluid filling level the magnet executes a movement corresponding to the change in the fluid filling; and
a magnetic field sensor disposed outside of the container in a zone of influence of the magnetic field generated by the magnet and outputs an electrical signal representative of a height of the fluid filling level of the container, the magnetic field sensor serving to obtain contactless information concerning the fluid filling level and the magnetic field sensor being a magnetoresistive sensor.
An essential aspect of the invention is for the magnetic field generated by the magnet to be detected by the magnetic field sensor and for information concerning the fluid level in the container to be obtained as a result of this, the information being obtained contactlessly. In this case, just the combination containing the float and the magnet, that is to say products that can be produced in an extremely cost-effective manner, is contained in the container.
A magnetoresistive sensor is preferably used as the magnetic field sensor. Magnetoresistive sensors generally have a thin layer made of a magnetoresistive material (for example Ni, Fe, Co, NiFe) which is magnetized in the plane of the layer. In the event of a rotation of the magnetization of the layer with respect to the direction of a measurement current flowing in the layer, the electrical resistance of the layer changes, and this change can be detected and measured as the signal which is representative of the height of the filling level of the container.
It is particularly preferable to use a giant magneto resistor (GMR) sensor for generating the electrical signal which is representative of the height of the filling level. A GMR sensor is a magnetic field sensor that is constructed from a magnetic multilayer system and has a particularly pronounced magnetoresistive effect. A GMR sensor that can be used according to the invention is described in European Patent EP 0 680 614 B1, for example.
With the use of a GMR sensor large measurement distances and adjustment tolerances between the GMR sensor and the magnet are made possible, and it is possible to attain virtually complete interference immunity with respect to changes in the measurement distance during use. This is due to the fact that the GMR sensor, in contrast to other known magnetic field sensors (for example Hall sensors), when configured suitably, measures only the direction—which is essentially independent of the measurement distance—of an external magnetic field with respect to a predetermined reference direction of the GMR sensor and not the intensity thereof.
A structurally simple embodiment variant of the invention is characterized by the fact that the magnet is a bar magnet.
The coupling between the magnet and the float can be realized in diverse ways depending on the specific application. A simple and much preferred measure consists in the magnet being coupled directly to the float, that is to say without the interposition of an actuating mechanism.
According to a preferred exemplary embodiment of the invention, the magnet is articulated on the container in a manner allowing it to rotate about an axis of rotation oriented essentially parallel to the filling level surface of the fluid. In this case, the axis of rotation may run through the magnet for example in a central region or in an end region in the transverse direction.
An alternative exemplary embodiment is characterized by the fact that the magnet is guided by a link in the container, the link extending essentially perpendicularly to the filling level surface.
The magnet and the float may also expediently be realized in the form of a single structural unit. By way of example, this structural unit may be realized by an optionally foamed plastic material with incorporated ferrite particles.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fluid level measuring device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
REFERENCES:
patent: 4881088 (1989-11-01), Fisher, Jr. et al.
patent: 5426271 (1995-06-01), Clark et al.
patent: 5648885 (1997-07-01), Nishioka et al.
patent: 5649450 (1997-07-01), Glab et al.
patent: 0 680 614 B1 (1995-11-01), None
Estevez-Garcia Jaime
Volpe Francesco
Greenberg Laurence A.
Lerner Herbert L.
Loo Dennis
Siemens Aktiengesellschaft
Stemer Werner H.
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