Measuring and testing – Liquid level or depth gauge
Reexamination Certificate
2000-07-13
2002-07-16
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
C073S29000R, C367S087000
Reexamination Certificate
active
06418787
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a level transmitter for a liquid container, more specifically a fuel tank in a motor vehicle, having a plurality of sensors and a method for determining the level in the liquid container.
2. Description of the Related Art
Level transmitters for determining levels in liquid containers are much used in practice and are therefore known. Depending on the site of installation of the liquid container, the containers can take the most varied forms. For example, the liquid containers used in motor vehicles such as fuel tanks are adapted very strongly to prescribed spaces. Thus, many of the fuel tanks currently used have two or more chambers. A level transmitter is arranged in each of these chambers to determine a level in the liquid container having more than one chamber. In these cases, the level transmitters comprise float-actuated lever transmitters or transmitters comprising a plurality of sensors.
European Patent reference EP 0 690 293 A2 discloses level transmitters with magnetostrictive sensors for use in aircraft. In each case a level transmitter comprises a tube with a float arranged for vertical movement. A magnet is arranged in this float. Sensors made from magnetostrictive material are fastened in the tube at one end on a strip made from magnetic material. A wire-wound resistor is located at the opposite end of the sensors. If the float passes with the magnet into the region of the sensor, the sensor makes contact with the wire-wound resistor. A measuring unit arranged on the bottom of the fuel tank is used to determine the level in the fuel tank at the site of the respective level transmitter via the magnitude of the measured resistance. These transmitters are expensive because each level transmitter has a plurality of sensors, which are interconnected to form a sensitive measuring arrangement. Furthermore, each of these measuring arrangements must be encapsulated separately. Moreover, each level transmitter requires a float with a magnet, to transmit the liquid level to the sensors. Additional expenditure on assembly results from the fact that the tube must be fastened to the bottom of the fuel tank. Finally, each level transmitter is connected to its own dedicated measuring unit. In addition to the high initial outlay required for installing the multiplicity of level transmitters, there is a rise in the susceptibility to faults of such a system because of the number of components used. A further disadvantage in the use of plural level transmitters in a liquid container is that the useful container volume is reduced to an extent which cannot be neglected.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a level transmitter and a method for determining the level which overcomes the problems of the prior art. The level transmitter according to the present invention is of a simple design and not susceptible to faults. Moreover, it is not to require any additional protective measures for electric lines or the evaluation unit. The level transmitter according to the present invention is to be capable of universal use, easy to assemble and cost-effective. The arrangement of the level transmitter is intended not to diminish the useful container volume substantially.
The object is achieved by a level transmitter for a liquid container, comprising, a plurality of sensors comprising a magnetostrictive material arranged within a liquid container, a transceiver unit operatively arranged for transmitting an alternating magnetic field and receiving mechanical oscillations produced by the plurality of sensors in response to the alternating magnetic field, said transceiver unit being arranged outside of the liquid container and, an evaluation unit operatively connected to said transceiver unit and arranged for receiving the measured oscillating values from the transceiver unit, wherein a dimension of each of said plural sensors differs from the dimensions of the others of said plural sensors such that each of the plural sensors has its own characteristic oscillatory behavior.
The level transmitter according to the present invention has a plurality of sensors made from a magnetostrictive material, a transmitter unit for transmitting an alternating magnetic field, a receiver unit for receiving mechanical, i.e., ultrasonic, oscillations, and an evaluation unit. The sensors are arranged in the liquid container. All other components of the level transmitter are located outside the liquid container. The transmitter applies the alternating magnetic field to the sensors to determine the level. Each sensor oscillates in response to the alternating magnetic field and the oscillations are detected in turn by the receiver unit. The measured oscillation values are fed thereafter to the evaluation unit. To determine whether the sensor is located in the liquid or in air, use is made of the circumstance that the oscillatory behavior of the sensor in the liquid differs from that in air.
If each of the sensors had the same physical dimensions, they would have the same oscillatory behavior and it would not be possible for the measured values to be assigned to the individual sensors by the evaluation unit. Accordingly, the dimensions of all the sensors differ in such a way that the oscillatory behavior of one sensor differs clearly from the others. By virtue of the fact that the frequency of the alternating magnetic field is adapted to the oscillatory behavior of each sensor, it is possible to measure the oscillatory behavior of each individual sensor. The measured oscillation values are fed to the evaluation unit, where each measured oscillation value is compared with a corresponding desired value, as a result of which the first signal for the level of the respective sensor is formed. After all the sensors have been interrogated, the evaluation unit likewise forms from the first signals a second signal which corresponds to the level in the liquid container.
An advantage of the level transmitter according to the present invention is that only the sensors are arranged in the liquid container. All the other components are located outside the liquid container. Since the sensors are a few square millimeters in size, and no electrical lines are required for making contact or for transmitting measured values to the sensors, the useful container volume is no longer reduced. Moreover, the level transmitter according to the invention comprises a very cost-effective design because one evaluation unit may be used to evaluate each of the sensors.
The fact that most of the components of the level transmitter are arranged outside the liquid container also keeps the cost of assembly particularly low. In some circumstances, the number of necessary separate openings in the liquid container may be economized.
The present invention also relates to a measuring method in which no forces arise, for example, from movements of floats or levers. Consequently, the fastening of the sensors in the liquid container is configured with particular ease. As stated above, the transceiver unit detects measured oscillation values without the use of cables. Accordingly, the site of installation of all the other parts of the level transmitter may be selected freely. This has the advantage, in turn, that the electrical components no longer have to be arranged in regions of danger to them, with the result that the susceptibility to faults is reduced, and the outlay for reliable operation is reduced.
The sensors may be mounted in a particularly simple way when they are fastened onto the container wall. The fastening, for example by bonding on or latching, may comprise any form if it is ensured that the sensors are not restricted in their oscillation. Owing to the arrangement at any desired points in the liquid container, the level may be determined exactly even in liquid containers of complicated shapes.
In a further embodiment, the sensors may be arranged on other built-in components in the liquid container. Thus, the outl
Cohen & Pontani, Lieberman & Pavane
Mannesmann VDO AG
Williams Hezron
Wilson Katina
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