Measuring and testing – Liquid level or depth gauge – Immersible electrode type
Reexamination Certificate
1999-04-02
2001-10-02
Patel, Harshad (Department: 2855)
Measuring and testing
Liquid level or depth gauge
Immersible electrode type
C073S307000, C361S284000
Reexamination Certificate
active
06295869
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a capacitive measurement probe for measuring the level of a liquid in a tank, of the type comprising a body for mounting the probe and a first plate which is supported by the body and is intended, together with a second plate, to form a measurement capacitor intended to be connected to an electrical voltage supply, which plates are intended to be partially immersed in the liquid and to define, between them, a space for receiving the liquid.
The invention applies in particular to the storage of nitrogen in liquid/vapour equilibrium, for example for the preservation of biological products.
BACKGROUND OF THE INVENTION
For a given use, for example for medical applications, nitrogen in liquid/vapour equilibrium is stored in a tank with a predetermined nominal level of liquid nitrogen depending on the use.
Such a tank is generally equipped with a probe of the aforementioned type, placed vertically in order to measure the liquid level and optionally to regulate this level to the predetermined nominal value. A probe of this type is conventionally incorporated into a capacitive measurement device comprising an electronic processing unit which incorporates the voltage supply. This electronic unit is designed to determine the height of the liquid in the tank from the value of the capacitance of the measurement capacitor of the probe since, because of the different dielectric constants of the liquid and gas that are contained in the tank, the capacitance of the capacitor varies proportionally to the height of liquid between its plates and therefore depends on the level of liquid in the tank.
Generally speaking, for a given tank, the probe must be able to measure a whole range of nominal liquid levels. This range comprises a low nominal level of liquid, for example in the case in which the user wishes to store biological products in gaseous nitrogen in the tank, and a high nominal level of liquid, for example in the case in which the user wishes to store biological products in liquid nitrogen in the tank.
Consequently, the height of the plates of such a probe is of the same order of magnitude as the maximum storage height in the tank in question. Thus, different probes are necessary for tanks having different maximum storage heights.
SUMMARY OF THE INVENTION
The object of the invention is to solve this problem, by providing a standard probe which can be used for tanks having different maximum storage heights.
For this purpose, the subject of the invention is a capacitive measurement probe for measuring the level of a liquid in a tank, of the aforementioned type, characterized in that the first plate is mounted on the body so that it can be adjusted between at least a high measurement position and a low measurement position.
Depending on particular embodiments, the probe may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:
the first plate can slide with respect to the mounting body between the said positions;
the second plate forms part of the probe and is mounted on the body of the probe so that it can be adjusted between at least a high measurement position and a low measurement position;
the said second plate is fastened to the first plate;
the or each plate is tubular and slides telescopically with respect to the body of the probe;
the probe comprises means for returning the or each plate towards one of the said positions; and
the return means are means for electrically connecting the or each plate to the voltage supply.
The subject of the invention is also a storage tank, especially for a cryogenic fluid in liquid/vapour equilibrium, characterized in that it is equipped with a probe as described above, the or each plate of which is placed in a cavity communicating with the tank.
Depending on particular embodiments, the tank may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:
the cavity comprises a fixed plate which is placed opposite a plate of the probe and, together with the latter, defines a space for receiving the fluid, forming a measurement capacitor; and
the tank comprises an electronic processing unit which includes a voltage supply and which is connected to the or each measurement capacitor, this unit being suitable for determining the level of the liquid and/or for controlling means for supplying the tank with cryogenic liquid and/or for actuating an alarm.
REFERENCES:
patent: 3901079 (1975-08-01), Vogel
patent: 4231250 (1980-11-01), Leber
patent: 4258444 (1981-03-01), Orszullok
patent: 4483463 (1984-11-01), Buschmann
patent: 5065139 (1991-11-01), Shefsky
patent: 5669263 (1997-09-01), Borchers et al.
patent: 195 07 616 A1 (1996-09-01), None
Delatte Daniel
Delatte Patrick and Anne-Marie
Delatte Patrick and Anne-Marie
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Patel Harshad
Young & Thompson
LandOfFree
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