Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2001-02-20
2003-04-01
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S300000
Reexamination Certificate
active
06541974
ABSTRACT:
PRIORITY CLAIM
This is a U.S. national stage of application No. PCT/DE99/02503, filed on Aug. 6, 1999. Priority is claimed on that application and on the following application:
Country: Germany, Application No.: 198 38 664.8, Filed: Aug. 19, 1998.
The present invention relates to a device for storing gaseous media, with a storage container for receiving the medium to be stored and a measuring device for measuring the nuclear magnetic resonance, according to the preamble of patent claim 1. Furthermore, the invention also relates to a method of measuring the filling level of a medium in a storage container.
In the storage of gaseous media in corresponding storage containers, for example in the storage of gaseous fuels such as hydrogen or natural gas in tank systems suitable for this purpose, the determination of the filling level, i.e. the stored amount of gaseous medium, in the storage container represents a major problem.
Until now, the filling level has generally been determined indirectly by the discharged amount of the gaseous medium. However, this measuring method has a series of disadvantages. For instance, firstly, a precise knowledge of the amount of the gaseous medium initially stored is required. Furthermore, possible losses, which may arise for example due to leaks in the storage container, cannot be taken into account by the known measuring method, so that inaccuracies can occur here. Due to the fact that, in the case of the known indirect measuring method, the exact filling data are required to allow indications concerning the filling level of the gaseous medium in the storage container to be given, this measuring method is not very suitable, particularly in the case of tank systems for storing gaseous fuels.
A further possible way of measuring the filling level of a gaseous medium in a storage container is to measure the pressure prevailing in the storage container. The pressure prevailing in the storage container provides information on the amount of stored gaseous medium indirectly in a manner dependent on the prevailing temperature. This measuring method can only be used, however, whenever the gaseous media are stored in the storage container with an increased pressure and there is a direct proportionality between the pressure and the amount stored.
WO 97/19 363 discloses a measuring device for determining the filling level of a gas pressure vessel which can be used in particular for space travel. This measuring device is based on the principle of nuclear magnetic resonance and has a means for generating an essentially uniform magnetic field along an axis of the gas pressure vessel and a means for generating an oscillating magnetic field transversely to the uniform magnetic field. The means for generating the two magnetic fields are formed in each case as electric windings which surround the gas pressure vessel on the outside. Such a construction requires respectively adapted electric windings for each form of container.
It is also known from U.S. Pat. No. 5,539,309 to use the principle of nuclear magnetic resonance to ascertain chemical or physical properties of samples. For this purpose, sample containers with solid or liquid content are introduced into an investigation area which lies in a static magnetic field. To generate the nuclear magnetic resonance, the sample is surrounded by an electrical winding, which generates a magnetic alternating field perpendicularly to the static magnetic field. The problem of filling level measurement of gas pressure vessels is not mentioned in this document.
SUMMARY OF INVENTION
Starting from the cited prior art, the present invention is based on the object of providing a device for storing a gaseous medium in a storage container so that the disadvantages mentioned are avoided. In particular it is intended to provide a device with as high a storage capacity as possible, in which the filling level of the gaseous medium can be determined directly in a simple, exact and uncomplicated way, without information on the history of the filling and removing operations being required and without uncontrolled losses due to leaks or the like falsifying the measurement result. Furthermore, a method of measuring the filling level of a gaseous medium in a storage container is to be provided.
The object is achieved according to the first aspect of the invention by a device for storing a gaseous medium, with a storage container for receiving the gaseous medium and with a measuring device for measuring the nuclear magnetic resonance of the gaseous medium located in the storage container. The measuring device generates a static magnetic field and an electromagnetic alternating field, the field lines of which are perpendicular to the field lines of the static magnetic field. This device is characterized in that the storage container is filled with a storage mass for storing the gaseous medium. The measuring device has a measuring head in which the static magnetic field and the electromagnetic alternating field are generated. Furthermore, the measuring head is arranged so that it covers a partial volume of the storage container, the partial volume being representative of the entire storage container with regard to the filling with the storage mass and the stored gaseous medium.
This creates the possibility of being able to measure the filling level of the stored medium directly. Apart from the type of stored medium and the temperature, no special additional knowledge is required concerning further values and data of the medium such as pressure or its filling history. The measuring principle is fundamentally suitable for all media that have atoms of which the nuclei have a magnetic moment, that is in particular hydrogen.
The basic idea of the present invention is that, for determining the filling level, the nuclear magnetic resonance (NMR) of the stored medium is measured. This makes use of the principle that some atomic nuclei, such as for example those of hydrogen, have a nuclear magnetic moment (nuclear spin). This is in interaction with an external magnetic field. In the case of hydrogen, which is considered here in more detail by way of example for better understanding, without however restricting the invention to hydrogen, the magnetic moment can be set by the external magnetic field in parallel or antiparallel to the applied magnetic field. The two setting possibilities are different in terms of energy, so that two different energy levels exist. These energy levels are differently populated in thermal equilibrium. That is to say, there are more nuclear spins in the lower energy level than in the upper energy level. The quantitative distribution between the two energy levels is dependent solely on the type of the respective medium and its temperature. If the filled medium is subject only to relatively small temperature fluctuations (for example +/−10° C.), it is possible, depending on the requirements for measuring accuracy, for the temperature influence to be ignored. In principle it is true that the difference in the population of the energy level is all the smaller the higher the temperature of the medium. Thus, if energy in the form of electromagnetic radiation is supplied to this system, with the amount of energy supplied corresponding to the difference between the two energy levels, nuclear spins are transferred from the lower energy level into the upper energy level. The result can be recorded and evaluated with regard to the actual filling of the storage container and transmitted.
Consequently, measurement of the nuclear magnetic resonance in a partial volume of the storage container covered by the measurement makes it possible, by means of extrapolation with regard to the total volume, to determine the filling level of the medium stored in the storage container via the actually prevailing quantity of atomic nuclei of the medium located in it. All that is needed for this purpose is appropriate calibration with respect to the storage volume existing in each case, in order that the ascertained measured values can be assign
Arana Louis
Cohen & Pontani, Lieberman & Pavane
Mannesmann AG
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