Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Patent
1986-10-03
1989-10-24
Karlsen, Ernest F.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
324127, 324105, G01R 3300, G01R 1500
Patent
active
048765031
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method of measuring the intensity of a DC current, particularly a high current; it also relates to a device implementing this method.
An electric current is traditionally measured by using a shunt, that is to say a device based on Ohm's law. Consequently, in order to be measurable, the voltage drop across the shunt must be significant and this voltage drop is also directly related to the dissipation by Joule effect of the shunt itself. Since any resistive material is related to a temperature coefficient, the temperature variations of the shunt cause systematic errors in measuring the current. This problem is particularly important for measuring high currents where the shunts are bulky and expensive sub assemblies. The purpose of the invention is to overcome this type of problem.
For this, the invention provides a method for measuring the intensity of a DC current flowing in the circuit, in which method said current is caused to flow in a magnetic coil for creating a magnetic field in a given volume of space, in determining at least the temperature of said coiled magnet and measuring the value of the magnetic field in said given volume, this value being representative of the strength of the current, knowing said temperature.
So as to have a more direct measurement of the strength of the current, the temperature of the magnetic coil may be stabilized by simple means. Furthermore, the magnetic field will be measured preferably by using the nuclear magnetic resonance phenomenon on a sample of chosen atoms, placed in a zone where the above mentioned magnetic field has a field sufficient homogeneity for using said phenomenon.
The invention also relates to a device for measuring the strength of a DC current flowing in a circuit, including a magnetic coil intended to be inserted in series in said circuit for generating a magnetic field in at least a given volume of space, means for determining at least the temperature of said magnet and means for measuring the magnetic field in said given volume.
Means will preferably be provided for stabilizing the temperature of the magnet, for example a control line regulating the temperature of a fluid cooling said magnet. As mentioned above, the magnetic coil will be preferably formed so that the magnetic field is sufficiently homogeneous in said given volume for allowing a nuclear magnetic resonance phenomenon to be used, and an NMR probe, known per se, will be placed in said given volume for measuring the value of the magnetic field.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other advantages thereof will appear from the following description of a devide conforming to its principle, given solely by way of example with reference to the accompanying drawings in which:
FIG. 1 is a block diagram of a device formed in accordance with the principal of the invention;
FIG. 2 is a detail view showing the structure of the magnetic coil, in longitudinal section;
FIG. 3 is a section through III--III of FIG. 2;
FIG. 4 is a detail view of the turns of said magnetic coil.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a device has been shown in FIG. 1 for measuring the current I flowing in the electric circuit 10 and including a magnetic coil 11, inserted electrically in series in circuit 10, a cooling fluid flow circuit 14 coupled thermally to said magnet and means 15 for measuring the magnetic field created by said magnet in the center of the coil.
More precisely, the measuring means 15 include an NMR probe 16 placed in the center of the magnetic field zone created by the magnet and, in the example, a radio frequency generator 17 as well as means 18 for measuring the radio frequency signal at the terminals of the NMR probe 16. All the elements forming the magnetic field measuring means are well known and are commercially available, particularly for spectrometry applications, such as shown in "a calibration standard for high DC currents" Control Engineering" vol. 26, no. 9
REFERENCES:
patent: 466087 (1891-12-01), Weston
patent: 548230 (1895-10-01), Shallenberger
patent: 2836791 (1958-05-01), Kaplan
patent: 2845595 (1958-07-01), Leete
patent: 3250995 (1966-05-01), Kalinowski et al.
patent: 4138641 (1979-02-01), Karlin et al.
patent: 4672972 (1987-06-01), Berke
patent: 4683434 (1987-07-01), Tschopp
Patents Abstracts of Japan, vol. 7, No. 198, (P-220)(1343), Sep. 2, 1983, & JP, A, 5897663 (MITSUBISHI DENKI K.K.), Jun. 10, 1983, voir resume.
Soviet Journal of Instrumentation and Control, No. 9, Sep. 1969, Oxford, (GM), L. K, Dondoshanshkii et al.: "A Device for Converting Current to Magnetic Induction for a Nuclear Magnetic Resonance Frequency Converter", pp. 61-62, voir l'article en entier.
Control Engineering, vol. 26, No. 9, Sep. 1979, N.Y., (US), "A Calibration Standard for High DC currents", p. 39, voir l'article en entier.
Karlsen Ernest F.
Thomson-CGR
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