Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2001-10-18
2003-11-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S11700H, C324S249000
Reexamination Certificate
active
06642705
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric current sensor for detecting the electric current flowing through a signal line by detecting the magnetic field from the electric current by means of a magnetic detector.
2. Related Background Art
Conventionally, a current transformer, a Hall-effect device or an MR (magnetoresistive effect) device is used for an electric current sensor. As a result of the ever-increasing demand for power-saving equipment, the market for electric current sensors has been expanding remarkably in recent years. Particularly, the demand for high precision electric current sensors that can monitor delicate changes in the electric current is high. However, the sensitivity of conventional electric current sensors is limited and the advent of novel and highly sensitive electric current sensors is expected.
The idea of using a magnetic impedance device (to be referred to as MI device hereinafter) as the magnetic detector of an electric current sensor for detecting the electric current flowing through a signal line by detecting the magnetic field from the electric current is known. When a high frequency electric current is applied to the magnetic detector made of a magnetic material of an MI device, the impedance between the opposite ends of the magnetic detector changes as a function of the external magnetic field and the change in the impedance is taken out as signal.
Particularly, an MI device having a magnetic detector formed by folding an oblong and straight magnetic thin film for a plurality of times as disclosed in Japanese Patent Application Laid-open No. 8-330644 or No. 9-127218, which are filed by the applicant of the present patent application, and described hereinafter by referring to
FIG. 8
of the accompanying drawings, provides an advantage that it is as small as a resistor chip but more than hundred times sensitive than an MR device.
Such a highly sensitive MI device is arranged near a signal line through which the electric current to be observed flows so that the device detects the electric current by detecting the magnetic field generated by the electric current. However, it is normally difficult to measure the electric current with a high S/N ratio, eliminating the influence of any external turbulent magnetism, by means of a single MT device.
The use of a pair of MI devices that are differentially operated is known.
FIG. 8
of the accompanying drawings schematically illustrates a known arrangement of a pair of MI devices. Referring to
FIG. 8
, there are shown a signal line
8
through which the electric current to be observed flows and a pair of MI devices
10
A,
10
E comprising respectively non-magnetic substrates
12
a,
12
b
and magnetic detectors
14
a,
14
b
arranged on the respective non-magnetic substrates
12
a,
12
b.
Each of the magnetic detectors
14
a,
14
b
is formed by folding an oblong and straight magnetic thin film for a plurality of times. The magnetic detectors
14
a,
14
b
are adapted to detect a magnetic field in the longitudinal direction of the folded pattern of the magnetic thin films.
In
FIG. 8
, a three axes system is used for the convenience of explanation of the MI devices. The central axis of the signal line
8
is denoted by z-axis, whereas the x-axis runs perpendicularly relative to the z-axis while the y-axis runs perpendicularly relative to both the z-axis and the x-axis. The MI devices
10
A.
10
B are arranged near the signal line
8
at diametrically disposed respective positions on a circle centered at the central axis of the signal line
8
. The MI devices are adapted to detect a magnetic field in the respective longitudinal directions that are running in parallel with each other and agree with respective tangential directions of the circle on the xy-plane defined by the x- and y-axes.
When detecting the electric current, a bias magnetic field Hb is applied to the MI devices
10
A,
10
B in a direction running along the x-axis. Thus, the magnetic field Hi generated by the electric current I of the signal line
8
shows opposite phases relative to the MI devices
10
A,
10
B, whereas all external magnetic fields are in phase relative to the latter. Therefore, all external magnetic fields other than the magnetic field Hi are offset by differentially operating the MI devices
10
A,
10
B to make it possible to detect the electric current with a high S/N ratio.
However, there is a strong demand for electric current sensors of this type showing an improved sensitivity for electric currents. Therefore, it is the object of the present invention to provide an electric current sensor with an improved sensitivity that is down-sized and highly resistive against external turbulent magnetic fields and shows a high S/N ratio.
SUMMARY OF THE INVENTION
According to the invention, the above object is achieved by providing an electric current sensor comprising:
a pair of magnetic detectors arranged near a signal line flowing an electric current to be detected; and
a differential amplifier for differentially amplifying two signals obtained by said paired magnetic detectors detecting a magnetic field from the electric current flowing through said signal line and outputting a detection signal for said detected electric current;
wherein said paired magnetic detectors are arranged adjacent to each other in a direction along the y-axis as sandwiching the x-axis with the magnetic field detecting direction running along the x-axis, the central axis of said signal line being defined as z-axis, the x-axis being perpendicular relative to the z-axis, the y-axis being perpendicular relative to both the z-axis and the x-axis.
In another aspect of the invention, there is provided an electric current sensor comprising:
a pair of magnetic detectors arranged near a signal line flowing an electric current to be detected; and
a differential amplifier for differentially amplifying two signals obtained by said paired magnetic detectors detecting a magnetic field from the electric current flowing through said signal line and outputting a detection signal for said detected electric current;
wherein said paired magnetic detectors are arranged adjacent to each other in a direction along the y-axis as sandwiching the x-axis with the magnetic field detecting direction running in a direction inclined relative to the x-axis in a plane parallel to the xz-plane defined by said x-axis and said z-axis, the central axis of said signal line being defined as z-axis, the x-axis being perpendicular relative to the z-axis, the y-axis being perpendicular relative to both the z-axis and the x-axis.
REFERENCES:
patent: 5041780 (1991-08-01), Rippel
patent: 5570034 (1996-10-01), Needham et al.
patent: 5764055 (1998-06-01), Kawase
patent: 5889403 (1999-03-01), Kawase
patent: 6310475 (2001-10-01), Kawase et al.
patent: 358 157 (1961-11-01), None
patent: 298 19 486 (2000-03-01), None
patent: 0 947 843 (1999-10-01), None
patent: 8-330644 (1996-12-01), None
patent: 9-127218 (1997-05-01), None
“Neues Messverfahren fur Echtzeitstromsensoren und die Anwendung in der Pruftechnik,” Kolb, Messen Prufen Automatisieren, Internationales Fachjournal, Hans Holzmann, Verlag., Bad Worishofen, DE, No. 12, Dec. 1989, pp. 600-611.
Canon Denshi Kabushiki Kaisha
Le N.
Nguyen Vincent Q.
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