Title: Current sensor and overload current protective device therewith
Abstract: A small, low-cost, wide-range current sensor excellent in environmental resistance and noise resistance and high in accuracy, and an application device, a DC magnetic field is applied to two magnetic elements (1a, 1b) having a magnetic impedance effect by means of a magnet (3), while a negative feedback magnetic field is applied to both elements by means of a coil (2). The variation of the magnetic field depending on the external magnetic field applied to the magnetic elements (1a, 1b) is detected by detection units (7a, 7b). The difference between the output is amplified by a differential amplifier unit (8). Thus, detection is achieved in a wide range while eliminating the influence of the noise.
Patent Number: 6,984,989 Issued on 01/10/2006 to Kudo, et al.
| Inventors:
|
Kudo; Takahiro (Kanagawa, JP);
Kitaide; Yujiro (Kanagawa, JP);
Ishikawa; Kimitada (Saitama, JP)
|
| Assignee:
|
Fuji Electric Co., Ltd. (Kawasaki, JP)
|
| Appl. No.:
|
468317 |
| Filed:
|
February 14, 2002 |
| PCT Filed:
|
February 14, 2002
|
| PCT NO:
|
PCT/JP02/01239
|
| 371 Date:
|
December 19, 2003
|
| 102(e) Date:
|
December 19, 2003
|
| PCT PUB.NO.:
|
WO02/065143 |
| PCT PUB. Date:
|
August 22, 2002 |
Foreign Application Priority Data
| Feb 16, 2001[JP] | 2001-040268 |
| Mar 29, 2001[JP] | 2001-097090 |
| Current U.S. Class: |
324/529; 324/117.R; 324/207.13; 351/44; 351/87; 351/115 |
| Current Intern'l Class: |
G01R 31/28 (20060101) |
| Field of Search: |
324/117 R,117.H,207.13,524-530
361/44,87,115
|
References Cited [Referenced By]
U.S. Patent Documents
| 3571656 | Mar., 1971 | Paine et al.
| |
| 4425596 | Jan., 1984 | Satou.
| |
| 4716366 | Dec., 1987 | Hosoe et al.
| |
| 6479990 | Nov., 2002 | Mednikov et al.
| |
| Foreign Patent Documents |
| 0 989 411 | Mar., 2000 | EP.
| |
| 1 037 056 | Sep., 2000 | EP.
| |
| 3065661 | Mar., 1991 | JP.
| |
| 6347489 | Dec., 1994 | JP.
| |
| 09178707 | Dec., 1995 | JP.
| |
| 2000/-284029 | Oct., 2000 | JP.
| |
Primary Examiner: Nguyen; Vincent Q.
Attorney, Agent or Firm: Greer, Burns & Crain, Ltd
Claims
What is claimed is:
1. A current sensor, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection elements;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
two detection units detecting variations in magnetic field by a current from
variations in alternating current varying depending on an external magnetic field
applied to the magnetic detection element corresponding to the magnetic detection
element;
a differential amplification unit differentiation amplifying output of the two
detection units; and
a negative feedback magnetic field applying unit applying a predetermined negative
feedback magnetic field to the magnetic detection element depending on the output
of the detection unit or the differential amplification unit.
2. The current sensor according to claim 1, characterized in that
the negative feedback magnetic field applying unit is configured by a negative
feedback coil provided near the magnetic detection element and a negative feedback
element.
3. The current sensor according to claim 1, characterized in that
the DC bias magnetic field is applied by a magnet provided near the magnetic
detection element.
4. The current sensor according to claim 3, characterized in that
a non-magnetic substrate is provided with two magnetic detection elements of
thin ferromagnet film, and a magnet for applying the DC bias magnetic field and
the negative feedback coil for applying the negative feedback magnetic field are
formed by thin film.
5. The current sensor according to claim 1, characterized in that
the two magnetic detection elements are arranged such that the elements can have
equal absolute values of output to magnetic flux generated by a current, and have
opposite polarity.
6. A current sensor, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection elements;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
a negative feedback magnetic field applying unit applying a negative feedback
magnetic field to the magnetic detection elements;
a predetermined magnetic field applying unit applying a predetermined magnetic
field to the magnetic detection elements;
a switch unit applying one of the negative feedback magnetic field and the predetermined
magnetic field to the magnetic detection elements;
two detection units detecting variations in magnetic field by a current from
variations in alternating current varying depending on an external magnetic field
applied to the magnetic detection element corresponding to the magnetic detection
element; and
a differential amplification unit differentiation amplifying output of the two
detection units, characterized in that
depending on the output of the detection unit or the output of the differential
amplification unit, a negative feedback magnetic field is applied to two magnetic
detection elements in a period, a predetermined magnetic field is applied to two
magnetic detection elements in another period, and a predetermined amendment is
made to the output of the differential amplification unit depending on the output
of the detection unit or the output of the differential amplification unit of each
period.
7. The current sensor according to claim 6, characterized in that
the negative feedback magnetic field applying unit is configured by a negative
feedback coil provided near the magnetic detection element and a negative feedback
element.
8. The current sensor according to claim 6, characterized in that
the DC bias magnetic field is applied by a magnet provided near the magnetic
detection element.
9. The current sensor according to claim 8, characterized in that
a non-magnetic substrate is provided with two magnetic detection elements of
thin ferromagnet film, and a magnet for applying the DC bias magnetic field and
the negative feedback coil for applying the negative feedback magnetic field are
formed by thin film.
10. The current sensor according to claim 6, characterized in that
the two magnetic detection elements are arranged such that the elements can have
equal absolute values of output to magnetic flux generated by a current, and have
opposite polarity.
11. A current sensor, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection elements;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
a negative feedback coil applying a negative feedback magnetic field to the magnetic
detection elements and a plurality of negative feedback elements;
a switch unit switching the plurality of negative feedback elements;
two detection units detecting variations in magnetic field by a current from
variations in alternating current varying depending on an external magnetic field
applied to the magnetic detection element corresponding to the magnetic detection
element; and
a differential amplification unit differentiation amplifying output of the two
detection units, characterized in that
depending on the output of the detection unit or output of the differential amplification
unit, the plurality of negative feedback elements are selected.
12. An overload current protective device which is provided with a switch for
supplying a current from a power source to a load or cutting it off, a current
detector for detecting the current, and a control power source for providing power
to each unit of the device, for cutting off the current to a load when an overcurrent
occurs, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection elements;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
two detection units detecting variations in magnetic field by a current from
variations in alternating current varying depending on an external magnetic field
applied to the magnetic detection element corresponding to the magnetic detection
element;
a differential amplification unit differentiation amplifying the output of the
two detection units; and
a negative feedback magnetic field applying unit applying a predetermined negative
feedback magnetic field to the magnetic detection element depending on output of
the detection unit or the differential amplification unit.
13. The overload current protective device according to claim 12, characterized
in that
the negative feedback magnetic field applying unit is configured by a negative
feedback coil provided near the magnetic detection element and a negative feedback
element.
14. The device according to claim 12, characterized in that
the DC bias magnetic field is applied by a magnet provided near the magnetic
detection element.
15. The device according to claim 14, characterized in that
a non-magnetic substrate is provided with two magnetic detection elements of
thin ferromagnet film, and a magnet for applying the DC bias magnetic field and
a negative feedback coil for applying the negative feedback magnetic field are
formed by thin film.
16. The device according to claim 12 characterized in that
the two magnetic detection elements are arranged such that the elements can have
equal absolute values of output to magnetic flux generated by a current, and have
opposite polarity.
17. An overload current protective device, which is provided with a switch for
supplying a current from a power source to a load or cutting it off, a current
detector for detecting the current, and a control power source for providing power
to each unit of the device, for cutting off the current to the load when an overcurrent
occurs, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection element;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
a negative feedback magnetic field applying unit applying a negative feedback
magnetic field to the magnetic detection elements;
a predetermined magnetic field applying unit applying a predetermined magnetic
field to the magnetic detection elements;
a switch unit applying one of the negative feedback magnetic field and the predetermined
magnetic field to the magnetic detection elements;
two detection units detecting variations in magnetic field by a current from
the variations in alternating current varying depending on an external magnetic
field applied to the magnetic detection element corresponding to the magnetic detection
element; and
a differential amplification unit differentiation amplifying output of the two
detection units, characterized in that
depending on the output of the detection unit or the output of the differential
amplification unit, a negative feedback magnetic field is applied to two magnetic
detection elements in a period, a predetermined magnetic field is applied to two
magnetic detection elements in another period, and a predetermined amendment is
made to the output of the differential amplification unit depending on the output
of the detection unit or the output of the differential amplification unit of each
period.
18. The overload current protective device according to claim 17, characterized
in that
the negative feedback magnetic field applying unit is configured by a negative
feedback coil provided near the magnetic detection element and a negative feedback
element.
19. The device according to claim 17, characterized in that
the DC bias magnetic field is applied by a magnet provided near the magnetic
detection element.
20. The device according to claim 19, characterized in that
the DC bias magnetic field is applied by a magnet provided near the magnetic
detection element.
21. The device according to claim 17, characterized in that
the two magnetic detection elements are arranged such that the elements can have
equal absolute values of output to magnetic flux generated by a current, and have
opposite polarity.
22. An overload current protective device, which is provided with a switch for
supplying a current from a power source to a load or cutting it off, a current
detector for detecting the current, and a control power source for providing power
to each unit of the device, for cutting off the current to the load when an overcurrent
occurs, comprising:
two magnetic detection elements which have a magnetic impedance effect and are
provided near the wiring leading a current;
a current applying unit applying an alternating current to both ends of the magnetic
detection elements;
a DC bias magnetic field applying unit applying a DC bias magnetic field to the
magnetic detection elements;
a negative feedback coil applying a negative feedback magnetic field to the magnetic
detection elements and a plurality of negative feedback elements;
a switch unit switching the plurality of negative feedback elements;
two detection units detecting variations in magnetic field by a current from
variations in alternating current varying depending on an external magnetic field
applied to the magnetic detection element corresponding to the magnetic detection
element; and
a differential amplification unit differentiation amplifying the output of the
two detection units, characterized in that,
depending on the output of the detection unit or the output of the differential
amplification unit, the plurality of negative feedback elements are selected.
Description
TECHNICAL FIELD
The present invention relates to a current sensor using a magnetic element having
a magnetic impedance effect, and an overload current protective device for use
with the current sensor.
BACKGROUND ART
Conventionally, a current transformer has been widely used as a current
sensor, but its low sensitivity requires a laminated iron core, and the iron core
generates magnetic saturation, thereby causing the problem of an insufficient current
detection range. The iron core also causes the problem of a large sensor unit.
On the other hand, there is a method in which a Hall element and a magnetoresistive
element are used as current detection elements. However, since they are low in
detection sensitivity, the sensitivity is commonly improved by providing a magnet
gathering core and a Hall element or a magnetic element mounted at the gain of
the magnet gathering core.
Like the current transformer, the above-mentioned method of using the magnet
gathering core uses a core of at least 3˜4 cm and requires a large sensor
unit, and generates the magnetic saturation by the iron core, thereby obtaining
an insufficient current detection range. Furthermore, since the Hall element and
the magnetoresistive element have large output fluctuations depending on the temperature,
a temperature compensating circuit is required.
A high-sensitive magnetic detection element for replacing the Hall element and
the magnetoresistive element can be, for example, a magnetic impedance element
of an amorphous wire disclosed by Japanese Patent Application Laid-open No. Hei
6-347489, and a thin film disclosed by Japanese Patent Application Laid-open No.
Hei 8-73835.
A magnetic impedance element of any shape indicates a high-sensitive magnetic
detection
characteristic, but the magnetic impedance element of an element itself has nonlinearity
like the example of the magnetic impedance characteristic by the amorphous wire
shown in FIG. 10. By adding the bias magnetic field, the linearity of the
dependence on the magnetic field to which an impedance variation is applied is
improved (Japanese Patent Application Laid-open No. Hei 6-176930), a negative feedback
coil is wound around the magnetic impedance element, a current proportional to
the voltages on both ends of the magnetic impedance element is applied to the coil,
and a negative feedback is provided, thereby obtaining an element excellent in
linearity (Japanese Patent Application Laid-open No. Hei 6-347489).
The above-mentioned bias magnetic field is normally obtained by applying power
to the coil wound around. However, in this case, two types of coils, that is, a
bias coil and a feedback coil, are required, thereby upsizing the entire system.
Furthermore, using a wire type or a thin film type magnetic impedance
element, there is the problem of variable element sensitivity depending on the
material (magnetic permeability, resistivity, etc.) used when a magnetic impedance
element is produced and the variance in element size (length, film thickness, film
width, etc.).
FIG. 11 shows a common example of a detection circuit of the magnetic impedance element.
The detection circuit obtains impedance of a magnetic impedance element 1
by outputting through the detection circuit A and the amplification circuit B the
output obtained when a high frequency current passes from a high frequency current
generator (OSC) 4 to the magnetic impedance element 1. At this time,
the output is adjusted by a variable resistor VR.
However, to reduce the variance in element sensitivity in the circuit, it
is necessary to adjust and correct each system, thereby requiring a larger cost.
Although each system can be adjusted and corrected, an automatic correction cannot
be made. Therefore, the output of a device varies with time depending on the variations
in temperature, etc., thereby causing the problem that high precision compensation
cannot be realized.
Accordingly, the object of the present invention is to measure a wide
current range with high precision using a small and low-cost system without reducing
the precision by an environmental feature or with time.
DISCLOSURE OF INVENTION
To solve the above-mentioned problems, one embodiment of the invention includes:
two magnetic detection elements which has a magnetic impedance effect and is provided
near the wiring leading a current; a current applying unit for applying an alternating
current to both ends of the magnetic detection element; a DC bias magnetic field
applying unit for applying a DC bias magnetic field to the magnetic detection element;
two detection units for detecting the variations in magnetic field by a current
from the variations in alternating current varying depending on an external magnetic
field applied to the magnetic detection element corresponding to the magnetic detection
element; a differential amplification unit for differentiation amplifying the output
of the two detection units; and a negative feedback magnetic field applying unit
for applying a predetermined negative feedback magnetic field to the magnetic detection
element depending on the output of the detection unit or the differential amplification unit.
Another embodiment of the invention includes: two magnetic detection elements
which has a magnetic impedance effect and is provided near the wiring leading a
current; a current applying unit for applying an alternating current to both ends
of the magnetic detection element; a DC bias magnetic field applying unit for applying
a DC bias magnetic field to the magnetic detection element; a negative feedback
magnetic field applying unit for applying a negative feedback magnetic field to
the magnetic detection element; a predetermined magnetic field applying unit for
applying a predetermined magnetic field to the magnetic detection element; a switch
unit for applying one of the negative feedback magnetic field and the predetermined
magnetic field to the magnetic detection element; two detection units for detecting
the variations in magnetic field by a current from the variations in alternating
current varying depending on an external magnetic field applied to the magnetic
detection element corresponding to the magnetic detection element; and a differential
amplification unit for differentiation amplifying the output of the two detection
units, characterized in that, depending on the output of the detection unit or
the output of the differential amplification unit, a negative feedback magnetic
field is applied to two magnetic detection elements in a period, a predetermined
magnetic field is applied to two magnetic detection elements in another period,
and a predetermined amendment is made to the output of the differential amplification
unit depending on the output of the detection unit or the output of the differential
amplification unit of each period.
In the inventions as previously discussed, the negative feedback magnetic field
applying unit can be configured by a negative feedback coil provided near the magnetic
detection element and a negative feedback element.
In another embodiment of the invention, two magnetic detection elements which
has a magnetic impedance effect and is provided near the wiring leading a current;
a current applying unit for applying an alternating current to both ends of the
magnetic detection element; a DC bias magnetic field applying unit for applying
a DC bias magnetic field to the magnetic detection element; a negative feedback
coil for applying a negative feedback magnetic field to the magnetic detection
element and a plurality of negative feedback elements; a switch unit for switching
the plurality of negative feedback elements; two detection units for detecting
the variations in magnetic field by a current from the variations in alternating
current varying depending on an external magnetic field applied to the magnetic
detection element corresponding to the magnetic detection element; and a differential
amplification unit for differentiation amplifying the output of the two detection
units, characterized in that, depending on the output of the detection unit or
the output of the differential amplification unit, the plurality of negative feedback
elements are selected.
In any of the inventions previously discussed, the DC bias magnetic field can
be applied by a magnet provided near the magnetic detection element, a non-magnetic
substrate can be provided with two magnetic detection elements of thin ferromagnet
film, and the magnet for applying the DC bias magnetic field and the negative feedback
coil for applying the negative feedback magnetic field are formed by thin film.
In any of the inventions previously discussed, the two magnetic detection elements
can be arranged such that they can have equal absolute values of the output to
the magnetic flux generated by a current, and have opposite polarity.
In another embodiment of the invention, in an overload current protective device,
which is provided with a switch for supplying a current from a power source to
a load or cutting it off, a current detector for detecting the current, and a control
power source for providing power to each unit of the device, for cutting off the
current to the load when an overcurrent occurs,
the current detector is configured by two magnetic detection elements which has
a magnetic impedance effect and is provided near the wiring leading a current;
a current applying unit for applying an alternating current to both ends of the
magnetic detection element; a DC bias magnetic field applying unit for applying
a DC bias magnetic field to the magnetic detection element; two detection units
for detecting the variations in magnetic field by a current from the variations
in alternating current varying depending on an external magnetic field applied
to the magnetic detection element corresponding to the magnetic detection element;
and a differential amplification unit for differentiation amplifying the output
of the two detection units; a negative feedback magnetic field applying unit for
applying a predetermined negative feedback magnetic field to the magnetic detection
element depending on the output of the detection unit or the differential amplification unit.
In another embodiment of the invention, in an overload current protective device,
which is provided with a switch for supplying a current from a power source to
a load or cutting it off, a current detector for detecting the current, and a control
power source for providing power to each unit of the device, for cutting off the
current to the load when an overcurrent occurs,
two magnetic detection elements which has a magnetic impedance effect and is
provided near the wiring leading a current; a current applying unit for applying
an alternating current to both ends of the magnetic detection element; a DC bias
magnetic field applying unit for applying a DC bias magnetic field to the magnetic
detection element; a negative feedback magnetic field applying unit for applying
a negative feedback magnetic field to the magnetic detection element; a predetermined
magnetic field applying unit for applying a predetermined magnetic field to the
magnetic detection element; a switch unit for applying one of the negative feedback
magnetic field and the predetermined magnetic field to the magnetic detection element;
two detection units for detecting the variations in magnetic field by a current
from the variations in alternating current varying depending on an external magnetic
field applied to the magnetic detection element corresponding to the magnetic detection
element; and a differential amplification unit for differentiation amplifying the
output of the two detection units, and depending on the output of the detection
unit or the output of the differential amplification unit, a negative feedback
magnetic field is applied to two magnetic detection elements in a period, a predetermined
magnetic field is applied to two magnetic detection elements in another period,
and a predetermined amendment is made to the output of the differential amplification
unit depending on the output of the detection unit or the output of the differential
amplification unit of each period.
In another embodiment of the invention, the negative feedback magnetic field
applying
unit is configured by a negative feedback coil provided near the magnetic detection
element and a negative feedback element.
In another embodiment of the invention, in an overload current protective device,
which is provided with a switch for supplying a current from a power source to
a load or cutting it off, a current detector for detecting the current, and a control
power source for providing power to each unit of the device, for cutting off the
current to the load when an overcurrent occurs,
the current detector includes: two magnetic detection elements which has a magnetic
impedance effect and is provided near the wiring leading a current; a current applying
unit for applying an alternating current to both ends of the magnetic detection
element; a DC bias magnetic field applying unit for applying a DC bias magnetic
field to the magnetic detection element; a negative feedback coil for applying
a negative feedback magnetic field to the magnetic detection element and a plurality
of negative feedback elements; a switch unit for switching the plurality of negative
feedback elements; two detection units for detecting the variations in magnetic
field by a current from the variations in alternating current varying depending
on an external magnetic field applied to the magnetic detection element corresponding
to the magnetic detection element; and a differential amplification unit for differentiation
amplifying the output of the two detection units, characterized in that, depending
on the output of the detection unit or the output of the differential amplification
unit, the plurality of negative feedback elements are selected.
In any of the inventions previously discussed, the DC bias magnetic field can
be applied by a magnet provided near the magnetic detection element, and in the
invention previously discussed, a non-magnetic substrate can be provided with two
magnetic detection elements of thin ferromagnet film, and the magnet for applying
the DC bias magnetic field and the negative feedback coil for applying the negative
feedback magnetic field are formed b ,.y thin film.
In any of the inventions previously discussed, the two magnetic detection elements
can be arranged such that they can have equal absolute values of the output to
the magnetic flux generated by a current, and have opposite polarity.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows the configuration of the first embodiment of the present invention;
FIG. 2 shows the influence of a current flowing through adjacent wiring;
FIG. 3 shows the configuration of the second embodiment of the present invention;
FIG. 4 shows the method for detecting the detection sensitivity in FIG. 3;
FIG. 5 shows the configuration of the third embodiment of the present invention;
FIG. 6 shows the current detection characteristic with the configuration shown
in FIG. 5;
FIG. 7 is an oblique view showing an example of the structure of a wire-type
current detection element according to the present invention;
FIG. 8 is an oblique view showing an example of the structure of a thin-film-type
current detection element according to the present invention;
FIG. 9 shows an example of the configuration of the system applied to an overload
current protective device;
FIG. 10 is a graph showing an example of a magnetic impedance characteristic; and
FIG. 11 shows the circuit of the conventional technology.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows the configuration of the first embodiment of the present invention.
In FIG. 1, magnetic impedance elements (also referred to simply as MI elements)
1a and
1b can be wire-shaped or thin-film-shaped. A
compensation coil
2 applies negative feedback to the MI elements
1a
and
1b. A magnet
3 applies a DC bias to the MI elements
1a and
1b. An oscillation unit
4 applies a DC
current to the MI elements
1a and
1b. Buffer units
5a and
5b are inserted depending on the level of the
current output by the oscillation unit
4. Reference numerals
6a
and
6b denote resistors. Detector means
7a and
7b detect the variations in alternating current depending on the
external magnetic field applied to the MI elements
1a and
1b.
A differential amplification unit
8 amplifies the differential of the
output of the detection unit. A negative feedback element
9 supplies a current
to the compensation coil
2 depending on the output of the differential amplification
unit
8. Wiring
10 leads a detection current.
As shown in FIG. 1, the magnetic impedance elements
1a and
1b
are arranged such that the absolute values of the magnetic flux (Hb
1,
Hb
2) generated by the current I flowing through the wiring
10 can
be equal and the directions of the magnetic flux can be opposite, and the output
difference is calculated by the differential amplification unit
8, thereby
obtaining the output proportional to the current.
The compensation coil
2 and the negative feedback element
9 apply
a magnetic field to the MI elements
1a and
1b in the
direction of decreasing the output of the differential amplification unit
8.
The negative feedback element
9 is normally configured by a resistor so
that the output sensitivity for the detection current can be reduced proportional
to the resistance. Therefore, the measurement precision can be improved by optimizing
the value of the negative feedback element
9 depending on the measurement range.
When the current sensor as shown in
1 is used as the receiving and distributing
equipment, it is necessary to eliminate the influence of a current flowing through
adjacent wiring. FIG. 2 shows the influence of a current flowing through adjacent
wiring. A current I
1 flows adjacent to a current I
1
The magnetic flux generated by the currents I
1 and I
2 is respectively
defined as φ
1 and φ
2. Using the magnetic flux φ
1
and φ
2, the output of the difference between the two MI elements
1a
and
1b is calculated below.
##EQU1##
Thus, the current I
1 can be detected without the influence of the current
I
2 flowing through adjacent wiring
10a.
When a uniform external magnetic field is applied as noise, two MI elements
1a and
1b indicate output equal in size and sign. Therefore,
the influence of noise of the external magnetic field can be removed as in the
case of the current flowing through the adjacent wiring.
FIG. 3 shows the configuration of the second embodiment of the present invention.
In FIG. 3, a constant current unit
91, a switch unit
92, an analog-digital
conversion unit
81, and an arithmetic control unit
82 configured
by a microcomputer, etc. are added to the configuration shown in FIG.
1.
With the above-mentioned configuration, a magnetic field is applied to the output
of the differential amplification unit
8 using the compensation coil
2
and the negative feedback element
9 in the direction of decreasing the output
of the differential amplification unit
8. The arithmetic control unit
82
controls the switch unit
92 to apply a constant current from the constant
current unit
91 to the compensation coil
2, and controls the analog-digital
conversion unit
81 to detect the output of the differential amplification
unit
8. The arithmetic control unit
82 controls the output obtained
when a constant current is applied under a predetermined condition to be stored
as a reference value, thereby comparing the output of the analog-digital conversion
unit
81 with the reference value, correcting the difference from the reference
value in the output result, and correcting the output of the apparatus by the environmental
characteristic such as a temperature, etc. and a characteristic change with time.
As a result, a high-precision and environmental resistant current sensor.
FIG. 4 shows the method for detecting the detection sensitivity in FIG.
3.
In FIG. 4, the characteristic of the output of the sensor to an external magnetic
field indicates the characteristic of a common magnetic impedance element, and
an arbitrary sensor output is obtained regardless of the direction of the magnetic
field based on the zero magnetic field.
In the case
1 shown in (a), (b), and (c) in FIG. 4, the median value of
the bias magnetic field indicates the zero magnetic field. Therefore, the outputs
of the detector means
7a and
7b are equal to each other,
and the output of the differential amplification unit
8 is zero.
In the case
2 shown in (d), (e), and (f), the median value of the bias
magnetic field is shifted by ΔH, the output difference between the detector
means
7a and
7b is ΔV, and the output of the
differential amplification unit
8 is α·ΔV (α indicates
a gain of the differential amplification unit). ΔV/ΔH is only the sensitivity
of the sensor.
FIG. 5 shows the configuration of the third embodiment of the present invention.
As clearly shown in FIG. 5, the example is characterized by the two negative
feedback
elements
9a and
9b. In this example, the negative feedback
elements
9a and
9b and the compensation coil
2
apply a magnetic field to the MI elements
1a and
1b in
the direction of decreasing the output of the differential amplification unit
8
depending on the output of the differential amplification unit
8. Since
the negative feedback elements
9a and
9b are normally
configured by resistors as describe above, the output sensitivity to the detected
current can be decreased proportional to the resistance. Therefore, the values
of the negative feedback elements
9a and
9b are set
depending on the measurement range, and the switch unit
92 automatically
switches the values based on the output of the differential amplification unit
8, thereby obtaining a high-precision current detection characteristic in
a wide measurement range.
In FIG. 5, two negative feedback elements are switched, but three or more negative
feedback elements can also be switched. In some measurement ranges, no negative
feedback can be performed without selecting a negative feedback element.
FIG. 6 shows the current detection characteristic according to the third embodiment.
In FIG. 6, two cases, that is, a case in which no negative feedback is carried
out, and another case in which a negative feedback is performed using a different
resistance, are shown. A wider range is used in the case where a negative feedback
element is performed.
FIG. 7 is an oblique view showing an example of the structure of a wire-type
current detection element according to the present invention.
In FIG. 7, the reference numerals
1a and
1b denote
MI elements. The compensation coil
2 applies a negative feedback to the
MI elements. The magnet
3 applies a DC bias to the MI elements. The wiring
10 leads a detection current. A shield plate
11 cancels the influence
of an external magnetic field. A shield plate
11 cancels the influence of
an external magnetic field. A through hole
13 retrieves a signal.
FIG. 8 shows an example of the structure of a thin-film-type current detection
element according to the present invention. FIG.
8(
a) is a top view,
FIG.
8(
b) is a sectional view.
In FIG. 8, a substrate
14 shown in (b) is a nonmagnetic substance. The
reference numerals
1a and
1b shown in (a) denote the
thin-film MI elements. The thin-film compensation coil
2 applies a negative
feedback to the MI elements. The MI elements
1a and
1b
and the compensation coil
2 are laid on the substrate
14 through
an insulator such as nitrogen silicide, etc. Thin-film magnets
3a and
3b apply a DC bias to the MI element. The wide portions on both ends
of the MI elements
1a and
1b and the compensation coil
2 are the pads for external wiring. Since the substrate
14 can have
dimensions of several millimeters, amazingly small, low-cost, and low power consumption
system can be realized.
A system using two magnetic impedance elements is described above, but three
or
more magnetic impedance elements can be used. Furthermore, the above-mentioned
1-phase current sensor can be obviously replaced with three or more required phases
can be applied to the current sensor when it is used for receiving and distributing
equipment, etc.
FIG. 9 shows an example of the overload current protective device to which the
above-mentioned current sensor is applied.
The reference characters R, S, and T denote power supply lines connected to a
three-phase AC power source, and are connected to a motor
30 through a 3-phase
contactor (switch)
20 and three power supply transformers
50a,
50b, and
50c. The current detectors
40a,
40b, and
40c are arranged for each phase between
the 3-phase contactor (switch)
20 and the three power supply transformers
50a, 50b, and
50c. The contactor
20
has three contact points
20a, 20b, and
20c
are coupled by the different power supply lines R, S, and T to the motor
30
through the primary coils of the power supply transformers
50a, 50b,
and
50c respectively. The set of contact points are mechanically
coupled to be simultaneously operated by the electromagnetic coil
20d.
The electromagnetic coil
20d is connected to the digital output
of a microcomputer
80. An electronic overload relay
100 is formed
by a control circuit including the microcomputer
80, the current detectors
40a, 40b, and
40c, the power supply transformers
50a, 50b, and
50c, etc.
In this example, the current detectors
40a, 40b, and
40c comprises an MI element
400 having the MI elements
1a
and
1b and a drive/detector
401. The output of each unit
is sequentially switched by a switch
60. The output of the power supply
transformers
50a, 50b, and
50c selected
by the switch
60 is connected to the analog input of the microcomputer
80
through a half-wave rectifier
70.
A control power source is connected from the secondary coils of the power supply
transformers
50a, 50b, and
50c to a first
capacitor C
0 through the diodes D
0, D
1, and D
2. The
first capacitor C
0 is connected between the positive input of a voltage
adjuster
90 and the ground, a capacitor C
1 is connected between the
positive output of the voltage adjuster
90 and the ground, and the voltage
Vcc at a predetermined level is provided as a control power source. D
3,
D
4, and D
5 are protective diodes.
Industrial Applicability
According to the present invention, the following effects can be expected.
(1) Since the magnetic flux by a current is detected by an MI element having
a magnetic impedance effect, the magnetic saturation from a widely and currently
used core does not occur. As a result, an apparatus of a wide current detection
range can be provided.
(2) When a bias magnetic field and a negative feedback magnetic field are
applied to an MI element to improve the linearity, the bias magnetic field is applied
from a magnet, and the negative feedback magnetic field is applied from a compensation
coil. Therefore, as compared with the conventional configuration in which a bias
magnetic field and a negative feedback magnetic field are applied from a coil,
a smaller, lower-cost, and lower power consumption apparatus can be realized. Furthermore,
by optimizing the value of a negative feedback element depending on the measurement
range, the linearity can be improved.
(3) By arranging the two MI elements such that the absolute values of the
magnetic flux generated by the detection currents can be equal but in the opposite
directions and obtaining the difference between the detection units, the current
can be detected without the influence of the disturbance magnetic field or the
magnetic field of the current flowing through the adjacent wiring. Therefore, the
current sensor of excellent environmental resistance without an influence of noise
can be provided.
(4) Since a common magnetic field can be applied to an MI element, and the
sensitivity of the magnetic detection element can be automatically detected from
the output at that time, an automatic correction can be made although the sensitivity
of an element is changed by the environmental characteristic or a change with time.
Therefore, an current sensor excellent in environmental resistance and change with
time can be provided.
(5) A high-precision current sensor excellent in linearity in a wide measurement
range can be provided by setting the resistance of a plurality of negative feedback
elements depending on the measurement range, and automatically switching the values
based on the output of the differential amplification unit.
(6) A current sensor of high environmental resistance which is not subject
to the influence of disturbance noise from the influence of the variance of the
sensitivity of a magnetic sensor, a position error, etc. can be provided by including
a magnetic shield to cut off an external magnetic field.
(7) Since an MI element, a bias magnet, and a negative feedback coil can
be formed by thin film, and a substrate can be configured with the dimensions of
several millimeters, an amazingly smaller, lower-cost, and lower power consumption
apparatus can be realized. Therefore, a small, mass-producible, and high-precision
current sensor can be provided.
(8) When the above-mentioned current sensor is applied to a overload current
protective device for controlling a power supply to a load with a current cut off
when a current flowing through a conductor is detected and the value of the current
exceeds a predetermined threshold, a small, lower-cost, high-current-detection,
and high-linearity overload current protective device can be obtained.
*
