Lead wire DC current sensor with saturated detecting core

A DC current sensor, comprising a detecting core consisting of an annular soft magnetic material having a hollow portion extending in a circumferential direction within the core; an excitation coil wound and disposed in a circumferential direction in the hollow portion; a detecting coil toroidally wound around the detecting core; a lead wire through which a DC current for non-contact detection flows, and extended through the center of the detecting core; an AC current supply for applying current to the excitation coil for periodically magnetically saturating the entire detecting core in both the circumferential and a direction perpendicular thereto, whereby the magnetic flux produced in the detecting core can be modulated according to the DC current flowing through the lead wire and being detected upon excitation of the excitation coil; and the detecting coil producing an electromotive force having a frequency twice the excitation current for detecting the DC current flowing through the lead wire.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a DC current sensor utilized in a wide 
range of field such as preventive maintenances of installations by leakage 
detections of, DC generating apparatus such as a solar cell, fuel cell 
generating system and the like, DC control circuits and the like of a 
power plant, a substation and a large switchboard for industrial plant, 
and further, insulation deterioration in various DC equipments, more 
particularly, it relates to a sensitive DC current sensor having a 
relatively simple construction and a good detecting capability for even a 
micro-current variation, realizing a stable detection. 
2. Description of the Prior Art 
In recent year, though equipments utilizing a DC current are used in a wide 
range of field, demands on a sensor for detecting load of a DC motor for 
necessary control and a DC current sensor used in a DC current leakage 
breaker and the like are enhanced in maintenance for operating the various 
equipments smoothly. 
As such DC current sensors, those consisting of a magnetic amplifier type, 
magnetic multi-vibrator type (Japanese Patent Application Laid Open Nos. 
Sho 47-1644, Sho 53-31176, Sho 49-46859), Hall device type and the like 
are well known. 
Both the magnetic amplifier type and magnetic multivibrator type use a core 
of soft magnetic material constituted by winding a detecting coil in a 
toroidal shape, wherein by extending a lead wire being detected through 
the core for DC magnetic deflection of the core of soft magnetic material 
within a saturated magnetic flux density (Bs) by a DC current flowing 
through the lead wire being detected, an alternating magnetic flux 
produced by applying an AC current to the coil wound around the core 
beforehand produces an unbalance when saturated in the positive and 
negative directions, and the variation is detected by the detecting coil. 
Since the magnetic flux variation is given in the core beforehand in the 
former type, a configuration of applying the AC current of a predetermined 
value by winding the excitation coil around the core is adopted, in the 
latter type, it is so constituted that the self-excitation takes place by 
the action of semiconductors and the like in a circuit connected to the 
detecting coil, and a duty ratio of an oscillation waveform is changed 
responsive to the current being detected for oscillation. 
Furthermore, the Hall device type is so constituted that, the lead wire 
being detected is wound in a toroidal shape directly around the core of 
soft magnetic material which is formed partly with a gap disposing the 
Hall device, and the magnetic flux variation in the core responsive to the 
DC current variation flowing through the lead wire being detected is 
detected directly by the Hall device. 
However, it is the present situation that, the DC current sensors of the 
above-mentioned types are not always constituted to respond to the 
micro-current variation of a DC leakage breaker and the like by the 
following reasons, the they are not being used practically as the 
sensitive DC current sensor. 
In the magnetic amplifier type and magnetic multivibrator type, as 
previously described, the core of soft magnetic material must be subjected 
to DC magnetic deflection by the DC current flowing through the lead wire 
being detected so as to saturate nearly to the saturated magnetic flux 
density (Bs), resulting in a low detecting sensitivity. And hence, in the 
case of using the well known soft magnetic material such as permalloy and 
the like as the core, for example, when the current flowing through the 
lead wire being detected is about several tens of mA, the lead wire being 
detected must be wound around the core of soft magnetic material by 
several tens to several hundreds of turns or more, thus it was difficult 
to use as the DC current sensor for the leakage breaker and the like where 
the lead wire being detected is required by one turn. 
Also in the Hall device type, since the detecting capability is determined 
inevitably by the characteristic of the Hall device, when the Hall device 
which is known at present is used, for example, when the current flowing 
through the lead wire being detected is about several tens of mA, the lead 
wire being detected must be wound around the core of soft magnetic 
material by several hundreds to several thousands of turns or more, thus 
as same as the aforementioned magnetic amplifier type and magnetic 
multivibrator type, it was difficult to use as the DC current sensor of 
the leakage breaker or the like where the lead wire being detected is 
required by one turn. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a sensitive DC current 
sensor which solves the aforementioned problems, and has a good detecting 
capability against a DC leakage breaker and the like, particularly, even 
against a micro-current variation with a simple construction. 
It is another object of the present invention to provide a sensitive DC 
current sensor, particularly, having a simply shaped detecting core 
constituting the DC current sensor and a high productivity. 
In view of the fact that, when a lead wire being detected is extended 
through a detecting core consisting of an annular soft magnetic material, 
around which a detecting coil is wound in a toroidal shape, and a DC 
current is applied thereto, through a clockwise magnetic field is produced 
in a direction of the DC current and a magnetic flux .PHI..sub.0 is 
produced in a detecting core, since the current flowing through the lead 
wire being detected is the DC current, the magnetic flux .PHI..sub.0 is 
constant and an electromotive force is not produced in the detecting coil, 
we have studied to produce the electromotive force in the detecting coil, 
by forming a magnetic gap partially in the detecting core, which is open 
and close by a magnetic substance to form a magnetic switch, and changing 
(ON-OFF) the magnetic flux .PHI..sub.0 against time by the magnetic 
switch. 
Furthermore, as the result of various studies carried out for higher 
realization of the above-mentioned configuration, we have confirmed that 
the object can be achieved by, in place of the mechanical magnetic switch, 
disposing means for forming a magnetic gap periodically at a portion of 
the detecting core by a magnetic flux which is produced substantially in a 
orthogonal direction, against the magnetic flux produced in a 
circumferential direction in the detecting core by the DC current flowing 
through the lead wire being detected to realize, practically, the same 
action as the above-mentioned magnetic switch. 
As a specific configuration, an excitation core consisting of an annular 
soft magnetic material connecting perpendicularly to the circumferential 
direction of the detecting core is disposed at a portion of the detecting 
core in a body, the detecting coil is wound around the detecting core in a 
toroidal shape, an excitation coil is wound around the detecting core in a 
circumferential direction thereof, and further, the excitation core is 
excited perpendicularly to the circumferential direction of the detecting 
core by applying the DC current to the excitation coil, and the 
intersection of the excitation core and the detecting core is magnetically 
saturated periodically to form a practical magnetic gap by the 
intersection which is magnetically saturated. 
That is, since a relative permeability .mu. of the magnetically saturated 
intersection of the detecting core approaches to 1 endlessly, the 
magnetically saturated portion serves similarly as the magnetic gap and 
the magnetic flux .PHI..sub.0 in the detecting core reduces at a constant 
period, and according to the variation of the magnetic flux, the 
electromotive force can be produced in the detecting coil. 
We have made various improvements on a DC current sensor consisting of the 
above-mentioned basic configuration, particularly, in view of the shape of 
the core consisting of the soft magnetic material, the shape of the core 
is made simple as much as possible to suit for mass-production, and the 
excitation coil and detecting coil are disposed effectively in conformity 
with the core shape to accomplish the improvement of detecting 
sensitivity. 
That is, the present invention is direct to a DC current sensor that, a 
hollow portion which communicates in the circumferential direction is 
formed in the detecting core consisting of the annular soft magnetic 
material, the excitation coil wound in the circumferential direction is 
disposed in the hollow portion, the detecting coil wound around the 
detecting core in a toroidal shape is disposed, and the lead wire being 
detected, through which the DC current for non-contact detection flows, is 
extended through the detecting core. 
The present invention also provides a DC current sensor constituted such 
that, in the aforementioned configuration, the core can be divided, at 
least, at one place in the circumferential direction when the lead wire 
being detected is extended therethrough. 
A DC current sensor of the present invention is that, by forming the hollow 
portion communicating in the circumferential direction in the detecting 
core consisting of the annular soft magnetic material, disposing thee 
excitation coil wound in the circumferential direction in the hollow 
portion, and disposing the detecting coil wound around the detecting core 
in a toroidal shape, the detecting core having an excellent productivity 
can be obtained. 
Also, in addition to the construction of the detecting core, by disposing 
the excitation coil and detecting coil effectively, effects of a coercive 
force peculiar to the soft magnetic material constituting the detecting 
core and a leakage flux from the excitation coil can be considerably 
reduced, and the DC current sensor capable of detecting c micro-current 
of, for example, about 5 mA or less very sensitively can be realized. 
Accordingly, when used in a DC leakage breaker or the like, a required 
sensitive detection can be achieved just by extending a lead wire being 
detected through the detecting core, and since the construction is simple, 
the DC current sensor can be made smaller, and further, not only an 
absolute value of the DC current flowing through the lead wire being 
detected, but also its direction can be detected, thus the range of use 
can be more broadened.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Details on Development of the Present Invention 
In the following, the operation of a DC current sensor of the present 
invention is described in detail with reference to the drawings. 
As previously described, the DC current sensor of the present invention has 
a basic core-shape construction, in which an excitation core consisting of 
an annular soft magnetic material connected in a perpendicular direction 
to a circumferential direction of a detecting core is disposed on a 
portion of the detecting core in a body, and has been accomplished by 
going through various improvements. The principle of operation is also 
substantially same as the case of DC current sensor having the 
above-mentioned basic construction, therefore, in the following 
description, first the principle of operation is described based on the DC 
current sensor having the above-mentioned construction, and further, the 
details on development of the present invention is described so that 
features of the DC current sensor of the present invention will become 
more clear. 
FIG. 7 is a perspective explanatory view for explaining the basic principle 
of operation of the DC current sensor of the present invention. FIG. 8 and 
FIG. 9 show the relationship between an excitation current and a magnetic 
flux passing through the detecting core, and further, an electromotive 
force produced in a detecting coil in this configuration. 
In FIG. 7, a lead wire being detected 1 extends through the detecting core 
2 consisting of an annular soft magnetic material. A detecting coil 3 is 
wound in a toroidal shape around a predetermined position of the detecting 
core 2, and is connected to a predetermined detecting circuit (not shown) 
as securing an electrical insulation with the lead wire being detected 1. 
An excitation core 4 consists of an annular soft magnetic material and 
connected to a circumferential portion of the detecting core 2 in a 
perpendicular direction to a circumferential direction of the detecting 
core 2, and by the operation to be described later, forming a magnetically 
saturated portion at a core intersection 6 of the detecting core 2 and the 
excitation core 4 shown by oblique line. An excitation coil 5 is wound 
circumferentially around the detecting core 2. 
In the figure, a modulation coil 43 is wound in the same direction as the 
lead wire being detected 1, for the purpose of reducing hysteresis of 
output characteristics assumed to be caused by an effect of magnetic 
characteristics (a coercive force) of the soft magnetic material 
constituting the detecting core 2. 
In the configuration of FIG. 7, when a DC current I is applied to the lead 
wire being detected 1, a magnetic field which is in a clockwise direction 
to the direction of the DC current I is produced in the detecting core 2, 
producing a magnetic flux .PHI..sub.0 in the detecting core. 
At this time, when a predetermined AC current is applied to the excitation 
coil 5 to produce a magnetic flux, which changes periodically in a 
direction .alpha. in the figure, in the excitation core 4 and to 
magnetically saturate it periodically, a relative permeability .mu. of the 
core intersection 6 (shown by oblique lines in the figure), which is a 
circumferential portion of the detecting core 2, reduces and approaches to 
1 endlessly to substantially from a so-called magnetic gap, reducing the 
magnetic flux .PHI..sub.0 in the detecting core to .PHI..sub.1. 
Hereupon, when the AC current applied to the excitation coil 5 has a 
frequency f.sub.0 and the excitation core 4 is saturated near a peak value 
of the current, the excitation core 4 is saturated twice in one period of 
the excitation current I, in the case where the DC current I flowing 
through the lead wire being detected 1 is in the positive direction 
(upward in the figure) as shown in FIG. 8, and in the case where the DC 
current I flowing through the lead wire being detected 1 is in the 
negative direction (downward in the figure) as shown in FIG. 9. 
In the case where the DC current I flowing through the lead wire being 
detected 1 is in the positive direction (upward in the figure) as shown in 
FIG. 8, by this saturation, the magnetic flux .PHI..sub.0 produced by the 
DC current I flowing through the lead wire being detected 1 produced in 
the detecting core 2 reduces to .PHI..sub.1 at the frequency 2f.sub.0 as 
shown in FIG. 8(B). That is the modulation takes place at 2f.sub.0. Thus, 
as the magnetic flux changes as above the voltage V.sub.DET of frequency 
2f.sub.0 is produced in the detecting coil 3. 
Also in the case where the DC current I flowing through the lead wire being 
detected 1 is in the negative direction (downward in the figure) as shown 
in FIG. 9, though the operation is substantially same as the case where 
the DC current I is in the positive direction (upward in the figure), 
since the DC current I is in the opposite direction, the direction of the 
magnetic flux produced in the detecting core 2 is also opposite, and the 
phase difference of the voltage V.sub.DET of frequency 2f.sub.0 produced 
in the detecting coil 3 becomes 180 degree. 
However, in spite of the direction of the DC current I flowing through the 
lead wire being detected 1, in either case, from the relation of magnetic 
flux .PHI..sub.0 .alpha. Dc current I and voltage V.sub.DET .alpha. 
magnetic flux .PHI..sub.0, voltage V.sub.DET .alpha. DC current I, thus 
the electromotive force proportional to the DC current I flowing through 
the lead wire being detected 1 can be detected by the detecting coil 3, 
and an absolute value of the DC current I flowing through the lead wire 
being detected I can be detected. 
In the DC current sensor having the above-mentioned configuration, through 
the DC current can be detected by the relatively simple configuration as 
compared with the conventional configuration, particularly, in measurement 
of the micro-current region, since a reference level at measurement 
changes due to a hysteresis phenomenon of the output voltage (output 
characteristics) influenced by the coercive force of the detecting core 2, 
and the measurement value changes each time and an accurate value can not 
be obtained, as shown in FIG. 7, the modulation coil 43 wound in the same 
direction as the lead wire being detected 1 is disposed in the detecting 
core 2. That is, in the DC current sensor having the above-mentioned 
configuration, through the detecting core 2 itself is demagnetized by the 
excitation current (AC current) flowing through the excitation coil 5, 
because the excitation coil 5 is wound around the detecting core 2, it is 
not sufficient, in addition to the demagnetization effect, an alternating 
magnetic field produced in the modulation coil 43 is superposed on the 
detecting core 2 to reduce the output characteristic hysteresis due to the 
residual magnetic flux of the core. 
Thus, when the AC current which is necessary to produce a magnetic field 
above the coercive force of the detecting core 2 is applied to the 
modulation coil 43, the hysteresis characteristic produced by the residual 
magnetic flux caused by the coercive force of the core material is 
eliminated, and the detecting sensitivity by the micro-current can be 
enhanced by removing the superposed alternating components in a detecting 
circuit. 
As shown in FIG. 7, the modulation coil 43 is that, besides winding around 
the detecting core 2 in the same direction as the lead wire being detected 
1 by one turn so as to extend through the detecting core 2, it is also 
wound around the detecting core 2 in the same direction as aforementioned 
by several turns depending upon the required intensity of the alternating 
magnetic field, particularly, in the case of winding several turns, it is 
wound around the detecting core 2 in a toroidal shape practically as same 
as the detecting coil 3. 
Also, as it is apparent from FIG. 7, since the modulation coil 43 is wound 
around the detecting core 2 practically in the same direction and at the 
same location as the detecting coil 3 which is wound in the toroidal 
shape, it can be commonly used with the detecting coil 3. 
That is, originally, the electric current flowing through the detecting 
coil 3 and that flowing through the modulation coil 43 have frequencies 
which differ largely, so that even they are used commonly, by suitably 
disposing a filter which passes the electric current having the frequency 
realizing respective functions, electric signals can be easily separated, 
and even when the modulation coil 43 and the detecting coil 3 are 
constructed in a body, the output characteristic hysteresis can be 
reduced. 
Furthermore, since the phase difference of the voltage V.sub.DET of 
frequency 2f.sub.0 produced in the detecting coil 3 depending upon the 
direction of the DC current I flowing through the lead wire being 
detecting 1 is 180 degree as described in FIG. 8 and FIG. 9, by applying 
an excitation current in a state, where two times of the frequency of the 
excitation current from an oscillator to the excitation coil 5 beforehand 
is divided into half, and detecting the phase difference of an output of 
the oscillator and an output of the detecting coil 3 by a phase comparison 
circuit, an absolute value as well as the direction of the DC current 
flowing through the lead wire being detected 1 can be detected easily. 
That is, since the frequency of the excitation current oscillated from the 
oscillator connected to the excitation coil 5 and that of the output 
V.sub.DET from the detecting coil 3 become the frequency 2f.sub.0 which is 
two times the excitation current applied finally to the excitation coil 5, 
the phase differences can be easily compared, and not only the absolute 
value of the DC current flowing through the lead wire being detected 1, 
but also its direction can be detected. 
For example, by connecting the electric circuit shown in FIG. 10 
respectively to the excitation coil 5 and the detecting coil 3, the 
above-mentioned operation can be realized. 
That is, as shown in FIG. 10, the excitation coil 5 is connected to AC 
current applying means 10. The AC current applying means 10 comprises, an 
OSC (oscillation circuit) 11 which oscillates the excitation current of 
frequency 2f.sub.0 which is two times the excitation current applied 
finally to the excitation coil 5, and a T-FF (trigger-flip-flop) 12 which 
divides the excitation current frequency into half, and connects the AC 
current whose frequency is once divided to f.sub.0 from 2f.sub.0 to the 
excitation coil 5 via a LPF (low-pass filter) 13 and a buffer amplifier 
14. 
When the DC current I of predetermined direction is applied to the lead 
wire being detected (refer to FIG. 7), by the excitation current whose 
frequency f.sub.0 is divided into half applied to the excitation coil 5, 
as same as a mechanism of producing the electromotive force previously 
described, a magnetic flux produced in the detecting core 2 is modulated, 
and the electromotive force of the frequency 2f.sub.0 of two times the 
excitation current proportional to the DC current I flowing through the 
lead wire being detected I can be outputted from the detecting coil 3, 
thereby an absolute value of the DC current I flowing through the lead 
wire being detected 1 can be known. 
As already described in FIG. 8 and FIG. 9, the phase difference of voltage 
V.sub.DET of frequency 2f.sub.0 produced in the detecting coil 3 is 180 
degree, depending upon the direction of the DC current I flowing through 
the lead wire being detected 1. 
The output (electromotive force) of frequency 2f.sub.0 produced in the 
detecting coil 3 in such a manner is inputted to a phase comparison 
circuit 20 shown in FIG. 10. 
Meanwhile, a portion of the excitation current of frequency 2f.sub.0 
oscillated from the OSC 11 constituting the AC current applying means 10 
is inputted to the phase comparison circuit 20 shown in FIG. 10 as keeping 
the frequency 2f.sub.0, via the LPF (low-pass filter) 3, a phase shifter 
32, a Schmitt trigger 33 and so on without being connected to the 
excitation coil 5 via the T-FF 12 and so on. 
Component parts used in the phase shifter 32 are preferably disposed so 
that their constants satisfy 
EQU f.sub.OSC =1/2IIRC. 
The phase comparison circuit 20 detects the phase difference of the output 
from the OSC 11 inputted to the circuit 20 and that from the detecting 
coil 3, and finally outputs the direction corresponding to the direction 
of the DC current I flowing through the lead wire being detected 1 as well 
as the output voltage V.sub.out showing the absolute value of the direct 
current I in analog. 
Also, by applying an electric current whose direction and intensity change 
linearly periodically against time such as the electric current, which 
changes in a triangular waveform, to the detecting coil 3, a deflection 
magnetic field may be given in the detecting core 2 and the absolute value 
as well as the direction of the DC current flowing through the lead wire 
being detected 1 can be detected easily. 
That is, when the electric current such as that changes into a triangular 
waveform is applied to the detecting coil 3 in the state where the DC 
current flows through the lead wire being detected 1, in the detecting 
coil 3, a magnetic flux produced by the triangular waveform current and a 
magnetic flux produced by the DC current flowing through the lead wire 
being detected 1 are superposed, thus by phase detection of the output 
after applying a crest restriction to the electromotive force produced in 
the detecting coil 3, and detecting the time ratio (duty ratio) of an 
output time on the positive side (+) and an output time on the negative 
side (-), an absolute value as well as the direction of the DC current 
flowing through the lead wire being detected 1 can be detected. 
Particularly, when a maximum value of the electric current applied to the 
detecting coil 3 is set highly enough to produce a magnetic field above 
the coercive force (.+-.Hc) of the material of the detecting core 2, the 
output characteristic hysteresis caused by the hysteresis of the material 
of the detecting core 2 an practically be reduced. 
Furthermore, by combining various known electric circuits effectively, 
essential advantages of the DC current sensor constituted as shown in FIG. 
7 can be utilized more effectively. 
Meanwhile, by adopting the configuration shown in FIG. 7 as the basic 
configuration, and particularly, by improving the Configuration of the 
detecting core and the excitation core, an electromagnetic unbalance and 
the like as the DC current sensor is reduced, thereby noises can be 
reduced and an S/N ratio can be improved. 
For example, the DC current sensor constituted as shown in FIG. 11 includes 
the aforementioned effects and is effective in realizing the stable 
measurement. 
That is, in the configuration shown in FIG. 7, since one excitation core 4 
is connected to the detecting core 2 an the detecting coil 3, excitation 
coil 5 and modulation coil 43 are disposed respectively at one location, 
though it is difficult to balance electromagnetically as the DC current 
sensor shown, the DC current sensor shown in FIG. 11 is constituted by 
considering the electromagnetic balance of the excitation core 4, 
detecting coil 3, excitation coil 5 and modulation coil 43. 
In FIG. 11, a lead wire being detected 1 is extended through the center of 
the rectangular frame-shaped detecting core 2. On respective opposite long 
sides of the rectangular frame-shaped detecting core 2, a pair of 
excitation cores 4a and 4b are disposed in a body so as to form a 
quadrangular cylinder. Meanwhile, the excitation coil 5 is wound in a 
circumferential direction around the rectangular frame-shaped detecting 
core 2. 
Around respective opposite short sides of the rectangular frame-shaped 
detecting core 2, a pair of detecting coils 3a and 3b are wound in a 
toroidal shape and are interconnected electrically. Furthermore, a pair of 
coils 43a and 43b are wound around the same location in the same direction 
as the lead wire being detected 1, and are connected electrically in 
series by predetermined means. 
When the DC current I is applied to the lead wire being detected 1 in such 
a configuration, a magnetic field which is clockwise relative to the 
direction of the DC current I is produced in the detecting core 2, 
producing a magnetic flux therein. 
At this time, when a predetermined AC current is applied to the excitation 
coil 5 to produce a magnetic flux, which changes periodically in a 
direction a in the figure, in the pair of excitation cores 4a, 4b and to 
magnetically saturate the excitation cores 4a and 4b periodically, a core 
intersection 6 of the long sides, which is a circumferential portion of 
the rectangular frame-shaped detecting core 2, substantially forms a 
so-called magnetic gap whose relative permeability p approaches very close 
to 1, and the magnetic flux .PHI..sub.0 in the detecting core reduces to 
.PHI..sub.1. 
Thus, in the DC current sensor shown above, a mechanism of producing the 
electromotive force to the pair of detecting coils 3a and 3b is same as 
the configuration shown in FIG. 7, and the effects according to this 
mechanism can be obtained similarly. Furthermore, in this configuration, 
not only the electromagnetic balancing effect due to the entire 
symmetrical configuration against the lead wire being detected 1, besides 
the effect of disposing the pair of modulation coils 43a and 43b, it is 
effective in reducing a residual magnetic flux density in the detecting 
core 2 according to the diamagnetic effect obtained by increasing a ratio 
of width d (refer to FIG. 7) of the connection of the excitation core 4 
against a magnetic path length of the detecting core 2, thus the effect of 
coercive force of the core material can be reduced further. 
By the DC current sensor constituted as shown in FIG. 11, though it was 
possible to provide the DC current sensor which is relatively simple in 
construction and capable of detecting an electric current in a 
micro-region at a high sensitivity, as compared with the DC current sensor 
consisting of the conventionally known magnetic amplifier type, magnetic 
multivibrator type, Hall device type or the like, in order to improve the 
productivity in mass-production in an industrial scale, the entire 
construction of the DC current sensor must be simplified further 
particularly, a shape of the core must be improved. 
In the configuration shown in FIG. 11, second higher harmonious of the 
excitation signal produced by a non-linearity of magnetic characteristics 
peculiar to the soft magnetic material consisting the detecting core 2 and 
the excitation cores 4a and 4b, is mixed into the detecting coil 3a, and 
besides, since the second higher harmonics and the detecting signal 
(electromotive force of the detecting coil 3a) have the same frequency, it 
is impossible to separate them electrically. 
Thus, it was difficult to provide the DC current sensor having an S/N ratio 
higher than that. 
As it is apparent from details of the various improvements described 
heretofore, the DC current sensor of the present invention has the basic 
configuration as shown in FIG. 7, later the configuration shown in FIG. 11 
in which the electromagnetic balance is considered and its weak points are 
improved has been developed, and in order to solve the aforementioned 
problems, more improvements were added thereto, namely, the DC current 
sensor of the present invention has been developed by mainly devising a 
shape of the core, or forming a hollow portion extending in a 
circumferential direction through the detecting core consisting of the 
annular soft magnetic material, disposing the excitation coils wound in a 
circumferential direction in the hollow portion and disposing the 
detecting coil which is wound in a toroidal shape around the detecting 
core. The specific configuration is described in detail by the embodiments 
shown in the following. 
Operation of a DC Current Sensor according to the Present Invention 
FIG. 1 is a perspective fragmentary sectional view showing one embodiment 
of a DC current sensor of the present invention, FIG. 2 is a longitudinal 
sectional view taken along a line a--a of FIG. 1, and FIG. 3 is a 
fragmentary detailed longitudinal sectional view of FIG. 1. 
In the figure, a lead wire being detected 1 is extended through an entirely 
annular detecting core 51. The detecting core 51 is provided with a hollow 
portion 52 which extending through in a circumferential direction by 
combining a plurality of detecting core members to be described later, and 
is formed into a so-called tubular shape. 
In the figure, numeral 53 designates an excitation coil which is wound in a 
circumferential direction in the hollow portion of the detecting core 51, 
and numeral 54 designates a detecting coil which is wound in a toroidal 
shape around the detecting core 51. 
In the DC current sensor of the present invention, as the configuration 
previously shown in FIG. 7 and FIG. 11, it is difficult to clearly 
distinguish component parts of the detecting core and the excitation core, 
and as to be described later, the detecting core 51 serves the same 
function as the detecting core 2 and the excitation core 4 having the 
configuration shown in FIG. 7 and FIG. 11 serve. 
In the configuration shown above, when a DC current I is applied to the 
lead wire being detected 1, as shown in FIG. 3, a magnetic flux 
.PHI..sub.0 is produced in a circumferential direction of the detecting 
core 51. When a predetermined excitation current (AC current) is applied 
to the excitation coil 53 in this state, a magnetic flux is produced in a 
direction shown by the arrow .alpha. in the detecting core 51. The 
magnetic flux in the direction .alpha. is produced substantially in the 
orthogonal direction against the magnetic flux .PHI..sub.0 in the 
circumferential direction produced by the DC current flowing through the 
lead wire being detected 1, and periodically interrupts a magnetic path by 
the magnetic flux .PHI..sub.0. 
That is, by a mechanism of producing an electromotive force which is 
basically same as the DC current sensor constituted as shown in FIG. 7 and 
FIG. 11 previously described, a desired output can be obtained in the 
detecting coil 54. 
However, though such a phenomenon, or the phenomenon of periodically 
interrupting the magnetic path by the circumferential magnetic flux 
.PHI..sub.0 is produced at a portion (portion indicated at numeral 6 in 
respective figures) of the detecting core 2 in the configuration of FIG. 7 
and FIG. 11 previously described, in the DC current sensor of the present 
invention, it is produced entirely in the detecting core 51. 
Thus, demagnetization effects of the detecting core 51 by the excitation 
current (AC current) applied to the excitation coil 53 is largely 
improved, and further, by using commonly with the modulation coil (refer 
to FIG. 7 and FIG. 11) previously described, the output characteristic 
hysteresis effected by a coercive force peculiar to the detecting core 51 
can be largely reduced, and a high sensitive measurement can be 
accomplished in detecting the micro-current. 
That is, since magnetic saturation is produced periodically all around in 
the circumferential direction and the perpendicular direction (direction 
.alpha. in the figure) of the detecting core 51 by the excitation current 
applied to the excitation coil 53, the residual magnetic flux in the 
circumferential direction (direction .PHI..sub.0 in the figure) is 
extinguished by the saturation. By such phenomenon, even when the material 
having a limited coercive force is used as the detecting core 51, the 
effect of magnetic hysteresis of the material is reduced considerably. 
Also, since the excitation coil 53 is disposed in the hollow portion 52 in 
the detecting core 51, practically the excitation coil 53 is surrounded by 
the soft magnetic material, thus leakage of the magnetic flux produced by 
the excitation current flowing through the excitation coil 53 is very 
small, and a mixing level of the excitation signal into the detecting coil 
54 can be lowered, as the result, the residual signal produced in the 
detecting coil 54 becomes smaller and an S/N ratio of the detecting signal 
can be largely improved. 
Meanwhile, since the detecting core 51 can be obtained by combining and 
integrating detecting core members consisting of the simple configuration 
as shown in the embodiment to be describe later, for example; the 
detecting core members can be obtained simply by press molding and the 
like, thus it is very effective in mass-production in an industrial scale. 
FIG. 4 is a fragmentary sectional perspective view showing another 
embodiment of the DC current sensor of the present invention, wherein the 
basic configuration is as same as the configuration shown in FIG. 1 except 
a shape of the detecting core 51. That is, in the configuration shown in 
FIG. 1, though the detecting core 51 takes the form of cylindrical shape 
as a whole, in the configuration shown in FIG. 4, the detecting core 51 
takes the form of quadrangular cylinder as a whole. These configurations 
may be selected suitably taking into consideration of the location where 
the DC current sensor is installed and the productivity. 
Various configurations may be adopted in the DC current sensor of the 
present invention within the scope of appended claims, without being 
restricted to the configurations shown in FIG. 1 and FIG. 4. 
For example, in the configurations shown in FIG. 1 and FIG. 4, though the 
location of the modulation coil 43 disposed in the configuration of FIG. 7 
and FIG. 11 is not shown, in either of the configurations shown in FIG. 1 
and FIG. 4, the same effect can be obtained by disposing the modulation 
coil 43, and even when adopting the configuration in which the modulation 
coil 43 and the detecting coil 54 are used commonly in a body, the output 
characteristic hysteresis can be reduced. 
Also, in order to detect the absolute value as well as the direction of the 
DC current flowing through the lead wire being detected 1 simply as same 
as the configuration of FIG. 7 and FIG. 11, the excitation current in the 
state, where the frequency of the excitation current oscillated from an 
oscillator at the frequency of two times the excitation current beforehand 
is divided into half, is applied to the excitation coil 53, or means for 
detecting the phase difference of an output of the oscillator and that of 
the detecting coil by a phase comparison circuit is adopted, or an 
electric current whose direction and intensity change linearly 
periodically against time such as the electric current which changes in a 
triangular waveform is applied to the detecting coil 54, and means for 
providing a deflection magnetic field in the detecting core may be 
adopted, and further, by combining various known electric circuits 
effectively, essential advantages of the DC current sensor of the present 
invention can be utilized more effectively. 
In the DC current sensor*of the present invention, as the annular soft 
magnetic material constituting the detecting core 51, it is preferable to 
select the soft magnetic material responsive to the intensity of electric 
current flowing through the lead wire being detected or the detecting 
sensitivity required for the sensor. Usually, though permalloy is 
preferable when considering the magnetic characteristics and workability, 
other known soft magnetic materials such as a silicon steel plate, 
amorphous, electromagnetic soft iron, soft ferrite and the like may be 
used independently or in combination. 
The annular soft magnetic materials need not be a so-called ring shape, 
they may be connected to form an electromagnetically closed circuit, 
particularly, as far as it is constituted to form a hollow portion 
communicating through the detecting core in a circumferential direction 
and to dispose the excitation coil wound in the circumferential direction 
in the hollow portion, various configuration which are in a cylindrical 
shape a quadrangular shape and the like as a whole may be adopted. 
Productivity can be improved considerably by taking into consideration of 
the quality of the magnetic material and the final shape of the detecting 
core previously described, and selecting the number of members 
constituting the detecting core and a processing method. For example, in 
the case of metal materials such as permalloy and the like, mechanical 
processings by a press or a lathe can be suitably combined, and in the 
case of soft ferrite, press molding can be adopted to obtain the detecting 
core members of desired shapes easily. 
In the DC current sensor of the present invention, with respect to magnetic 
saturation in the detecting core 51, it is not necessary to accomplish the 
complete saturation throughout the detecting core 51, the required 
detection can be accomplished by just saturating roughly. 
Thus, by selecting the optimum condition on shapes and sizes of the soft 
magnetic material and the number of turns of the detecting coil and the 
excitation coil, together with the quality of the soft magnetic materials, 
it is possible to provide a sensor having a higher availability. 
Also, by surrounding the DC current sensor of the present invention with a 
shield case consisting of permalloy, non-oriented silicon steel plate and 
the like, it is possible to prevent external induction noises, results in 
a more stale detection. 
In either of the aforementioned configurations, the lead wire being 
detected extended through the detecting core is not restricted to one, a 
plurality of lead wires may be employed responsive to the size of the 
required sensor. However, the effect of the DC current sensor of the 
present invention can be realized most effectively by employing one lead 
wire being detected. 
DC Current Sensor Which can be Divided 
Furthermore, as a configuration of the DC current sensor which is very easy 
to mount on a lead wire being detected which has been wired already and 
has a high versatility, the DC current sensor which can be divided, at 
least, at one location in a circumferential direction when extending the 
lead wire being detected through the core, is proposed. 
An example shown in FIG. 12, in which a ring-shaped detecting core 62 is 
divided into half, is constituted as follows; a single turn excitation 
coil is formed in semicircular detecting core members 62a, 62b forming a 
body of the detecting core 62 which is shaved out from a soft magnetic 
material block, for example, semicircular excitation coil members 65a, 65b 
(where, only 65b is not shown) formed by processing a Cu block material 
are inserted, then assembled in a ring shape by placing semicircular 
plates 66a, 66b made of soft magnetic material and forming the inner 
surface of the detecting core 62, then clamped by a clamp band 67 
contacting to the outer surface of the core, and further, tightening 
projections 68a, 68b are provided on one end face of the semicircular 
excitation coil members 65a, 65b so as to be tightened by a bolt extending 
therethrough, on another end face, a screw 69 which is inserted from the 
outside of the core (refer to a screw hole 62c open in the detecting core 
member 62a) is provided to tighten the semicircular excitation coil 
members 65a, 65b, thereby a pair of semicircular excitation coil members 
65a, 65b are tightened firmly. 
In order to secure insulation between the component members 62a, 62b, 66a, 
66b of the detecting core 62 and the semicircular excitation coil members 
65a, 65b, for example, besides interposing an insulation plate 68c between 
one butt contact of the coil members 65a, 65b, an insulation substance is 
coated on the surface of the coil members 65a, 65b except the butt 
contact. 
Detecting coils 63a, 63b are wound around the assembled semicircular 
detecting core, the excitation coil being energized between the tightening 
projections 68a, 68b. 
In this configuration, since the excitation coil is practically one turn, 
by exciting the vicinity of the tightening projections 68a, 68b via an 
impedance matching transformer, the operation effect as same as the 
configuration of FIG. 1 can be obtained. 
In the configuration of FIG. 12, though a contact surface of the 
semicircular excitation coil members 65a, 65b constituting the excitation 
coil is large enough to realize the required excitation effect, since a 
contact surface with the detecting core members 62a, 62b constituting the 
detecting core 62 is small, it is difficult to reduce a magnetic 
resistance, deteriorating the detecting sensitivity. As a configuration 
derived from improving the configuration shown in FIG. 12, a DC current 
sensor shown in FIG. 13 is proposed. 
An example shown in FIG. 13 is constituted by using a cylindrical core 
which is divided into half. The detecting core 70 is formed into an 
elliptical shape by combining horseshoe-shaped detecting core members 71, 
72, the horseshoe-shaped detecting core member 71 on the left hand side in 
the figure is an integrated-type detecting core member constituted by 
laminating a pair of horseshoe-shaped cylinders vertically in a body, in 
the figure, the cylinders which are divided into upper and lower sections 
by a partition plate are formed into a horseshoe shape, and hereupon, 
though it is formed with a pair of U-shaped materials in cross section and 
the partition plate, an excitation coil 73 formed by bending an elliptical 
coil as shown in FIG. 13 (B) is incorporated therein. 
Another horseshoe-shaped detecting core member 72 is the separate-type 
detecting core member constituted by a pair of horseshoe-shaped cylinders 
forming a predetermined gap therebetween. In the figure, a pair of 
detecting core members 72a, 72b formed with U-shaped groove members in 
cross section and cover plate members are disposed in parallel, and an 
excitation coil member 74 formed by bending an elliptical coil as shown in 
FIG. 13(B), a bent portion positioning at an outer portion of the 
assembled detecting core 70, is incorporated therein so as to be clamped 
by the pair of detecting core members 72a, 72b at the time of butting 
against the horseshoe-shaped detecting core member 71 in a body. 
In the figure, a detecting coil portion 75 wound in a toroidal shape around 
the integrated-type detecting core member 71, and numeral 76 designates a 
detecting coil portion wound in a toroidal shape around the separate-type 
detecting core member 72. 
In the pair of U-shaped material and the partition plate of the 
horseshoe-shaped detecting core member 71, a thickness of the partition 
plate is preferably about two times the U-shaped material. By arranging a 
non-magnetic hold member (not shown) of a predetermined size between the 
detecting core members 72a, 72b of the horseshoe-shaped detecting core 
member 72, integration with the detecting core member 71 is facilitated 
and more convenient handling can be effected. 
As such, by employing the configuration, in which the excitation coil is 
wound independently without being disposed across the divided detecting 
cores, it is not necessary to connect the excitation coil in the detecting 
core for integration. 
That is, by partitioning a hollow portion of the divided detecting core 
member 71 with a same material as the core into two sections or more, and 
winding the excitation coil 73 in the divided hollow portions, as same as 
the excitation coil 53 shown in FIG. 1, the detecting core member 71 can 
be magnetically saturated periodically throughout the circumferential 
direction and the orthogonal direction of the longitudinal direction. 
Also in the detecting core members 72a, 72b, by the excitation coil 74 
wound in the hollow portions, the core members 72a, 72b can be 
magnetically saturated periodically throughout as same as the detecting 
core member 71. 
Meanwhile, in this configuration, by inserting and clamping one detecting 
core member 71 between other detecting core members 72a, 72b so as to be 
tightened vertically for integration, a magnetic resistance at the contact 
portion can be reduced. 
That is, it is possible to increase the overlapping and contact area of the 
detecting core members 71, 72, and as compared with the configuration of 
FIG. 12, the magnetic resistance at the contact portion is considerably 
reduced and the detecting sensitivity as about same as the case of using 
the integrated core shown in FIG. 1 can be obtained. 
The separated-type DC current sensor shown above is very simple to mount to 
a lead wire being detected wired already and its versatility is high, thus 
the same operation effect as the integrated type previously described is 
accomplished, and the configuration for dividing the core other than the 
aforementioned configuration can be suitably employed. 
EMBODIMENT 1 
The detecting core members 51a, 51b shown in FIG. 5(A)and FIG. 5(C) were 
shaved from a block material consisting of permalloy C (78% 
Ni-5%Mo-4%Cu-balFe) and processed into a mould. Thickness of the resulting 
members 51a, 51c was 1.0 mm. 
The detecting core member 51a has a cylindrical shape with bottom and 
includes a through hole in the center of the bottom to constitute an 
external cylinder portion of the detecting core 51, and the detecting core 
member 51c has a collar around one end portion of the cylinder to 
constitute a inner cylinder portion of the detecting core 51. Where, rough 
sizes of the respective parts are that, in the detecting core member 51a, 
outside diameter D.sub.1 =20 mm, inside diameter D.sub.2 =10 mm and height 
H.sub.1 =9 mm, and in the detecting core member 51c, outside diameter 
D.sub.4 =20 mm, inside diameter D.sub.5 =10 mm and height H.sub.3 =9 mm. 
The detecting core members 51a and 51c were subjected to heat treatment for 
multi-stage cooling at 100.degree. C./hour between 600.degree. C. and 
400.degree. C., after processing and heating in a hydrogen gas atmosphere 
at 1100.degree. C. for 3 hours. 
After winding the excitation coil 53 consisting of an enamel wire of 0.2 mm 
outside diameter around a plastic bobbin 51b of outside diameter D.sub.3 
=15 mm and height H.sub.3 =7 mm shown in FIG. 5(B) by 100 turns, the 
plastic bobbin 51b was fit around the detecting core members 51c and 
covered with the detecting core members 51a for integration. That is, the 
detecting core 51 incorporating the plastic bobbin 51b, around which the 
excitation coil 53 is wound, was constituted by the detecting core member 
51a and the detecting core member 51c. 
After containing the detecting core 51 is a plastic case (not shown) and 
securing an electrical insulation, the detecting coil 54 consisting of an 
enamel wire of 0.1 mm outside diameter was wound around the plastic case 
(detecting core 51) in a toroidal shape by 300 turns as shown in FIG. 1, 
and the vinyl coated lead wire being detected 1 of 8 mm outside diameter 
was extended through the detecting core 51 to complete the DC current 
sensor of the present invention shown in FIG. 1. 
In the DC current sensor of the present invention constituted as above, 
when an AC signal of f.sub.0 =500 Hz and 1 Vrms was applied to the 
excitation coil 53, an excitation current of 0.1 Arms was produced. At 
this time, when a micro-current of .+-.5 mA was applied to the lead wire 
being detected 1 to measure the AC current of f=1000 Hz (f=2f.sub.0) 
produced in the detecting coil 54, a detection result as shown in FIG. 6 
was obtained. 
Since the configuration shown in FIG. 5 was shaved out from a block 
material for processing, the core thickness or the section area is large 
and it is effective in increasing a magnetic flux in the core and the 
output. 
EMBODIMENT 2 
Using the DC current sensor of Embodiment 1, AC current applying means 
provided with an oscillator producing an excitation current having a 
frequency of two times the excitation current applied finally to the 
excitation coil 53, and a phase comparison circuit are disposed 
perspectively on the excitation coil 53 and the detecting coil 54 to apply 
the practically same excitation signal as the Embodiment 1 from the 
oscillator to the excitation coil 53, and to apply a sine-wave Ac current 
of 30 Hz, 0.1 mA (at peak) so that the detecting coil 54 serves as the 
excitation coil, and further, an output variation after removing an 
alternating component of 30 Hz by a low-pass filter from an electromotive 
force (output) of the detecting coil 3 outputted via the phase comparison 
circuit, when the DC current I was applied to the lead wires being 
detected 1 in a range of .+-.5 mA, was measured. As a result, it has been 
confirmed that 1 mA can be detected at an S/N ratio of 10 or higher. 
As it is apparent from the above measurement result, according to the DC 
current sensor of the present invention, in spite of the very simple 
configuration of the detecting core 51, an error output due to 
reciprocating currents is very small, and even with a micro-current of 1 
mA, it can be measured at the S/N ratio of ten times or more, thus a very 
sensitive detection is possible. 
EMBODIMENT 3 
As shown in FIG. 14(A) and (C), plates made of permalloy 
C(78Ni-3.5Mo-4.5Cu-Fe) material of 0.35 mm thick were bent outwardly and 
inwardly by press molding respectively at one end to prepare an inner 
cylinder 80 and an outer cylinder 81 which were assembled together to form 
a cylinder, which was annealed to secure magnetic characteristics after 
washed in triclene, then heated in H.sub.2 gas at 1000.degree. C. for 3 
hours and cooled at 100.degree. C./hour between 600.degree. C. and 
400.degree. C. 
Also, as shown in FIG. 14(B), an enamel wire of 0.18 mm diameter was wound 
by 100 turns around a plastic bobbin 82 of 25.5 mm inside diameter, 0.2 mm 
thick and 7 mm long in a solenoid fashion to prepare an excitation coil 83 
by impregnating instantaneous adhesives which is commercially available to 
solidify the wire. 
As shown in FIG. 14, the inner cylinder 80 and the outer cylinder 81 were 
inserted into the excitation coil 83 from the upper and lower sides for 
engagement to prepare a detecting core 84 incorporating the excitation 
coil 83 as shown in FIG. 15(B). The contact of the inner cylinder 80 and 
the outer cylinder 81 was secured by the instantaneous adhesives 
commercially available. 
Furthermore, after covering the detecting core 84 shown in FIG. 15(B) with 
plastic cases 85, 86 shown in FIG. 15(A) and (C) to prevent from 
distortion, an enamel wire of 0.18 mm diameter was wound by 300 turns in a 
toroidal shape as a detecting coil 87, which is commonly used as a 
modulation coil, to prepare a DC current sensor according to the present 
invention shown in FIG. 16. 
An oscillator was connected to an excitation coil of the resulting DC 
current sensor, and a wide-band AC voltage meter was connected to the 
detecting coil, which is commonly used as the modulation coil, via a 
band-pass filter of resonance frequency f.sub.0 =7 kHz, Q=5, a lead wire 
connected to a DC power supply is extended through the detecting core. 
When an AC signal of 3.5 kHz and 10 Vrms was applied to the excitation 
coil, an electric current of 25 m Arms was produced. When an output 
voltage was measured after demagnetizing the core, it shows a point P 
(about 10 m Vrms) in FIG. 17, and when applying a through current the 
output voltage is incremented substantially linearly from P to Q. 
As the through current I of 10 mA, the output voltage was 200 mV. When the 
through current I of 10 mA was applied again after increasing it to 1 A, 
though the output voltage is incremented by 2 to 3 mV, it shows 
approximately the same value as the initial value. 
Thereafter, as the electric current reduces a locus Q.fwdarw.O' is 
obtained, and since the residual output at the time of O' is about 25 mV, 
when the direction of current is reversed, it takes a minimum value (about 
10 mV) at I=-1 mA, and after passing a point R the output increases again 
(200 m Vrms at I=-10 mA). Thereafter, when the electric current is changed 
from -10 mA to +10 mA, the output changes as following the path 
S.fwdarw.O'.fwdarw.T.fwdarw.Q. 
Thus, the DC current sensor according to the present invention is that, the 
effect of hysteresis of the material of the detecting core 2 is constant, 
and the output characteristics is substantially proportional linearly to 
the electric current I flowing through the lead wire being detected, so 
that it is understood that a good detecting capability of the DC current 
is accomplished. 
EMBODIMENT 4 
In a same manner as the Embodiment 3, an enamel wire of 0.1 mm diameter was 
wound by 100 turns around a paper bobbin of 3.5 mm height to prepare an 
excitation coil, which was contained in a detecting core of 5 mm height, 
25 mm inside diameter and 31 mm outside diameter consisting of a permalloy 
material C of 0.25 mm thick, and after containing again in a plastic case, 
an enamel wire of 0.1 mm diameter was wound by 300 turns to obtain a 
detecting coil, which is used commonly as a modulation coil, and finally a 
DC current sensor of 8 mm height, 22 mm inside diameter and 34 mm outside 
diameter was obtained. 
Then, the excitation coil and detecting coil of the DC current sensor were 
connected to a detecting circuit consisting of an electronic circuit shown 
in FIG. 18, and a lead wire connected to a DC powder supply is extended 
through the detecting core. 
Describing in detail, a rectangular wave of 10 kHz was inputted to the 
excitation coil from an oscillator G via a 1/2 dividing circuit, an LPF 
(low-pass filter), a phase shifter PS and a power amplifier PA, and when 
an AC current of 5 kHz and 7 Vrms was applied to the excitation coil, and 
electric current of 20 m Arms was produced. Also, the triangular wave of 
10 Hz is applied to the detecting coil, which is used commonly as the 
modulation coil, from a function generator FG, at this time, a peak value 
of a triangular wave current is 0.5 mA, and an output Vout of the 
detecting coil is inputted to a counter U/D.C via a diode limiter, a band 
pass filter BPF and a phase detector and displayed on a display D 
numerically. 
In the following the principle of operation of the DC current sensor 
constituted as aforementioned is described with reference to the drawings. 
FIG. 19 is an explanatory view of an output produced in the detecting coil 
in the state, where the electric current I is not flowing through the lead 
wire being detected. 1. 
When a triangular waveform current whose direction and intensity change 
linearly periodically is applied to the detecting coil, a magnetic flux 
.PHI..sub.3 as shown in FIG. 19(A) is produced in the detecting core, and 
an electromotive force as shown in FIG. 19(B) is produced in the detecting 
coil. In the figure, a direction of the arrow shows a phase of the 
electromotive force, and in FIG. 19(B), it shows that the phase difference 
between a-b, b-c is 180 degree. That is for the purpose of understanding 
the principle of operation of the present invention clearly, for the 
electromotive force having the phase difference as shown in FIG. 20(A), 
the direction of phase is shown by the arrow as shown in FIG. 20(B). (It 
is also same in the description of FIG. 21.) 
When the electromotive force as shown in FIG. 19(B) is passed through the 
limiter for crest restriction, the output as shown in FIG. 19(C) is 
obtained, and by the phase detection of this output, the output as shown 
in FIG. 19(D) is obtained. 
In FIG. 19(D), an output time T.sub.1 of the positive side (+) and an 
output time T.sub.2 of the negative side (-) are measured to detect the 
time ratio (duty ratio). 
In the state where the electric current I is not flowing through the lead 
wire being detected 1, as shown in FIG. 19(D), the output time T.sub.1 of 
the positive side (+) and the output time T.sub.2 of the negative side (-) 
are equal and their difference (T.sub.1 -T.sub.2) is zero. 
FIG. 20 is an explanatory view of an output produced in the detecting coil 
in the state where the electric current I is flowing through the lead wire 
being detected 1. 
When the triangular waveform current whose direction and intensity change 
linearly periodically is applied to the detecting coil, a magnetic flux 
.PHI..sub.4 as shown in FIG. 21(A) is produced in the detecting core 2, 
and an electromotive force as shown in FIG. 21(B) is produced in the 
detecting coil. That is, the magnetic flux produced by the triangular 
waveform current and the magnetic flux produced by the electric current I 
flowing through the lead wire being detected 1 are superposed (.PHI..sub.4 
=.PHI..sub.3 +.PHI..sub.0). 
When an electromotive force as shown in FIG. 21(B) is passed through the 
limiter for crest restriction, an output as shown in FIG. 21(C) is 
obtained, and by the phase detection of this output an output as shown in 
FIG. 21(D) is obtained. 
In FIG. 21(D), an output time T.sub.1 of the positive side (+) and an 
output time T.sub.2 of the negative side (-) are measured to detect the 
time ratio (duty ratio). 
In the state where the electric current I is flowing through the lead wire 
being detect 1, as shown in FIG. 21(D), the output time T.sub.1 of the 
positive side (+) is longer that the output time T.sub.2 of the negative 
side (-) are measured to detect the time ratio (duty ratio). 
In the state where the electric current I is flowing through the lead wire 
being detected 1, as shown in FIG. 21(D), the output time T.sub.1 of the 
positive side (+) is longer that the output time T.sub.2 of the negative 
side (-), and their difference (T.sub.1 -T.sub.2) is positive (T.sub.1 
-T.sub.2 &gt;0). 
Since the difference (T.sub.1 -T.sub.2) is proportional to the electric 
current I flowing through the lead wire being detected, an absolute value 
of the electric current I can be known by measuring a correlation of the 
detecting value and the electric current I beforehand. 
Also, by confirming and setting the case where the difference (T.sub.1 
-T.sub.2) is positive (T.sub.1 -T.sub.2 &gt;0) or negative (T.sub.1 -T.sub.2 
&lt;0) and the direction of the electric current I flowing through the lead 
wire being detected beforehand, the direction and the absolute value of 
the electric current I can be detected simultaneously. 
Furthermore, when a maximum value of the electric current applied to the 
detecting coil is set large enough to produce a magnetic field above the 
coercive force (.+-.Hc) of the detecting core material, output 
characteristic hysteresis caused by the hysteresis of the detecting core 2 
material can be reduced. 
That is, when the principle of operation described with reference to FIG. 
19 and FIG. 20 is studied taking into consideration of the coercive force 
of the detecting core 2 material, the magnetic flux produced in the 
detecting core shows a rectangular wave, and the output produced finally 
in the detecting coil also shows the same characteristics. 
In the case where the electric current I is not flowing through the lead 
wire being detected 1, when the triangular waveform current is applied to 
the detecting coil, a magnetic field as H.sub.3 shown in FIG. 22(B) is 
applied to the detecting core 2. At this time, the magnetic flux produced 
in the detecting core 2 is that, its direction changes (reverses) as the 
time changes as shown in FIG. 22(C) by the hysteresis of the detecting 
core 2 as shown in FIG. 22(A). 
In this case, a producing time T.sub.1 of the magnetic flux of the positive 
side (+) and a producing time T.sub.2 of the magnetic flux of the negative 
side (-) are equal, and the difference (T.sub.1 -T.sub.2) is zero. 
Meanwhile, in the case where the electric current I is flowing through the 
lead wire being detected 1, when the triangular waveform current is 
applied to the detecting coil, a magnetic field as H.sub.4 shown in FIG. 
22(B) is applied to the detecting core. At this time, the magnetic flux 
produced in the detecting core is that, its direction changes (reverses) 
as the time changes as shown in FIG. 22(D) by the hysteresis of the 
detecting core as shown in FIG. 22(A). 
In this case, the producing time T.sub.1 of the magnetic flux of the 
positive side (+) is longer than the producing time T.sub.2 of the 
magnetic flux of the negative side (-) and the difference (T.sub.1 
-T.sub.2) is positive (T.sub.1 -T.sub.2 &gt;9). 
As it can be understood from the description of FIG. 19 and FIG. 20, output 
characteristics obtained by the phase detection of the electromotive force 
produced in the detecting coil by the magnetic flux shown in FIG. 22(C) 
and FIG. 22(D), after passing the electromotive force through the limiter 
for crest restriction, shows the same output time characteristics shown in 
FIG. 22(C) and FIG. 22(D). 
Thus, by setting a maximum value of the electric current applied to the 
detecting coil large enough to produce the magnetic field above the 
coercive force of the detecting core material, the effect of hysteresis of 
the detecting core material becomes constant (a same hysteresis loop is 
always drawn), and since the difference (T.sub.1 -T.sub.2) is proportional 
to the electric current I flowing through the lead wire being detected, it 
is understood that the output characteristics obtained finally is linear. 
When the difference (T.sub.1 -T.sub.2) was measured by using the 
aforementioned detecting circuit shown in FIG. 18, the characteristics as 
shown in FIG. 23(A) was obtained. Now, the relationship between a read 
value obtained by reading the difference (T.sub.1 -T.sub.2) by the pulse 
count number, after operating an Up-Down Counter by the output Vout and 
applying a pulse of 15 kHz, and the through current is shown in FIG. 
23(B). 
As shown in FIG. 23, it is also substantially linear even below 1 mA and 
error is .+-.0.1 mA, results in a good measurement accuracy at a 
micro-current.