JP2011247765A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized and low-cost current detector which is less affected by ambient environment conditions and is capable of detecting a micro current in a wide range.SOLUTION: The current detector includes: an excitation coil 3 and a detection coil 5 wound around a magnetic core 2 surrounding a conductor 1 where a current to be measured flows, so as to be electrically insulated but magnetically coupled; excitation means 4 for supplying a magnetizing current to the excitation coil, whereby a rectangular wave voltage is applied which brings the magnetic core into a saturated state or a state approximating the saturated state; and current detection means 6 for detecting the magnetizing current flowing in the excitation coil 3 supplied by the excitation means 4 using the detection coil 5 and for detecting the current to be measured on the basis of timing of an abrupt change in magnitude of the magnetizing current detected by the detection coil.

Description

  The present invention relates to a current detection device that uses the non-linear characteristics of a high magnetic permeability material used for leakage detection and the like.

As this type of current detection device, devices having various configurations have been proposed and implemented, but a flux gate type current sensor is known as a device that is structurally simple and capable of detecting a minute current. (For example, refer to Patent Document 1).
The conventional example described in Patent Document 1 has the configuration shown in FIG. That is, the same shape and isometrically formed cores 101 and 102 made of a soft magnetic material, the exciting coil 103 wound around the cores 101 and 102, and the cores 101 and 102 in a lump. And a wound detection coil 104.

An AC power supply (not shown) is connected to the excitation coil 103, and a detection circuit (not shown) is connected to the detection coil 104. And the to-be-measured conducting wire 105 which is an object which measures an electric current is inserted in the center of both the cores 101 and 102.
The exciting coil 103 is wound around the cores 101 and 102 so that the magnetic fields generated in the cores 101 and 102 are opposite in phase when they are energized and cancel each other.

  When the exciting current iex is supplied to the exciting coil 103, the change with time in the magnetic flux density B generated in each of the cores 101 and 102 is as shown in FIG. The magnetic characteristics of the soft magnetic cores 101 and 102 have a linear relationship between the magnetic field magnitude H and the magnetic flux density B when the magnetic field magnitude H is within a predetermined range. However, when the magnitude H of the magnetic field exceeds a predetermined value, the magnetic flux density B does not change and the magnetic saturation state is established. Therefore, when the exciting current iex is supplied to the exciting coil 103, it is generated in each of the cores 101 and 102. The magnetic flux density B to be changed changes to a vertically symmetric trapezoidal wave shape as shown by the solid line, and the phases are 180 ° out of phase with each other.

Assuming that a direct current value I is energized downward as shown by an arrow in the lead 105 to be measured, a magnetic flux density corresponding to this direct current component is superimposed. As a result, the magnetic flux density B is as shown in FIG. As indicated by the broken line, the upper trapezoidal wave has an enlarged width while the lower trapezoidal wave has a reduced width.
Here, when the change in the magnetic flux density B generated in both the cores 101 and 102 is expressed by a sine wave (corresponding to the electromotive force), it is as shown in FIG. In FIG. 7C, a sine wave (electromotive force) having a frequency f shifted by 180 ° as shown in the solid line corresponding to the trapezoidal wave shown in the solid line in FIG. 7B is shown. Are offset by 180 °, so they cancel each other. On the other hand, corresponding to the trapezoidal wave shown by the broken line in FIG. 7B, the second harmonic of the double frequency 2f as shown by the broken line appears in FIG. 7C. Since the second harmonics are 180 ° out of phase, when they are superimposed on each other, a sine wave signal as shown in the lowermost stage of FIG. 7C is obtained, and this is detected by the detection coil 104.
The detection signal captured by the detection coil 104 corresponds to the direct current value I flowing through the conductor 105 to be measured, and the current value I can be detected by processing this.

  Further, as another conventional example, a primary winding for passing a current to be detected, and a secondary winding electrically insulated from the primary winding and magnetically coupled to the primary winding by a magnetic core For periodically driving the magnetic core to saturation, including one or more first sensing transformers comprising: and means for detecting saturation and reversing the direction of the magnetization current accordingly A current sensor is proposed comprising sensing means comprising means for alternately supplying magnetizing currents in opposite directions to the secondary winding and processing means for outputting an output signal substantially proportional to the sensed current. (For example, refer to Patent Document 2). The current sensor further includes a low-pass filter that separates a low frequency or direct current component of the magnetizing current generated in the secondary winding by a current sensed by being connected to the secondary winding of the first sensing transformer. And a primary winding through which a sensed current passes, and a secondary winding, the input side of the secondary winding being coupled to the output of the low-pass filter, the output side of which is the device And a second sensing transformer installed by a resistor from which an output signal is generated.

JP 2000-162244 A Japanese Patent No. 2923307

  However, in the conventional example described in Patent Document 1, since the two cores 101 and 102 are used, it is actually difficult to completely match the magnetic characteristics of the cores 101 and 102. Due to the difference in magnetic characteristics, the voltage generated by the exciting current iex is generated without being completely canceled out. This deteriorates the S / N ratio of the detection voltage corresponding to the second-order harmonic component, and there is a problem of seeing and solving that it is difficult to detect a minute current.

  Further, the second harmonic corresponding to the current value I output from the detection coil 104 has a trapezoidal wave shape distorted as shown by the broken line in FIG. 7C when the current value I becomes too large. In addition, the relationship between the current I and the second harmonic component is not proportional. Accordingly, since the detection range of the current value I is limited, there is an unsolved problem that a wide range of current cannot be detected.

Moreover, since at least two cores are used, there is an unsolved problem that it is difficult to realize miniaturization and cost reduction.
Further, even in the conventional example described in Patent Document 2, it is necessary to provide the first detection transformer and the second detection transformer, and it is not possible to detect a wide range of current by one magnetic core. There is a problem to be solved.
Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and is hardly affected by ambient environmental conditions, and can detect a small current in a wide range with a small size and low cost. The object is to provide a current sensing device.

  In order to achieve the above object, an electric current detection device according to an embodiment of the present invention includes an excitation coil and a detection coil wound so as to be electrically insulated and magnetically coupled to a magnetic core surrounding a conducting wire through which a measurement current flows. A coil is provided. A magnetizing current is supplied to the exciting coil by applying a rectangular wave voltage from the exciting means to bring the magnetic core into a saturated state or a state in the vicinity thereof. The magnetizing current flowing through the exciting coil is detected by the detecting coil by the exciting means. The detection current flowing through the detection coil is supplied to the current detection means, and the measurement current is detected based on the timing at which the magnitude of the detection current suddenly changes.

According to this configuration, when a rectangular wave voltage is applied to the excitation coil by the excitation means, a current determined by the magnetic core inductance flows, and when the magnetic core inductance is saturated, a current determined by the resistance of the secondary winding flows. As a result, the current waveform flowing in the exciting coil changes suddenly. The timing at which the inductance disappears is proportional to the measured current of the conductor surrounded by the magnetic core.
By detecting the current waveform flowing in the exciting coil with the detection coil and detecting the timing when the current waveform suddenly changes with the current detection means, the measurement current can be detected.

In the current detection device according to another aspect of the present invention, the excitation means includes an oscillation circuit that generates a rectangular wave voltage, and the rectangular wave voltage output from the oscillation circuit is converted into an excitation current to generate the secondary current. It is characterized by comprising a current booster supplied to the winding.
According to this configuration, a rectangular wave voltage is generated in the oscillation circuit, supplied to the current booster, converted into a magnetizing current, and supplied to the exciting coil, thereby controlling the magnetic core to a saturated state or a state in the vicinity thereof. Thus, the current sudden change timing based on the inductance characteristics can be reliably formed.

In the current detection device according to another aspect of the present invention, the current detection unit is supplied with a current-voltage conversion circuit that converts a detection current flowing through the detection coil into a voltage, and an output of the current-voltage conversion circuit. And a current detection circuit for detecting a duty change and outputting an output signal corresponding to the measurement current.
According to this configuration, it is possible to obtain a voltage signal corresponding to the measurement current by detecting the duty change in a state where the detection current flowing through the detection coil is converted into a voltage.

In the current detection device according to another aspect of the present invention, the excitation unit includes a frequency selection unit that selects a frequency of a rectangular wave voltage to be applied, and the frequency of the frequency selection unit is set to the magnitude of the measurement current. It is characterized by selecting it accordingly.
According to this configuration, since the frequency of the rectangular wave voltage of the excitation means can be selected according to the magnitude of the measurement current, a wider range of current detection can be performed by changing the detection range.

According to the present invention, a rectangular wave voltage is applied to the exciting coil by the exciting means by utilizing the fact that the characteristic that the inductance of the magnetic core suddenly disappears near the saturation current is shifted by the current of the conducting wire passing through the inside. Then, a magnetizing current that makes the magnetic core saturated or in the vicinity thereof is supplied, a current change is caused in the exciting coil due to the disappearance of the inductance of the magnetic core, and this current change is detected by the detection coil. The measurement current is detected based on the timing at which the magnitude of the detection current changes suddenly. For this reason, the current detection device can be configured using one magnetic core, and the S / N ratio does not decrease due to the difference in the material characteristics of the magnetic core, and a minute current can be detected with high accuracy. .
In addition, since the current detection device can be composed of one magnetic core and two windings, it is possible to reduce the size and cost.
Furthermore, since a magnetic sensor or the like is not used, it is possible to provide a current detection device that is robust and less affected by ambient environmental conditions.
In addition, by configuring the frequency of the rectangular wave voltage applied to the secondary winding to be selectable, it is possible to detect a wide range of currents by selecting a frequency according to the measurement current.

1 is a configuration diagram illustrating a first embodiment of a current detection device according to the present invention. FIG. It is a circuit diagram which shows an example of the excitation circuit of FIG. It is explanatory drawing which shows the characteristic of a magnetic core, Comprising: (a) is a characteristic diagram which shows the relationship between the magnetic flux density of a magnetic core, and the strength of a magnetic field, (b) shows the relationship between the measurement current of a magnetic core, and an inductance. It is a characteristic diagram. It is a schematic diagram which shows the current waveform which flows into an exciting coil. FIG. 2 is a circuit diagram illustrating an example of a detection circuit in FIG. 1. It is a circuit diagram which shows the excitation circuit in the 2nd Embodiment of this invention. It is explanatory drawing which shows a prior art example, Comprising: (a) The block diagram of a sensor part, (b) is a figure which shows the magnetic flux density of each magnetic core when an exciting current is supplied to an exciting coil, (c) is each magnetic core It is the figure which expressed the magnetic flux density of sine wave.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a current detection device according to the present invention. In the figure, reference numerals 1a and 1b denote conductors, for example, 10A to 800A of a reciprocating current I provided on an object such as leakage detection, and the sum of currents flowing to the conductors 1a and 1b is zero in a healthy state. However, the sum of the currents flowing through the conductors 1a and 1b does not become zero due to electric leakage or ground fault, and a minute difference current of, for example, about 15 mA to 500 mA to be detected flows. A ring-shaped magnetic core 2 is disposed around the conducting wires 1a and 1b. That is, the conducting wires 1 a and 1 b are inserted into the magnetic core 2.

An exciting coil 3 is wound around the magnetic core 2 with a predetermined number of turns, and a magnetizing current is supplied to the exciting coil 3 from an exciting circuit 4 as an exciting means.
The magnetic core 2 is wound with a detection coil 4 having the same number of turns as the excitation coil 3 that is electrically insulated from the excitation coil 3 and magnetically coupled. Current is supplied to a detection circuit 6 as current detection means.

As shown in FIG. 2, the excitation circuit 4 is an oscillation circuit that generates a square wave voltage as a rectangular wave voltage composed of three inverter ICs 11, 12, and 13, two resistors 14 and 15, and one capacitor 16. 17 and a current booster 18 for converting the oscillation output voltage of the oscillation circuit 17 into a current.
In the oscillation circuit 17, a resistor 14 for protecting the inverter IC and three inverter ICs 11, 12, and 13 are connected in series. A resistor 15 is inserted between the end of the resistor 14 opposite to the inverter IC11 and the output side of the inverter IC13. Further, a capacitor 16 is inserted between the end of the resistor 14 opposite to the inverter IC 11 and the connection point of the inverter ICs 12 and 13.

The oscillation frequency f of the oscillation circuit 17 is calculated by the following equation (1), where α is the proportionality constant, R is the resistance value of the resistor 15, and C is the capacitance of the capacitor 16.
f = 1 / (α × C × R) (1)
It is assumed that the oscillation operation of the oscillation circuit 17 is at the first stage, for example, the input side of the inverter IC11 is at a low level and the output side is at a high level. In this first stage, the input side of the inverter IC 12 is at a high level and the output side is at a low level. Further, the input side of the inverter IC13 is at a low level and the output side is at a high level.

For this reason, the capacitor 16 is charged by forming a current path through which the current output from the inverter IC 13 is grounded through the resistor 15 through the capacitor 16 and through the output side of the inverter IC 12.
When the charging of the capacitor 16 progresses and the potential on the plus side of the capacitor 16, that is, the resistance 15 side reaches the threshold voltage Vth of the inverter IC11, the output of the inverter IC11 is inverted and becomes a low level, and the output of the inverter IC12 is correspondingly Is inverted to a high level and the output of the inverter IC13 is inverted to a low level.

  In this second stage, the current path is opposite to that described above, that is, the current output from the inverter IC 12 passes through the capacitor 16 and the resistor 15 and is grounded from the output side of the inverter IC 13. 16 becomes a discharge state. At this time, in the initial state of discharge, the potential on the resistor 15 side of the capacitor 16 is a potential obtained by adding the charging voltage of the capacitor 16 to the power supply voltage.

  Thereafter, even if all the electric charge accumulated in the capacitor 16 is discharged, the output of the inverter IC 12 still maintains a high level, and the current continues to flow in the same direction as it is. For this reason, the capacitor has a polarity opposite to that described above, that is, the third stage in which the inverter IC side of the capacitor is charged positively. When the charge of the capacitor 16 is zero, the potential on the resistor 15 side of the capacitor 16 becomes the same as the power supply voltage, but gradually decreases as the charging progresses, and when the voltage decreases to the threshold voltage Vth, the output of the inverter IC11 is inverted and the first voltage is inverted. There are four stages.

  In this fourth stage, the output of the inverter IC12 is inverted to a low level and the output of the inverter IC13 is inverted to a high level, so that the current output from the inverter IC13 passes through the resistor 15 and the capacitor 16 and is output to the inverter IC12. A current path to be grounded is formed. As a result, when the capacitor 16 is in a discharging state, the potential on the resistor 15 side gradually increases and the capacitor 16 is emptied, the process returns to the first stage and charging with the reverse polarity starts.

When the capacitor 16 is charged / discharged, a square wave voltage having a predetermined frequency f calculated by the equation (1) is output from the output side of the inverter IC 13, and this square wave voltage is input to the current booster 18. Here, the square wave voltage output from the oscillation circuit 17 is set to a voltage that can be excited with a current that sufficiently saturates the magnetic core 2 when applied to the exciting coil 3 as will be described later.
The current booster 18 has a configuration in which an NPN transistor 19 and a PNP transistor 20 whose bases are connected to each other are connected in series between a power supply voltage and the ground, and a square wave voltage output from the oscillation circuit 17 is used as a magnetizing current. The converted magnetization current is supplied to the exciting coil 3.

  As shown in FIG. 3A, the magnetic core 2 has a BH characteristic representing a relationship between a magnetic flux density B having a large squareness ratio and a magnetic field strength H, and is a linear characteristic of a high permeability material. Have The inductance of the magnetic core 2 having this BH characteristic disappears rapidly near the saturation current as shown in FIG. When a minute measurement current C to be detected is applied to the conducting wires 1a and 1b penetrating the magnetic core 2, the BH characteristic of FIG. 3B shows the magnetic field intensity H direction according to the measurement current C. And the timing at which the inductance disappears changes.

When a pulsed square wave voltage is applied to the exciting coil 3 using the magnetic core 2 having the material characteristics shown in FIG. 3 and the magnetic core 2 is excited with a current that is sufficiently saturated, the current flowing through the exciting coil 3 is: It can be schematically represented as shown in FIG.
When a pulse voltage is applied, a current determined by the inductance of the magnetic core 2 first flows, and when the inductance of the magnetic core 2 is saturated (point F in FIG. 4), a current determined by the resistance of the exciting coil 3 flows.

When an arbitrary minute measurement current is passed through the conducting wires 1a and 1b penetrating the magnetic core 2, as shown in FIG. 3B, the inductance corresponding to the current value C disappears and the timing changes as shown in FIG. The timing at which the inductance disappears also changes from point F to point H. That is, the duty ratio of the current flowing through the exciting coil 3 changes.
A waveform similar to the excitation current waveform shown in FIG. 5 can be obtained from the detection coil 4 by winding the detection coil 5 around the magnetization coil 2 with the same number of turns as the excitation coil 3.

Therefore, the current value C flowing through the conductors 1a and 1b can be measured by detecting the duty change of the pulse due to the disappearance of the inductance of the detection current of the detection coil 5.
Therefore, the detection circuit 6 connected to the detection coil 5 is, as shown in FIG. 5, a current-voltage conversion circuit composed of an operational amplifier 21 whose input side is connected to both ends of the detection coil 5 and its feedback resistor 22. And a duty ratio-voltage conversion circuit 24 for converting the output voltage duty change of the current-voltage conversion circuit 23 into a voltage.

Here, the current-voltage conversion circuit 23 outputs, from the operational amplifier 21, a voltage proportional to the product of the current value of the same current flowing in the detection coil 5 as in FIG. 4 and the resistor 22.
The duty ratio-voltage conversion circuit 24 receives the voltage output output from the current-voltage conversion circuit 23 via the series circuit of the resistor 25 and the capacitor 26 on the inverting input side. An operational amplifier 28 is input to the non-inverting input side via a series. Here, the resistor 27 and the non-inverting input side of the operational amplifier 28 are connected to the ground via the capacitor 29.

A voltage output corresponding to the duty ratio of the voltage output input from the current-voltage conversion circuit 23 from the output side of the operational amplifier 28, that is, a voltage output corresponding to the measurement current flowing through the conductors 1 a and 1 b penetrating the magnetic core 2 is obtained. It is output to the output terminal 30.
From the voltage output output from the output terminal 30, it is possible to detect a minute current flowing through the conducting wires 1a and 1b penetrating the magnetic core 2.

  As described above, according to the first embodiment, the magnetic core 2 including the conducting wire through which the measurement current flows is provided, and the excitation coil 3 and the detection coil 5 wound around the magnetic core 2 are provided. An excitation circuit 4 that supplies a magnetizing current for applying a square wave voltage to the coil 3 to bring the magnetic core 2 into a saturated state or a state in the vicinity thereof, and a detection current corresponding to the measurement current I flowing through the detection coil 5 Based on a simple configuration in which a detection circuit 6 for detecting a measurement current is simply provided, a minute current flowing through the conductors 1a and 1b penetrating the magnetic core 2 can be reliably detected in a wide range, and the cost can be reduced. be able to.

Further, unlike the case of using the two magnetic cores as in the conventional example described above, the S / N ratio is not lowered due to the difference in core material characteristics, and a minute current can be detected with high accuracy.
In addition, since current detection is possible without using a magnetic sensor or the like as in the conventional example described above, it is possible to provide a current detection device that is robust and less affected by ambient environmental conditions.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, the optimum square wave oscillation frequency can be set for the current value of a minute detection target current flowing through the conducting wires 1a and 1b penetrating the magnetic core 2.
That is, in the second embodiment, as shown in FIG. 6, the oscillation circuit 17 of the excitation circuit 4 has the frequency adjustment circuit 40 in series with the resistor 15 in the configuration of FIG. Except for being provided, it has the same configuration as FIG. 2 described above. 2 corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

Here, the frequency adjustment circuit 40 is connected to frequency adjustment resistors 41 and 42 set in different resistance values in series with the resistor 15, and includes an analog switch IC or the like in parallel with the frequency adjustment resistors 41 and 42. Open / close switches 43 and 44 are connected. The on / off switches 43 and 44 are on / off controlled by a switch control unit 45.
The switch controller 45 can individually control the on / off switches 43 and 44. The oscillation frequency f of the square wave voltage due to the on / off of the open / close switches 43 and 44 by the switch control unit 45 is as shown in Table 1 below, where the resistance value of the resistor 41 is R1 and the resistance value of the resistor 42 is R2. become.

  As is apparent from Table 1, when both the open / close switches 43 and 44 are controlled to be in the on state, the oscillation frequency f is the same as that in the above-described equation (1) in the first embodiment. Further, when the open / close switch 43 is controlled to be in the off state and the open / close switch 44 is controlled to be in the on state, the oscillation frequency f1 is calculated based on the resistance value (R + R1) obtained by adding the resistance values R and R1 of the resistors 15 and 41. . Further, when the open / close switch 43 is controlled to be on and the open / close switch 44 is controlled to be off, the oscillation frequency f2 is calculated based on a resistance value (R + R2) obtained by adding the resistance values R and R2 of the resistors 15 and 42. Further, the oscillation frequency f3 is calculated based on the resistance value (R + R1 + R2) obtained by adding the resistance values R, R1, and R2 of the three resistors 15, 41, and 42 that turn off the open / close switches 43 and 44.

Therefore, when each resistance value is set to R <R1 <R2, the relationship between the oscillation frequencies f to f3 is f>f1>f2> f3.
Here, the on / off control of the open / close switches 43 and 44 by the switch control unit 45 is preferably selected according to the magnitude of the measurement current to be detected flowing in the conducting wires 1a and 1b penetrating the magnetic core 2. For example, by selecting a small frequency f3 when the measurement current is large and selecting frequencies f2, f1, and f that increase as the measurement current decreases, the detection range of the duty change with respect to the measurement current can be changed. By selecting an oscillation frequency that is optimal for the size of the current, it is possible to detect a wider range of minute currents with higher accuracy than in the first embodiment described above.

  In the second embodiment, the case where the two frequency adjusting resistors 41 and 42 are provided in series with the resistor 15 has been described. However, the present invention is not limited to this, and one or three or more resistors are provided. By connecting frequency adjusting resistors and providing on / off switches corresponding to the number of connected resistors, the oscillation frequency can be adjusted more finely. In addition, a variable resistor may be applied instead of the fixed resistor, and the point is that the entire resistance value may be adjusted to a desired stage.

  In the first and second embodiments, the case where the oscillation circuit 17 is configured to output a square wave voltage using the three inverter ICs 11 to 13 as the oscillation circuit 17 is described. However, the present invention is not limited to this. In addition, the inverter IC 11 is omitted, and an oscillation circuit using two inverter ICs can be applied by reversing the arrangement positions of the resistor 15 and the capacitor. Furthermore, a rectangular shape using one Schmitt inverter can be used. An oscillation circuit that outputs a wave voltage can be applied, and any square wave oscillation circuit can be applied.

Further, the rectangular wave voltage output oscillated by the oscillation circuit 17 is not limited to the square wave voltage output, and can be any rectangular wave voltage output having a different waveform height and width. As shown in FIG. 4, any current can be used as long as current at which the current value changes abruptly due to the disappearance of the inductance at the time of saturation depends on the value of the measured current.
Moreover, although the case where the difference electric current of the two conducting wires 1a and 1b was detected was demonstrated in the said embodiment, it is not limited to this, The minute electric current of one conducting wire can also be detected.

  DESCRIPTION OF SYMBOLS 1a, 1b ... Conductor, 2 ... Magnetic core, 3 ... Excitation coil, 4 ... Excitation circuit, 5 ... Detection coil, 6 ... Detection circuit, 11-13 ... Inverter IC, 14, 15 ... Resistance, 16 ... Capacitor, 17 ... Oscillation circuit, 18 ... current booster, 21 ... operational amplifier, 22 ... resistance, 23 ... current-voltage conversion circuit, 24 ... duty ratio-voltage conversion circuit, 25, 27 ... resistance, 26, 29 ... capacitor, 28 ... operational amplifier, 30 ... Output terminal, 40 ... Frequency adjustment circuit, 41,42 ... Resistance, 43,44 ... Open / close switch, 45 ... Switch control unit

Claims (4)

An excitation coil and a detection coil wound around a magnetic core surrounding a conducting wire through which a measurement current flows to be electrically insulated and magnetically coupled;
Excitation means for supplying a magnetizing current to the excitation coil to apply a rectangular wave voltage to bring the magnetic core into a saturated state or a state in the vicinity thereof;
A current detection means for detecting the measurement current based on a timing at which the magnitude of the detection current in the detection current flowing in the detection coil suddenly changes by detecting the magnetization current flowing in the excitation coil by the excitation means. And a current detection device.   The excitation means includes an oscillation circuit that generates a rectangular wave voltage, and a current booster that converts the rectangular wave voltage output from the oscillation circuit into an excitation current and supplies the excitation current to the excitation coil. The current detection device according to claim 1.   The current detection means is a current-voltage conversion circuit that converts a detection current flowing through the detection coil into a voltage, and an output of the current-voltage conversion circuit is supplied to detect a change in duty and output according to the measurement current The current detection device according to claim 1, further comprising: a current detection circuit that outputs a signal.   The excitation means includes frequency selection means for selecting a frequency of a rectangular wave voltage to be applied, and the frequency of the frequency selection means is selected according to the magnitude of the measurement current. The current detection device according to any one of claims.

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