JP2016125863A - Current detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection device which is less affected by an ambient environment condition, which is compact, low cost, and consumes less current, and with which it is possible to detect a wide range of currents from a minute current to a large current.SOLUTION: The current detection device comprises: one exciting coil 4 wound around a magnetic core 3 enclosing a conductor wire in which a measurement current flows; an oscillation circuit 5 for generating, in accordance with a set threshold, a rectangular wave voltage for inverting the polarity of an excitation current supplied to the exciting coil 4 while the magnetic core 3 is in a saturated state or a state close thereto; a first current detection unit 6 for detecting a measurement current of small current domain on the basis of a change in the duty cycle of the rectangular wave voltage generated from the oscillation circuit 5; a second current detection unit 7 for detecting the frequency of the rectangular wave voltage generated from the oscillation circuit 5 and detecting a measurement current of large current domain larger than the small current domain; and noise rejection capacitors NC1, NC2 for bypassing and rejecting a noise impressed to the exciting coil 4 and the oscillation circuit 5.SELECTED DRAWING: Figure 1

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 a 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 107 which is an object which measures an electric current is inserted in the center of both core 101 and 102.
The exciting coil 103 is wound around the cores 101 and 102 so that the magnetic fields generated in both the cores 101 and 102 when they are energized are in opposite phases 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, if 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, the cores 101 and 102 are generated. 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 107 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. 10C, 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. 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. 10B, the second harmonic of the double frequency 2f as shown by the broken line appears in FIG. 10C. Since the second harmonics are 180 ° out of phase, if they are superimposed on each other, a sine wave signal as shown in the lowermost stage of FIG. 10C 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 107 to be measured, and the current value I can be detected by processing this.

Moreover, the structure shown by patent document 2 is known as another flux gate type current sensor. FIG. 11 is a block diagram for explaining the operation of the current sensor disclosed in Patent Document 2. In FIG.
In the figure, a sensed current 201 flows through the primary winding of a saturable core magnetic sensing element 204 which is a miniature transformer having a soft ferrite toroidal core. One end of the secondary winding of the transformer is connected to the power switch 203, and the power switch 203 alternately switches the polarity of the voltage supplied from the power source 202 to the secondary winding. The other end of the secondary winding is connected to the detection device 205.

  When the power switch 203 supplies a positive current, the core is saturated by the current flowing through the secondary winding of the saturable core magnetic sensing element 204. When the core is saturated, the voltage across the detection device 205 suddenly increases, and the control signal 207 output from the detection device 205 is supplied to the hysteresis switch 206. When the control signal 207 reaches a certain level, the polarity of the current flowing in the secondary winding of the saturable core magnetic sensing element 204 is switched by inverting the power switch 203.

  As a result, a negative current is supplied to the saturable core magnetic sensing element 204, the core magnetization decreases, and the core is saturated in the opposite direction. Then, the voltage across the detection device 205 rapidly increases in the negative direction, and the power switch 203 switches the polarity via the hysteresis switch 206 to invert the polarity of the voltage supplied to the secondary winding. Thus, the system repeats operation in a stable periodic pattern.

  In order to obtain an output proportional to the sensed current 201, a low pass filter 208 is connected to the output of the power switch 203 to remove most of the mixed magnetizing current component. The signal on the output line 209 of the low-pass filter 208 is the output signal of the transformer 211 because the high frequency component of the current 201 to be sensed is induced in the secondary winding of the saturable core magnetic sensing element 204, which is a small transformer. 212 includes a very low frequency component and a high frequency component including a DC component obtained by amplifying the signal on the output line 209 by the power amplifier 210. Thereby, the current can be measured over a wide frequency band.

JP 2000-162244 A Japanese Patent No. 2923307

  However, since the current sensor described in Patent Document 1 uses two cores 101 and 102, it is actually difficult to completely match the magnetic characteristics of the cores 101 and 102. As a result, the voltage generated by the excitation current Iex is generated without being completely canceled. This deteriorates the S / N ratio of the detection voltage corresponding to the second harmonic component, and there is a problem that it is difficult to detect a minute current.

Further, since at least two cores are used, there is a problem that it is difficult to realize downsizing and cost reduction.
Furthermore, since it is necessary to excite the cores 101 and 102 to the saturation region, there is a problem that a large excitation current is required and the consumption current of the sensor is large.
Further, in the current sensor described in Patent Document 2, when a large current having a very low frequency component including a DC component is measured, the power switch 203 is switched before the saturable core magnetic sensing element 204 is saturated. Therefore, the signal at the output line 209 of the low-pass filter 208 approaches zero. For this reason, the current sensor of Patent Document 2 has a problem that it cannot measure a wide current range from a minute current to a large current. Furthermore, since at least two transformers are used, there is a problem that it is difficult to reduce the size and cost.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a current detection device that can be detected in a wide current range from a minute current to a large current with a small size and low cost, which is less affected by ambient environmental conditions. Yes.

  In order to achieve the above object, one aspect of the current detection device according to the present invention is to saturate a magnetic core in accordance with a single excitation coil wound around a magnetic core surrounding a conducting wire through which a measurement current flows and a set threshold value. An oscillation circuit that generates a rectangular wave voltage that inverts the polarity of the excitation current supplied to the excitation coil in a state near it, and a small current region based on a duty change of the rectangular wave voltage output from the oscillation circuit. A first current detection unit for detecting a measurement current; a second current detection unit for detecting a frequency of a rectangular wave voltage output from the oscillation circuit to detect a measurement current in a large current region larger than the small current region; And a noise removing capacitor that bypasses and removes noise applied to the coil and the oscillation circuit.

According to one embodiment of the present invention, detection from a very small current to a large current can be realized by a single magnetic core, so that a current detection device capable of monitoring a wider range of currents can be reduced in size and provided at low cost.
Furthermore, since it is not necessary to use a magnetic sensor, a magnetic flux collecting core, or the like, it is possible to provide a highly reliable current detection device that is robust and less affected by the ambient temperature.
Moreover, since the noise resistance can be improved, it is possible to provide a current detection device with excellent environmental resistance.

1 is a schematic configuration diagram illustrating a current detection device according to a first embodiment of the present invention. FIG. 3 is a circuit diagram illustrating an example of an oscillation circuit that can be applied to the first embodiment. It is a block diagram which shows the specific structure of the electric current detection apparatus of FIG. FIG. 4 is a circuit diagram illustrating an example of a comparison circuit in the output determination circuit of FIG. 3. FIG. 4 is a circuit diagram illustrating another example of a comparison circuit in the output determination circuit of FIG. 3. It is a schematic diagram which shows the output voltage waveform of an oscillation circuit, and the current waveform of an exciting coil. It is a characteristic diagram which shows the relationship between the magnetic field strength of a magnetic core, and magnetic flux density, and a characteristic diagram which shows the inductance characteristic of a magnetic core. It is a schematic diagram which shows the output voltage waveform of the 1st current detection circuit and 2nd current detection circuit in 1st Embodiment, (a) is an output waveform figure of a 1st current detection circuit, (b) is a 2nd current detection circuit. It is an output waveform diagram of a circuit. It is the same block diagram as FIG. 3 which shows the modification of 1st Embodiment. 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. It is a block diagram for demonstrating operation | movement of the current sensor of another prior art example.

Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.
Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

  As shown in FIG. 1, the current detection device 1 according to one aspect of the present invention has a minute difference between the conductors 2 a and 2 b through which a reciprocating current I of, for example, 10 A to 800 A flows, for example, provided on an object such as leakage detection. Detect current. Here, in the healthy state, the sum of the currents flowing through the conductors 2a and 2b is zero, but the sum of the currents flowing through the conductors 2a and 2b is not zero due to electric leakage or ground fault, and the detection target is, for example, 15 mA to 500 mA. A very small difference current flows. Around these conducting wires 2a and 2b, a ring-shaped magnetic core 3 is disposed so that the conducting wires 2a and 2b serve as primary windings. That is, the conducting wires 2 a and 2 b are inserted into the magnetic core 3 as primary windings.

An exciting coil 4 as a secondary winding is wound around the magnetic core 3 with a predetermined number of turns. An oscillation circuit 5 is connected to the excitation coil 4, and an excitation current Ib is supplied from the oscillation circuit 5 to the excitation coil 4.
Here, between the connection point between one end of the excitation coil 4 and the oscillation circuit 5 and the ground, noise removal is performed by bypassing the noise applied to the excitation coil 4 and the oscillation circuit 5 or the connection line between the two to the ground. Capacitor NC1 is connected. Similarly, between the other end of the exciting coil 4 and the connection point of the oscillation circuit 5 and the ground, noise applied to the excitation coil 4 and the oscillation circuit 5 or a connection line between them is bypassed to the ground and removed. A capacitor NC2 is connected.

These noise removing capacitors NC1 and NC2 are not limited to bypassing noise applied to the exciting coil 4, the oscillation circuit 5, or the connecting line between them to the ground, but can also be bypassed to the power supply side. The point is that the noise resistance can be improved by removing the noise applied to the exciting coil 4, the oscillation circuit 5, or the connecting line between them.
Further, on the output side of the oscillation circuit 5, a first current detection circuit 6 as a first current detection unit that detects a duty ratio of an output voltage output from the oscillation circuit 5 and detects a measurement current in a small current region; A second current detection circuit 7 is connected as a second current detection unit that detects the frequency of the output voltage output from the oscillation circuit 5 and detects a measurement current in a large current region larger than the small current region. An output determination circuit 8 serving as an output determination unit is connected to the output sides of the two current detection circuits 6 and 7.

  As shown in FIG. 2, the oscillation circuit 5 includes an operational amplifier 51 that operates as a comparator and outputs a rectangular wave voltage Va. The output side of the operational amplifier 51 is connected to the coil connection terminal tc1 and the output terminal to1. The inverting input side of the operational amplifier 51 is connected to the coil connection terminal tc2 through the first low-pass filter 52. Further, a current detection resistor 53 is connected between a connection point between the coil connection terminal tc2 and the first low-pass filter 52 and the ground.

Further, voltage dividing resistors 54 and 55 are connected in series between the output side of the operational amplifier 51 and the ground. A connection point between the voltage dividing resistors 54 and 55 is connected to the non-inverting input side of the operational amplifier 51 and supplies the threshold voltage Vth to the non-inverting input side of the operational amplifier 51.
This threshold voltage Vth is expressed by the following equation (1), where R1 is the resistance value of the voltage dividing resistor 54, R2 is the resistance value of the voltage dividing resistor 55, and Va is the output voltage of the operational amplifier 51.

Vth = Va {R2 / (R1 + R2)} (1)
Further, as shown in FIG. 2, the first low-pass filter 52 includes a resistor 52a connected between the inverting input terminal of the operational amplifier 51 and the coil connection terminal tc2, and the inverting input terminal of the resistor 52a and the operational amplifier 51. And a capacitor 52b connected between the connection point between the voltage dividing resistors 54 and 55 and a connection point between the voltage dividing resistors 54 and 55, can be configured as a primary low-pass filter.

  In this oscillation circuit 5, the threshold voltage Vth at the connection point E between the voltage dividing resistors 54 and 55 is supplied to the non-inverting input side of the operational amplifier 51, and the connection point between the threshold voltage Vth and the exciting coil 4 and the resistor 53. The voltage D is compared with the voltage F obtained by removing the high-frequency component by the first low-pass filter 52. And it is output from the oscillation circuit 5 as the rectangular wave voltage Va which becomes a rectangular wave shown in FIG.

Further, the exciting coil 4 is connected between the coil connection terminals tc1 and tc2, and the above-described noise removing capacitors NC1 and NC2 are connected to both ends of the exciting coil 4, respectively.
As shown in FIG. 3, the first current detection circuit 6 includes a second low-pass filter 61 that averages the rectangular wave voltage Va output from the oscillation circuit 5, and a filter output of the second low-pass filter 61. And an absolute value circuit 62 that converts the absolute value of the voltage to the absolute value, and a voltage output corresponding to the measured current value in the small current region according to the duty change of the rectangular wave voltage Va of the oscillation circuit 5 can be obtained.

As shown in FIG. 3, the second current detection circuit 7 includes a high-pass filter 71 that performs frequency-voltage conversion on the rectangular wave voltage va output from the oscillation circuit 5 and outputs a voltage signal, and an absolute value circuit 72. The increase in the frequency of the rectangular wave voltage Va of the oscillation circuit 5 can be detected, and the measurement current in the large current region larger than the small current region can be detected.
Further, the output determination circuit 8 includes a first comparison circuit 81 and a second comparison circuit 82 to which outputs of the first current detection circuit 6 and the second current detection circuit 7 are individually supplied, and these two comparison circuits 81 and 82. And an OR circuit 83 to which the output is input.

  As shown in FIG. 4, one mode of the first comparison circuit 81 includes a comparator 90 configured with, for example, an operational amplifier. An absolute value circuit 62 is connected to the non-inverting input side of the comparator 90, and a movable element of a variable resistor 92 connected between the DC power source 91 and the ground is connected to the inverting input side. Therefore, the comparator 90 maintains the low level when the current detection voltage Vi1 input from the absolute value circuit 62 is less than the threshold voltage Vth2 as the first setting signal output from the movable element of the variable resistor 92. When the current detection voltage Vi becomes equal to or higher than the threshold voltage Vth2, the comparison signal Sc1 that is at a high level is output.

  In another mode of the first comparison circuit 81, as shown in FIG. 5, the threshold voltage Vth2 supplied to the inverting input side of the comparator 90 is set by a threshold voltage setting circuit 95 instead of the variable resistor 92. You can also. That is, the threshold voltage setting circuit 95 includes an arithmetic processing unit 96 such as a CPU, a non-volatile storage element 97 such as a ROM, EEPROM, or flash memory connected to the arithmetic processing unit 96, and an output side of the arithmetic processing unit 96. The DA converter 98 can be connected, and voltage dividing resistors 99a and 99b connected in series between the output side of the DA converter 98 and the ground.

  In the threshold voltage setting circuit 95, the threshold voltage command value Vt stored in the nonvolatile memory element 97 is read out by the arithmetic processing unit 96, converted into an analog voltage by the DA converter 98, and the analog voltage is divided into the voltage dividing resistors 99a and 99b. Is supplied to the non-inverting input side of the comparator 90 as the first setting signal divided by the voltage dividing resistors 99a and 99b.

  By configuring the first comparison circuit 81 as shown in FIG. 5, only the threshold voltage command value Vt, which is the stored value stored in the nonvolatile storage element 97, is read and supplied to the voltage dividing resistors 99a and 99b. The threshold voltage Vth2 can be set. Therefore, by adopting the configuration of FIG. 5 as the first comparison circuit 81, manual adjustment of the resistance value is not required unlike the variable resistor 92 shown in FIG. 4, and the cost of the first comparison circuit 81 is reduced. High accuracy can be realized.

4 and 5 can also be applied to the second comparison circuit 82. The current detection voltage Vi2 output from the absolute value circuit 72 by the comparator 90 and the variable resistor 92 or threshold voltage setting can be applied. The threshold voltage Vth3 as the second setting signal set by the circuit 95 is compared.
Next, the operation of the above embodiment will be described.

  As shown in FIG. 6A, when the rectangular wave voltage Va on the output side of the operational amplifier 51 becomes high level at time t1, this is applied to the exciting coil 4. For this reason, the exciting coil 4 is excited with the exciting current Ib corresponding to the rectangular wave voltage Va and the resistance value of the resistor 53. At this time, as shown in FIG. 6B, the exciting current Ib has a parabolic shape that rises relatively steeply from the rising point of the rectangular wave voltage Va and then gradually increases.

At this time, a relatively small threshold obtained by dividing the rectangular wave voltage Va to the non-inverting input side of the operational amplifier 51 by the resistance values R1 and R2 of the voltage dividing resistors 54 and 55 obtained at the connection point E of the voltage dividing resistors 54 and 55. The voltage Vth is input.
On the other hand, the voltage Vd at the connection point D between the exciting coil 4 on the inverting input side of the operational amplifier 51 and the resistor 53 increases as the exciting current Ib of the exciting coil 4 increases, and further includes a first resistor 52a and a capacitor 52b. When the voltage F from which the high-frequency component is removed by the low-pass filter 52 exceeds the threshold voltage Vth on the non-inverting input side at time t2, that is, + Ith1 in FIG. 6B, the rectangular wave voltage Va output from the operational amplifier 51 is shown. As shown in FIG. 6 (a), it is inverted to a low level. In response to this, the polarity of the excitation current Ib flowing through the excitation coil 4 is reversed, and the excitation current Ib decreases sharply at first and then decreases in a parabolic shape that gradually decreases.

  At this time, the threshold voltage Vth is also a low voltage because the rectangular wave voltage Va is at a low level. Then, the voltage at the connection point D between the excitation coil 4 on the inverting input side of the operational amplifier 51 and the resistor 53 decreases in accordance with the decrease in the excitation current Ib of the excitation coil 4, and the voltage F is the threshold value on the non-inverting input side at time t3. When falling below the voltage Vth, that is, −Vth1 in FIG. 6B, the rectangular wave voltage Va of the operational amplifier 51 is inverted to a high level as in the time t1, as shown in FIG. 6A.

Therefore, as shown in FIG. 6A, the rectangular wave voltage Va becomes a rectangular wave voltage that repeats a high level and a low level, and the oscillation circuit 5 operates as an astable multivibrator. The exciting current Ib of the exciting coil 4 has a waveform that repeatedly increases and decreases as shown in FIG.
By the way, the magnetic core 3 has a BH characteristic representing a relationship between a magnetic flux density B having a large squareness ratio and a magnetic field strength H as shown in FIG. It has special characteristics. The inductance of the magnetic core 3 having the BH characteristic disappears abruptly in the vicinity of the saturation current G as shown in FIG. 7B when the difference current between the conductors 2a and 2b is zero. When a small difference current C to be detected is generated in the conducting wires 2a and 2b penetrating the magnetic core 3, the inductance characteristic in FIG. 7B disappears in accordance with the difference current C as shown by the broken line. Timing changes.

  For this reason, the current at which the inductance is saturated when the current is zero (G in FIG. 7B) and the current at which the polarity of the excitation current Ib switches (P in FIG. 6B) are matched. Then, since the current at which the inductance is saturated (J in FIG. 7B) changes according to the current value C of the difference current between the conductors 2a and 2b, the current at which the polarity of the exciting current Ib switches (FIG. 6B). H) also changes in the same manner.

  By changing the current value at which the polarity of the excitation current Ib changes, the timing at which the filter output voltage Vf exceeds the threshold voltage Vth is delayed, and the falling time of the rectangular wave voltage Va output from the operational amplifier 51 is the lead wire. Delayed as shown by the broken line in FIG. 6A in accordance with the current value C of the difference current 2a and 2b. As a result, the duty ratio of the rectangular wave voltage Va changes according to the current value C of the difference current between the conductors 2a and 2b.

  Here, noise removing capacitors NC1 and NC2 are provided between a connection point between both ends of the exciting coil 4 and the coil connection terminals tc1 and tc2 of the oscillation circuit 5 and the ground or the power supply side. Therefore, noise applied to the exciting coil 4 and the oscillation circuit can be bypassed to the ground or the power supply side by the noise removing capacitors NC1 and NC2, and the noise affects the generation of the rectangular wave voltage Va of the oscillation circuit 5. Can be reliably prevented.

  Therefore, the first current detection circuit 6 as the first current detection unit for detecting the duty ratio is connected to the output terminals to1 and to2 of the oscillation circuit 5, and the first current detection circuit 6 uses the high level of the rectangular wave voltage Va. By measuring the time during which the state is maintained and the time during which the low level state is maintained, the duty ratio can be detected, and a small current region including a minute current of several amperes or less can be detected. . The small current region indicates a current in which the output of the first current detection circuit 6 changes linearly in FIG.

In the present embodiment, the first current detection circuit 6 can be configured by a second low-pass filter 61 that performs averaging of the rectangular wave voltage Va and an absolute value circuit 62, as shown in FIG.
Next, detection of a large current region of several amperes or more will be described with reference to FIGS. Here, the large current region indicates a current region larger than the current at which the output of the first current detection circuit 6 starts to be saturated in FIG.

In FIG. 1, in the present embodiment, a rectangular current voltage output from the output terminals to1 and to2 of the oscillation circuit 5 shown in FIG. Va is also supplied to the second current detection circuit 7.
As shown in FIG. 3, the second current detection circuit 7 can be composed of a high-pass filter 71 and an absolute value circuit 72, and detects an increase in the frequency of the rectangular wave voltage Va output from the oscillation circuit 5. Is.

Here, output voltages of the first current detection circuit 6 and the second current detection circuit 7 will be described with reference to FIG. 8A and 8B are schematic diagrams showing output voltage waveforms of the detection circuits of the present embodiment. FIG. 8A is an output waveform diagram of the first current detection circuit 6, and FIG. 8B is an output waveform of the second current detection circuit 7. FIG.
In the figure, the output voltage of the first current detection circuit 6 changes linearly as shown in FIG. 8A, but first saturates as the current increases, then continues to decrease, and finally becomes zero. . This is because the excitation current Ib shown in FIG. 6B also becomes larger than the magnitude of the measurement current, so that the threshold voltage (+ Ith1, −Ith1) is reached before the magnetic core 3 is sufficiently saturated. .

As a result, the frequency of the rectangular wave voltage Va of the oscillation circuit 5 also increases rapidly, and finally the oscillation stops.
Further, as shown in FIG. 8B, the output voltage of the second current detection circuit 7 starts to increase at the same time as the output of the first current detection circuit 6 starts to saturate, and is almost constant over a certain current. Maintain frequency.

  Therefore, by detecting the current based on the outputs of the first current detection circuit 6 and the second current detection circuit 7 as shown in Table 1 below, current detection in a wide current range from a minute current to a large current can be performed. It becomes possible. Table 1 shows the relationship between the measured current and the two current detection circuits 6 and 7.

In Table 1, as shown in FIG. 8A, when the measured current is in the region X not exceeding a certain current value + I1, −I1, the magnitude of the output voltage of the first current detection circuit 6 is detected. .
Further, as shown in FIG. 8B, in the region Y where the measured current is larger than a certain current value + I1, −I1, the output voltage of the second current detection circuit 7 is a certain value, that is, the certain current value + I1, −I1. By detecting that the voltage is larger than the voltage V1 corresponding to, current values larger than + I1 and -I1 can be detected.

Thus, by detecting the output voltages of the first current detection circuit 6 and the second current detection circuit 7 in accordance with the X and Y regions in FIG. 8, the current in a wide current region from a small current to a large current is obtained. Can be detected.
That is, when the measured current is in the X region, the duty ratio of the rectangular wave voltage Va of the oscillation circuit 5 is detected by the first current detection circuit 6 so that the small current region including a minute current of + I1 to −I1 is detected. Detect the measurement current. When the measured current is in the Y region, the second current detection circuit 7 performs frequency-voltage conversion, detects an increase in the frequency of the rectangular wave voltage Va of the oscillation circuit 5, and has a current value greater than + I1 and -I1. The measurement current in the large current region is detected.

  Here, as shown in FIG. 3, the output determination circuit 8 individually outputs the output voltages Vi1 and Vi2 output from the absolute value circuit 62 of the first current detection circuit 6 and the absolute value circuit 72 of the second current detection circuit 7. In the first comparison circuit 81 and the second comparison circuit 82, the measurement current in the small current region is generated in the first current detection circuit 6 when the output voltage Vi1 is equal to or higher than the desired threshold voltage Vth2. Can be easily detected.

  As described above, according to the embodiment, since the noise removing capacitors NC1 and NC2 are connected between the exciting coil 4 and the oscillation circuit 5, the noise removing capacitors NC1 and NC2 connect the exciting coil 4 and the oscillation circuit. The applied noise can be removed by bypassing to the ground or power supply side. Therefore, it is possible to reliably suppress the amplification of noise by the operational amplifier 51 of the oscillation circuit 5 and to output the rectangular wave voltage Va from which the influence of the noise is removed from the oscillation circuit 5. Therefore, it is possible to accurately detect a measurement current in a wide current range with a simple configuration.

  In addition, the first low-pass filter 52 is also arranged in the oscillation circuit 5, and the high-frequency component of the voltage at the connection point D corresponding to the excitation current Ib that has passed through the excitation coil 4 by the first low-pass filter 52 is obtained. Since it is removed and supplied to the inverting input side of the operational amplifier 51, the voltage F from which noise is reliably removed by the operational amplifier 51 and the threshold voltage Vth are compared. For this reason, the influence of noise on the rectangular wave voltage Va output from the operational amplifier 51 can be reliably removed. Accordingly, it is possible to more accurately detect the measurement current based on the rectangular wave voltage Va.

  Further, the rectangular wave voltage Va output from the oscillation circuit 5 is supplied to the first current detection circuit 6 and the second current detection circuit 7, and the first current detection circuit 6 uses a small current based on the duty ratio of the rectangular wave voltage Va. And the second current detection circuit detects the measurement current in the high current region higher than the small current region based on the increase in the frequency of the rectangular wave voltage Va. Can be detected.

Here, since the first current detection circuit 6 can be configured by the second low-pass filter 61 and the second current detection circuit 7 can be configured by the high-pass filter 71, both are simple. The measurement current can be detected with a simple configuration.
Further, since the output signals of the first current detection circuit 6 and the second current detection circuit 7 are supplied to the output determination circuit 8 having the first comparison circuit 81 and the second comparison circuit 82, a wide range can be obtained with a simple configuration. The measurement current can be detected.

  In the above embodiment, since the OR circuit 83 is provided in the output determination circuit 8, the comparison output output from the second comparison circuit 82 in the large current region where the comparison output of the first comparison circuit 81 is at a low level. By setting the threshold voltage Vth3 so that becomes high level, it is possible to detect a measured current equal to or higher than the threshold voltage Vth2 in the small current region including the minute current set by the first comparison circuit 81.

  However, since the filter output Vi1 output from the second low-pass filter 61 of the first current detection circuit 6 is sinusoidal as shown in FIG. 8A, the first comparison circuit 81 of the output determination circuit 8 is used. When the threshold voltage Vth2 supplied to is set to a voltage corresponding to a minute current value greater than 0 as shown in FIG. 8A, the comparison output output from the first comparison circuit 81 exceeds the X region. Even in this case, the high level will be maintained. For this reason, it is impossible to determine whether the measurement current is the small current region X or the large current region Y only by the logical sum output of the logical sum circuit 83.

On the other hand, when the threshold voltage Vth3 supplied to the second comparison circuit 82 is set to a threshold voltage capable of detecting the current in the Y region, as shown in FIG. Can be detected.
That is, when determining whether the measurement current is a small current region or a high current region, the comparison output of the second comparison circuit 82 is low level, and only the comparison output of the first comparison circuit 81 is high level. In some cases, it is a small current region, and regardless of the comparison output of the first comparison circuit 81, when the comparison output of the second comparison circuit 82 becomes high level, it can be determined that it is a high current region.

  As a result, the output determination circuit 8 supplies the comparison output of the first comparison circuit 81 to one input side of the AND circuit 86, omitting the OR circuit 83, as shown in FIG. The comparison output of the circuit 82 is inverted in level by the inverter 85 and supplied to the other input side of the AND circuit 86, whereby the small current region indicating that the measured current in the small current region X is detected from the AND circuit 86. The detection output SS can be obtained, and by outputting the output of the second comparison circuit 82 as it is, the large current region detection output SL can be obtained.

In the above embodiment, the case where the output determination circuit 8 is provided has been described. However, the present invention is not limited to this, and the output signals of the first current detection circuit 6 and the second current detection circuit 7 are AD-converted. Then, it may be converted into a digital value, and the measured current value may be calculated by supplying the digital value to an arithmetic processing unit such as a microcomputer.
Moreover, in the said embodiment, although the case where the difference electric current of the two conducting wires 2a and 2b was detected was demonstrated, it is not limited to this, The minute electric current which flows into one conducting wire can also be detected. .

  DESCRIPTION OF SYMBOLS 1 ... Current detection apparatus, 2a, 2b ... Conductor, 3 ... Magnetic core, 4 ... Excitation coil, 5 ... Oscillation circuit, 6 ... 1st current detection circuit, 7 ... 2nd current detection circuit, 8 ... Output determination circuit, NC1 , NC2 ... Noise removing capacitor, 51 ... Operational amplifier, 52 ... First low pass filter, 53-55 ... Resistor, 61 ... Second low pass filter, 62 ... Absolute value circuit, 71 ... High pass filter, 72 ... absolute value circuit, 81 ... first comparison circuit, 82 ... second comparison circuit, 83 ... logical sum circuit, 90 ... comparator, 92 ... variable resistor, 96 ... arithmetic processing unit, 97 ... non-volatile memory, 98 ... DA Converter, 99a, 99b ... voltage dividing resistor

Claims (7)

One exciting coil wound around a magnetic core surrounding the conducting wire through which the measurement current flows;
In accordance with a set threshold value, an oscillation circuit that generates a rectangular wave voltage that reverses the polarity of the excitation current supplied to the excitation coil in a state where the magnetic core is saturated or in the vicinity thereof,
A first current detection unit that detects the measurement current in a small current region based on a duty change of the rectangular wave voltage output from the oscillation circuit;
A second current detection unit that detects a frequency of the rectangular wave voltage output from the oscillation circuit and detects the measurement current in a large current region larger than the small current region;
A current detection device comprising: a noise removing capacitor that bypasses and removes noise applied to the exciting coil and the oscillation circuit.   A first comparison circuit that compares an output signal of the first current detection unit and a first setting signal; a second comparison circuit that compares an output signal of the second current detection unit and a second setting signal; 2. The current detection device according to claim 1, further comprising: an output determination unit including a first comparison circuit and a logical sum circuit to which a comparison output of the second comparison circuit is supplied.   The current detection device according to claim 2, wherein a setting signal is set in at least one of the first comparison circuit and the second comparison circuit based on a stored value stored in a storage element.   The oscillation circuit connects the excitation coil between an output side and an inverting input side, and an operational amplifier in which the output side is connected to an output terminal to generate the rectangular wave voltage, an inverting input side of the operational amplifier, and the excitation coil And a voltage dividing resistor connected between the output side of the operational amplifier for supplying a threshold voltage to the non-inverting input side of the operational amplifier and the ground. The current detection device according to claim 1, wherein the current detection device is a current detection device.   The first low-pass filter includes a resistor connected between the inverting input side of the operational amplifier and the exciting coil, and between the resistor and the inverting input side of the operational amplifier and an intermediate point of the voltage dividing resistor. The current detection device according to claim 4, comprising a connected capacitor.   6. The current detection device according to claim 1, wherein the first current detection unit includes a second low-pass filter that detects a duty change of the rectangular wave voltage. .   The said 2nd electric current detection part is comprised by the high-pass filter which passes the said rectangular wave voltage only at the time of the frequency increase of the said rectangular wave voltage, The any one of Claim 1 to 6 characterized by the above-mentioned. Current sensing device.

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