JP4884384B2 - Broadband current detector - Google Patents

Description

The present invention relates to a broadband current detector that can measure a low-frequency (referred to as a frequency of about 8 to 10 kHz) current from a direct current using a saturable reactor.

As a current detector using a saturable reactor, for example, the one described in Japanese Patent Publication No. Sho 63-25487 is known, and a primary winding and a pair of a current to be measured wound around a saturable iron core are known. A saturable reactor having a secondary winding, a load resistor, and an AC power source for causing currents to flow in opposite phases to the secondary winding.
Further, as described in Japanese Patent Application Laid-Open No. 61-245511, a current detector that detects the strength of a magnetic field generated when a current flows using a Hall element or the like has been put into practical use and has become mainstream. ing.

However, in the technique described in Japanese Patent Publication No. Sho 63-25487, the region in which the current flowing through the primary winding is proportional to the output value is limited, and the region is narrow. In addition, there is a problem that the measurement accuracy is relatively poor because of having a saturation region. In addition, it is not considered for alternating current, and is for direct current measurement.
In addition, in an ammeter using a Hall element as described in Japanese Patent Application Laid-Open No. 61-245511, it is difficult to maintain high measurement accuracy because the characteristics of the Hall element change due to a temperature change or the like. There is a problem that there is.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a broadband current detector that has a relatively high measurement accuracy (for example, within 0.01%) and can measure from direct current to alternating current.

The broadband current detector according to the first invention that meets the above-mentioned object has a space part through which a conductor to be measured for passing a measurement current can be inserted, and the first and second movable detectors are disposed so as to surround the space part. A saturated ring core,
First and second high-frequency coils that are wound around the first and second saturable ring cores with the same number of turns in the same direction or in the opposite direction, and generate a magnetic field in the opposite direction when a current is passed ;
First and second unsaturated ring cores arranged with the first and second high-frequency coils sandwiched between both radial sides;
A cancel coil wound around the first and second unsaturated ring cores around the center,
A high-frequency current that saturates the first and second saturable ring cores is caused to flow through the first and second high-frequency coils, a differential voltage applied to the first and second high-frequency coils is extracted, and the differential voltage is handled. An electric current is passed through the cancellation coil, and the first and second unsaturated ring cores are excited in the opposite direction to the excitation by the measurement current to cancel the differential voltage. The current flowing through the conductor to be measured in the low frequency region is measured.

A wideband current detector according to a second invention is the wideband current detector according to the first invention, comprising a detection coil wound around the first and second unsaturated ring cores in the center. Then, the current detected by the detection coil is amplified and passed through the cancel coil, and the current flowing through the measured conductor in the high frequency region is measured from the current passed through the cancel coil.

A wideband current detector according to a third invention is the wideband current detector according to the second invention, wherein the first and second saturable ring cores have the same shape and are arranged side by side in the axial direction. ing.
The broadband current detector according to the fourth invention is the broadband current detector according to the second and third inventions, wherein resistors having the same value are connected in series to the first and second high-frequency coils, respectively. The bridge output is used as the differential voltage, and the differential voltage is synchronously rectified at a frequency twice that of the alternating current flowing through the first and second high-frequency coils and smoothed by an amplifier. Amplify and flow through the cancellation coil.

It is sectional drawing of the wideband type | mold current detector main body concerning one Example of this invention. (A), (B) is a graph which shows the magnetic characteristic of a saturable ring core and an unsaturated ring core, respectively. It is a circuit diagram of the broadband current detector. (A)-(F) are the wave form diagrams for demonstrating operation | movement of the broadband type current detector. (A)-(C) is a wave form chart for explaining operation of the broadband current detector. It is a graph which shows the characteristic of the broadband current detector.

Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIGS. 1 and 3, the broadband current detector 10 according to an embodiment of the present invention includes an insulator that forms a space portion 11 into which a conducting wire 26, which is an example of a conductor to be measured, can be inserted. A guide cylinder 12 made of a non-magnetic material (for example, plastic or ceramic) is provided. Around the guide tube 12, first and second saturable ring cores 13 and 14 having the same shape are arranged side by side in the axial direction, and each of the first and second saturable ring cores 13 and 14 has the same number of turns. The first and second high-frequency coils 15 and 16 are wound so as to generate a magnetic field in the opposite direction when a current in the same direction is passed.
The first and second high-frequency coils 15 and 16 have first and second unsaturated ring cores 17 and 18 disposed sandwiched from both sides in the radial direction, and the first and second The unsaturated ring cores 17 and 18 are set in the center, and a cancel coil 19 having n turns and a detection coil 20 having m turns are wound on the outside thereof. The magnetic characteristics when the first and second unsaturated ring cores 17 and 18 are DC-excited are shown in FIG.

As shown in FIG. 3, the first and second high-frequency coils 15 and 16 having the same number of turns p have predetermined values via a frequency converter 22 that drops the output from the high-frequency oscillator 21 having the frequency 2f to a half frequency. A square wave of frequency f amplified to voltage Va (in this embodiment, a high frequency of 50 kHz, see FIG. 4A) is applied via resistors (fixed resistors) 23 and 24 (the resistance values are the same). . The first and second saturable ring cores 13 and 14 are composed of saturable cores having characteristics as shown in FIG. When a square wave voltage Va having a frequency f is applied to the first and second high-frequency coils 15 and 16 (that is, when a high-frequency current having a frequency f is applied), the first and second saturable ring cores 13 and 13 The number of turns p of the first and second high-frequency coils 15, 16 and the first and second saturable ring cores 13, so that 14 saturates at about 3/8 · λ and 7/8 · λ wavelengths, 14 cross-sectional areas are set.
Therefore, when a voltage as shown in FIG. 4A is applied to the first and second high-frequency coils 15 and 16, the voltage shown in FIG. The voltage shown in FIG. 4C is generated in the high frequency coil 16.

The winding directions of the first and second high-frequency coils 15 and 16 may be the same (for example, right-handed or left-handed) or in the reverse direction, but a conducting wire for passing a measurement current inserted through the guide tube 12 When a current is passed through 26, the voltage is connected to the resistors 23 and 24 so that one voltage of the first and second high-frequency coils 15 and 16 decreases and the other voltage increases. The resistors 23 and 24 and the first and second high frequency coils 15 and 16 are connected in series to form a bridge circuit, and the primary side coil 28 of the input transformer 27 is connected to the midpoint output thereof. Yes. The secondary coil 29 of the input transformer 27 is provided with an intermediate tap so that outputs different in phase by 180 degrees are generated in the coils on both sides thereof.
Therefore, when no current flows through the conductor 26, the voltage applied to the first high-frequency coil 15 shown in FIG. 4B is the same as the voltage applied to the second high-frequency coil 16 shown in FIG. 4C. Therefore, the difference is output to the input transformer 27 and eventually becomes 0 (zero) as shown in FIG.

However, when a current (direct current flows for the sake of explanation) flows through the conductor 26, the magnetic saturation state of the first and second saturable ring cores 13 and 14 changes, and FIG. 4 (E) and FIG. As shown in F), the voltage applied to the first and second high-frequency coils 15 and 16 changes. This is because the zero point moves in the hysteresis curve of the saturable ring core shown in FIG.
When the difference between the voltages applied to the first and second high-frequency coils 15 and 16 is detected by the bridge circuit and the difference is output by the input transformer 27, the voltages as shown in FIGS. 27 on the basis of the center tap on the secondary side.

The voltage signals (A) and (A) ′ generated on the secondary side of the input transformer 27 are synchronously rectified at a frequency generated by the high frequency oscillator 21 of 2f (ie, 100 kHz). Here, the synchronous rectification means that switching elements (for example, CMOS type semiconductor elements) are alternately switched by square wave signals generated by the high frequency oscillator 21 with voltages different in phase by 180 degrees generated on the secondary side of the input transformer 27. And the signals generated from the input transformer 27 are aligned (that is, rectified). 5B shows a control signal used for synchronous rectification, and FIG. 5C shows an output of the synchronous rectification circuit 30.

Here, the difference between the rectifier circuit configured by combining the synchronous rectifier circuit 30 and a normal silicon diode or the like is that in a rectifier circuit using a silicon diode, a voltage drop (for example, 0.5 to 0.7 V) of the silicon diode itself. ) Is present, there is a problem that a minute signal cannot be rectified and all signals flow into a direct current through a constant direction. However, in the synchronous rectifier circuit 30, there is no voltage drop in the element itself (ie, The same as a normal contact), and depending on the phase of the input signal and the control signal, not only a current in one direction but also a current in the reverse direction is generated (thus, it is not completely DC).
By using this synchronous rectifier circuit 30, the direction and magnitude of the current flowing through the conductor 26 can be accurately measured.

When the output of the synchronous rectifier circuit 30 is passed through the filter circuit 31 as it is, the voltage waveform shown in FIG. 5C is averaged (smoothed) to become direct current. Here, the amplifier 32 performs voltage amplification, the amplifier 33 performs current amplification, and the output is passed through the cancel coil 19 to which the resistor 34 is connected in series. The magnetic flux generated in the first and second unsaturated ring cores 17 and 18 by the current flowing through the cancel coil 19 is changed to the first and second unsaturated ring cores 17 and 18 and the first and second unsaturated ring cores 17 and 18 by the current flowing through the conducting wire 26. The magnetic flux generated in the saturable ring cores 13 and 14 is canceled out. That is, if the current flowing through the conductor 26 is d1 and the number of turns is 1, d2 is the current flowing through the cancel coil 19 and the number of turns is n, the relationship d1 × 1 = d2 (1 + 1 / α) × n is established. Therefore, if d2 = d1 / {n (1 + 1 / α)}, that is, d2≈d1 / n, and d2 is measured, the value of d1 is known. Furthermore, since the magnetic fields of the first and second saturable ring cores 13 and 14 are canceled out by about (d1 × 1−d2 × n), the magnetic flux is reduced and a wide range of currents can be measured, resulting in the small size of the device. Can be achieved. “Α” represents the amplification factor of the signal from the input transformer 27 to the amplifier 33, and actually has an amplification factor of about 10 ⁵ to 10 ⁶ . Accordingly, the current flowing through the cancel coil 19 is detected from the voltage across the resistor 34, and is appropriately calibrated to obtain the measurement current.

In this embodiment, for the sake of explanation, a case where a direct current flows through the conductor 26 has been described. However, the synchronous rectification circuit 30 can measure the magnitude of the polarity while determining the polarity. It can be measured without hindrance. The high frequency cannot be measured by the control signal for driving the synchronous rectifier circuit 30, and the AC measurement frequency is determined by the pass band of the filter circuit 31 provided next. For example, if the filter circuit 31 is set to about 10 kHz and is set to attenuate with respect to a frequency higher than that, it is possible to measure an alternating current of about 10 kHz.
The first and second saturable ring cores 13 and 14 respond to a frequency higher than f, but perform synchronous rectification at the frequency 2f. Therefore, the first and second saturable ring cores within the period of the synchronous rectification. Even if the ring cores 13 and 14 react, they are averaged and cannot be detected by this circuit. However, since synchronous rectification is not performed for the detection coils 20 of the first and second unsaturated ring cores 17 and 18, a frequency higher than f can be detected. Further, when the measurement current has a low frequency, if it is attempted to detect only with the detection coil 20, a core cross-sectional area that does not saturate at that frequency is required, and the size and weight cannot be reduced.

Next, the detection coil 20 is arranged in the first and second unsaturated ring cores 17 and 18, the output is input to the amplifier 33, the output is passed to the cancel coil 19, and the magnetic flux flowing through the conductor 26 is canceled out. In this case, the alternating current flowing through the conductor 26 can also be measured from the voltage across the resistor 34. Since this technique is well known, detailed description is omitted.
In this case, a circuit A that measures the current flowing through the conductor 26 from the differential voltage detected by the first and second saturable ring cores 13 and 14 and the first and second high-frequency coils 15 and 16 wound around them. When combined with the circuit B that measures the alternating current using the detection coil 20, the characteristics shown in FIG. 6 are obtained, and a wide range of currents from direct current to high frequency alternating current can be measured.

The present invention is not limited to the embodiments described above, and can be improved or partially omitted without changing the gist of the present invention. For example, in the above-described embodiment, the broadband current detector 10 is configured by combining the circuit A that can measure from direct current to alternating current and the circuit B that measures normal alternating current. The present invention is also applied to the case where the circuit A that can measure from AC to AC and the circuit B that measures normal AC current are operated separately. In this case, when the circuit A that can measure from direct current to alternating current or the circuit B that measures normal alternating current is stopped, a switch is provided so that these input signals do not enter the amplifier 33.

As mentioned above, although the embodiment of the present invention has been described, the present invention is not limited to this embodiment, and can be changed without changing the gist of the invention. Some or all of the examples may be combined.

In the wideband current detector according to the present invention, the current corresponding to the differential voltage between the first and second high-frequency coils wound around the first and second saturable ring cores is caused to flow through the cancel coil. The current prevents the saturation of the first and second unsaturated ring cores and the saturation of the first and second saturable ring cores, so that the current in the DC to low frequency region can be accurately measured from a small current to a large current. It can be measured.
Since the first and second high frequency coils wound around the first and second saturable ring cores are sandwiched between the first and second unsaturated ring cores from both sides in the radial direction, the first, The saturation state of the magnetic flux of the second saturable ring core is more accurately controlled, and the measurement accuracy is improved.

In particular, the broadband current detector of the present invention is provided with a detection coil wound around the center of the first and second unsaturated ring cores, and a current detected by the detection coil is amplified to cancel the coil. When the current flowing through the conductor to be measured in the high frequency region is measured from the current flowing in the cancel coil, the broadband current detector also serves as a normal CT, and the high frequency region ( AC current can be measured at a frequency exceeding the low frequency region. Therefore, in the present invention, the current from the direct current to the high frequency region can be accurately measured.

In the broadband current detector of the present invention, the first and second saturable ring cores have the same shape and are arranged side by side in the axial direction, so that the accuracy of the differential voltage is increased and more accurate current measurement is performed. Can do.

In the broadband current detector of the present invention, the first and second high-frequency coils are connected in series with resistors of the same value in series to form a bridge circuit, and the bridge output is set as a differential voltage. Is amplified by an amplifier and passed through a cancel coil, so that a more accurate current measurement can be performed without being affected by a temperature change or the like.

Claims (4)

A first and second saturable ring cores having a space part through which a conductor to be measured for passing a measurement current can be inserted, and arranged to surround the space part;
First and second high-frequency coils that are wound around the first and second saturable ring cores with the same number of turns in the same direction or in the opposite direction, and generate a magnetic field in the opposite direction when a current is passed ;
First and second unsaturated ring cores arranged with the first and second high-frequency coils sandwiched between both radial sides;
A cancel coil wound around the first and second unsaturated ring cores around the center,
A high-frequency current that saturates the first and second saturable ring cores is caused to flow through the first and second high-frequency coils, a differential voltage applied to the first and second high-frequency coils is extracted, and the differential voltage is handled. An electric current is passed through the cancellation coil, and the first and second unsaturated ring cores are excited in the opposite direction to the excitation by the measurement current to cancel the differential voltage. A wide-band current detector for measuring a current flowing through the conductor to be measured in a low frequency region. 2. The broadband current detector according to claim 1, further comprising a detection coil wound around the first and second unsaturated ring cores around the center, and amplifies the current detected by the detection coil. A wide-band current detector for measuring a current flowing through the conductor to be measured in a high frequency region from a current passed through the cancel coil and a current passed through the cancel coil. 3. The broadband current detector according to claim 2, wherein the first and second saturable ring cores have the same shape and are arranged side by side in the axial direction. 4. The wideband current detector according to claim 2, wherein resistors having the same value are connected in series to the first and second high-frequency coils to form a bridge circuit. The bridge output is the differential voltage, and the differential voltage is synchronously rectified at a frequency twice that of the alternating current flowing through the first and second high-frequency coils, smoothed, amplified by an amplifier, and passed through the cancellation coil. A wideband current detector.

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