JP2000065867A - Current measuring device - Google Patents

Abstract

(57) [Problem] To provide a current measuring device which can form a power supply by acquiring a current flowing through an electric wire to be measured, and has a small, light and simple structure. SOLUTION: A secondary output of a current transformer 51 is branched into two, and one of them is provided with a full-wave rectifier circuit 55 and a smoothing capacitor 5.
6 and a constant voltage circuit 57 are connected in order, and a switch element 58 that opens and closes periodically is connected to the other side.
A calculation for calculating and outputting a primary-side input current value of the current transformer 51 from a voltage drop due to the full-wave rectifier circuit 59, the smoothing capacitor 60, the load resistor 61 for current detection, and the load resistor 61 /
An output circuit 62 is connected, and a current measuring circuit 54 provided with an oscillator 63 for controlling the opening and closing of the switch element 58 is connected. The current transformer 51 is connected to the current measuring circuit 54 and the power supply circuit 5.
3 to obtain the required voltage for each of them, supply power from the power supply circuit 53 to the current measurement circuit 54, and enable current measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current measuring device which does not require an external power supply or a battery.

[0002]

2. Description of the Related Art There is a current measuring device that obtains a current flowing through a measured wire without using an external power source or a battery to form a power source, and uses the power source as a power source for operating current measurement. In this case, the current measuring device is provided with two current transformers, a current transformer for power supply and a current transformer for measurement. FIG. 6 is a block circuit diagram of a current measuring device showing the example. The current measuring device passes a current flowing through a wire under test 1 to a current transformer 2 for power supply and a current transformer 3 for measurement. A power supply circuit is formed which converts the output of No. 2 into a direct current by a rectifier circuit 4 and a smoothing capacitor 5 and outputs a constant voltage by a constant voltage circuit 6.

On the other hand, the output of the measuring current transformer 3 is connected to a rectifier circuit 7.
And a smoothing capacitor 8 converts the current to a direct current, passes the load to a load resistor 9, calculates a voltage drop of the load resistor 9, and outputs the result.
The output circuit 10 forms a measurement circuit that outputs measurement data corresponding to the current flowing through the electric wire 1 to be measured, that is, the primary-side input current of the current transformer 3. Then, electric power for operating the arithmetic / output circuit 10 of the measurement circuit is supplied from the power supply circuit.

FIG. 7 is a perspective view showing the structure of a clamp-type current measuring device having such two current transformers (a circuit portion is omitted in the drawing). The periphery of the through hole 14 is
An iron core 21a around which the secondary winding 22 of the current transformer 2 is wound, and an iron core 21b which can be separated from the iron core 21a by a dividing surface 21c.
Are surrounded by the current transformer 3 and further arranged in parallel with the current transformer 2.
An iron core 31a around which the next winding 32 is wound and an iron core 31b separated from the iron core 31a by a dividing surface 31c are surrounded.

[0005] Reference numerals 16 and 17 denote support members rotatably supported at a fulcrum 15. The iron core 21a and the iron core 31a are fixed to one support member 16, and the iron core 21b and the iron core 31b are fixed to the other support member 17. I have. The clamp of the electric wire to be measured is performed by the support 1 to which the iron core 21b and the iron core 31b are fixed.
7 is rotated about the fulcrum 15 in the direction of arrow A, and the iron cores 21a and 31a and the iron cores 21b and 31b are rotated.
The space is separated and opened, and the electric wire to be measured is introduced into the through hole 14.

After the electric wire to be measured is introduced into the through hole 14, the support 17 is rotated about the fulcrum 15 in the direction of the arrow B, and the cores 21a and 31a, the cores 21b and 31b are rotated.
This is performed by closing the gaps by contacting each other.

[0007]

However, such a current measuring device that obtains the current flowing through the electric wire to be measured and forms a power supply uses two current transformers, so that the number of components is large and the structure is large. There are limits to reducing complexity and size and weight, and when manufacturing a clamp-type current measuring device using a separable core as described above, each of the divided cores must be Therefore, it is necessary to remarkably increase the dimensional accuracy of parts and assembly, and it is difficult to reduce the cost.

The present invention has been made in view of the above circumstances, and provides a current measuring device that can obtain a current flowing through an electric wire to be measured to form a power supply, and has a small, lightweight, and simple structure. The purpose is to:

[0009]

The above object of the present invention is achieved by the following (1) to (5).

(1) A secondary circuit output of a current transformer is branched into two, a power supply circuit for inputting one of the branched outputs and outputting DC power, and periodically inputting the other of the branched outputs. A current measurement circuit for outputting measurement data corresponding to the 1 o'clock side input current of the current transformer, and supplying power of the power supply circuit to the current measurement circuit.

(2) In the measuring instrument according to (1), the current measuring circuit has a switch element for periodically opening and closing the secondary output of the current transformer, and an oscillating circuit for setting the switching cycle of the switch element. And calculating and outputting a 1 o'clock side input current value of the current transformer based on a load resistance energized through the switch element and a voltage drop of the load resistance.
Current measuring device used as an output circuit.

(3) A power supply circuit for branching the secondary output of the current transformer into two via half-wave rectifiers having opposite phases, and inputting one of the branched outputs to output DC power; And a current measurement circuit for receiving the other output and outputting measurement data according to the 1:00 input current of the current transformer, and supplying the power of the power supply circuit to the current measurement circuit. Current measuring device.

(4) In the measuring device of (1) to (3), a tap is provided on the secondary winding of the current transformer, and one of a power supply circuit and a current measuring circuit is connected to the tap. A current measuring device.

(5) A current measuring device using any one of the current clamp type current transformer and the current feed-through type current transformer in the measuring device in the above (1) to (4).

According to the present invention, for example, a secondary output of a current transformer is branched into two, one of which is provided with a full-wave rectifier circuit forming a power supply circuit, a smoothing capacitor and, if necessary, a stabilization of an output voltage. A constant voltage circuit is connected in order, and a switch element that periodically opens and closes to form a current measuring circuit, a load resistance for current detection, and a current transformer based on a voltage drop due to the load resistance at both ends of the load resistance. Is connected to a calculation / output circuit for calculating and outputting the primary-side input current value of the above, and an oscillator (not required when the switching element is a diode) for controlling the opening and closing of the switching element is provided to measure the current. The power supply circuit is connected to a circuit, and a current measuring device is assembled so that power for driving the current measurement circuit is supplied from the power supply circuit.

In the current measuring device assembled in this manner, the secondary output of the current transformer is switched and supplied to the power supply circuit and the current measuring circuit in a time sharing manner. In other words, while the switch element is open, only the power supply circuit including the rectifying and smoothing circuit is connected to the current transformer. In this case, the current transformer can be regarded as a current source, but a voltage is generated by the input impedance of the power supply circuit, and DC power required to drive the current measurement circuit is obtained.

While the switch element is closed, a power supply circuit and a load resistance for current detection are connected to the current transformer as a load, but the load resistance for current detection is far greater than the input impedance of the power supply circuit. The secondary voltage of the current transformer is lower than the charging voltage of the power supply circuit because it is small (the resistance value of the load resistor is set small to obtain the linearity of the secondary current with respect to the primary input current of the current transformer). As a result, all the current from the current transformer flows through the load resistor, and a voltage proportional to the primary input current of the current transformer is generated across the load resistor.

While the switch element is open, the supply of current to the load resistor is cut off, but is corrected by averaging over time by analog or digital arithmetic. However,
The switching element is opened and closed with a period sufficiently shorter than the temporal change of the current (effective value). In this way, current data corresponding to the primary-side input current of the current transformer is obtained by the arithmetic circuit, and desired data is output from the output circuit.

While the switch element is closed, the input voltage of the power supply circuit drops and the power supply is cut off as described above. However, by storing the power when the switch element is opened in the capacitor, Power can be supplied continuously. In addition, by making the opening time of the switch element sufficiently longer than the closing time, most of the power from the current transformer can be used for the power supply. It can be constructed with almost the same dimensions and weight as the ones.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram of a current measuring device according to the first embodiment, FIG. 2 is a block circuit diagram of a current measuring device according to the second embodiment, and FIG.
FIG. 4 is a block diagram showing a calculation example, and FIG. 5 shows a structure in a case where the present invention is applied to a crumb type current measuring device using a split iron core. A perspective view (a circuit portion is omitted in the drawing).
It is. In FIGS. 1 to 4, common and identical portions are denoted by the same reference numerals.

In FIG. 1, reference numeral 51 denotes a current transformer, 52 denotes an electric wire to be measured, 53 denotes a power supply circuit, and 54 denotes a current measuring circuit.
The power supply circuit 53 includes a full-wave rectifier circuit 55 and a smoothing capacitor 5.
6, a constant voltage circuit 57 is connected in order, and a current measuring circuit 54 includes a bidirectional switch element 58, a full-wave rectifier circuit 59, a smoothing capacitor 60, and a load resistor 6 for current detection.
1 are connected in order, and an arithmetic / output circuit 62 for inputting a voltage drop due to a load resistor 61 and an oscillation circuit 63 for opening and closing the switch element 58 are provided.

The power supply circuit 53 is connected to one of the two branches of the secondary output of the current transformer 51, and the current measurement circuit 54 is connected to the other. The power supply circuit 53 and the current measurement circuit 54 are supplied so as to supply the operation / output circuit 62 and the oscillation circuit 63.
And are connected.

The bidirectional switch element 58 is connected to the electric wire 5 to be measured.
2 is a switch that takes in a current corresponding to the current flowing through the switch 2. When a solid state relay or an analog switch is used, a single unit may be used, but when a photocoupler or a photo MOS relay is used, two elements are connected in anti-parallel. The opening and closing are controlled by the output of the oscillation circuit 63.

The oscillating circuit 63 outputs a rectangular wave at a constant cycle and opens and closes the switch element 58. The cycle is set so that the open time is sufficiently longer than when the switch element is closed. For example, the current flowing through the measured electric wire 52, that is, one of the current transformers 51
If the next current is the commercial frequency, the closing time is set to about one cycle (20 seconds), and the opening time is set to about 5 to 10 times the same.

The operation / output circuit 62 inputs the voltage drop due to the load resistor 62 to the operation circuit, calculates the value of the current flowing through the wire under test 52 from the input voltage drop value, and as a result,
That is, the measurement data corresponding to the primary-side input current of the current transformer 51 is output from the output circuit. In this case, the operation / output circuit 62 can select various types according to a desired output form, and an example thereof will be described with reference to FIG.

FIG. 4 (a) is a diagram in which the voltage across the load resistor 61 is amplified by an analog amplifier circuit and output as it is.
This is used when it is desired to obtain an analog signal output proportional to the effective value of the primary current by using the full-wave rectifier circuit 59 and the smoothing capacitor 60 together. FIG. 4B is used when it is desired to obtain a digital signal output through an A / D conversion circuit. FIG. 4C is used when it is desired to obtain a pulse signal output having a repetition frequency proportional to the execution value of the primary current through the V / F conversion circuit.

FIG. 4 (d) shows through an E / O conversion circuit.
Used to obtain an optical signal. FIG. 4E is used when a numeral corresponding to the primary current is to be displayed through a microcomputer circuit built in the A / D converter. In this case, if the A / D converter supports positive and negative inputs, the full-wave rectifier circuit 59 and the smoothing capacitor 61 can be omitted, and the average value can be calculated by the microcomputer and the execution value can be displayed.

When the input of the arithmetic circuit is an AC input, a full-wave rectifier circuit 59 and a smoothing capacitor 60 are used.
Becomes unnecessary.

Next, the operation of the first embodiment will be described. When an alternating current flows through the primary side of the current transformer 51 (the measured wire 52), the secondary side of the current transformer 51 can be considered as a current source. When the switch element 58 is in the open state, the full-wave rectifier circuit 55, the smoothing capacitor 56, the constant voltage circuit 57
The voltage between terminals of the current transformer 51 is generated by the input impedance of the power supply circuit 53 composed of

In the case of this embodiment, the output voltage of the power supply circuit 53 is +5 V, the current consumption is 3 mA on average, and the input voltage for maintaining this is 6 V as an effective value, and the input impedance of the power supply circuit 53 is 2 kΩ. Is set to When the minimum input current on the primary side for maintaining this voltage is 10 A or less, the power supply side function is lost.

When the switch element 58 is opened, the full-wave rectifier circuit 59 and the smoothing capacitor 6 are connected in parallel with the power supply circuit 53.
0, a load resistor 61 for current detection is connected in this order.
In this embodiment, the load resistance of the current transformer 51 is 100Ω.
In the case of, since the linearity between the input and output is good up to the primary side input current 100A, the load resistance 61 is 100Ω.
Is set to When a larger current is measured, the resistance may be reduced.

As described above, since the resistance value of the load resistor 61 for measuring current is small, the output voltage of the current transformer 51 becomes 2 V or less, which is smaller than the voltage of the smoothing capacitor 56 of the power supply circuit 53. All the current flows to the full-wave rectifier circuit 59. That is, when the switch element 58 is open, the output current of the current transformer 51 is completely switched to the power supply circuit 53 side, and when the switch element 58 is closed, the output current is completely switched to the load resistor 61 side, and when the switch element 58 is closed, it is proportional to the input current. Data can be obtained from the voltage across the load resistor 61.

In this embodiment, since the full-wave rectifier circuit 56 and the smoothing capacitor 60 are used, the average value of the DC voltage across the load resistor 61 becomes a value proportional to the effective value of the primary current. Of course, if the capacity of the smoothing capacitor 60 is made sufficiently large, the ripple is reduced, and the DC current and the primary current can be set to a value proportional to the primary current. This load resistance 6
The voltage at both ends of 1 is input to the arithmetic / output circuit 62, and the arithmetic / output circuit 62 obtains desired measurement data. For example, if the arithmetic / output circuit 62 is (a) of the arithmetic / output circuit shown in FIG. 4 described above, an analog output signal proportional to the input current can be obtained.

When the switch element 58 is closed, the current transformer 5
Although the current supply from 1 to the power supply circuit 53 is cut off, the charge can be compensated for by appropriately selecting the capacity of the smoothing capacitor 56.

FIG. 2 shows a second embodiment of the present invention. The second embodiment is different from the first embodiment in the structure of the current The switch element 58 that opens and closes is connected to the input side of the full-wave rectifier circuit 59 in the first embodiment, whereas the switch element 58 opens and closes in the second embodiment. That is, it is connected between the full-wave rectifier circuit 59 and the smoothing capacitor 60.

Even if the switch element 58 is connected in this way, the operation is the same as that of the first embodiment. Therefore, the description of the first embodiment is referred to, and the description is omitted. Here, the switch element may be a unidirectional element such as a photocoupler or a photoMOS relay. In this embodiment, the switch element 58 is a photocoupler, and 64 is a current limiting resistor of the photocoupler.

The difference between the first embodiment and the second embodiment is as follows. In the first embodiment, since a switch element is provided in an AC circuit, it is necessary to use a bidirectional switch element. On the other hand, in the second embodiment, since the switch element exists in the DC circuit, a unidirectional switch element may be used. Also, in the second embodiment, the rectifier circuit 59 is always required on the load resistor 61 side, whereas in the first embodiment, if an arithmetic circuit corresponding to the AC input is used, the rectifier circuit can be used. do not need.

FIG. 3 shows a third embodiment of the present invention. In the third embodiment, a power supply circuit 53 comprises a rectifier diode 71 of a positive half-wave rectifier circuit, a smoothing capacitor 72, The current measuring circuit 54 is formed by connecting a rectifying diode 74 of a negative half-wave rectifying circuit, a smoothing capacitor 75, and a load resistor 76 for current detection in order. And an arithmetic / output circuit 77 for inputting a voltage drop due to the above.

Then, one end of the secondary side output of the current transformer 51 is branched into two, one of which is connected to the positive electrode of the rectifier diode 71 of the power supply circuit 53 and the other is connected to the negative electrode of the rectifier diode 74 of the current measuring circuit 54. Are connected to each other, and the power supply circuit 53
The power supply circuit 53 and the current measurement circuit 5 are configured to supply the DC power formed by
4 are connected.

Next, the operation of the third embodiment will be described. In the half cycle of the primary input current of the current transformer 51, the power supply circuit 53 is turned on by the positive half-wave rectifier circuit, the power is supplied to the power supply circuit 53, and the power is supplied to the arithmetic / output circuit 77 at a constant voltage. Supply. In the next half cycle, a voltage proportional to the primary input current is generated across the load resistor 76. This voltage can be calculated and output as in the first and second embodiments.

In this embodiment, the power supply circuit 53
Since only half of the power that can be supplied from the current transformer 51 is supplied to the current transformer 51, it is necessary to approximately double the cross-sectional area of the iron core of the current transformer 51.

Although the three embodiments have been described above, in any case, a secondary winding tap is provided in the current transformer 51 so that either the power supply circuit 53 or the load side of the current measurement circuit 54 is used as a tap. You may connect. in this case,
The number of turns for the power supply and the number of turns for the ammeter side can be optimized. Furthermore, it is also possible to use only the iron core of the current transformer 51 in common and separately configure the windings on the power supply circuit 53 side and the load side of the current measurement circuit 54. In this case, since both are insulated, in the case of the third embodiment,
Operation / output circuit 77 for calculating the output voltage of load resistor 76 with positive polarity
Can be connected to

FIG. 5 shows a structure in which the present invention is applied to a clamp-type current measuring device using a split-type iron core. The conventional clamp-type current measuring device using a split-type iron core shown in FIG. This is the same as the current measurement device except that one current transformer is removed and the device is miniaturized. The detailed description of the structure is omitted and will be described briefly. In FIG. 5, reference numeral 84 denotes a through-hole for clamping the electric wire to be measured, and an iron core 85 of the current transformer surrounds the hole. The iron core 85 of the current transformer can be separated up and down at a division surface 86. 87 is a secondary winding of the current transformer.

The whole is divided into an upper part 88 and a lower part 89, and the upper part 88 is opened as shown by an arrow A around the fulcrum 80. In the opened state, the electric wire to be measured is guided to the through hole 84 and clamped by closing.

As described above, according to the present invention, when applied to a clamp-type current measuring device using a split core, FIG.
As is clear from the conventional clamp-type current measuring device using the split iron core shown and described above, the number of parts is greatly reduced and a simple structure can be realized. Although the current clamp type current transformer has been described, it may be a current through type current transformer.

[0046]

As described above in detail, according to the present invention, since the power supply power and the measurement current can be obtained with one current transformer, the current measurement is small, lightweight, simple and easy to design and manufacture. Vessels can be provided. In addition, when the present invention is applied to a clamp-type current measuring device using a split iron core, a high-precision one can be easily manufactured without requiring dimensional density and assembling accuracy of parts as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a current measuring device according to a first embodiment of the present invention.

FIG. 2 is a block circuit diagram of a current measuring device according to a second embodiment of the present invention.

FIG. 3 is a block circuit diagram of a current measuring device according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a calculation example of the present invention.

FIG. 5 is a perspective view showing a structure when the present invention is applied to a clamp-type current measuring device using a split iron core.

FIG. 6 is a block circuit diagram of a conventional current measuring device.

FIG. 7 is a perspective view showing the structure of a clamp-type current measuring device using a conventional split-type iron core.

[Explanation of symbols]

 51 Current transformer 52 Electric wire to be measured 53 Power supply circuit 54 Current measurement circuit 55 Full-wave rectifier circuit 55, 60, 72, 75 Smoothing capacitor 57, 73 Constant voltage circuit 58 Switch element 59 Full-wave rectifier circuit 61, 76 Load resistance 62, 77 Operation / Output Circuit 63 Oscillation Circuit 71, 74 Rectifier Diode 80 Supporting Point 84 Through Hole 85 Current Transformer Core 86 Core Dividing Surface 87 Secondary Winding

 ──────────────────────────────────────────────────の Continuing on the front page (72) Koichi Kondo, Inventor Koichi Kadoichi, Teradocho, Kyoto 18-year repair ceremony Stock company In-house Inoue Electric Works F-term (reference) 2G025 AA05 AB04 AC03 AC04 AC05 AC06 2G035 AA00 AB07 AB08 AC03 AC04 AC13 AD04 AD10 AD14 AD19 AD20 AD23 AD28 AD38 AD43 AD47 AD51 AD65

Claims (5)

[Claims] 1. A power supply circuit for branching a secondary output of a current transformer into two, inputting one of the branched outputs and outputting DC power, and periodically inputting the other of the branched outputs. A current measurement circuit that outputs measurement data corresponding to the 1 o'clock side input current of the current transformer, and supplies power of the power supply circuit to the current measurement circuit. 2. A switch element for periodically opening and closing a secondary output of a current transformer, an oscillation circuit for setting an opening and closing cycle of the switch element, a load resistor energized through the switch element, 2. The current measuring device according to claim 1, further comprising: a current measuring circuit including a calculation / output circuit that calculates and outputs a 1:00 input current value of the current transformer according to a voltage drop of a load resistance. 3. A power supply circuit for branching a secondary output of a current transformer into two via a half-wave rectifier having phases opposite to each other, inputting one of the branched outputs and outputting DC power, and a branch circuit. A current measurement circuit that receives the other output and outputs measurement data corresponding to the 1:00 input current of the current transformer, and supplies power of the power supply circuit to the current measurement circuit. Current measuring device. 4. The current transformer according to claim 1, wherein a tap is provided on a secondary winding of the current transformer, and one of a power supply circuit and a current measuring circuit is connected to the tap. Current measuring device. 5. The current measuring device according to claim 1, wherein one of the current clamp type current transformer and the current through type current transformer is used.