JPH11230994A - Ac current measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC current measuring apparatus in which a current can be measured with high accuracy regardless of fluctuation or temperature characteristics of elements by separating the power supply function from the current measuring function. SOLUTION: The AC current measuring apparatus comprises a transformer 1 for inducing a secondary current from a primary current, a circuit 4 for rectifying the induced secondary current, a charging/discharging capacitor 6 for the rectified current, a Zener diode 7 for controlling the capacitor 6 to be charged until a voltage induced by the secondary current reaches a specified level and then discharging the capacitor 6, a load resistor 12 provided in the circuit passing the secondary current, a circuit 10 for converting a voltage appearing across the load resistor 12 when power is supplied by a discharge current from the capacitor 6 into a frequency, and an electrooptical conversion circuit 11 and an optical fiber 13 for transmitting a measuring signal from the voltage/frequency conversion circuit 10 externally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alternating current measuring device, and more particularly, to an alternating current used for measuring a current requiring high insulation, such as when measuring an alternating current flowing at a high voltage. The present invention relates to a current measuring device.

[0002]

2. Description of the Related Art In general, when measuring an alternating current flowing at a high voltage such as a distribution line in a power receiving and distribution facility, a transmission line in a power generation facility, a load requiring a large amount of power in a factory, etc., a high insulation property is required. In such a case, for example,
As disclosed in U.S. Pat. No. 6,264,264, an alternating current measuring device that converts a current into an optical signal and detects the signal is used.

FIG. 11 is a circuit diagram showing a conventional AC current measuring device. As shown in FIG. 11, a conductor 52 penetrates through a transformer 51, and the transformer 51 is excited by a primary alternating current flowing through the conductor 52.

[0004] A diode 54 is connected to the secondary coil 53 of the transformer 51. The diode 54 is connected to the conductor 52
The secondary current generated in the coil 53 on the secondary side of the transformer 51 by the primary AC current flowing through the transformer 51 is half-wave rectified. A capacitor 55 that charges the current rectified by the diode 54 is connected to the cathode of the diode 54.

A Zener diode 56 through which a current flows when the charged voltage of the capacitor 55 becomes higher than a constant voltage is connected to the cathodes of the capacitor 55 and the diode 54. A coil 57 is provided at the cathode of the Zener diode 56.
The light emitting diode 59 is connected via the resistor 58. The light emitting diode 59 is connected to a thyristor 60 that turns on and discharges the capacitor 55 when the charging voltage of the capacitor 55 becomes higher than the constant voltage and a current flows through the zener diode 56. The gate of the thyristor 60 is connected between the anode of the Zener diode 56 and the resistor 61.

Next, the operation of the conventional AC current measuring device will be described. When a primary alternating current flows through the conductor 52 to be measured, a voltage is generated in the coil 53 wound around the transformer 51,
Secondary current starts to flow. This secondary current is half-wave rectified by the diode 54 and charged in the capacitor 55. At this time, since the Zener diode 56 and the thyristor 60 are off, the capacitor 55 is not discharged.

When the charging voltage of the capacitor 55 gradually rises and becomes higher than the constant voltage of the Zener diode 56, a current flows through the Zener diode 56 and the resistance 61
, A voltage is applied to the gate of the thyristor 60.
As a result, the thyristor 60 is turned on, and the capacitor 5
5 discharges and flows to the light emitting diode 59 via the coil 57 and the resistor 58, and the light emitting diode 59
Emit light in pulses.

The discharge current of the capacitor 55 is
, The capacitor 55 is charged in the reverse direction, and when a reverse voltage is applied to the thyristor 60, the thyristor 60
Turns off.

When the thyristor 60 is turned off, charging of the capacitor 55 is newly started, and when a predetermined charging voltage is reached, the light emitting diode 59 emits light again, and then the thyristor 60 is turned off.

By such repetition, the light emitting diode 59 emits light (flashes) intermittently and generates a pulse.
The frequency of the generated pulse is determined by the charging speed of the capacitor 55, and the charging speed is determined by the voltage induced in the coil 53, that is, the current flowing through the conductor 52.

Therefore, the optical signal generated from the light emitting diode 59 is transmitted to the observation site through the optical fiber 70,
By measuring the frequency of the light emission pulse, the current flowing through the conductor 52 at the insulated observation site can be measured.

According to the conventional AC current measuring device, since the light emitting diode 59 emits light by the secondary current generated by the transformer 51, there is no need to supply operating power from the outside, and the insulation from the outside is easy. is there.

[0013]

[SUMMARY OF THE INVENTION] However, the conventional alternating current measurement apparatus, even if the thyristor 60 is ON, resulting in the forward voltage V _f of the saturation voltage V _S and the light emitting diode 59 at the time of ON of the thyristor 60 So the capacitor 55
Are not completely short-circuited. Therefore, even when the thyristor 60 is turned on, a constant charge remains in the capacitor 55, which has an adverse effect of shortening the next charging time.

It should be noted that a coil 55 is used, and a capacitor 55 is used.
Is charged in the reverse direction, but this is for turning off the thyristor 60 effectively, and does not contribute to the improvement of accuracy at all. The amount of reverse charge also affects the influence of these _VS and _Vf. I will receive it.

The saturation voltage V _{S of the} thyristor 60 is
If the forward voltage _Vf of the light emitting diode 59 is constant, it is possible to cancel this effect, but it is actually difficult because of variations due to variations in elements and temperature characteristics.

Further, the charge / discharge time of the capacitor 55 is
The capacitance is determined by the capacitance of the capacitor 55, and the capacitance also varies greatly between elements, and the influence of a temperature change cannot be ignored. In particular, in order for the light emitting diode 59 to emit light sufficiently, a capacitor 55 having a relatively large capacitance is required. However, in general, the larger the capacitance 55, the larger the variation among elements and the change in temperature characteristics. .

Therefore, in the conventional AC current measuring device, the power procurement function and the current measuring function are performed by the same element, so that the variation between the devices is large and the device is easily affected by the temperature. Current measurement could not be performed.

The present invention has been made in order to solve the above-mentioned problems. By separating the power supply function and the current measurement function from each other, it is possible to obtain a highly accurate device without being affected by variations in elements and temperature characteristics. It is an object of the present invention to provide an AC current measuring device capable of measuring current.

[0019]

SUMMARY OF THE INVENTION An AC current measuring apparatus according to the present invention comprises a transformer for generating a secondary current on the secondary side by a primary AC current flowing on a primary side, and a secondary generator generated by the transformer. Rectifying means for rectifying the current, charging and discharging means for charging and discharging the current rectified by the rectifying means, and charging and discharging the charging and discharging means until the voltage generated by the secondary current reaches a predetermined value; Charge / discharge control means for controlling to discharge when the value is higher than a value, a load resistance provided in a circuit through which a secondary current flows, and a discharge current from the charge / discharge means is supplied for operating power, and a voltage generated at the load resistance A voltage-frequency converter for converting a value into a frequency value, and a transmitter for transmitting a measurement signal output from the voltage-frequency converter to the outside, in which a discharge current from the charging / discharging unit is supplied for operating power. Features It is intended to.

According to the present invention, the power supply function and the current measurement function are separated, and the voltage frequency conversion means is used as the current measurement function, and the discharge current from the charging / discharging means is used for the operating power of the voltage frequency conversion means. Since it is used only, it is not affected by variations of elements and temperature characteristics.

The charging / discharging control means includes a Zener diode through which a current flows when a voltage generated by the secondary current becomes higher than a predetermined value, and a saturation of the voltage generated by the secondary current when the current flows through the Zener diode. It is preferable to have a thyristor that reduces the voltage to a voltage, and a backflow prevention diode that prevents the discharge current from the charging / discharging means from flowing back into the thyristor. In this case, even when the voltage induced by the secondary current is large, the thyristor is turned on,
Since the voltage drops to the saturation voltage of the thyristor, the power consumption of the entire processing circuit can be reduced.

When the voltage generated by the discharge current from the charging / discharging means becomes lower than the set operation stop voltage value, the supply of the discharge current is stopped, and when the voltage becomes higher than the set operation start voltage value, the supply of the discharge current is started. Switching means for switching to perform the switching may be further provided. In this case, even if the primary AC current is weak, the voltage frequency conversion means can be operated intermittently, so that current measurement can be performed.

The rectifying means may be a means for full-wave rectifying the secondary current or a means for half-wave rectifying the secondary current.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an AC current measuring device according to a first embodiment of the present invention.

As shown in FIG. 1, a rectifier circuit 4 is connected to the secondary coil 3 of the transformer 1. The rectifier circuit 4 is 4
This is a bridge circuit composed of two diodes, and full-wave rectifies the secondary current i ₂ generated in the coil 3 on the secondary side of the transformer ₁ by the primary alternating current i ₁ flowing through the conductor 2. The rectifier circuit 4, the capacitor 6 for charging the secondary current i ₂ is connected via a diode 5 for preventing reverse current (a forward voltage V _f).

Between the rectifier circuit 4 and the anode of the diode 5, a Zener diode 7 through which a current flows when the charging voltage of the capacitor 6 becomes higher than a constant voltage, and turns on when a current flows through the Zener diode 7. Secondary current i
Thyristor 8 to decrease the voltages V ₁ generated by ₂ to the saturation voltage V _S is connected in parallel. The gate of the thyristor 8 is connected between the anode of the Zener diode 7 and the resistor 9.

A voltage / frequency conversion circuit 10 (hereinafter, referred to as a V / F conversion circuit) is connected to the cathode of the capacitor 6 and the diode 5 via a power supply path K ₁ for supplying power required for current measurement. And electric / optical conversion circuit 11
(Hereinafter, referred to as an E / O conversion circuit). V / F
As the conversion circuit 10, it is preferable to use, for example, VFC62B manufactured by Burr Brown Inc. in the United States. This device is
It is possible to realize an extremely difficult accuracy of a combination of individual elements, that is, a non-linearity of 0.004% within a range of -20 ° C to 70 ° C. As the E / O conversion circuit 11, a light emitting diode may be used.

Between the V / F conversion circuit 10 and the rectifier circuit 4, a current measurement path K ₂ (to distinguish it from K ₁₎ for sending a current measurement signal to the V / F conversion circuit 10. , Shown by dotted lines). One end of the current measurement path K ₂ is connected between the rectifying circuit 4 and the load resistor 12, the other end is connected to the V / F conversion circuit 10. One end of the load resistor 12, the resistor 9, the capacitor 6, and the cathode of the thyristor 8 are grounded.

The E / O conversion circuit 11 is connected to an optical / electrical conversion unit 14 (hereinafter referred to as an O / E conversion unit) to which a signal is transmitted via an optical fiber 13.
The O / E converter 14 is connected to a frequency / voltage converter 15 (hereinafter, referred to as an F / V converter).

Next, the operation of the first embodiment will be described. First, it is assumed that a first alternating current i ₁ (for example, 50 Hz or 60 Hz) having a waveform as shown in FIG. 2A is flowing through the conductor 2 to be measured.

The first AC current i ₁ causes the transformer 1
The voltage generated in the coil 3 wound around the flows secondary current i ₂ (and the number of winding coil 3 is N, the _{i 2 = i 1 / N)} . The secondary current i ₂ flows through the capacitor 6 via the rectifier circuit 4 and the diode 5 and is charged.

The discharge current of the capacitor 6 flows to the V / F conversion circuit 10 and the E / O conversion circuit 11 via the power supply path K ₁ . Therefore, the V / F conversion circuit 10 and the E /
The supply of operating power to the O conversion circuit 11 can be performed internally.

Of the voltages induced by the secondary current i ₂ , the voltage V _{1 at} the cathode of the Zener diode 7
Is as shown in FIG. 2 (C). In advance, the constant voltage V _TH of the Zener diode 7 is set in advance in the circuit (V /
Than the voltage V ₃ to F converter 10 and E / O conversion circuit 11) requires, is set to a large value by the forward voltage V _f of the diodes 5. Also, this voltage V ₃ is
(A), the smoothed-DC by the capacitor 6 becomes a constant voltage V _D (V _D = V _TH over V _f). For example,
In the required voltage of the subsequent processing circuit 5V, V _TH when the forward voltage V _f of the diodes 5 is 0.7V may be set to 5.7 V. If the primary alternating current i ₁ is large, therefore, even when the voltage induced by the secondary current i ₂ is large, for more than V _TH min, the thyristor 8 is ON
Voltage and V ₁ was lowered to V _S is the saturation voltage of the thyristor 8. As a result, the power consumption of the entire processing circuit is reduced (assuming that the saturation voltage V _{S of the} thyristor 8 is 1.5 V, the power consumption of the circuit is about 1.5 W), and the secondary current i _{2 due} to heat generation is reduced. Can be reduced.

Here, since the transformer 1 does not pass a direct current,
The secondary current i ₂ at predetermined time intervals is always becomes zero. for that reason,
The thyristor 8 is always turned off, and the same operation as the previous cycle is repeated (see FIG. 2C). For example, when the secondary current i ₂ is a sine wave of 50 Hz, every 10 msec:
The same operation will be repeated. Given this behavior,
The capacity of the capacitor 6 connected to the cathode side of the diode 5 reduces the current consumption by the subsequent processing circuit by 10 msec.
It can be understood that it is sufficient to set the value to be able to cover only during the period.

The diode 5 is connected to the thyristor 8
Since the saturation voltage V _S at the time of N is lower than the voltage of V ₃ , the charge stored in the capacitor 6 is prevented from flowing back to the thyristor 8 that has been turned on.

On the other hand, the transformer 1 functions as a constant current source as long as the load resistance 12 is not extremely large. Therefore, the transformer 1, the variation of the saturation voltage V _S during the ON forward voltage and the thyristor 8 of the rectifier circuit 4 diodes,
To change due to temperature characteristics to flow a secondary current i ₂ is a constant current regardless is the ability to adjust their own generation voltage.

Accordingly, a secondary current i ₂ that accurately reflects the current flowing through the conductor 2 and the number of windings N flows through the load resistor 12. In the first embodiment, since the rectifier circuit 4 performs full-wave rectification, a current i ₂ having a full-wave rectified waveform flows through the load resistor 12 as shown in FIG.

The secondary current i ₂ is generated by the load resistor 12 to generate a voltage V ₂ having a waveform as shown in FIG. 2D (in FIG. 5, when the reference potential is taken as shown in FIG. 1, the polarity becomes negative). . This voltage V ₂ is converted into a pulse train frequency by the V / F conversion circuit 10 provided at one end of the current measurement path K ₂ , as shown in FIG. The converted frequency measurement signal is converted into an optical signal by the E / O conversion circuit 11, and the optical signal is transmitted to a remote place insulated by the optical fiber 13. The transmitted optical signal is converted by the O / E converter 14 and the F / V converter 15
It is demodulated into demodulated voltage V ₅ shown in Figure 3 (C). Thereby, the current flowing through the conductor 2 can be measured at the insulated observation site.

According to the first embodiment, the thyristor 8
And the zener diode 7 is arranged before the capacitor 6 and the load resistor 12 for measuring the current is provided.
Current measurement and power procurement can be performed at the same time by one transformer 1, and the capacitor 6 that performs the two functions of power procurement and current measurement in the prior art is used only for power procurement. I did not. As a result, the device is not affected by variations and temperature characteristics. Therefore, variation in characteristics between products can be suppressed, and high-precision current measurement can be performed in a wide temperature range.

Further, the thyristor 8 is used for the power procurement function.
Therefore, power that is not required by the subsequent processing circuit is not taken in except for the minimum power, so that heat generation can be suppressed. Thereby, a wide current measurement range can be obtained. In particular, the primary alternating current i ₁ is large, even when large secondary current i _2, heating is small, effective at high current side of the secondary current i _2.

Next, a second embodiment of the present invention will be described. As shown in FIG. 4, an alternating current measuring device according to the second embodiment, the diode 20 is used to half-wave rectifying the secondary current i _2. Therefore, when the primary AC currents i ₁ as shown in FIG. 5 (A) flowing the load resistance 1
5, a current i ₂ having a half-wave rectified waveform flows as shown in FIG. The voltage V _{1 at} the cathode of the Zener diode 7, the coil 3 and the load resistor 12
Voltage V ₂ between each view 5 (C) and 5
The waveform is as shown in FIG.

Next, a third embodiment of the present invention will be described. As shown in FIG. 6, in the alternating current measuring device according to the third embodiment, for example, a zener diode 30 having a constant voltage of 5.7 V is used without using the thyristor 8 as in the first embodiment. Used. Therefore, when the primary alternating current i ₁ flows as shown in FIG. 7A, the voltage V _{1 at} the cathode of the Zener diode 7 becomes V _TH for a certain period as shown in FIG. 7B. In the third embodiment,
Since the thyristor 8 is not used unlike the first embodiment, the number of parts can be reduced, and the structure can be simplified.

Next, a fourth embodiment of the present invention will be described. In the AC current measuring device according to the first embodiment, when the primary AC current i ₁ is sufficiently large, the voltage V ₃ is set to the level shown in FIG.
3A, the voltage V _D exceeds the operation guarantee voltage of the V / F conversion circuit 10 and the E / O conversion circuit 11 and operates stably. Therefore, the output voltage V _D shown in FIG.
₄ is obtained. However, as the primary AC current i ₁ becomes smaller, V _D becomes smaller. As shown in FIG. 8, when the voltage V ₃ becomes lower than the operation guarantee voltage V _K of the circuit, the operation of the circuit is stopped. Therefore, in the first embodiment, the lower limit (i _1min ) of the operating current is determined, and it becomes impossible to measure the lower limit of the operating current i _1min or less.

On the other hand, although the voltage is lower than the operation guarantee voltage V _K , power is supplied to the V / F conversion circuit 10 and the E / O conversion circuit 11, so that useless power is consumed by a circuit that does not operate. You are doing. In addition, as a general characteristic of the transformer 1, when a connected circuit consumes current, the generated voltage decreases in accordance with the current consumption.
Below a certain operation lower limit current, the voltage falls below the operation guarantee voltage, and the circuit does not operate.

Therefore, in the fourth embodiment, when the voltage drops to a predetermined voltage, the V / F conversion circuit 10 and the E /
The power supply of the / O conversion circuit 11 is cut off.

FIG. 9 is a circuit diagram showing an AC current measuring device according to a fourth embodiment of the present invention. The alternating current measurement device according to the fourth embodiment is provided with a circuit operation switching unit 40 added to the first embodiment. The circuit operation switching unit 40 includes a zener diode 41 for setting a circuit operation start voltage, a PNP transistor 42 for performing ON / OFF switching of the circuit operation, a thyristor 43 for controlling the transistor 42, and a circuit operation stop voltage setting. A Zener diode 44 and resistors 45 and 46.

The emitter of the transistor 42 is connected to the cathode of the zener diode 41 for setting the circuit operation start voltage, the base is connected to the anode of the thyristor 43, and the collector is connected to the V / F conversion circuit 10 and the E / E converter.
Connected to O conversion circuit 11.

The gate of the thyristor 43 is connected between the circuit operation start voltage setting zener diode 41 and the resistor 45, and the cathode thereof is connected to the cathode of the circuit operation stop voltage setting zener diode 44.

Next, the operation of the fourth embodiment will be described. When the primary AC current i ₁ is sufficiently large and the power supplied to the circuit is abundant, the voltage V ₃ becomes the value of V _CONT by the constant voltage set by the Zener diode 7. As a result, the circuit operation start voltage setting Zener diode 4
Since the set voltage V _{ON of} 1 is smaller than the set voltage V _CONT of the zener diode 7, it is always in the ON state. As a result, the thyristor 43 for controlling the transistor is turned on.
Then, since the transistor 42 is turned on, the V / F
Power is always supplied to the conversion circuit 10 and the E / O conversion circuit 11, and these circuits operate continuously.

When the primary alternating current i ₁ decreases and the power of the subsequent processing circuit cannot be supplied, the voltage V ₃ across the capacitor 6 decreases. This voltage V ₃ is the set voltage V of the zener diode 44 for setting the circuit operation stop voltage.
_When the voltage falls below _OFF , the current of the diode 5 is cut off, and the transistor controlling thyristor 43 is turned OFF. As a result, the transistor 42 is also turned off, and the power to the V / F conversion circuit 10 and the E / O conversion circuit 11 at the subsequent stage is cut off.

When the transistor 42 is turned off, the V
The / F converter 10, and E / O conversion circuit 11 is interrupted, the load of the transformer 1 is increased, the voltages V ₁ increases. The voltages V ₁ charges the capacitor 6, the voltage V ₃ in proportion to the accumulated charge will be gradually boosted.

When the voltage V ₃ exceeds the set voltage V _on of the zener diode 41 for setting the circuit operation start voltage, the transistor 42 is turned on, and power is supplied to the V / F conversion circuit 10 and the E / O conversion circuit 11 at the subsequent stage. And start operation.

[0053] By setting the V _ON> V _OFF, the circuit now has a hysteresis characteristic, V from V _ON
The circuit at the subsequent stage operates for a certain period of time until _{turning off} , and at other times, the circuits at the subsequent stage stop operating and the capacitor 6
Charge is accumulated in the At this time, the voltage V ₆ on the collector side of the transistor 42 changes as shown in FIG. Also, V _{OFF is set} to the operation guarantee voltage V _K of the circuit.
With the above setting, the processing circuit at the subsequent stage can be reliably operated during the period from V _{ON to} V _OFF .

The voltages V ₂ , V ₃ , V ₄ and V
₅ are as shown in FIGS. 10B to 10E, respectively. The voltage V ₂ generated across the load resistor 12 is the same as in the first embodiment, as shown in FIG. Further, a V / F conversion circuit 10 and an E / O conversion circuit 11
Operates only during the period from V _{ON to} V _OFF as shown in FIG. 10A, so that the output voltage V ₄ of the V / F conversion circuit 10 is obtained only during the above period, and is shown in FIG. 10D. Become like Therefore, the transmission destination of the output voltage (demodulated voltage) V ₅ becomes the solid line portion in FIG. 10 (E). Note that the dotted line portion where the signal is interrupted from the solid line portion shown in FIG. 10E can be interpolated by estimation.

As described above, the set voltage V _CONT of the zener diode 7, the set voltage V _ON of the zener diode 41 for setting the circuit operation start voltage, and the set voltage V _OFF of the zener diode 44 for setting the circuit operation stop voltage are represented by V _CONT
By setting> V _ON > V _OFF , continuous operation is performed during the period of V ₃ > V _ON , intermittent operation is performed during the falling period of V _ON > V ₃ > V _OFF , and during the period of V _OFF > V ₃ , The intermittent operation stops. In addition, V _ON > V ₃ > V after once lowering V _{OFF
In the OFF} rising period, the intermittent operation is stopped (see FIG. 10).
(C)).

According to the fourth embodiment, the current can be measured even when the primary current is low, and the circuit operation stop voltage V _OFF is set higher than the circuit operation guarantee voltage V _K. It can avoid unstable operation of the circuit in the circuit operation guarantee voltage V _K vicinity.

The present invention is not limited to the above embodiment, and various changes can be made within the scope of the technical matters described in the claims. For example, since power is supplied internally, the E / O conversion circuit 11
For example, a wireless transmission device as disclosed in U.S. Pat. No. 4,384,289 can be used. Also, the rectifier circuit 4 in the third embodiment and the fourth embodiment in place of the one diode may be a secondary current i ₂ such that half-wave rectification.

[0058]

According to the present invention, the following excellent effects can be obtained. (1) The power supply function and the current measurement function are separated, and the voltage frequency conversion means is used as the current measurement function, and the discharge current from the charging / discharging means is used only for the operating power of the voltage frequency conversion means. It is not affected by variations or temperature characteristics. Therefore, variation in characteristics between products is suppressed, and highly accurate current measurement can be performed in a wide temperature range. (2) Since the separate power supply function and current measurement function can be realized by one transformer, the size of the device can be reduced. (3) Since the power procurement function and the current measurement function are separated, it is easy to replace the transmission method using an optical fiber with another transmission method using wireless communication.

[Brief description of the drawings]

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

Figure 2 (A) shows a waveform of a primary alternating current i _1, (B) shows a waveform of the secondary current i _2, (C) shows a waveform of the voltage V _1,
(D) is a waveform diagram of the voltage V _2.

3 (A) shows a waveform of the voltage V _3, (B) shows a waveform of the voltage V _4, a waveform diagram (C) the voltage V _5.

FIG. 4 is a circuit diagram showing an AC current measuring device according to a second embodiment of the present invention.

[5] (A) shows a waveform of a primary alternating current i _1, (B) shows a waveform of the secondary current i _2, (C) shows a waveform of the voltage V _1,
(D) is a waveform diagram of the voltage V _2.

FIG. 6 is a circuit diagram showing an AC current measuring device according to a third embodiment of the present invention.

7 (A) shows a waveform of a primary alternating current i _1, (B) is a waveform diagram of the voltage V _1.

8 is a waveform diagram of the voltage V ₃ in the first embodiment.

FIG. 9 is a circuit diagram showing an AC current measuring device according to a fourth embodiment of the present invention.

[10] (A) is a waveform diagram of the voltage V _6, (B) the voltage V ₂
Waveform diagram, (C) shows a waveform of the voltage V _3, (D) the voltage V ₄
Waveform diagram, (E) is a waveform diagram of the voltage V _5.

FIG. 11 is a circuit diagram showing a conventional AC current measuring device.

[Explanation of symbols]

i ₁ : Primary alternating current i ₂ : Secondary current 1: Transformer 2: Conductor 3: Coil 4: Rectifier circuit 5: Diode 6: Capacitor 7: Zener diode 8: Thyristor 9: Resistance 10: Voltage / frequency conversion circuit ( (V / F conversion circuit) 11: Electric / optical conversion circuit (E / O conversion circuit) 12: Load resistance 13: Optical fiber 14: Optical / electric conversion section (O / E conversion section) 15: Frequency / voltage conversion section ( F / V conversion unit) 20: Diode 30: Zener diode 40: Circuit operation switching unit 41: Zener diode for circuit operation start voltage setting 42: Transistor 43: Thyristor 44: Zener diode for circuit operation stop voltage setting 45: Resistance 46: resistance

Claims (5)

[Claims] 1. A transformer for generating a secondary current on the secondary side by a primary alternating current flowing on a primary side, rectifying means for rectifying a secondary current generated by the transformer, and rectifying by the rectifying means. Charging / discharging means for charging and discharging the charged current, and charging / discharging means for controlling the charging / discharging means to charge until the voltage generated by the secondary current reaches a predetermined value, and to discharge when the voltage exceeds the predetermined value. Control means, a load resistor provided in a circuit through which the secondary current flows, and a voltage for supplying a discharge current from the charge / discharge means for operating power, and converting a voltage value generated at the load resistor into a frequency value AC current characterized by comprising: frequency conversion means, and a transmission means to which a discharge current from the charging / discharging means is supplied for operating power, and which transmits a measurement signal output from the voltage frequency conversion means to the outside. Total Measuring device. 2. The charge / discharge control means includes: a Zener diode through which a current flows when a voltage generated by the secondary current becomes higher than a predetermined value; and a current generated by the secondary current when a current flows through the Zener diode. 2. The alternating current measurement according to claim 1, further comprising: a thyristor for reducing a voltage to a saturation voltage; and a backflow prevention diode for preventing a discharge current from the charging / discharging means from flowing back to the thyristor. apparatus. 3. When the voltage generated by the discharge current from the charging / discharging means becomes lower than a set operation stop voltage value, the supply of the discharge current is stopped. When the voltage becomes higher than the set operation start voltage value, the discharge current is stopped. The alternating current measuring device according to claim 1 or 2, further comprising a switching unit that switches so as to start the supply. 4. The alternating current measuring device according to claim 1, wherein said rectifying means performs full-wave rectification of said secondary current. 5. The alternating current measuring device according to claim 1, wherein said rectifier rectifies the secondary current by half-wave rectification.