JP4055196B2 - Current detection device - Google Patents

Description

  The present invention relates to an alternating current detection device using a current transformer.

  The current detection device is used in various electric devices. For example, the current detection device that controls the electromagnetic brake of the induction motor controls the electromagnetic brake when detecting that the alternating current supplied to the induction motor is cut off. Then, the induction motor that rotates by inertia is stopped. There is also a current detection device that detects and cuts off an excessive alternating current that flows through the induction motor when the mechanical load becomes excessive, thereby protecting the induction motor. These current detection devices generally detect an alternating current using a current transformer.

  FIG. 8A shows an example of a conventional current detection device in which a secondary AC voltage (secondary voltage) induced by electromagnetic coupling from the primary coil L01 to the secondary coil L02 of the current transformer T01. Is detected, and an alternating current (primary current) Ia is detected (see, for example, Patent Document 1). The secondary side voltage is a voltage obtained by flowing a secondary side alternating current (secondary side current) induced by the alternating current Ia through the load resistor R01, and the waveform of the secondary side voltage is the waveform of the alternating current Ia. (Sine wave) and a similar waveform.

By the way, in the current detection device, in order to reduce power loss in the current transformer T01, the voltage drop of the primary side coil L01 is set to a voltage as low as possible. Then, since the secondary side voltage also becomes a low voltage, in the conventional current detection device, it is necessary to set the resistance value of the load resistor R01 to a relatively low value (for example, 10 ohms to several hundreds ohms). Such a low voltage is also intended to reduce the size and cost of the current transformer T01 and the current detection device.
Japanese Patent Application Laid-Open No. 61-248387 (2nd page, FIG. 2)

  The conventional current detection device reduces the voltage drop (primary voltage) as much as possible by setting the number of turns of the primary coil L01 of the current transformer T01 to one turn, while increasing the primary voltage to a detectable voltage. The number of turns of the side coil L02 is set to 500 turns, for example (Tokin (registered trademark) current transformer product name CT-05). The load resistance R01 connected to the secondary coil is, for example, 10 ohms (Ω), and the primary current (sine wave) Ia is about 1 A (peak value, hereinafter, current and voltage are peak values). ) (See FIG. 8B), a secondary side voltage of about (1/500) × 10 = about 20 mV is generated in the load resistor R01 (see FIG. 8C). ). Even when the load resistance R01 is set to 100Ω, the secondary side voltage is about 200 mV, and in order to increase this to, for example, 1 V or more, the number of turns of the secondary side coil L02 must be about 2500 turns. The transformer T01 becomes larger and the cost increases.

  That is, the conventional current detection device has to detect a secondary side voltage having a small amplitude of about 20 to 200 mV, for example, to detect a current of 1 A, or a comparison circuit that can detect a slight voltage difference, or An operational amplifier having a high amplification degree is required. A circuit that handles such a small-amplitude electric signal has a complicated circuit configuration and is easily affected by voltage drift, which causes problems such as an increase in cost and an increase in size of the current detection device. Further, in the current detection device that detects the secondary side voltage (for example, about 200 mV) generated in the load resistor R01 by converting it into a direct current with a diode rectifier circuit, as shown in FIG. Therefore, the influence of the voltage drift is further increased.

  The present invention has been made in view of the above circumstances, and is based on the assumption that a small current transformer with a reduced number of turns of the coil is used, and the configuration of a circuit related to detection of the secondary side voltage is simple. It is another object of the present invention to provide a current detection device that is not easily affected by the draft, further reduces costs, and does not increase the size of the device itself.

In order to achieve the above-mentioned object, the present invention induces an electromotive force in the secondary coil of the current transformer by flowing an alternating current through the primary coil of the current transformer, and detects the electromotive force to detect the alternating current. A current detection device for detecting a current, which regulates a secondary side alternating current induced in the secondary side coil by using a resistance value of a high load that makes it possible to obtain a voltage having a high pulse peak value. When the polarity of the alternating current is reversed, the secondary load of the current transformer that induces a pulse voltage in the secondary coil corresponding to the value of the primary current, and the amplitude of the pulse voltage is Detection means for detecting that the amplitude is equal to or greater than a predetermined amplitude, and signal conversion means for outputting a continuous signal when the detection means detects that the amplitude of the pulse voltage is equal to or greater than the predetermined amplitude, With the features Current detecting device.
Here, the high load resistance described above is possible in order to perform detection by reflecting the current on the primary side faithfully on the secondary side, such as 10 Ω for the load resistance on the secondary side in the conventional current detection device. Although the voltage obtained by the secondary coil is almost equal to the product of the load resistance and the current, the voltage obtained by the secondary coil is easy to detect. This means that the resistance value is higher than the load resistance in the secondary coil of the conventional current detection device.

In the current detection device having such a configuration, the secondary load of the present invention has a higher resistance value (or impedance) than the secondary load of the conventional current detection device, and the magnetic core of the current transformer is magnetically saturated. It is set to be. In this way, by regulating the secondary side alternating current, the magnetic flux generated in the magnetic core changes rapidly only in a short time when the polarity of the alternating current is reversed, and changes almost at other times. There is nothing.
Therefore, a sudden voltage change when the polarity is reversed generates a pulsed voltage corresponding to this, and this pulsed voltage is much higher than the secondary voltage generated by the current transformer of the conventional current detection device. A voltage is obtained. Therefore, unlike the conventional secondary side voltage, the secondary side alternating current obtained in the present invention is a pulse voltage with a high amplitude, and the detection means easily detects a pulse voltage with a high amplitude. It becomes possible. Here, the secondary pulse voltage detected by the detecting means is converted into a continuous signal longer than the period of the initial state by the signal converting means and outputted.

Similarly, another invention of the present application induces an electromotive force in the secondary side coil of the current transformer by flowing an alternating current through the primary side coil of the current transformer, and detects the electromotive force to generate the alternating current. A current detection device for detecting, using a high load resistance value that enables obtaining a voltage having a high pulse peak value, and regulating a secondary side alternating current induced in the secondary side coil, Detecting means for inducing a pulse voltage in the secondary coil and detecting that the amplitude of the pulse voltage is equal to or greater than a predetermined amplitude when the polarity of the alternating current is reversed; And a signal converter that outputs a continuous signal when it is detected that the amplitude of the voltage is greater than or equal to a predetermined amplitude.
In the invention with such a configuration, the magnetic core of the current transformer is magnetically saturated by the action of the detection means. As in the first invention, the load on the secondary side of the invention is the same as that of the conventional current detection device. The resistance value (or impedance) is higher than that of the secondary load, and the magnetic core of the current transformer is set to be magnetically saturated.
In this way, by regulating the secondary side alternating current, the magnetic flux generated in the magnetic core changes rapidly only in a short time when the polarity of the alternating current is reversed, and changes almost at other times. There is nothing.
Therefore, a sufficiently high voltage is surely generated as compared with the secondary side voltage generated by the current transformer of the conventional current detection device. Therefore, a circuit for detecting such a voltage can be simply configured. It is possible.

  When the detecting means detects that the positive and negative pulses of the pulse voltage are greater than or equal to a predetermined amplitude, the current detecting device is generated in a half cycle of the alternating current cycle. The alternating current can be quickly detected by the pulse voltage (Claim 3). The current detecting device for detecting that the positive or negative pulse of the pulse voltage is greater than or equal to a predetermined amplitude is generated by the detection means at a cycle equal to the cycle of the alternating current with a simple circuit configuration. The alternating current can be detected by a pulsed voltage.

  As described above, according to the current detection device of the present invention, the current transformer of the conventional current detection device is generated without increasing the number of turns of the secondary coil by regulating the secondary side alternating current of the current transformer. Thus, a pulse voltage having a peak value voltage higher than the secondary side voltage can be obtained. Therefore, an AC current can be easily detected without being affected by drift with a simple circuit configuration, and without causing problems such as an increase in the cost and size of the current detector and current transformer (preferably an AC current is quickly detected). Detection).

Hereinafter, with reference to the drawings, a current detection device according to the present invention will be described using a commercial alternating current of 60 Hz as an example.
(First embodiment)
A current detection apparatus according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1A is a schematic configuration of the current detection device according to the first embodiment, and FIGS. 1B to 1G are waveform diagrams for explaining the operation thereof. The current detection device according to the first embodiment includes a current transformer T10, load resistors (secondary side loads) R13 and 14, detection means 20, and signal conversion means 30, and a primary side coil L11 of the current transformer T10. AC current flows to an electric device (not shown) such as an induction motor.

  In the current transformer T10, for example, similarly to the conventional current transformer T01, the number of turns of the primary side coil is 1 turn, and the number of turns of the secondary side coil is 500 turns. The load resistors R13 and R14 connected in series between the first output terminal L12h and the second output terminal L12c of the secondary coil L12 of the current transformer T10 are secondary AC that is induced in the secondary coil L12. The current is regulated, and a pulsed voltage is induced in the secondary side coil L12 as the polarity of the alternating current Ia flowing through the primary side coil L11 is reversed. The load resistors R13, 14 have the same resistance value, and the connection point (middle point) of the load resistors R13, 14 is grounded.

  When detecting means 20 detects that the amplitude (peak voltage) of the pulsed voltage generated in secondary coil L12 is greater than or equal to a predetermined amplitude, it outputs a pulse signal. The first input terminal 21 of the detection means 20 is connected to the first output terminal L12h of the secondary coil L12, and the second input terminal 22 of the detection means 20 is the second output terminal L12c of the secondary coil L12. And the ground terminals 23 and 24 of the detecting means 20 are grounded. The output terminal 25 is a terminal that outputs a pulse signal of the detection means 20. A transistor TR 27 that performs a switching operation is connected between the output terminal 25 and the ground terminal 24, and the detection means 20 is connected to the power supply terminal 26. Power to operate is supplied.

The signal conversion means 30 shown in FIG. 1 converts the pulse signal of the detection means 20 input to the pulse input terminal 31 into a signal continuous for a predetermined time and outputs it to the continuous signal output terminal 32.
Next, the regulation of the secondary current and the generation of the pulse voltage will be described with reference to FIGS.
As the series resistance value of the load resistors R13 and 14 increases, the magnetic core of the current transformer T10 becomes magnetically saturated with a small current. For example, when the series resistance value of the load resistors R13 and 14 shown in FIG. 2A is 10 KΩ, when a 1 A alternating current Ia (FIG. 2B) is passed through the primary coil L11 of the current transformer T10, When the magnetic core of the current transformer T10 is saturated and the polarity of the alternating current Ia is reversed (inflection point), the secondary coil L12 has an amplitude (peak value) of about 1.8 V (about 3.6 Vp-p). The pulse voltage is generated (FIG. 2C).

  The generation of this pulse voltage will be described using the magnetic characteristics of the magnetic core of the current transformer T10 shown in FIG. In the first saturation region B1 where the magnetic flux density of the magnetic core is saturated, the magnetic flux density does not increase or decrease so much even if the alternating current Ia increases or decreases and the magnetomotive force H increases or decreases. When the alternating current Ia eventually decreases to zero and the polarity of Ia further reverses, the polarity of the magnetomotive force H also reverses, and the magnetic flux density changes instantaneously to the second saturation state (saturation region B2). Even in the region B2, the magnetic flux density does not increase or decrease so much due to the increase or decrease of the alternating current Ia. However, in the first magnetic pole reversal region Bd1 that changes from the saturation region B1 to the saturation region B2, the magnetic flux density changes instantaneously, and a pulse voltage is generated in the secondary coil L12. Similarly, in the second magnetic pole inversion region Bd2 that changes from the saturation region B2 to the saturation region B1, a pulse voltage is generated in the secondary coil L12. In these magnetic pole reversal regions Bd1 and Bd2, the direction of increase / decrease of the magnetic flux is opposite, so the polarity of the pulse voltage is different (see FIG. 2C).

As shown in FIG. 2D, the current detection device according to the first embodiment performs full-wave rectification on a pulse voltage having a frequency of 60 Hertz (period: about 16.7 mS) generated in the secondary coil L12. And a positive pulse having a frequency of 120 Hz (period: about 8.3 mS) is obtained.
That is, a large amplitude voltage (pulse voltage) can be generated in the secondary coil L12 without increasing the number of turns of the secondary coil L12 (without increasing the size of the current transformer T10). It can be easily detected that the alternating current Ia is equal to or greater than the predetermined value by detecting that the voltage is equal to or greater than the predetermined value. Further, since the period of the pulse voltage is ½ of the alternating current Ia, the alternating current Ia can be detected quickly.

  FIG. 4 shows the measured waveform in the current transformer (CT-05). 4A shows the current waveform (sine wave) of the primary current (1A), and FIG. 4B shows the primary current as 1A when the series resistance value of the load resistors R13 and 14 is 10 KΩ. The secondary side voltage waveform (peak value about 1.8V) is shown, and the secondary side voltage waveform (peak value about 6V) shown in FIG. 4C is obtained when the primary side current is increased to 100A. Is.

An example (Example 1) of the current detection device according to the first embodiment is shown in FIG.
When the alternating current Ia is about 1 A, a pulse voltage having an amplitude (peak value) of about 1.8 V is generated in the secondary coil L12 of the current transformer T10. Here, the sum of the forward voltages between the base and the emitter of the diode TR28a connected to the first input terminal 21 of the detection means 20 (or CD28b connected to the second input terminal 22) and the transistor TR27 is: Usually about 1.4V. Therefore, a current flows from the secondary coil L12 to the base / emitter of the transistor TR27 and the load resistor R14 (or R13) via the diode CD28a (or CD28b). That is, the transistor TR27 performs a switching operation with a positive pulse (Rec in FIG. 5A) having a period of about 8.3 mS, which is full-wave rectified by the diodes CD28a and CD28b, and is connected to the output terminal 25 of the detection means 20 at about A pulse signal having a period of 8.3 mS is output (Out in FIG. 5A).

  The signal conversion means 30 has a retriggerable monostable multivibrator and is triggered at the leading edge (falling edge of the pulse signal) of the pulse signal input to the pulse input terminal 31, and for example, a pulse having a pulse width of 9 mS. appear. Then, as long as pulse signals (with a period of about 8.3 mS) are continuously output from the output terminal 25, the signal conversion means 30 continues to output a high level (H) signal (for example, 5 V) to the continuous signal output terminal 32. Here, the pulse width needs to be at least one half of the period of the alternating current Ia (about 8.3 mS), and is preferably set within the period of the alternating current Ia (about 16.7 mS).

  For example, when the alternating current Ia is 0.5 A, the pulse voltage generated in the secondary coil L12 is the sum of the forward voltages between the base and emitter of the diode CD28a (or CD28b) and the transistor TR27. The voltage becomes lower than 4 V, the current for switching the transistor TR27 does not flow, and no pulse signal is output to the output terminal 25. That is, the pulse signal appears at the output terminal 25 only when the alternating current Ia flows over a predetermined value (for example, about 1 A), and the detection threshold of the alternating current Ia (the minimum current value that can be detected by the current detection device) is the predetermined value. (For example, about 1A).

  Therefore, as shown in FIG. 1 (b), when the alternating current Ia is flowing 1A or more, the alternating current Ia is cut off at time t2 (time t2 is within about 8.3 mS that is delayed from time t1). When (or decreased to 0.5 A), as shown in FIG. 1C, the pulse signal output to the output terminal 25 of the detection means 20 is not output after time t2. Then, the continuous signal output terminal 32 of the signal conversion means 30 that was at the high level (H) before the time t1 is changed to a low level (L) signal (for example, 0 V) after the time t3 after 9 mS has elapsed from the time t1. Change (see FIG. 1D). That is, the detection of the alternating current Ia (interruption or reduction of the alternating current Ia) by the current detection device of the first embodiment is not delayed from the time of the pulse width generated by the signal conversion means 30 (for example, 9 mS).

  As shown in FIG. 1 (e), 1 A of alternating current Ia started to flow (or increased from 0.5 A to 1 A at time t4 (time t4 is within about 8.3 mS preceding time t5). 1), the pulse signal is continuously output to the output terminal 25 after time t5, as shown in FIG. Then, the continuous signal output terminal 32 of the signal converting means 30 that output the low level (L) before time t5 changes from the time t5 to the high level (H) output (see FIG. 1 (g)). That is, the detection of the alternating current Ia (the alternating current Ia has started to flow or has increased) by the current detection device of the first embodiment is delayed from a half cycle (about 8.3 mS) of the alternating current Ia. There is no.

  In this way, the current detection device according to the first embodiment can detect that the alternating current has flowed to a predetermined value or more within a half cycle of the alternating current, and can detect that the alternating current has become a predetermined value or less. It can be detected quickly without delay from one to one cycle. Therefore, the current detection device according to the first embodiment can quickly perform control of the electromagnetic brake, protection from the overload of the induction motor, and the like using the signal of the continuous signal output terminal 32 as the detection signal of the alternating current Ia.

  Note that the pulsed voltage generated in the secondary coil L12 (FIG. 2C) and the rectified voltage of the pulsed voltage (FIG. 2D) have a large amplitude (in Example 1, the AC current Ia is 1 A). In this case, these voltages can be easily detected by a comparison circuit (for example, a comparator IC), and the configuration of the detection means 20 is not limited to the configuration of a rectifier diode and a transistor. The signal conversion means 30 can also be realized by a timer circuit other than the retriggerable monostable multivibrator, a microprocessor for determining the presence or absence of a pulse, and the continuous signal output signal of the signal conversion means 30 is a relay contact signal. Such a signal may be a mechanical element signal or an optical signal, and is not limited to the voltage signal output described above. On the other hand, when the rapid current detection as described above is not required, the pulse width generated by the signal conversion means 30 may be set to be equal to or longer than the cycle of the alternating current, or the output terminal 25 of the detection means 20 may be set. The signal conversion means 30 can be simplified by converting the output pulse signal into a DC voltage by a smoothing circuit having a time constant.

The current detection device (embodiment 2) shown in FIG. 5B is a modification of the embodiment 1. Components having the same functions as those in the embodiment 1 are denoted by the same reference numerals, and the description thereof is omitted. .
The detection means 20a has the same function as the detection means 20, but is different from the detection means 20 in that the pulsed voltage output from the secondary coil L12 is full-wave rectified using the bridge-connected diodes CD28a to CD28d. Different. When the current for switching the transistor TR27 flows from the secondary coil L12 to the diode CD28c (or CD28d), the base / emitter of the transistor TR27, and the diode CD28b (or CD28a), the output terminal 25 of the detection means 20a. The same pulse signal (period approximately 8.3 mS) as that of Out in FIG.

  In the second embodiment, the transistor TR27 is switched unless the peak value of the pulse voltage is equal to or greater than the sum (eg, 2.1 V) of the forward voltage of two diodes and the forward voltage between the base and emitter of the transistor TR27. Since the operation is not performed, the detection threshold value of the alternating current Ia is different from that in the first embodiment.

The current detection device (Embodiment 3) shown in FIG. 5C is also a modification of Embodiment 1, and components having the same functions as those in Embodiment 1 are denoted by the same reference numerals and description thereof is omitted. .
The detection means 20b has the same function as the detection means 20, but includes two transistors: a transistor TR27a whose base is connected to the first input terminal 21, and a transistor TR27b whose base is connected to the second input terminal 22. On the other hand, it differs from the detection means 20 in that it does not have a rectifier diode. The collectors of these transistors TR27a and TR27b are connected to the output terminal 25, respectively.

  For example, when a positive pulse voltage of 0.7 V or more is generated on the first output terminal L12h side of the secondary coil L12, the first output terminal L12h, the base / emitter of the transistor TR27a, the load resistor R14, and When a current flows to the second output terminal L12c of the secondary coil L12 and a positive pulse voltage of 0.7 V or more is generated on the second output terminal L12c side, the second output terminal L12c and the transistor TR27b are generated. Current flows to the base / emitter, the load resistor R13, and the first output terminal L12h. Therefore, the detection means 20b outputs a pulse signal (period approximately 8.3 mS) similar to Out in FIG.

  As described above, in the current detection device according to the third embodiment, when the peak value of the pulse voltage is equal to or higher than the forward voltage (eg, 0.7 V) between the base and emitter of the transistor, the transistors TR27a and TR27b perform the switching operation. Therefore, the detection threshold value of the alternating current Ia is different from those in the first and second embodiments.

(Second Embodiment)
In the current detection device according to the second embodiment, instead of the load resistors R13 and 14 of the current detection device according to the first embodiment, the current detection means is a secondary of the current transformer T10 at the inflection point of the alternating current Ia. A pulse voltage (FIG. 2C) is generated in the side coil L12. In the current detection device according to the second embodiment that does not use the load resistors R13 and 14, the magnetic core of the current transformer T10 is magnetically saturated with a smaller primary current as compared with the current detection device according to the first embodiment. Therefore, the threshold value for detecting the alternating current Ia can be set to a current value smaller than that of the current detection device according to the first embodiment.

An example (Example 4) of the current detection device according to the second embodiment is shown in FIG. Components having the same functions as those of the current detection device according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the detection means 20c having the same function as the detection means 20, the diode CD28a causes a forward current to flow from the ground terminal 23 to the first input terminal 21, and the diode CD28b passes from the ground terminal 23 to the second input terminal 22. The transistor TR27a has a transistor TR27a having a base connected to the first input terminal 21, a transistor TR27b having a base connected to the second input terminal 22, and the collectors of the transistors TR27a and TR27b are respectively provided in terms of forward current flow. It differs from the detection means 20 in that it is connected to the output terminal 25.

  For example, when a positive pulse voltage of 1.4 V or higher is generated on the first output terminal L12h side of the secondary coil L12, the first output terminal L12h, the base / emitter of the transistor TR27a, the diode CD28b, When a current flows to the second output terminal L12c of the secondary coil L12 and a positive pulse voltage of 1.4 V or more is generated on the second output terminal L12c side, the second output terminal L12c and the transistor TR27b are generated. Current flows to the base / emitter, the diode CD28a, and the first output terminal L12h.

  As described above, in the current detection device according to the fourth embodiment, when the peak value of the pulse voltage is equal to or greater than the sum of the forward voltage between the base and the emitter of the diode and the transistor TR27 (for example, 1.4 V), the detection unit 20c The same pulse signal (period approximately 8.3 mS) as that of Out in FIG. 5A is output.

The current detection device (Embodiment 5) shown in FIG. 6B is a modification of Embodiment 4, and components having the same functions as those in Embodiments 1 and 4 are denoted by the same reference numerals and the description thereof is omitted. Omitted.
The detecting means 20d has the same function as that of the detecting means 20a of the second embodiment, and the current for switching the transistor TR27 from the secondary coil L12 to the diode CD28c (or CD28d) and the base / emitter of the transistor TR27. Then, the signal flows to the diode CD28b (or CD28a), and a pulse signal (period approximately 8.3 mS) similar to the output Out in FIG. 5A is output to the output terminal 25 of the detection means 20d.

  In the current detection device of the fifth embodiment, the peak value of the pulse voltage is not greater than or equal to the sum (for example, 2.1 V) of the forward voltage of two diodes and the forward voltage between the base and emitter of the transistor TR27. Since the transistor TR27 does not perform a switching operation, the detection threshold value of the alternating current Ia is larger than that of the current detection device of the fourth embodiment.

(Third embodiment)
In the current detection device according to the third embodiment, the rectification circuit of the current detection device according to the first embodiment is a half-wave rectification circuit, and the circuit configuration of the current detection device can be simplified. The current detection device according to the third embodiment uses a load resistor R13a instead of the load resistors R13, 14 of the current detection device according to the first embodiment (the resistance value of the load resistor R13a is, for example, the load resistor R13). , 14 series resistance value).

An example (Example 6) of the current detection apparatus according to the third embodiment is shown in FIG. Components having the same functions as those of the current detection device according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the sixth embodiment, the load resistor R13a is connected between the first input terminal 21 and the ground terminal 23 of the detection means 20e. The detection means 20e has the same function as the detection means 20, but the diode is only the CD 28 and does not have the second input terminal 22. Therefore, only the positive pulse of the pulse voltage generated at both ends of the load resistor R13a is half-wave rectified by the diode CD28 to drive the transistor TR27.

  In the sixth embodiment, when the peak value of the pulse voltage is the sum of the forward voltage between the diode CD28 and the base-emitter of the transistor TR27 (for example, 1.4 V) or more, the current for switching the transistor TR27 is two. Flowing from the secondary coil L12 to the diode CD28 and the base / emitter of the transistor TR27, a pulse signal similar to Out in FIG. 5A is output to the output terminal 25 of the detection means 20e. However, in Example 6, the rectified output waveform of the diode CD28 is about 16.7 ms which is the same as the period of the alternating current Ia as shown in FIG. 2E, and the pulse signal output from the detecting means 20e is also about 16.7 ms. . Therefore, the signal conversion means 30 needs to generate a pulse having a pulse width of about 16.7 mS or more, for example, 18 mS. Thus, the width of the pulse generated by the signal conversion means 30 needs to be equal to or longer than the cycle of the alternating current Ia, and is preferably set within two cycles of the alternating current Ia.

  That is, according to the current detection device of Example 6 described above, with a simple circuit configuration, it can be detected that the alternating current has flowed above a predetermined value within the period of the alternating current, and the alternating current has become below the predetermined value. Detection can be performed without delay from one to two cycles of the alternating current.

The current detection device (Example 7) shown in FIG. 7B is a modification of Example 6, and the same reference numerals are given to components having the same functions as those of the current detection devices of Examples 1 and 6. The description is omitted.
In the seventh embodiment, the detection unit 20f has the same function as the detection unit 20e of the sixth embodiment, but is different from the detection unit 20e in that the diode CD28 is not provided. In the seventh embodiment, when the positive peak value of the pulse voltage is equal to or higher than the forward voltage (for example, 0.7 V) between the base and the emitter of the transistor TR27, the transistor TR27 performs the switching operation. The detection threshold value is smaller than that of the current detection device of the sixth embodiment. As in the sixth embodiment, a pulse having the same cycle (about 16.7 ms) as the cycle of the alternating current Ia is output from the detection means 20f.

  In any of the current detection devices of the first to seventh embodiments, a base current limiting resistor may be connected in series to the base of the transistor. The present invention is not limited to the above-described embodiment, and can be modified and implemented without departing from the spirit of the present invention.

It is a figure which shows schematic structure of the electric current detection apparatus which concerns on 1st Embodiment based on this invention, its operation | movement, and a waveform. It is a figure which shows the example of a waveform of the primary side current (alternating current) and the secondary side voltage (pulse-like voltage) which flow into a current transformer in this invention. It is a characteristic curve explaining the magnetomotive force and magnetic flux density of the current transformer in this invention. It is a figure which shows the example of an actual measurement waveform of the pulse voltage which the current transformer in this invention generate | occur | produces. FIGS. 5A to 5C are diagrams showing a schematic configuration of the current detection device (Examples 1 to 3) according to the first embodiment. FIGS. 6A and 6B are diagrams showing a schematic configuration of a current detection device (Examples 4 and 5) according to the second embodiment. FIGS. 7A and 7B are diagrams showing a schematic configuration of a current detection device (Examples 6 and 7) according to the third embodiment. It is a figure which shows the example of schematic structure of the conventional electric current detection apparatus, and the waveform example of the primary side electric current and secondary side voltage.

Explanation of symbols

Ia AC current T10 Current transformer L11 Current transformer primary coil L12 Current transformer secondary coil R13, 14, 13a Load resistance (secondary load)
20, 20a, 20b, 20c, 20d, 20e, 20f Detection means 30 Signal conversion means

Claims (3)

An electric current is induced in the secondary coil of the current transformer by flowing an alternating current through the primary coil of the current transformer, and the alternating current is detected by detecting the electromotive force.
When the secondary side alternating current induced in the secondary side coil is regulated by using a high load resistance value that makes it possible to obtain a voltage having a high pulse peak value, and the polarity of the alternating current is reversed A secondary load of the current transformer that induces a pulsed voltage in the secondary coil corresponding to a value of the primary current;
Detecting means for detecting that the amplitude of the pulse voltage is equal to or greater than a predetermined amplitude;
Signal converting means for outputting a continuous signal when the detecting means detects that the amplitude of the pulsed voltage is equal to or greater than a predetermined amplitude; and
A current detection device comprising: An electric current is induced in the secondary coil of the current transformer by flowing an alternating current through the primary coil of the current transformer, and the alternating current is detected by detecting the electromotive force.
When the secondary side alternating current induced in the secondary side coil is regulated by using a high load resistance value that makes it possible to obtain a voltage having a high pulse peak value, and the polarity of the alternating current is reversed Detecting means for inducing a pulsed voltage in the secondary coil and detecting that the amplitude of the pulsed voltage is equal to or greater than a predetermined amplitude;
A signal converting means for outputting a continuous signal when the detecting means detects that the amplitude of the pulsed voltage is equal to or greater than a predetermined amplitude; and
A current detection device comprising:   The detecting means detects that the positive and negative pulses of the pulse voltage have a predetermined amplitude or more, or the positive or negative pulse of the pulse voltage has a predetermined amplitude or more. The current detection device according to claim 1, wherein the current detection device is detection means for detecting.

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