JP2015232489A - Current measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current measuring device in which a magnetic material core of a current sensor is not magnetized at power-on and power shutdown.SOLUTION: A current measuring device comprises: a magnetic material core magnetically coupled with a conductor through which a measured current flows; and a current detection circuit detecting current using a Hall-effect element. The current measuring device further comprises: a feedback coil wound around the magnetic material core; a voltage current conversion circuit receiving a signal outputted from the Hall-effect element, and causing, to flow through the feedback coil, a current in proportion to the measured current and in a direction for cancelling a magnetic flux generated by the measured current; difference detection means for detecting that an absolute value difference in voltages of plus power and minus power of a bipolar power source is equal to or more than a predetermined value; and switching means for cutting current flowing to the feedback coil based on an output of the difference detection means. Magnetization of the magnetic material core is prevented at power-on and power shutdown.

Description

  The present invention relates to a direct current measuring device, and more particularly to a direct current measuring device including a current sensor using a Hall effect element.

  Conventionally, various current measurement circuits using Hall effect elements have been proposed. For example, Patent Document 1 below discloses a watt-hour meter using a Hall effect element. This watt-hour meter outputs a Hall voltage corresponding to the product of the measurement voltage and the measurement current by the Hall element, and inverts the positive / negative polarity of the Hall voltage at every predetermined period by the switching means SWa1 to SWb2, thereby differential amplification means And the polarity of the differential amplification output is inverted again by the inverting means to the state where the polarity inversion by the switching means has returned, and is integrated by the integrating means. The Hall element has the same polarity as the Hall element. Two Hall elements that output an unbalanced voltage with a polarity different from the voltage are used, and the unbalanced voltage adjusting means adjusts the two Hall elements so that the unbalanced voltages are equal to each other. Thus, the differential amplification outputs of the two Hall elements are added.

JP 2001-159646 A

In the current measuring circuit using the conventional Hall effect element as described above, a magnetic core having a whole or ring shape is used in order to couple the magnetic field generated by the current to be measured and the Hall effect element. However, in the case of a DC current measuring device, the magnetic core has a hysteresis characteristic. When a strong magnetic field is applied, the magnetic core is magnetized and the characteristic changes. For example, even if there is no current to be measured, residual magnetic flux remains and the measurement error is large. There is a problem of becoming.
In view of this, a method has been proposed in which a feedback circuit that causes a current in a direction to cancel the magnetic flux due to the current to be measured is provided in a feedback coil wound around the magnetic core so that a strong magnetic field is not applied to the magnetic core.

  However, in the current measuring device including the feedback circuit as described above, the rise time or the fall time of the positive power source and the negative power source may be different depending on the difference in the + − load of the bipolar power source circuit. As a result, when the power source of the current measuring device is turned on or off, an undesired current flows through the feedback coil and the magnetic core is magnetized.

  An object of the present invention is to solve the above-mentioned conventional problems and to provide a current measuring device in which the magnetic core of the current sensor is not magnetized even when the device is turned on or off.

  A current measuring device of the present invention includes a magnetic core magnetically coupled to a conductor through which a current to be measured flows, and a current measuring device including a current detection circuit that detects a magnetic flux passing through the magnetic core using a Hall effect element In this embodiment, a feedback coil wound around the magnetic core and a bipolar power source are used, and a differential amplifier circuit to which a signal output from the Hall effect element is input is proportional to the current to be measured. A voltage-current converter that outputs a signal to the feedback coil in a direction that is proportional to the measured current and that cancels out the magnetic flux generated in the magnetic core by the measured current; and the voltage-current converter Based on the difference detection means for detecting that the difference between the absolute values of the positive power supply and the negative power supply voltage of the bipolar power supply is greater than or equal to a predetermined value, and the output of the difference detection means To mainly characterized in that a switch means for interrupting the flow of current to the feedback coil.

  Further, in the above-described current measuring device, the difference detecting means also outputs a signal indicating that there is a difference only when the absolute value of the negative power source is larger than the positive power source voltage by a predetermined value or more. There is. Further, in the above-described current measuring device, the difference detecting means has a resistance circuit composed of a plurality of resistors connected in series between the minus power source and the plus power source, and a base connected to a connection point between the resistors of the resistor circuit. The switch means is composed of a photo MOS relay.

  According to the present invention, it is possible to prevent the magnetic core from being magnetized due to an undesired current flowing through the feedback coil when the power is turned on or when the power is turned off, thereby preventing an increase in measurement error. There is an effect that the measurement accuracy can be improved.

FIG. 1 is a block diagram showing a configuration of a current measuring apparatus according to the present invention. FIG. 2 is a block diagram showing the configuration of the current sensor circuit in the present invention. FIG. 3 is a circuit diagram showing the configuration of the current sensor circuit in the present invention. FIG. 4 is a waveform diagram showing the operation of the magnetization preventing circuit in the present invention. FIG. 5 is a circuit diagram showing a second embodiment of the magnetization preventing circuit according to the present invention. FIG. 6 is a circuit diagram showing a third embodiment of the magnetization preventing circuit according to the present invention. FIG. 7 is a circuit diagram showing a fourth embodiment of the magnetization preventing circuit according to the present invention. FIG. 8 is a circuit diagram showing a fifth embodiment of the magnetization preventing circuit according to the present invention. FIG. 9 is a circuit diagram showing a sixth embodiment of the magnetization preventing circuit according to the present invention.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a current measuring apparatus according to the present invention. The current measuring device includes a magnetic coupling device and a current sensor circuit 40 described later. The magnetic coupling device is wound around the magnetic cores 43 and 44 magnetically coupled to the conductor (electric wire) 45 through which the current to be measured flows, the Hall effect element 41 disposed in the gap between the magnetic cores 43, and the magnetic core 43. Feedback coil 42.

  The B-shaped magnetic core is divided, and one of the magnetic cores 44 is removed and the conductor 45 is passed through the internal space. The conductor 45 can be magnetically coupled. Further, when feedback (servo) control described later is performed, the magnetic flux density inside the magnetic cores 43 and 44 is small, and the magnetic cores 43 and 44 are attached to the conductor 45 during operation of the device under measurement. However, the magnetic cores 43 and 44 are not magnetized.

  FIG. 2 is a block diagram showing the configuration of the current sensor circuit 40 in the present invention. The voltage-current conversion circuit 52 is composed of a differential amplifier circuit having a predetermined amplification factor to which a signal output from the Hall effect element 41 is input. The output signal of the voltage / current conversion circuit 52 is connected to one end of a resistor 54 via a magnetization preventing circuit 53 and a feedback coil 42 described later, and the other end of the resistor 54 is grounded. Therefore, a current approximately proportional to the current flowing through the conductor 45 flows through the resistor 54, and a voltage approximately proportional to the current flowing through the conductor 45 is generated at both ends of the resistor 54. One end of the resistor 54 is output as a current sensor output signal to an external measuring device (not shown). In the measuring device, the current value of the conductor 45 is obtained by reading the output voltage from the current sensor circuit 40.

  The voltage-current conversion circuit 52 is connected so that a current proportional to the current to be measured passing through the magnetic cores 43 and 44 and flowing in the direction to cancel the magnetic flux due to the current to be measured flows through the feedback coil 42. Therefore, a current proportional to the current flowing through the conductor 45 flows through the feedback coil 42, but negative feedback is applied. Therefore, the magnetic flux density inside the magnetic cores 43 and 44 is higher than the magnetic flux density due to the current flowing through the conductor 45. It is a fairly small value. As a result, since the magnetic flux density inside the magnetic cores 43 and 44 does not become a large value, the magnetic cores 43 and 44 are not magnetized, and the occurrence of measurement errors due to magnetization can be prevented.

  If the rise times of the two power sources, the positive power source and the negative power source, are different when the current sensor circuit 40 is turned on and off, the two power sources, + Vb and -Vb, also have different rise times. Current may flow and the magnetic cores 43 and 44 may be magnetized. The magnetization prevention circuit 53 is a circuit that disconnects the connection between the voltage-current conversion circuit 52 and the feedback coil 42 in order to prevent this magnetization, as will be described in detail later.

  The power supply circuit 55 generates + Vb and −Vb (for example, + 12V and −12V) power supplies from a positive power supply and a negative power supply, which are bipolar power supplies supplied from a power supply circuit of a device (not shown), and further generates a + Vh (for example, This is a known constant voltage power supply circuit that generates a power supply of + 3V).

  FIG. 3 is a circuit diagram showing a configuration of the current sensor circuit 40 in the present invention. The voltage-current conversion circuit 52 to which a signal output from the Hall effect element 41 is input includes a differential amplification circuit having a predetermined amplification rate composed of two operational amplifiers 62 and 63, and a demagnetization signal generation circuit 72.

The differential amplifier circuit uses a bipolar power supply, inputs a voltage signal proportional to the current to be measured output from the Hall effect element 41, and substantially supplies the current to be measured to the feedback coil 42 and the resistor 54 serving as a load resistance. It functions to pass a proportional current in the opposite direction. Accordingly, since negative feedback is applied via the feedback coil 42, the magnetic flux density inside the magnetic cores 43 and 44 is considerably smaller than the magnetic flux density caused by the current flowing through the conductor 45. As a result, since the magnetic flux density inside the magnetic cores 43 and 44 does not become a large value, the magnetic cores 43 and 44 are not magnetized, and the occurrence of measurement errors due to magnetization can be prevented.
In the embodiment, the bipolar power supplies + Vb and -Vb having the same absolute voltage value are used. However, the differential amplifier circuit may be used even if the positive power supply voltage and the negative power supply voltage of the bipolar power supply are not equal. Can operate normally as long as they do not enter the saturation region, and the present invention can be implemented.

  The demagnetization signal generation circuit 72 normally has an output of 0 volts, but is activated by a demagnetization control signal output from an external device (not shown), and is attenuated by alternating polarity signals (polarized at a predetermined cycle and with time). AC signal whose amplitude is reduced to 0) is generated. Any known method can be adopted as a method for generating the attenuated AC signal. For example, an AC signal generator (Japanese Patent Laid-Open No. 2011-176661) filed by the applicant of the present application and published may be used. .

  When the attenuated AC signal is output from the degaussing signal generation circuit 72 during the feedback control, the operational amplifier 63 adds a voltage signal proportional to the attenuated AC signal and the current to be measured, and the feedback coil 42 is proportional to the current to be measured. Current "+" current proportional to the attenuated AC signal "flows in the opposite direction. However, since the magnetic flux density due to the “current proportional to the measured current” almost cancels out the magnetic flux density due to the measured current, the magnetic flux density in the magnetic cores 43 and 44 is almost due to the “current proportional to the attenuated AC signal”. Magnetic flux cores 43 and 44 are demagnetized due to the magnetic flux density. The degaussing signal generation circuit 72 is not an essential circuit for implementing the present invention and may be omitted.

  The anti-magnetization circuit 53 includes a known photo MOS relay element 71 for disconnecting the connection between the voltage-current conversion circuit 52 and the feedback coil 42, and the voltage value of the + Vb power source is a predetermined value than the absolute value of the voltage of the -Vb power source. It includes a transistor 69 that is turned on when lower than this. The photo MOS relay element 71 is an A contact type (normally off type), and when the built-in light emitting diode is turned on, the output terminals are turned on (low resistance).

  The base of the transistor 69 is connected to a connection point between resistors of two or more resistor circuits connected in series between the + Vb power source and the −Vb power source of the bipolar power source. The resistor 66 and the resistor 67 are resistors having the same value, and the resistor 68 is a resistor having a larger value. Accordingly, the combined resistance of the resistors 67 and 68 is a little smaller than that of the resistor 66. When the voltages of the + Vb power source and the −Vb power source are normally applied, a PNP type transistor 69 is formed by a resistor circuit composed of three resistors. Is maintained at a slightly higher voltage (for example, about −0.3 V) than a voltage at which the transistor 69 is turned on (for example, −0.6 V), and the transistor 69 is turned off. is there.

  As a result, a current flows through the path of the ground, the light emitting diode, the resistor 70, and the Vb power source, and the light emitting diode of the photo MOS relay element 71 is turned on, so that the photo MOS relay element 71 is maintained in an on state. The diode connected to the base is for protecting the transistor 69 from destruction, and the capacitor is for absorbing noise, and there is almost no delay due to this capacitor.

  FIG. 4 is a waveform diagram showing the operation of the magnetization preventing circuit according to the present invention when the power is turned on and when the power is turned off. When the current measuring device is turned on (left side in FIG. 4), the load of the + Vb power supply is generally heavier, so that the rise of the + Vb power supply is delayed from the −Vb power supply. At this time, during the period when the voltage value of the + Vb power source is lower than the absolute value of the voltage of the −Vb power source by a predetermined value or more, the voltage at the connection point of the resistor 66 and the resistor 67 becomes low, and the base current of the PNP type transistor 69 flows. Thus, the transistor 69 is turned on. Then, the voltage between the input terminals of the photo MOS relay element 71 becomes almost 0 V, and the current stops flowing through the light emitting diode connected between the input terminals, and the light is turned off.

  Thereafter, when the + Vb power supply rises, the transistor 69 is turned off, and a current flows through the light emitting diode of the photoMOS relay element 71 to light it. Then, the photo MOS relay element 71 is in the on state, that is, the output conductivity becomes a predetermined value or more. Accordingly, the photoMOS relay element 71 is turned on after the + Vb power supply is turned on.

  When the power is shut off (right side in FIG. 4), the fall of the + Vb power supply is faster than that of the -Vb power supply. At this time, when the voltage value of the + Vb power source becomes lower than the absolute value of the voltage of the −Vb power source by a predetermined value or more, the voltage at the connection point of the resistor 66 and the resistor 67 becomes low, and the base current of the PNP type transistor 69 flows. 69 is turned on. Then, no current flows through the light emitting diode of the photo MOS relay element 71 and the light is turned off, so that the photo MOS relay element 71 is turned off.

  Thereafter, when the difference between the voltage value of the + Vb power supply and the absolute value of the voltage of the −Vb power supply becomes small, the transistor 69 is turned off. At this time, the absolute value of the voltage of both the + Vb power supply and the −Vb power supply decreases. Therefore, an undesired current that causes the magnetic cores 43 and 44 to be magnetized does not flow through the feedback coil 42.

  FIG. 5 is a circuit diagram showing a second embodiment of the magnetization preventing circuit according to the present invention. In the first embodiment, the A contact type (normally off type) is used as the photo MOS relay element 71, but in the second embodiment, the B contact type (normally on type) is used as the photo MOS relay element. It is an example. The difference from the first embodiment is that a B-contact type is used as the photo MOS relay element 72 and that the transistor 113 is connected in series with the light emitting diode of the photo MOS relay element 72.

  Normally, the transistor 113 is off, the light emitting diode is off, and the photoMOS relay element 72 is on. In a period in which the voltage value of the + Vb power supply is lower than the absolute value of the voltage of the −Vb power supply by a predetermined value or more, the transistor 113 is turned on, the light emitting diode is turned on, and the photoMOS relay element 72 is turned off. Accordingly, magnetization can be prevented as in the first embodiment.

  FIG. 6 is a circuit diagram showing a third embodiment of the magnetization preventing circuit according to the present invention. In the first and second embodiments, it is assumed that the rise of the + Vb power supply is slower than the rise of the −Vb power supply and the fall of the + Vb power supply is faster than the fall of the −Vb power supply. In this example, the rise of the Vb power supply is slower than the rise of the + Vb power supply. The difference from the first embodiment is that the configurations of the resistance circuits 105 to 107 are + -inverted and that an NPN type transistor is used as the transistor 108.

  Normally, the transistor 108 is off, the light emitting diode is lit, and the photoMOS relay element 71 is on. In a period in which the absolute value of the voltage value of the −Vb power supply is lower than the voltage of the + Vb power supply by a predetermined value or more, the transistor 108 is turned on, the light emitting diode is turned off, and the photoMOS relay element 71 is turned off. Accordingly, magnetization can be prevented as in the first embodiment.

  FIG. 7 is a circuit diagram showing a fourth embodiment of the magnetization preventing circuit according to the present invention. In the third embodiment, the A contact type is used as the photoMOS relay element 71, but in the fourth embodiment, the B contact type is used as the photoMOS relay element. The difference from the third embodiment is that a B contact type is used as the photoMOS relay element 72 and that the transistor 103 is connected in series with the light emitting diode of the photoMOS relay element 72.

  Normally, the transistor 103 is off, the light emitting diode is off, and the photoMOS relay element 72 is on. In a period in which the absolute value of the voltage value of the −Vb power supply is lower than the voltage of the + Vb power supply by a predetermined value or more, the transistor 103 is turned on, the light emitting diode is turned on, and the photoMOS relay element 72 is turned off. Accordingly, magnetization can be prevented as in the first embodiment.

  FIG. 8 is a circuit diagram showing a fifth embodiment of the magnetization preventing circuit according to the present invention. In the first to fourth embodiments, it is premised that either the rise of the + Vb power supply or the rise of the −Vb power supply is always slower than the other, but the fifth embodiment is any of the rise of the + Vb power supply and the rise of the −Vb power supply. This is an example applicable to the case where one of them is slower than the other. In this embodiment, the output of the magnetization preventing circuit of the first embodiment shown in FIG. 3 and the output of the magnetization preventing circuit of the third embodiment shown in FIG. 6 are connected in series. The resistance circuits 120 to 122 are shared by both magnetization prevention circuits.

  Normally, both the NPN type transistor 123 and the PNP type transistor 124 are in an off state, both the light emitting diodes are lit, and the photoMOS relay element 72 is in an on state. In a period in which the voltage value of the + Vb power supply is lower than the absolute value of the voltage of the −Vb power supply by a predetermined value or more, the transistor 124 is turned on, the light emitting diode is turned off, and the photoMOS relay element 71-2 is turned off.

  Further, the transistor 123 is turned on during a period in which the absolute value of the voltage value of the −Vb power supply is lower than the voltage of the + Vb power supply by a predetermined value or more, the light emitting diode is turned off, and the photoMOS relay element 71-1 is turned off. Become. Therefore, in the fifth embodiment, magnetization can be prevented even when either the rise of the + Vb power supply or the rise of the -Vb power supply is slower than the other.

  FIG. 9 is a circuit diagram showing a sixth embodiment of the magnetization preventing circuit according to the present invention. As in the fifth embodiment, the sixth embodiment is an example applicable to the case where either the rise of the + Vb power supply or the rise of the −Vb power supply is slower than the other. In this embodiment, the output of the magnetization preventing circuit of the second embodiment of FIG. 5 and the output of the magnetization preventing circuit of the fourth embodiment shown in FIG. 7 are connected in series. The resistance circuits 130 to 132 are shared by both magnetization preventing circuits.

  Normally, both the NPN type transistor 133 and the PNP type transistor 134 are off, the light emitting diodes are both extinguished, and the photoMOS relay element 72 is on. In a period in which the voltage value of the + Vb power supply is lower than the absolute value of the voltage of the −Vb power supply by a predetermined value or more, the transistor 134 is turned on, the light emitting diode is turned on, and the photoMOS relay element 72-2 is turned off.

  In addition, the transistor 133 is turned on in a period in which the absolute value of the voltage value of the −Vb power supply is lower than the voltage of the + Vb power supply by a predetermined value or more, the light emitting diode is turned on, and the photoMOS relay element 72-1 is turned off. Become. Therefore, in the sixth embodiment, magnetization can be prevented even when either the rise of the + Vb power supply or the rise of the -Vb power supply is slower than the other.

  The present invention can be applied to any apparatus that needs to measure a direct current with high accuracy.

DESCRIPTION OF SYMBOLS 40 ... Current sensor circuit 41 ... Hall effect element 42 ... Feedback coil 43 ... Magnetic body core 44 ... Magnetic body core

Claims (3)

In a current measuring device including a magnetic core magnetically coupled to a conductor through which a current to be measured flows, and including a current detection circuit that detects a magnetic flux passing through the magnetic core using a Hall effect element,
A feedback coil wound around the magnetic core;
Using a bipolar power supply, comprising a differential amplifier circuit to which a signal output from the Hall effect element is input, outputting a signal proportional to the measured current, proportional to the measured current, and A voltage-current conversion circuit for passing a current in a direction to cancel the magnetic flux generated in the magnetic core by the measured current to the feedback coil;
A difference detection means for detecting that the difference between the absolute values of the positive power source and the negative power source voltage of the bipolar power source of the voltage-current conversion circuit is a predetermined value or more;
A current measuring apparatus comprising: a switching unit that cuts off a current flowing to the feedback coil based on an output of the difference detecting unit.   2. The current measurement according to claim 1, wherein the difference detection unit outputs a signal indicating that there is a difference only when the absolute value of the negative power source is larger than the voltage of the positive power source by a predetermined value or more. apparatus.   The difference detecting means includes a resistor circuit composed of a plurality of resistors connected in series between the minus power source and the plus power source, and a transistor having a base connected to a connection point between the resistors of the resistor circuit. 2. The current measuring device according to claim 1, comprising a photo MOS relay.

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