JPWO2015119087A1 - DC watt-hour meter and current sensor calibration method - Google Patents

Abstract

Provided are a DC watt-hour meter and a current sensor calibration method using a DC current measurement circuit capable of mounting, calibrating, and demagnetizing a current sensor even when a device under measurement is in operation. The DC watt-hour meter is a ring that can be divided, and is provided with a magnetic core having a feedback coil and a calibration coil, and a signal output from a Hall effect element is input to cancel the magnetic flux generated in the magnetic core by the current to be measured. A differential amplifier circuit for flowing a current in the direction to the feedback coil, a constant current circuit capable of flowing a desired amount of current with a desired polarity, means for connecting the calibration coil and the constant current circuit, and generation of a reference voltage A circuit and its switching means, an A / D conversion means, an electric energy calculation means, and a control means for calculating the electric energy and calibrating the DC current detection circuit. Remote calibration and degaussing of the current sensor of the DC watt-hour meter is possible even when the device under measurement is in operation.

Description

  The present invention relates to a DC watt-hour meter and a current sensor calibration method, and more particularly to a DC watt-hour meter including a DC current sensor using a Hall effect element and a calibration method thereof.

  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 measurement circuit using the conventional Hall effect element as described above, the current sensor is mounted, the current sensor is calibrated, or the current sensor Hall effect element is mounted while the device under test is in operation. The magnetic core that is being used cannot be degaussed, so it is necessary to stop the device under test or remove the current sensor for calibration and demagnetization, and it is necessary to go to the site and work. At the same time, there is a problem that the measurement is temporarily interrupted.

  The object of the invention is to solve the above-mentioned conventional problems, and to measure and calibrate a DC watt-hour meter and a current sensor using a DC current measuring circuit capable of mounting, calibrating and demagnetizing a current sensor even when the device under test is in operation. It is to provide a method.

  A DC watt-hour meter according to the present invention includes a magnetic core that is magnetically coupled to a conductor through which a current to be measured flows, and includes a current detection circuit that detects a magnetic flux passing through the magnetic core using a Hall effect element. The current detection circuit is (1) annular, and includes a wound feedback coil and a calibration coil. The magnetic core (2) differential amplification to which a signal output from the Hall effect element is input. A voltage-current conversion circuit comprising a circuit and passing a current in a direction to cancel the magnetic flux generated in the magnetic core by the measured current to the feedback coil. (3) A current signal output for outputting a voltage signal proportional to the measured current A current measuring circuit for measuring an output signal of the current signal output circuit, a voltage measuring circuit for measuring an input voltage to be measured, and a control means A constant current circuit capable of flowing a desired amount of current with a desired polarity based on the control, a connection means for connecting the calibration coil and the constant current circuit based on the control from the control means, and a predetermined A reference voltage generating circuit for generating a voltage of the reference voltage, a switching means for switching a voltage to be measured input based on control from the control means and an output voltage of the reference voltage circuit to connect to the voltage measuring circuit, and the current A measurement circuit and A / D conversion means for converting the output voltage of the voltage measurement circuit into a digital signal, a power amount calculation means for calculating a power amount from the digital signal, and a power amount by controlling each circuit and means And a control means for calibrating the DC current detection circuit.

  In the above-mentioned DC watt-hour meter, the calibration process first measures the current value to be measured and records it as a current value before calibration, and then the measured current value before calibration is equal to or greater than a predetermined value. When a measured current value before calibration is less than a predetermined value, a predetermined value is added in the same direction as the measured current. It is also possible to measure the calibration current value by supplying a current, and then determine whether the calibration current value is normal or not based on whether the pre-calibration current value and the additional current value are added. There are features.

  Further, in the above-described DC watt-hour meter, after determining whether or not the calibration process is normal, the additional current is stopped and the measured current value is measured again. This measured value is different from the pre-calibration current value by a predetermined value or more. In some cases, the calibration process is performed again.

  Further, in the above-described DC watt-hour meter, the voltage-current conversion circuit further includes a degaussing signal generation circuit capable of flowing a degaussing current to the feedback coil based on control from the control means. There are features.

In the DC watt-hour meter, the degaussing signal generation circuit generates a damped AC signal, and the voltage-current conversion circuit cancels the magnetic flux generated in the magnetic core by the measured current in the feedback coil. Another characteristic is that a damped alternating current flows in addition to the current.
Further, the above-described DC watt-hour meter is characterized in that the magnetic core can be divided.

  The current sensor calibration method of the present invention includes a DC current detection circuit for detecting a magnetic flux passing through a magnetic core magnetically coupled to a conductor through which a current to be measured flows using a Hall effect element, and a calibration wound around the magnetic core. A constant current circuit capable of flowing a desired amount of current with a desired polarity based on control from the control means, and the calibration coil and the constant current circuit based on control from the control means. In the DC watt-hour meter provided with a connecting means for connecting, a step of measuring a measured current value and recording it as a pre-calibration current value, controlling the constant current circuit and the connecting means, and measuring the pre-calibration current When the value is greater than or equal to a predetermined value, an additional current of a predetermined value is passed through the calibration coil in the direction opposite to the current to be measured. When the measured current value before calibration is less than a predetermined value, the current to be measured It is normal depending on a step of flowing a predetermined value of additional current in the same direction, a step of measuring a calibration current value, and whether the calibration current value is a value obtained by adding the pre-calibration current value and the additional current value. The main feature is to include a step of determining whether or not.

  Further, in the current sensor calibration method described above, the flow of the additional current is stopped after the step of measuring the calibration current value, the current value after calibration is measured, and the current value after calibration is the current value before calibration. Another characteristic is that the calibration process is re-executed when the value differs by a predetermined value or more.

The present invention has the following effects.
(1) Since the calibration coil wound around the magnetic core is provided, the current sensor of the DC watt-hour meter can be remotely calibrated even when the device under measurement is in operation.
(2) A DC watt hour meter can be mounted even when the device under measurement is in operation by providing a split core and performing negative feedback control.
(3) Remote demagnetization processing is possible even when the device under test is in operation by using a servo circuit that applies a current in a direction to cancel the magnetic flux due to the current to be measured to the feedback coil wound around the magnetic core. .

FIG. 1 is a block diagram showing the configuration of a system using a DC watt-hour meter according to the present invention. FIG. 2 is a block diagram showing the configuration of the DC watt-hour meter of the present invention. FIG. 3 is a flowchart showing the processing contents 1 of the CPU of the DC watt-hour meter of the present invention. FIG. 4 is a flowchart showing the processing contents 2 of the CPU of the DC watt-hour meter of the present invention. FIG. 5 is a block diagram showing the configuration of the current sensor device according to the present invention. FIG. 6 is a block diagram showing the configuration of the current sensor circuit in the present invention. FIG. 7 is a circuit diagram showing a configuration of a current sensor circuit according to the present invention. FIG. 8 is a flowchart showing the load on calibration processing of the CPU of the DC watt-hour meter of the present invention. FIG. 9 is a flowchart showing the load off calibration processing of the CPU of the DC watt-hour meter of the present invention.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of an example of use of the DC watt-hour meter of the present invention. The DC power supply 11 converts commercial AC power into DC and supplies it to a plurality of loads 12 of DC power. The DC watt-hour meter 10 of the present invention can be used for applications that measure the amount of power supplied to these load devices.

  The DC watt-hour meter 10 is supplied with DC power from the power supply device 16 via a communication LAN cable. In the DC watt-hour meter 10 of the present invention, the communication line has a specification of RS485, not a LAN, and is bus-connected in the power supply device 16. However, connectors, cables, and power supply are supplied by the same wiring as the well-known LAN PoE power supply standard, and power supply and RS485 communication are performed by using a general-purpose PoE power supply device 16 and a general-purpose LAN cable. Can do.

  The host device PC 17 can control the DC watt-hour meter 10 via a cable and can read various measurement values. Note that Ethernet (registered trademark) may be adopted as a communication standard. Since the calibration power supply 18 is used for the calibration process, only one circuit of one DC watt-hour meter 10 can execute the calibration process at the same time. Accordingly, the PC 17 transmits a command to each DC watt-hour meter 10 and controls each DC watt-hour meter 10 so as to perform calibration processing one by one and one circuit at a time.

  The DC power supply is supplied from the DC power supply 11 to the load 12 by two electric wires. Although the details will be described later, the current sensor device 13 is magnetically coupled to one of the two wires connected to the load 12 and measures the value of the current flowing through the wire. The voltage input wire 14 is connected to two wires connected to the load 12, and the voltage value is measured by the DC watt-hour meter 10. The DC watt-hour meter 10 calculates the electric energy from the measured current value and voltage value.

Only one power supply device 18 for calibration is provided for a plurality of DC watt-hour meters 10. The control circuit 70 of the calibration power supply device 18 is connected to a plurality of DC watt-hour meters 10 via a communication circuit 73 by, for example, RS485 specification bus type communication lines. The control circuit 70 controls the constant current circuit 71 and the reference voltage circuit 72 based on an instruction from each DC watt-hour meter 10 to generate a DC current having a specified polarity and current value and a predetermined reference voltage. Supplied to DC watt-hour meter 10. Since these currents and voltages are used for calibration of the current sensor and voltage sensor (A / D conversion circuit of the CPU) of the DC watt-hour meter 10, the calibration power supply device 18 needs to be calibrated by a standard device.

  FIG. 2 is a block diagram showing the configuration of the DC watt-hour meter 10 of the present invention. A microcomputer circuit (hereinafter referred to as CPU) 20 is a well-known one-chip microcomputer circuit that is commercially available. The CPU 20 includes a CPU, a ROM, a RAM, a digital input / output circuit, an analog input circuit (multi-channel A / D conversion circuit), a hardware timer circuit, and the like. The ROM stores a program for executing processing to be described later.

  As will be described in detail later, the current sensor device 13 is magnetically coupled to the electric wire, measures the current value flowing through the electric wire using a Hall effect element, and outputs a voltage proportional to the current value flowing through the electric wire. The current measurement circuit 21 amplifies a voltage proportional to the current value output from the current sensor device 13 with a predetermined amplification factor, and outputs the amplified voltage to the analog input terminal of the CPU 20.

  The voltage measurement circuit 22 divides the voltage between the two wires connected to the load 12 inputted by the voltage input wire 14 through a known insulation amplifier at a predetermined rate and outputs it to the analog input terminal of the CPU 20. To do. One circuit for measuring electric energy is composed of one current sensor device 13, current measuring circuit 21, and voltage measuring circuit 22, and the DC watt-hour meter 10 of the present invention is equipped with multiple circuits.

  The pulse output circuit 24 is a circuit that outputs a number of pulses proportional to the measured electric energy to the test connector 30 for the test of the DC watt-hour meter 10. The LCD circuit 25 drives the LCD display device 26 attached to the panel of the DC watt-hour meter 10 so that desired information is displayed based on the control from the CPU 20. The state of the switch 31 comprising a switch mounted on the panel of the DC watt-hour meter 10 for selecting information displayed on the LCD display device 26 and a DIP switch provided on the substrate for calibration etc. Via the CPU 20.

  The communication circuit 27 is a well-known RS485 interface circuit, and communicates with an external device such as the PC 17 via the communication connector 28. The calibration communication circuit 37 is a well-known RS485 interface circuit, and is used to control the calibration power supply device 18. The flash memory circuit 27 is a well-known nonvolatile memory circuit that can be read from and written to by the CPU 20, and is used for storing a measured value (a value of electric energy) at the time of a power failure or the like.

  The power supply circuit 29 generates + 15V and −15V power from the DC power supplied via the communication connector 28, further generates + 5V power from the + 15V power, and −5V power from the −15V power. To each circuit.

  Further, the power supply circuit 29 is provided with a power failure detection circuit that detects that a DC power source is applied by a photocoupler and outputs a power failure detection signal to the CPU 20 when the DC power source is cut off (power failure). ing. When the CPU 20 detects the power failure detection signal, the CPU 20 performs processing for storing the measured value in the flash memory circuit 27.

  The changeover switch 36 may be, for example, a relay device provided for each circuit. Based on the control from the CPU 20, the output line from the constant current circuit 71 of the calibration power supply device 18 and the current sensor device are controlled on a circuit basis. The 13 calibration coils are connected / disconnected, and the input voltage to be measured and the output voltage of the reference voltage circuit 72 of the calibration power supply device 18 are switched and connected to the voltage measurement circuit 22. When the present invention is implemented in one DC watt-hour meter 10, a constant current circuit 71 and a reference voltage circuit 72 may be provided in the DC watt-hour meter 10 as shown by a dotted line in FIG.

  FIG. 3 is a flowchart showing the processing contents 1 of the CPU of the DC watt-hour meter of the present invention. When the power is turned on (including the case of recovering from a power failure), in S10, if there is a measured value (amount of power) stored from the flash memory circuit 27, it is read. This process is a process for continuously counting the measured value when returning from a power failure. In S11, all the display devices are turned on. This is performed to check the display device failure. In S12, it is determined whether or not the initial setting has been completed, and if the determination result is affirmative, that is, if recovery from a power failure, S13 is skipped and the process proceeds to S14, but if negative, the process proceeds to S13. . Note that the initial setting is the setting of calibration information and serial number.

  In S13, it is determined whether or not the initial current is OK (= 0). If the determination result is negative, the process proceeds to an error stop state, but if the determination is affirmative, the process proceeds to S14. Immediately after the power is first turned on, the measured value of the current sensor must be 0.000 A, so a check is performed assuming that the sensor is magnetized or malfunctioned. In S14, it is determined whether or not the internal power supply is normal. If the determination result is negative, the process shifts to an error stop state. If the determination is positive, the process shifts to S15.

  In S15, every time the display switch SW is pressed, the state of the display switch SW is determined in order to display the circuit on the display device. In S16, the weighing state is determined. Weighing state means no measurement (current is almost 0A), weighing / reverse current (reversed connection, power is reversed), power failure (voltage and current are 0) These contents are display functions necessary for the watt-hour meter. In S17, the measurement value is displayed according to the state of the display switching SW.

  In S18, it is determined whether or not there is data received from the PC 17 as the host device. If the determination result is negative, the process proceeds to S27, but if the determination is affirmative, the process proceeds to S19. In S19, it is determined whether or not the received data is a transmission request. If the determination result is negative, the process proceeds to S21, but if the determination is affirmative, the process proceeds to S20. In S20, a data transmission process is performed. In the data transmission process, the received command (request) is analyzed, necessary information is read to generate response information, for example, a response is returned to the PC 17, and the process proceeds to S27.

  In S21, it is determined whether or not the received data is a request for calibration processing. If the determination result is negative, the process proceeds to S25, but if the determination is affirmative, the process proceeds to S22. In S22, it is determined whether or not the load-on calibration process is performed (load-off calibration process). If the determination result is negative, the process proceeds to S24, but if the determination is affirmative, the process proceeds to S23. In S23, a load-on calibration process described later is performed, and the process proceeds to S27. In S24, a load-off calibration process described later is performed, and the process proceeds to S27.

  In S25, it is determined whether the received data is a request for degaussing. If the determination result is negative, the process proceeds to S27, but if the determination is affirmative, the process proceeds to S26. In S26, a degaussing signal generating circuit 72 in the current sensor device 13 to be described later is activated, and after waiting for a time when the attenuated AC signal becomes 0, the process proceeds to S27.

  In S27, it is determined whether or not the switch SW1 on the board is on. If the determination result is negative, the process proceeds to S29, but if the determination is affirmative, the process proceeds to S28. In S28, an unbalanced voltage (offset) calibration process is performed. In S29, it is determined whether or not the switch SW2 on the board is on. If the determination result is negative, the process proceeds to S31, but if the determination is affirmative, the process proceeds to S30. In S30, gain calibration processing is performed.

  In S31, it is determined whether or not the switch SW3 on the substrate is on. If the determination result is negative, the process proceeds to S33, but if the determination is affirmative, the process proceeds to S32. In S32, the circuit abnormality is canceled. In S33, it is determined whether or not the switch SW4 on the board is on. If the determination result is negative, the process proceeds to S14, but if the determination is affirmative, the process proceeds to S34. In S34, the calibration value is initialized.

  FIG. 4 is a flowchart showing the processing contents 2 of the CPU of the DC watt-hour meter of the present invention. The power amount measurement process is repeatedly activated at regular intervals by the hardware timer function of the CPU independently of the main process. In S40, the voltage value and current value of each circuit are read using an A / D converter (ADC) built in the CPU. In S41, the unit of current value is converted. That is, the read binary value is converted into a decimal value. In S42, the unit of voltage value is converted. That is, the read binary value is converted into a decimal value.

  In S43, the power value (= voltage × current) of each circuit is calculated. In S44, the electric energy (Ws) of each circuit is calculated. That is, the current power amount (= current power value × sampling period) is added to the previous power amount value, and the result is stored in the memory. In S45, the average value of the current, voltage and power of each circuit for one second is calculated and stored in the memory.

  In S46, a test pulse is calculated and a test pulse is output. In S47, it is determined whether or not a power failure has been detected. If the determination result is negative, the interrupt process is terminated, but if the determination is affirmative, the process proceeds to S48. In S48, the measured value is stored in the flash memory 27.

  FIG. 8 is a flowchart showing the load on calibration process (S23) of the CPU of the DC watt-hour meter of the present invention. This process is a calibration process for one specific circuit, and the measurement process in FIG. 4 is prohibited during the calibration process. In S60, the current value before calibration of a specific circuit is read. In S61, the power source is switched to the calibration power source. That is, the changeover switch 36 is controlled to connect the calibration coil of a specific circuit and the constant current circuit 71 of the calibration power supply device 18.

  In S62, it is determined whether or not the current value read in S60 is 50% or less of the rating. If the determination result is negative, the process proceeds to S64, but if the determination is affirmative, the process proceeds to S63. In S63, the constant current circuit 71 is controlled by transmitting a command to the control circuit 70 of the calibration power supply device 18 via the calibration communication circuit 37, and the + calibration current, that is, the current in the same direction as the current of the electric wire is controlled. Current is passed through the calibration coil 46. In S64, a negative calibration current is passed through the calibration coil 46.

  For example, when the rating is 100 amperes and the measured current is less than 50 amperes, the constant current circuit 71 is controlled to generate a current corresponding to, for example, +10 amperes as a calibration current. If the measured current is 50 amperes or more, the constant current circuit 71 is controlled to generate a current corresponding to −10 amperes as a calibration current. Note that it is arbitrary how much of the rating is switched between + and − and how much the calibration current flows.

  In S65, the current value after adding the calibration current is read. In S66, the calibration current is stopped. In S67, it is determined whether or not the current value is normal, that is, for example, if the current value before calibration is 30 amperes, whether or not 10 amperes is added to 40 amperes (the error is equal to or greater than a predetermined value). If the result is negative, the process proceeds to S68, but if the result is affirmative, the process proceeds to S69. In S68, the current addition error information is transmitted to the PC 17, and the process ends.

  In S69, the current value after calibration is read. In S70, it is determined whether or not the current value after calibration is normal, that is, whether or not the absolute value of the difference between the current value before calibration and the current value after calibration is within a predetermined value, and the determination result is negative However, if the result is affirmative, the process proceeds to S72. In S71, current fluctuation error information is transmitted to the PC 17, and the process is terminated.

  When the load 12 is a communication device, for example, the current value hardly changes in a short time. If the current change is greater than or equal to a predetermined value before and after the current measurement, the measurement process is restarted according to an instruction from the host device. Therefore, even if the calibration process is performed while the apparatus is operating (load on) by the above-described process, the current sensor device 13 does not exceed the rating, and the calibration current can be measured normally.

  In S 72, the selector switch 36 is controlled to switch to the reference voltage circuit 72 of the calibration power supply device 18. In S73, the voltage value is read. In S74, the changeover switch 36 is controlled to restore the connection. In S75, it is determined whether or not the voltage measurement value is normal, that is, whether or not the absolute value of the difference between the measurement value and the voltage value output from the reference voltage circuit 72 is within a predetermined value, and the determination result is negative. If YES, the process proceeds to S76, but if YES, the process proceeds to S77. In S76, the voltage value error information is transmitted to the PC 17, and the process ends. In S77, the calibration result is transmitted to the PC 17 and the process is terminated. With the above processing, the current and voltage sensors can be calibrated even when the device under measurement is in operation.

  FIG. 9 is a flowchart showing the load off calibration processing of the CPU of the DC watt-hour meter of the present invention. This process is performed after the load is turned off when the load can be turned off or after the current sensor device 13 is removed from the electric wire. This process is a calibration process for one specific circuit, and the measurement process in FIG. 4 is prohibited during the calibration process. In S80, the current value is read. In S81, it is determined whether or not the current value is 0. If the determination result is negative, the process proceeds to S82, but if the determination is affirmative, the process proceeds to S83. In S82, current value error information is transmitted to the PC 17, and the process is terminated.

  In S83, the power source is switched to the calibration power source. That is, the changeover switch 36 is controlled to connect the calibration coil of a specific circuit and the constant current circuit 71 of the calibration power supply device 18. In S84, a calibration current corresponding to + 100% of the rating is passed through the calibration coil. In S85, the calibration current value is read. In S86, the calibration current is stopped. In S87, it is determined whether or not the calibration current value is normal. If the determination result is negative, the process proceeds to S88, but if the determination is affirmative, the process proceeds to S89. In S88, current addition error information is transmitted to the PC 17, and the process is terminated.

In S89, a calibration current corresponding to + 10% of the rating is passed through the calibration coil. In S90, the calibration current value is read. In S91, the calibration current is stopped. In S92, it is determined whether or not the calibration current value is normal. If the determination result is negative, the process proceeds to S93, but if the determination is affirmative, the process proceeds to S94. In S93, current addition error information is transmitted to the PC 17, and the process is terminated.

  In S94, the changeover switch 36 is controlled to switch to the reference voltage circuit 72 of the calibration power supply device 18. In S95, the voltage value is read. In S96, the changeover switch 36 is controlled to restore the connection. In S97, it is determined whether or not the voltage value is normal. If the determination result is negative, the process proceeds to S98, but if the determination is affirmative, the process proceeds to S99. In S98, voltage value error information is transmitted to the PC 17, and the process is terminated. In S99, the calibration result is transmitted to the PC 17 and the process is terminated.

  FIG. 5 is a block diagram showing the configuration of the current sensor device 13 according to the present invention. The current sensor device 13 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 cores 43 and 44. It consists of a rotated feedback coil 42 and a calibration coil 46.

  The annular (b-shaped) magnetic core is divided into a core 44 and a core 43. One of the magnetic cores 44 is removed, a conductor 45 is passed through the internal space, and the magnetic core 44 is attached to the device under test. Can be magnetically coupled to a conductor 45 such as an electric wire even during operation. 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. 6 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 the resistor 54 via the feedback coil 42. This connection point is output to the current measurement circuit 21 as a current sensor output. The other end of the resistor 54 is grounded.

  The voltage-current conversion circuit 52 is connected so that a current in a direction to cancel the magnetic flux due to the current to be measured passing through the magnetic cores 43 and 44 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.

  The power supply circuit 55 generates bipolar power supplies, + Vb and −Vb necessary for the differential amplifier circuit, from the + 15V and −15V power supplies supplied from the power supply circuit 29 of the DC watt-hour meter 10 main body. This is a power supply circuit that generates a power supply of + Vh required for 41. The calibration coil 46 is connected to the changeover switch 36 of the DC watt-hour meter 10 main body.

  FIG. 7 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 factor composed of two operational amplifiers 62 and 63 and a demagnetization signal generation circuit 64.

  The operational amplification circuit functions to input a voltage signal proportional to the current to be measured output from the Hall effect element 41 and to cause a current substantially proportional to the current to be measured to flow through the feedback coil 42 and the resistor 54 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.

  The demagnetization signal generation circuit 72 normally has an output of 0 volts, but is activated by a demagnetization control signal output from the CPU 20, and is switched to a bipolar attenuated alternating current signal (polarized at a predetermined cycle and having an amplitude of 0 with time). AC signal that is reduced to Any known method can be adopted as the method for generating the attenuated AC signal. For example, the present applicant has applied for a patent and disclosed an AC signal generator (Japanese Patent Laid-Open No. 2011-176661), and the CPU Generates two unipolar rectangular waves with slightly different frequencies, and outputs the difference obtained by subtracting the voltage value of the other rectangular wave from the voltage value of one rectangular wave by the bipolar differential amplifier. The AC signal may be generated by a low-pass filter.

  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 present invention is applicable to any apparatus that needs to measure a direct current value with high accuracy.

DESCRIPTION OF SYMBOLS 10 ... DC power meter 11 ... DC power supply 12 ... Load 13 ... Current sensor device 14 ... Electric wire for voltage input 16 ... Power feeding device 17 ... PC (personal computer)
18 ... Power supply for calibration

Claims (8)

In a DC watt hour meter including a magnetic core that is magnetically coupled to a conductor through which a current to be measured flows, and a current detection circuit that detects a magnetic flux passing through the magnetic core using a Hall effect element
The current detection circuit includes the following devices or circuits (1) to (3):
(1) The magnetic core having an annular, wound feedback coil and calibration coil (2) comprising a differential amplifier circuit to which a signal output from the Hall effect element is input, and the device to be measured A voltage-current conversion circuit for passing a current in a direction to cancel the magnetic flux generated in the magnetic core by the current to the feedback coil; and (3) a current signal output circuit for outputting a voltage signal proportional to the current to be measured.
A current measurement circuit for measuring an output signal of the current signal output circuit;
A voltage measuring circuit for measuring the input measured voltage;
A constant current circuit capable of flowing a desired amount of current with a desired polarity based on control from the control means;
Connection means for connecting the calibration coil and the constant current circuit based on control from a control means;
A reference voltage generating circuit for generating a predetermined voltage;
Switching means for switching the voltage to be measured input based on control from the control means and the output voltage of the reference voltage circuit to connect to the voltage measurement circuit;
A / D conversion means for converting the output voltages of the current measurement circuit and the voltage measurement circuit into digital signals, respectively.
Electric energy calculation means for calculating electric energy from the digital signal;
A direct current watt-hour meter comprising: control means for calculating the amount of electric power by controlling each of the circuits and means and calibrating the direct current detection circuit.   The calibration process first measures the current value to be measured and records it as a current value before calibration. Next, when the measured current value before calibration is equal to or greater than a predetermined value, the calibration coil is measured. A predetermined value of additional current is passed in the direction opposite to the current, and if the measured current value before calibration is less than the predetermined value, a predetermined value of additional current is passed in the same direction as the current to be measured to measure the calibration current value. Then, it is determined whether the calibration current value is normal based on whether or not the calibration current value is a value obtained by adding the pre-calibration current value and the additional current value. Force meter.   After determining whether or not the calibration process is normal, the additional current is stopped and the measured current value is measured again. If the measured value differs from the pre-calibration current value by a predetermined value or more, the calibration process is repeated. The DC watt-hour meter according to claim 2.   2. The voltage-current conversion circuit further includes a degaussing signal generation circuit capable of causing a degaussing current to flow through the feedback coil based on control from the control unit. DC watt hour meter.   The degaussing signal generating circuit generates a damped alternating current signal, and the voltage-to-current conversion circuit passes a damped alternating current to the feedback coil in addition to a current in a direction to cancel the magnetic flux generated in the magnetic core by the measured current. The DC watt-hour meter according to claim 4.   The DC magnetic energy meter according to claim 1, wherein the magnetic core is separable. A DC current detection circuit for detecting a magnetic flux passing through a magnetic core magnetically coupled to a conductor through which a current to be measured flows by using a Hall effect element, and a calibration coil wound around the magnetic core; A constant current circuit capable of flowing a desired amount of current with a desired polarity based on the control from the control circuit and a DC power supply comprising a connection means for connecting the calibration coil and the constant current circuit based on the control from the control means. In the force meter,
Measuring the measured current value and recording it as a current value before calibration;
By controlling the constant current circuit and the connection means, when the measured current value before calibration is a predetermined value or more, an additional current having a predetermined value is passed through the calibration coil in a direction opposite to the current to be measured, When the measured current value before calibration is less than a predetermined value, a step of passing an additional current of a predetermined value in the same direction as the current to be measured,
Measuring the calibration current value;
A current sensor calibration method comprising a step of determining whether or not the calibration current value is normal based on whether or not the calibration current value is a value obtained by adding the pre-calibration current value and the additional current value.   Stop the flow of the additional current after the step of measuring the calibration current value, measure the current value after calibration, and if the current value after calibration differs from the current value before calibration by a predetermined value or more, a calibration process The current sensor calibration method according to claim 7, wherein:

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