JP2013200250A - Power measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power measurement device that removes unnecessary components from detection voltage output by a magnetic sensor used for measuring the power supplied from an external power source to a load, in order to perform accurate power measurement.SOLUTION: A magnetic sensor is disposed near part of a load line for supplying power to a load from an external power source, and the magnetic sensor is supplied with current from the external power source. A filter is provided for removing fundamental frequency components and harmonic components from detection voltage output from the magnetic sensor, and load power is obtained on the basis of the resulting DC components.

Description

  The present invention relates to a power measuring device for measuring load power supplied to a load by using a change in a magnetic field that varies with a load current flowing through a load line connecting an external power source to the load.

  As shown in Non-Patent Document 1 and Non-Patent Document 2, a power measuring device designed to obtain power consumed by a load by using a magnetic sensor such as a magnetoresistive element or a Hall element has been proposed. Has been. These magnetic sensors use a phenomenon in which the detection voltage changes due to the influence of magnetism generated by the current flowing from the power source to the load. Since the detection voltage includes a component indicating power, the required power is the detection voltage. Expressed as a function of However, since the detection voltage output from this type of magnetic sensor includes a component that is not directly related to the required power, it is desirable to calculate the power more accurately.

Thin-film wattmeter using magnetic film (The Institute of Electrical Engineers of Japan Magnetics Study Group data VOL.MAG-05No.182) Thin film wattmeter using magnetic film (The Institute of Electrical Engineers of Japan Magnetics Study Group data VOL.MAG-08No.192)

  The present invention has been made in view of the above problems, and its object is to accurately measure the power supplied from an external power source to a load based on the detection voltage output from the magnetic sensor. It is to provide a power measuring device that can be performed.

  In order to realize this object, the power measuring device of the present invention uses a magnetic sensor that outputs a detection voltage that changes under the influence of a magnetic field generated by a load current flowing in a load line, and is consumed by a load. It is a technical problem to remove fluctuation components not related to electric power.

  It is a power measuring device for measuring load power supplied to a load using a change in a magnetic field that varies with a load current flowing through a load line connecting an external power source to the load. The power measuring device includes a magnetic sensor disposed close to a part of the load line, and a power calculator that calculates load power based on a detection voltage output from the magnetic sensor. The magnetic sensor has a current input terminal to which current from an external power source is input. The magnetic sensor is affected by a magnetic field generated by a load current flowing through a load line, and a sensor current flowing through the magnetic sensor itself changes. The detection voltage corresponding to the change in the sensor current is output. The detection voltage includes a DC voltage component, a fundamental frequency component, and a harmonic component. The power measuring device includes a filter that removes a fundamental frequency component and a harmonic component from the detection voltage output from the magnetic sensor.

  The external power source is an AC power source having a predetermined frequency. The filter is preferably a low-pass filter that allows a frequency component less than the frequency of the AC power supply to pass.

The magnetic sensor is composed of a plurality of magnetoresistive elements whose electrical resistance values change under the influence of a magnetic field generated by a load current. It is preferable that a detection voltage corresponding to a change in the resistance value of the magnetoresistive element is output.

  The magnetoresistive element constitutes a full bridge circuit, and the bridge circuit is configured such that a current input terminal thereof is connected to the external power source and the detection voltage is generated between voltage output terminals of the bridge circuit. preferable.

  The power calculator has a voltage average output unit. An adder circuit is provided for obtaining an added voltage obtained by adding the detected voltages over a unit period that is an integral multiple of the period of the AC power supply. It is preferable that the power is calculated based on an average detection voltage obtained by dividing the added voltage by a unit period.

  The power measuring device includes an amplifier that amplifies an analog detection voltage output from the magnetic sensor, an AD converter that converts an output of the amplifier into a digital detection voltage, and a detection voltage output from the magnetic sensor. A gain determination circuit for determining a gain indicating the magnitude of the value. The power measuring device is configured to calculate power based on the digital detection voltage. The gain determination circuit is preferably configured to change an upper limit reference voltage applied to the AD converter based on the gain so that a decomposition level of the AD converter corresponds to a detected voltage.

  The magnetoresistive element is a thin film resistive element, a plurality of thin film resistive elements are arranged on the same sensor arrangement surface, and a line holder for holding a part of the load line in a state parallel to the sensor arrangement surface It is preferable that it is provided.

  It is preferable to include a magnetic field applying means for applying a constant external DC magnetic field to the magnetoresistive elements constituting the full bridge circuit.

  Preferably, the magnetic field applying means is configured to cause the external DC magnetic field to act in a direction orthogonal to a magnetic field generated by a load current flowing through a load line around a load line in a vicinity of the magnetic sensor. It is characterized by that.

  The full bridge circuit is configured such that each magnetoresistive element is positioned on each of four line segments connected to each other at an angle of 90 degrees, and the magnetoresistive elements in each line segment have a meander shape. It is preferable.

  Preferably, the magnetic sensor includes a Hall element, and includes a line holder that holds a part of the load line in a direction perpendicular to the surface of the Hall element.

  A magnetic sensor is disposed close to a part of a load line for supplying power from an external power source to a load, and current from the external power source is supplied to the magnetic sensor. A filter for removing the fundamental frequency component and the harmonic component from the detection voltage output from the magnetic sensor is provided, and the load power is obtained based on the DC component obtained as a result. Thereby, unnecessary components are removed and accurate power measurement is performed.

1 is a schematic perspective view showing a power measuring device according to an embodiment of the present invention. The block diagram which shows the circuit of an electric power measuring apparatus same as the above. The wave form diagram which shows the detection voltage output from the magnetic sensor used with an electric power measuring apparatus same as the above. The graph explaining the system which correct | amends the dispersion | variation in the output characteristic of a magnetic sensor same as the above. (A) The circuit diagram which shows the case where an amplification factor is set small with the gain switching circuit switch which determines the amplification factor of the amplifier used with an electric power measuring device same as the above. (B) The circuit diagram which shows the case where an amplification factor is set largely with the gain switching circuit switch same as the above. (A) (B) (C) The circuit diagram which shows the change of a state when changing to a correction mode from electric power measurement mode in the offset voltage correction | amendment part used with the electric power measurement apparatus same as the above. (D) (E) (F) The circuit diagram which shows the change of a state in the case of shifting to a power measurement mode from correction mode in the offset voltage correction part same as the above. Schematic which shows the full bridge circuit of four magnetoresistive elements which comprise the magnetic sensor same as the above. The schematic plan view which shows the sensor unit containing a magnetic sensor same as the above. The top view which shows the sensor unit used in other embodiment of this invention. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) The side view of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) The partial cross section side view of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) The partial cross section side view of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) The partial cross section side view of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) Sectional drawing of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) Sectional drawing of a sensor unit same as the above. (A) The top view which shows the sensor unit used in other embodiment of this invention. (B) Sectional drawing of a sensor unit same as the above. Schematic which shows the positional relationship of a sensor unit same as the above, a load line, and one part. (A) The top view which shows the magnetic sensor used in other embodiment of this invention. (B) Schematic which shows the bridge circuit comprised with a magnetic sensor same as the above. Schematic which shows the positional relationship of the magnetic sensor and load line which are used in each embodiment same as the above. Schematic which shows the positional relationship of a Hall element and a part of load line when the magnetic sensor used by other embodiment of this invention is comprised with a Hall element.

(First embodiment)
The power measuring device 150 of the present invention measures load power 320 supplied to the load 300 using a change in magnetic field that varies with a load current flowing through a load line 310 that connects an external power source to the load 300. The magnetoresistive element 15 and the hall element 450 are used as elements for detecting a change in the magnetic field. When a current from an external power source is supplied to this type of magnetic sensor 10 and a part of the load line 310 that connects the external power source to the load 300 is disposed close to the magnetic sensor 10, it is generated by the load current flowing through the load line 310. Under the influence of the magnetic field, the current flowing through the magnetic sensor 10 changes. A voltage corresponding to this change is output from the magnetic sensor 10. The detection voltage (V) output from the magnetic sensor 10 is generally expressed as a product of a component (P) representing the power supplied to the load 300 and a parameter (K) unique to the magnetic sensor 10 (V = P · K). Therefore, the load power (P) is obtained by dividing the detected voltage (V) by the parameter (K) (P = V / K). The present invention is configured to measure the power consumed by the load using this principle.

As shown in FIG. 1, the power measuring device 150 of the present invention includes a housing 200 containing the magnetic sensor 10 and a line holder 210 that holds a part of the load line 310 close to the magnetic sensor 10. The housing 200 includes a processing circuit for processing the detection voltage (V) output from the magnetic sensor 10 to obtain the load power (P). By holding a part of the load line 310 to be measured on the line holder 210, the magnetic sensor 10 is configured to be affected by the magnetic field generated in the load line 310. The track holder 210 includes an openable / closable door 220 formed at one end of the housing 200, and a part of the load track 310 is guided to a guide hole 215 formed inside the door 220 with the door 220 opened. Positioning means for maintaining a part of the load line 310 at a constant distance from the magnetic sensor 10 is provided inside the door 220. As positioning means, a spring 214 is used to bring a part of the load line 310 into contact with the peripheral wall of the guide hole 215.

  FIG. 2 shows a circuit of an embodiment of the power measuring device 150 of the present invention. The power measuring device 150 basically includes the magnetic sensor 10, the amplifier 20, the AD converter 40, and the power calculator 100. Composed.

  In this embodiment, a full bridge circuit of four magnetoresistive elements 15 is used as the magnetic sensor 10. The magnetoresistive elements 15 are arranged in a plane, and are arranged close to the magnetoresistive elements 15 so that a part of the load line 310 held by the line holder 210 is parallel to the plane as shown in FIG. Is done. The first current input terminal 11 and the second current input terminal 12 of the full bridge circuit are connected to each other at a power input terminal 111 via a current limiting resistor 110 so that a current from an external power supply is input. The voltage output terminal 13 and the second voltage output terminal 14 are connected to the amplifier 20. As a result of the full bridge circuit being arranged close to a part of the load line 310, the resistance value of the magnetoresistive element 15 is changed by the current flowing through the load line 310, and the first voltage output terminal 13 and the second voltage output terminal 13 of the bridge circuit are changed. A detection voltage is generated between the voltage output terminals 14, and this detection voltage is input to the amplifier 20.

  The detection voltage V output from the magnetic sensor 10 is expressed by the following equation.

  The above expression indicates that the detection voltage output from the magnetic sensor 10 is composed of a fundamental frequency component (ω), a DC voltage component (DC), and a harmonic number component (2ω). I 1 indicates a load current flowing through the load line 310, and I 2 indicates a sensor current input to the magnetic sensor 10. V1 indicates the load power 320. K1K2K3 is a unique parameter of the magnetic sensor 10 that is fixed by the resistance value of the magnetic sensor 10. R1, R2, R3, and R4 are resistance values of the magnetoresistive elements. The waveform of the detection voltage is as shown in FIG. In FIG. 3, the DC voltage component is 2.5 V, and the combination of the fundamental frequency component (ω) and the harmonic number component (2ω) is the waveform represented by the dotted line. This waveform is the output of the amplifier 20. By passing through the current limiting resistor 110, the load power 320 can be converted into a sensor current I 2 having a small current value, and the current can be stably passed through the magnetic sensor 10.

  The amplifier 20 amplifies the analog detection voltage output from the first voltage output terminal 13 and the second voltage output terminal 14 of the magnetic sensor 10. The output of the amplifier 20 is converted to a digital value by the AD converter 40 and then input to the power calculator 100. The power calculator 100 calculates a load power value from the detected voltage output from the AD converter 40 and the parameter (K) indicating the output characteristics of the magnetic sensor 10.

  A filter 30 is provided between the amplifier 20 and the AD converter 40. The external power source is an AC power source having a predetermined frequency. For this reason, the filter 30 is a low-pass filter that allows a frequency component lower than the frequency of the AC power supply to pass. As a result, only the DC voltage component (DC) is extracted from the detected voltage (see Equation 1) and transmitted to the AD converter 40. Hereinafter, the DC voltage component is expressed by a mathematical expression.

  The amplifier 20 is configured to amplify the detection voltage output from the first voltage output terminal 13 and the second voltage output terminal 14 of the magnetic sensor 10 with a variable amplification factor corresponding to the gain. The amplifier 20 includes a gain changeover switch circuit 21 as shown in FIG. The amplifier 20 has an inverting input terminal, a non-inverting input terminal, and an output terminal, and includes an operational amplifier circuit (OP amplifier) 25. A first resistor 26 and a second resistor 27 connected in series are provided between the voltage output terminal 13 of the magnetic sensor 10 and the inverting input terminal of the operational amplifier circuit 25. Further, a third resistor 28 is provided between the output terminal of the operational amplifier circuit 25 and the inverting input terminal. The output terminal of the amplifier 20 is connected to the input terminal of the AD converter 40. The gain changeover switch circuit 21 is configured to switch between the first state and the second state. In the first state, as shown in FIG. 5A, the inverting input terminal is connected to the voltage output terminal 13 of the magnetic sensor 10 through a series circuit of the first resistor 26 and the second resistor 27, and A third resistor 28 is connected between the connection point 24 between the second resistor 27 and the inverting input terminal and the output terminal of the operational amplifier circuit 25. In the second state, as shown in FIG. 5B, the inverting input terminal is connected to the voltage output terminal 13 of the magnetic sensor 10 via the first resistor 26 and is inverted with respect to the output terminal of the operational amplifier circuit 25. A series circuit of the second resistor 27 and the third resistor 28 is connected as a feedback resistor between the input terminals. The gain changeover switch circuit 21 is configured to be switched to the first state when the gain is equal to or lower than a predetermined value, and to be switched to the second state at other times. The magnitude of the gain is determined by the output of the element. When the element output is small, the gain is high, and when the element output is large, the gain is low. The determination of the predetermined gain value is performed by a gain determination circuit 60 described later, and the determination result is transmitted to the gain changeover switch circuit 21. As described above, since the magnitude of the gain can be varied depending on the magnitude of the detection voltage output from the magnetic sensor 10, it is possible to accurately measure the power even when the detection voltage is relatively small.

  On the other hand, in addition to or instead of the configuration in which the amplification factor of the amplifier 20 is variable, the AD converter 40 adjusts the resolution to the detection voltage, that is, the step width of the AD converter 40 is set according to the detection voltage. Configured to change. For this purpose, the lower limit reference voltage of the AD converter 40 is fixed to 0 V, and the upper limit reference voltage supplied to the AD converter 40 is configured to change according to the detection voltage. For example, when the resolution of the AD converter 40 is 10 bits, the value divided by 1023 can be used as the step width by changing the upper limit reference voltage according to the value of the detection voltage. As a result, even when the detection voltage is small, it is possible to accurately recognize the fluctuation of the detection voltage and perform accurate power measurement.

  The detected voltage output from the AD converter 40 is converted into a power value by the power calculator 100. As illustrated in FIG. 2, the power calculator 100 includes a voltage average output unit 50, a coefficient determination unit 80, and a power value calculation unit 90.

The voltage average output unit 50 includes an addition processing unit 51 and an average processing unit 52. The addition processing unit 51 includes an addition circuit, adds the instantaneous DC voltage component transmitted from the AD converter 40 over a certain unit time, and outputs an addition voltage. The average processing unit 52 calculates the average detection voltage by dividing the addition voltage output from the addition processing unit 51 by the unit period. The unit time is set to, for example, twice the cycle of the frequency of the load power source that is an AC power source having a predetermined frequency. The start and end control of the unit period is performed by the oscillator 53 and the timer 54.

  The power value calculation unit 90 determines a power value consumed by the load based on the average detection voltage output from the average processing unit 52, and the determined power value is provided in the power measurement device or provided outside. It is transmitted to the display means 91 where the power value is displayed.

  The power value calculation unit 90 calculates the power value consumed by the load based on the average detection voltage output from the average processing unit 52. The power value calculation unit 90 integrates the load power with the unique parameter (K) of the magnetic sensor 10 stored in the coefficient determination unit 80.

  The parameter (K) is calculated by the coefficient determining unit 80 and stored here. The coefficient determination unit 80 selectively selects an appropriate parameter for the coefficient giving unit 81 for calculating the parameter (K), the coefficient storage unit 82 for storing a plurality of parameters (K1, K2), and the power value calculation unit 90. And a coefficient switching circuit 83 that outputs the signal.

  The coefficient giving means 81 is configured to obtain an appropriate parameter that matches the output characteristic specific to the magnetic sensor 10 to be used, and calibrates the magnetic sensor 10 by measuring a known load power with the power measuring device 150. To eliminate the influence of variations in output characteristics of the magnetic sensor 10 used in each power measuring device 150. For this reason, the power measuring apparatus 150 of the present invention includes a calibration mode for determining this parameter, and in this calibration mode, an appropriate parameter is obtained for each of a parameter when the power value is large and a case where the power value is small.

  The known load power 320 is supplied from, for example, a constant-voltage test AC power supply. Two parameters are obtained by the coefficient applying means 81. As shown in FIG. 4, when obtaining a first parameter when a small current is passed, for example, a current of 2A is a first reference current and a current of 7A is a second reference current. The means 81 obtains a first detection voltage and a second detection voltage output from the magnetic sensor 10. A ratio between the difference between the first detection voltage and the second detection voltage and the difference between the first reference current and the second reference current is calculated as the first parameter (K1), and the obtained first parameter (K1) is calculated. ) Is stored in the coefficient storage means 82.

  On the other hand, as shown in the figure, when obtaining a second parameter when a large current is passed, a current is applied to 10A as a third reference current, and a current of 30A is set as a fourth reference current. The means 81 obtains the third detection voltage and the fourth detection voltage output from the magnetic sensor 10, and determines the difference between the third detection voltage and the fourth detection voltage and the difference between the third reference current and the fourth reference current. The ratio is calculated as the second parameter (K2).

Thus, the first parameter (K1) and the second parameter (K2) obtained and stored in the calibration mode are selectively supplied to the power value calculation unit 90 by the coefficient switching circuit 83 in the actual power measurement mode. Is output. When the detected voltage is equal to or lower than the predetermined value, that is, when the load power indicated by the detected voltage is equal to or lower than the predetermined value, the coefficient switching circuit 83 outputs the first parameter (K1) to the power value calculating unit 90, otherwise The two parameters (K2) are configured to be output to the power value calculator 90. More specifically, the coefficient switching circuit 83 outputs the first parameter (K1) to the power value output unit 90 when the gain switching switch circuit 21 of the amplifier 20 indicates the first state, and the gain switching circuit 21 Indicates the second state, the second parameter (K2) is output to the power value output unit 90.

  A gain determining circuit 60 is provided between the voltage average output unit 50 and the coefficient determining unit 80. The gain determination circuit 60 determines the magnitude of the gain with respect to the average detection voltage output from the voltage average output unit 50. If the gain is within a certain voltage value range, the gain is determined to be low, and if it exceeds the certain voltage value range, the gain is recognized as a high gain. Further, after the determination, a low gain signal or a high gain signal is transmitted to the amplifier 20. By transmitting this signal, the amplifier 20 switches the gain changeover switch circuit 21.

  An offset voltage correction unit 70 is provided between the voltage average output unit 50 and the coefficient determination unit 80. The offset voltage correction unit 70 obtains an offset voltage, which is a DC voltage inevitably generated in each circuit of the amplifier 20, the AD converter 40, and the voltage average output unit 50, and is input to the power determination unit 90 through these circuits. The offset voltage is removed from the detected voltage from the sensor 10. That is, the offset voltage is subtracted from the average detection voltage output from the voltage average output unit 50. As a result, the power measuring apparatus is calibrated, and the excess offset voltage is deleted from the average detection voltage, and a detection voltage that more accurately reflects the required load power is obtained. In particular, since the amplifier 20 includes a DC voltage component that varies depending on the temperature of the place where the amplifier 20 is used, an output error due to a temperature change can be eliminated by removing the DC voltage component.

  In order to periodically perform such offset voltage correction, the power measuring device 150 includes a mode switching unit. The mode switching means is configured to selectively determine a correction mode for detecting the offset voltage and a power measurement mode for measuring the load power. As shown in FIG. 6, the current limiting resistor 110 and the first current input are configured. An input changeover switch 120 inserted between the end 11 is provided. The input changeover switch 120 includes a main changeover switch 121 and a sub changeover switch 125. The main changeover switch 121 is inserted between the external power supply and the first current input terminal 11 of the magnetic sensor 10 to selectively connect and disconnect the external power supply and the first current input terminal 11 of the magnetic sensor 10. Configured as follows. The sub changeover switch 125 is configured to selectively connect and disconnect an external power supply and a reference potential (ground potential) 129 lower than the external power supply before the main changeover switch 121.

  As shown in FIGS. 6A and 6F, the mode switching unit is configured to allow a current from the external power source to the magnetic sensor 10 when the power measurement mode is selected. When the correction mode is selected, the mode switching unit is configured as shown in FIGS. As shown in FIG. 5, the DC component output from the magnetic sensor 10 in a state where the current from the external power source to the magnetic sensor 10 is interrupted is extracted. When switching from the power measurement mode shown in FIG. 6A to the correction mode shown in FIG. 6C, the main changeover switch 121 is connected to the first current input terminal 11 of the magnetic sensor 10 as shown in FIG. 6B. The mode switching means is configured to disconnect the main changeover switch 121 from the external power supply after the sub changeover switch 125 is operated to switch the external power supply to the reference potential 129.

  On the other hand, when switching from the correction mode shown in FIG. 6D to the power measurement mode shown in FIG. 6F, as shown in FIG. 6E, the main selector switch 121 is connected with the external power source connected to the ground potential 129 by the sub selector switch 125. As shown in FIG. 6F, the mode switching means is configured to operate the sub changeover switch 125 to disconnect the external power supply from the ground potential 129 after connecting to the external power supply. As described above, the mode switching means is configured to create a provisional state as shown in FIGS. 6B and 6E when switching between the power measurement mode and the correction mode. As a result, a large current does not instantaneously flow to the switch provided for selectively switching the external power source between the magnetic sensor and the reference potential, and the switch can be protected from excessive stress.

  Details of the magnetic sensor 10 will be described below.

  As shown in FIG. 7, the magnetic sensor 10 of the present embodiment is configured by a full bridge circuit of four magnetoresistive elements 15. The magnetoresistive element 15 is a thin film structure, and is formed as a thin film as shown in FIG. As shown in FIG. 7, the four magnetoresistive elements 15 are arranged in a bridge connection in the same plane, the four sides of the bridge are orthogonal to each other, and the magnetoresistive elements 15 forming one side of the bridge are in a meander shape. The

  As shown in FIG. 7, the meander shape is a length (L) of flowing a current in a direction substantially perpendicular to a line segment on one side of the bridge and a width (A) for flowing a current in a direction substantially parallel to the line segment on one side of the bridge. W) and the shape formed so as to be repeated in order. For example, the length L is 1 mm and the width W is 10 μm. For this reason, the current direction in one meander shape is two directions: a main line perpendicular to one side of the bridge and a sub-line parallel to one side of the bridge. That is, the main line has two-direction conductors with currents differing by 180 degrees. Furthermore, by configuring the meander-shaped magnetoresistive element 15 on each side of the bridge, the effective length of the magnetoresistive element 15 is increased within a limited range. Therefore, the resistance value of the magnetoresistive element 15 itself can be increased, and the output voltage representing the variation in resistance value can be increased.

  In the magnetic sensor 10, the four sides of the bridge are 90 degrees from each other. As a result, the resistance change between the adjacent magnetoresistive elements 15 is reversed, and the resistance value can be unbalanced efficiently. Can be increased.

  The magnetoresistive element 15 is preferably covered with a protective film such as an epoxy resin. This protective film prevents the magnetic powder contained in the atmosphere from directly adhering to the magnetoresistive element 15 and stabilizes the output characteristics.

  As the magnetoresistive element 15, in addition to a ferromagnetic thin film having a single layer structure, an antiferro (coupled) thin film having a (ferromagnetic / nonmagnetic conductor) structure, (high coercive force ferromagnetic / nonmagnetic conductor / low Inductive ferri (non-coupled) type thin film having a coercive force ferromagnetic structure, spin valve type thin film having a (semi-ferromagnetic / ferromagnetic / non-magnetic conductor / ferromagnetic) structure, and non-solid Co / Ag family It is formed by selecting from a molten granular thin film.

  In order to increase the detection voltage output from the magnetic sensor 10 having the above-described configuration, a constant external DC magnetic field can be applied to the magnetic sensor 10.

Hereinafter, various embodiments for applying an external DC magnetic field to the magnetic sensor 10 will be described. Each embodiment is the same as the first embodiment except that a magnetic field applying unit for applying an external DC magnetic field is provided.
(Second Embodiment)
The power measuring apparatus according to the present embodiment includes a magnetic field outside the sensor unit 18 in which a terminal for connection to an external power source and a terminal for connection to the amplifier 20 are integrally formed in addition to the magnetic sensor 10. It has a configuration in which the providing means is arranged. As shown in FIG. 9, the magnetic field applying means is defined by a pair of permanent magnets 400 arranged on both sides of the sensor unit 18, and is a bias that is a DC magnetic field in a direction parallel to the plane on which the four magnetoresistive elements 15 are arranged. A magnetic field (Hb) is applied. A part of the load line 310 disposed close to the magnetic sensor 10 is positioned by the line holder 210 so that the magnetic field generated by the current flowing therethrough and the bias magnetic field (Hb) are orthogonal to each other. With this configuration, the bias magnetic field (Hb) uniformly affects the magnetic sensor 10 by the magnetic field applying means, and the output characteristics from each magnetoresistive element 15 can be stabilized. In this way, by applying a bias magnetic field (Hb) to the magnetic sensor 10, magnetization reversal does not occur even when a large current such as an inrush current is applied, and stable power measurement is possible. In this case, it is desirable to use a ferromagnetic resistive element as the magnetoresistive element 15.
(Third embodiment)
The power measuring apparatus according to the third embodiment uses the magnetic sensor 10 having the configuration used in the second embodiment, and, as shown in FIG. The sensor unit 18 and the permanent magnet 400 are realized as one block by being arranged on the back surface of the sensor. Also in this embodiment, a bias magnetic field (Hb) that is a DC magnetic field is applied in a direction parallel to the plane on which the four magnetoresistive elements 15 are arranged, and this bias magnetic field (Hb) is positioned by the line holder 210. Perpendicular to the magnetic field generated by the current flowing through part of the load line 310.
(Fourth embodiment)
The power measuring device according to this embodiment is basically the same as that of the third embodiment, and the difference is that a pair of yokes 410 are arranged on both sides of the sensor unit 18 as shown in FIG. . The yoke 410 is disposed at a position corresponding to the magnetic pole end of the permanent magnet 400, absorbs the leakage flux of the external DC magnetic field generated by the permanent magnet 400, and efficiently applies the external DC magnetic field to the magnetic sensor 10. , Improve the magnetic efficiency. As a result, the relatively small permanent magnet 400 can be used, and the sensor unit 18 can be downsized. Also in this embodiment, it is desirable to use a ferromagnetic resistance element as the magnetoresistive element 15.
(Fifth embodiment)
In the power measuring apparatus according to the present embodiment, the magnetic sensor 10 having the configuration used in the second embodiment is used, and as shown in FIG. The sensor unit 18 and the permanent magnet 400 are realized as one block by being arranged on the front surface and the back surface. Also in this embodiment, a bias magnetic field (Hb) that is a DC magnetic field is applied in a direction parallel to the plane on which the four magnetoresistive elements 15 are arranged, and this bias magnetic field (Hb) is positioned by the line holder 210. Perpendicular to the magnetic field generated by the current flowing through part of the load line 310. Also in the present embodiment, it is desirable to use a ferromagnetic resistive element as the magnetoresistive element 15.
(Sixth embodiment)
The power measuring apparatus according to this embodiment is basically the same as that of the fifth embodiment, and is different in that a pair of yokes 410 are arranged on both sides of the sensor unit 18 as shown in FIG. The yoke 410 is disposed between the same magnetic pole ends of the two permanent magnets 400, absorbs the leakage flux of the external DC magnetic field generated by the permanent magnets 400, and efficiently applies the external DC magnetic field to the magnetic sensor. In order to improve the magnetic efficiency. As a result, a relatively small permanent magnet can be used, and the sensor unit 17 can be downsized. Also in this embodiment, it is desirable to use a ferromagnetic resistance element as the magnetoresistive element 15.
(Seventh embodiment)
As shown in FIG. 14, the power measuring apparatus according to the present embodiment has a pair of permanent magnets 400 mounted on both sides of the magnetic sensor 10 on the glass substrate 16 together with the magnetic sensor 10 having the same configuration as that of the first embodiment. With the structure. The permanent magnet 400 defines external DC magnetic field applying means for applying a bias magnetic field (Hb) that is a DC magnetic field in a direction parallel to the plane in which the four magnetoresistive elements 15 are arranged, as in the above-described embodiment. In this embodiment, a meander-shaped pattern magnetoresistive element 15 made of a NiCo thin film and a NdFeB permanent magnet 400 are formed on a frosted glass substrate 16.
(Eighth embodiment)
In the power measuring apparatus according to this embodiment, as shown in FIG. 15, a sensor unit having a structure in which an insulating thin film 17 in which a magnetic sensor 10 having the same configuration as that of the first embodiment is embedded is sandwiched between a pair of magnetic thin films 19. 18 is provided on a glass substrate 16. The magnetic thin film constitutes a magnetic field applying unit that applies a bias magnetic field (Hb) that is a direct current magnetic field in a direction parallel to a plane in which the four magnetoresistive elements 15 are arranged. A part of the load line 310 disposed close to the magnetic sensor 10 is positioned by the line holder 210 so that the magnetic field generated by the current flowing therethrough and the bias magnetic field (Hb) are orthogonal to each other. According to this configuration, the sensor unit 18 can be realized as a thin film structure, and the entire apparatus can be reduced in thickness.

  In the first to eighth embodiments, a configuration is adopted in which the sensor unit 18 mounted with the magnetic sensor 10 is mounted on a printed wiring board on which electronic components that configure processing circuits such as the amplifier 20 and the AD converter 40 are mounted. Is done. Instead of this, it is also possible to form the magnetoresistive element 15 defining the magnetic sensor 10 on the printed wiring board together with the electronic components constituting the processing circuit. In any case, the amplifier 20 and the AD converter 40 can be constituted by chip parts to integrate the processing circuit. It is also possible to stack the magnetic sensor 10 on a printed wiring board on which a processing circuit is mounted via an insulating film to form a monolithic element.

In the above-described embodiment, the example in which the magnetic sensor 10 is configured by a plurality of meander-shaped magnetoresistive elements has been described. However, the present invention is not limited to these embodiments, and other forms of magnetoresistive elements are used. It is possible to use.
(Ninth embodiment)
In this embodiment, as shown in FIGS. 16 to 18, a magnetoresistive ring 510 in which four magnetoresistive elements 15 are connected in an annular shape and a circular auxiliary resistive element 520 arranged on the inside thereof are on the same plane. An arrayed magnetic sensor 10 is used. A part of the load line 310 arranged close to the magnetic sensor 10 is arranged along the diameter direction of the magnetoresistive ring 510, and both ends in the diameter direction of the magnetoresistive ring 510 parallel to the load line 310 are external. Both ends in the diameter direction of the magnetoresistive ring 510 that coincide with the direction orthogonal to the load line 310 become the output ends 540 of the detection voltage. The magnetoresistive ring 510 and the auxiliary resistance element 520 are formed by a thin film formed on a glass substrate or a silicon substrate. The auxiliary resistance element 520 electrically isolated in the inner space of the magnetoresistive ring 510 does not affect the electrical resistance value of the magnetoresistive ring 510, but is magnetically coupled to the magnetic resistance ring 510. A large amount of magnetic flux can be generated, and the sensitivity of the magnetic sensor 10 can be increased.
(Tenth embodiment)
In this embodiment, as shown in FIG. 18, the magnetic sensor 10 including the magnetoresistive ring 550 in which the four magnetoresistive elements 15 are arranged in a square is used. A part of the load line 310 arranged close to the magnetic sensor 10 is arranged along one diagonal line of the magnetoresistive ring 550, and both ends of the diagonal line of the magnetoresistive ring 550 parallel to the load line 310 are external. The both ends of the diagonal line of the magnetoresistive ring 550 that coincides with the direction orthogonal to the load line 310 become the output terminal 580 of the detection voltage. The magnetoresistive ring 550 and the auxiliary resistance element 560 are formed by a thin film formed on a glass substrate or a silicon substrate.

In any of the above-described embodiments, a part of the load line 310 arranged close to the magnetic sensor 10 is positioned by the line holder so as to be a fixed distance with respect to the plane on which the magnetoresistive elements 15 are arranged. The magnetic field generated by the current flowing through a part of the load line 310 is set so as to cover the plane on which the magnetoresistive elements 15 are arranged as shown in FIG.
(Eleventh embodiment)
The present embodiment shows an example in which the magnetic sensor 10 is configured by a Hall element 450 instead of the magnetoresistive element 15. Other configurations and operations are the same as those of the embodiment shown in FIG. Similarly to the magnetic sensor 10 of the above-described embodiment, the Hall element 450 used here includes an input end and an output end, and is disposed close to a part of the load line. The input terminal of the Hall element 450 is connected to an external power supply via a current limiting resistor, so that a current from the external power supply is input. The Hall element 450 outputs a detection voltage that fluctuates under the influence of a magnetic field generated by a current flowing through the load line from an output terminal. Since this detection voltage includes the same components as those in the first embodiment, the load power is reduced by using the amplifier 20, the AD converter 40, the filter 30, and the power calculator 100 similar to those in the first embodiment. Calculated. In this case, as shown in FIG. 20, a part of the load line 310 is formed by the line holder 210 so that the magnetic field generated by the current flowing through the load line 310 is perpendicular to the widest surface of the Hall element 450. Positioning with respect to the Hall element 450 is desired.

  An unnecessary component is removed from the detection voltage output from the magnetic sensor used to measure the power supplied to the load from the external power supply, and accurate power measurement is performed.

10 Magnetic sensor 11 Current input terminal (first current input terminal)
12 Current input terminal (second current input terminal)
13 Voltage output terminal (first voltage output terminal)
14 Voltage output terminal (second voltage output terminal)
DESCRIPTION OF SYMBOLS 15 Magnetoresistance element 20 Amplifier 30 Filter 40 AD converter 50 Voltage average output part 60 Gain judgment circuit 100 Power calculator 150 Power measuring device 210 Line holder 310 Load line 320 Load power 450 Hall element

Claims (11)

A power measuring device for measuring load power supplied to a load using a change in a magnetic field that varies with a load current flowing through a load line connecting an external power source to the load,
This power measuring device
A magnetic sensor disposed close to a part of the load line;
A power calculator that calculates load power based on the detection voltage output from the magnetic sensor,
The magnetic sensor has a current input terminal to which a current from an external power source is input,
The magnetic sensor is configured to change a sensor current flowing in the magnetic sensor itself under the influence of a magnetic field generated by a load current flowing in a load line, and output a detection voltage corresponding to the change in the sensor current, The detection voltage includes a DC voltage component, a fundamental frequency component, and a harmonic component, and the power measurement device includes a filter that removes the fundamental frequency component and the harmonic component from the detection voltage output from the magnetic sensor. A power measuring device characterized by that. The external power source is an AC power source having a predetermined frequency,
The power measuring apparatus according to claim 1, wherein the filter is a low-pass filter that allows a frequency component less than the frequency of the AC power supply to pass therethrough. The magnetic sensor is composed of a plurality of magnetoresistive elements whose electric resistance values change under the influence of a magnetic field generated by a load current, and outputs a detection voltage corresponding to the change in the resistance value of the magnetoresistive elements. The power measuring device according to claim 1, wherein the power measuring device is configured as described above. The magnetoresistive element forms a full bridge circuit, and the bridge circuit is configured such that the current input terminal is connected to the external power source and the detection voltage is generated between the voltage output terminals of the bridge circuit. The power measuring device according to claim 3, wherein The power calculator includes a voltage average output unit, and includes an addition circuit that obtains an addition voltage obtained by adding the detection voltage over a unit period that is an integral multiple of the cycle of the AC power supply. The power measurement device according to claim 2, wherein the power measurement device is configured to calculate power based on an average detection voltage divided by. The power measuring device is
An amplifier for amplifying an analog detection voltage output from the magnetic sensor;
An AD converter for converting the output of the amplifier into a digital detection voltage;
A gain determination circuit that determines a gain indicating the magnitude of the value of the detection voltage output from the magnetic sensor;
The power measuring device is configured to calculate power based on the digital detection voltage,
The gain determination circuit is configured to change an upper limit reference voltage applied to the AD converter based on the gain so that a decomposition level of the AD converter corresponds to a detection voltage. Item 6. The power measuring device according to any one of Items 1 to 5. The magnetoresistive element is a thin film resistive element, and a plurality of thin film resistive elements are arranged on the same sensor array surface,
The power measuring device according to claim 3, further comprising a line holder for holding a part of the load line in a state parallel to the sensor array surface. 5. The power measuring apparatus according to claim 4, further comprising a magnetic field applying unit for applying a constant external DC magnetic field to the magnetoresistive elements constituting the full bridge circuit. The magnetic field applying means is configured to cause the external DC magnetic field to act in a direction orthogonal to a magnetic field generated by a load current flowing through a load line around a load line in a region close to the magnetic sensor. The power measuring apparatus according to claim 8, wherein the power measuring apparatus is characterized. The full bridge circuit is configured such that the magnetoresistive element is located on each of four line segments connected to each other at an angle of 90 degrees.
The power measuring apparatus according to claim 4, wherein the magnetoresistive element in each line segment has a meander shape. The magnetic sensor is composed of a Hall element,
The power measuring device according to claim 1, further comprising a line holder that holds a part of the load line so as to be perpendicular to a surface of the Hall element.