Current sensors and watt-hour meters

Abstract

To provide a current sensor and a wattmeter that are small in size and highly sensitive and are not easily affected by external magnetic fields.SOLUTION: An end P1 of a first coil 2a and an end P2 of a second coil 2b are connected by a via d1 connecting front and back surfaces of a multilayer printed circuit board, the other end P0 of the first coil 2a is connected in the same surface to an external connection terminal 22a, the other end P3 of the second coil 2b is connected to an external connection terminal 22b via a via d2 connecting the front and back surfaces of the multilayer printed circuit board, and the via d1 and via d2 are arranged on different sides with respect to a center plane LC passing through a center axis C10 of the first coil 2a and a center axis C11 of the second coil 2b. A via b1 arranged on an outer peripheral side of the first coil 2a among interlayer connection vias connecting the layers of the first coil 2a and a via b2 arranged on an outer peripheral side of the second coil 2b among interlayer connection vias connecting the layers of the second coil 2b are arranged on different sides with respect to the center plane LC.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a current sensor and a watt-hour meter that are small, highly sensitive, and less susceptible to the influence of external magnetic fields. [Background technology]

[0002] Current sensors that have been used so far include current transformers (CTs), sensors configured with a magnetic detection element such as a Hall element placed in the gap of a magnetic core, and sensors configured with an element in the gap of a magnetic core, such as a wound coil or a coil pattern formed on a dielectric substrate. These methods use magnetic materials, which make the size larger to prevent saturation at large currents, and are therefore costly.

[0003] There is also a method of using only a coil pattern formed on a printed circuit board without using a magnetic core. These methods have the advantage of being small and inexpensive, since they are constructed using only a coil pattern formed on a printed circuit board.

[0004] In Patent Document 1, in order to detect the magnetic flux generated by the measurement current, a pair of first coils C1, each formed by a conductive pattern of multiple turns on both sides of a circuit board and shaped symmetrically on the front and back, and a second coil C2, arranged symmetrically with the first coil with respect to the position where the measurement wiring is arranged, are configured. By arranging the coils symmetrically above and below the position of the measurement wiring, the coils arranged symmetrically above and below the measurement wiring detect the magnetic flux around the measurement wiring, and the current can be measured by bringing the coil close to the measurement target without cutting or changing the circuit wiring. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5846421 Summary of the Invention [Problem to be solved by the invention]

[0006] The current sensor in Patent Document 1 is designed to measure relatively high-frequency signals with a pulse width of approximately 10 μs. For example, if this configuration is applied to a current sensor installed in a power meter or the like, the low frequency of approximately 50 Hz to 60 Hz can result in insufficient current detection sensitivity. One solution to this problem is to increase the coil area and the number of coil turns, but this results in the sensor becoming larger in size in order to achieve sufficient sensitivity. Another method is to use a multilayer board instead of the double-sided board described in Patent Document 1 to increase the number of coil turns. However, this method can result in the sensor being more susceptible to external noise (external magnetic fields) depending on the connection positions of the first and second coils and the connection positions of each layer of the first and second coils.

[0007] The present invention has been made in view of the above, and has an object to provide a current sensor and a watt-hour meter that are small, highly sensitive, and less susceptible to the influence of external magnetic fields. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the present invention provides a current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar, the current sensor comprising: a first coil and a second coil that detect the magnetic field formed on a multilayer printed circuit board; one end of the first coil and one end of the second coil are connected by a first via that connects the front and back surfaces of the multilayer printed circuit board; one of the other ends of the first coil and the second coil is connected to an external connection terminal within the same plane, and the other is connected to an external connection terminal via a second via that connects the front and back surfaces of the multilayer printed circuit board; the first via and the second via are arranged on different sides of a central plane that passes through the central axis of the first coil and the central axis of the second coil; and a first interlayer connection via that is arranged on the outer periphery of the first coil among the interlayer connection vias that connect the layers of the first coil and a second interlayer connection via that is arranged on the outer periphery of the second coil among the interlayer connection vias that connect the layers of the second coil are arranged on different sides of the central plane.

[0009] In addition, the present invention is characterized in that, in the above invention, the multilayer printed circuit board is made up of four or more layers, and a coil pattern is formed on each layer.

[0010] In addition, in the above invention, the present invention is characterized in that the first coil and the second coil are connected in series so as to reinforce the induced voltages generated by the magnetic field generated by the current flowing through the current bar.

[0011] The present invention is also characterized in that the amount of power flowing through the current bar is calculated based on a current signal detected by a current sensor described in any one of the above inventions and a voltage signal detected by a voltage sensor. [Effects of the Invention]

[0012] According to the present invention, by increasing the number of turns in a coil pattern formed on a multilayer printed circuit board, it is possible to measure commercial frequency currents with high sensitivity in a small size, and by connecting two coils so as to cancel out the effects of external noise (external magnetic fields), it is possible to provide a high-precision current sensor that is less susceptible to such effects. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a current sensor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the current sensor. [Figure 3] FIG. 3 is a diagram showing the pattern configuration of each layer of the current sensor. [Figure 4] FIG. 4 is a diagram showing the results of analyzing the influence of an external magnetic field on this embodiment and other connection examples A and B. [Figure 5] FIG. 5 is an explanatory diagram illustrating the influence of an external magnetic field in the Z direction in this embodiment and in another connection example A. [Figure 6] FIG. 6 is an explanatory diagram illustrating the influence of an external magnetic field in the X direction in this embodiment and in another connection example B. [Figure 7] FIG. 7 is a block diagram showing an example of a watt-hour meter using the current sensor described in the embodiment. [Figure 8] FIG. 8 is a vector diagram between three-phase currents and three-phase voltages. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0015] FIG. 1 shows a schematic configuration of a current sensor 3 according to an embodiment of the present invention, with FIG. 1(a) showing a side view of the current sensor 3 and FIG. 1(b) showing a perspective view of the current sensor 3. As shown in FIG. 1, the current sensor 3 is disposed near a current bar 1 through which a current to be measured flows. The current sensor 3 has a first coil 2a and a second coil 2b, which are pattern coils, disposed on a multilayer printed circuit board. The first coil 2a and the second coil 2b have a four-layer structure of the same size and are positioned at equal positions on the left and right of the current bar 1.

[0016] Fig. 2 is a plan view of the current sensor 3. Fig. 3 is a diagram showing the pattern configuration of each layer of the current sensor 3. As shown in Fig. 2, the external connection terminals 22a and 22b are terminals for connection to a signal processing circuit (not shown).

[0017] The first coil 2a and the second coil 2b detect the magnetic field generated by the current I flowing through the current bar 1, and generate an induced voltage according to the current and frequency. The first coil 2a and the second coil 2b are arranged at equal positions on the left and right of the current bar 1, and detect the magnetic flux Φ of different directions generated by the current I. The first coil 2a and the second coil 2b are connected in series so that the induced voltages generated in each coil are added together. This induced voltage is then integrated by a signal processing circuit to output a detection signal proportional to the current I.

[0018] The induced voltage output increases with the coil area and number of turns. Therefore, the induced voltage generated is small at low frequencies, such as commercial frequencies of 50 Hz to 60 Hz. Therefore, sensitivity can be ensured by increasing the coil area or number of turns. Increasing the coil area results in a larger current sensor, so it is preferable to increase the number of turns within a limited area. However, since the wiring spacing and conductor width of coil patterns formed on a printed circuit board are limited by manufacturing limits, it is desirable to increase the number of layers of the printed circuit board to ensure a larger number of turns and ensure detection sensitivity. Therefore, in this embodiment, if a coil pattern is formed with four layers, an area of approximately 10 mm square, and wiring conductor width and spacing of 0.1 mm, an induced voltage of approximately 0.1 mV / A (50 Hz) can be obtained, calculated as the sum of the two coils.

[0019] As shown in Figure 3, the four layers L1, L2, L3, and L4 are the front surface, first inner layer, second inner layer, and back surface, respectively. The first coil 2a and the second coil 2b each have a coil pattern of the same area arranged on each layer L1, L2, L3, and L4. The coil patterns are formed in the same winding direction so that the induced voltages of the layers L1, L2, L3, and L4 are added together.

[0020] The first coil 2a is connected to the external connection terminal 22a through end P0 of the first coil via vias a1, b1, c1, and d1 in this order. Here, the lower position of the via d1 on layer L4 is end P1 of the first coil 2a. The via d1 on layer L1 is connected to end P2 of the second coil 2b on layer L1, and the second coil 2b is connected to end P3 of the second coil 2b vias a2, b2, c2, and d2 in this order, and is then connected to the external connection terminal 22b. Here, the lower position of the via d2 on layer L4 is end P3 of the second coil 2b. Then, by connecting end P1 of the first coil 2a and end P2 of the second coil 2b, the induced voltage of the first coil 2a and the induced voltage of the second coil 2b become added.

[0021] Vias a1 and c1 are arranged on the central axis C10 of the first coil 2a, and vias b1 and d1 are arranged on the outer periphery of the first coil 2a. Similarly, vias a2 and c2 are arranged on the central axis C11 of the second coil 2b, and vias b2 and d2 are arranged on the outer periphery of the second coil 2b. Vias a1, c1, and b1 are interlayer connection vias of the first coil 2a, and vias a2, c2, and b2 are interlayer connection vias of the second coil 2b. Furthermore, via d1 is a via that connects end P1 of the first coil 2a to end P2 of the second coil 2b. Furthermore, via d2 is a via that connects end P3 of the second coil 2b to the external connection terminal 22b.

[0022] That is, end P1 of the first coil 2a and end P2 of the second coil 2b are connected by via d1 connecting the front surface (layer L1) and the back surface (layer L4) of the multilayer printed circuit board, the other end P0 of the first coil is connected to external connection terminal 22a on the front surface, and the other end P3 of the second coil 2b is connected to external connection terminal 22b through via d2 connecting the front surface and the back surface of the multilayer printed circuit board. The vias d1 and d2 are arranged on different sides of a central plane LC that passes through the central axis C10 of the first coil 2a and the central axis C11 of the second coil 2b.

[0023] Furthermore, among the interlayer connection vias that connect the layers of the first coil 2a, vias a1 and c1 pass near the central axis C10, and via b1 is located on the outer periphery of the first coil 2a. Similarly, among the interlayer connection vias that connect the layers of the second coil 2b, vias a2 and c2 pass near the central axis C11, and via b2 is located on the outer periphery of the second coil 2b. Vias b1 and via b2 are located on different sides of the central plane LC.

[0024] Such inter-coil connections and via arrangements can suppress the influence of external magnetic fields. Figure 4 shows the results of an analysis of the influence of external magnetic fields on this embodiment and other connection examples A and B. In other connection example A, vias d1 and d2 are eliminated, and the inter-coil connections are made directly on the front or back surface. Therefore, the first coil 2a and the second coil 2b in other connection example A have the same winding direction. In addition, in other connection example B, vias b1 and d1 and vias b2 and d2 are arranged on the same side of the center plane LC.

[0025] The analysis results show that the other connection example A is affected by an external magnetic field in the Z direction, and the other connection example B is affected by an external magnetic field in the X direction, but in this embodiment, there is no influence from any external magnetic field.

[0026] 5(a) and 5(b), in this embodiment, the direction of the induced current flowing from the vias a1, b1, and c1 toward via d1 is different from the direction of the induced current flowing from the vias a2, b2, and c2 toward via d2, and the currents are connected so that they cancel each other out, thereby canceling out the induced voltage. On the other hand, in another connection example A, as shown in FIGS. 5(c) and 5(d), the direction of the currents flowing through vias b1 and b2 is different from each other, and the currents are connected so that they overlap each other, forming a loop R1, which causes the external magnetic field in the Z direction to be detected.

[0027] On the other hand, as for the external magnetic field in the X direction, in this embodiment, as shown in Figures 6(a) to 6(c), because the vias d1 and d2 are arranged on different sides with respect to the central plane LC, the current directions of the loop R1 formed by the vias a1, c1 and d1 as viewed from the X direction are different from those of the loop R2 formed by the vias a2, c2 and d2, and therefore the induced voltages are canceled out. In contrast, in other connection example B, as shown in Figures 6(d) to 6(f), because the vias d1 and d2' are arranged on the same side with respect to the central plane LC, the current directions of the loop R3 formed by the vias a1, c1 and d1 as viewed from the X direction are the same as those of the loop R4 formed by the vias a2, c2 and d2', and therefore an induced voltage is detected.

[0028] Although the above embodiment shows an example of a four-layer coil, the present invention is not limited to this, and any coil may be used as long as the number of layers is an even number.

[0029] <Power meter> Fig. 7 is a block diagram showing an example of a watt-hour meter 200 using the current sensor described in the embodiment. This watt-hour meter 200 measures the three-phase power between a power source SP and a load LD, and calculates the power using the two-wattmeter method. Fig. 8 shows a vector diagram of the three-phase currents IR, IS, IT and the three-phase voltages VR, VS, VT.

[0030] As shown in Fig. 7, the watt-hour meter 200 includes current sensors 3a and 3b corresponding to the current sensor 3 described in the embodiment, voltage sensors 201a and 201b, a watt-hour calculation unit 202, and an output unit 203. The current sensor 3a detects an R-phase current signal. The current sensor 3b detects a T-phase current signal. The voltage sensor 201a detects a voltage signal between the R and S phases. The voltage sensor 201b detects a voltage signal between the T and S phases.

[0031] The power amount calculation unit 202 multiplies the current signal from the current sensor 3a by the voltage signal from the voltage sensor 201a to generate an instantaneous power signal, smooths this signal using a low-pass filter to obtain active power, and multiplies the current signal from the current sensor 3b by the voltage signal from the voltage sensor 201b to generate an instantaneous power signal, smooths this signal using a low-pass filter to obtain active power, and calculates the active power by adding up each active power as the amount of power. The output unit 203 displays or outputs the calculated amount of power to an external device.

[0032] The three-phase power P calculated using the two-wattmeter method is: P = VRS·IR + VTS·IT =(VR-VS) IR + (VT-VS) IT =VR IR + VS (-IR - IT) + VT IT =VR·IR+VS·IS+VT·IT This is the same as calculating the total power of each phase.

[0033] Furthermore, the configurations illustrated in the above embodiments are merely functional schematics and are not necessarily physically configured as shown. In other words, the distribution and integration of each device and component is not limited to that illustrated, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage situations, etc. [Explanation of symbols]

[0034] 1 current bar 2a First coil 2b Second coil 3, 3a, 3b Current sensor 22a, 22b External connection terminals 200 Energy meter 201a, 201b Voltage sensor 202 Electric energy calculation section 203 Output section a1, a2, b1, b2, c1, c2, d1, d2 vias C10,C11 center axis I current IR, IS, IT three-phase current L1, L2, L3, L4 layers LC center plane LD load P Three-phase power P0~P3 end R1~R4 ループ SP Power Supply VR, VS, VT three-phase voltage Φ magnetic flux

Claims

1. A current sensor that detects a magnetic field formed around a current bar through which a current flows and detects a current signal flowing through the current bar, a first coil and a second coil for detecting a magnetic field are formed on a multilayer printed circuit board having a coil pattern formed on each layer; one end of the first coil and one end of the second coil are connected by a first via that connects the front and back surfaces of the multilayer printed circuit board, one of the other end of the first coil or the other end of the second coil is connected to an external connection terminal within the same plane, and the other is connected to an external connection terminal through a second via that connects the front and back surfaces of the multilayer printed circuit board, the first via and the second via are arranged on different sides of a central plane that passes through a central axis of the first coil and a central axis of the second coil, A current sensor characterized in that a first interlayer connection via, among the interlayer connection vias connecting the layers of the first coil, which is arranged on the outer periphery of the first coil, and a second interlayer connection via, among the interlayer connection vias connecting the layers of the second coil, which is arranged on the outer periphery of the second coil, are arranged on different sides of the center plane.

2. 2. The current sensor according to claim 1, wherein the multilayer printed circuit board is configured with four or more layers.

3. 3. The current sensor according to claim 1, wherein the first coil and the second coil are connected in series so as to reinforce induced voltages generated by a magnetic field generated by a current flowing through the current bar.

4. A watt-hour meter characterized by calculating the amount of power flowing through the current bar based on a current signal detected by the current sensor according to any one of claims 1 to 3 and a voltage signal detected by the voltage sensor.

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