Abstract
A current sensor for measuring an electric current of a bus bar includes a ferromagnetic core and a circuit board. The bus bar extends through the ferromagnetic core. The ferromagnetic core includes a first air gap having a first width and a second air gap having a second width. The first width is greater than the second width. The circuit board includes a single sensor chip or two spatially separated sensor chips. The circuit board positions the sensor chip or the sensor chips relative to the first air gap and the second air gap. The single sensor chip includes two spatially separated magnetic sensing points, or the two sensor chips each include one magnetic sensing point. Each magnetic sensing point is disposed in one of the first air gap or the second air gap.
Claims
1. A current sensor for measuring an electric current of a bus bar comprises: a ferromagnetic core including a first air gap having a first width and a second air gap having a second width, the first width being greater than the second width; and a circuit board including a single sensor chip or two spatially separated sensor chips, the circuit board positions the sensor chip or the sensor chips relative to the first air gap and the second air gap; wherein the single sensor chip has two spatially separated magnetic sensing points or the two sensor chips each have a magnetic sensing point, and each magnetic sensing point is arranged in one of the first air gap or the second air gap; wherein the bus bar extends through the ferromagnetic core.
2. The current sensor according to claim 1, further comprising a housing accommodating the ferromagnetic core the circuit board.
3. The current sensor according to claim 2, wherein the housing includes two opposite end faces, the opposite end faces each have a cutout through which the bus bar extends.
4. The current sensor according to a claim 1, wherein the first width is two times larger than the second width.
5. The current sensor according to claim 1, wherein the two spatially separated sensor chips are of a same type and have a same range for an output voltage.
6. The current sensor according to claim 1, wherein the ferromagnetic core is one piece and has a cutout that encloses the bus bar except for at the second air gap.
7. The current sensor according to claim 1, wherein the ferromagnetic core is two pieces and includes a first E-shaped core and a second E-shaped core arranged in such a way relative to each other that the first air gap and the second air gap are formed.
8. The current sensor according to claim 7, wherein the ferromagnetic core defines a cutout for accommodating the bus bar, the cutout forming a distance, opposite from the second air gap (13), that is smaller than a width of the bus bar.
9. The current sensor according to claim 1, wherein the ferromagnetic core is two pieces and includes a first F-shaped core and a second F-shaped core arranged in such a way relative to each other that the first air gap and the second air gap are formed.
10. The current sensor according to claim 9, wherein the ferromagnetic core defines a cutout for accommodating the bus bar, the cutout forming a distance opposite from the second air gap (13), that is greater than a width of the bus bar.
11. A current sensor, comprising: a ferromagnetic core forming: a first air gap having a first width; a second air gap having a second width, the first width being greater than the second width; and a cutout; a bus bar extending through the cutout; and a sensor chip having a magnetic sensing point, the magnetic sensing point being arranged in one of the first air gap or the second air gap.
12. The current sensor of claim 11, wherein the sensor chip includes a further magnetic sensing point spaced from the magnetic sensing point, the further magnetic sensing point being arranged in the other of the first air gap or the second air gap.
13. The current sensor of claim 11, further comprising a further sensor chip having a further magnetic sensing point, the further magnetic sensing point being arranged in the other of the first air gap or the second air gap.
14. The current sensor of claim 11, wherein the second air gap extends to the cutout.
15. The current sensor of claim 14, wherein the cutout encloses the bus bar except for at the second air gap.
16. The current sensor of claim 14, wherein the ferromagnetic core includes a first E-shaped core and a second E-shaped core arranged in such a way relative to each other so as to form that the first air gap and the second air gap.
17. The current sensor of claim 16, wherein the cutout forms a distance, opposite the second air gap, that is less than a width of the bus bar.
18. The current sensor of claim 14, wherein the ferromagnetic core includes a first F-shaped core and a second F-shaped core arranged in such a way relative to each other so as to form that the first air gap and the second air gap.
19. The current sensor of claim 18, wherein the cutout forms a distance, opposite the second air gap, that is greater than a width of the bus bar.
20. The current sensor of claim 14, wherein the first air gap is spaced from the second air gap, the second air gap being arranged between the first air gap and the cutout.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] With reference to the accompanying drawings, the disclosure and its advantages will now be explained in more detail by means of exemplary embodiments, without thereby limiting the disclosure to the exemplary embodiment shown. The proportions in the figures do not always correspond to the real proportions, since some shapes are simplified and other shapes are shown enlarged in relation to other elements for better illustration.
[0032] FIG. 1 shows a perspective view of a current sensor for measuring the electric current of a bus bar.
[0033] FIG. 2 shows a side view of the current sensor from FIG. 1.
[0034] FIG. 3 shows a front view of an exemplary embodiment of internal structure of the current sensor without the protective housing.
[0035] FIG. 4 shows a perspective view of the internal structure of the current sensor from FIG. 3.
[0036] FIG. 5 shows a side view of the internal structure of the current sensor from FIG. 3.
[0037] FIG. 6 shows a representation of the dimensions of the housing for the current sensor.
[0038] FIG. 7 shows a representation of the dimensions of the ferromagnetic core of the current sensor for concentrating the magnetic flux.
[0039] FIG. 8 shows a representation of the dimensions of the positioning of the sensor chips in the ferromagnetic core of the current sensor.
[0040] FIG. 9 shows a representation of the result of the simulation of the magnetic field distribution of the flux in the ferromagnetic core.
[0041] FIG. 10 shows the geometry of the ferromagnetic core for the FEM simulation.
[0042] FIG. 11 shows the flux density as a function of the distance from the bus bar at 1000 A.
[0043] FIG. 12 shows the flux density as a function of the primary current at a maximum current of 1000 A.
[0044] FIG. 13 shows another exemplary embodiment of the internal structure of the current sensor.
[0045] FIG. 14 shows another exemplary possible embodiment of the internal structure of the current sensor.
[0046] FIG. 15 shows output voltages for each measurement range as a function of the primary current.
DETAILED DESCRIPTION
[0047] Identical reference numerals are used for elements of the disclosure that are the same or have the same effect. Furthermore, for the sake of clarity, only those reference numerals that are necessary for the description of the respective figure are shown in the individual figures. The figures merely represent exemplary embodiments of the disclosure without, however, restricting the disclosure to the exemplary embodiments shown.
[0048] FIG. 1 shows a perspective view of a current sensor 1 for measuring an electric current IP of a bus bar 4. The electric current IP runs in a Z-direction Z in the representation shown here. The current sensor 1 comprises a housing 2 to which a plug connection 3 for inputs and outputs of the current sensor 1 is attached. The plug connection 3 comprises multiple pins 5, for example. The position of the plug connection 3 and the number of pins 5 can vary depending on the application design of the current sensor 1. The housing 2 of the current sensor 1 has a cutout 6 (indicated by the dashed line) formed on both opposite end faces 7, through which the bus bar 4 extends and thus extends through the housing 2. The electric current IP to be measured flows in the bus bar 4. The shape of the cutout 6 in the housing 2 essentially corresponds to the cross-sectional shape 8 of the bus bar 4.
[0049] FIG. 2 shows a side view of the current sensor 1 from FIG. 1. It can be clearly seen from the side view that the bus bar 4 extends through the housing 2. The housing 2 has a depth T2 and the bus bar 4 has a depth T4. The depth T4 of the bus bar 4 is greater than the depth T2 of the housing 2. Consequently, the bus bar 4 extends through the two opposite end faces 7 of the housing 2. The plug connection 3 with the pins 5 is provided on an upper side 9O of the housing 2.
[0050] FIG. 3 shows a front view of an internal structure of the current sensor 1, and FIG. 4 shows a perspective view of the internal structure of the current sensor 1 without the protective housing 2 according to an exemplary embodiment of the current sensor 1. The internal structure of the current sensor 1 comprises a ferromagnetic core 10, which acts as a magnetic flux concentrator to improve the flux density generated by the current IP flowing through the bus bar 4. The ferromagnetic core 10 has formed a cutout 11 through which the bus bar 4 extends. According to the embodiment shown here, the bus bar 4 is at a distance from the cutout 11. Furthermore, the ferromagnetic core 10 has formed a first air gap 12 and a second air gap 13. A sensor chip 14 protrudes into each of the first air gap 12 and the second air gap 13. As can be seen from the representation in FIG. 4, the sensor chips 14 are attached to a circuit board 15 in such a way that when the circuit board 15 is positioned in relation to the ferromagnetic core 10, the two sensor chips 14 are located in the first air gap 12 and in the second air gap 13 of the ferromagnetic core 10, respectively. The circuit board 15 is supported on the bus bar 4. Furthermore, the circuit board 15 comprises the multiple pins 5, which form part of the plug connection 3 shown in FIG. 1 on the upper side 9O of the housing 2, to provide an electrical connection to outside of the housing 2.
[0051] As can be seen from the illustration in FIG. 3, the ferromagnetic core 10 (for example Fe core) is fitted around the bus bar 4 in order to concentrate the magnetic flux. The first air gap 12 has a width B12. The second air gap 13 has a width B13. In the embodiment shown here, the width B12 of the first air gap 12 is greater than the width B13 of the second air gap 13. As can be seen from FIGS. 3 and 4, the respective sensor chip 14 (magnetic sensor element) is arranged in the first air gap 12 and in the second air gap 13 in order to measure the magnetic field. The magnetic field to be measured is proportional to the electric current I.sub.P (primary current) in the bus bar 4. Consequently, the sensor chip 14 in the first air gap 12 measures in a low current range and the sensor chip 14 in the second air gap 13 measures in a high current range. A person skilled in the art would understand that the design of the ferromagnetic core 10 can vary. The embodiment of the ferromagnetic core 10 shown in FIGS. 3 and 4 is for descriptive purposes only and should not be construed as a limitation of the disclosure. Most importantly, the ferromagnetic core 10 (flux concentrator) generates two different magnetic fluxes by means of the first air gap 12 and the second air gap 13, which are clearly different from one another.
[0052] In order to measure the magnetic flux, the sensor chip 14 is arranged in the first air gap 12 in such a way that a magnetic sensing point 16 of the sensor chip 14 is located in the first air gap 12. The sensing point 16 defines the physical position where the sensor chip 14 or the sensor chips 14 is/are to be placed. A magnetic sensing point 16 of the other sensor chip 14 is also located in the second air gap 13. The exact location of these magnetic sensing points 16 can vary depending on the sensor chip technology. A sensor chip 14 with two magnetic sensor elements or at least two sensor chips 14 can be used at the sensing points 16 as possible designs. The sensor chip technology can be based, for example, on the Hall effect, magnetic resistance or similar technologies.
[0053] FIG. 5 shows a side view according to the exemplary embodiment of the internal structure of the current sensor 1 from FIG. 3. The usual housing 2 of the current sensor 1 is shown in dashed lines in order to clarify the internal structure of the current sensor 1. The bus bar 4 reaches through the cutout 11 of the ferromagnetic core 10. The circuit board 15 is connected to the one sensor chip 14 or the two sensor chips 14 with corresponding pins 17. The one sensor chip 14 with the two magnetic sensing points 16 (see FIG. 3) or the two sensor chips 14 with one sensing point 16 each are positioned in the ferromagnetic core 10. The circuit board 15 sits on the bus bar 4 and is arranged at a distance 18 from the ferromagnetic core 10. The circuit board 15 further comprises the pins 5 for the electrical connection to the outside of the housing 2. The circuit board 15 with additional electrical components (not shown), if necessary, is responsible for the electronic signal processing after the signal has been output by the sensor chip(s) 14.
[0054] FIG. 6 shows the dimensions of the bus bar 4 and the housing 2 of the current sensor 1 according to an exemplary embodiment. As the bus bar 4 has to be inserted into the housing 2 through the cutout 6 (slot), the cutout 6 in the housing 2 must be larger than the bus bar 4. The cutout 6 of the housing 2 has a width B6 and a height H6. The bus bar 4 has a width B4 and a height H4. As can be seen from FIG. 6, the width B4 and the height H4 of the bus bar 4 are each smaller than the width B6 and the height H6 of the cutout 6 in the housing 2, respectively. The upper side 9O and a lower side 9U of the housing 2 are spaced apart from one another by a height H2. A first side wall 2.sub.1 and a second side wall 2.sub.2 of the housing 2 are spaced apart from one another by a width B2. The bus bar 4 inserted into the housing 2 is spaced apart from the first side wall 2.sub.1 by a distance A2.sub.1 and from the second side wall 2.sub.2 by a distance A2.sub.2. Furthermore, the bus bar 4 is spaced apart from the upper side 9O of the housing 2 by a distance A9O and from the lower side 9U of the housing 2 by a distance A9U.
[0055] FIG. 7 shows a representation of the dimensions of the ferromagnetic core 10 of the current sensor 1 for concentrating the magnetic flux according to an exemplary embodiment. The ferromagnetic core 10 has a height H10, a width B10 and a depth T10. The height H10, the width B10 and the depth T10 of the ferromagnetic core 10 are each smaller than the height H2, the width B2 and the depth T2 of the housing 2 (not shown in FIG. 7), respectively. The bus bar 4 extends through the ferromagnetic core 10 at a distance A. The first air gap 12 has the width B12 and the second air gap 13 has the width B13. The width B12 of the first air gap 12 is greater than the width B13 of the second air gap 13.
[0056] The flux density at each of the magnetic sensing points 16 (see FIG. 3) depends on the width B12 of the first air gap 12 and the width B13 of the second air gap 13, respectively. In view of this, the low current range can be measured in the first air gap 12 and the high current range can be measured in the second air gap 13. The flux density in the first air gap 12 must be lower than the flux density in the second air gap 13. Therefore, the first air gap 12 must be wider or at least equal to the width B13 of the second air gap 13 since the magnetic resistance decreases with the width of the air gap.
[0057] FIG. 8 shows a representation of the dimensions of the positioning of the sensor chips 14 in the ferromagnetic core 10 of the current sensor 1 according to an exemplary embodiment. In the first air gap 12, the sensor chip 14 positioned there has a distance A12 on both sides from the ferromagnetic core 10. In the second air gap 13, the sensor chip 14 positioned there has a distance A13 on both sides from the ferromagnetic core 10. The sensor chips 14 should preferably be placed in the center of the first air gap 12 and the second air gap 13, respectively. However, the placement of the sensor chips 14 can deviate from the center placement depending on the application design.
[0058] The horizontal distance A12 or A13 between the first air gap 12 or the second air gap 13 and the sensor chip(s) 14 positioned there has an influence on the sensing points 16 (see FIG. 3). The horizontal distance A12 or A13 must be greater than 4 mm to ensure that the measured signals can be distinguished from one another. The height H12 of the first air gap 12 or the height H13 of the second air gap 13 (see FIG. 7) of the ferromagnetic core 10 must be high enough to ensure that the positioning of the sensor chips 14 within the air gaps 12 or 13 is possible within the required tolerances. The depth T10 of the ferromagnetic core 10 must be greater than a structural depth (not shown) of the sensor chip 14.
[0059] FIG. 9 shows a representation of a result of a 2D-FEM simulation of the flux in the ferromagnetic core 10. In this simulation of the current sensor 1 (not shown here), an electric current I.sub.P (primary current) of 1000 A is assumed. In this simulation, the length of the second air gap 13 is two times shorter than that of the first air gap 12. The flux density in the first air gap 12 and in the second air gap 13 is homogeneous. The flux density in the second air gap 13 is higher than the flux density in the first air gap 12. In particular, in the exemplary embodiment of the ferromagnetic core 10 shown here, the flux density in the second air gap 13 is twice as high as in the first air gap 12.
[0060] FIG. 10 shows the geometry of the ferromagnetic core 10 for the FEM simulation according to an exemplary embodiment. The magnetic sensing points 16 are arranged in the center of the first air gap 12 and the second air gap 13, respectively. The first air gap 12 has the height H12. The second air gap 13 has the height H13. Furthermore, a distance A.sub.12-13 between the two air gaps 12 and 13 is also shown. The aforementioned parameters have an influence on the positioning tolerance (measurable positions) of the sensor chips 14 within the air gaps 12 and 13. The arrow P shows the direction of a Y-direction Y from the original position (bus bar 4) to the limits of the ferromagnetic core 10. The arrow P represents a distance to the bus bar 4.
[0061] FIG. 11 shows the flux density (Tesla) as a function of the distance (mm) from the bus bar 4 (identified by the arrow P). A constant primary current I.sub.P of 1000 A flows through the bus bar 4. The flux density for the sensing point 16 in the second air gap 13 with the height H13 is twice as high as the flux density for the sensing point 16 in the first air gap 12 with the height H12. Within the air gaps 12 and 13, the flux density is homogeneous. Large heights H12 or H13 of the air gaps 12 or 13 and a greater horizontal distance A.sub.12-13 can deliver a stable sensor signal.
[0062] FIG. 12 shows the flux density as a function of the primary current I.sub.P up to a maximum current of 1000 A. The flux density (Tesla) is shown as a function of the primary current (Ampere). The flux density is measured or simulated at the sensing points 16 in the first air gap 12 or in the second air gap 13 (see FIG. 10).
[0063] In this simulation, the second air gap 13 is two times shorter than the first air gap 12. As a result, the flux density in the second air gap 13 is twice as high as the flux density in the first air gap 12.
[0064] If the second air gap 13 is x times shorter than the first air gap 12, the flux density in the second air gap 13 is generally x times higher than the flux density in the first air gap 12.
[0065] As can be seen from FIG. 12, the relationship between the primary current I.sub.P and the flux density is almost linear and has only small hysteresis errors. The two curves have the same shape but different amplification or sensitivity: The sensitivity at the sensing point 16 in the second air gap 13 is approximately twice that at the sensing point 16 in the first air gap 12. On the one hand, this leads to a better sensitivity for the low current range compared to the high current range. On the other hand, due to the higher sensitivity, the sensing point 16 in the second air gap 13 could saturate earlier for the low current range when the low current range is exceeded. The electronic signal processing of the current sensor should detect the saturation and switch to the sensor chip 14 in the first air gap 12 to measure the high current range.
[0066] FIG. 13 shows another exemplary embodiment of the structure of the ferromagnetic core 10, which is arranged in the housing 2 (not shown here) of the current sensor 1. The ferromagnetic core 10 consists of a first E-shaped core 10.sub.1E and a second E-shaped core 10.sub.2E. The first E-shaped core 10.sub.1E and the second E-shaped core 10.sub.2E are arranged relative to one another in such a way that the first air gap 12 and the second air gap 13 are formed, respectively. Likewise, a cutout 11 of the ferromagnetic core 10 is formed, which accommodates the bus bar 4. The cutout 11 defines a distance A11, opposite from the second air gap 13, which is smaller than the width B4 (see also FIG. 6) of the bus bar 4.
[0067] This design of the ferromagnetic core 10 offers a lower flux concentration ratio than the entire ferromagnetic core 10 as illustrated in FIGS. 3 and 4. This exemplary embodiment described here consequently leads to a lower flux density within the first air gap 12 or the second air gap 13, respectively. An advantage of this embodiment is a lower hysteresis effect and a reduction in cost and weight.
[0068] FIG. 14 shows a further exemplary embodiment of the internal structure of the current sensor 1. This embodiment of the ferromagnetic core 10 comprises a first F-shaped core 10.sub.1F and a second F-shaped core 10.sub.2F. The first F-shaped core 10.sub.1F and the second F-shaped core 10.sub.2F are arranged relative to one another in such a way that the first air gap 12 and the second air gap 13 are formed, respectively. Likewise, a cutout 11 of the ferromagnetic core 10 is formed, which accommodates the bus bar 4. The cutout 11 defines a distance A11, opposite from the second air gap 13, which is greater than the width B4 (see FIG. 6 or 13) of the bus bar 4.
[0069] As already mentioned in the description of FIG. 13, the first F-shaped core 10.sub.1F and the second F-shaped core 10.sub.2F also result in a lower flux concentration ratio compared to the ferromagnetic core 10 of FIGS. 3 and 4. The current embodiment results in a lower magnetic field within the first air gap 12 and the second air gap 13, respectively. The sensor chip 14 or the sensor chips 14 with the magnetic sensing points 16 for registering the magnetic field must be more sensitive. As already mentioned in the description of FIG. 13, this embodiment has a lower hysteresis effect. Furthermore, the cost and the weight are reduced. In addition, since the first F-shaped core 10.sub.1F and the second F-shaped core 10.sub.2F do not have a horizontal core element, it is possible to fix the current sensor 1 to the bus bar 4 directly. The bus bar 4 therefore no longer needs to be laboriously guided through the current sensor 1, which makes assembly easier.
[0070] FIG. 15 shows output voltages for each measurement range as a function of the primary current IP. The output voltages V.sub.out for each measurement range (considered as the same range V.sub.out=0.5, . . . , 4.5V) are plotted as a function of the primary current I.sub.P. The two sensor chips 14 are of the same type, but with different amplification factors. The amplification factor between the two sensor chips 14 is positive. This amplification factor is to be selected according to the desired measurement ranges, but also according to the factor that represents the width ratio between the second air gap 13 and the first air gap 12. Since the output voltage ranges are the same, the maximum output voltages must also be the same. If currents up to a current I.sub.Pmax can be measured with the sensor chip 14 in the first air gap 12, currents up to a current I.sub.Pmax/x can be measured with the sensor chip 14 in the second air gap 13. Here x represents the width ratio between the first air gap 12 and the second air gap 13. The sensor chips 14 are of the same type. This means that the total full-scale error should be the same. However, since the sensitivity is different, the accuracy of the measurement in the second air gap 13 is increased. The increase in accuracy is therefore proportional to the width ratio between the second air gap 13 and the first air gap 12.
[0071] It is believed that the present disclosure and many of the advantages noted therein will be understandable from the preceding description. It will be apparent that various changes in the shape, construction and arrangement of the components can be made without departing from the disclosed subject matter. The form described is illustrative only and it is the intent of the appended claims to comprise and incorporate such changes. Accordingly, the scope of the disclosure should be limited only by the appended claims.
LIST OF REFERENCE NUMERALS
[0072] 1 Current sensor
[0073] 2 Housing
[0074] 21 First side wall
[0075] 22 Second side wall
[0076] 3 Plug connection
[0077] 4 Bus bar
[0078] 5 Pin
[0079] 6 Cutout of the end faces of the housing
[0080] 7 End face
[0081] 8 Cross-sectional shape
[0082] 9O Upper side
[0083] 9U Lower side
[0084] 10 Ferromagnetic core
[0085] 10.sub.1E First E-shaped core
[0086] 10.sub.2E Second E-shaped core
[0087] 10.sub.1F First F-shaped core
[0088] 10.sub.2F Second F-shaped core
[0089] 11 Cutout of the ferromagnetic core
[0090] 12 First air gap
[0091] 13 Second air gap
[0092] 14 Sensor chip
[0093] 15 Circuit board
[0094] 16 Magnetic sensing point
[0095] 17 Pin
[0096] 18 Distance
[0097] A Distance
[0098] A2.sub.1 Distance
[0099] A2.sub.2 Distance
[0100] A9O Distance
[0101] A9U Distance
[0102] A11 Distance
[0103] A12 Distance
[0104] A13 Distance
[0105] A.sub.12-13 Distance
[0106] B2 Width
[0107] B4 Width
[0108] B6 Width
[0109] B10 Width
[0110] B12 Width
[0111] B13 Width
[0112] H2 Height
[0113] H4 Height
[0114] H6 Height
[0115] H10 Height
[0116] H12 Height
[0117] H13 Height
[0118] I.sub.P Electric current
[0119] P Arrow
[0120] T2 Depth
[0121] T4 Depth
[0122] T10 Depth
[0123] X X-direction
[0124] Y Y-direction
[0125] Z Z-direction
