Patent Application
20250102542
The invention relates to a current measuring device for measuring an electric current according to the four-wire technique with a low-resistance current measuring resistor and a circuit board connected to the current measuring resistor. The invention also relates to a corresponding production method for manufacturing such a current measuring device.
It is known from the state of the art (e.g. EP 0 605 800 B1) to measure an electric current using the four-wire technique. Here, the electrical current to be measured is passed through a low-resistance current measuring resistor (‘shunt’) and the electrical voltage dropping across the current measuring resistor is measured. In accordance with Ohm's law, the measured voltage then forms a measure of the electrical current flowing through the low-resistance current measuring resistor.
It is also known from the state of the art to permanently connect a circuit board (PCB: Printed Circuit Board) to the current measuring resistor, whereby a measuring circuit is arranged on the PCB which measures the voltage drop across the low-ohmic current measuring resistor. For example, the measuring circuit may be an application-specific integrated circuit (ASIC: application-specific integrated circuit), such as that known from EP 1 363 131 A1.
Firstly, the circuit board with the measuring circuit must be electrically connected to the current measuring resistor in order to be able to measure the voltage drop across the resistor element of the low-resistance current measuring resistor. This electrical connection can be made using a soldered connection, for example.
On the other hand, the circuit board with the measuring circuit must also be mechanically connected to the current measuring resistor, which is typically done differently in order to achieve the required mechanical resilience of the mechanical connection.
A disadvantage of the known current measuring device described above is therefore the connection between the circuit board on the one hand and the current measuring resistor on the other, which is not yet completely satisfactory. For example, the soldered connections between the circuit board and the current measuring resistor have a relatively large spatial extent, which makes it difficult to measure the voltage at the connection parts of the current measuring resistor with pinpoint accuracy.
For the general technical background of the invention, reference should also be made to DE 10 2010 010 152 U1, DE 10 2020 003 458 A1 and DE 10 2006 019 895 A1.
The invention is therefore based on the task of creating a correspondingly improved current measuring device and a corresponding manufacturing process for it.
This task is solved by a current measuring device according to the main claim of the invention and by a corresponding production method according to the independent claim.
The current measuring device according to the invention is used to measure an electric current and for this purpose, in accordance with the known current measuring device described at the beginning, firstly comprises a low-resistance current measuring resistor.
In accordance with the known current measuring resistor described at the beginning, the current measuring resistor comprises two connection parts made of a conductor material (e.g. copper) in order to introduce the electrical current to be measured into the current measuring resistor or to conduct it out of the current measuring resistor.
A low-resistance resistor element consisting of a low-resistance resistance material (e.g. Manganin®) is arranged in the direction of current flow between the two connection parts and is traversed by the electric current to be measured during a measurement. Such current measuring resistors are known from the prior art (e.g. EP 0 605 800 B1).
It should be mentioned here that the invention is not limited to copper with regard to the conductor material of the connection parts, but can also be realised with a copper alloy, aluminium or an aluminium alloy as conductor materials, for example.
It should also be mentioned that the invention is also not limited to Manganin® with regard to the resistance material. Thus, the invention can also be realized with other resistance alloys, as will be described in detail.
Furthermore, in accordance with the known current measuring device described at the beginning, the current measuring device according to the invention comprises a circuit board which is connected to the two connection parts of the current measuring resistor at at least two connection points.
The current measuring device according to the invention is now characterized by the fact that the connection between the circuit board on the one hand and the current measuring resistor on the other hand is made by a press connection, which creates a material bond between the circuit board and the current measuring resistor.
In one variant of the invention, the press connection is a press-sinter connection. Such press-sinter connections are known per se from the prior art and therefore need not be described in detail. At this point, it should only be mentioned that the press-sinter connection can optionally contain an additional sinter material, such as silver or copper.
In another variant of the invention, on the other hand, the press connection is a press-adhesive connection which can, for example, contain an epoxy adhesive as the adhesive.
In both variants (press-sinter connection and press-adhesive connection), the joining partners (connection parts of the current measuring resistor and/or circuit board) can have a surface structuring at the connection points, for example a nano-structuring. The surface structuring can have material elevations on the surface of the joining partners, which are subjected to pressure during the pressing process and then produce the desired press connection locally at these points, while the space between the material elevations is not pressed, so that no press connection is produced at these points. This surface structuring makes it possible to limit the spatial extent of the press connection, which enables precise voltage measurement on the connection parts. For example, the individual crimped connections can each have a horizontal extension parallel to the circuit board that is at most 1 mm, 500 μm, 250 μm or 100 μm, which enables precise voltage measurement at the connection parts.
It should also be mentioned that the surface structuring can contain one or more of the following materials:
In practice, the above-mentioned press connection between the circuit board and the current measuring resistor according to the invention establishes both a mechanical connection and an electrical connection. It is possible to electrically decouple the mechanical connection from the electrical connection. For example, this can be achieved by the above-mentioned surface structuring with material elevations on the surface of the joining partners (circuit board and connection parts of the current measuring resistor). The press connection is then only made in the area of the material elevations. The material elevations can then be spatially separated from each other, with one material elevation creating the mechanical connection while another material elevation creates the electrical connection.
In a preferred embodiment of the invention, the circuit board for contacting the current measuring resistor has several contact fingers that protrude from the circuit board.
For example, these contact fingers can be produced by making slots in the side of the circuit board, which then separate the contact fingers from one another. The contact fingers therefore preferably protrude from the circuit board in the same direction and parallel to each other.
The contact fingers on the circuit board can then contact the current measuring resistor on its upper side and/or underside.
It should be mentioned here that the current measuring resistor can have recesses (‘uncoverings’) into which one of the contact fingers of the circuit board can protrude. In the area of these recesses, the current measuring resistor then has a reduced thickness compared to the rest of the current measuring resistor. By adjusting the depth of the recesses, the temperature coefficient (TCR: temperature coefficient of resistance) of the resistance value of the current measuring resistor can also be adjusted.
In one embodiment of the invention, there is a recess in each of the two connection parts of the current measuring resistor for one of the contact fingers of the circuit board. These recesses are preferably adjacent to the resistor element, but it is also possible for the recesses to extend into the resistor element. It should also be mentioned that the recesses in the connection parts of the current measuring resistor preferably extend from a side edge of the current measuring resistor, so that the contact fingers of the circuit board can be orientated at right angles to the current measuring resistor and extend from the side into the recesses in the connection parts of the current measuring resistor.
Furthermore, within the scope of the invention, it is also possible that a recess for one of the contact fingers of the circuit board is also located in the resistor element of the current measuring resistor, this recess preferably being arranged on the same side edge of the current measuring resistor as the recesses in the connection parts of the current measuring resistor. One of the contact fingers of the circuit board then protrudes into the recesses in the resistor element, which enables a center tap. However, it should be mentioned here that the center tap on the resistor element is only optional.
Furthermore, it is possible that at least one of the contact fingers of the circuit board contacts the current measuring resistor on its underside, while the other contact fingers can contact the current measuring resistor on its upper side.
In the preferred embodiment of the invention, the circuit board is fitted with at least one electrical or electronic component. In this case, it is possible that this component is also connected to the circuit board by a press connection, in particular by a press-sinter connection or by a press-adhesive connection. The idea of a press connection according to the invention is therefore not limited to the connection between the circuit board and the current measuring resistor, but can also be used for the connection between the circuit board and the components located thereon.
For example, the circuit board can be fitted with at least one of the following components:
With regard to the microprocessor, it should be mentioned that it can be arranged either on the high side or on the low side of the module for electrically potential-separated data transmission.
It has already been mentioned at the beginning that the current measuring device according to the invention enables current measurement according to the four-wire technique. In this case, the voltage dropping across the resistor element of the current measuring resistor is measured at two connection points on the connection elements of the current measuring resistor. From the voltage across the resistor element measured in this way, the current flowing through the current measuring resistor can then be calculated according to Ohm's law. In the context of the invention, this voltage can also be measured at more than two connection points. For example, the circuit board can be connected to the two connection parts of the current measuring resistor at at least four connection points in order to measure the voltage dropping across the resistor element at several points. For example, the four connection points can form a rectangle, whereby the connection points can each form several measuring channels in pairs, whereby the measuring channels each measure the voltage between the two connection parts of the current measuring resistor.
The connection points of the two measuring channels can be arranged crosswise, as is known, for example, from DE 10 2021 103 241.5. Alternatively, it is possible for the connection points of the two measuring channels to be arranged in parallel, as is known, for example, from WO 2014/161624 A1.
In a simple embodiment of the invention, however, the circuit board is only connected at two connection points to the two connection parts of the current measuring resistor in order to measure the voltage dropping across the resistor element of the current measuring resistor. A center tap can optionally be provided here by also connecting the circuit board to the resistor element.
In another variant, three connection points can be provided to connect the circuit board to the connection parts, whereby the three connection points form a closed voltage mesh.
It should also be mentioned that the circuit board can also contain an interface in order to transmit measured values of the voltages dropping between the connection parts and/or measured values of a temperature sensor arranged on the circuit board to an external evaluation unit via the interface, the interface preferably being an analog interface.
Alternatively, within the scope of the invention, it is possible for the circuit board to carry an evaluation unit which calculates the electrical current flowing through the current measuring resistor from the measured values of the voltage dropping between the connection parts. The evaluation unit can optionally be connected to a temperature sensor on the circuit board and take the temperature into account when calculating the current flowing through the current measuring resistor for temperature correction. The circuit board can optionally also have a digital interface that is connected to the evaluation unit on the circuit board in order to output the electrical current calculated by the evaluation unit. In addition, the actual measured values of the measured voltage and the measured temperature can also be transmitted via the digital interface.
In the context of the invention, the circuit board can be a rigid circuit board, as is known per se from the prior art. Such circuit boards can, for example, be made of glass fiber composite material. In a preferred embodiment of the invention, however, the circuit board is a flexible circuit board (FPC: Flexible Printed Circuit). Furthermore, there is also the possibility of a hybrid circuit board that is partially flexible and partially rigid, whereby such circuit boards are also referred to as rigid-flex circuit boards.
It should also be mentioned that the current measuring resistor is preferably of low resistance with an electrical resistance of at most 10μΩ, 25μΩ, 50μΩ, 100μΩ, 200μΩ or 500 μΩ.
Furthermore, the current measuring resistor can have a current carrying capacity of at least 100 A, 200 A, 500 A, 1 kA, 2 kA or 5 kA.
In general, it should also be mentioned that the connection parts of the current measuring resistor, the resistive element of the current measuring resistor or the current measuring resistor as a whole are preferably plate-shaped, in particular flat or bent.
Within the scope of the invention, the resistor element of the current measuring resistor can have a smaller thickness than the connection parts of the current measuring resistor.
Furthermore, it should be noted that in the current measuring resistor, the resistor element can be connected to the connection parts by a welded connection, in particular by electron beam welding.
The invention also makes it possible for the current measuring resistor to have an electrical resistance value with a temperature coefficient of at most 200 ppm/K, 100 ppm/K, 50 ppm/K, 20 ppm/K or 10 ppm/K.
It should also be mentioned that the conductor material of the connection parts of the current measuring resistor can be copper, a copper alloy, aluminium or an aluminium alloy.
For example, the resistance material of the resistor element of the current measuring resistor can be one of the following alloys:
However, the conductor material of the connection parts of the current measuring resistor should have a lower specific electrical resistance than the resistance material of the resistor element of the current measuring resistor.
It should also be mentioned that the current measuring resistor preferably has a length in the range of 5 mm-200 mm along the main current flow direction. The width of the current measuring resistor transverse to the main current flow direction, on the other hand, is preferably in the range of 10 mm-100 mm, while the current measuring resistor preferably has a thickness in the range of 1 mm-5 mm.
It should also be mentioned with regard to the press connections according to the invention that these can have a very low electrical contact resistance, which is preferably less than 1 μΩ/mm2.
In addition to the current measuring device according to the invention described above, the invention also claims protection for a corresponding production method, whereby the individual process steps of the production method according to the invention are already apparent from the above description of the current measuring device according to the invention and therefore need not be described again separately.
It should only be mentioned that during the production of the press-sintering temperature, heat is preferably applied to the connection points in order to heat them to a sintering temperature. This sintering temperature is preferably below the melting temperature of the conductor material and also below the melting temperature of the resistance material. The sintering temperature can therefore be in the range of 100° C. to 500° C., for example.
In the case of the press-adhesive connection according to the invention, on the other hand, preferably no heat input takes place.
Other advantageous further embodiments of the invention are characterized in the dependent claims or are explained in more detail below together with the description of the preferred embodiments of the invention with reference to the figures.
In the following, the embodiment of a current measuring device according to the invention is described, which is shown in
The invention initially comprises a low-resistance current measuring resistor 1, which consists of two connection parts 2, 3 made of a conductor material (e.g. copper) and a resistor element 4 made of a resistance material (e.g. Manganin®), whereby the resistor element 4 is arranged in the direction of current flow between the two connection parts 2, 3. The electrical current I to be measured is introduced into the current measuring resistor 1 via the connection part 2 and discharged from the current measuring resistor 1 via the connection part 3. The voltage drop across the resistor element 4 is then a measure of the electrical current I flowing through the current measuring resistor 1 in accordance with Ohm's law.
A bore 5 or 6 is arranged in each of the two connection parts 2, 3, which serves to make contact between the two connection parts 2, 3, as is known from the prior art and is also described, for example, in EP 0 605 800 B1.
In addition, the current measuring device according to the invention comprises a circuit board 7, which in this embodiment is a flexible circuit board (FPC: flexible printed circuit).
The circuit board 7 is connected to an interface 8, which is used to output measured values of the electrical voltage across the resistor element 4 of the current measuring resistor 1 to an external evaluation unit.
For this purpose, the interface 8 enables a plug connection, as is known from the prior art.
The circuit board 7 has several contact fingers 9-11 for the electrical contacting of the current measuring resistor 1. The contact finger 9 is used to make electrical contact with the connection part 2, while the contact finger 11 is used to make electrical contact with the other connection part 3. The center contact finger 10, on the other hand, is used to make electrical contact with the resistor element 4 and thus enables a center tap.
The contact fingers 9-11 protrude from the same side of the circuit board 7 and project in the same direction. For example, the contact fingers 9-11 can be produced by making slots in the circuit board 7.
There is a recess 12 in the connection part 2 to accommodate the contact finger 9. There is also a corresponding recess 13 in the other connection part 3 to accommodate the other contact finger 11. The two recesses 12, 13 extend from the same side edge of the current measuring resistor 1 and are directly adjacent to the resistor element 4. However, it should be mentioned here that there is also the alternative possibility that the two recesses 12, 13 extend into the resistor element 4. In the area of the recesses 12, 13, the two connection parts 2, 3 have a reduced thickness. It should be mentioned here that the temperature coefficient (TCR) of the resistance value of the current measuring resistor 1 can be adjusted by reducing the thickness in the area of the recesses 12, 13, as will be described later.
It should also be mentioned that the contact fingers 9-11 each contact the connection parts 2, 3 or the resistor element 4 on their upper side. This means that the contact finger 10 rests on the upper side of the resistor element 4, while the other contact fingers 9, 11 rest on the upper side of the connection parts 2, 3 in the area of the recesses 12, 13.
When the current measuring resistor 1 is electrically contacted by the circuit board 7, the contact fingers 9-11 are first positioned in the position shown in
A press connection is then created by placing a pressing plunger 14 on the ends of the contact fingers 9-11 and then pressing on the ends of the contact fingers 9-11 with a pressing force. The pressing force is so great that a press connection is created between the contact fingers 9-11 on the one hand and the connection parts 2, 3 or the resistor element 4 on the other. This press connection can be either a press-adhesive connection or a press-sinter connection, as will be described in detail.
The schematic representations according to
It can be seen from the illustrations that the connection parts 2, 3 are connected to the resistor element 4 by a weld seam 15, as is also known, for example, from EP 0 605 800 B1.
Furthermore, not only the upper pressing plunger 14 is shown in the drawings, but also a lower pressing plunger 16, so that a pressing force is exerted both from above and from below when the press connection is produced.
In the invention variants according to
In the invention variant according to
In the variant of the invention according to
The embodiment according to
The embodiment according to
The embodiment according to
A special feature of this embodiment is that a temperature sensor 23 is additionally arranged on the circuit board 7, which measures the temperature at the resistor element 4. This makes it possible to take into account the temperature dependence of the resistance value of the resistor element 4 when calculating the current I flowing through the current measuring resistor 1 from the measured voltage, which allows temperature compensation.
The embodiment according to
A special feature of this design example is that several additional electronic components are arranged on the circuit board 7, namely an analog/digital converter 24, a microprocessor 25 and a component 26 with an insulation path 27 for potential-separated data transmission. The component 26 for potential-separated data transmission is located between the microprocessor 25 and the interface 8.
The embodiment example shown in
A special feature of this embodiment is that the component 26 for potential-separated data transmission is located between the analog/digital converter 24 and the microprocessor 25.
It can be seen from this that the connection parts 2, 3 each have a specific thickness dA, while the resistor element 4 has a reduced thickness dW. In the area of the recesses 12, 13, the thickness of the connection parts 2, 3 is reduced, whereby the recesses 12, 13 have a depth dV. The temperature coefficient TCR of the current measuring resistor 1 can also be adjusted by setting the depth dV.
In each of the recesses 12, 13 there is a mechanical connection area 28, 29, which is only used for the mechanical connection between the circuit board 7 and the current measuring resistor 1. In the mechanical connection areas 28, 29, the surface of the joining partners has a material elevation which is subjected to pressure during the press connection and thus creates a press connection, whereby this material elevation is electrically decoupled.
In addition, there is an electrical connection area 30, 31 in each of the recesses 12, 13 for establishing an electrical connection.
It should be mentioned here that the mechanical connection areas 28, 29 on the one hand and the electrical connection areas 30, 31 on the other hand are spatially separated and electrically decoupled.
Finally,
In the invention variant according to
The flow chart shown in
In a first step S1, a current measuring resistor with a resistor element and two connection parts is first provided.
In a second step S2, the recesses described above are then formed in the connection parts and optionally in the resistor element of the current measuring resistor, which can be done by milling, for example.
In the next step S3, a circuit board is then provided and contact fingers are formed in the circuit board in a step S4, which are used to make contact with the current measuring resistor.
In the next step S5, the connection points of the current measuring resistor can be nano-structured.
The current measuring resistor and the circuit board are then joined together in step S6 so that the contact fingers of the circuit board lie in the recesses and/or on the back of the recesses.
In the next step S7, the connection points are then heated to a sintering temperature that is sufficient to produce a press-sinter connection.
In the next step S8, the circuit board and the current measuring resistor are then pressed together at the connection points to create the desired press-sinter connection.
The invention is not limited to the preferred embodiments described above. Rather, a large number of variants and modifications are possible which also make use of the inventive concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and the features of the dependent claims independently of the respective claims referred to and, in particular, also without the features of the main claim. The invention thus comprises various aspects of the invention which enjoy protection independently of each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 109 708.0 | Apr 2022 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/058185 | 3/29/2023 | WO |
