Measuring setup for current measurement

Abstract

Measuring setup for current measurement using a measuring resistor (R) M ) with a positive temperature coefficient, which is designed as a conductor track section of a printed circuit board, characterized in that - the printed circuit board is designed as a multilayer printed circuit board (1), - the measuring resistor (R M ) is designed as a conductor track section (2) of an inner layer (1.1) of the multilayer printed circuit board (1), - for temperature compensation of the measuring resistor (R M ) a compensation resistor (R1) is provided, which is arranged as a single component (K) on a component surface (1.0) of the printed circuit board (1) in a position perpendicular to the area of ​​the conductor track section (2), wherein the substrate material of the printed circuit board (1) between the inner layer (1.1) supporting the conductor track section (2) and the single component (K) as compensation resistor (R1) causes thermal coupling, - the compensation resistor (R1) with the temperature coefficient of the measuring resistor (R) M ) is trained, - the measuring resistor (R M ) and the compensation resistor (R1) are connected in series, the series connection being connected to two measuring inputs of a measuring circuit (MS), - the measuring circuit (MS) is configured to produce a measurement signal (U) representing the current value a to generate.

Description

[0001] The invention relates to a measuring arrangement for current measurement by means of a measuring resistor designed as a conductor track section of a printed circuit board according to the preamble of patent claim 1.

[0002] From the generic document DE 10 2006 007 741 A1, a measuring arrangement for current measurement is known in which a current-carrying conductor track of the circuit is used as a measuring resistor, also called a shunt resistor, in a line of an electrical circuit. The absolute resistance of the conductor track between two voltage sampling points is determined at the factory from a calibration measurement using a test current. The temperature response of the conductor track's resistance is known. To measure the current, the voltage drop between the voltage sampling points of this conductor track is measured. The temperature of the conductor track is determined via the voltage drop when an applied test current is applied to a conductor track of known resistance and temperature response that is thermally coupled to the measuring resistor. If there is good thermal coupling between this conductor track and the measuring resistor, this is also the conductor's temperature.After the temperature has been determined, the absolute resistance of the current-carrying conductor in the circuit is calculated as the measuring resistance. Finally, the current is calculated from the voltage drop between the voltage sampling points of the current-carrying conductor and its calculated absolute resistance.

[0003] Furthermore, DE 10 2006 006 328 A1 also describes a measuring arrangement for current measurement using a measuring resistor formed by a meandering conductor section on a circuit board. To compensate for the temperature dependence of the measuring resistor formed as a conductor section, a temperature sensor is provided, which is partially enclosed by the meandering conductor. The current resistance value of the measuring resistor is calculated by software from the measuring voltage of the measuring resistor, amplified by a measuring amplifier, and a temperature determined by the temperature sensor. The current current is calculated by forming the quotient between the voltage drop across the measuring resistor and its currently determined resistance value.

[0004] A measuring arrangement for current measurement using a measuring resistor designed as a single component is also described in DE 102 11 117 A1. To compensate for the temperature dependence of the measuring resistor, a winding of a wire made of the same material as the measuring resistor, e.g., copper, is wound around the resistor as a compensation resistor along its length between its taps. This winding can also be bifilar. This temperature-compensating copper winding then has the same temperature coefficient as the measuring resistor and, over the winding length, replicates the temperature profile of the measuring resistor located within the winding, which is why this winding is ideally suited as a compensation resistor for temperature compensation.

[0005] According to DE 102 11 117 A1, the compensation resistor, designed as a winding around the measuring resistor, is connected in series with the measuring resistor and coupled to an operational amplifier configured as a non-inverting amplifier. The feedback path of this operational amplifier is formed by the compensation resistor, which is connected to the inverting input of the operational amplifier. The measuring resistor is connected to the non-inverting input of the operational amplifier. The output of the operational amplifier provides a temperature-compensated measurement signal representing the current value. Furthermore, DE 102 11 117 A1 proposes an operational amplifier configured as an inverting amplifier as the measuring circuit instead of a non-inverting operational amplifier.

[0006] Based on this prior art, it is the object of the invention to provide an improved measuring arrangement for current measurement of the type mentioned at the beginning.

[0007] This problem is solved by a measuring arrangement having the features of patent claim 1.

[0008] Such a measuring arrangement for current measurement by means of a measuring resistor with a positive temperature coefficient, which is designed as a conductor track section of a printed circuit board, is provided according to the invention that - the circuit board is designed as a multi-layer circuit board, - the measuring resistor is designed as a conductor track section of an inner layer of the multilayer printed circuit board, - for temperature compensation of the measuring resistor, a compensation resistor is provided, which is arranged as a single component on a mounting surface of the printed circuit board in a position perpendicular to the area of ​​the conductor track section, wherein the carrier material of the printed circuit board effects a thermal coupling between the inner layer carrying the conductor track section and the single component as a compensation resistor, - the compensation resistor is designed with the temperature coefficient of the measuring resistor, - the measuring resistor and the compensation resistor are connected in series, the series circuit being connected to two measuring inputs of a measuring circuit, - the measuring circuit is designed to generate a temperature-compensated measuring signal representing the current value.

[0009] In this measuring arrangement according to the invention, the compensation of the temperature dependence of the measuring resistor is performed exclusively on a hardware basis, meaning that the measured value supplied by the measuring circuit for temperature compensation does not require any software-based calculation. This is achieved by means of a compensation resistor that is thermally coupled to the measuring resistor via the intermediate carrier material, thus in addition to the naturally occurring thermal coupling via electrical contacts of the compensation resistor. In particular, this measuring arrangement according to the invention has the advantage that resistors can be used as measuring resistors and as compensation resistors with a temperature coefficient TK significantly greater than 100.

[0010] The operational amplifiers known from DE 102 11 117 A1 with a non-inverting or an inverting circuit are suitable as a measuring circuit.

[0011] Further advantages of the measuring arrangement according to the invention are that the influence of the measurement on the measured variable "current" is reduced, which also reduces power losses during the measurement conversion. Furthermore, parasitic and undesirable contact resistances caused by assembly are avoided. This parasitic power loss reduction enables a smaller design on the circuit board, since power loss is usually the determining factor in the circuit board layout.

[0012] According to an advantageous embodiment of the invention, the inner layer forming the measuring resistor is arranged directly adjacent to the component surface of the circuit board. This achieves optimal thermal coupling of the measuring resistor to the compensation resistor. Preferably, the inner layer forming the conductor track section as a measuring resistor is designed as the ground of the measuring arrangement.

[0013] An advantageous development of the invention is provided in that the conductor track section forming the measuring resistor is designed as a tongue-like punched-out section of the inner layer. This offers the advantage that it is not necessary to create additional through-holes in another circuit board level of the multilayer circuit board or to use such through-holes in addition. As a rule, the ground connection (GND) exists as a continuous inner layer that can be used to create the measuring resistor. If the measuring resistor is connected to a positive potential as a conductor track section, there is also a corresponding inner layer for this. By reducing the number of through-holes, it is possible to reduce parasitic contact resistance in the layout and thus the power loss in the control unit.In some cases, this can also lead to an improvement in the supply voltage range of the load to be controlled.

[0014] According to a further advantageous embodiment of the invention, the compensation resistor is designed as a chip component with a small-signal inductance. This makes it possible to use commercially available and therefore cost-effective components, and it has been found that the small-signal inductance has no negative impact on temperature compensation up to the range of a few mH.

[0015] It is particularly advantageous if, according to a further development, the measuring circuit is designed as an amplifier with feedback. Preferably, the measuring circuit is designed as a non-inverting operational amplifier, with the feedback formed by a temperature-independent resistor and the temperature-dependent compensation resistor, and the measuring voltage generated by the measuring resistor being supplied to the operational amplifier as the input voltage.

[0016] Finally, instead of an operational amplifier configured as a non-inverting amplifier, a comparator with a sigma-delta converter can be used. This offers the advantage that, when the measurement setup is integrated into an integrated circuit (IC), a simple A / D conversion of the measurement voltages can be performed. Matching and switched current sources are available on the integrated circuit for such an A / D conversion, which can be easily and effectively implemented within the integrated circuit. This eliminates the need for a voltage-based A / D conversion detour.

[0017] The invention is described and explained below using exemplary embodiments with reference to the accompanying figures. They show: Fig. 1 a schematic diagram of a power output stage for an electric motor in an H-bridge with a low-side resistor as a measuring resistor, Fig. 2 a sectional view through a multilayer printed circuit board with a measuring resistor and an associated compensation resistor according to the measuring arrangement according to the invention, Fig. 3 a sectional view of an inner layer of the circuit board implementing the compensation resistor according to Fig. 2, Fig. 4 a circuit diagram of a measuring arrangement as an embodiment of the invention with a measuring circuit having an operational amplifier in non-inverting circuitry, a measuring resistor and a compensation resistor according to the Fig. 2 and Fig. 3, and Fig. 5 a circuit diagram of a measuring arrangement as a further embodiment of the invention with an alternative measuring circuit, a measuring resistor and a compensation resistor according to the Fig. 2 and Fig. 3.

[0018] To control an electric motor used as an actuator, the operating current must be measured using a measuring resistor (shunt resistor). Such an electric motor M is controlled, for example, by an H-bridge consisting of power transistors T1 to T4, with a load current I being measured. L a low-side resistor as measuring resistor R M used, as shown schematically in Fig. 1. The H-bridge is powered by an operating voltage V CC A high-side resistor can also be used as a measuring resistor.

[0019] This measuring resistor R M is in a Fig. 4 is realized as a conductor track section of a conductor track of a multilayer printed circuit board (multilayer printed circuit board). Such a multilayer printed circuit board 1 shows sections of the Fig. 2 and Fig. 3. This multilayer printed circuit board 1 has several inner layers, with the inner layer 1.1 located directly below a component level 1.0 providing the measuring resistance R M is realized as conductor section 2. This measuring resistor R M has a temperature coefficient TK corresponding to the conductor material of the multilayer printed circuit board 1, i.e. corresponds to that of copper, which is used as the conductor material of this multilayer printed circuit board 1.

[0020] This conductor section 2 is according to Fig. 3 tongue-shaped with a width B and a length L in the form of a tongue-shaped cutout, where the length L is given by the distance between two terminals A2 designed as through-holes around A3. The load current I L (e.g. of the engine M according to Fig. 1) is fed to a through-hole A1 with connection to the inner layer 1.1, so that the load current I Lvia the conductor track section 2 and then via the connecting area 2.0 of the tongue shape of the conductor track section 2 with the inner layer 1.1 onto the same, whereby this inner layer 1.1 is Fig. 4 serves as the mass of the measuring arrangement.

[0021] According to Fig. 2, a chip component K is arranged directly above this conductor track section 2 on the assembly surface 1.0, which in the circuit diagram according to Fig. 4 is designated as compensation resistor R1 and is used for temperature compensation of the temperature-dependent measuring resistor R M is used. After Fig. 3 shows a top view of the inner layer 1.1, the position of the chip component K relative to the conductor track section 2, indicated by dashed lines. According to this, in a vertical projection onto the conductor track section 2, the chip component K is located in a central region of the tongue shape of the conductor track section 2.

[0022] In order to enable such temperature compensation, this chip component K has the same temperature coefficient TK as the measuring resistor R formed from the conductor material. M and on the other hand, these two components, i.e. the chip component K and the conductor track section 2, are arranged adjacent to each other, so that a thermal coupling is created, ie that the chip component K is heated in the same way as the load current I L heated conductor section 2 or has the same temperature when the temperature change is introduced from the outside. According to the Fig. 2 and Fig. 3 is the chip component K with the position of the measuring resistor R MThe inner layer 1.1, with which the conductor track section 2 is realized, is located directly adjacent to the assembly surface 1.0 of the multilayer printed circuit board 1, so that only thin carrier material of the multilayer printed circuit board 1 is located between these two levels, whereby a high thermal coupling of the conductor track section 2 carried by the load current I L through which the conductor track section 2 is carried to the chip component K is ensured.

[0023] This chip component K is connected with one terminal to terminal A3 of the conductor track section 2, while the other terminal serves as the measuring signal line L1 of a measuring circuit MS (cf. Fig. 4). Another measuring signal line L2 is connected to the other terminal A2 of the conductor section 2 and is also fed to the measuring circuit MS (see Fig. 4).

[0024] For the conductor section 2 as measuring resistor R M It is advantageous if its resistance value is between 250µOhm and 1.2 mOhm to resolve motor peak currents up to approximately 120A. The compensation resistor R1 should have a resistance value of approximately 5 to 10 Ohms. The resistance material for the chip component K as the compensation resistor R1 corresponds to the material of the measuring resistor R M realized conductor section 2 to ensure the most accurate possible match of the temperature coefficients of these two components. The chip component K can also have a small-signal inductance of up to a few mH without this having a negative effect on the temperature compensation of the measuring resistor R M would have.

[0025] In the following, the structure and function of the measuring circuit MS according to Fig. 4 will be explained.

[0026] This measuring circuit MS according to Fig. 4 comprises an operational amplifier OP, which is wired as a non-inverting amplifier. This non-inverting amplifier circuit includes, in a known manner, resistors R1 and R2 consisting of the feedback circuit, with resistor R1 corresponding to the compensation resistor embodied as chip component K, and resistor R2 being temperature-independent.

[0027] The resistor R2 is connected between the output A of the operational amplifier OP and its inverting input, while the compensation resistor R1 is connected between the inverting input of the operational amplifier OP and the ground GND.

[0028] Between the non-inverting input of the operational amplifier OP and the ground GND is the measuring resistor R M switched, whose voltage drop is the input voltage U eis applied to the non-inverting input of the operational amplifier OP. This completes the series circuit consisting of the compensation resistor R1 and the measuring resistor R M connected to the two measuring inputs of the measuring circuit MS, i.e. the non-inverting and the inverting input of the operational amplifier OP.

[0029] The output voltage U a the measuring circuit according to Fig. 4 is obtained in a manner known to the person skilled in the art according to the following formula: Ua=Ue×(1+R2 / R1).

[0030] The compensation resistor R1 has the same temperature coefficient TK as the measuring resistor R M , ie the output voltage U a decreases with increasing temperature of the compensation resistor A1, ie the gain of the measuring circuit MS decreases with increasing temperature of the measuring resistor R M away.

[0031] Since only the differential voltage U D between the measuring voltage U M (ie the input voltage U e ) and the voltage drop U K is regulated at the compensation resistor R1 and the two resistors R1 and R M have an identical temperature coefficient and are thermally coupled, the heating of the two resistors R1 and R M compensated for the increase in voltage drop. This means that the regulation of the currents by the two resistors R1 and R M by means of the operational amplifier OP is carried out in such a way that at the two resistors R1 and R M the same voltage drop occurs. This results in a temperature-compensated output signal U at the output A of the operational amplifier OP. a available, which determines the current value of the load current I L represents.

[0032] This output signal U a is fed to a digital-to-analog converter DA via a resistor R 3 for further processing.

[0033] To adjust the offset of the operational amplifier (OP), a temperature-adjusted value is added to the input voltage at the non-inverting input of the operational amplifier (OP) using a digital-to-analog converter or a PWM-modulated square wave signal. A corresponding control output (St) is required for this purpose. A connected to the non-inverting input of the operational amplifier OP via a series circuit consisting of a resistor R4 and a resistor R5, the connecting branch of these two resistors R4 and R5 being connected to ground GND via a capacitor C.

[0034] According to Fig. 4, the listed components are arranged on the circuit board 1 together with other components not mentioned, whereby in addition to the measuring resistor R Mand the chip component K as compensation resistor R1, all listed components can be implemented in an integrated circuit to achieve a more cost-effective implementation. Fig. Figure 5 shows an alternative measuring circuit MS implemented on an integrated circuit (IC). This measuring circuit MS comprises a comparator Comp, a sigma-delta converter Σ / Δ, and several current sources S switched by the output of this sigma-delta converter Σ / Δ. The two inputs of the comparator Comp are supplied with the measuring voltage U M via a measuring signal line L2 and the voltage drop U K of the compensation resistor R1 via a measurement signal line L1. The output of this comparator Comp is fed to the input of the sigma-delta converter Σ / Δ. The current sources S are switched by the output of the sigma-delta converter Σ / Δ.

[0035] The operation of such a sigma-delta converter Σ / Δ is known to those skilled in the art and therefore not described in detail. The comparator Comp records the difference between the measuring voltage U M and the voltage drop U K of the compensation resistor R1, so that depending on this difference, the current sources S are controlled by the sigma-delta converter Σ / Δ. The control is carried out in such a way that the difference between U M and U K to zero (+- 1 digit). For example, if the current sources S are controlled via the power 2 n staggered, this results in the digital raw value of the load current I to be converted and measured L . This embodiment shows how the use of integrated and matched current sources S in an integrated circuit IC for providing the current in the compensation resistor for adjusting U M and U Kcan be used advantageously. Reference symbol: 1 multilayer circuit board 1.0 Assembly surface of the multilayer circuit board 1 1.1 Inner layer of the multilayer circuit board 1 2 Conductor track section of the inner layer 1.1 2.0 Connection area of ​​the conductor track section 2 to the inner layer 1.1 A1 Through-hole plating of the multilayer circuit board 1 A2 Connection of the multilayer circuit board 1 A3 Connection of the multilayer circuit board 1 B Width of the conductor track section 2 C capacity Comp Comparator DA digital-to-analog converter GND Ground I L Load current K chip component L Length of the conductor track section 2 L1 measuring signal line L2 measurement signal line M electric motor MS measuring circuit OP operational amplifier R1 compensation resistor R2 temperature-independent resistor R3 resistor R4 resistor R5 resistor R M measuring resistor S Power sources St A Control output U a Output voltage of the operational amplifier OP U e Input voltage of the operational amplifier OP U K Voltage drop across compensation resistor R1 U M Measuring voltage of the measuring resistor R M V CC Operating voltage Σ / Δ Sigma-Delta converter T1 - T4 power transistors

Claims

[1] Measuring arrangement for current measurement using a measuring resistor (R M ) with a positive temperature coefficient, which is designed as a conductor track section of a printed circuit board, characterized by , that - the printed circuit board is designed as a multi-layer printed circuit board (1), - the measuring resistance (R M ) is designed as a conductor track section (2) of an inner layer (1.1) of the multilayer printed circuit board (1), - for temperature compensation of the measuring resistor (R M ) a compensation resistor (R1) is provided, which is arranged as an individual component (K) on a mounting surface (1.0) of the printed circuit board (1) in a position perpendicularly aligned with the area of ​​the conductor track section (2), wherein the carrier material of the printed circuit board (1) effects a thermal coupling between the inner layer (1.1) carrying the conductor track section (2) and the individual component (K) as a compensation resistor (R1), - the compensation resistor (R1) with the temperature coefficient of the measuring resistor (R M ) is trained, - the measuring resistance (R M ) and the compensation resistor (R1) are connected in series, the series circuit being connected to two measuring inputs of a measuring circuit (MS), - the measuring circuit (MS) is designed to generate a measuring signal (U a ) to generate. [2] Measuring arrangement according to claim 1, characterized by that the conductor section (2) as a measuring resistor (R M ) forming inner layer (1.1) is advantageously arranged directly adjacent to the assembly surface (1.0) of the printed circuit board (1). [3] Measuring arrangement according to claim 1 or 2, characterized by that the measuring resistance (R M ) forming inner layer (1.1) is designed as the mass of the measuring arrangement. [4] Measuring arrangement according to one of the preceding claims, characterized bythat the conductor track section (2) serves as a measuring resistor (R M ) is designed as a tongue-like cut-out located within the inner layer (1.1). [5] Measuring arrangement according to one of the preceding claims, characterized by that the compensation resistor (R1) is designed as a chip component (K) with a small-signal inductance. [6] Measuring arrangement according to one of the preceding claims, characterized by that the measuring circuit (MS) is designed as an amplifier with feedback. [7] Measuring arrangement according to claim 6, characterized by that the measuring circuit (MS) is designed as a non-inverting operational amplifier (OP), wherein the feedback is formed by a temperature-independent resistor (R2) and the temperature-dependent compensation resistor (R1) and the feedback is formed by the measuring resistor (R M ) generated measuring voltage (U M ) as input voltage (U e) is fed to the operational amplifier (OP). [8] Measuring arrangement according to one of the preceding claims 1 to 5, characterized by that the measuring circuit (MS) is designed as a comparator (Comp) with a sigma-delta converter (Σ / Δ). [9] Measuring arrangement according to claim 8, characterized by that current sources (S) switched by the sigma-delta converter (Σ / Δ) are provided. [10] Measuring arrangement according to claim 9, characterized by that the switched current sources (S) together with the sigma-delta converter (Σ / Δ) are implemented on an integrated circuit (IC).

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