Method for detecting the resistance value of a measuring resistor and module for performing the method.

Abstract

The present invention relates to a method for detecting the resistance value of a measuring resistor, the method comprising the steps of: a) providing a module for measuring the intensity of a current, the module including a measuring resistor and a reference resistor; b) setting a resistance ratio; c) measuring the resistance value of the measuring resistor with a first measuring device; d) measuring the resistance value of the reference resistor; e) adjusting the resistance value of the reference resistor so that the ratio of the resistance value of the reference resistor to the resistance value of the measuring resistor is the same as the set resistance ratio; f) integrating the module into an application execution environment; g) measuring the resistance value of the reference resistor in the application execution environment with a second measuring device; and h) detecting the resistance value of the measuring resistor from the resistance value of the reference resistor measured in step g) and a known resistance ratio from step b). Furthermore, the present invention also relates to a module for performing such a method.

Description

Technical Field

[0001] The present invention relates to a method for detecting the resistance value of a measuring resistor and a module for carrying out the method.

Background Art

[0002] For current measurement in electronic circuits, a measuring resistor connected in series with a component to be monitored is used. In this case, the current value is determined according to Ohm's law from the voltage dropped across the measuring resistor, which is called a shunt resistor. In this case, it is assumed that the resistance value is known within a specific accuracy limit. Accurate measurement of current values is particularly important, for example, in battery management systems of electric vehicles or hybrid vehicles. Here, due to the high current values, measuring resistors of 10 μOhm to 200 μOhm are usually used.

[0003] Due to the high requirements for the accuracy of current measurement, it is necessary to reduce the uncertainty in the information of the resistance value of the measuring resistor. It is necessary to reduce this uncertainty to less than ±0.5%. For technical reasons, even within a batch of measuring resistors, the resistance values of individual measuring resistors may fluctuate significantly more than ±0.5%. In order to maintain the tolerance range, resistors whose resistance values are outside the tolerance range can be sorted out, but this increases waste and may ultimately lead to an increase in manufacturing costs.

[0004] Instead of selecting individual resistors, the individual resistance values ​​of each resistor can be measured and calibrated to the required precision, and this information can be provided in an appropriate manner to the user of the resistor or the execution environment of the application in which the resistor is used. The application execution environment may be, for example, a battery management system. Measuring resistances in the 100 μOhm range requires precision measuring instruments. For such small resistance values, the resistance of the measuring leads must also be considered, making resistance measurement using four-wire technology essential. Since such measurement technology is usually not available in the application execution environment in which the resistor must be used, calibrating each individual resistor within that application execution environment, i.e., on-site, would be impossible or at least incur significant additional costs. However, individual resistor calibration can be performed by the resistor manufacturer without incurring substantial costs. The individual resistance values ​​of each resistor measured there, i.e., product-specific resistance values, must be attached to each resistor as product-specific information so that these measurements can be used when integrating the resistor into its application execution environment.

[0005] Patent Document 1 describes how individual resistance values ​​of shunt resistors can be stored as information in a code display area on the shunt. This code may be a DataMatrix-Code (DMC). Furthermore, Patent Document 2 proposes protecting such a code display area from damage by mounting it in a recess on the shunt surface. However, reading the code requires a suitable reading device on the shunt user's side and a secure process to correctly assign the read information, i.e., precisely programmed into the battery management system using the shunt resistor. This process is complex and involves risks. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] German Patent Application Publication No. 112016002799 Specification [Patent Document 2] German Utility Model Publication No. 202022104228 Specification [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the present invention is based on the problem of providing an alternative method for detecting the resistance value of a measurement resistor. Furthermore, the present invention is also based on the problem of providing a module that enables the execution of that method. [Means for solving the problem]

[0008] The present invention is described with respect to the features of claim 1 with respect to the method and with respect to the features of claim 7 with respect to the module. Other relevant claims are advantageous embodiments and variations of the present invention.

[0009] The present invention relates to a method for detecting the resistance value of a measuring resistor, and this method is a) A module for measuring the intensity of current, wherein the module includes a measuring resistor and a reference resistor, b) A step of setting the resistance ratio, c) A step of measuring the resistance value of the measuring resistor using the first measuring device, d) A step of measuring the resistance value of the reference resistor, e) A step of adjusting the resistance value of the reference resistor so that the ratio between the resistance value of the reference resistor and the resistance value of the measured resistor becomes the same as the set resistance ratio. f) The process of integrating the module into the application execution environment, g) A step of measuring the resistance value of a reference resistor in the application execution environment using a second measuring device, h) A step to detect the resistance value of the measurement resistor from the resistance value of the reference resistor measured in step g) and the known resistance ratio from step b). Includes.

[0010] In this context, the present invention is based on the idea that resistors of at least 1000 ohms can be measured far more easily and precisely than resistors of 100 μOhms. In the case of 1000 ohms, the resistance of the measurement lead wire is not significant due to the large resistance value, so a two-wire technique can be used to obtain sufficiently accurate results. To measure the resistance value, it is sufficient to apply a current of only a few milliamperes to the resistor and obtain a voltage drop of a few volts as the measurement signal.

[0011] Against this background, the present invention proposes to provide a module including a measuring resistor and a reference resistor. Furthermore, a specific resistance ratio is set between the resistance value of the reference resistor and the resistance value of the measuring resistor. The resistance ratio is preferably at least 100,000, particularly preferably at least 1,000,000, and maximum 100,000,000,000, particularly preferably maximum 1,000,000,000. That is, if the resistance value of the measuring resistor is, for example, 100 μOhm, the resistance value of the reference resistor may be, for example, 1000 Ohm, in which case the resistance ratio is 10,000,000.

[0012] The resistance value of the measurement resistor is measured with sufficient accuracy using a first measuring device. The resistance value of the reference resistor is measured in the same manner. To minimize systematic errors, this is preferably done using the same measuring device. If the ratio of the resistance value of the reference resistor to the resistance value of the measurement resistor does not match a pre-set resistance ratio, the resistance value of the reference resistor is adjusted by modifying the reference resistor (step e). This can be done, for example, by laser trimming. In this case, the reference resistor is adjusted (usually increased) by up to 10% of its original resistance value by removing and / or cutting the resistive layer or resistive material. Preferably, the resistance value is trimmed by removing and / or cutting perpendicular to the direction of current flow in the resistor. The perpendicular trimming can be done several times in a row or in a meandering manner. Furthermore, this perpendicular trimming operation can be combined with removal and / or cutting in further directions, such as L-shaped cuts, thereby achieving the most precise adjustment possible for the reference resistor. The adjustment of resistance values ​​is performed using an active procedure in which the reference resistance is continuously measured during the adjustment process, and the adjustment is terminated when the target value is reached. In other words, the reference resistance is adjusted until the ratio of the measured resistance values ​​closely matches a pre-set resistance ratio. Thus, the resistance value of the reference resistance becomes a defined multiple of the resistance value of the measured resistance. In this way, the reference resistance is associated with information based on individual measurements of how much resistance the measured resistance actually has. Therefore, the reference resistance is calibrated to a precisely known multiple of the measured resistance.

[0013] This process can be performed on multiple modules, for example, each module in a batch or each module of a specific type. In this case, the resistance value of the reference resistor is always adjusted, so even if the resistance values ​​of individual measured resistors vary from module to module, the resistance ratios of all modules match with sufficient accuracy. Therefore, the resistance ratio is a characteristic that applies equally to all modules.

[0014] A module having a measuring resistor and a reference resistor adjusted to this measuring resistor is incorporated into the application execution environment. The resistance ratio, a consistent characteristic for all modules, is known to the user or operator of the application execution environment, for example, from a datasheet or other source. In the application execution environment, the resistance value of the reference resistor is measured by a second measuring device. Since the resistance value of the reference resistor is several orders of magnitude larger than that of the measuring resistor, simple measurement techniques can achieve sufficient accuracy. The resistance value of the module's measuring resistor is detected by division from the measured resistance value of the reference resistor and the known resistance ratio that applies similarly to each module.

[0015] A particular advantage is that a simple measurement technique, commonly used in many applications, can be used to measure the resistance of the reference resistor in the application execution environment. Due to the high resistance, the resistance of the measurement leads can be ignored, eliminating the need for a four-wire technique. A voltage signal of several volts can be obtained by applying only a few milliamperes of current to the reference resistor. A voltage of several volts can be measured accurately without significant cost. Furthermore, parasitic voltages, such as contact voltage and thermal voltage, are not a problem within this measurement range.

[0016] Furthermore, in the application execution environment, steps g) and h) can be automated and performed by software control. For example, after integrating the module into the application execution environment, the software-controlled measuring device can perform resistance measurement of a reference resistor. The detected measurement value is read by the program, divided by a pre-known resistance ratio, and the resulting resistance value of the measured resistor is stored in the program for further use in current measurement. Thus, a high level of automation can be achieved. This reduces costs and minimizes problems caused by human error. [Modes for carrying out the invention]

[0017] In one embodiment, the module may comprise a support element, in particular a printed circuit board, and the reference resistor may be mounted on said support element. Accordingly, the reference resistor is arranged on a component that is already present in many cases.

[0018] In a further embodiment, the reference resistor may be an SMD resistor, in particular a thin-film or thick-film SMD resistor. SMD resistors are particularly well suited for mounting on printed circuit boards. Furthermore, the resistance value of an SMD resistor can be adjusted particularly well and precisely. Structures of type 1206, 0612, 0805 or 0603 are particularly advantageous.

[0019] In a further embodiment, the first measurement device may be a precision measuring instrument suitable for measuring resistance values on the order of 100 μOhm with an uncertainty of at most 0.5%, preferably at most 0.2%.

[0020] In a further embodiment, the application execution environment may be a battery management system. A battery management system is typically provided with a measurement device suitable for measuring a reference resistor with sufficient accuracy.

[0021] In a further embodiment, the second measurement device may be suitable for measuring resistance values on the order of 1000 Ohm with an uncertainty of at most 0.5%, preferably at most 0.2%. In particular, the second measurement device may comprise an analog-to-digital converter.

[0022] Here, with regard to further technical features and advantages of the method according to the present invention, the description and embodiments relating to the module according to the present invention are explicitly incorporated herein by reference.

[0023] A further aspect of the present invention relates to a module for carrying out the method described above. This module comprises a measuring resistor and a tap for measuring the voltage drop across the measuring resistor when current flows through it. Furthermore, this module comprises a reference resistor and at least one further tap for measuring the voltage drop across the reference resistor when current flows through it. This further tap may be, for example, a pin. The voltage drop across the reference resistor can typically be measured against a zero charge where a tap already exists on the module.

[0024] In one embodiment, the reference resistor may be machined so that its resistance value is altered relative to its original resistance value. This machining may include, or may not include, removal of the resistive material, particularly a reduction in the thickness of the resistive material. The machining may also create at least one notch in the resistive material. Preferably, the resistance value is trimmed by removing and / or cutting perpendicular to the direction of current flow in the resistor. The perpendicular trimming may be performed several times in succession or in a meandering manner. Furthermore, this perpendicular trimming procedure may be combined with removal and / or cutting in further directions, for example, an L-shaped notch. In this way, high-precision adjustment of the reference resistor is achieved. The machining described above usually increases the resistance value of the reference resistor. Therefore, the reference resistor should be selected such that, in its unmachined state, its resistance value is small enough to be adjusted to the minimum resistance value of the measurement resistor. The machining can usually increase the resistance value of the reference resistor by up to 10% of its original resistance value.

[0025] Herein, further technical features and advantages of the module according to the present invention are explicitly described, along with descriptions and examples related to the method according to the present invention.

[0026] The present invention will be described in detail using examples.

[0027] Numerous modules are manufactured, each containing one measuring resistor and one reference resistor, both with a rated resistance of 100 μOhm. Due to manufacturing limitations, the variation in the measuring resistor's resistance value is ±5%, and therefore the actual resistance value of the measuring resistor can range from 95 to 105 μOhm. The resistance ratio of the reference resistor to the measuring resistor is set to 10,000,000. The resistance value of the reference resistor is appropriately adjusted by laser trimming. Therefore, depending on the actual resistance value of the measuring resistor, the resistance value of the reference resistor after adjustment can be between 950 and 1050 Ohm. Next, each module is installed in a battery management system. The battery management system has a 3.3V voltage source and a voltage divider with a fixed resistor of 1000 Ohm, to which the module's reference resistor is connected in series. When the reference resistor is 950 Ohm, the voltage drop across this resistor is 1.608V. When the reference resistor is 1050 Ohm, the voltage drop across this resistor is 1.690V. In other words, the tolerance range of a total measurement resistance of 10 μOhm is represented by a voltage signal with a fluctuation range of 82 mV. When using a simple 3.3 V 10-bit analog-to-digital converter for voltage measurement, the resolution is 3.2 mV per digit. Thus, the fluctuation range of the voltage signal is divided into 25 digits. Each digit corresponds to a resistance change of 0.4 μOhm or 0.4% of the measurement resistance relative to the rated value of 100 μOhm. Therefore, the proposed method makes it possible to improve the accuracy of information regarding the resistance value of the measurement resistance by approximately 10 times using a simple analog-to-digital converter. Higher accuracy can be achieved by increasing the resolution of the analog-to-digital converter.

Claims

1. A method for detecting the resistance value of a measuring resistor, a) A step of providing a module for measuring the intensity of current, wherein the module includes a measuring resistor and a reference resistor, b) A step of setting the resistance ratio, c) A step of measuring the resistance value of the measuring resistor using the first measuring device, d) A step of measuring the resistance value of the reference resistor, e) A step of adjusting the resistance value of the reference resistor so that the ratio between the resistance value of the reference resistor and the resistance value of the measurement resistor becomes the same as the set resistance ratio, f) The step of incorporating the module into the application execution environment, g) A step of measuring the resistance value of the reference resistor in the application execution environment using a second measuring device, h) A step of detecting the resistance value of the measurement resistor from the resistance value of the reference resistor measured in step g) and the resistance ratio known from step b), Methods that include...

2. The method according to claim 1, characterized in that the module includes a support element, and the reference resistor is mounted on the support element.

3. The method according to claim 1 or 2, characterized in that the reference resistor is an SMD resistor.

4. The method according to any one of claims 1 to 3, characterized in that the first measuring device is suitable for measuring a resistance value of 100 μOhm with a maximum uncertainty of 0.5%.

5. The method according to any one of claims 1 to 4, characterized in that the application execution environment is a battery management system.

6. The method according to any one of claims 1 to 5, characterized in that the second measuring device is suitable for measuring a resistance value of 1000 ohms with a maximum uncertainty of 0.5%.

7. A module for performing the method according to any one of claims 1 to 6, comprising a measuring resistor and a tap for measuring the voltage drop across the measuring resistor, wherein the module further comprises a reference resistor and at least one additional tap for measuring the voltage drop across the reference resistor.

8. The module according to claim 7, characterized in that the reference resistor has been modified, and as a result, its resistance value has changed from its original resistance value due to the modification.

Images