MEASURING DEVICE FOR DIFFERENTIAL VOLTAGE MEASUREMENT

Description

[0001] The invention relates to a device, in particular a switching arrangement, for measuring a voltage, in particular an alternating voltage or a direct voltage (e.g. the intermediate circuit voltage of a switched-mode power supply or motor electronics).

[0002] A household appliance, such as a washing machine or dishwasher, typically has a mains connection, in particular a switched-mode power supply, which allows the appliance to be connected to an alternating current (AC) power supply network. The mains voltage provided by a power supply network can fluctuate in terms of voltage level and / or frequency. Such fluctuations can lead to overvoltage situations and / or fluctuations in the power consumption of a household appliance, and thus potentially impair its operation.

[0003] Measuring devices for detecting voltages are described, for example, in JP 2011 064559 A, WO 2006 / 085771 A1, US 2018 / 279413 A1, US 2003 / 168995 A1, JP 2015 023608 A , JP 2012 002542 A, CN 105 870 931 B or DE 10 2017 205359 A1.

[0004] This document addresses the technical challenge of enabling efficient and precise measurement of the mains or supply voltage of an electrical device, particularly a household appliance, in order to ensure reliable and stable operation of the electrical device even in the event of fluctuations in the supply voltage.

[0005] The problem is solved by the subject matter of the independent patent claim. Advantageous embodiments are defined in particular in the dependent patent claims, described in the following description, or illustrated in the accompanying drawing.

[0006] According to one aspect of the invention, a household appliance measuring device for determining measurement information with respect to an input voltage according to claim 1, in particular with respect to an alternating current (AC) input voltage or with respect to a direct current (DC) input voltage, is described. The measuring device can be configured, in particular, to provide one or more measurement voltages for the input voltage, which can be reliably and efficiently read by a microprocessor in a safety extra-low voltage (SELV) or protective extra-low voltage (PELV) environment. The input voltage, in particular the AC input voltage, can, for example, be a 230 volt (V) supply voltage.

[0007] The measuring device comprises a first input node for coupling to a first pole (e.g., a phase conductor or the neutral conductor) of the input voltage. Furthermore, the measuring device comprises a first voltage divider with a first offset resistor and a first measuring resistor, arranged between an operating voltage (also referred to in this document as "VDD") and a reference potential (also referred to in this document as "GND") of the measuring device. A first measuring point of the measuring device may be arranged between the first offset resistor and the first measuring resistor. The first measuring resistor may be arranged between the first measuring point and the reference potential of the measuring device, and the first offset resistor may be arranged between the first measuring point and the operating voltage of the measuring device.

[0008] The measuring device further comprises a first insulation resistor that connects the first input node to the first measuring point. Measurement information regarding the input voltage can be provided at the first measuring point. In particular, a first measurement voltage (relative to the input voltage) can be provided at the first measuring point.

[0009] Similarly, the measuring device includes a second input node for coupling to a second pole (complementary to the first pole, e.g., the neutral conductor or the phase conductor) of the input voltage. Furthermore, the measuring device includes a second voltage divider with a second offset resistor and a second measuring resistor, arranged between the operating voltage and the reference potential of the measuring device. A second measuring point of the measuring device can be arranged between the second offset resistor and the second measuring resistor. The second measuring resistor can be arranged between the second measuring point and the reference potential of the measuring device, and the second offset resistor can be arranged between the second measuring point and the operating voltage of the measuring device.

[0010] Furthermore, the measuring device includes a second insulation resistor that connects the second input node to the second measuring point. Measurement information regarding the input voltage can be provided at the second measuring point. In particular, a second measurement voltage (relative to the input voltage) can be provided at the second measuring point.

[0011] The measuring device can be configured, in particular, to provide measurement information regarding the input voltage based on a difference between the first and second measurement voltages. This allows for efficient and reliable measurement of the input voltage (especially across an isolation barrier).

[0012] The input voltage can be part of a first voltage reference system. The input voltage can, for example, have an amplitude of 100 V or more. The first voltage reference system can be, for example, a supply voltage (e.g., a 230 V supply voltage) or an intermediate circuit voltage (such as that of a switched-mode power supply or electronics for a BLDC motor, i.e., a brushless DC motor). On the other hand, the operating voltage and / or the reference potential can be part of a second voltage reference system, in particular a SELV or PELV voltage reference system. The first and / or the second measurement voltage can each, for example, have an amplitude of 50 V or less. An isolation barrier can be arranged between the two voltage reference systems, provided in particular by the insulation resistances of the measuring device.This allows for an efficient and reliable measurement of the input voltage from a different voltage reference range.

[0013] According to the invention, the first insulation resistor and the second insulation resistor can each have such a high resistance value that galvanic isolation is achieved with a leakage current that is less than a predefined leakage current threshold (within a specification). According to the present invention, the first insulation resistor has a resistance value that is 10 or more, 100 or more, 1000 or more, or 10000 or more higher than the resistance value of the first offset resistor and / or the first measuring resistor. Similarly, the second insulation resistor can have a resistance value that is 10 or more, 100 or more, 1000 or more, or 10000 or more higher than the resistance value of the second offset resistor and / or the second measuring resistor.This allows for a particularly efficient provision of an isolation barrier between the first voltage reference range and the second voltage reference range.

[0014] The measuring device can be configured to determine measurement information relating to the input voltage based on the first measurement voltage at the first measuring point, in particular based on the first measurement voltage between the first measuring point and the reference potential, and based on the second measurement voltage at the second measuring point, in particular based on the second measurement voltage between the second measuring point and the reference potential. The measurement information can be determined, in particular, based on the difference between the first and second measurement voltages. The measurement information can include the amplitude of the input voltage, the polarity of the input voltage, the frequency of the input voltage, and / or the time of at least one zero crossing of the input voltage.Due to the use of multiple measurement voltages, especially due to the calculation of differences between multiple measurement voltages, the measurement information can be provided in a particularly precise and robust manner.

[0015] The measuring device can be configured to provide a first measuring voltage for the input voltage at the first measuring resistor and / or at the first measuring point, which exhibits no polarity reversals. This can be achieved, in particular, by using the first voltage divider between the operating voltage and the reference potential of the measuring device. Similarly, the measuring device can be configured to provide a second measuring voltage for the input voltage at the second measuring resistor and / or at the second measuring point, which also exhibits no polarity reversals. This can be achieved, in particular, by using the second voltage divider between the operating voltage and the reference potential of the measuring device.By providing measurement voltages that do not exhibit polarity changes, but still display information regarding an input voltage, particularly efficient further processing of the measurement voltages (by unipolar analog-to-digital converters) can be enabled.

[0016] The measuring device can include a first capacitor arranged in parallel with the first measuring resistor, particularly between the first measuring point and the reference potential. Similarly, the measuring device can include a second capacitor arranged in parallel with the second measuring resistor, particularly between the second measuring point and the reference potential. The capacitors can provide low-pass filtering to reduce noise and / or aliasing when sampling by an analog-to-digital converter.

[0017] The measuring device can include a comparator, with the first input of the comparator being coupled to the first measurement point and the second input to the second measurement point. The comparator can be configured to indicate a polarity reversal and / or a zero crossing of the input voltage as its output signal. Furthermore, the measuring device can include a (micro)processor configured to determine the frequency of the input voltage based on the comparator's output signal. By providing a comparator, measurement information regarding the input voltage, particularly regarding one or more zero crossings of the input voltage, can be obtained efficiently and precisely.

[0018] The measuring device can include a first analog-to-digital converter configured to convert the first measurement voltage at the first measuring point into a first digital measurement voltage. Similarly, the measuring device can include a second analog-to-digital converter configured to convert the second measurement voltage at the second measuring point into a second digital measurement voltage. The measuring device can further include a (micro)processor configured to determine a measured value for the input voltage, in particular a measured value for the amplitude of the input voltage, based on the first and second digital measurement voltages as measurement information. The current measured value can be determined repeatedly, for example, to ascertain the waveform of the input voltage and / or the time course of the amplitude of the input voltage.

[0019] The processor can be configured to approximately calculate the measured value for the input voltage based on the following formula, U 1 _ U 2 = U _ M 1 _ GND ∗ R _ 1 ∗ R _ M 1 + R _ 1 ∗ R _ OS 1 + R _ M 1 ∗ R _ OS 1 R _ M 1 ∗ R _ OS 1 − VDD ∗ R _ 1 R _ OS 1 − U _ M 2 _ GND ∗ R _ 2 ∗ R _ M 2 + R _ 2 ∗ R _ OS 2 + R _ M 2 ∗ R _ OS 2 R _ M 2 ∗ R _ OS 2 − VDD ∗ R _ 2 R _ OS 2

[0020] In the above formula: U1_U2 is the measured value of the input voltage; U_M1_GND is the value of the first digital measurement voltage; R_1 is the value of the first insulation resistance; R_M1 is the value of the first measuring resistor; R_OS1 is the value of the first offset resistor; VDD is the value of the operating voltage relative to the reference potential; U_M2_GND is the value of the second digital measurement voltage; R_2 is the value of the second insulation resistance; R_M2 is the value of the second measuring resistor; and R_OS2 is the value of the second offset resistor.

[0021] The measured value of the input voltage can therefore be determined in a particularly precise manner.

[0022] According to another aspect, a household appliance (e.g., a washing machine, dishwasher, oven, stove, food processor, vacuum cleaner, dryer, refrigerator, etc.) is described that includes the measuring device described in this document. The household appliance may, in particular, include a mains connection for connecting the appliance to an AC supply voltage. The measuring device may be configured to determine measurement information related to the supply voltage based on the AC supply voltage.

[0023] The appliance may also include a control unit configured to operate a function of the appliance based on measurement information, particularly on a measured value of the supply voltage amplitude. For example, the appliance's power output can be controlled or regulated based on this measurement information. This ensures particularly safe and reliable operation of the appliance.

[0024] It should be noted that all aspects of the measuring device described in this document can be combined in a variety of ways. In particular, the features of the patent claims can be combined in a variety of ways.

[0025] The invention will now be described in more detail with reference to exemplary embodiments illustrated in the accompanying drawing. Figure 1 is a block diagram of an exemplary household appliance; Figure 2a is a block diagram of an exemplary measuring device for voltage measurement; and Figure 2b is an exemplary measuring device with a comparator.

[0026] As stated at the beginning, this document deals with enabling the stable and reliable operation of a household appliance in an efficient manner, even with fluctuations in the supply voltage. In this context, it shows Fig. 1 An exemplary household appliance 100, e.g., a washing machine, with a mains connection 102, in particular with a switched-mode power supply, via which the household appliance 100 can be connected to an AC supply voltage 103. The household appliance 100 includes a measuring device 110, which is configured to acquire one or more measurement signals with respect to the supply voltage 103. The one or more measurement signals (e.g., a first measurement voltage, a second measurement voltage, and / or the output signal of a comparator) can be evaluated by a control unit 101, e.g., by a microprocessor, of the household appliance 100, in particular to adapt the operation of the household appliance 100 to a current characteristic, e.g., amplitude and / or frequency, of the supply or mains voltage 103. In this way, stable and reliable operation of the household appliance 100 can be ensured even in the event of fluctuations in the supply voltage 103.

[0027] Fig. 1 Figure 100 shows a household appliance that can be connected to the public power grid via a mains plug and thus supplied with electrical energy. The public power grid can be considered "voltage reference system A". Live parts in and on the household appliance that are connected to this voltage reference system typically need to be electrically insulated and protected from contact by a user of the household appliance. This reliably prevents electric shocks caused by the relatively high voltage of this voltage reference system. Such insulation may not be possible in a household appliance, for example, in the area of ​​the user interface or with attachments such as a meat thermometer, or it may involve considerable effort.

[0028] For this reason, a household appliance 100 typically has its own electrical network, which can be referred to as "voltage reference system B" and which has a reduced (operating) voltage (also referred to as VDD in this document) compared to the mains voltage 103, thus reliably preventing electric shocks to a user. Non-insulating components of the household appliance 100 can be safely supplied with electrical energy within voltage reference system B.

[0029] One pole of the public power grid is typically connected to earth, which necessitates galvanic isolation between voltage reference systems A and B. This galvanic isolation can be achieved using an isolation barrier. Energy transfer between the two voltage reference systems can be magnetic, using a transformer (as part of the isolation barrier).

[0030] An isolation barrier typically has a maximum permissible leakage current (also known as leakage current) and / or one or more other insulation properties, such as a specific geometric distance and / or a specific dielectric strength. An isolation barrier usually results in the loss of the electrically defined reference between the two voltage reference systems, which are galvanically isolated from each other by the barrier. Therefore, if the voltage of voltage reference system A is to be measured within voltage reference system B, it is typically necessary to transmit this relative voltage information to voltage reference system B without disabling the isolation barrier.

[0031] An example of a voltage measurement across an insulation barrier in a household appliance 100 is the measurement of the mains voltage 103. Measured information regarding the mains voltage 103 can be used, for example, to activate a protective function in the household appliance 100 or to optimize one or more processes, such as defrosting a refrigerator using heaters, in terms of energy efficiency.

[0032] This document describes a measuring device 110 for measuring an electrical voltage 103 across an insulation barrier, which meets a maximum permissible leakage current provided for the insulation barrier and / or one or more other insulation properties or insulation requirements.

[0033] Fig. 2a Figure 1 shows a circuit diagram of an exemplary measuring device 110. The measuring device 110 is set up to uniquely determine the potential difference 103 "U1_U2" between points 211 "U1" and 221 "U2" (i.e., the input voltage 103) by the difference of the measuring voltages 219 "U_M1_GND" (between the first measuring point 217 "U_M1" and the reference potential 202 "GND") and 229 "U_M2_GND" (between the second measuring point 227 "U_M2" and the reference potential 202 "GND").

[0034] The offset resistors 214 "R_OS1" and 224 "R_OS2" connect the measuring points 217 "U_M1" and 227 "U_M2" to the operating voltage 201 "VDD" of the second voltage reference system B 232. The operating voltage 201 "VDD" can have a fixed value relative to the reference potential 202 "GND". Thus, an offset voltage can be added to the measuring voltages 219 "U_M1_GND" and 229 "U_M2_GND", which makes it possible to keep the measuring voltages 219 and 229 exclusively in the positive range. This is advantageous for acquiring the individual measuring voltages 219 and 229 via a unipolar analog-to-digital converter in a microprocessor.

[0035] The resistors 212 "R_1", 214 "R_OS1" and 215 "R_M1" as well as the resistors 222 "R_2", 224 "R_OS2" and 225 "R_M2" each form a voltage divider 213, 223 between the voltage 218 "U1_GND" and the first measuring voltage 219 "U_M1_GND" or between the voltage 228 "U2_GND" and the second measuring voltage 229 "U_M2_GND".

[0036] The potential difference between input nodes 211 "U1" and 221 "U2" represents the input voltage 103 "U1_U2". The potential differences or voltages 218 "U1_GND" and 228 "U2_GND" are typically insignificant in absolute terms. Interference, common-mode voltages, or additional impedances between input nodes 211 "U1" and 221 "U2" and the reference potential 202 "GND" cancel each other out through the differential calculation, leaving only the input voltage 103 "U1_U2" as the result. In a system where point 202 is defined as the potential reference point ("GND"), it is possible to measure a voltage between two input nodes 211, 221 ("U1" and "U2"), regardless of the respective absolute potential differences 218, 228 of the individual input nodes 211, 221 to the potential reference point 202 ("GND") of the system. This enables a high-impedance connection of both input nodes 211, 221 ("U1" and "U2") to the measuring device 110.

[0037] Capacitors 216 "C_F1" and 226 "C_F2" can be used for low-pass filtering of the measured voltage. If low-pass filtering is not required, capacitors 216 and 226 can be omitted.

[0038] By using relatively high resistance values ​​for the insulation resistances 212 "R_1" and 222 "R_2" and by limiting the electrical currents across the insulation resistances 212, 222, it is possible to measure the voltage across an insulation barrier between the first voltage reference system A 231 and the second voltage reference system B 232.

[0039] The higher the resistance values ​​of the insulation resistances 212 "R_1" and 222 "R_2" are chosen, the greater the interference from parasitic capacitances on the absolute voltages 218 "U1_GND" and 228 "U2_GND" typically becomes. However, these interferences completely cancel each other out during differential voltage measurement, so that even when the leakage currents of the insulation barrier are reduced by increasing the resistance values ​​of the insulation resistances 212 "R_1" and 222 "R_2", a precise measurement of the input voltage 103 is possible via the difference between the measured voltages 219 and 229. The [method] used in Fig. 2a The measuring device 110 shown consists exclusively of passive components and thus enables a particularly efficient implementation.

[0040] The relationship between the first measuring voltage 219 "U_M1_GND" and the second measuring voltage 229 "U_M2_GND" (in the second voltage reference system B 232) on the one hand and the input voltage to be measured 103 "U1_U2" (in the first voltage reference system A 231) on the other hand can be approximately described by the following formula: U 1 _ U 2 = U _ M 1 _ GND ∗ R _ 1 ∗ R _ M 1 + R _ 1 ∗ R _ OS 1 + R _ M 1 ∗ R _ OS 1 R _ M 1 ∗ R _ OS 1 − VDD ∗ R _ 1 R _ OS 1 − U _ M 2 _ GND ∗ R _ 2 ∗ R _ M 2 + R _ 2 ∗ R _ OS 2 + R _ M 2 ∗ R _ OS 2 R _ M 2 ∗ R _ OS 2 − VDD ∗ R _ 2 R _ OS 2

[0041] For the sake of clarity, the frequency dependence caused by the influence of capacitors 216 "C_F1" and 226 "C_F2" is neglected.

[0042] The in Fig. 2a The measuring device 110 shown can be used to measure the mains voltage 103 in a household appliance 100. For this purpose, the first input node 211 "U1" can be connected to the live conductor or phase conductor and the second input node 221 "U2" to the neutral conductor of the mains supply. Alternatively, the first input node 211 "U1" can be connected to the neutral conductor and the second input node 221 "U2" to the live conductor or phase conductor of the mains supply. The measuring voltages 219 "U_M1_GND" and 229 "U_M2_GND" can each be measured by an analog-to-digital converter (not shown), the analog-to-digital converters being located in the second voltage reference system B 232, which is galvanically isolated from the mains supply. The evaluation of the converted and / or digital measurement voltages 219, 229 can be carried out by a microcontroller (not shown) which is designed to determine the mains voltage 103, e.g., based on the above.Formula to calculate from the measured voltages 219, 229.

[0043] The only connection between the measuring device 110 and the power grid across the insulation barrier is provided by the insulation resistances 212 "R_1" and 222 "R_2". If the resistance values ​​for the insulation resistances 212 "R_1" and 222 "R_2" are chosen to be sufficiently high, the current through the insulation resistances 212 and 222, and thus the current across the insulation barrier, will be kept sufficiently low. This ensures that the insulation barrier remains intact.

[0044] The measuring device 110 described in this document makes it possible to measure any input voltage 103 in a first voltage reference system A 231 without connecting the potential reference point of the first voltage reference system A 231 with a low-impedance connection to the potential reference point 202 of the second voltage reference system B 232, from which the input voltage 103 in the first voltage reference system A 231 is to be measured.

[0045] The measuring device 110 can, as exemplified in Fig. 2b The device shown is used to detect the zero crossing of the mains voltage 103. Zero crossing detection can be used, for example, for mains voltage-synchronous switching of an actuator of a household appliance 100. Furthermore, the measuring device 110 can be used (by zero crossing detection) to measure the mains frequency (e.g., as a clock signal for one or more processes of a household appliance 100).

[0046] As described above, input nodes 211 "U1" and 221 "U2" are connected to the mains power supply. At the moment of a zero crossing of the mains voltage 103, the voltage between input nodes 211 "U1" and 221 "U2", and consequently the difference between the measured voltages 219 "U_M1_GND" and 229 "U_M2_GND", changes sign. This change in sign can be evaluated using a comparator 240, connected to measuring points 217 "U_M1" and 227 "U_M2". Each falling or rising signal edge at the comparator output 241 then indicates a zero crossing of the mains voltage 103. The current signal state of the comparator output 241 (high or low) also indicates the current polarity of the mains voltage 103.

[0047] The measuring device 110 described in this document can be implemented efficiently with a small number of components (in particular, with only six resistors). The insulation resistances 212 "R_1" and 222 "R_2" can each be implemented by a combination of several resistors, if necessary. Furthermore, the measuring device 110 enables mains voltage measurement and / or zero-crossing detection in devices 100 where no mains potential-related measuring circuit is provided or can be implemented. Since the measuring device 110 only has passive components, interferences caused by component tolerances can be calculated efficiently and precisely and taken into account when determining measurement information with respect to the input voltage 103. Furthermore, efficient and precise calibration of the measuring device 110 is possible because the components of the measuring device 110 exhibit, to a first approximation, linear behavior.

[0048] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed measuring device.

Claims

1. Household appliance measurement apparatus (110) for determining measurement information relating to an input voltage (103) across an isolation barrier; wherein the household appliance measurement apparatus (110) comprises, - a first input node (211) for coupling to a first pole of the input voltage (103); - a first voltage divider (213), with a first offset resistor (214) and a first measurement resistor (215) which are arranged between an operating voltage (201) and a reference potential (202) of the household appliance measurement apparatus (110); - a first isolation resistor (212) which connects the first input node (211) to a first measurement point (217) arranged between the first offset resistor (214) and the first measurement resistor (215) for measurement information relating to the input voltage (103); - a second input node (221) for coupling to a second pole of the input voltage (103); - a second voltage divider (223), with a second offset resistor (224) and a second measurement resistor (225), which are arranged between the operating voltage (201) and the reference potential (202) of the household appliance measurement apparatus (110); and - a second isolation resistor (222) which connects the second input node (221) to a second measurement point (227) arranged between the second offset resistor (224) and the second measurement resistor (225) for measurement information relating to the input voltage (103), - wherein the first isolation resistor (212) has a resistance value which is greater by a factor of 10 or more, or 100 or more or 1000 or more or 10000 or more than a resistance value of the first offset resistor (214) and / or of the first measurement resistor (215); and / or - the second isolation resistor (222) has a resistance value which is greater by a factor of 10 or more, or 100 or more or 1000 or more or 10000 or more than a resistance value of the second offset resistor (224) and / or of the second measurement resistor (225).

2. Household appliance measurement apparatus (110) according to claim 1, wherein the first isolation resistor (212) and the second isolation resistor (222) have in each case a resistance value that is high enough such that a galvanic isolation with a leakage current is caused by way of the first isolation resistor (212) and by way of the second isolation resistor (222), which leakage current is smaller than a predefined leakage current threshold value.

3. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein - the input voltage (103) is part of a first voltage reference system (231), in particular an electricity supply network or an intermediate circuit of an electrical device (100); and / or - the operating voltage (201) and / or the reference potential (202) is / are part of a second voltage reference system (232), in particular a Safety Extra Low Voltage, or SELV for short, or a Protective Extra Low Voltage, or PELV for short, voltage reference system.

4. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein the household appliance measurement apparatus (110) is designed to determine measurement information relating to the input voltage (103) on the basis of a first measurement voltage (219) at the first measurement point (217), in particular a first measurement voltage (219) between the first measurement point (217) and the reference potential (202), and on the basis of a second measurement voltage (229) at the second measurement point (227), in particular a second measurement voltage (229) between the second measurement point (227) and the reference potential (202).

5. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein - the first measurement resistor (215) is arranged between the first measurement point (217) and the reference potential (202) of the household appliance measurement apparatus (110); and - the first offset resistor (214) is arranged between the first measurement point (217) and the operating voltage (201) of the household appliance measurement apparatus (110); and / or - the second measurement resistor (225) is arranged between the second measurement point (227) and the reference potential (202) of the household appliance measurement apparatus (110); and - the second offset resistor (224) is arranged between the second measurement point (227) and the operating voltage (201) of the household appliance measurement apparatus (110).

6. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein the household appliance measurement apparatus (110) is designed - to provide a first measurement voltage (219) for the input voltage (103) at the first measurement resistor (215) and / or at the first measurement point (217), which has no change in polarity; and / or - to provide a second measurement voltage (229) for the input voltage (103) at the second measurement resistor (225) and / or at the second measurement point (227), which has no change in polarity.

7. Household appliance measurement apparatus (110) according to claim 6, wherein - the input voltage (103) has an amplitude of 100 V or more; and - the first and / or the second measurement voltage (219, 229) have an amplitude of 50 V or less in each case.

8. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein the household appliance measurement apparatus (110) comprises - a first capacitor (216), which is arranged parallel to the first measurement resistor (215), in particular between the first measurement point (217) and the reference potential (202); and / or - a second capacitor (216), which is arranged parallel to the second measurement resistor (225), in particular between the second measurement point (227) and the reference potential (202).

9. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein - the household appliance measurement apparatus (110) comprises a comparator (240); - a first input of the comparator (240) is coupled to the first measurement point (217); - a second input of the comparator (240) is coupled to the second measurement point (227); and - the comparator (240) is designed to indicate, as an output signal (241), a change in polarity and / or a zero crossing of the input voltage (103).

10. Household appliance measurement apparatus (110) according to claim 10, wherein the household appliance measurement apparatus (110) comprises a processor which is configured to determine a frequency of the input voltage (103) on the basis of the output signal (241) of the comparator (240).

11. Household appliance measurement apparatus (110) according to one of the preceding claims, wherein the household appliance measurement apparatus (110) comprises - a first analogue-digital converter, which is configured to convert a first measurement voltage (219) at the first measurement point (217) into a first digital measurement voltage; and / or - a second analogue-digital converter, which is configured to convert a second measurement voltage (229) at the second measurement point (227) into a second digital measurement voltage.

12. Household appliance measurement apparatus (110) according to claim 11, wherein the household appliance measurement apparatus (110) comprises a processor, which is configured to determine, on the basis of the first digital measurement voltage and on the basis of the second digital measurement voltage, as measurement information, a measurement value for the input voltage (103), in particular a measurement value for an amplitude of the input voltage (103).

13. Household appliance measurement apparatus (110) according to claim 12, wherein the processor is designed to calculate the measurement value for the input voltage (103) approximately, on the basis of U 1 _ U 2 = U _ M 1 _ GND ∗ R _ 1 ∗ R _ M 1 + R _ 1 ∗ R _ OS 1 + R _ M 1 ∗ R _ OS 1 R _ M 1 ∗ R _ OS 1 − VDD ∗ R _ 1 R _ OS 1 − U _ M 2 _ GND ∗ R _ 2 ∗ R _ M 2 + R _ 2 ∗ R _ OS 2 + R _ M 2 ∗ R _ OS 2 R _ M 2 ∗ R _ OS 2 − VDD ∗ R _ 2 R _ OS 2 wherein - U1U2 is the measurement value of the input voltage (103); - U_M1_GND is a value of the first digital measurement voltage (219); - R_1 is a value of the first isolation resistor (212); - R_M1 is a value of the first measurement resistor (215); - R_OS1 is a value of the first offset resistor (214); - VDD is a value of the operating voltage (201) relative to the reference potential (202); - U_M2_GND is a value of the second digital measurement voltage (229); - R_2 is a value of the second isolation resistor (222); - R_M2 is a value of the second measurement resistor (225); and - R_OS2 is a value of the second offset resistor (224).

14. Household appliance (100), which comprises - a network connection (102) for connecting the household appliance (100) to an AC supply voltage (103); - a household appliance measurement apparatus (110) according to one of the preceding claims, wherein the household appliance measurement apparatus (110) is configured to determine measurement information relating to the AC supply voltage (103) on the basis of the AC supply voltage (103); and - a control unit (101), which is configured to operate a function of the household appliance (100) as a function of the measurement information.