[0001] The present invention relates to energy harvesting from smart meters in a supply grid or monitoring network. More specifically comprising energy harvesting on the output port of a measuring instrument.

BACKGROUND

[0002] In recent years, so-called smart electricity meters, or advanced measurement systems (AMS) in industrial buildings and houses have become commonplace, and the suppliers of electric power may now receive consumption and meter data almost continuously. These meters also have a connection port, which may have different names, but which is generally referred to as the HAN (Home Area Network) port where consumers may access their data via third-party equipment and optimize their consumption, almost in real time. Typical data streamed on the HAN port may be, for example, energy consumption, power consumption, power and voltage quality. For the physical interface, in one example, an RJ45 plug is used.

[0003] Initially, the Meter-Bus (M-Bus) standard was to be used as a starting point for the electrical interface, but the present standard has been interpreted differently by the suppliers, and now several different M-Bus interfaces has to be dealt with.

[0004] The M-Bus is designed as a master-slave solution. The master is located in the smart meter, and equipment that is attached in parallel behaves like slave units that can communicate with the master unit. In most systems, there is currently only one-way communication from master to slave. It is therefore important that the slave receives the messages sent when they are sent. In addition to communication, the M-Bus delivers voltage to the slave units comprising the possibility of a limited current draw.

[0005] The M-Bus basically consists of two electrical conductors.

[0006] When no data is transmitted over the bus, the M-Bus will have a DC voltage potential that can be used to some extent to drive the slaves. According to the M-Bus standard, a voltage range is defined so that the voltage between master and slave should be in the range between 42 and 12 V DC. In Norway, this voltage is approx. 24-27V.

[0007] The M-Bus is also used for signaling between master and slave. This signaling is done by lowering the direct voltage, e.g. in that 12 V DC indicates digital "0", and 24 V DC indicates a digital "1", but this may vary somewhat between equipment from different suppliers. [0008] Since the messages are sent at a baud rate of 2400, transmitting data can thus significantly reduce available energy. This also varies between the meters, as they have both different lengths of messages and different transmission intervals.

[0009] In addition to this, different equipment also has different maximum current draw. If the current draw becomes too large, it can possibly cause the port to be blocked for a certain period of time.

[0010] All this means that the power that can be extracted from the HAN bus at any time will vary greatly with the type of electricity meter used. In particular, it is noticeable that available power decreases noticeably during the periods when there is signaling between master and slave. [0011] The available power may in many contexts be too small to drive the circuits needed in the slave modules. The slave modules are often equipped with wireless interfaces for communication with a consumer, e.g. an app on a mobile phone with Wifi or Bluetooth interface. The driver interfaces of the wireless interface require some power which can be difficult to extract from the M- bus. [0012] A common solution to this problem has been to equip the slave modules with their own power supply, e.g. in the form of a 220 V adapter that can be plugged into an outlet. However, this will significantly increase the cost and complicate the use of the slave modules, making them less interesting to a consumer. In many places, there is also no socket available near the electricity meter, so this incurs an extra installation cost. [0013] In addition, the limit of the startup current, "inrush", will often be different from the limit of maximum continuous current draw in operation for the same type of electricity meter.

[0014] CN 207517176 U discloses a power adaption circuit adapted to extract energy from an Ethernet port on an electricity meter, wherein the power adaption circuit comprises a current limiter adapted to limit the current draw of the Ethernet port such that maximum current draw from the HAN port is determined by the electricity meter type to which the power adaption circuit is connected.

[0015] In US 2017/0285711 Al, voltage control techniques for electronic circuits consisting of voltage regulators are described, wherein the voltage regulator regulates the voltage to an electronic element consisting of several integrated circuits. [0016] Therefore, a solution to these problems are needed so that the slave module can work with different types of electricity meters and that the slave module does not necessarily need external power supply, even if the available power varies from one type of electricity meter to another.

SUMMARY [0017] It is therefore an objective of the present invention to come up with a solution which means that the slave module does not necessarily need external power supply even if the available power varies from one type of electricity meter to another and that it should be able to work with different types of electricity meters.

[0018] This is achieved by a power adaption circuit and a method for adjusting power consumption on an output of a measuring instrument according to the independent claims.

BRIEF EXPLANATION OF THE FIGURES

[0019] Fig. 1A shows an overview block diagram of an embodiment of the power adaption circuit 1. Continuous line arrows denote energy transfer, while dotted-line arrows indicate communication between the blocks.

[0020] Figures 1B-E show overview block diagrams of alternative embodiments of the power adaption circuit with a generic port connection and general current limiter module.

[0021] Fig. 2 shows in a detailed embodiment the dynamic current limiter in the form of an electronic circuit diagram. In this case, the circuit includes a Buck regulator. The maximum current draw through the limiter is determined by a current limiting parameter sent to the current limiter (U602).

[0022] Fig. 3 shows in a detailed embodiment the fixed current limiter in the form of an electronic circuit diagram.

[0023] Fig. 4 shows in a detailed embodiment the energy storage in the form of an electronic circuit diagram.

[0024] Fig. 5 shows in a flow diagram an embodiment of a start-up mode of the power adaption circuit.

[0025] Fig. 6 shows in a flow diagram an embodiment of a charging mode for the power adaption circuit. [0026] Fig. 7 shows in a flow diagram an embodiment of a message receiving mode for the power adaption circuit.

[0027] Fig. 8 shows in a flow diagram an embodiment of a power monitoring mode for the power adaption circuit.

EMBODIMENTS

[0028] In the following part of the specification, various examples and embodiments of the invention are shown to give the skilled person a more detailed understanding of the invention. The specific details associated with the various embodiments and the reference to the accompanying drawings are not to be construed as limiting the invention. The protection of the invention is provided by the appended claims.

[0029] When in association to the following examples it is discussed a solution related to Figure 1A where the output connected is a FIAN port and the meter type is an electricity meter, it should be understood that the invention is not limited to such. Neither is M-Bus an absolute requirement for electricity meters, but the present invention can equally well be used with other interfaces. In Figures IB to IE several embodiments are shown where any output port from a measuring instrument can be used which is suitable for transmitting data and / or power. Furthermore, such measuring instruments are just as often used for monitoring, for example, water consumption, gas consumption or, for example, weather stations or other measuring instruments having an output port often used for connecting communication equipment, and those should also be comprised in the present invention. Typical data streamed on such output ports may be, for example, gas consumption, water consumption, power consumption, weather, wind and flow data, and others. The following description is to be understood in such a way that any equipment, which can advantageously be operated without external power supply, but supplied with energy by the present invention, should be comprised by possible embodiments of the present invention.

[0030] Based on tests, there is reason to assume that a type of electricity meter will cut the power supply at the FIAN port for a certain amount of time, if the startup current becomes too high.

[0031] Furthermore, it may appear that other electricity meters can supply a greater current during start-up, but if the current draw is too high, the voltage on the port may be gradually reduced, and then come back at rapid intervals. It is also assumed that some meter types reduce the voltage first before cutting the supply completely. [0032] Available voltage from the various electricity meters is assumed to be in the range 24-27 volts for digital "1", or fixed DC voltage at the same level if no data is transmitted. Digital "0" is approx. 12 -15 V.

[0033] The maximum available current draw in operation may appear to vary between approx. 6 mA and 30 mA.

[0034] Furthermore, it may appear that the transmission intervals vary from approx. 2 seconds to approx. 10 seconds, while message lengths vary with both the type of meter and the transmission interval of the meter. For example, the message length may vary from approx. 330 bits for one meter at 2 second to approx. 4000 bits for one of the other meters at transmission interval of one hour.

[0035] The maximum available documented power may also vary, for example, between 144mW and 700mW. When transmitting data this will be noticeably reduced, down to half during some sequences.

[0036] In a first circuit embodiment, the invention is a power adaption circuit adapted to extract energy from a Flome Area Network (HAN) port on an electricity meter, wherein the power adaption circuit comprises a dynamic current limiter 2 adapted to limit the current draw from the FIAN port depending on a constraint parameter 8 such that maximum current draw from the FIAN port is determined by the electricity meter type to which the FIAN port is connected.

[0037] In a second circuit embodiment which can be combined with the first circuit embodiment, the power adaption circuit comprises an energy storage 4 and a processing unit 6, wherein the processing unit is arranged to monitor available energy in the energy storage.

[0038] The second circuit embodiment may further comprise any combination of the following features; the processing unit is designed to control the charging of the energy in the energy storage, while at the same time keeping the operating voltage above a lower voltage level. the energy storage comprises a main energy storage C501 and an auxiliary energy storage C500. the energy storage comprises an electronic switch Q500 in series with the main energy storage, where the series connection of the main energy storage and the electronic switch is arranged in parallel with the auxiliary energy storage. the processing unit is designed to monitor the voltage across the main energy storage. the processing unit is designed to monitor the voltage across the auxiliary energy storage. the processing unit is adapted to switch on the electronic switch if the voltage across the auxiliary energy storage is above a predetermined minimum value. the main energy storage is arranged to store an amount of energy that is at least 10, 15 or 20 times the amount of energy in the auxiliary energy storage.

[0039] In a third circuit embodiment which may be combined with the first or second circuit embodiment, the dynamic current limiter comprises a control port adapted to receive the constraint parameter, wherein the power adaption circuit comprising a digital potentiometer connected to the control port.

[0040] In an alternative, simplified embodiment, discrete resistors controlled by switches connected to the control port can be used.

[0041] The third circuit embodiment may further comprise any combination of the following features; the processing unit is arranged to control the digital potentiometer. the potentiometer is designed to read a value of the constraint parameter from a memory when connected to the HAN port. a value for the constraint parameter can be set via a wireless interface associated with the processing unit.

[0042] In a fourth circuit embodiment which can be combined with any of the preceding circuit embodiments, the power adaption circuit comprises an input port 7 arranged to be connected to the HAN port, wherein the processing unit is adapted to interpret signals from the input port, determining the electricity meter type based on the interpreted signals, and send a value for the limiting parameter to the dynamic current limiter based on the electricity meter type.

[0043] In a fifth circuit embodiment which can be combined with any of the preceding circuit designs, the power adaption circuit comprises any combination of the following features; a stored list of known electricity meter types and respective stored signal signatures and parameters representing the maximum current draw for each electricity meter type. the processing unit, by connecting the input port to the HAN port, is arranged to send a value of the limiting parameter to the dynamic current limiter corresponding to the electricity meter type with the lowest maximum output power of the known electricity meter types. the signal signature comprises a combination of any of; DC voltage for digital "1", DC voltage for digital "0", baud rate, transmission interval and message length. - the dynamic current limiter includes a buck-regulator. the power adaption circuit comprises a fixed current limiter 3 arranged between the input port and the dynamic current limiter, the fixed current limiter being adapted to limit the starting current by connecting the input port to the HAN port. the power adaption circuit is designed to detect the electricity meter type and send a value of the limiting parameter to the dynamic current limiter so that the maximum current draw from the HAN port is automatically determined by the electricity meter type to which the HAN port is connected.

[0044] The invention is also, in a first method embodiment, a method for adjusting the current draw of a Home Area Network (HAN) port on an electricity meter comprising: - limiting the current flow from the HAN port depending on a constraint parameter 8, so that the maximum current flow from the HAN port is determined by the electricity meter type to which the HAN port is connected.

[0045] A second method embodiment which can be combined with the first method embodiment comprises: - storage of energy from the HAN port in an energy storage, monitoring the energy in the energy storage, and limit the extraction of energy from the energy storage if the energy is below a threshold value.

[0046] The second method embodiment may further comprise any combination of the following features; disabling or restricting a communication interface, e.g. a wired or wireless interface if the energy is below the threshold. intermediate storage of incoming data from the HAN port, and forwarding of data only when the energy storage contains energy above a certain minimum limit.

[0047] In a third process embodiment which can be combined with the second method embodiment, the energy storage comprises a main energy storage and an auxiliary energy storage, the method comprising; transfer energy from the auxiliary energy storage to the main energy storage only when the voltage across the auxiliary energy storage is above a lower switching limit.

[0048] The third method embodiment may further comprise any combination of the following features; transferring energy from the auxiliary energy storage to the main energy storage in pulses as long as the voltage is below an upper charge limit, and continuously as the voltage rises above the upper charge limit, where the upper charge limit is greater than the lower charge limit. maintain continuous charging if the voltage drops below the upper charge limit, resume pulse transmission of energy if voltage drops below the lower charge limit. start transferring the energy from the auxiliary energy storage to the main energy storage if the voltage across the auxiliary energy storage exceeds an upper switching limit, and continue the transfer of energy until the voltage across the auxiliary energy storage drops to a lower switching limit which is below the upper switching limit.

[0049] In a fourth method embodiment which can be combined with any of the first to third method embodiments above, comprising: detecting a signature for an incoming signal from the HAN port, and determine the type of electricity meter based on the signature.

[0050] The fourth method embodiment may further comprise any combination of the following features; determine the electricity meter type by comparing the signature with stored signatures for a list of known electricity meter types. limiting the starting current when connecting the input port to the HAN port. [0051] The signature may comprise a combination of any of; DC voltage for digital "1", DC voltage for digital "0", baud rate, transmission interval and message length.

[0052] The following will explain in more detail how the power adaption circuit and the method for adjusting the current draw from a HAN port can be performed. [0053] Fig. 1A shows an overall block diagram of an embodiment of the power adaption circuit 1.

Continuous-line arrows denote energy transfer, while dotted-line arrows indicate communication between the blocks.

[0054] The block labeled M-Bus 7, is an interface to the HAN port that provides data received over the M-Bus interface. [0055] The fixed current limiter 3 has a fixed current limiting value, with a fast response to prevent the energy storage 4 from drawing a high start-up current from the M-Bus.

[0056] The dynamic current limiter 2, can be set to different current limiting values, mainly below the fixed current limiting value.

[0057] The voltage regulator 5 provides controlled voltage supply to the processing unit 5, and other circuits as required.

[0058] The processing unit 6 typically contains a data processing unit. A memory for storing commands to be executed and messages may also be in the same unit, or in separate units. In addition, this block in this embodiment includes a WiFi interface. However, different wireless or fixed interfaces for data may be in communication with the processor, either integrated in the same device, or standalone.

[0059] The wireless interface is a candidate for deactivation when there is no need for it in order to conserve energy, which is done in an embodiment of the invention.

[0060] The energy storage 4 can be recharged from the M-Bus when sufficient energy is present.

The signal processing unit 6 monitors available energy in the energy storage and determines when to charge it.

[0061] The processing unit 6 receives data from the M-Bus 7 and, after startup, attempts to interpret data entering the M-Bus. In addition, the processing unit 6 determines the current limitation in the dynamic current limiter 2. [0062] Fig. IB shows an overall block diagram of an embodiment of the power adaption circuit 1'. Continuous-line arrows denote energy transfer, while dashed-line arrows denote communication between the blocks.

[0063] The block labeled Output-Port 7' is an interface to the output port that provides data received over the output data interface.

[0064] The current limiter 2[, 3' can be set to different current limiting values, or adjusted according to the detection method described below to find the maximum current draw available.

[0065] The voltage regulator 5' provides controlled voltage supply to the processing unit 6', and other circuits as required. [0066] The processor 6' typically contains a data processor. A memory for storing commands to be executed and messages may also be in the same unit, or in separate units. In addition, this block may contain a WiFi interface or other forms of communication protocols. However, different wireless or wired interfaces for data may be in communication with the processor, either integrated in the same device, or standalone. [0067] The wireless interface is a candidate for deactivation when there is no need for it in order to conserve energy, which is done in an embodiment of the invention.

[0068] The energy storage 4' can be recharged from the output port when sufficient energy is present. The signal processing unit 6' monitors available energy in the energy storage and determines when to charge it. [0069] The processor 6' receives data from the output port 7' and, upon startup, attempts to interpret data entering the output port. In addition, the processing unit 6' determines the current limitation in the current limiter 2'.

[0070] Although the present invention is not to be limited to that, Fig. 1C shows the example of an electricity meter, in Fig. ID is a water meter, and in Fig. IE a gas meter. [0071] Fig. 2 shows in a detailed embodiment the dynamic current limiter in the form of an electronic circuit diagram. In this case, the circuit includes a Buck regulator. The maximum current through the limiter is determined by a current limiting parameter sent to the current limiter (U602).

[0072] Fig. 3 shows in a detailed embodiment the fixed current limiter in the form of an electronic circuit diagram. [0073] Fig. 4 shows in a detailed embodiment the energy storage in the form of an electronic circuit diagram. In this case, the terminal labeled POS is connected to both the output VOUT of the dynamic current limiter 2 in Fig. 2 and the input to the voltage regulator 5 in Fig. 1A. This wiring will thus connect the energy storage 4 with both the dynamic current limiter and subsequent regulator, and thus also include the arrow indicated between the energy storage and the regulator in Fig. 1A.

[0074] The main energy storage C501 shall ensure that it has sufficient energy to execute forwarding of the messages e.g. over a wireless interface, even in cases where there is not enough energy directly available over the M-Bus.

[0075] In the specific embodiment shown in Fig. 4, the dynamic current limiter 2 will convert the voltage from the M-Bus to the nominal main voltage of approx. 5.5V when possible.

[0076] The problem with continuous charging of the main energy storage is that it may cause the main voltage, at the terminal POS, to decrease so much that the regulator 5 fails to supply sufficient voltage to the processing unit 6.

[0077] To counteract this, the main energy storage is not charged below a lower switching limit of the auxiliary energy storage. This minimum value is just above the voltage required to operate the processing unit.

[0078] During charging, in one embodiment, the electronic switch Q500 will be turned on and off to transfer energy in pulses from the auxiliary energy storage to the main energy storage, and the main voltage will increase as long as it is possible to supply energy from the M-Bus.

[0079] In this embodiment, it is also envisaged that the voltage across the main storage should rise to an upper charge limit before the switch Q500 is permanently switched on, and the situation can continue as long as it is supplied about as much energy as it is extracted.

[0080] Thereafter, the switch can be kept permanently switched on, until the voltage drops below a lower charge limit which is below the upper charge limit, and then start pulse charging.

[0081] The auxiliary energy storage (C500) is an intermediate storage of energy, which ensures that the main energy storage can be recharged safely for short periods of time without turning off the processing unit due to insufficient available energy. This is mainly required before the upper charging limit is reached.

[0082] Viewed from the auxiliary energy storage point of view, the transfer of energy to the main energy storage starts when the voltage across the auxiliary energy storage is above an upper switching limit. The upper switching limit is slightly below the auxiliary power supply voltage when the auxiliary power supply is fully charged.

[0083] Charging is maintained until the voltage across the auxiliary energy storage has dropped to a lower switching limit which is below the upper switching limit, but still greater than a minimum value for the main voltage, so that the processing unit is able to terminate the charge in time before the voltage becomes too low.

[0084] If we assume a startup situation, as illustrated in Fig. 5, where a slave unit with a power adaption circuit as described above is physically connected to the HAN port, the power adaption circuit will limit the current flow to the electricity meter type which allows the lowest current flow.

[0085] Here, the processor may be set to automatically start in a startup mode, where power consuming circuits, such as e.g. a wireless interface is disabled.

[0086] In this embodiment, the electricity meter types and their respective maximum current draw are known to the power adaption circuit, and stored in a memory. This can be a fixed value e.g. stored in a fixed memory, as in an internal program or in a program (firmware or software), at production. In one embodiment, both the values and the number and type of electricity meter types may be updated, e.g. in the form of a software update via a physical interface on the slave module, or over a wireless network if a wireless interface is provided.

[0087] The current draw at startup is limited e.g. in that the processing unit sends a value of the limiting parameter to the dynamic current limiter so that the maximum current draw for the electricity meter type allowing the lowest current draw is set.

[0088] Alternatively, the current limiter may always start at the lowest maximum current draw, without having to receive a command from the processor. This can be done, e.g. by allowing the power limiter to read a startup value from a memory.

[0089] The power adaption circuit will then begin to receive data over the M-Bus interface. This data is interpreted by the processing unit and stored in a local memory.

[0090] The processor will also detect values for selected signal parameters for the incoming data messages on the M-Bus over a certain period of time. This can for example be: DC voltage for digital "1", DC voltage for digital "0", baud rate, transmission interval and message length.

[0091] The values of the signal parameters are compared to signal signatures for each of the known electricity meter types, and if a hit is obtained, i.e., the detected values of the signal parameters coincide with one specific signal signature, then the electricity meter type can be determined. As long as a hit is not reached, the current draw will be limited to the electricity meter type which allows the lowest current draw.

[0092] Once a hit is achieved, the processor will send a value of the limiting parameter to the dynamic current limiter such that the maximum power or current draw is set according to the maximum current output of the detected electricity meter type.

[0093] In an alternative start-up procedure, the connected electricity meter type, and thus also the maximum current draw for the meter can be set at start-up, instead of being detected by the power adaption circuit. E.g. the meter type can be set using a connected device, such as a smartphone with a custom app that is able to communicate with the processing unit over a wireless interface. One can, e.g. select the meter type and / or power limit.

[0094] In this case, the signature describing the message format of the data on the HAN port may also be selected by setting or selecting the current meter type, so that the message format is uniquely determined based on the prior knowledge of the message signatures of the different current meter types. One can thus start receiving data immediately after the electricity meter type is selected.

[0095] After startup mode, the processing unit will usually switch to a charging mode as illustrated in Fig. 6. In charging mode, current demanding circuits or tasks are still limited or deactivated, and the power adaption circuit's task is to charge an internal energy storage, e.g. in the form of the capacitor (C501) as shown in Fig. 4, as quickly as possible. At the same time, it is important that incoming data can still be interpreted and stored in memory. It is therefore important that the processing unit and associated circuits can continue to operate normally in charging mode.

[0096] In addition to the large capacitor, referred to as the main energy storage in Fig. 6, the energy storage therefore also includes a smaller capacitor (C500), referred to as auxiliary energy storage, connected in parallel with the large capacitor. The energy storage with both the large and the small capacitor is thus connected to the M-Bus.

[0097] The small capacitor allows the processing unit to supply sufficient energy in charging mode, without the use of an additional separate power supply or controller to ensure continuous signal processing of incoming data on the M-Bus. [0098] The large capacitor gets supplied energy from the small capacitor, e.g. in pulses. This is done by an electrical switch (Q500), e.g. a PMOS in series with the large capacitor, which is controlled from the processing unit.

[0099] The pulse length and / or pulse frequency is determined by the voltage across the small capacitor. As long as the large capacitor is not sufficiently charged, i.e., the voltage across the large capacitor is less than the upper charge limit mentioned previously in connection with Fig. 4, a pulse which switches in the large capacitor will cause the amount of energy, and thus the voltage, across the small capacitor to be reduced.

[0100] If the voltage across the large capacitor rises above the upper charge limit, the charging can take place permanently.

[0101] Permanent charging may continue even if the voltage across the large capacitor drops below the upper charge limit, but switch to pulsed charge if it drops to a lower charge limit below the upper charge limit.

[0102] At the same time, pulsing and the accompanying transfer of energy from the small to the large capacitor will only be made if the voltage across the small capacitor is above the lower switching limit which has also been discussed previously.

[0103] As soon as the pulse charge ends, the voltage across the small capacitor can rise quite rapidly, depending on the maximum current of the meter type connected.

[0104] A new pulse charge can start when the voltage across the small capacitor reaches the upper switching limit. In this way, the pulsed switching may have a hysteresis, where switching in is determined by an upper switching limit, and switching out is determined by a lower switching limit of the voltage across the small capacitor.

[0105] The pulses may be voltage controlled and have different lengths, or have a fixed pulse length for switching in the large capacitor, where the start and stop of the pulse train is determined by the voltages over respectively the large and the small capacitor.

[0106] When the voltage across the large capacitor has reached the desired upper charge limit, the charging mode will be completed and the processor switches to the energy monitoring mode.

[0107] Another alternative is that the large capacitor may be charged continuously as long as the voltage across the small capacitor is above the lower switching limit. [0108] In order to achieve faster charging of the large capacitor, in one embodiment, parts of the power adaption circuit may go to sleep to reduce the current draw in the charging mode. This can, e.g. mean that the parts of the circuit used for signal processing are deactivated as long as no incoming messages are detected on the M-Bus, as illustrated in the right portion of Fig. 6. As soon as messages are detected, the circuits will be activated so that all messages are received, processed and stored locally.

[0109] In energy monitoring mode, illustrated in Fig. 8, the voltage across the large capacitor is above the upper charge limit, and thus may be charged continuously without the voltage across the small capacitor decreasing noticeably. Flowever, there is a need to control the power draw, in cases where it is necessary to extract more power than can be supplied from the M-Bus. For example a wireless interface used to transmit the messages, or other wireless communication, may involve a current draw that exceeds the maximum current draw from the connected meter type. Over time, therefore, the energy in the energy storage will be consumed.

[0110] Therefore, to control the current draw, the processing unit may continuously monitor the voltage across the large capacitor, and as long as the voltage is above the lower charge limit, the current consuming circuit will be active. It means, for example, that messages stored in memory may be sent over the wireless interface.

[0111] If the voltage drops below the lower charge limit, the processing unit will return to charging mode, where the messages are stored locally, until the large capacitor is sufficiently charged.

[0112] If there are no more stored messages in memory, the processing unit may disable power consuming circuits used to send messages, even if the main voltage is above the minimum value.

[0113] It is desirable that messages that can be interpreted from data on the M-Bus are processed as soon as possible after the device is connected to the FIAN port.

[0114] The message reception mode illustrated in Fig. 7 can therefore start as soon as the device is connected to the FIAN port and ready to receive data, and later continue regardless of whether the device is in charge mode or energy monitoring mode. As long as data can be interpreted, this mode will continue.

[0115] As can be seen, this mode is run in parallel with the startup mode. In the case where received data is used to detect electricity meter type, this mode will be seen as part of the startup mode, but it will continue after the startup mode is complete. [0116] One can imagine that it is physically possible to move a slave unit from one HAN port to another while having a lot of energy stored in the large capacitor. For example, if the power adaption circuit is set to an electricity meter type with a higher maximum current draw than the electricity meter type to which it is moved to.

[0117] In this case, the processing unit will quickly notice that the values of the signal parameters do not match the expected signal signature, and it may then e.g. go to startup mode to adjust to the new electricity meter. There may also be other reasons why the device does not recognize the data. The unit may then return to startup mode as shown at the bottom of Fig. 7.

[0118] The dynamic current limiter is adapted to limit the current draw from the HAN port based on the limiting parameter from the processing unit. This dynamic requires a certain capacitance in the current limiter.

[0119] Although the maximum current draw of the dynamic current limiter is set to a certain level to satisfy the electricity meter type, due to the capacitance, when connected to the HAN port, short current pulses above the maximum current draw allowable by the electricity meter may occur. Such current pulses are often referred to as inrush current.

[0120] In some cases, the electricity meters will not be further protected against inrush current higher than the maximum current draw in an operating situation, and thus deactivate the M-Bus, with the result that it becomes difficult to carry out start-up and charging mode as described above.

[0121] In the case where it is the electricity meter type with the highest permissible maximum current that allows very little extra inrush current compared to the maximum current, the power adaptation circuit may in one embodiment comprise a fixed current limiter in series with the dynamic current limiter. The fixed current limiter is static and has a fixed current limiting value. The fixed current limiting value may thus be set just below the maximum current value for the electricity meter type. One problem with this arrangement, however, is that some energy may disappear in the fixed current limiter. To solve this, the maximum current in the dynamic current limiter can be set to a value which is just below the current limiting value of the fixed current limiter.

[0122] If there is a different electricity meter type other than the one with the highest allowed maximum current which allows very little extra inrush current, it may be appropriate to use several static current limiters instead of the first dynamic, possibly a combination of dynamic and static current limiters which can be switched in depending on the electricity meter type . [0123] Standard communication protocols, e.g. an I2C bus may be used between modules, e.g. between the processor and the first limiter. Here, the communication bus may be used to transmit the constraint parameter.

[0124] In a further embodiment of the invention, there is provided a method for finding maximum current draw by: connect the device to the meter and start on a low current draw (for example, maximum current draw for the meter that provides the least power), increase the current flow gradually while verifying that outgoing data is valid (for example, can be verified by checking checksum), store the highest functioning value to date (i.e. current draw that still provide valid data), and when the unit detects that the current draw is too large, for example by data being corrupted, the meter cuts the power, the unit is restarted, or otherwise detects that the current draw has become or has been too large, the unit adjusts the current draw to the last recorded value that worked and provided valid data.

[0125] In the embodiments shown, which are examples of how the invention can be practiced, various features and details are shown in combination. Although several features are described as belonging to a particular embodiment, this does not necessarily mean that these features must be implemented together in all embodiments of the invention. Likewise, features described in different designs should not be considered to exclude combinations with each other. Those skilled in the art will appreciate that embodiments comprising some of the features which are not specifically described together but which are also not described as being excluded from being combined with one another are part of the invention. An explicit description of all embodiments will not contribute to understanding the concept of the invention, and thus some of the combinations have been omitted to make the application simpler and shorter.

[0126] In a further first embodiment, according to the present invention, a power adaption circuit 1 is provided for extracting energy from an output port of a measuring instrument, wherein the power adaption circuit comprises a current limiter 2, 3, 2', 3' which is adapted to limit the current draw from the output port depending on a limiting parameter 8, 8', such that maximum current draw from the output port is determined by the measuring instrument to which the power adaption circuit is connected and which is characterized in that the power adaption circuit comprises an energy storage 4, 4' and a processing unit 6, 6', wherein the processing unit is arranged to monitor available energy in the energy storage.

[0127] A further second embodiment of the power adaption circuit in the further first embodiment is provided, wherein the processing unit is arranged to control the charge of the energy in the energy storage, and the energy storage comprises a main energy storage C501 and an auxiliary energy storage C500.

[0128] A further third embodiment of the power adaption circuit in the further second embodiment is provided, wherein the energy storage comprises an electronic switch Q500 in series with the main energy storage, wherein the series connection of the main energy storage and the electronic switch is arranged in parallel with the auxiliary energy storage.

[0129] A further fourth embodiment of the power adaption circuit in the further third embodiment is provided, wherein the processing unit is arranged to monitor the voltage across the main energy auxiliary storage and the processing unit is adapted to switch on the electronic switch if the voltage above the auxiliary supply is above a preset minimum value. [0130] A further fifth embodiment of the power adaption circuit in one of the further first to fourth embodiments is provided, wherein the measuring instrument is an electricity meter.

[0131] A further sixth embodiment of the power adaption circuit in one of the further first to fourth embodiments is provided, wherein the measuring instrument is a water meter.

[0132] A further seventh embodiment of the power adaption circuit in one of the further first to fourth embodiments is provided, wherein the measuring instrument is a gas meter.

[0133] A further first method of the present invention is to adjust the current draw from the output of a measuring instrument comprising: limiting the current draw from the output port depending on a limiting parameter 8, 8 ', so that maximum current draw from the output port is determined by the measuring instrument to which the power adaption circuit is connected, and the method further comprises: storing of energy from the output port in an energy storage, monitoring the energy in the energy storage, and limiting the extraction of energy from the energy storage if the energy is below a threshold value. [0134] A further second method of the further first method comprises: deactivating or limiting a communication interface if the energy is below the threshold value.

[0135] A further third method of one of the further first to second methods comprises: intermediate storage of incoming data from the output port, and - forwarding data via the communication interface only when the energy storage contains energy above a certain minimum limit.

[0136] A further fourth method of one of the further first to third methods, wherein the energy storage comprises a main energy storage and an auxiliary energy storage, the method further comprises: - transferring energy from the auxiliary energy storage to the main energy storage in pulses as long as the voltage is below an upper charge limit, and continuously as the voltage rises above the upper charge limit, where the upper charge limit is greater than the lower charge limit, maintain continuous charging if the voltage drops below the upper charge limit, resuming transfer of energy in pulses if voltage drops below the lower charge limit, - starting transfer of the energy from the auxiliary energy storage to the main energy storage if the voltage across the auxiliary energy storage exceeds an upper switching limit, and continue the transfer of energy until the voltage across the auxiliary energy storage drops to a lower switching limit which is below the upper switching limit.