Arranged to detect fraudulent opening of an electricity meter

Abstract

An electricity meter (1) comprises: a housing (4) comprising at least one normally closed housing element (5, 6); a supercapacitor (C1) and a supply circuit (8) arranged to charge the supercapacitor whenever the electricity meter is connected to a power source; a charge maintenance circuit (25) arranged to prevent the supercapacitor from discharging as long as the housing element remains closed whenever the electricity meter has been disconnected from the power source, and a discharge circuit (16) arranged to discharge the supercapacitor if the housing element is open; and a processor circuit (27) arranged to detect, after the electricity meter has been reconnected to the power source and if the supercapacitor is discharged, that the housing element has been opened since the electricity meter was disconnected from the power source.

Description

Technical Field

[0001] The present invention relates to the field of smart electricity meters. Background Art

[0002] Typically, an electric meter has a housing that includes end caps and a hood. In operation, when the meter is installed on a customer's premises, the end caps and hood are usually closed. They can be opened under special circumstances, but usually only by operators working for the electricity distributor.

[0003] However, it is possible that a malicious person may attempt to commit fraud by opening the meter's housing and wiring the metered utility upstream of the meter (ie, on its network side) so that the meter does not record the metered utility's electricity consumption.

[0004] Once the meter is assembled at the factory, the cover is typically sealed to the rest of the housing by thermoplastic staking. Similarly, once the meter is installed and connected, the end caps are sealed to the rest of the housing. This seal enables the operator to detect any fraudulent opening of the end caps or covers when they subsequently appear in front of the meter.

[0005] However, it would be advantageous to enable the meter itself to detect any opening of the end cap or cover automatically, i.e., such detection does not require the presence of an operator. The meter would then send an alarm message to the distributor's information system (IS) so that, if the opening was unexpected, the distributor could take action to prevent fraudulent manipulation.

[0006] Automatic detection can be achieved relatively simply when the meter is powered on (ie, when the meter is connected to a power source).

[0007] In contrast, when the meter is not powered, detection is more difficult to achieve because power must be managed to the detector device contained in the meter.

[0008] Prior art detector devices are known in which an end cap and a cover are each associated with a respective switch. The open or closed state of the switch depends on the presence or absence of the end cap or cover, respectively. The meter includes a battery such that when the meter is not powered, the battery continues to power the real-time clock (RTC) portion of the microcontroller. The microcontroller operates in real time to monitor the state of the switch in order to detect any opening of the end cap and / or cover.

[0009] This solution requires the microcontroller to remain functional the entire time the meter is unpowered, and therefore requires a battery capable of providing a significant amount of energy. Consequently, the battery is expensive. Furthermore, some customers refuse to use meters that include batteries.

[0010] Therefore, it has been proposed to replace batteries with supercapacitors with high capacitance (typically 1 Farad (F)) to be able to keep these functions active when the meter is not powered, typically for 5 to 7 days. However, supercapacitors also come with a significant cost, and this cost is again related to the high charge storage capacity required for this application.

[0011] In both cases (battery and supercapacitor), the life of the detection function is not very long and after only a few days without power the meter is no longer able to detect any opening of the end cap and / or cover.

[0012] Purpose of the Invention

[0013] An object of the present invention is to detect fraudulent opening of a housing element of an electricity meter that occurs when the meter is not powered, wherein the detection is performed in a simple and inexpensive manner, does not require the use of batteries, and remains effective even after the meter has been unpowered for a long time. Summary of the Invention

[0014] To achieve this purpose, an electric meter is provided, comprising:

[0015] a housing comprising at least one housing element which is normally closed in operation but capable of being opened;

[0016] supercapacitors;

[0017] a power supply circuit arranged to charge the supercapacitor whenever the electricity meter is placed in connection with a power source;

[0018] a charge maintenance circuit arranged to prevent the supercapacitor from discharging whenever the meter is disconnected from the power source after having been previously connected thereto, as long as the housing element remains closed;

[0019] a discharge circuit arranged to discharge the supercapacitor whenever the electricity meter has been disconnected from the power supply and with the housing element opened;

[0020] A processor circuit is arranged to acquire a detection signal representative of the voltage across the terminals of the supercapacitor, and hence the charge level of the supercapacitor, each time the electricity meter is reconnected to the power supply after being disconnected from the power supply, and, if the supercapacitor is discharged, to detect that the housing element has been opened since the electricity meter was disconnected from the power supply.

[0021] Therefore, when the meter is powered on, the power supply circuit charges the supercapacitor.

[0022] Thereafter, whenever the meter is disconnected from the power supply, the supercapacitor is discharged quickly through the discharge circuit when the housing element is opened. In contrast, with the circuit of the present invention, the supercapacitor is discharged only very slowly due to its inherent leakage current characteristics as long as the housing element remains closed.

[0023] The detection function does not require a battery. Since the supercapacitor does not power any components (neither the microcontroller nor any other system for recording events), and since there is no discharge path other than the path actively established by opening the housing element, the detection function remains operational even after the meter has not been powered for a long time (up to several months). The supercapacitor can have a smaller size than prior art solutions, so the present invention can be implemented in an inexpensive manner.

[0024] There is also provided an electricity meter as described above, wherein the discharge circuit comprises at least one switch connected in parallel with the supercapacitor, the switch being arranged to cooperate with the housing element in such a way that when the housing element is closed, the switch is open, and when the housing element is open, the switch is closed and discharges the supercapacitor.

[0025] There is also provided an electricity meter as described above, wherein the electricity meter comprises two housing elements, the two housing elements comprising end caps and a cover, the discharge circuit having a first switch arranged to cooperate with the end caps and a second switch arranged to cooperate with the cover, the first and second switches being connected in parallel with each other and in parallel with the supercapacitor.

[0026] There is also provided an electricity meter as described above, wherein the processor circuit is connected to a charge maintenance circuit, wherein the charge maintenance circuit is connected to the terminals of a supercapacitor and assumes a non-conductive state when the electricity meter is not powered and assumes a conductive state when the electricity meter is powered, the processor circuit and the charge maintenance circuit being arranged in such a way that when the electricity meter is powered, when the supercapacitor is charged, the voltage across the terminals of the supercapacitor is applied to the input of the processor circuit via the charge maintenance circuit, and when the supercapacitor is discharged, a voltage of 0 volts (V) is applied to the input.

[0027] There is also provided an electricity meter as described above, wherein the charge maintenance circuit comprises two first transistors and a second transistor, the two first transistors being connected back to back, one of the first transistors having a terminal connected to said terminal of the supercapacitor and the other of the first transistors having a terminal connected to an input of the processor circuit, the second transistor being arranged to place the first transistors in a conducting state when the electricity meter is powered on and the supercapacitor is charged.

[0028] There is also provided an electric meter as described above, wherein the first transistor is a P-channel MOSFET type transistor and the second transistor is an N-channel MOSFET type transistor, the gate of the second transistor is connected to the power supply circuit, the source of the second transistor is connected to electrical ground, and the drain of the second transistor is connected to the gate of the first transistor.

[0029] There is also provided a detection method executed in a processor circuit of an electricity meter as described above and comprising a detection phase comprising steps performed each time the electricity meter is reconnected to the power supply after being disconnected from the power supply, said steps comprising acquiring a detection signal representative of the voltage across the terminals of the supercapacitor and therefore the charge level of the supercapacitor, and, if the supercapacitor is discharged, detecting that a housing element has been opened since the electricity meter was disconnected from the power supply.

[0030] There is also provided a detection method as described above, wherein a semaphore is defined by a computer program executed in the processor circuit, the semaphore having a first predefined value at the end of manufacture of the electricity meter, the detection method further comprising steps performed each time the electricity meter is connected to a power source, the steps comprising:

[0031] Read the value of the semaphore; and:

[0032] If the value of the semaphore is equal to the first predefined value, waiting for a predefined duration and then giving the semaphore a second predefined value in a deterministic manner;

[0033] If the value of the semaphore is equal to a second predefined value, a detection phase is performed.

[0034] There is also provided a detection method as described above, the method further comprising the step of generating and sending an alarm message in case the processor circuit has detected that a housing element has been opened since the meter was disconnected from the power supply.

[0035] There is also provided a computer program comprising instructions for causing a processor circuit of an electricity meter as described above to perform the steps of the detection method as described above.

[0036] A computer-readable storage medium is also provided, which stores the computer program.

[0037] The present invention may be better understood in view of the following description of certain non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] With reference to the accompanying drawings, in which:

[0039] [ Figure 1 ] Figure 1 The electric meter of the present invention is shown;

[0040] [ Figure 2 ] Figure 2 The steps of the detection method performed by the electricity meter are shown. DETAILED DESCRIPTION

[0041] refer to Figure 1 The electric meter 1 of the present invention is used to measure the energy consumption of the subscriber's electric appliance 2 provided by the power distribution network 3.

[0042] The electricity meter 1 may be a single-phase or multi-phase electricity meter, for example, a three-phase electricity meter.

[0043] The electricity meter 1 includes a housing 4 that contains all control components of the electricity meter 1. The term "housing" as used herein refers to the physical casing that separates the interior of the electricity meter 1 from the exterior.

[0044] The housing 4 comprises at least one housing element which is normally closed in operation but can be opened. The housing element can be potentially removable, but when it is opened, it can also be permanently attached to the rest of the housing 4.

[0045] In this example, the housing 4 has two housing elements, specifically an end cap 5 and a cover 6 , both of which are removable.

[0046] The electricity meter 1 includes a detector device 7 for detecting the opening of the end cap 5 and / or cover 6 when the electricity meter 1 is not powered, and even after the electricity meter 1 has not been powered for a long period of time (typically 3 months or more). The detector device 7 is therefore used to identify fraud attempts and to alert the IS if such an attempt occurs, thereby enabling the operator to take action against the identified fraud attempt.

[0047] The detector device 7 firstly comprises a supercapacitor C1 and a power supply circuit. The power supply circuit comprises a power supply circuit 8 connected in parallel with the supercapacitor C1.

[0048] The supercapacitor C1 has a first terminal 10 connected to an electrical ground 11 of the electricity meter 1. The power supply circuit 8 has a port 12 connected to the electrical ground 11. The power supply circuit 8 also has an output 14 connected to a second terminal 15 of the supercapacitor C1 via a Schottky diode D1 and a resistor R1. The power supply circuit 8 is powered only when the electricity meter 1 is powered, in which case it generates a direct current (DC) voltage Vc at its output 14, specifically a voltage equal to 3.3 volts (V).

[0049] Thus, when the power supply circuit 8 itself is powered, it charges the supercapacitor C1 .

[0050] The detector device 7 further comprises a discharge circuit 16 arranged to discharge the supercapacitor C1 when the meter 1 is not powered, if the end cap 5 is opened, or the cover 6 is opened, or both are opened.

[0051] The discharge circuit 16 includes at least one switch connected in parallel with the supercapacitor C1, the switch being arranged to cooperate with the housing elements in such a manner that when the housing elements are closed, the switch is open, and when the housing elements are open, the switch is closed and causes the supercapacitor C1 to discharge. In this example, there are two housing elements, and the discharge circuit 16 has a first switch I1 arranged to cooperate with the end cap 5 and a second switch I2 arranged to cooperate with the cover 6, the first and second switches I1 and I2 being connected in parallel with each other and with the supercapacitor C1.

[0052] The first switch I1 has a first terminal 18 and a second terminal 19. The second switch I2 has a first terminal 20 and a second terminal 21. The first terminals 18 and 20 are connected to each other and to electrical ground 11. The second terminals 19 and 21 are connected together and to a first terminal 23 of a resistor R2, and a second terminal 24 of the resistor R2 is connected to the second terminal 15 of the supercapacitor C1.

[0053] The first switch I1 and the end cap 5 work together as follows. Due to its design, the first switch I1 is a "normally closed" switch. When the end cap 5 is closed and thus mounted on the housing 4 of the electricity meter 1, a pin attached to the end cap 5 presses against the first switch I1, thereby opening the first switch I1. Therefore, when the electricity meter 1 is operating under normal operating conditions (with the end cap 5 closed), the first switch I1 is in the open state. Conversely, when the end cap 5 is opened, the pin no longer faces the first switch I1, and the first switch then switches to the closed state (conducting).

[0054] The second switch 12 cooperates with the cover 6 in the same way.

[0055] When the end cap 5 is opened, the first switch I1 is closed, thereby causing the supercapacitor C1 to discharge. Similarly, when the cover 6 is opened, the second switch I2 is closed, thereby causing the supercapacitor C1 to discharge.

[0056] The detector device 7 further comprises a charge maintaining circuit 25 arranged to prevent the supercapacitor C1 from discharging whenever the electricity meter 1 is disconnected from the power supply as long as the end cap 5 and the cover 6 remain closed, i.e. as long as both the first switch I1 and the second switch I2 remain open.

[0057] The charge maintenance circuit 25 is connected to the second terminal 15 of the supercapacitor C1 and is in a non-conductive state when the meter 1 is not powered or when the meter 1 is powered and the supercapacitor C1 is discharged, and is in a conductive state when the meter 1 is powered and the supercapacitor C1 is charged.

[0058] The charge holding circuit 25 has two first transistors Q1 and Q2 , a second transistor Q3 , a resistor R3 , and a resistor R4 .

[0059] The two first transistors are P-channel MOSFET transistors and are connected back-to-back: they are thus connected in series, with the source of the first transistor Q1 connected to the source of the first transistor Q2. The gates of the first transistors Q1 and Q2 are connected together at point P1, which is itself connected to the sources of the first transistors Q1 and Q2 via a resistor R3. By way of example, the resistor R3 may have a resistance of 10 kiloohms (kΩ).

[0060] The drain of the first transistor Q1 is connected to the second terminal 15 of the supercapacitor C1 .

[0061] The second transistor Q3 is an N-channel MOSFET type transistor, whose gate is connected to the output 14 of the power supply circuit 8, whose source is connected to the electrical ground 11, and whose drain is connected to the point P1 (and thus to the gates of the first transistors Q1 and Q2) via a resistor R4. By way of example, the resistor R4 may have a resistance of 1 kΩ.

[0062] The charge holding circuit 25 further includes the aforementioned Schottky diode D1 .

[0063] Detector circuit 7 also includes a processor circuit 27 connected to charge maintenance circuit 25. By way of example, processor component 27 includes a processor component that can be a general-purpose processor, a processor dedicated to signal processing (called a digital signal processor (DSP)), a microcontroller, or indeed a programmable logic circuit, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). Processor circuit 27 also includes one or more memories connected to or incorporated into the processor component. At least one of these memories constitutes a computer-readable storage medium that stores a computer program including instructions that enable the processor component to perform at least some of the steps of the detection method described below.

[0064] In this example, the electricity meter 1 presents a dual microcontroller architecture: a metering microcontroller forming part of the metering portion of the electricity meter 1 , and an application microcontroller forming part of the application portion of the electricity meter 1 .

[0065] In this example, the processor component is an application microcontroller 28 .

[0066] The microcontroller 28 is supplied with 3.3 V by the supply circuit 8 , and it is connected to the electrical ground 11 .

[0067] The microcontroller 28 has an input terminal 29 connected to the drain of the first transistor Q2. The input terminal 29 is an input / output (I / O) configured in an input (I) mode.

[0068] The resistor R5 is connected to have a first terminal 30 connected to the electrical ground 11 and a second terminal 31 connected to a point P2, which is itself connected to the drain of the first transistor Q2 and to an input 29 of the microcontroller 28. When the electricity meter 1 is powered on and the supercapacitor C1 is discharged, this causes a voltage of 0 V to be provided to the input 29 of the microcontroller 28.

[0069] The electricity meter 1 further comprises a communication module, which is specifically a power line communication (PLC) modem 32. The PLC modem 32 uses the G3 PLC standard, but other types of standards may also be used, such as the PLC Prime standard.

[0070] The microcontroller 28 and the PLC modem 32 are connected together via a serial link 33 which in this example uses the Universal Asynchronous Receiver / Transmitter (UART) protocol. It is naturally possible to use some other type of link, such as a Serial Peripheral Interface (SPI) link.

[0071] The operation of the detector device 7 of the electricity meter 1 will be described in more detail below.

[0072] Whenever the electricity meter 1 is placed in connection with the mains, the power supply circuit 8 is also placed in connection with the mains and it charges the supercapacitor C1 . The maximum voltage Umax across the terminals of the supercapacitor C1 is equal to 3.3 V (ie to Vc).

[0073] The time T1 to charge the supercapacitor C1 to 63% (the time from 0% to 63% of Umax) is equal to:

[0074] T1=R1*C1.

[0075] For example, the following values ​​can be used for R1 and C1:

[0076] R1 = 1200 ohms (Ω) and C1 = 0.1F.

[0077] thus:

[0078] T1=120s=2 minutes.

[0079] The time to charge to 95% is equal to 3*T1, which is therefore equal to 360s (or 6 minutes).

[0080] Thus, as a result of the electricity meter 1 being previously connected to the mains, the supply circuit 8 is also connected to the mains and it charges the supercapacitor C1. The term "previously connected to the mains" covers any situation in which the electricity meter 1 is connected to the mains during its service life.

[0081] When the electricity meter 1 is disconnected from the mains (after having previously been initially placed in connection with the mains), the supply circuit 8 is no longer energized.

[0082] The charge maintenance circuit 25 acts to prevent the supercapacitor C1 from discharging, and this continues as long as the end cap 5 and cover 6 remain closed.

[0083] Specifically, when the power supply circuit 8 is not powered, the voltage on the gate of the second transistor Q3 is zero, and the second transistor Q3 is therefore in a non-conducting state. The internal diodes of the two first transistors Q1 and Q2 prevent current from flowing from the supercapacitor C1 to the input terminal 29 of the microcontroller 28 (and also in the opposite direction) because they are connected back to back. The supercapacitor C1 therefore does not discharge to the electrical ground 11 via the microcontroller 28.

[0084] At the same time, when the meter is not powered, the Schottky diode D1 is used to prevent the supercapacitor C1 from discharging via a path through the resistor R1 and the power supply circuit 8 to the electrical ground 11 .

[0085] Whenever the electricity meter 1 is disconnected from the power supply and the end cap 5 is open and / or the cover 6 is open, the first and / or second switches I1 and / or I2 are switched to a closed state. The two plates of the supercapacitor C1 are then connected together via the resistor R2, and the supercapacitor C1 is rapidly discharged.

[0086] The time T2 for supercapacitor C1 to discharge to 37% (the time from 100% to 37% of Umax) is equal to:

[0087] T2=R2*C2.

[0088] For example, the following values ​​can be used for R2:

[0089] R2=10Ω.

[0090] thus:

[0091] T2=1s.

[0092] The time to discharge to 95% is equal to 3*T2 and therefore equal to 3s.

[0093] Thus, with one or the other of the two switches I1 or I2 in the closed state, the supercapacitor C1 is discharged, even if this state lasts only for 3 seconds.

[0094] Thereafter, once the electricity meter 1 is reconnected to the power supply, the microcontroller 28 acquires a detection signal representing the voltage across the terminals of the supercapacitor C1 and, therefore, the charge level in the supercapacitor C1, and, in the event that the supercapacitor C1 is discharged, the microcontroller 28 detects that the end cap 5 or the cover 6 (or both) have been opened since the electricity meter 1 was disconnected from the power supply.

[0095] The term "reconnecting to the mains" refers to reconnecting to the mains after being disconnected from the mains, and specifically reconnecting immediately after the meter was previously connected to the mains.

[0096] When the electricity meter 1 is powered on, and when the supercapacitor C1 is charged, the voltage across the terminals of the supercapacitor C1 is applied to the input 29 of the microcontroller 28 via the charge maintenance circuit 25. In this example, the detection signal is therefore the voltage across the terminals of the supercapacitor C1 itself (but it may also be some other signal derived from this voltage).

[0097] Specifically, whenever the electricity meter 1 is powered on and the supercapacitor C1 is charged, the power supply circuit 8 is also powered on and generates a voltage Vc equal to 3.3 V at its output 14. Consequently, the second transistor Q3 is in an on-state, connecting the gates of the first transistors Q1 and Q2 to the electrical ground 11 (via the resistor R4). Since the drain of the first transistor Q1 is at the same potential as the second terminal 15 of the charged supercapacitor C1, both the first transistors Q1 and Q2 are in an on-state, and the second terminal 15 of the supercapacitor C1 is connected to the input 29 of the microcontroller 28.

[0098] Whenever the electricity meter 1 is powered on and the supercapacitor C1 is discharged, the first transistors Q1 and Q2 are in a non-conducting state and the electrical ground 11 is applied to the input 29 of the microcontroller 28 (via the resistor R5 ).

[0099] Specifically, whenever the electricity meter 1 is powered on and the supercapacitor C1 is discharged, even if the second transistor Q3 is in a conductive state so that the gates of the first transistors Q1 and Q2 are connected to the electrical ground 11, since the drain of the first transistor Q1 is biased to 0V, the first transistors Q1 and Q2 are in a non-conductive state, and the electrical ground 11 is applied to the input terminal 29 of the microcontroller 28 via the resistor R5.

[0100] The microcontroller 28 then compares the voltage at its input 29 with a first predefined threshold value and a second predefined threshold value.

[0101] In this example, the first predefined threshold is equal to 1.8V, and the second predefined threshold is equal to 0.8V.

[0102] If the voltage at the input 29 is higher than the first predefined threshold, the microcontroller 28 reads a “1” state (high state), which corresponds to a normal charge state of the supercapacitor C1 , so there is no fraud.

[0103] If the voltage at input 29 is below a second predefined threshold, microcontroller 28 reads a "0" state (low state), which corresponds to an undercharged state of supercapacitor C1. Microcontroller 28 detects that one or both of end cap 5 and cover 6 have been opened since meter 1 was disconnected from the power source, and thus detects that fraud has occurred.

[0104] Once the electricity meter 1 has been restarted, the power supply circuit 8 recharges the supercapacitor C1 (the charging circuit has a time constant of 2 minutes). Therefore, the reading needs to be taken very quickly, for example within a few seconds of the electricity meter 1 being restarted. In these few seconds, the charge of the supercapacitor C1 does not have enough time to change significantly.

[0105] This avoids the charge value of the supercapacitor C1 being significantly different between when the meter 1 is reconnected to the power supply and when a reading is taken, thereby avoiding reading a high state (a "false negative") even though the end cap 5 and / or cover 6 have been opened.

[0106] In the event that the end cap 5 or the hood 6 is detected to be open, the microcontroller 28 generates an alarm message and sends it to the IS using the PLC modem 32 .

[0107] Each time the meter is reconnected to the mains, it takes no more than 6 minutes for the supercapacitor C1 to be fully charged (to 95%), even if it has been discharged since it was previously disconnected from the mains. This means that, even in the event of a detected opening (resulting in an alarm message being sent to the IS), the supercapacitor C1 is recharged and the detector device 7 is ready again to detect any new fraud attempt that occurs after the meter is subsequently disconnected from the mains.

[0108] It should be observed that, in the case of a discharge of the supercapacitor C1, when the microcontroller 28 is reading the voltage across the terminals of the supercapacitor C1, the first transistors Q1 and Q2 are in a non-conducting state and the resistor R5 connected to the ground 11 serves to impose a zero voltage on the input of the microcontroller 28, which therefore reads a 0 state.

[0109] As can be seen, when electricity meter 1 is not powered, no components of detector circuit 7 need to be powered. Specifically, charge maintenance circuit 25 does not require any power to maintain supercapacitor C1 charged, and the energy stored in supercapacitor C1 is not used to power any components. Furthermore, charge maintenance circuit 25 is used to prevent supercapacitor C1 from discharging. Consequently, supercapacitor C1 discharges very slowly when electricity meter 1 is not powered, allowing fraud detection to remain operational long after the electricity meter has been disconnected from power and enabling the selection of a relatively small-capacitance supercapacitor C1.

[0110] Next is described the detection phase performed by the microcontroller 28, which phase therefore occurs after the meter 1 has been reconnected to the mains after having been previously connected and then disconnected from it, and which consists in reading a detection signal representative of the voltage across the terminals of the supercapacitor C1 and, in the case of the supercapacitor C1 being discharged, indicating that one or both of the end caps 5 and the cover 6 have been opened since the meter 1 was disconnected from the mains.

[0111] Preferably, the voltage level across the terminals of the supercapacitor C1 is not tested when the meter 1 is first connected to the mains, as would occur immediately after the meter 1 is installed on the customer's premises. When the supercapacitor C1 is first connected to the mains, it can be a priori expected to be discharged, and any fraudulent operation is still unlikely to occur.

[0112] To this end, the electricity meter 1 uses a semaphore, which is a variable defined by a computer program executed in the microcontroller 28 .

[0113] Once the electricity meter 1 is manufactured, ie when it leaves the factory, a first predefined value is assigned to the semaphore: S1=0.

[0114] refer to Figure 2 Whenever the electricity meter 1 is connected to the power source (including initially), the microcontroller 28 performs the following detection method.

[0115] The detection method begins at step E0 . The microcontroller 28 then reads the value of the semaphore and verifies whether S1 = 0 (step E1 ).

[0116] If so, the microcontroller 28 knows that the meter has been connected to power for the first time.

[0117] The microcontroller 28 therefore does not detect whether the end cap 5 or the cover 6 has been opened, and therefore does not detect whether fraud has occurred, but instead waits for a predefined duration D (step E2 ).

[0118] The predefined duration D corresponds to a length of time that is long enough for the charge of the supercapacitor C1 to reach a sufficient level.

[0119] In this example, the sufficiency level is equal to 95%.

[0120] thus:

[0121] D=3*T1=3*R1*C1=6 minutes.

[0122] At the end of the predefined duration D, the microcontroller 28 assigns a second predefined value to the semaphore in a deterministic manner: S1 = 1 (step E3 ). The detection method ends here (step E4 ).

[0123] In step E1, if the value of the signal quantity is equal to the second predefined value (i.e., if S1=1), the microcontroller 28 knows that this is not the first time the meter has been connected to the power supply. The microcontroller 28 then performs a detection phase and reads a detection signal representing the voltage across the terminals of the supercapacitor C1 (i.e., specifically, the voltage across the terminals of the supercapacitor C1 itself). The microcontroller 28 thus verifies whether the supercapacitor C1 is charged (step E5).

[0124] If the supercapacitor C1 is still charged, the detection method ends here (step E4). Otherwise, the microcontroller 28 generates an alarm message and sends it to the IS via the PLC modem 32 to warn that there has been a fraudulent opening of the end cap 5 and / or the cover 6. The detection method ends here.

[0125] Naturally, the invention is not limited to the implementations described, but covers any variant coming within the ambit of the invention as defined by the appended claims.

[0126] The values ​​of the components used can naturally differ from those mentioned above. Likewise, the charge and discharge times of the supercapacitors can vary.

[0127] The components used may be different from those described above.

[0128] In the charge retention circuit, different transistors can be used and / or connected in different configurations. The first transistor can be an N-channel MOSFET type, while the second transistor can be a P-channel MOSFET type. The transistors do not have to be MOSFETs. The number of transistors used can also vary.

[0129] The microcontroller that reads the voltage across the terminals of the supercapacitor is not necessarily the application microcontroller and, for example, in a dual microcontroller architecture, it can be the metering microcontroller. In this case, it should be observed that the PLC modem is preferably connected to the application microcontroller.

[0130] Some other components can be used to read the voltage across the terminals of the supercapacitor. For example, one terminal of the supercapacitor can be connected to the input of an analog-to-digital converter (perhaps incorporated into a microcontroller). This would make it possible to measure the voltage level across the terminals of the supercapacitor, instead of reading a "binary" detection signal that assumes a high or low state. This measurement could be used, for example, to monitor the maximum charge of the supercapacitor and, therefore, its aging.

[0131] The communication module does not necessarily have to be a PLC modem. Alarm messages can be transmitted via any existing communication means, whether wired or wireless. For example, cellular communication compliant with the Long Term Evolution Machine Type Communication (LTE-M) standard or the Narrowband Internet of Things (NB-IoT) standard can be used.

[0132] It is also possible to use multiple supercapacitors, for example connected in parallel.

Claims

1. An electric meter (1), comprising: a housing (4) comprising at least one housing element which is normally closed in operation but can be opened; Supercapacitor (C1); a power supply circuit (8) arranged to charge the supercapacitor whenever the electricity meter is connected to a power source; a charge maintenance circuit (25) arranged to prevent the supercapacitor from discharging whenever the meter is disconnected from the power supply after having been previously connected thereto, as long as the housing element remains closed; a discharge circuit (16) arranged to discharge the supercapacitor whenever the electricity meter has been disconnected from a power source and when the housing element is opened; as well as a processor circuit (27) arranged to acquire a detection signal representing the voltage across the terminals of the supercapacitor and therefore the charge level of the supercapacitor each time the electricity meter is reconnected to the power supply after being disconnected from the power supply, and to detect, if the supercapacitor is discharged, that the housing element has been opened since the electricity meter (1) was disconnected from the power supply; The invention is characterized in that the charge maintenance circuit comprises two first transistors (Q1, Q2) and a second transistor (Q3), the two first transistors being connected back to back, wherein one of the first transistors (Q1) has a terminal connected to the second terminal (15) of the supercapacitor, the other of the first transistors (Q2) has a terminal connected to the input (29) of the processor circuit, and the second transistor is arranged to put the first transistor into a conducting state when the meter is powered on and the supercapacitor (C1) is charged.

2. The electric meter according to claim 1, characterized in that The discharge circuit (16) comprises at least one switch (I1, I2) connected in parallel with the supercapacitor (C1), the switch being arranged to cooperate with the housing element such that when the housing element is closed, the switch is open, and such that when the housing element is open, the switch is closed and causes the supercapacitor (C1) to discharge.

3. The electric meter according to claim 2, characterized in that The electric meter comprises two housing elements, the housing elements comprising an end cap (5) and a cover (6), the discharge circuit having a first switch (I1) arranged to cooperate with the end cap (5) and a second switch (I2) arranged to cooperate with the cover (6), the first and second switches (I1, I2) being connected in parallel with each other and with the supercapacitor (C1).

4. An electric meter according to any preceding claim, characterised in that The processor circuit (27) is connected to the charge maintenance circuit (25), wherein the charge maintenance circuit (25) is connected to the second terminal (15) of the supercapacitor (C1) and assumes a non-conductive state when the electricity meter (1) is not powered and assumes a conductive state when the electricity meter (1) is powered, the processor circuit (27) and the charge maintenance circuit (25) being arranged in such a way that when the electricity meter (1) is powered, when the supercapacitor (C1) is charged, the voltage across the terminals of the supercapacitor is applied to the input (29) of the processor circuit (27) via the charge maintenance circuit (25), and when the supercapacitor (C1) is discharged, a voltage of 0V is applied to the input (29).

5. The electric meter according to claim 1, characterized in that The first transistor (Q1, Q2) is a P-channel MOSFET type transistor, and the second transistor (Q3) is an N-channel MOSFET type transistor, the gate of the second transistor is connected to the power supply circuit, the source of the second transistor is connected to the electrical ground (11), and the drain of the second transistor is connected to the gate of the first transistor (Q1, Q2).

6. A detection method executed in a processor circuit (27) of an electricity meter (1) according to any preceding claim, and comprising a detection phase comprising steps performed each time the electricity meter (1) is reconnected to the power supply after being disconnected from the power supply, the steps comprising acquiring a detection signal representative of the voltage across the terminals of the supercapacitor and therefore representative of the charge level of the supercapacitor, and detecting, in the event of discharge of the supercapacitor, that the housing element has been opened since the electricity meter (1) was disconnected from the power supply.

7. The detection method according to claim 6, characterized in that The signal quantity is defined by a computer program executed in the processor circuit (27), the signal quantity having a first predefined value at the end of manufacturing the electricity meter (1), the detection method further comprising steps performed each time the electricity meter is connected to a power source, the steps comprising: Read the value of the semaphore; and: If the value of the semaphore is equal to the first predefined value, waiting for a predefined duration and then giving the semaphore a second predefined value in a deterministic manner; If the value of the semaphore is equal to the second predefined value, the detection phase is performed.

8. The detection method according to claim 6 or claim 7, characterized in that Also included is the step of generating and sending an alarm message if the processor circuit (27) has detected that the housing element has been opened since the meter was disconnected from the power supply.

9. A computer program product comprising instructions for causing a processor circuit (27) of an electricity meter (1) according to any one of claims 1 to 5 to perform the steps of the detection method according to any one of claims 6 to 8. 10 . A computer-readable storage medium storing the computer program product according to claim 9 .

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