Verify the meter's measurement accuracy

Abstract

An electric meter (1) comprises: a test circuit (25) comprising a test component (Rt) and a connection component (26), the connection component being arranged to place the test component in a connected configuration and a disconnected configuration, in which the test component is connected to a phase conductor and a neutral conductor, and in which the test component is disconnected from the phase conductor and / or the neutral conductor; and a processor component (15) being arranged to control the connection component in such a way that the test component is placed in the connected configuration during a predetermined test duration to measure excess energy consumption, and a measurement error of the electric meter is estimated based on the excess energy.

Description

Technical Field

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

[0002] During the life of an electricity meter, drift in its metering accuracy may have the result of significantly overestimating or underestimating the electrical energy consumption.

[0003] Overestimation is disadvantageous to the subscriber, while underestimation is disadvantageous to the energy distributor (especially if a large number of meters are subject to the same drift).

[0004] Drift in metrology accuracy is very difficult to detect when it occurs slowly, and the resulting measurements remain trustworthy even if they are erroneous.

[0005] Since it would be very complex and burdensome to have operators regularly and systematically intervene to verify the metering accuracy of all meters, attempts are being made to develop meters that can act autonomously to verify their own accuracy. The meters evaluate their own metering accuracy error and if it is not within the required accuracy range, they generate an alarm message and send it, for example, to the information system (IS) of the energy distributor.

[0006] Known meters are therefore provided with a measuring circuit which has the main function of measuring the energy consumption of the installation and which also performs a self-measurement of the metering accuracy. The measuring circuit comprises a current generator for injecting a test current upstream of the meter.

[0007] This solution only works on low levels of phase current (i.e., the current in the phase line). In addition, the test current is usually injected at a frequency different from that of the distribution network, which requires filtering to separate the injected energy from the energy normally received by the meter. Therefore, this solution is complex and relatively heavy to design.

[0008] Purpose of the Invention

[0009] The object of the present invention is to provide a solution which enables an electricity meter to estimate its own measurement error in a reliable, simple and inexpensive manner and which is suitable for use whatever the level of the phase current. Summary of the invention

[0010] To achieve this object, there is provided an electric meter arranged to measure energy consumption supplied to an installation by an electric power distribution network comprising phase and neutral conductors, the electric meter comprising:

[0011] · phase conductors and neutral conductors arranged to be connected to the phase line and the neutral line respectively;

[0012] a test circuit comprising a test assembly and a connection assembly arranged to selectively place the test assembly in a connected configuration, in which the test assembly is connected in parallel with the installation to the phase conductor and the neutral conductor so as to form an additional load, and in a disconnected configuration, in which the test assembly is disconnected from the phase conductor and / or the neutral conductor;

[0013] A processor component arranged to control the connection component in such a way as to place the test component in a connected configuration during a predetermined test duration so as to function during the predetermined test duration to measure excess energy due to the additional load and to estimate a measurement error of the meter based on the excess energy.

[0014] The measurement error assessment performed by the electricity meter of the invention consists in diverting the current to flow inside the meter by the timed addition of a controllable internal load.

[0015] The electric meter of the invention thus estimates its own measurement error without using a current generator and without using complex filtering. The test circuit is simple and inexpensive to provide.

[0016] The measurement error assessment is very accurate and very reliable (no false positives) and can be performed regardless of the level of the phase current.

[0017] The present invention may be better understood in light of the following description of certain non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] With reference to the accompanying drawings, in which:

[0019] [ Figure 1 ] Figure 1 The electric meter in the first embodiment of the present invention is shown, and the electric meter is a single-phase electric meter;

[0020] [ Figure 2 ] Figure 2 The steps of a method for evaluating the measurement error of an instrument are shown;

[0021] [ Figure 3 ] Figure 3 The electric meter in the second embodiment of the present invention is shown, and the electric meter is a single-phase electric meter;

[0022] [ Figure 4 ] Figure 4 The electric meter in the third embodiment of the present invention is shown, and the electric meter is a three-phase electric meter;

[0023] [ Figure 5 ] Figure 5 A fourth embodiment of the present invention is shown in which an electric power meter is a three-phase electric power meter. DETAILED DESCRIPTION

[0024] Reference Figure 1 , the electricity meter 1 in the first embodiment of the invention is a single-phase meter for measuring the consumption of energy of an electrical installation 2 supplied to a subscriber by an electricity distribution network 3. The electrical installation 2 is represented by a load Z.

[0025] The power distribution network 3 comprises a phase line 4 and a neutral line 5 .

[0026] The circuit breaker 6 is positioned between the meter 1 and the installation 2. The circuit breaker 6 (which is operable by the subscriber) is used in particular to protect the installation 2 by opening, for example, in case of a surge current occurring in the distribution network 3, for example as a result of a short circuit downstream of the circuit breaker 6.

[0027] The meter 1 has an upstream phase port P connected to the phase line 4 and an upstream neutral port N connected to the neutral line 5. The meter 1 also has a downstream phase port P' and a downstream neutral port N'.

[0028] In this example, the term “upstream” means on the side of the power distribution network 3 , and the term “downstream” means on the side of the facility 2 .

[0029] The downstream phase port P′ and the downstream neutral port N′ of the meter 1 are connected to the installation 2 via respective switches 8 and 9 , both incorporated in the circuit breaker 6 .

[0030] The meter 1 also has a phase conductor 10 connected to the phase line 4 of the distribution network 3 via an upstream phase port P and a neutral conductor 11 connected to the neutral line 5 via an upstream neutral port N. The meter 1 has an electrical ground 12 connected to the phase conductor 10 near the upstream phase port P.

[0031] The meter 1 further comprises a disconnection means 13 comprising a switch 14 connected in the phase conductor 10. The disconnection means 13 is used in particular to remotely interrupt or reestablish the power supply to the installation 2, for example in the event of cancellation of a subscription or non-compliance with a subscription contract.

[0032] The meter 1 also has a metering component.

[0033] The metering assembly comprises a processor assembly, in particular a metering microcontroller 15, which has the main function of generating measured values ​​of a number of parameters that enable evaluation of the electricity consumption of the installation 2. The microcontroller 15 generates measurements of the phase currents Ip flowing in the phases 4 of the distribution network 3, of the network voltage Vr between the phases 4 and the neutral conductor 5 of the distribution network 3 (and therefore in this example between the electrical ground 12 of the meter 1 and the neutral conductor 11), together with measurements of the power and energy consumed by the installation 2. The root mean square (RMS) value of the network voltage vr is theoretically equal to 230 volts (V).

[0034] The microcontroller 15 is also suitable for executing instructions of a program for carrying out the method for evaluating a measurement error described below. The program is stored in a memory 16 which is integrated into or connected to the microcontroller 15 .

[0035] The microcontroller 15 includes a first analog-to-digital converter (ADC) 17 , a second ADC 18 , a voltage measurement module 19 , and a current measurement module 20 .

[0036] The metering assembly further comprises a voltage divider bridge comprising a first measuring resistor R1 and a second measuring resistor R2. The first measuring resistor R1 has a first terminal connected to the neutral conductor 11. The second measuring resistor R2 has a first terminal connected to the electrical ground 12. The second terminals of the first measuring resistor R1 and the second measuring resistor R2 are connected together and to an input of a microcontroller 15, which input is also connected to an input of a first ADC 17.

[0037] The voltage Vm1 measured by the first ADC 17 is a mirror image of the network voltage vr.

[0038] The level of the voltage Vm1 is adapted (by means of the voltage divider bridge R1 , R2 ) in order to avoid saturating the first ADC 17 and in order to apply a signal at a meaningful level (corresponding to the input range of the first ADC 17 ) to the input of the first ADC 17 .

[0039] The first ADC 17 thus digitizes the voltage Vm1. Based on the samples produced by the first ADC 17, the voltage measurement module 19 produces a measure of the RMS value of the network voltage vr.

[0040] The metering assembly also comprises a current sensor, in particular a shunt 22, which is connected upstream of the cut-off means 13 in the phase conductor 10 and is associated with a current measurement circuit 23 exhibiting a known gain. The current measurement circuit 23 is connected downstream of the shunt 22 to the terminals of the shunt 22. The voltage across the terminals of the shunt 22 is thus applied as input to the current measurement circuit 23.

[0041] The output of the current measuring circuit 23 is connected to an input of a microcontroller 15 which has a second ADC 18 connected thereto.

[0042] The voltage vm2 at the output of the current measurement circuit 23 is a mirror image of the phase current Ip.

[0043] The level of voltage Vm2 is adapted (by means of the gain of current measurement circuit 23 ) in order to avoid saturating second ADC 18 and in order to apply a signal at a meaningful level (corresponding to the input range of second ADC 18 ) to the input of second ADC 18 .

[0044] The voltage Vm2 is digitized by the second ADC 18. From the samples produced by the second ADC 18, the current measurement module 20 produces a measurement of the phase current Ip.

[0045] The meter 1 also has a test circuit 25 comprising a test component and a connection component.

[0046] In this example, the test component is a test resistor Rt having a first terminal connected to a first conductor selected from a phase conductor 10 and a neutral conductor 11. The first conductor is the phase conductor 10 in this example.

[0047] The connecting component acts as a switch. Specifically, the connecting component is a metal oxide field effect transistor (MOSFET) on silicon 26. The transistor 26 has a first terminal connected to the second terminal of the test resistor Rt and a second terminal connected to a second conductor selected from the phase conductor 10 and the neutral conductor 11. The second conductor is the neutral conductor 11.

[0048] The first terminal of transistor 26 is its source S and the second terminal of transistor 26 is its drain D.

[0049] A third terminal of the transistor 26 , ie its gate G, is connected to an output of the microcontroller 15 .

[0050] The microcontroller 15 can control the transistor 26 by generating a command Cmde applied to the gate G of the transistor.

[0051] The transistor 26 is controllable so as to be conductive or non-conductive and it can thus selectively place the test resistor Rt in a connected configuration or a disconnected configuration. In the connected configuration, the test resistor Rt is connected to the phase conductor 10 and the neutral conductor 11 in parallel with the installation 2 so as to form an additional load added to the load Z of the installation 2. In the disconnected configuration, the test resistor Rt is disconnected from the phase conductor 10 and / or the neutral conductor 11 (in this example, from the neutral conductor 11).

[0052] The normally non-conductive transistor 26 is controlled by the command Cmde from the microcontroller 15. If the command Cmde has a high voltage level, the transistor 26 is conductive. If the command Cmde has a low voltage level, the transistor 26 is non-conductive.

[0053] refer to Figure 2 , the following describes how instrument 1 estimates the measurement error.

[0054] The evaluation method as executed by the microcontroller 15 begins with a step E0 .

[0055] The variable N is also initialized to 0 (step E1 ).

[0056] The variable N is used to count the number of consecutive occasions where the precision error was measured to be outside a specified acceptable range.

[0057] The method moves to step E2 . The microcontroller 15 attempts to detect a first stability period, both for the energy consumption and for the network voltage Vr, and having a first predetermined duration.

[0058] In this example, the first predetermined duration is equal to three (consecutive) seconds.

[0059] The microcontroller 15 therefore attempts to detect a three second period during which both the energy consumption and the network voltage Vr are stable. In this example, an amplitude is said to be "stable over a period" if it does not vary by more than ±0.1% during said period.

[0060] As long as the first period of complete stability has not yet been detected, the method remains at step E2 .

[0061] If a first stability period is detected, at the end of this first stability period, ie at the beginning of the fourth second after the start of the first stability period, the microcontroller 15 controls the transistor 26 so as to place the test resistor Rt in its connected configuration for a predetermined test duration (step E3 ).

[0062] In this example, the predetermined test duration is equal to 1 second (s).

[0063] The microcontroller 15 then measures the total energy consumed over the predetermined test duration.

[0064] The total energy Et is such that:

[0065] Et=E+Ec.

[0066] Where E corresponds to the "base" energy consumption, ie the stable level as measured during the first stability period. Ec is the excess energy consumed during the predetermined test duration and due to the additional load (test resistor Rt).

[0067] The microcontroller 15 verifies that the network voltage vr is stable during the fourth second (ie the predetermined test duration).

[0068] The microcontroller 15 also verifies that this predetermined test duration is followed by a second stability period, both for the energy consumption and for the network voltage Vr, and having a second predetermined duration (step E4 ). The second predetermined duration is equal to three (consecutive) seconds.

[0069] The microcontroller 15 therefore verifies that the energy consumption is stable (again equal to E, in particular with a tolerance of ±0.1%) and that the network voltage vr is stable during the 5th, 6th and 7th seconds and equal to the voltage vr measured during the 1st, 2nd and 3rd seconds, in particular with a tolerance of ±0.1%.

[0070] This verification serves to confirm that the “base” energy consumed during the fourth second and neglecting excess energy continues to be equal to E and that the network voltage vr remains stable at the same voltage before, during and after the measurement.

[0071] If the microcontroller 15 does not detect a second stability period, the method returns to step E2 ; the measurement performed in step E3 is not taken into account.

[0072] If, on the other hand, a second stability period is in fact detected, the microcontroller 15 estimates the measurement error of the meter 1 as a function of the excess energy (step E5 ).

[0073] The measurement error is estimated as follows.

[0074] The microcontroller 15 estimates the excess energy due to the additional load:

[0075] Ec=Et–E.

[0076] The microcontroller compares the excess energy with an expected value. However, this expected value depends on the network voltage Vr that is actually present (and may differ slightly from 230V).

[0077] Calibration is performed at the factory, whereby a reference value Ec for excess energy is generated ref For this purpose, the value of the current through the test resistor Rt at 230 V is measured, which value depends on the exact resistance of the test resistor Rt, and the excess energy consumed by the test resistor Rt during 1 s at 230 V is deduced therefrom. The reference value Ec of the excess energy ref are pre-recorded and stored in the factory calibration parameters stored in the memory 16 .

[0078] This value is obtained during calibration at a network voltage Vr exactly equal to 230V.

[0079] In order to calculate the measurement error during operation, the microcontroller 15 calculates the ideal value Ec of the excess energy ideal , which corresponds to the excess energy obtained with perfect accuracy. The ideal value of the excess energy Ec ideal It consists in calculating the reference value of the excess energy at the “real” RMS value of the network voltage Vr as follows:

[0080] Ec ideal =Ec ref ×VRMS / 230;

[0081] Among them, V RMS is the RMS value of the network voltage Vr.

[0082] The microcontroller 15 then estimates the measurement error by using the following formula:

[0083]

[0084] The microcontroller 15 then verifies whether the measurement error is within the required accuracy range (step E6 ).

[0085] If yes, the variable N is reinitialized to 0 (step E7 ).

[0086] The method then moves to a waiting step (step E8 ), for example having a duration of 24 hours (h), after which the method returns to step E2 .

[0087] If the measurement error found in step E6 is not within the required accuracy, the variable N is incremented (step E9).

[0088] The microcontroller 15 then compares the value of N with a predefined achievement threshold, which in this example is equal to 3 (step E10 ).

[0089] If N is not equal to 3, the method moves to a waiting step (step E11 ), for example lasting 24 h, and then returns to step E2 .

[0090] When N is equal to 3, the microcontroller 15 generates an alarm message which is sent by the meter 1 to the IS of the energy distributor (step E12 ).

[0091] The method ends (step E13 ).

[0092] Therefore, it is necessary to detect measurement error anomalies at three consecutive occasions in order to issue an alarm message.

[0093] It should be observed that the excess energy Ec consumed during the fourth second is not taken into account when calculating the accumulated energy consumption for billing the subscriber.

[0094] The resistance of the test resistor Rt is calibrated at the factory and its characteristics are accurately known. In this example, the resistance of the test resistor Rt is selected to be equal to 4.7 kilo-ohms (kΩ), thereby having the result of adding about 50 milliamperes (mA) of current when the transistor 26 is turned on.

[0095] The theoretical current added by such a test resistor is specifically equal to 230 V / 4.7 kΩ=48.936 mA.

[0096] In this example, the measurement error is estimated at low currents (about 1 ampere (A)): the stability period therefore corresponds to the period during which the phase current Ip is low.

[0097] It should be noted that the test circuit 25 also has a thermistor 28 connected between the transistor 26 and the neutral conductor 11. More precisely, the drain D of the transistor 26 is connected to the neutral conductor 11 via the thermistor 28. The thermistor 28 is of the positive temperature coefficient (ptc) type.

[0098] The thermistor 28 makes it possible to comply with safety requirements.

[0099] A fault may render transistor 26 permanently conductive. Such a fault may apply, by way of example, to the command Cmde from microcontroller 15, or it may be a fault of transistor 26 itself. In this case, current continues to flow through test resistor Rt, thereby tending to increase its temperature in a manner that may cause problems for other components of meter 1.

[0100] The thermistor 28 is located near the test resistor Rt, so that in the event of a fault which renders the transistor 26 permanently conductive, the resistance generated between the phase conductor 10 and the neutral conductor 11 increases as the temperature of the test resistor Rt increases.

[0101] Thermistor 28 is chosen so as to present a (nearly) zero resistance at ambient temperature. Therefore, if transistor 26 remains permanently conductive, an abnormal increase in the temperature of test resistor Rt will also increase the resistance of thermistor 28, and in a significant manner, thereby reducing the current flowing through test resistor Rt (and thus reducing its heating).

[0102] refer to Figure 3 , the electric meter 101 in the second embodiment of the present invention is described.

[0103] Again, meter 101 is a single-phase electricity meter.

[0104] This time, the test resistor Rt has a first terminal connected to the neutral conductor 111 .

[0105] The transistor 126 has a first terminal connected to the second terminal of the test resistor Rt and a second terminal connected to the neutral conductor 110. The first terminal of the transistor 126 is its source S and the second terminal of the transistor 126 is its drain D. Again, the transistor 126 is controlled by the microcontroller 115 which generates a command Cmde on the gate G of the transistor 126.

[0106] The thermistor 128 is connected between the transistor 126 and the phase conductor 110. More precisely, the source S of the transistor 126 is connected to the phase conductor 110 via the thermistor 128.

[0107] The test circuit 125 also has a monitoring component for monitoring whether the connection component, ie the transistor 126 , has responded correctly to the command Cmde reduced by the microcontroller 115 .

[0108] The monitoring assembly comprises a third ADC 121 integrated in the microcontroller 115, a first monitoring resistor R3 having a first terminal connected to the phase conductor 110, and a second monitoring resistor R4, the first terminal of which is connected to the source S of the transistor 126. The second terminals of the first monitoring resistor R3 and the second monitoring resistor R4 are connected together and to an input of the microcontroller 115, which input is also connected to an input of the third ADC 121.

[0109] In this example, the first monitoring resistor R3 has the same resistance as the second measuring resistor R2 , and the second monitoring resistor R4 has the same resistance as the first measuring resistor R1 .

[0110] The first monitoring resistor R3 and the second monitoring resistor R4 form a voltage dividing bridge.

[0111] The voltage divider bridge R3 , R4 is used to generate a voltage Vm3 , which is a mirror image of the voltage present at the source S of the transistor 126 .

[0112] The voltage divider bridge R3 , R4 is used to obtain an acceptable level of voltage Vm3 at the input to the third ADC 121 .

[0113] The monitoring component serves to verify that the command Cmde on the gate G transistor 126 is indeed valid. When the microcontroller 115 has controlled the transistor 126 so as to put the test resistor Rt in the disconnected configuration, the monitoring component serves in particular to verify that the current flowing through the test resistor Rt is zero.

[0114] Specifically, when the microcontroller 115 sends a command to turn off the transistor 126 (it switches to a non-conductive state), the voltage Vm3 read by the third ADC 121 is generally equal to 0V in the absence of any abnormality in the command Cmde applied to the transistor 126 .

[0115] If the third ADC 121 reads a significant monitoring voltage, it means that the test resistor Rt has been heated, thereby increasing the resistance of the thermistor 128 and thereby flowing a significant current in the test resistor Rt, even though this would not have occurred if the command Cmde had indeed caused the transistor 126 to be turned off. Therefore, there is a fault that has an effect on the demand Cmde applied to the transistor 126.

[0116] Therefore, before executing the method for evaluating the measurement error, the microcontroller 115 uses a monitoring component to verify whether the command Cmde applied to the transistor 126 operates correctly.

[0117] To perform this verification, the microcontroller 115 generates a command Cmde at a low voltage level, which should put the transistor 126 in a non-conductive state. The microcontroller 115 then compares the voltage Vm3 measured by the third ADC 121 with a predefined monitoring threshold, and if the voltage Vm3 is greater than the predefined monitoring threshold, the microcontroller 115 detects a failure of the command Cmde.

[0118] The method of evaluating the measurement error is only carried out if the microcontroller 115 has not detected a fault in the command Cmde. If the microcontroller 115 detects a fault, it generates an alarm message which is sent by the meter 101 to the IS of the energy distributor.

[0119] refer to Figure 4 , the following is a description of the electric meter 201 in the third embodiment of the present invention.

[0120] The meter 201 is a three-phase meter.

[0121] The meter 201 has a plurality of phase conductors 210 , each of which is connected to a phase 204 of the power distribution network 203 .

[0122] A different test circuit 225 is associated with each phase 204 of power distribution network 203 .

[0123] Each test circuit 225 has a test component and a connection component, specifically a test resistor Rt and a transistor 226 .

[0124] In this example, the test resistor Rt has a first terminal connected to the neutral conductor 211 .

[0125] The transistor 226 has a first terminal connected to the second terminal of the test resistor Rt and a second terminal connected to the neutral conductor 210. The first terminal of the transistor 226 is its source S and the second terminal of the transistor 226 is its drain D. The transistor 226 is controlled by the microcontroller 215 which generates a command Cmde on the gate G of the transistor 226.

[0126] The thermistor 228 is connected between the transistor 226 and the phase conductor 210. More precisely, the drain D of the transistor 226 is connected to the neutral conductor 210 via the thermistor 228.

[0127] This time, the current sensor is not a shunt, but a ring 230 mounted on the phase conductor 210 upstream of the cut-off member 213. A measuring resistor Rm is connected across the output terminals of the ring 230. A current measurement circuit 223 is connected to one terminal of the measuring resistor Rm, the other terminal of which is connected to the electrical ground of the meter 201 and to 212.

[0128] For each phase 204 , the measurement error is estimated in the same manner as for meters 1 and 101 .

[0129] It should be observed that the measurement error is preferably estimated one by one and not simultaneously for each of the phases 204 . To apply the command Cmde, the microcontroller 215 therefore preferably comprises three different outputs, each connected to the gate G of the transistor 226 of a respective one of the test circuits 225 .

[0130] Advantageously and with reference Figure 5 Each phase 304 of the distribution network 303 to which the three-phase meter 301 is connected is associated with a corresponding test circuit 325, which also includes a circuit similar to Figure 3 monitoring components.

[0131] The monitoring component is used to monitor whether the connection component (ie, the transistor 326 ) has correctly responded to the command Cmde generated by the microcontroller 315 .

[0132] Again, the monitoring assembly comprises a third ADC 321 integrated in the microcontroller 315, a first monitoring resistor R3 having a first terminal connected to the phase conductor 311, and a second monitoring resistor R4 having a first terminal connected to the source S of the transistor 326. The second terminals of the first monitoring resistor R3 and the second monitoring resistor R4 are connected together and to an input of the microcontroller 315, which input is also connected to an input of the third ADC 321.

[0133] In a similar manner, the second monitoring resistor R4 has the same resistance as the first measuring resistor R1 , and the first monitoring resistor R3 has the same resistance as the second measuring resistor R2 .

[0134] As mentioned above, the measurement error is estimated at low currents. However and regardless of the type of meter (single-phase, three-phase), the measurement error can be evaluated regardless of the level of the current phase Ip.

[0135] Thus, for each phase, the meter may have at least a first and a second respective test circuit associated with the phase, the microcontroller evaluating the measurement error by using the first test circuit when the phase current Ip in the phase conductor connected to the phase is less than a predefined current threshold, and the microcontroller evaluating the measurement error by using the second test circuit when the phase current is greater than the predefined current threshold.

[0136] In particular, the meter may have three test circuits per phase: a first test circuit is dedicated to improving verification at low currents (about 1A) and includes a test resistor Rt, a second test circuit is dedicated to improving verification at medium currents (5A to 20A) and includes a test resistor Rmedium, and a third test circuit is dedicated to improving verification at high currents (greater than 40A) and includes a test resistor Rhigh. The test resistors Rt, Rmedium and Rhigh may have different acceptable maximum powers.

[0137] Therefore, for each phase, the meter comprises three test circuits, each with a test resistor, a transistor and a thermistor, and the microcontroller generates three separate commands Cmde.

[0138] The microcontroller then uses two predefined current thresholds to select the test circuit to be used. The first current threshold for selecting between the first test circuit and the second test circuit may be in the range of, for example, 2A to 4A, and the second current threshold for selecting between the second test circuit and the third test circuit may be in the range of, for example, 25A to 35A.

[0139] Each of the above meters also includes a temperature sensor that measures the ambient temperature within the meter box.

[0140] The measurements produced by this temperature sensor can be used to estimate the temperature of the test resistor Rt. The microcontroller knows how the resistance of the test resistor Rt varies with temperature (curve provided by the supplier).

[0141] Thus, the microcontroller can acquire ambient temperature measurements produced by the temperature sensor and then estimate a temperature-corrected value of the test resistor's resistance based on these measurements, and it can use the temperature-corrected resistance to improve the accuracy of measuring excess energy and thereby improve the accuracy of the measurement error of the measuring instrument.

[0142] Advantageously, the method of evaluating the meter measurement error is performed at night, when the ambient temperature is typically lower, thereby ensuring less heating of the test resistor during the test.

[0143] Naturally, the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims.

[0144] The invention can be implemented with a single phase or indeed a multiphase electricity meter connected to any number of phases.

[0145] The architecture of the instrument can naturally differ from that described above.

[0146] Two or three ADCs are described as being incorporated into the microcontroller. However, it is possible to utilize and integrate a single ADC into the microcontroller. The microcontroller would then have a first input connected to the voltage divider bridge R1, R2 of the metering component, a second input connected to the current measurement circuit, and possibly a third input connected to the voltage divider bridge R3, R4 of the monitoring component.

[0147] These inputs of the microcontroller are connected to an ADC which comprises a multiplexer having (at least) two or three inputs respectively connected to a first input, to a second input and possibly to a third input and to an output of a converter core of the ADC.

[0148] One or more ADCs may also be located external to the microcontroller.

[0149] The microcontroller implementing the present invention does not necessarily need to be a metering microcontroller, but can be a different component.

[0150] The processor component that performs the invention does not necessarily need to be a microcontroller, but may be some other component, for example it may be a conventional processor, a digital signal processor (DSP), or indeed it may be a programmable logic circuit such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC).

[0151] The test component does not necessarily need to be a (single) resistor, but may comprise one or more arbitrary components (capacitors, inductors, etc.) suitable for forming an additional load. The connecting component may be any type of component capable of placing the test component in a connected configuration or a disconnected configuration (e.g. it may be a transistor of some type).

[0152] The processor component and the connectivity component may be a single component.

Claims

1. An electric meter (1) arranged to measure the consumption of energy supplied to an installation (2) by an electric distribution network comprising a phase line (4) and a neutral line (5), the electric meter comprising: a phase conductor (10) and a neutral conductor (11) arranged to be connected to the phase line and the neutral line respectively; a test circuit (25) comprising a test component (Rt) and a connection component (26) arranged to selectively place the test component in a connected configuration, in which the test component is connected in parallel with the installation to the phase conductor and the neutral conductor so as to form an additional load, and in a disconnected configuration, in which the test component is disconnected from the phase conductor and / or the neutral conductor; a processor component (15) arranged to control the connection component in such a way that the test component is placed in the connected configuration during a predetermined test duration, characterised in that the processor component (15) is arranged to measure excess energy consumed during the predetermined test duration and caused by the additional load and to estimate a measurement error of the electricity meter based on the excess energy.

2. The electric meter according to claim 1, characterized in that The processor component (15) is arranged to attempt to detect stability in both the energy consumption and the network voltage (Vr) between the phase conductor (4) and the neutral conductor (5) for a first stability period having a first predetermined duration, and to control the connection component to place the test component in the connected configuration only after the first stability period has been detected.

3. The electric meter according to claim 2, characterized in that: The processor component (15) is arranged to verify that the predetermined test duration is followed by stability of both energy consumption and network voltage (Vr) for a second stabilization period having a second duration, and to estimate the measurement error only if the second stabilization period is detected.

4. An electric meter as claimed in any preceding claim, characterised in that The processor component (15) is arranged to measure a network voltage (Vr), calculate an ideal value of the excess energy by associating a pre-recorded reference value of the excess energy with the network voltage (Vr), and estimate a measurement error from the excess energy and the ideal value of the excess energy.

5. The electric meter according to any one of claims 1 to 3, characterized in that: The test assembly has a first terminal connected to a first conductor selected from the phase conductor (10) and the neutral conductor (11), and wherein the connecting assembly has a switching function and comprises a first terminal connected to a second terminal of the test assembly and a second terminal connected to a second conductor selected from the phase conductor and the neutral conductor.

6. The electric meter according to claim 5, characterized in that The second terminal of the connection assembly is connected to the second conductor via a thermistor (28) so that in the event of a fault causing the connection assembly to remain continuously conducting, the resistance generated between the phase conductor (10) and the neutral conductor (11) increases as the temperature of the test assembly increases.

7. The electric meter according to any one of claims 1 to 3, characterized in that Also included is a monitoring component arranged to verify that the current flowing in the test component is zero when the processor component (15) has controlled the connection component to place the test component in the disconnected configuration.

8. The electric meter according to claim 7, characterized in that: The monitoring assembly comprises an analog-to-digital converter (121) and a voltage divider bridge (R3, R4) arranged to generate a voltage which is an image of the voltage present at the second terminal of the connection assembly.

9. The electric meter according to any one of claims 1 to 3, characterized in that: Also included is a temperature sensor arranged to measure the ambient temperature within the electricity meter (1), the processor component (15) being arranged to acquire the measurement of the ambient temperature, estimate a temperature corrected value for the test component, and use the temperature corrected value to improve the accuracy of measuring excess energy and thereby improve the accuracy of estimating the measurement error of the electricity meter.

10. The electric meter according to any one of claims 1 to 3, characterized in that: The invention comprises at least a first test circuit and a second test circuit associated with the phase line, wherein the processor component (15) is arranged to use the first test circuit to evaluate the measurement error of the electric meter when the phase current (Ip) flowing through the phase line (4) is less than a predefined current threshold, and to use the second test circuit to evaluate the measurement error of the electric meter when the phase current is greater than the predefined current threshold.

11. The electric meter according to any one of claims 1 to 3, characterized in that: The electricity meter is a multiphase meter and the electricity distribution network has a plurality of phases, the electricity meter having at least one respective test circuit associated with each phase.

12. The electric meter according to any one of claims 1 to 3, characterized in that The test component is a resistor (Rt).

13. The electric meter according to any one of claims 1 to 3, characterized in that The connecting component is a MOSFET (26).

14. The electric meter according to any one of claims 1 to 3, characterized in that The processor assembly (15) is also arranged to measure the phase current (Ip) flowing in the phase conductor (4), the network voltage (Vr) between the phase conductor and the neutral conductor, and the energy consumption of the installation.

15. A method of evaluating a measurement error of an electricity meter (1) as claimed in any preceding claim, the method comprising the following steps: controlling the connection component so that it places the test component in the connected configuration during a predetermined test duration; The method is characterized in that it comprises the following steps: During the predetermined test duration, measuring excess energy due to the additional load; - Evaluating the measurement error of the electricity meter based on the excess energy.

16. The method for evaluating measurement error according to claim 15, characterized in that It also includes detecting a first stable period in both the energy consumption and the network voltage (Vr) between the phase conductor (4) and the neutral conductor (5), and placing the test assembly in the connected configuration only after the first stable period has been detected.

17. The method for evaluating measurement error according to claim 16, characterized in that The following steps are also included: After said predetermined test duration, an attempt is made to detect a second stability period both of the energy consumption and also of the network voltage, and the measurement error is estimated only if said second stability period is detected.

18. A method for evaluating a measurement error according to any one of claims 15 to 17, characterized in that The following steps are also included: It is verified whether the measurement error is within the required accuracy range, if not a variable is incremented and the previous steps are then repeated and an alarm is generated when the variable becomes equal to a predefined increment threshold.

19. A computer-readable storage medium storing a computer program, the computer program comprising instructions for driving a processor component (15) of an electricity meter (1) according to any one of claims 1 to 14 to perform the steps of the method for evaluating a measurement error according to one of claims 15 to 18.

20. A computer program product comprising instructions, the instructions being executed to perform the steps of the method of estimating a measurement error as claimed in any one of claims 15 to 18.

Images