WO2007039780A1

WO2007039780A1 - Electric meter supplied with control device

Info

Publication number: WO2007039780A1
Application number: PCT/HU2006/000086
Authority: WO
Inventors: Antal Gasparics; Gyözö KMETHY; János SZÖLLÖSY
Original assignee: Antal Gasparics; Kmethy Gyoezoe; Szoelloesy Janos
Priority date: 2005-10-05
Filing date: 2006-10-02
Publication date: 2007-04-12
Also published as: HUP0500922A2; HU0500922D0; HU228288B1

Abstract

Electric meter with measuring instrument supplied with control device controlling the correct operation of the measuring instrument. The control device has got on-board electronics (4) inside the housing of the electric meter. The on-board electronics (4) contains a magnetic field sensor (1) and/or temperature sensor (2), a non-volatile storage media (5) and an indicator (8), where the magnetic sensor (1) is arranged in the magnetic field of the voltage coil or of an other element of the measuring instrument, and/or the temperature sensor (2) is arranged on the iron core and/or on the coil and/or on the bearing of the measuring instrument.

Description

Electric meter with measuring instrument supplied with control device controlling the correct operation of the measuring instrument

The subject of the application is an electric meter with measuring instrument supplied with control device controlling the correct operation of the measuring instrument.

The inductive, electronic or hybrid type electric meters of common principle of operation can work continuously for long years and even for decades, practically without supervision. It is important therefore that the correct operation of the main components of the meter which may influence its functioning and particularly, its precision should be supervised and their eventual failures should be detected and indicated.

Electric meters are basically composed of a measuring instrument, a container-/display unit, and eventually of an auxiliary power supply unit. It is practical to supervise every change of the components which may influence the meter's original functions (particularly its precision) or may inhibit to carry out its functions. An important requirement towards the control device of the correct operation of the measuring instrument is that the accuracy and calibration of the electric meter shall not be compromised, it shall not affect directly the physical functioning of the different components, still, it shall indicate reliably the eventual failures. An other special requirement that can be formulated towards the electric meters is that - since the electric meter measures a consumption integrated in time - the control device may not indicate disturbing effects causing short and only temporary, reversible problems. Power companies or operators of the electric meters shall deal with every notice, which may result on one hand in relatively much higher costs compared to the loss of income caused by a brief change in the accuracy, and on the other hand it may cause the supervising instrument to be discalibrated and therefore useless.

The major effects compromising the operation of the electric meters and eventually causing their failure can be grouped as follows:

• Disturbances spreading through the electrical network having short or permanent duration compared to the life of the meter: o Overloads (short circuit currents, overvoltages, transients); o Asymmetrical voltages and/or loads in three-phase networks; o Electromagnetic disturbances spread by and arriving through the electric network; o Signal shape distortions (direct current components, sub- harmonics and superior harmonics).

• Environmental factors: o Temperature fluctuations; o Humidity; o Mechanical vibrations; o Disturbances caused by electromagnetic fields arriving from the outside of the network;

Over the above mentioned effects, other factors can cause the failure of the electric meter such as the failure or wearing out of certain mechanical, electromagnetic or electronic components or fittings, or tampering.

The international and harmonised international standards on electric meters (IEC/EN 62052-11, IEC/EN 62053-11, IEC/EN 62053-21, IEC/EN 62053-22, IEC/EN 62053-23, IEC/EN 61000-4-2, IEC/EN 61000-4-3, IEC/EN 61000-4- 5, IEC/EN 61000-4-6, IEC/EN 61000-4-8, IEC/EN 61000-4-12, ANSI C12.1, EN 50470-1, EN 50470-2, EN 50470-3) prescribe a disturbance bearing capacity for the electric meters within the disturbance limits and under the conditions set by the standars. In order to fulfil these requirements, electric meters are supplied with appropriate (constructive, active or passive) protections. At the same time, electric meters can be affected by stronger disturbances than those set by the standards, by the time when, for example, the meter's environment changes: when a new equipment capable of disturbing the meter is installed, or when a tampering attempt occurs. In order to sense these disturbing effects, different supervising and self-controlling solutions can be applied. These supervising and self-controlling solutions, however, can be carried out effectively only if the strength and the other characteristics of the disturbing effects are not analysed alone, but the effective changes originating from the mechanism of the effects are sensed on the different components. As a matter of fact, complex disturbing effects arriving form the outside of the meter (like strongly inhomogeneous, interfering electric fields) cannot be described by simple relations in order to find out their real effects on the meter's operation.

The following patents and patent applications present the already developed procedures to detect the external disturbing effects on the electric meters:

The patent specification US 6,885,302 presents a solution where one or more magnetic sensors are fitted in the housing of the electric meter, around the measuring instrument, in order to sense electric fields of external origin in inductive, electronic or hybrid meters. By regulating the sensitivity of the applied magnetic sensors and of the connecting circuits the detecting device can be fitted in different or even in changing magnetic environments. The deficiency of the above mentioned solution is that it concludes through the signals of the magnets and/or other sensors fitted near the electric meter - of unknown operation - that a tampering attempt has occured in order to disturb the electric meter's operation. The correct operation of a measuring instrument is influenced by disturbing effects that are of predefmeable type and rate acting on the measuring elements inside the measuring instrument, and it is not influenced by general effects from the external environment. Therefore the later solution is not suitable for the independent supervision of the electric meter's measuring instrument and to its self-controlling. An other deficiency of this solution is that it neglects the protective solutions described by the standards on electric meters in order to have a suitable disturbance bearing capacity and neglects their effects. Because of these protections, for example the applied magnetic shielding, it is not evident what kind of external magnetic vector field dispersion is causing malfunction in the measuring instrument. However, what really affects the operation of the measuring instrument is not the external magnetic induction, but the magnetic field component resulting from the complex interaction of the different electric components inside the measuring instrument that effectively induces the magnetic parts of the measuring instrument. However, the external field dispersion that is able to create a magnetic field inside the measuring instrument and that may constitute a danger to the measuring element is impossible to define, even in case of well-known measuring instruments, because it is an inverse space-calculation mathematical problem. It is a matter of common knowledge that the inverse mathematical problems don't have results or don't have explicit solutions.

A further deficiency of the presented solution is that it cannot detect if the failure of the electric meter is the result of internal causes (for example the slow demagnetization of the brake magnet of the inductive meters ) or it is a result of electrical network disturbances; or if the electric meter has lost its calibration.

It is a further drawback too that the presented solution cannot make a difference between the unimportant, independent and short external disturbing magnetic effects resulting from the additive, integrative characteristics of the electric meters and causing only reversible disturbances in the meter; and the important effects of long, or sometimes of short duration that may cause permanent and irreversible malfunctions, because the applied sensor gives an alarm only when the limit of the external field intensity is reached, and there is no retardation. The lack of retardation causes immediate, unjustified alarms on unimportant cases regarding the electric meter, and it is not the right means eather to prevent tampering by deceiving/making uncertain the tamperer.

The patent specification US 5,086,292 presents a system which, in order to detect tampering attempts, is supplied with tilting-, electric field-, magnetic field-, temperature-, and voice sensors and with a further reverse motion sensor of the disc of the inductive measuring instrument. This solution also allows to estimate - by computer analysis - the real consumption. The main deficiency of the presented system is that it offers a solution only for the detection of the deliberate, external, physical tampering attempts and cannot detect the failure of the electric meter due to internal causes. The applied sensors do not detect the malfunction of certain internal elements of the electric meter but the device concludes to the fact that an eventual tampering ha occured from the sampled and stored signals of the sensors, combining them with the computer analysis of the consumption. A further deficiency of the presented solution is that it is applicable only for electric meters with moving components (rotating disc).

The patent specification US 4,707,679 presents a solution with a magnetically sensible switching element that detects strong magnetic fields outside the electric meter, in its surroundings. The described solution allows to transmit the information about the state of the switch and to receive other messages too through the high tension network. By this means the system, taking into account other conditions as well, is able to find out if tampering has occured. The deficiency of this solution is that the presence of a detectable magnetic 5 field near the electric meter cannot evidently mean the malfunction of the measuring elements of the electric meter. A further drawback of the system is that it cannot detect failures of the measuring device resulting from other causes, therefore this solution is not suitable for the supervision of the measuring elements and for self-control.

The patent specification US 6,054,930 describes a solution which is capable of detecting the illicit opening of the electric meter, when the malfunction of the electric meter is due to a serious violation of its integrity. This solution is not capable of sensing the electric meter's malfunctions in case that its integrity is not violated.

The patent specification GB 2409528 describes an lay-out with a magnetic shielding that covers the measuring instrument and a sensing coil connected to it magnetically. The computer of the device follows the impedance change of the coil. The impedance, in case of a strong external magnetic field; changes due to the shifting of its magnetic work point of the iron core. Therefore the device is suitable to detect important- scale external fields that disturb the meter's operation.

This solution has got some major deficiencies. On the one hand, an iron-cored sensor of such a construction is sensible only for the magnetic space component concerning the inner longitudinal axis of the coil or for the component transmitted by the shielding iron core into that direction, therefore transversal influencing fields cannot be detected. On the other hand, the solution described in the patent presumes that the protectable electric meter has got magnetic shielding. It is known from the laws of physics that, contrarily to electrostatic fields, magnetic fields and their effects can be reduced and shielded by passive means only to a certain level. Therefore the penetration of the magnetic fields into the protected volume cannot be fully prevented by these means, partially because of the phenomenon of the magnetic saturation and the continuity laws as well. That is why the passive magnetic shielding cannot protect against an influencing field of a discretional size. The fact, that the applied iron cored coil is placed outside the measuring device and it is connected to the external shielding, it can be easily tampered, which is a further drawback. An other disadvantage of this system is that it does not detect the effective tampering - that may take place inside the measuring device - but only its possibility, therefore it can give false alarm.

The patent specification WO 03065055 describes a mechanical solution that is inside the closed housing of the protected device and detects affecting external magnetic fields above a certain level. The patent specification describes a solution which detects if the magnetic field intensity reaches a certain level and after such event it generates a non-deletable signal. For the detection of the magnetic fields, the patent describes different solutions. It is possible, for example, to apply a ferromagnetic, mechanic structure of flexible material that undergoes definitive deformation due to a strong external magnetic field; other possibility is to apply a combination of a reed-relay and a resistor, where the resistor changes colour after the closing of the reed-relay due to an electromagnetic field; or a combination of a reed-relay and a bimetal; or a magnetic sensor that is connected to a circuit. Ferromagnetic foils can be applied as sensors: their magnetization changes because of an external magnetic field of high intensity which can be detected by a fluxmeter; but a magnetic field sensor can be also composed of several layers, where, due to the presence of a strong external magnetic field, the uneven magnetization of the upper and lower magnetizable elements becomes visible. According to an other solution, the change in the state of the reed relays arranged in three different directions due to a high intensity, external magnetic field generates a sound and/or light signal.

The described instrument inside the protected device is immediately activated by a magnetic field of a given intensity. The disadvantage of the described instrument is that its operation depends only from the intensity of the external magnetic field and it does not detect if the elements of the protected measuring instrument are affected by the magnetic field of a certain dispersion created inside the protected device. It is an other important deficiency that because the lack of retardation, the device manufactured according to the specification cannot make a difference between the unimportant, disturbing magnetic fields; and the influencing, important magnetic fields of longer duration that may cause serious measuring errors. Since some versions of this solution are based on the external field intensity treshold sensor, the device in the patent specification in not able to measure the signal shape changes in time and their distortions, therefore it is not able to detect other disturbances caused by electromagnetic interference below the threshold. A further drawback of this solution is that it can be used only for protective purposes as far as the external magnetic field is concerned, and it is not able to detect failures resulting from other causes (such as overtemperature because of internal failure).

The patent specification US 4,514,683 presents a solution for measuring devices operating by induction to prevent deliberately caused malfunction due to the inverse rotation of the disc. This solution is only applicable at the ordinary meters with rotary disc operating by induction, and it only serves for checking the inverse rotation. It is not able to detect malfunctions (such as the disproportionate deceleration or acceleration of the disc) causing problems in the measurement and resulting from the failure of the rotary disc (or of its bearing, for example) or from the failure of any other component of the meter. The presented solution cannot be applied in electronic and/or digital meters.

The magnetic field intensity measuring instrument also applicable to electric meters is described in the patent specification US 4,992,776, which, in the presence of a magnetic field and in function of its actual intensity sends out y an immediate alarm signal. Therefore, this field intensity measuring equipment is not able to detect alone the failure of the measuring elements of the electric meter or a change in the accuracy because of their failure. Moreover, based on the momentaneous intensity values of the disturbing fields, even if the magnetic fields have got a strength in principle capable of disturbing the meter, the field sensor cannot make a difference between the magnetic fields of short duration not compromising the measured values, therefore unimportant for the meter, and the magnetic fields that can cause serious measuring errors. That is why this magnetic field measurer device is not able alone to supervise the meter's operation.

The detecting device described in the patent specification US 5,910,774 has got the objective to detect disturbances due to the tampering in the measuring instruments' operation. The described sensor is able to sense the gradient of the static energy fields.

But the gradient in itself does not characterise the size of a field, while other physical data, such as the work point, the non linear-range and the saturation limit can be described only by the size of the field. Therefore this device is not suitable for the supervision of the electric meters' measuring elements and to their self-control.

The system described by the patent specification US 6,000,034, developed for the protection of the electronic, digital meters, offers protection against the subsequent faking of the measured values. Therefore this solution is not suitable for the supervision of the electric meter's measuring elements and for its self-controlling.

The system presented in the patent specification US 5,140,258 detects the removal of the electric meter from the socket and it is not able to detect the disturbances during its operation. The patent specification US 6,239,558 describes a magnetic shielding procedure for electric meters with plastic housing.

The solutions and the devices described in the patents no. US 6,232,886 and US 4,833,455 detect the illicit inactivation of the electric meter.

In the light of the above, the question to resolve through the invention is to elaborate a controlling device for the measuring instrument that permits the self-controlling and the supervision of the measuring elements of the meter device in order to prevent failures that could stop the meter from performing its task, in a way that the device controlling the correct operation of the measuring instrument does not intervene into the physical operation of the measuring elements, therefore does not influence the accuracy/calibration of the measuring instrument. It is a further criteria that the device controlling the correct operation of the measuring instrument shall be sensible only for the functioning disturbances that are relevant for the meter and affect the measured values over an accuracy limit.

The solution proposed by us is based on the perception that the correct operation of magnet circles, magnetic bearings and certain electronic components can be supervised by magnetic sensors and/or temperature sensors and/or voltage sensors fitted on the measuring elements to be supervised or inside the measuring instrument, without directly affecting the physical operation of the different measuring elements, therefore not compromising the meter's calibration. As a result of this, our technical solution can be applied on the already existing electric meter constructions as well. The solution according to our invention is detailed at the patent claims. The solution according to our invention is an electric meter with measuring instrument supplied with control device controlling the correct operation of the measuring instrument, which has got on-board electronics inside the housing of the electric meter. The on-board electronics contains a magnetic field sensor and/or temperature sensor, a non-volatile storage media and an indicator. The magnetic sensor is arranged in the magnetic field of the voltage coil or of an other element of the measuring instrument and/or the temperature sensor is arranged on the iron core and/or on the coil and/or on the bearing of the measuring instrument.

In order to prevent the generation of redundant signals because of the temporary disturbances which does not affect the measured values, the device that controls the correct operation of the measuring instrument can contain a retarding circuit that inhibits the signal in case the operation disturbance comes to an end before the end of the retardation time. However, these repetitive disturbances in the operation may seem unimportant independently, but because of their high number their additive effect is important and together they affect considerably the measured/counted values, and because of the retarding circuit, they could not be detected. Therefore it is practical to apply an event counter which counts every event that is qualified by the onboard electronics to be a disturbed state of operation, even if by the time of the event the non- volatile memory does not save any data. In case the number of these events reaches its maximum, an average set for a predefined period for the counter, the on-board electronics regards it as an important disturbing event and saves it in the non- volatile memory.

Since after a tampering attempt or a long duration disturbance in the operation the value measured by the electric meter has to be regarded as erratic, the information about the relevant malfunction state shall be stored, even on only one bit, in a way that after returning into the normal operation, and after the switch-off of the electric meter this information shall be preserved, shall not be deletable after a tampering attempt.

The reliable and non-deletable storage of one or a few bits of information can be resolved in a common way, for example by the application of one or a few fuses.

In those cases when the functioning disturbance, beyond the erratic value measurement, does not have any irreversible effects on the calibration of the electric meter, it is advisable that the signal of the functioning disturbance may be cut without violating the calibration of the meter. By putting the nonvolatile memory and its deleting function under the terminals' cover sealed by the power company or by the operator of the electric meters, the error message can be deleted without hurting the integrity of the measuring instrument.

The correct operation of the measuring instrument can be controlled by sensors fitted on the measuring elements or in their magnetic field. Such magnetic fields can be found on the electric meters operating by induction near the iron core of the voltage and current coils, inside the braking magnet, in the current sensors and/or voltage sensors of the electronic or hybrid meters, and in the electronic auxiliary power-supply unit. By means of analogue magnetic sensors (such as Hall probes, magneto-resistive probes, fluxgate probes) the time function of the magnetic field formed in the dispersed field of the magnet circles can be measured, therefore the malfunctions can be detected (lack of flux, saturation, signal distortion). In case of magnetic sensors with a digital output (such as the reed-type sensors) it becomes detectable if the operation is outside of the normal range. If the magnetic conducting material (for example the iron core) applied in the magnet circle of the electromagnets becomes saturated partially or in its entire volume, the electromagnet's impedance decreases and its electric consumption Ii increases. Such electromagnet is the inductive electric meter's tension coil with iron core. The increase in the consumption of the tension coil generates the increase of the ohm-loss that heats the coil and its iron core. Therefore the abnormal, excessive warming caused by a malfunction can be detected by a temperature-sensor as well. Because of the construction of the electric meter, its internal temperature can change generally much more slowly compared to the magnetic field intensity inside the measuring instrument, therefore the retardation through the temperature sensors to suppress the short, irrelevant functioning disturbances, can be reached naturally as well. In this case the retarding circuit can be omitted.

The evaluation of the signals received from the magnetic and/or temperature sensor is carried out by the on-board electronics inside the housing of the electric meter. The operation of the electronic system needs power that can be supplied directly from the electric meter's voltage terminals or from the internal, auxiliary power supply unit in case of hybrid or electronic meters.

When a reed-relay is applied, which is a magnetic sensor that does not need any power supply, the on-board electronic system can be developed in a way that it should use energy only when it receives a signal from the sensor. By this means it is possible that the on-board electronics may have power supply from stored-energy. It becomes possible as well through the reed-relay applied in the field of the electric coil of the meter to indicate malfunctions, when, for example, as a result of tampering, the terminals parallelly connected to the electric network are disconnected.

The indication of the erratic state of functioning detected by the on-board electronics and stored in the non-volatile memory that happens inside the electric meter, on a visible place, can be carried out by an optical indicator working in the wavelength range visible for the human eye, such as a light bulb, a LED, or a glimm-light, or by a common acoustic indicator; or in a way that it may only be read by a special reading device. These data can be made accessible to standard remote supervision systems and the telemetries of the electric network as well.

The examples for implementation forms of the device that serves for the self- controlling and the protection of the measuring elements of an electric meter are shown in detail on the drawings, where the following are presented:

Figure 1 : block diagram of a possible implementation form of the invented device controlling the correct operation of the measuring instrument

Figure 2: the compact, integrated implementation form of the inveted device conrolling the correct operation of the measuring instrument, and its electric diagram

Figure 3: the principal measuring elements of an inductive electric meter (with rotary disc), and the arrangement of the magnetic sensors according to the invention.

Figure 1 shows a block diagram of a possible implementation form of the invented control device controlling the correct operation of the measuring instrument that consists of an on-board electronic system (4) made up of a retarding circuit (6) and an event counter (7) connected with a magnetic sensor (1), a temperature sensor (2) and a voltage sensor (3); a non-volatile storage media (5) and an indicator (8). The power for the on-board electronic system (4) is supplied from the voltage terminals of the electric meter. In case of the implementation form shown in the example, the non-volatile storage media (5) is made up of a fuse, which is placed under the electric meter's terminal cover closed by the power company or by the operator of the electric meters, while the indicator (8) is a LED, which is practically put besides the 1.5 counter/display of the electric meter.

Figure 2 shows an electric diagram of a possible, compact implementation form of the invented control device controlling the correct operation of the measuring instrument, that consists of an on-board electronic system (4) built together with a magnetic sensor (1), a non- volatile storage media (5), a retarding circuit (6) and an indicator (8). The retarding circuit (6), in its implementation form shown in diagram 2, also works as an event counter which is able to add the signals of the magnetic sensor (1) for a given time period. The electric power (9) for the on-board electronic system (4) is supplied from the terminals of the voltage coil of the electric meter. The onboard electronic system (4) is placed in the field of the magnet circles of the voltage coil. In this case, the magnetic sensor (1) built together with the onboard electronic system (4) is a magnetic sensor with a digital output (SWl): reed-relay, which detects the critical flux level due to the saturation of the iron core of the supervised voltage coil. The sensitivity of the applied CELDUC AC051015-type reed-relay was set to the level needed by the application by a 5 mm wide permalloy strip bound around on the external glass body of the relay. The retarding circuit (6) of the on-board electronic system (4) consists of a 470 μF/50 V condenser (C2), of a 220 kΩ resistor (R4), of a 39 kΩ resistor (R3) and of a 2 MΩ resistor (R2) shown in the figure. The nonvolatile storage media (5) that consists of a 80 mA fuse (Fl) is also built together with the on-board electronic system (4). The indicator is a red light LED diode (D4).

Example 1:

The device according to the invention, in its implementation form shown in diagram 1 is inside the housing of the measuring instrument of the inductive, single-phase electric meter. The applied magnetic sensor (1) which is now a Hall-probe, is inside the magnetic field of the voltage coil of the measuring I O instrument. The voltage sensor (3) which is here a simple voltage distributor, emits a signal proportional to the voltage measured on the terminals of the voltage coil. In this case, the temperature sensor (2) is a thermo-element that detects the temperature of the iron core of the current coil.

The invented device, while functioning, supervises the operation of the voltage coil and of the rotary disc supplied with magnetic bearing. The onboard electronic system (4) controls the reply signal of the magnetic sensor (1) comparing it to the reply signal of the voltage sensor (2). In case of normal operation, the network frequency component of the voltage coil's magnetic field is proportional to the current of the voltage coil, and the impedance of the voltage coil can be determined from its voltage without intervening into its operation. The on-board electronics (4) supervises the impedance of the voltage coil in order to recognize even its partial saturation due to a strong intensity external influencing field. The temperature sensor protects the measuring instrument from an abnormal warming-up caused for example by mechanical friction because of strong mechanic vibrations. If on the basis of the signals received from any of the sensors or on the basis of the combination of the reply signals a deviation is detected in the normal operating conditions, the retarding circuit (6) is started in the on-board electronics and the value of the event counter increases by one. In case the signals received from all of the sensors and the combination of the reply signals as well return to the normal state during the retardation time (1-2 minutes in the example), the retarding circuit (6) of the on-board electronics (4) returns to its original state according to an other time constant in approx. 5-6 minutes. If during these 5-6 minutes an other error signal is received, the retarding circuit (6), since it does not start its operation from the original state, proportionally reduces the time needed to make a record in the non- volatile storage media. In case the retardation time is over or the value of the event counter (7) reaches the maximum set in total or for a defined time period, the i / on-board electronics stores the record about the malfunction in the nonvolatile storage media (5) by burning the fuse. Since the LED (D4) of the indicator (8) is turned on if the fuse that makes up the non-volatile memory- has been cut out, even if the electric meter is switched off and switched on again, the record about the malfunction persists.

Example 2:

The device according to our invention, in its implementation form shown in diagram 2 is placed inside the housing of the measuring instrument of an inductive, single phase electric meter. The applied magnetic sensor (1) incorporated into the on-board electronics (4) is placed in the magnetic field of the supervised voltage coil in the arrangement shown in diagram 3, that indicates a flux above the critical level.

The invented device that controls the correct operation of the measuring instrument, while functioning, supervises the operation of the voltage coil within the linear range. The magnetic sensor (1) that is a SWl switch, remains in an open state until the flux of the voltage coil does not exceed the preset critical value. If there is no signal from the magnetic sensor (1) (switch SWl is open), the condenser (C2) of the retarding circuit (6) discharges through the discharge resistor connected in parallel to it, in a rate defined by its time constant. If there is a signal from the magnetic sensor (1) (switch SWl is closed), the condenser (C2) is charged through the resistor network connected to it (resistors R4, R3 and R2) in a rate set by the time constant defined by the resistor network and by the capacity of the condenser (C2). The retardation by the retarding circuit (6) lasts until the voltage of the condenser (C2) reaches the breakdown voltage of the DB3-type diac (D5) which is 30 V. Than the diac (D5) opens and the current flowing across it, which is limited by a Rl resistor of 1,2 kΩ, lights the TIC106D-tyρe tiristor (TRl) that connects the charged condenser (C2) to the fuse (Fl) working as a non- volatile storage I O media. The electric energy stored in the condenser (C2) burns through the fuse (Fl) that is cut off irreversibly. In case of power supply from the electric network, the diode of the LED (D4) of the indicator (8) is turned on only if there is a record in the non- volatile storage media (5), say the fuse (Fl) is cut out, otherwise the fuse (Fl) shunts the diode of the LED (D4) of the indicator (8) into open state through the lN4148-tyρe diode (D2). The event counter (7) function is carried out by the applied 470 mF/50 V condenser (C2) and a discharge resistor (R2). If there is no signal from the magnetic sensor (1) (switch SWl is open), the discharging resistor (R2) retards the discharge of the condenser (C2). Therefore the applied circuit solution is able to add the short duration signals of the magnetic sensor (1) (not enough long to charge the C2 condenser) if these arrive in a frequency commensurable with the time constant of the discharge process of the condenser (C2). By means of this additive mechanism as well, the condenser C2 is able to reach the breakdown voltage of the diac D5 that results in a registration in the non- volatile storage media.

In figure 3 an example is shown through a common lay-out measuring instrument about the magnetic sensor (1) fitted on the iron core (13) of the voltage coil (12).There is a flux dispersing gap (10) inside the iron core, and a magnetic sensor (1) is arranged in the way of the dispersed flux. The magnetic sensor (1) arranged this way is suitable to measure the flux inside the iron core (13) of the voltage coil (12). This arrangement does not affect the correct operation of the measuring instrument. The measuring instrument in Figure 3 is a Ferraris-disc inductive measuring instrument which has got further measuring elements: a current coil arranged on the iron core (15) and a (non-illustrated ) braking magnet.

Claims

Patent claims

1. Electric meter with measuring instrument supplied with control device controlling the correct operation of the measuring instrument. The control device has got on-board electronics (4) inside the housing of the electric meter. The on-board electronics (4) contains a magnetic field sensor (1) and/or temperature sensor (2), a non-volatile storage media (5) and an indicator (8), characterized by the fallowings: the magnetic sensor (1) is arranged in the magnetic field of the voltage coil or of an other element of the measuring instrument, and/or the temperature sensor (2) is arranged on the iron core and/or on the coil and/or on the bearing of the measuring instrument.

2. Electric meter according to claim point no. 1 characterized by the fallowings: the on-board electronics (4) contains a retarding circuit (6).

3. Electric meter according to claim point no. 1 characterized by the fallowings: the on-board electronics (4) contains an according to claim

(7).

4. Electric meter according to claim point no. 1 characterized by the fallowings: the on-board electronics (5) contains a retarding circuit (6).

5. Electric meter according to claim point no. 1 characterized by the fallowings: the magnetic sensor (1) is a reed-relay of regulated sensitivity.

6. Electric meter according to claim point no. 1 characterized by the fallowings: the magnetic sensor (1) is a Hall probe of regulated sensitivity.

7. Electric meter according to claim point no. 1 characterized by the fallowings: the magnetic sensor (1) is a magneto resistive probe of regulated sensitivity.

8. Electric meter according to claim point no. 1 characterized by the fallowings: the magnetic sensor (1) is a Fluxgate probe. ^

9. Electric meter according to claim point no. 1 characterized by the followings: it has got an indicator (8) that emits visible optical signals. lO.Electric meter according to claim point no. 1 characterized by the followings: it has got an indicator (8) that emits optical signals non- visible to the unaided eye.

11. Electric meter according to claim point no. 1 characterized by the followings: it has got an indicator (8) that emits acoustic signals.

12. Electric meter according to claim point no. 1 characterized by the followings: it has got a remote reading indicator (8).