The subject matter of the present invention, in general, relates to detecting abnormal magnetic fields and more particularly, pertains to a method and an energy meter for detecting abnormal magnetic fields.
BACKGROUND OF INVENTION
Electricity service providers employ electricity meters to the total monitor energy consumption by customers (or other entities). Electricity meters track the amount of energy consumed by a load (e.g. the customer), typically measured in kilowatt-hours, at each customer's facility. The service provider uses this consumption information primarily for billing, but also for resource allocation forecasting and other purposes.
Electricity meter tampering is a form of energy theft that has a significant impact on costs for utilities and customers billing. Electricity meter tampering typically involves modification of the meter to bypass, alter or disconnect the consumption metering function of the meter, such that less than all of the actual energy consumption is registered.
An emerging type of meter tampering involves the use of a high power magnet. In particular, electricity meters using standard current transformers are susceptible to tampering using high-power magnetics. The CT current sensor behaviour can be impacted if a large magnet such as a neodymium iron boron magnet (rare earth magnet) is placed in close proximity. The high intensity magnetic field will result in an error in sensing current and potentially a significant under-registration of (and consequent under billing for) energy consumed.

To combat this issue, it has been known to place a ferromagnetic shielding structure around the CT or the entire interior of the meter to reduce the impact of the magnetic field on interior components. However, magnetic shielding requires additional material, a careful design to meet high voltage insulation requirements and labour cost, and undesirably increases the cost, manufacturability complexity and weight of the meter.
For some state of the art technology, reference is made to US 7965085 B2 which teaches about systems, methods, and devices involving a ground-fault sensor that has a plurality of conductors each disposed one inside of another except for an outer conductor and a field sensor configured to sense an electric field, a magnetic field, or both. In some embodiments, the field sensor is disposed adjacent the outer conductor. Thus, this document teaches about utilizing differential current sensing methodology.
Reference is also made to US 7112957 B2 which teaches about a Giant Magneto Resistive (GMR) sensor with flux concentrators. A proximity sensor that is capable of producing a relatively larger output signal than past proximity sensors, and in some cases, an output signal that is relatively independent of the speed at which a target passes the sensor. The proximity sensor includes a first magnetoresistive resistor and a second magnetoresistive resistor connected in a bridge configuration. The first magnetoresistive resistor is spaced from the second magnetoresistive resistor along the path of a moving ferrous target. A bias magnet source is positioned behind the proximity sensor, and the ferrous target passes in front of the proximity sensor. The ferrous target alters the direction of the bias magnetic field in the vicinity of the first and second magnetoresistive resistors as the ferrous target passes by the proximity sensor. Flux concentrators are positioned proximate to each of the first and second magnetoresistive resistors. The flux concentrators may help redirect or shunt the magnetic field component produced by the bias magnet source that is perpendicular to the direction of motion of the target through the first and second magnetoresistive resistors in a

direction that is parallel to the direction of motion of the target. Thus, this invention teaches about magnetic sensing employing the magneto resistive principle.
Reference is further made to US 8519704 B2 which teaches about a magnetic-balance-system current sensor that includes: a magnetoresistive element, a resistance value of the magnetoresistive element being changed by applying an induction magnetic field generated by a measurement target current; magnetic cores disposed near the magnetoresistive element; a feedback coil disposed near the magnetoresistive element and configured to generate a cancelling magnetic field that cancels out the induction magnetic field; and a magnetic-field detecting bridge circuit having two outputs. The measurement target current is measured on the basis of a current flowing through the feedback coil when the induction magnetic field and the induction magnetic field and the cancelling magnetic field cancel each other out. The feedback coil, the magnetic cores, and the magnetic-field detecting bridge circuit are formed on a same substrate. The feedback coil is of a spiral type, and the magnetic cores are provided above and below the feedback coil. Thus, this invention teaches bout magnetic sensing using magneto¬resistive balancing principle involving a balanced bridge network.
Thus, detection of abnormal AC/DC magnetic fields in energy meters is a challenging task and the conventional energy meters utilize one of the following:
1. 2D/3D magnetic sensors that work on the principle of Hall Effect;
2. magneto resistive elements that change their resistance according to the magnetic field strength; and
3. coiled conductor that is nothing but a basic implementation of Faradays' law of electromagnetic induction.
The drawbacks associated with these existing alternative solutions are that they require additional components/circuitry to detect abnormal magnetic fields which increase the cost of manufacturing these electric meters, space occupied etc. In

particular, using 2D/3D magnetic sensors increase the cost while the sensitivity is reduced with increase in the size of meter. Further, the coiled conductor is more expensive and requires more space. Moreover, the magneto resistive material has the following disadvantages, namely, a) narrow or limited temperature range, b) short or limited shelf life, and c) cross-sensitivity of other gases. Furthermore, the existing techniques may be used to detect the magnetic tamper, however, none of the existing techniques can provide tamper proofing.
Accordingly, there is a need to overcome the drawbacks associated with the conventional mechanisms for detecting abnormal magnetic fields in an energy meter. In particular, to there is a need for detecting abnormal AC magnetic fields in energy meter to provide tamper proof metering.
The above-described need for an apparatus for detecting abnormal magnetic fields is merely intended to provide an overview of some of the shortcomings of conventional systems / mechanism / techniques, and are not intended to be exhaustive. Other problems/ shortcomings with conventional systems/ mechanism /techniques and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

An object of the present invention is to alleviate the drawbacks associated with conventional mechanisms for detecting abnormal magnetic fields in energy meters.
Another object of the present invention is to provide tamper proof metering of electric meters.
Yet another object of the present invention is to provide a method for accurate detection of abnormal magnetic fields in an energy meter with enhanced precision.
Yet another object of the present invention is to provide an energy meter for detecting abnormal magnetic fields with enhanced precision.
According to a first aspect of the present invention, there is provided a method for detecting abnormal magnetic fields in an energy meter. The method comprising the steps of: obtaining voltage samples from a first and second analogue-to-digital converter (ADCi, ADC2) by measuring the voltage drop across primary shunt (Si) of first analogue-to-digital converter (ADCi) and secondary shunt (S2) of second analogue-to-digital converter (ADC2); processing the obtained voltage samples to determine current Ii across first analogue-to-digital converter (ADCi) and current I2 across second analogue-to-digital converter (ADC2); determining the difference between currents (Ii, I2) across the first and second analogue-to-digital converters; and detecting abnormal magnetic fields in the energy meter when Ii-b^O.
In one possible implementation of the method according to the first aspect, before obtaining voltage samples from a first and second analogue-to-digital converter (ADCI, ADC2), the method comprises the steps of: initializing the first and second analogue-to-digital converters converter (ADCi, ADC2) to default value.

In another possible implementation of the method according to the first aspect, further comprises the step of initiating accuracy correction protocol for energy recording.
According to a second aspect of the present invention, there is provided an improved energy meter for detecting abnormal magnetic fields, said energy meter is characterized by comprising: a first analogue-to-digital converter (ADCi); a second analogue-to-digital converter (ADC2); a primary shunt (Si); and a secondary shunt (S2). The primary shunt (Si) is connected across the first analogue-to-digital converter (ADCi), and the secondary shunt (S2) is connected across the second analogue-to-digital converter (ADC2).
In one possible implementation of the energy meter according to the second aspect, the primary shunt (Si) and the secondary shunt (S2) are in the same axis.
In another possible implementation of the energy meter according to the second aspect, the primary shunt (Si) and the secondary shunt (S2) are in different axis.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates the basic connection diagram of two shunts whose orientation can be in any axis, in accordance with an aspect of the present invention.

Figure 2 illustrates the connection diagram of both primary and secondary shunts, in accordance with another aspect of the present invention.
Figure 3 illustrates the placement and orientation of both primary and secondary shunts, in accordance with another aspect of the present invention.
Figure 4 illustrates the connection diagram of an existing energy meter, in accordance with the prior art of the present invention.
Figure 5 illustrates the connection diagram of both primary and secondary shunts for detection of abnormal magnetic fields in an energy meter, in accordance with an embodiment of the present invention.
Figure 6 illustrates a flow-chart for detection of abnormal magnetic fields in an energy meter, in accordance with an embodiment of the present invention.
It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.
Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a ", "an ", and "the " include plural referents unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
The present invention lies in providing a method and an energy meter for detecting abnormal magnetic fields.

Conventional detection of abnormal AC/DC magnetic fields in energy meters involves mechanisms that utilize 2D/3D magnetic sensors that work on the principle of Hall Effect; magneto resistive elements that change their resistance according to the magnetic field strength; and coiled conductor that is nothing but a basic implementation of Faradays' law of electromagnetic induction.
The drawbacks associated with these existing mechanisms are that they require additional components/circuitry to detect abnormal magnetic fields which increase the cost of manufacturing these electric meters, space occupied etc. In particular, using 2D/3D magnetic sensors increase the cost while the sensitivity is reduced with increase in the size of meter. Further, the coiled conductor is more expensive and requires more space. Moreover, the magneto resistive material has the following disadvantages, namely, a) narrow or limited temperature range, b) short or limited shelf life, and c) cross-sensitivity of other gases. Furthermore, the existing techniques may be used to detect the magnetic tamper, however, none of the existing techniques can provide tamper proofing.
To overcome said drawbacks of conventional systems, the exemplary embodiments of present invention disclose a method and an energy meter for detecting abnormal magnetic fields by employing the shunt splitting principle to provide tamper proof and precision metering. In particular, the present invention aids with detecting magnetic field with an existing component (shunt which is used for current sensing) of an electric meter. Figure 1 illustrates the basic connection diagram of two shunts whereas the orientation can be in any axis. In this technique, the shunt (which is used for measurement of current) is modified as follows:
1. The shunt is divided into two portion or two shunt portions (primary and secondary shunt) as illustrated in Figure 2; and

2. Two portions of shunt/two shunt portions are placed apart in same/different axis (x, y, z). For better resolution, the two portions of shunt/two shunt portions are placed in different axis.
In energy meters, shunt (resistive element) is used for measurement of current. When the current is flowing through the shunt, according to Ohm's law voltage drop will appear across it. This voltage drop is proportional to the magnitude of current flowing. Using Analog to Digital Converter (ADC) of Micro Controller Unit/External ADC voltage drop across the shunt will be measured by passing voltage signal. The present invention provides accurate abnormal magnetic detection with more precision less than 1% accuracy.
In an embodiment of the present invention, the primary shunt is connected to ADC1 (ADC 1-0, ADC 1-2) terminals to snap current for measurement of energy, i.e. the primary shunt being used as current sensor of energy meter. The secondary shunt voltage drop is passed to ADC2 (ADC2-0, ADC2-2) terminals to measure voltage drop across the shunt in presence of abnormal magnetic field. Figure 2 illustrates the connection diagram of both the shunts, in accordance with an embodiment of the present invention.
In ideal scenario, the voltage drop of both primary and secondary shunts will be same i.e., VADC1-VADC2 = 0. According to Electromagnetic induction principle, when the meter is subjected to external abnormal magnetic fields, EMF will induce in both primary and secondary shunts. As the principle of Electromagnetic induction states, EMF induced is directly proportional to magnetic flux linkages.
Since primary and secondary shunts are placed apart, the Flux linkages will differ which results difference in induced EMF. This difference in Voltage is equal to difference of readings of ADC1 and ADC2. VADC1-VADC2 = Finite. Thus, it

can be inferred that if there is a finite amount of voltage difference that confirms presence of abnormal AC magnetic fields.
Figure 3 illustrates the placement and orientation of both primary and secondary shunts according to this invention. By measuring the differential voltage of two shunt portions/two portions of shunt, abnormal AC Magnetic field can be detected with precision and accuracy. The invention is applicable for all types of metering and non-metering applications.
Reference is made to patent application CN101598746A which teaches about an energy meter with two shunts. However, both shunts here are connected to two current channels, i.e., one shunt is connected for measurement of phase channel current while the second shunt is connected for measurement of second for neutral channel. It reduces the common mode voltage of the current sampling signal on the first line by using a bridge sampling circuit, and changes the sampling voltage of the shunt in proportion to the signal processing circuit to realize shunting. Since the shunt is directly sampled through a resistor, it does not need to transfer energy through the magnetic field, thereby avoiding the measurement error and accuracy degradation caused by the current phase shift and core saturation. Especially when the DC component is very large, it can still be accurately measured, which avoids the loopholes in preventing theft of electricity. However, this energy meter cannot detect abnormal magnetic field since the two shunt currents will vary, not only with respect to Magnetic field, but also with the load disturbance. That is even thought there is no magnetic field and load is earthed, there will be difference in the current measured by two shunts, thereby ensuring that this energy meter cannot be used for detecting of abnormal Magnetic fields. In contrast, in the present invention, the two shunts are connected to the phase channel, in series, to measure the induced EMF difference due to external magnetic fields.
Figure 4 shows a connection diagram of an existing energy meter. Here the shunt connected in phase channel will measure the phase channel current, and the CT

connected in the neutral channel will measure the neutral channel current. This is done by processing voltage drop across the shunt/CT Output voltage to the ADC section and ADC will collect the voltage samples and sends to the Processor. This processor will process the samples and with the help of software logic the processes samples will be converted into measured value which is Phase/Neutral current. The ADC is connected across the shunt and measures the voltage drop across the shunt which is proportional to the current flowing through the shunt.
Figure 5 shows the connecting diagram of the present invention. The shunt here has two portions or two shunt portions that are separated with finite distance. Notably, the distance is indicated to be a finite distance since the same is dependent on the size of the energy meter and accordingly can have a wide range. For example, the range may be 1cm to length of the shunt. The energy meter also comprises two ADC sections to measure the two voltage drops across the two shunts of the present invention. In particular, the primary shunt is connected to ADC1 while the secondary shunt is connected to ADC2. These two ADC's measure the voltage drop across respective shunts which is proportional to the current flowing through the channel of the energy meter. In the absence of abnormal magnetic field, the EMF induced due to external magnetic field in the shunt portions would be zero and The voltage drop due to the current flow in the shunts will be finite. As the two shunts are connected in series the voltage drop will be same and the difference between two ADC voltages will be zero. In contrast, when the energy meter is tampered with external AC magnetic field influence, the two shunt portions of the present invention will measure different currents due to difference in external magnetic field strength across those shunts. The distance of about 0.1 cm to 25 cm between the primary and secondary shunts will result in a difference in field strengths across each shunt. Accordingly, by comparing the readings of ADC1 and ADC2, it is possible to detect the presence of magnetic field. Further, tamper proofing can be provided with software algorithm.

For example, two shunts when placed 3 cm apart results in a current measurement difference of 0.5Amp.
Figure 6 illustrates a flow-chart for detection of abnormal magnetic fields in an energy meter, in accordance with a first embodiment of the present invention. The method for detecting abnormal magnetic fields in an energy meter, said method comprising the steps of:
initializing (S601) the first and second analogue-to-digital converters converter (ADCi, ADC2) to default value, wherein the default value is Zero in all buffers;
obtaining (S602) voltage samples from a first and second analogue-to-digital converter (ADCi, ADC2) by measuring the voltage drop across primary shunt (Si) of first analogue-to-digital converter (ADCi) and secondary shunt (S2) of second analogue-to-digital converter (ADC2);
processing (S603) the obtained voltage samples to determine current Ii across first analogue-to-digital converter (ADCi) and current I2 across second analogue-to-digital converter (ADC2);
determining (S604) the difference between currents (Ii, I2) across the first and second analogue-to-digital converters (ADCi, ADC2);
detecting (S605) abnormal magnetic fields in the energy meter when Ii-I2#); and
initiating (S606) accuracy correction protocol for energy recording.
A second embodiment of the present invention is an improved energy meter for detecting abnormal magnetic fields. The energy meter is characterized by comprising: a first analogue-to-digital converter (ADCi); a second analogue-to-digital converter (ADC2); a primary shunt (Si); and a secondary shunt (S2). The primary shunt (Si) is connected across the first analogue-to-digital converter (ADCi), and the secondary shunt (S2) is connected across the second analogue-to-digital converter (ADC2). The primary shunt (Si) and the secondary shunt (S2) can be in the same axis or in different axis.

The present invention finds its application in energy meters.
Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
a) Additional component/circuitry such as Hall effect senor, magneto resistive element and circuitry to integrate mentioned sensors may be eliminated;
b) It detects abnormal AC magnetic field with precision and accuracy of about 1 %; and
c) It is applicable to all types of metering and non-metering applications.
Although a method and an energy meter for detecting abnormal magnetic fields has been described in language specific to structural features and/or methods as indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations for abnormal AC magnetic field detection using shunt splitting principle.

WE CLAIM ;

1. A method for detecting abnormal magnetic fields in an energy meter, said
method comprising the steps of:
obtaining (S602) voltage samples from a first and second analogue-to-digital converter (ADCi, ADC2) by measuring the voltage drop across primary shunt (Si) of first analogue-to-digital converter (ADCi) and secondary shunt (S2) of second analogue-to-digital converter (ADC2);
processing (S603) the obtained voltage samples to determine current Ii across first analogue-to-digital converter (ADCi) and current I2 across second analogue-to-digital converter (ADC2);
determining (S604) the difference between currents (Ii, I2) across the first and second analogue-to-digital converters (ADCi, ADC2); and
detecting (S605) abnormal magnetic fields in the energy meter when Ii-
I2#).
2. The method as claimed in claim 1, wherein before obtaining voltage
samples from a first and second analogue-to-digital converter (ADCI, ADC2), the
method comprises the steps of:
initializing (S601) the first and second analogue-to-digital converters converter (ADCi, ADC2) to default value.
3. The method as claimed in claim 1, further comprising the step of initiating (S606) accuracy correction protocol for energy recording.
4. An improved energy meter for detecting abnormal magnetic fields, said energy meter is characterized by comprising:
a first analogue-to-digital converter (ADCi); a second analogue-to-digital converter (ADC2); a primary shunt (Si); and

a secondary shunt (S2);
wherein the primary shunt (Si) is connected across the first analogue-to-digital converter (ADCi), and the secondary shunt (S2) is connected across the second analogue-to-digital converter (ADC2).
4. The energy meter as claimed in claim 3 wherein, the primary shunt (Si) and the secondary shunt (S2) are in the same axis.
5. The energy meter as claimed in claim 3 wherein, the primary shunt (Si) and the secondary shunt (S2) are in different axis.