Claims:1. A method for accurate energy metering in an electrical circuit, said method comprising the steps of:
sampling an input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit;
measuring, at a computing device, the value of a first output signal from the signal conditioning circuit;
sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit;
measuring, at the computing device, the value of a second output signal from the reference circuit;
increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and
determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit,
wherein, the computing device is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
2. The method as claimed in claim 1, wherein the method comprises the steps of:
splitting, by the computing device, the predetermined range into two or more second ranges, each of said two or more second ranges being a subset of the predetermined range;
sampling the input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit;
measuring, at the computing device, the value of a first output signal from the signal conditioning circuit;
sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit;
measuring, at the computing device, the value of a second output signal from the reference circuit;
increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and
determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit,
wherein, the computing device is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
3. The method as claimed in claim 1, wherein the method comprises the step of fitting, by the computing device, deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit into a predetermined correlation such that the difference between the predetermined correlation and the corresponding deviation is minimum.
4. The method as claimed in claim 3, wherein the predetermined correlation is a straight line.
5. The method as claimed in claim 3, wherein a least-squares regression technique is employed for fitting.
6. The method as claimed in claim 1, wherein the input signal is any of a current signal and a voltage signal.
7. The method as claimed in claim 1, wherein the input signal is any of an AC signal and a DC signal.
8. A system for accurate energy metering in an electrical circuit, said system comprising:
a signal conditioning circuit configured to receive an input signal, said input signal received from a transformer configured to sample the input signal from a source;
a reference circuit configured to receive the input signal, said input signal received from a reference transformer configured to sample the input signal from the source; and
a processor operatively coupled with a memory, said memory storing instructions executable by the processor to:
measure the value of a first output signal from the signal conditioning circuit;
measure, at the computing device, the value of a second output signal from the reference circuit;
increase the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and
determine a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit,
wherein, the processor is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
9. The system as claimed in claim 8, wherein the signal conditioning circuit comprises:
a current gain stage configured to increase voltage of the received input signal to a required value;
a voltage attenuation stage configured to suppress voltage of the received input signal to the required value;
an analogue to digital converter configured to convert the input signal with the required voltage value to a digital output signal; and
a serial communications bus configured for communications between the signal conditioning circuit and the processor.
10. A device for accurate energy metering in an electrical circuit, said device comprising:
a signal conditioning circuit configured to receive an input signal, said input signal received from a transformer configured to sample the input signal from a source;
a reference circuit configured to receive the input signal, said input signal received from a reference transformer configured to sample the input signal from the source; and
a processor operatively coupled with a memory, said memory storing instructions executable by the processor to:
measure the value of a first output signal from the signal conditioning circuit;
measure, at the computing device, the value of a second output signal from the reference circuit;
increase the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and
determine a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit,
wherein, the processor is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
, Description:TECHNICAL FIELD
[1] The present disclosure relates generally to the field of measurement of current or voltage. In particular, the present disclosure relates to accurate metering of current or voltage in an electrical circuit.

BACKGROUND
[2] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[3] An electronics trip unit (ETU) is a microprocessor-based numerical relay which provides different functionalities like metering, protection, and trip functions. Circuit breakers are used to isolate a faulty bus from the main system in case of unhealthy condition. Using current-based and voltage-based sensors, electronics trip unit measures the input values of current and voltage and determines if input current and voltage exceeds a threshold value and, if it does, provides a trip command to circuit breaker to isolate the faulty line from rest of system. The electronics trip unit provides different current-based protections such as instantaneous, overload, long inverse, short circuit and thermal. The electronics trip unit also provides different voltage-based protection like overvoltage, under voltage, frequency as well as power-based directional protections.
[4] In remote areas where auxiliary power supply is not readily available, there is a big challenge to energize the electronics trip unit without any auxiliary power source. For this purpose, current based self-powered supply sources are used to power up the electronics trip unit. A limitation of such an application is protection trip time. If the input measurement value of current and voltage exceeds a threshold value from a pickup value, electronics trip unit sends a trip command to trip the circuit breaker to isolate the unhealthy section from rest of system. However, the electronics trip unit itself has some latency or delay in determining the current and voltage and applying trip command to circuit breaker. If this latency is significant, the total time for tripping the circuit breaker also increases.
[5] Another feature of the electronics trip unit is the metering and measurement of energy, for which accuracy of input current and voltage is important. Current sensors play an important role in metering accuracy. Due to large dynamic range of AC current (>20 times of rated current), it is very difficult of maintain a linearity of a sensor. Nonlinearity of current sensor is more for lower current due to low signal to noise ratio (SNR).
[6] There is, therefore, a requirement in the art for an approach to accurately measure or meter the current or voltage in an electrical circuit.
[7] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[8] In some embodiments, the numbers expressing quantities or dimensions of items, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[9] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[10] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTS OF THE INVENTION
[11] A general object of the present invention is to provide a method and system for accurate energy metering in an electrical circuit.
[12] Another object of the present invention is to provide a method for calibrating against non-linear characteristics of a current or a voltage sensor.
[13] Another object of the present invention is to provide a multipoint calibration to improve accuracy of metering.
[14] Another object of the present invention is to provide a method for accurate metering for different measuring ranges.

SUMMARY
[15] The present disclosure relates generally to the field of measurement of current or voltage. In particular, the present disclosure relates to accurate metering of current or voltage in an electrical circuit.
[16] In an aspect, the present disclosure provides a method for accurate energy metering in an electrical circuit, said method comprising the steps of: sampling an input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit; measuring, at a computing device, the value of a first output signal from the signal conditioning circuit; sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit; measuring, at the computing device, the value of a second output signal from the reference circuit; increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit, wherein, the computing device is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[17] In an embodiment, the method comprises the steps of: splitting, by the computing device, the predetermined range into two or more second ranges, each of said two or more second ranges being a subset of the predetermined range; sampling the input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit; measuring, at the computing device, the value of a first output signal from the signal conditioning circuit; sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit; measuring, at the computing device, the value of a second output signal from the reference circuit; increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit, wherein, the computing device is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[18] In another embodiment, the method comprises the step of fitting, by the computing device, deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit into a predetermined correlation such that the difference between the predetermined correlation and the corresponding deviation is minimum. In another embodiment, the predetermined correlation is a straight line. In another embodiment, a least-squares regression technique is employed for fitting.
[19] In another embodiment, the input signal is any of a current signal and a voltage signal.
[20] In another embodiment, the input signal is any of an AC signal and a DC signal.
[21] In an aspect, the present disclosure provides a system for accurate energy metering in an electrical circuit, said system comprising: a signal conditioning circuit configured to receive an input signal, said input signal received from a transformer configured to sample the input signal from a source; a reference circuit configured to receive the input signal, said input signal received from a reference transformer configured to sample the input signal from the source; and a processor operatively coupled with a memory, said memory storing instructions executable by the processor to: measure the value of a first output signal from the signal conditioning circuit; measure, at the computing device, the value of a second output signal from the reference circuit; increase the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and determine a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit, wherein, the processor is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[22] In an embodiment, the signal conditioning circuit comprises: a current gain stage configured to increase voltage of the received input signal to a required value; a voltage attenuation stage configured to suppress voltage of the received input signal to the required value; an analogue to digital converter configured to convert the input signal with the required voltage value to a digital output signal; and a serial communications bus configured for communications between the signal conditioning circuit and the processor.
[23] In an aspect, the present disclosure provides a device for accurate energy metering in an electrical circuit, said device comprising: a signal conditioning circuit configured to receive an input signal, said input signal received from a transformer configured to sample the input signal from a source; a reference circuit configured to receive the input signal, said input signal received from a reference transformer configured to sample the input signal from the source; and a processor operatively coupled with a memory, said memory storing instructions executable by the processor to: measure the value of a first output signal from the signal conditioning circuit; measure, at the computing device, the value of a second output signal from the reference circuit; increase the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and determine a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit, wherein, the processor is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[24] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS
[25] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain the principles of the present disclosure.
[26] FIG. 1 illustrates an exemplary block diagram of a system for accurate energy metering in an electrical circuit, in accordance with an embodiment of the present disclosure.
[27] FIG. 2 illustrates an exemplary flow diagram for a method for accurate energy metering in an electrical circuit, in accordance with an embodiment of the present disclosure.
[28] FIGs. 3A and 3B illustrate exemplary flow diagrams for processes of DC offset calibration and AC magnitude calibration respectively, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[29] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[30] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[31] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[32] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.
[33] The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non – claimed element essential to the practice of the invention.
[34] In microprocessor-based relays, for metering purpose, current and voltage sensors are used. A sensor can be a current transformer, which steps down current in transformer secondary. The secondary current passes through a low resistance, which develop voltage. This developed voltage is used for further signal conditioning. In case of nonlinear sensor, gain and phase error of current at secondary terminal can vary for different values of primary current.
[35] The output of the sensors goes to a signal conditioning electronics circuit and then finally goes to an analogue to digital converter. Due to tolerance of electronic component and sensors, the final input may be clamped with some DC offset value. Further, in case of switching load conditions, the DC offset from the sensor may change again. Due to poor signal-to-noise ratio (SNR) for lower current values, the DC offset and AC magnitude measurement can introduce errors.
[36] In an aspect, the present disclosure provides a method for accurate energy metering in an electrical circuit, said method comprising the steps of: sampling an input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit; measuring, at a computing device, the value of a first output signal from the signal conditioning circuit; sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit; measuring, at the computing device, the value of a second output signal from the reference circuit; increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range; and determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit, wherein, the computing device is configured to modify the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[37] FIG. 1 illustrates an exemplary block diagram of a system for accurate energy metering in an electrical circuit, in accordance with an embodiment of the present disclosure. The system 100 can include: a current and voltage source 102 (hereinafter, also referred to as “source”); a meter under test 104 (hereinafter, also referred to as “MUT”); a reference meter 106 (hereinafter, also referred to as “RM”); a computing device 108; and a control circuit 110.
[38] In an embodiment, the MUT 104 can include: a current gain stage 104-2; a voltage attenuation stage 104-4; an analogue to digital converter 104-6 (hereinafter, also referred to as “ADC”); a microprocessor 104-8 and a serial communications bus 104-10.
[39] In another embodiment, the MUT 104 is coupled with a current transformer CT1. In another embodiment, the RM 106 is coupled with a reference current transformer CT ref.
[40] In another embodiment, the CT1 steps down the input current from the source 102 and the stepped down current is passed to the MUT 104. In the MUT 104, the stepped down current is passed through the current gain stage 104-2 to step up the voltage to a level that is required for the ADC 104-6. In another embodiment, in the MUT 104, the stepped down current is passed through the voltage attenuation stage 104-4 to suppress the voltage to a level that is required for the ADC 104-6. The ADC 104-6 converts an analogue signal to digital counts, and effective number of bits (ENOB) of an ADC defines the resolution of the ADC. It is preferable that the ENOB of the ADC is higher.
[41] In another embodiment, the microprocessor 106-8 is configured for sampling and amplitude calculations.
[42] In another embodiment, the MUT 104 can communicate with the computing device through the serial communications bus 104-10.
[43] In another embodiment, the RM 106 can communicate with the computing device and provides analogue parameters to the computing device.
[44] In another embodiment, the control circuit 110 provides a control command to the source 102 during injection.
[45] In an embodiment, to calibrate the metering of current and/or energy values, the system 100 is configured to use two key calibration steps: DC offset calibration; and AC magnitude calibration. Further, DC calibration is performed in two steps: power-up DC offset; and dynamic DC offset.
[46] In an embodiment, the DC offset can be calculated by averaging the number of samples captured during one complete cycle. This offset can include signal conditioning as well as offset error.
V0=?_(i=0)^(N-1)¦Xi
Where,
Xi is the instantaneous sampled of current and voltage that will be captured over N cycles; and
V0 is the corresponding DC offset error.
[47] In another embodiment, AC magnitude error can be performed by a least square regression technique. This can be used for calibrating non-linear sensors. Non-linear sensors provide different gain error corresponding to different input. SNR also decreases if input current range is low. Thus, when input current is low, the overall error of measurement is significant. A single point calibration cannot sufficiently account for the error. For a given data,
e_i=y_i-(ax_i+b)
Where, i = 1, 2, 3…n
[48] Sum of square error is determined as,
E= ?_(i=1)^n¦?e_i?^2
[49] For least error,
?E/?a=?E/?b=0
[50] To calculate value of a and b for best fit of equation,
a?_(i=1)^n¦?x_i?^2 +b?_(i=1)^n¦?x_i?^2 =?_(i=1)^n¦?x_i y_i ?…………(1)
a?_(i=1)^n¦?x_i+nb?=?_(i=1)^n¦y_i …………(2)
[51] During calibration, known sequence of input (current or voltage) is injected in the sensor and corresponding output samples are stored. For instance, if measurement current range is 0.1 to 1.2 units, then input current values can be 0.1 to 1.2 units in step size of 0.05 units or less. Ideally, sensor characteristics during measurement should be linear, i.e., it should follow a straight-line equation.
[52] Straight-line equation,
Y=aX+b
[53] Where, Y is the desired input value with respect to sensor output X.
[¦(y_0@y_1@y_m )]=a[¦(x_0@x_1@x_m )]+b
Where, m is the number of input and output values for specified range and depends on the step size of input current or voltage sample.
[54] During calibration, user can read a desired input value from the RM 106 and sensor measurement value from the MUT 104. The user can then store the number of input and output values, depending on step size of input current or voltage sample. A curve fitting technique can be applied on behalf of the stored samples, such as a least squares method.
[55] On behalf of stored X, Y matrix, using equation (1), and equation (2), coefficients a and b can be calculated.
[56] Once the values of a and b are calculated, Y’ (a modified value of Y) can be calculated,
[¦(?y'?_0@?y'?_1@?y'?_m )]=a[¦(x_0@x_1@x_m )]+b

[57] The calibration error matrix,
E_m=(?Y'?_m-Y_m)/Y_m ×100
[58] The value of Em depends on claimed measurement accuracy. In the case the error of any element of matrix Em is higher than the desired value, then the range is split in two, and the values of a and b are re-calculated, and subsequently, the values of Y’ and Em are re-calculated. If, on checking, the error is still above the desired value, the range is again split in two and the steps are followed.
[59] If the error is within the desired value, the parameters such as number of split ranges, a and b values for each range are noted.
[60] It can be demonstrated that using the system 100, accuracy of current and voltage metering can be increased by up to 0.2%.
[61] FIG. 2 illustrates an exemplary flow diagram for a method for accurate energy metering in an electrical circuit, in accordance with an embodiment of the present disclosure. In an embodiment, the method 200 can include the steps of:
202 – sampling an input signal from a source by a signal conditioning circuit from a transformer operatively coupled to the source and the signal conditioning circuit;
204 – measuring, at a computing device, the value of a first output signal from the signal conditioning circuit;
206 – sampling the input signal from the source by a reference circuit from a reference transformer operatively coupled to the source and the reference circuit;
208 – measuring, at the computing device, the value of a second output signal from the reference circuit;
210 – increasing, by the computing device, the value of the input signal from the source by a predefined step, such that the value of the increased signal is within a predetermined range, value of said step being lower than the predetermined range;
212 – determining, at the computing device, a correlation between measured values of input signal from the signal conditioning circuit and that from the reference circuit; and
214 – modifying the values of the measured signal from the signal conditioning circuit by applying the correlation to enable deviation between measured values of input signal from the signal conditioning circuit from that of the reference circuit to under a threshold value.
[62] FIGs. 3A and 3B illustrate exemplary flow diagrams for processes of DC offset calibration and AC magnitude calibration respectively, in accordance with an embodiment of the present disclosure. In an exemplary embodiment, measurement range is 0.1 to 1.2 units with a step size of 0.05 units. During calibration,
calibrator writes default calibration factor inside the MUT;
calibrator injects 0.1 rated value and waits for a stabilisation;
calibrator reads measured value from MUT and RM, and stores the values;
calibrator increases injected value with the step size and store new measured values from MUT and RM, where the process is repeated until injected value reaches 1.2 units;
calibrator uses least square technique for calculating coefficients of straight-line equation for the particular range;
once coefficients are calculated, they are applied on the current measured samples (X) and the calibrated values (Y’) are calculated as described earlier;
error (Em) is calculated as described earlier;
if error is larger than desired, range is split in two, for instance range1 is 01. To 0.6 units and range2 is 0.6 to 1.2 units; and
above steps are followed until the error is within the desirable value.
[63] After calibration, calibration parameters such as number of split slabs, specific threshold values for each slab, and calibration coefficients for each slab are noted.
[64] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive patent matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “includes” and “including” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practised with modification within the spirit and scope of the appended claims.
[65] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[66] The present disclosure provides a method and system for accurate energy metering in an electrical circuit.
[67] The present disclosure provides a method for calibrating against non-linear characteristics of a current or a voltage sensor.
[68] The present disclosure provides a multipoint calibration to improve accuracy of metering.
[69] The present disclosure provides a method for accurate metering for different measuring ranges.