Claims:1. A system comprising:
an electrical device; and
a power metering unit coupled to the electrical device, wherein the power metering unit comprises:
a carrier wave generator for generating a predefined sample wave;
a comparator operatively coupled to the carrier wave generator and the electrical device, wherein the comparator is configured to:
receive a first input signal from the electrical device and the predefined sample wave from the carrier wave generator;
compare the predefined sample wave to the first input signal; and
generate a control signal based on comparison of the predefined sample wave with the first input signal; and
a switching device operatively coupled to the electrical device and the comparator and configured to be operated based on the control signal, wherein the switching device is further configured to receive a second input signal from the electrical device and output a modulated signal based on operation of the switching device, wherein the modulated signal is representative of a quantity of estimated power of the electrical device.

2. The system of claim 1, wherein the power metering unit further comprises:
a first input filtering unit operatively coupled to the electrical device and the comparator, wherein the first input filtering unit is configured to receive a first sensed electrical parameter from the electrical device and generate a first filtered output signal representative of the first input signal;
a second input filtering unit operatively coupled to the electrical device and the switching device, wherein the second input filtering unit is configured to receive a second sensed electrical parameter from the electrical device and generate a second filtered output signal representative of the second input signal; and
an output filtering unit operatively coupled to the switching device and configured to receive the modulated signal from the switching device and generate a third filtered output signal.

3. The system of claim 2, wherein each of the first input filtering unit, the second input filtering unit, and the output filtering unit comprises a low pass filter.

4. The system of claim 2, wherein the electrical device comprises a controller.

5. The system of claim 4, wherein the controller is configured to determine a quantity of actual power consumed by the electrical device based on the modulated signal, the first sensed electrical parameter, and the second sensed electrical parameter.

6 The system of claim 2, wherein the first sensed electrical parameter comprises an input current of the electrical device.

7. The system of claim 2, wherein the first sensed electrical parameter comprises an output current of the electrical device.

8. The system of claim 2, wherein the second sensed electrical parameter comprises an input voltage of the electrical device.

9. The system of claim 2, wherein the second sensed electrical parameter comprises an output voltage of the electrical device.

10. The system of claim 2, further comprising a display device operatively coupled to the output filtering unit.

11. The system of claim 1, wherein the control signal comprises a high signal, a low signal, or a combination thereof.

12. The system of claim 11, wherein the comparator is configured to generate the high signal when an amplitude of the first input signal is greater than an amplitude of the predefined sample wave.

13. The system of claim 12, wherein the comparator is configured to generate the low signal when the amplitude of the first input signal is less than the amplitude of the predefined sample wave.

14. The system of claim 11, wherein the switching device is configured to open based on the high signal.

15. The system of claim 11, wherein the switching device is configured to close based on the high signal.

16. The system of claim 11, wherein the switching device is configured to close based on the low signal.

17. The system of claim 11, wherein the switching device is configured to open based on the low signal.

18. The system of claim 1, wherein the electrical device comprises a solid state driver coupled to the power metering unit.

19. The system of claim 1, wherein the electrical device comprises a lighting fixture.

20. A method, comprising:
transmitting a first input signal and a second input signal from an electrical device to a power metering unit, wherein the power metering unit comprises a carrier wave generator, a comparator, and a switching device, wherein the comparator is operatively coupled to the carrier wave generator and the electrical device, the switching device is coupled to the electrical device and the comparator;
transmitting a predefined sample wave from the carrier wave generator to the comparator;
comparing the predefined sample wave to the first input signal, using the comparator;
transmitting a control signal from the comparator to the switching device, based on comparison of the predefined sample wave with the first input signal;
operating the switching device based on the control signal;
receiving the second input signal from the electrical device and output a modulated signal via the switching device, based on operation of the switching device, wherein the modulated signal is representative of a quantity of estimated power of the electrical device.

21. The method of claim 20, further comprising:
transmitting a first sensed electrical parameter from the electrical device to a first input filtering unit;
generating a first filtered output signal representative of the first input signal via the first input filtering unit;
transmitting a second sensed electrical parameter from the electrical device to a second input filtering unit; and
generating a second filtered output signal representative of the second input signal via the second input filtering unit.

22. The method of claim 21, further comprising determining a quantity of actual power consumed by the electrical device based on the modulated signal, the first sensed electrical parameter, and the second sensed electrical parameter, via a controller of the electrical device.

23. The method of claim 20, further comprising:
transmitting the modulated signal to an output filtering unit; and
generating a third filtered output signal.

24. The method of claim 20, wherein the electrical device comprises a lighting fixture.

25. A system comprising:
a plurality of lighting fixtures; and
a power metering unit coupled to the plurality of lighting fixtures, wherein the power metering unit comprises:
a carrier wave generator for generating a predefined sample wave;
a comparator operatively coupled to the carrier wave generator and the plurality of lighting fixtures, wherein the comparator is configured to:
receive a first input signal from the plurality of lighting fixtures and the predefined sample wave from the carrier wave generator;
compare the predefined sample wave to the first input signal; and
generate a control signal based on comparison of the predefined sample wave with the first input signal; and
a switching device operatively coupled to the plurality of lighting fixtures and the comparator and configured to be operated based on the control signal, wherein the switching device is further configured to receive a second input signal from the plurality of lighting fixtures and output a modulated signal based on operation of the switching device, wherein the modulated signal is representative of a quantity of estimated power of the plurality of lighting fixtures.
, Description:BACKGROUND
Embodiments of the present disclosure generally relate to metering systems and more specifically to a metering system for lighting fixtures.
A wide variety of lighting fixtures are available with power rating ranging from few tens of watts to hundreds of watts. Such lighting fixtures are employed for indoor lighting as well as outdoor/landscape lighting. The energy consumed by any lighting fixture depends on the luminosity of emitted light and the current fed to the lighting fixture. It may be noted that large facilities such as high bays, conference halls, super markets, and the like have a plurality of lighting fixtures. The rental cost for such facilities is determined by the energy consumed in the facility. Generally, such facilities employ a centralized power metering system. However, for smart energy management of the facilities, an accurate measurement of energy consumed by the lighting fixtures in the facility is necessary. Therefore, it is desirable to have a localized energy metering system on each lighting fixture.
In general, dedicated metering integrated circuits (ICs) are available for measuring energy consumed by the lighting fixtures. However, the dedicated metering ICs employ expensive components such as analog multipliers, controllers, microprocessors, and the like. The use of such devices results in a considerable increase in the cost of the meters.
Accordingly, there is a need for an improved metering system to measure the power consumed by the lighting fixtures.
BRIEF DESCRIPTION
In accordance with aspects of the present disclosure, a system includes an electrical device. Further, the system includes a power metering unit coupled to the electrical device. The power metering unit includes a carrier wave generator for generating a predefined sample wave and a comparator operatively coupled to the carrier wave generator and the electrical device. The comparator is configured to receive a first input signal from the electrical device and the predefined sample wave from the carrier wave generator, compare the predefined sample wave to the first input signal, and generate a control signal based on comparison of the predefined sample wave with the first input signal. Further, the power metering unit includes a switching device operatively coupled to the electrical device and the comparator and configured to be operated based on the control signal. The switching device is further configured to receive a second input signal from the electrical device and output a modulated signal based on operation of the switching device. The modulated signal is representative of a quantity of estimated power of the electrical device.
In accordance with another aspect of the present disclosure, a method involves transmitting a first input signal and a second input signal from an electrical device to a power metering unit. The power metering unit includes a carrier wave generator, a comparator, and a switching device. The comparator is operatively coupled to the carrier wave generator and the electrical device. The switching device is coupled to the electrical device and the comparator. Further, the method involves transmitting a predefined sample wave from the carrier wave generator to the comparator. Also, the method involves comparing the predefined sample wave to the first input signal, using the comparator. The method further involves transmitting a control signal from the comparator to the switching device, based on comparison of the predefined sample wave with the first input signal. The method also involves operating the switching device based on the control signal. The method further involves receiving the second input signal from the electrical device and output a modulated signal via the switching device, based on operation of the switching device. The modulated signal is representative of a quantity of estimated power of the electrical device.
In accordance with yet another aspect of the present disclosure, a system includes a plurality of lighting fixtures. Further, the system includes a power metering unit coupled to the plurality of lighting fixtures. The power metering unit includes a carrier wave generator for generating a predefined sample wave and a comparator operatively coupled to the carrier wave generator and the plurality of lighting fixtures. The comparator is configured to receive a first input signal from the plurality of lighting fixtures and the predefined sample wave from the carrier wave generator, compare the predefined sample wave to the first input signal, and generate a control signal based on comparison of the predefined sample wave with the first input signal. Further, the power metering unit includes a switching device operatively coupled to the plurality of lighting fixtures and the comparator and configured to be operated based on the control signal. The switching device is further configured to receive a second input signal from the plurality of lighting fixtures and output a modulated signal based on operation of the switching device. The modulated signal is representative of a quantity of estimated power of the plurality of lighting fixtures.
DRAWINGS
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 is a block diagram of a system having a power metering unit for measuring power consumed by an electrical device in accordance with certain embodiments of the present invention;
FIG. 2 is a diagrammatical representation of an embodiment of the power metering unit;
FIG. 3 is a graphical representation of a plurality of waveforms generated in an exemplary power metering unit in accordance with certain embodiments of the present invention; and
FIG. 4 is a flow chart illustrating a plurality of steps involved in an exemplary method for operation of a power metering unit for measuring power consumed by an electrical device in accordance with certain embodiments of the present invention.
DETAILED DESCRIPTION
Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “or” is meant to be inclusive and mean one, some, or all of the listed items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. Furthermore, terms such as “circuit”, “circuitry”, and “controller” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function. Also, the term operatively coupled as used herein includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio communication, software based communication, or combinations thereof.
As will be described in detail hereinafter, various embodiments of an exemplary energy metering system and a method of operation of the energy metering system are disclosed. Specifically, a power metering unit to be employed in a lighting fixture, such as, a light emitting diode (LED) is disclosed.
Turning now to the drawings and by way of example in FIG. 1, a block diagram of an exemplary energy metering system 100, in accordance with certain embodiments of the present invention is shown. The energy metering system 100 includes an electrical device 102, a power metering unit 104, and a display device 106. The electrical device 102 is operatively coupled to the power metering unit 104. Further, the display device 106 is operatively coupled to the power metering unit 104.
The electrical device 102 includes a solid state driver 108 coupled to a LED 109. The solid state driver 108 includes an electrical parameter sensing unit (not shown in FIG. 1). The electrical parameter sensing unit is configured to sense first and second electrical parameters of the electrical device 102. In one embodiment, the first sensed electrical parameter includes a current and the second sensed electrical parameter includes a voltage. It should be noted herein that the terms “first electrical parameter” and “first sensed electrical parameter” may be used interchangeably. Similarly, the terms “second electrical parameter” and “second sensed electrical parameter” may be used interchangeably. In accordance with aspects of the present invention, the electrical parameter sensing unit includes a voltage divider for sensing voltage and a current transformer for sensing current. In certain other embodiments, other types of electrical parameter sensing units for sensing current and voltage may be employed. In one specific embodiment, an isolation circuitry, such as an optocoupler, may be provided between the voltage divider and the power metering unit 104 to provide adequate voltage isolation between the voltage divider and the power metering unit 104.
The first and second sensed electrical parameters are transmitted to the power metering unit 104. In one embodiment, the first and second sensed electrical parameters are obtained from an input side of the electrical device 102. In another embodiment, the first and second sensed electrical parameters are obtained from an output side of the electrical device 102.
Furthermore, the solid state driver 108 is operatively coupled to a controller 110. The controller 110 is configured to process the first and second sensed electrical parameters of the electrical device 102. The controller 110 is further configured to determine an estimated and an actual power consumed by the electrical device 102. The term “estimated power of the electrical device” as used herein, may refer to a measure of approximate power consumed by the electrical device. The term “actual power consumed by the electrical device,” as used herein, may refer to a measure of the total power consumed by the LED and the solid state driver. The controller 110 may include a storage device for storing the first and second sensed electrical parameters. In one embodiment, the controller 110 may include a processor. The electrical device 102 may include any electrical device which consumes power, such as a lighting fixture or a plurality of lighting fixtures.
FIG. 2 is a diagrammatical representation of an embodiment of the power metering unit 104. The power metering unit 104 is operatively coupled to the electrical device 102 shown in FIG. 1. The power metering unit 104 includes a first input filtering unit 202, a carrier wave generator 204, and a comparator 206. Further, the power metering unit 104 includes a second input filtering unit 208, a switching device 210, and an output filtering unit 212. The carrier wave generator 204 may include a 555-timer. The comparator 206 includes two input terminals, such as an inverting terminal and a non-inverting terminal.
The electrical device is operatively coupled to the first input filtering unit 202 and the second input filtering unit 208. The first input filtering unit 202 and the carrier wave generator 204 are operatively coupled to the two input terminals of the comparator 206. Further, the second input filtering unit 208 is operatively coupled to the switching device 210. Also, an output terminal of the comparator 206 is operatively coupled to the switching device 210. The switching device 210 is further operatively coupled to the output filtering unit 212.
Each of the first input filtering unit 202, the second input filtering unit 208, and the output filtering unit 212, includes a low pass filter. In one embodiment, each of the first input filtering unit 202, the second input filtering unit 208, and the output filtering unit 212, may include an active low pass filter or a passive low pass filter. In certain embodiments, the first input filtering unit 202, the second input filtering unit 208, and the output filtering unit 212 may include elliptical filters, Butterworth filter, resistor-capacitor (RC) filter, inductor-capacitor (LC) filter, inductor-capacitor-inductor (LCL) filter, and the like.
The first input filtering unit 202 is configured to receive a first sensed electrical parameter 201 from the electrical device. In the illustrated embodiment, the first sensed electrical parameter 201 includes current. In particular, the first sensed electrical parameter 201 may include an alternating current (AC) current or a direct current (DC) current. The first sensed electrical parameter 201 may be an input current or an output current. The term “input current” as used herein, may refer to current at an input side of the electrical device. The term “output current” as used herein, may refer to current at an output side of the electrical device.
The first sensed electrical parameter 201 is filtered via the first input filtering unit 202 to generate a first filtered output signal 304. The first filtered output signal 304 is representative of a first input signal provided to one terminal of the comparator 206. It should be noted herein that the terms “first filtered output signal” and “first input signal” may be used interchangeably. In certain embodiments, when the first sensed electrical parameter 201 is a DC current devoid of any noise or higher order harmonics, the first sensed electrical parameter 201 may be directly provided to the comparator 206 without filtering.
The carrier wave generator 204 is configured to generate a predefined sample wave 302. In one example, the predefined sample wave 302 may include a triangular wave or a saw tooth wave. The triangular wave or saw tooth wave has negligible offset. The predefined sample wave 302 is transmitted to the other input terminal of the comparator 206. Further, the comparator 206 compares the first input signal 304 with the predefined sample wave 302 to generate a control signal 310.
The second input filtering unit 208 is configured to receive a second sensed electrical parameter 207 from the electrical device. The second sensed electrical parameter 207 is filtered via the second input filtering unit 208 to generate a second filtered output signal 314 representative of a second input signal. It should be noted herein that the terms “second filtered output signal” and “second input signal” may be used interchangeably. The second input signal 314 is transmitted to the switching device 210.
In one embodiment, the switching device 210 may include a semiconductor switch, a mechanical switch, an electromechanical switch, a relay, or combinations thereof. The electromechanical switch may include a Micro-Electro-Mechanical Systems (MEMS) based switch. The semiconductor switch may include a bipolar transistor, an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor, a field effect transistor, an injection enhanced gate transistor, an integrated gate commutated thyristor, or combinations thereof.
In the illustrated embodiment, the second sensed electrical parameter 207 is voltage. The second sensed electrical parameter 207 may include an alternating current (AC) voltage or a direct current (DC) voltage. Further, the second sensed electrical parameter 207 may be an input voltage or an output voltage. The term “input voltage” as used herein, may refer to voltage across the input side of the electrical device. The term “output voltage” as used herein, may to refer to voltage across the output side of the electrical device. In certain embodiments, when the second sensed electrical parameter 207 is a DC voltage devoid of any noise or higher order harmonics, the second sensed electrical parameter 207 may be directly transmitted to the switching device 210 without filtering.
The switching device 210 is operated based on the control signal 310 transmitted from the comparator 206. The control signal 310 is a combination of the high signal and the low signal (not shown in FIG. 2). The switching device 210 is closed when the control signal 310 having the high value is transmitted to the switching device 210. The switching device 210 is opened when the control signal 310 having the low value is transmitted to the switching device 210. In another embodiment, the switching device 210 is configured to close based on the low signal and the switching device is configured to open based on the high signal.
When the switching device 210 is closed, the second input signal 314 is transmitted through the switching device 210. Particularly, the switching device 210 is configured to receive the second input signal 314 from the electrical device and output a modulated signal 318. The term “modulated signal” as used herein, may to refer to a pulse width modulated second input signal obtained through the switching device 210. The modulated signal 318 is representative of the estimated power of the electrical device. Further, the modulated signal 318 is filtered via the output filtering unit 212 to generate a third filtered output signal 213. In particular, the output filtering unit 212 is configured to provide an average value of the modulated signal 318. When the switching device 210 is opened, the second input signal 314 is not transmitted through the switching device 210.
Turning now to FIG. 3, a diagrammatical representation 300 of a plurality of waveforms generated in an exemplary power metering unit in accordance with embodiment of FIG. 2 is shown. The x-axis 308 is representative of time and the y-axis 306 is representative of amplitude of a signal. In the illustrated embodiment, the predefined sample wave 302 is a triangular wave. In the illustrated embodiment, the first input signal 304 is a filtered DC current sensed from the electrical device.
As noted hereinabove, the predefined sample wave 302 is compared to the first input signal 304 by the comparator 206. In the illustrated embodiment, the amplitude of the first input signal 304 is represented as Io. During the duration from time instant t1 to time instant t2, the first input signal 304 has a greater amplitude than the predefined sample wave 302. Accordingly, a signal 309 having a high value is generated during the duration from time instant t1 to time instant t2. During the duration from time instant t2 to time instant t3, the predefined sample wave 302 has greater amplitude than the first input signal 304. Accordingly, a signal 311 having a low value is generated during the duration from time instant t2 to time instant t3. Accordingly, a control signal 310 is generated from the comparator 206. The control signal 310 is represented with reference to an x-axis 312 and the y-axis 306. The x-axis 312 represents time. The control signal 310 includes a combination of the high signal 309 and the low signal 311. In one embodiment, the high signal 309 has a positive value and the low signal 311 has a zero value or a negative value. The high signal 309 is represented as “1” and the low signal 311 is represented as “0”.
As noted hereinabove, the second input signal 314 is a voltage signal represented with reference to x-axis 316 and y-axis 306. The x-axis 316 is representative of time. The amplitude of second input signal 314 is represented by Vo. As noted hereinabove, the second input signal 314 is transmitted through the switching device 210, when the switching device 210 is closed. In the illustrated embodiment, during the duration from time instant t1 to time instant t2 and from time instant t3 to time instant t4, the control signal 310 has a high value. When the control signal 310 has a high value, the switching device 210 is closed, thereby allowing the transmission of second input signal 314. When the control signal 310 has a low value, the switching device 210 is opened thereby blocking the transmission of the second input signal 314. Accordingly, the modulated signal 318 is output from the switching device 210. The modulated signal 318 is represented with reference to x-axis 320 and the y-axis 306. The x-axis 320 is representative of time. The modulated signal 318 has a high value during the duration from time instant t1 to time instant t2 and during duration from time instant t3 to time instant t4. The modulated signal 318 has zero value during the duration from time instant t2 to time instant t3.
Reference numeral 322 is representative of one cycle of the modulated signal 318. The time period from time instant t1 to time instant t3, for one cycle of the modulated signal 318, is represented as Ts. During the time period Ts, the modulated signal 318 has a high value for time duration from time instant t1 to time instant t2. The time duration from time instant t1 to time instant t2 is represented as DTs. D is the duty cycle of the modulated signal 318. The term “duty cycle” as used herein, may refer to the percentage of one period in which a signal has a high value. In the illustrated embodiment, reference numeral 324 is representative of a high value of the modulated signal 318. The amplitude of the high value of the modulated signal 318 is represented by Vpk.
The modulated signal 318 is generated based on the control signal 310. The control signal 310 is generated based on comparison of the first input signal 304 with the predefined sample wave 302. A pattern of the modulated signal 318 is dependent based on the first input signal 304. In particular, a time duration of the modulated signal 318 is a function of the first input signal 304. More particularly, the duty cycle of the modulated signal 318 is a function of the first input signal 304. The amplitude of the modulated signal 318 is a function of the amplitude of second input signal 314.
The average voltage Vavg of the modulated signal 318 for time period Ts, is determined based on the below equations:
V_pk=f(V_o)
D =f(I_o)
V_avg=(Area of a cycle of signal 318)/(time period)
V_avg=(V_pk*D*T_s)/T_s
V_(avg )=V_pk*D
V_(avg )=f(V_o )*f(I_o ), where f(V_o )*f(I_o ) is proportional to P_(avg ), P_(avg ) is proportional to V_(avg ), where Pavg is an estimated power of the electrical device. V_(avg ) is representative of a measure of the estimated power of the electrical device. In one embodiment, V_pk=k_1*V_o and D=k_2 ?*I?_o, where k_1 and k_2 are constants.
With reference to both FIGs. 2 and 3, the estimated power of the electrical device is transmitted to the controller. The controller is configured to determine a quantity of actual power consumed by the electrical device based on the modulated signal 318, the first sensed electrical parameter 201, and the second sensed electrical parameter 207. If the first sensed electrical parameter 201 and the second sensed electrical parameter 207 are an input current and an input voltage respectively, then the controller determines the estimated power of the electrical device as an actual power consumed by the electrical device. If the first sensed electrical parameter 201 and the second sensed electrical parameter 207 are an output current and an output voltage respectively, the controller determines the actual power consumed by the electrical device from a predetermined look-up table based on the determined estimated power of the electrical device. The predetermined look-up table may be stored in the controller. The predetermined look-up table provides information pertaining to a correlation between the estimated power of the electrical device, the actual power consumed by the electrical device, and the efficiency of the electrical device.
Further, if the first sensed electrical parameter 201 and the second sensed electrical parameter 207 are an alternating current current and alternating current voltage, a scaling factor is multiplied to the estimated power of the electrical device to determine the actual power consumed by the electrical device. The scaling factor is dependent on the shape of the waveforms representative of the first and second sensed electrical parameters 201, 207. If there is an offset in the triangular wave or saw tooth wave generated by the carrier wave generator, then a predetermined calibration factor is multiplied with the estimated power of the electrical device for determining the actual power consumed by the electrical device. In one embodiment, the modulated signal 318 may be provided to a digital controller or an analog controller via a wireless transmitter.
Turning now to FIG. 4, a flow chart 400 illustrating a plurality of steps involved in an exemplary method of operation of the system employing a power metering unit in accordance with an exemplary embodiment is shown. At block 402, a first input signal and a second input signal from an electrical device are transmitted to a power metering unit. As noted hereinabove, the first input signal is current and the second input signal is voltage. Furthermore, at block 404, a predefined sample wave is transmitted from the carrier wave generator to the comparator. The predefined sample wave may be a triangular wave or a saw tooth wave. The predefined sample wave has minimal offset.
At block 406, the predefined sample wave is compared to the first input signal using the comparator. When the amplitude of the predefined sample wave is greater than the first input signal, a high signal is generated from the comparator. If the amplitude of the predefined sample wave is less than the first input signal, a low signal is generated from the comparator. Accordingly, a control signal is generated from the comparator. The control signal is a combination of a high signal and a low signal.
At block 408, a control signal is transmitted from the comparator to the switching device. The control signal is generated based on comparison of the predefined sample wave with the first input signal. Further, at block 410, the switching device is operated based on the control signal. When the control signal is high, the switching device is closed and when the control signal is low, the switching device is opened.
At block 412, the second input signal from the electrical device is transmitted via the switching device, when the switching device is closed. Accordingly, a modulated signal is output from the switching device. The modulated signal is representative of the quantity of estimated power of the electrical device. The modulated signal is transmitted to the output filtering unit. Accordingly, the output filtering unit may provide a filtered output signal which is representative of an average value of the second input signal transmitted via the switching device. When the second input signal is voltage, the filtered output signal provides an average value of the voltage. As noted hereinabove, the average value of the voltage is proportional to the average value of power. The average value of power is also referred to as estimated power of the electrical device. The actual power of the electrical device is determined based on the estimated power of the electrical device and the first and second sensed electrical parameters.
In accordance with the embodiments discussed herein, the components employed in the power metering unit such as the input filtering units, the comparator, the switching device, and the output filtering unit employ resistors, capacitors, operational amplifiers, transistors, and other readily available switches. In particular, the exemplary power metering unit is cheaper than the conventional localized metering systems. Also, the exemplary power metering unit may be easily integrated to each lighting fixture, thereby providing a localized power measurement.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.