Solid state electric power usage meter and method for determining power usage
First Claim
1. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power network having a network frequency and voltage and current waveforms, the power usage meter comprising:
- first means coupled to each phase of the electric power network for sensing current in each phase;
second means coupled to each phase of the electric power network for detecting the voltage level on each phase;
third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for periodically sampling said current and voltage related signals at predetermined times at a frequency which is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and for converting said samples to digital signals representing said current and voltage levels at the predetermined times;
processor means for calculating instantaneous values of power at the predetermined times from the digital signals; and
means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network.
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Accused Products
Abstract
A digital solid state electric power usage meter for determining power usage by a load attached to an electric power network. The meter has a current sensor coupled to each phase of the electric power network for sensing current in each phase, a voltage divider coupled to each phase of the power network for detecting the voltage level on each phase, an analog to digital (A/D) converter coupled to the current sensors and voltage dividers receiving signals from the current sensors related to the current in each phase and signals from the voltage dividers related to the voltage on each phase. The A/D converter samples the current and voltage related signals at predetermined times at a rate which insures that samples of the current and voltage related signals do not repeat for a large number of cycles of the network frequency or never repeat and which rate is at least twice as fast as the rate of change of the current and voltage related signals and converts the samples to digital signals representing the voltage levels and current at the predetermined times. A processor calculates instantaneous values of power at the predetermined times from the digital signals and a memory accumulates the instantaneous values so as to form a value representative of electric power usage by the load attached to the network.
119 Citations
43 Claims
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1. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power network having a network frequency and voltage and current waveforms, the power usage meter comprising:
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first means coupled to each phase of the electric power network for sensing current in each phase; second means coupled to each phase of the electric power network for detecting the voltage level on each phase; third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for periodically sampling said current and voltage related signals at predetermined times at a frequency which is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and for converting said samples to digital signals representing said current and voltage levels at the predetermined times; processor means for calculating instantaneous values of power at the predetermined times from the digital signals; and means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power network having a network frequency and voltage and current waveforms, the power usage meter comprising:
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first means coupled to each phase of the electric power network for sensing current in each phase; second means coupled to each phase of the electric power network for detecting the voltage level on each phase; third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for periodically sampling said current and voltage related signals at predetermined times at a rate which is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and which rate is at least twice as fast as the rate of change of the current and voltage related signals, and for converting said samples to digital signals representing said current and voltage levels at the predetermined times; processor means for calculating instantaneous values of power at the predetermined times from the digital signals; and means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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40. Apparatus for providing improved precision in the sampling of a periodic signal which may be subject to load variations comprising:
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first means coupled to a source of the periodic signal for detecting the instantaneous value of the signal; and second means coupled to the first means for periodically sampling the periodic signal at predetermined times at a frequency which is non-synchronous with the periodic signal frequency such that samples defining a cycle of the periodic signal are taken over a plurality of cycles of the periodic signal frequency and are not made at the same points on a plurality of successive cycles of the periodic signal and for converting the samples to digital signals representing the instantaneous levels at the predetermined times.
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41. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power network having a network frequency and voltage and current waveforms, the power usage meter comprising:
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first means coupled to each phase of the electric power network for sensing current in each phase; second means coupled to each phase of the electric power network for detecting the voltage level on each phase; third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for periodically sampling said current and voltage related signals at predetermined times at a frequency which is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and for converting said samples to digital signals representing said current and voltage levels at the predetermined times; processor means for calculating instantaneous values of power at the predetermined times from the digital signals; means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network; and
further comprisingmeans for producing a periodic signal non-synchronous with the network frequency and for superimposing said periodic signal on said signals from said first means, thereby to increase resolution of the conversion of said signals from said first means to digital signals without adding net power to the accumulated power usage.
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42. An electric power usage meter for determining electric power usage by a load attached to an electric power network, the power network having a network frequency and voltage and current waveforms, the power usage meter comprising:
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first means coupled to each phase of the electric power network for sensing current in each phase; second means coupled to each phase of the electric power network for detecting the voltage level on each phase; third means coupled to the first and second means receiving signals from the first means related to the current in each phase and signals from the second means related to the voltage on each phase, said means comprising means for periodically sampling said current and voltage related signals at predetermined times at a rate which is non-synchronous with the network frequency such that samples defining a cycle of each of the current and voltage related signals are taken over a plurality of cycles of the network waveforms and are not made at the same points on a plurality of successive cycles of the network waveforms of the respective current and voltage related signals and which rate is at least twice as fast as the rate of change of the current and voltage related signals, and for converting said samples to digital signals representing said current and voltage levels at the predetermined times; processor means for calculating instantaneous values of power at the predetermined times from the digital signals; and means for accumulating said instantaneous values so as to form a value representative of electrical power usage by the load attached to the network; and
further comprisingmeans for producing a periodic signal non-synchronous with the network frequency and for superimposing said periodic signal on said signals from said first means, thereby to increase resolution of the conversion of said signals from said first means to digital signals without adding net power to the accumulated power usage.
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43. Apparatus for providing improved precision in the sampling of a periodic signal which may be subject to load variations comprising:
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first means coupled to a source of the periodic signal for detecting the instantaneous value of the signal; and second means coupled to the first means for periodically sampling the periodic signal at predetermined times at a frequency which is non-synchronous with the periodic signal frequency such that samples defining a cycle of the periodic signal are taken over a plurality of cycles of the periodic signal frequency and are not made at the same points on a plurality of successive cycles of the periodic signal and for converting the samples to digital signals representing the instantaneous levels at the predetermined times; and
further comprisingmeans for producing a periodic signal non-synchronous with the periodic signal frequency and for superimposing said periodic signal on said signals from said first means, thereby to increase resolution of the conversion of said signals from said first means to digital signals without adding a net value due to the superimposed signal to an accumulated sum of said instantaneous levels.
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Specification