Apparatus for measuring electrical power
First Claim
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1. An apparatus for measuring power delivered at an alternating voltage by an alternating current to a loadcomprising in combination:
- sampling means for periodically sampling the alternating voltage and the alternating current delivered to the load at selected sampling points,converter means, including impulse generator means, for converting the sampled points to first and second sequences of a plurality of pulses, the number of pulses in each sequence being substantially proportional to the instaneous values of the alternating voltage and of the alternating current, respectively,first counting means for counting the first sequence of pulses,second counting means for counting the second sequence of pulses,averaging means for determining the average value of said first and second sequence of pulses, respectively, over at least one period of the alternating current,subtractor measns for obtaining difference values between said average value, and said first and second sequences of pulses, respectively,multiplier means for multiplying said respective difference values, to obtain successive product values,integrating means for integrating said successive product values over said at least one period so as to measure the power delivered to said load, whereby any error in determining said average value is eliminated from the power measurement.
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Abstract
An apparatus for measuring a.c. power which subtracts an average value of current and voltage from sampled instantaneous current and voltage values, respectively. The resultant current and voltage values are multiplied, so as to obtain a power measurement substantially free of any sampling errors and any d.c. levels.
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Citations
11 Claims
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1. An apparatus for measuring power delivered at an alternating voltage by an alternating current to a load
comprising in combination: -
sampling means for periodically sampling the alternating voltage and the alternating current delivered to the load at selected sampling points, converter means, including impulse generator means, for converting the sampled points to first and second sequences of a plurality of pulses, the number of pulses in each sequence being substantially proportional to the instaneous values of the alternating voltage and of the alternating current, respectively, first counting means for counting the first sequence of pulses, second counting means for counting the second sequence of pulses, averaging means for determining the average value of said first and second sequence of pulses, respectively, over at least one period of the alternating current, subtractor measns for obtaining difference values between said average value, and said first and second sequences of pulses, respectively, multiplier means for multiplying said respective difference values, to obtain successive product values, integrating means for integrating said successive product values over said at least one period so as to measure the power delivered to said load, whereby any error in determining said average value is eliminated from the power measurement. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for measuring power delivered at an alternating voltage by an alternating current to a load
comprising in combination: -
sampling means for periodically sampling the alternating voltage and the alternating current delivered to the load at selected sampling points, converter means, including impulse generator means, for converting the sampled points to first and second sequences of a plurality of pulses, the number of pulses in each sequence being substantially proportional to the instaneous values of the alternating voltage and of the alternating current, respectively, first counting means for counting the first sequence of pulses, second coupling means for counting the second sequence of pulses, averaging means for determining the average value of at least one of said first and second sequence of pulses, over at least one period of the alternating current, subtractor means for obtaining a difference value between said average value and said at least one of said first and second sequence of pulses, multiplier means for multiplying said difference value with the other of said first and second sequences of pulses to obtain a product value, and integrating means for integrating said successive product values over said at least one period so as to measure the power delivered to said load, whereby any error in determining said average value is eliminated from the power measurement.
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11. In a method of measuring power delivered at an alternating voltage by an alternating current to a load, the steps comprising:
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obtaining first and second sequences of a plurality of pulses, the number of pulses in each sequence being substantially proportional to the instantaneous values of the alternating voltage, and of the alternating current, respectively, determining the average values of said first and second sequences of pulses, respectively, over at least one period of the alternating current, subtracting said average values from said first and second sequences of pulses, respectively, to obtain first and second difference values, multiplying said difference values to obtain a product value, and integrating successive product values over said at least one period, so as to measure the power delivered to said load, whereby any error in determining the average value is substantially eliminated from the power measurement.
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Specification