Accuracy improvement of the stochastic digital electrical energy meter
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The paper describes the problem and a solution for the elimination of the systematic error in a stochastic flash ADC caused by the offset present in fast voltage comparators, when measuring voltage RMS and active power and energy using the stochastic digital measurement method. By the means of simple periodical cross-switching of inverting and non-inverting inputs of used comparators and inverting their digital outputs, it is possible to suppress offset induced error for over 80 dB. Main condition for the method is that input signals (one for voltage RMS measurement, two for power and energy measurements) are stationary during at least two (or even number) of signal cycles. A prototype of a stochastic energy meter was built. It has the offset suppression method implemented, based on the solution proposed in the paper. The prototype was used for measurements in a laboratory, in an industrial plant and on a large power load. The measurement results confirm high accuracy of the instrument... and validity of its aforementioned condition. The stochastic digital electrical energy meter prototype has 0.13% accuracy while the stochastic measurement instrument in its core has 0.007% accuracy. High precision and high accuracy of the stochastic instrument enables it to be used as a reference meter for calibration of energy meters at the national level. Full measurement results are presented.
Keywords:stochastic processes / energy measurement / Flash ADC / sampling / precision
Source:Measurement, 2017, 98, 139-150
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