A method for measuring a Noise RMS of a periodic signal, used to obtain a noise of a target periodic signal, wherein the target periodic signal is a target periodic digital signal obtained by sampling, by an analog-to-digital converter, an analog periodic signal, and comprises following steps:
- Step A, sampling, by the analog-to-digital converter, the analog periodic signal, to obtain a sampled signal, and then entering Step B;
- Step B, obtaining, through an analog means or a digital means, a continuous zero-crossing time series Tz1, . . . , Tzk, . . . , TzK of at least two periods on the sampled signal after passing a negative peak value or a positive peak value, wherein K denotes a number of zero-crossing time instants in the continuous zero-crossing time series, and Tzk denotes a k-th zero-crossing time instant in the continuous zero-crossing time series;
- and then initializing j=K+1 and entering Step C;
- Step C, calculating and obtaining, according to Tz(j−1), . . . , Tz(j−m), an average period T, and further calculating and obtaining, according to a preset parameter c that satisfies a value range (0.5,1), a digital initial integration point time instant Tsj corresponding to a j-th zero-crossing time instant Tzj through Tsj=Tz(j−1)+T×c, and then entering Step D, wherein 1<m<j, Tzj denotes the j-th zero-crossing time instant;
- Step D, selecting, on a basis of each sampling point on a sampling signal, two sampling points that are adjacent front and back to the digital initial integration point time instant Tsj, and sequentially forming a first sampling point to be analyzed, and a second sampling point to be analyzed, forming, by combining a time instant corresponding to the sampling point and a sampling value corresponding to the sampling point, a coordinate of the sampling point to be analyzed, and then entering Step E;
- Step E, obtaining, according to the digital initial integration point time instant Tsj, a sampling value xsj corresponding to Tsj and at a position between a first sampling point and a second sampling point through a rectangular interpolation means or a trapezoidal interpolation means, to form a coordinate (Tsj, xsj) of a digital integration starting point, and then initializing V=2, sequentially defining each sampling points after the first sampling point and the second sampling point on the sampling signal as the sampling point to be analyzed, and entering Step F;
- Step F, executing a digital integration operation on the sampling signal from a coordinate position of the digital integration starting point to a coordinate position of a v-th sampling point to be analyzed, to form a digital integration result Sy;
- and executing a digital integration operation on the sampling signal from a coordinate position of the digital integration starting point to a coordinate position of a v+1-th sampling point to be analyzed, to form a digital integration result Sv+1, and then entering Step G;
- Step G, determining whether a product of the digital integration result Sv and the digital integration result Sv+1 is greater than 0, updating, in a case of yes, a value for v by adding 1 and returning to Step F;
- otherwise, entering Step H;
- Step H, obtaining, according to a condition that a sum of a digital integration from the digital integration starting point to an digital integration ending point is zero, a coordinate (Tej, xej) of an digital integration ending point located between the v-th sampling point to be analyzed and the v+1-th sampling point to be analyzed through the rectangular interpolation means or the trapezoidal interpolation means, and then entering Step I;
- Step I, obtaining, according to
- T
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- ,
- the j-th zero-crossing time instant Tzj, and then entering Step J;
- Step J, executing, according to a preset time constant TC that is not greater than a period value for the target periodic signal, following steps on the zero-crossing time instant Tzj, obtaining a signal voltage value Vj at a time instant Tzj+TC, constructing or updating a signal voltage value series {VK+1, . . . , Vj}, and then entering Step K;
- steps:
- obtaining a signal voltage value Vj corresponding to a time instant Tzj+TC position on the target periodic signal for an analog-to-digital conversion;
- or obtaining a signal voltage value Vj corresponding to a sampled time instant Tzj+TC position on the target periodic signal after the analog-to-digital conversion;
- or obtaining a signal voltage value Vj corresponding to a time instant position adjacent to and closest to a time instant Tzj+TC position on the target periodic signal after an analog-to-digital conversion;
- or obtaining, by selecting signal voltage values corresponding to an adjacent time instant positions respectively on both sides of a time instant Tzj+TC position on the target periodic signal after the analog-to-digital conversion, a signal voltage value Vj at the time instant Tzj+TC position through a linear interpolation;
- Step K, determining, whether a length of the signal voltage value series {VK+1, . . . , Vj} is less than a preset threshold n, entering, in a case of yes, Step L;
- otherwise, selecting latest generated n signal voltage values from the signal voltage value series {VK+1, . . . , Vj}, and through a following formula:
- V
- noisePower
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- j
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- obtaining a target periodic signal noise VnoisePower,j, wherein V denotes an average voltage value for the n signal voltage values that are selected to participate in a calculation, and then entering Step L;
- and
- Step L, updating, by adding 1, a value for j, and returning to Step C.