New Emendatory FFT Algorithm of Measuring Dielectric Loss Factor tan δ

The paper analyses and calculates the remarkable error of dielectric loss factor tan $. The cause of the error is that the data sampling rate of hardware cannot change with the power system frequency when the latter is drifting. A simple and useful emendatory fast Fourier transform (FFT) algorithm which can solve the bottleneck above is presented in this paper. That is, the algorithm emendates the data sequence and figures out the emendatory quantum AT, by checking the cycle of signal and then it increases the sampling cycle if AT, is bigger than zero and decreases it if not. The whole process of the algorithm is presented in the paper and an analog circuit used for both labs and in field to change phase angle via the variable resistance and capacitor is also introduced. The calculation and experimental data has demonstrated that the error of tan S is less than 5×10-4 under the condition of 12 bit A/D sampling and ±0.2 Hz power system frequency change. It could be easily applied to the widely used MCU.