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Calculation of the low-frequency noise impedance

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In order to plot the time evolution of the low-frequency noise impedance, the value of the low-frequency noise impedance at each iteration must be extracted. This is performed by averaging a given number of points at the low-frequency end of the time-averaged noise impedance spectrum. The number of points from the low frequency end of the noise impedance spectrum that are used to perform such operation can be selected in the preferences menu (Points Average for low frequency impedance). The point obtained from FFT at 0 frequency is excluded from this computation.

 

figure9

Figure 9.0 Calculation of low frequency noise impedance

 

The calculation of the average charge of a corrosion event is performed for each segment by the following equation

 

 q =   ( v VPSD   *  v CPSD )  /  B                                      (Equation 1.0 )

                                   

Where VPSD and  CPSD  are the low-frequency values of potential and current power spectral densities, and B is the Stearn-Geary coefficient. The low frequency value of the potential and current power spectral density is obtained averaging a number of points in the low-frequency end of the potential and current power spectral density spectra.     The number of points for such average and the appropriate value for the Stearn-Geary coefficient can be selected in the preference window.