## 4 The Concept of Validation of Measurement Algorithms  
Validation is the technique used to compare the results to be validated with the results obtained through other numerical methods previously validated. In other words, one technique has been validated before it is used as a reference to validate the second method. The idea of the reliable validation of measurement algorithms, applicable for the E/A instrument (and probably for other devices as well), relies on the assumption that the dataset used for the calculation of coefficients in the examined instrument is the same as the one used in the reference system. This assumption is met if the measurement data, processed in the DSP for the designation of coefficients, are stored and further used in the reference system to calculate the corresponding coefficients (Figure 14). Figure 14: The experimental setup for the verification of the measurement algorithms using registered samples and the corresponding coefficients, also in addition to the PC-based estimation system. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**f (Hz)** & **Size** & **Unit** & **L1** & **L2** & **L3** \\ \hline \multirow{3}{*}{45} & \(U_{E/A}\) & (V) & 221.4 & 220.7 & 220.3 \\  & \(U_{DXI}\) & (V) & 220.9 & 220.4 & 220.8 \\  & \(\Delta\) & (V) & 0.5 & 0.3 & \(-\)0.5 \\  & \(\delta\) & (\%) & 0.23 & 0.14 & \(-\)0.23 \\ \hline \multirow{3}{*}{50} & \(U_{E/A}\) & (V) & 221.4 & 220.9 & 220.5 \\  & \(U_{DXI}\) & (V) & 220.9 & 220.4 & 220.8 \\  & \(\Delta\) & (V) & 0.5 & 0.5 & \(-\)0.3 \\  & \(\delta\) & (\%) & 0.23 & 0.23 & \(-\)0.14 \\ \hline \multirow{3}{*}{55} & \(U_{E/A}\) & (V) & 221.4 & 220.8 & 220.3 \\  & \(U_{DXI}\) & (V) & 220.9 & 220.4 & 220.8 \\ \cline{1-1}  & \(\Delta\) & (V) & 0.5 & 0.4 & \(-\)0.5 \\ \cline{1-1}  & \(\delta\) & (\%) & 0.23 & 0.19 & \(-\)0.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The voltage deviations with reference to the network frequency. Figure 4 shows the resources of the DSM STSL module applied in the E/A instrument (Figure 2). The module is additionally equipped with 128 MB of the synchronous dynamic random access memory (SDRAM). This memory was not used in the E/A operations, because of the sufficient capacity of the internal memory of the DSP (24 Mb) for the calculation of the adopted coefficients of the electrical power quality. The proposed idea of measurement algorithms validation assumes the use of the SDRAM memory (in Figure 4 marked in red ellipse) for storing the selected samples from the ADC, but only those which were used by the DSP for the coefficients calculation, together with the designated coefficients. The capacity of the SDRAM enables one to accumulate the data from several processing cycles, corresponding to measurement windows of approximately 200 ms. For example, for the \"estimator\" operating option (Figure 5), for memorizing the data collected from the samples from three voltage channels, converted in the ADC at the rate of 210 kS/s, no more than 256 kB of memory is needed for one measurement window. To perform the validation of embedded algorithms, the original source data, together with the DSP processing results, are sent to the external system. In this way, it is possible to assess the real characteristics of data processing, as well as those corresponding to the DA part as embedded in the DSP software, in the DDP part of the instrument. The implementation of the proposed method in the E/A instrument is not connected with any hardware modifications. Only software changes are needed to obtain the fixed goal. The reference system stores the set of data received from the instrument and uses them for the independent off-line calculation of respective coefficients, resulting from the sequentially selected measurement functions of the E/A. The system is under development in the LabVIEW environment. The estimation part of the reference system compares the values of the coefficients designated in the E/A with the results obtained off-line in the PC estimation system.