## 3 Procedures for Assessing the Characteristics of the E/A
### The Designation of Characteristics of Measurement Channel
Table 2 contains the measurement results of the three-phase triangle signal (experimental setup as in Figure 11b), generated using a Chroma type 6590 Programmable AC Power Source (Chroma ATE Inc., Taipei Hsien, Taiwan) (declared values of \(U_{rms}\), \(U_{1}\) and THD for standard triangle signal DST017 from its waveforms library) [40], combined with the results obtained from the E/A instrument and as a result of the raw samples processing in the PC system (experimental setup as in Figure 11c). Figure 12: The block diagram of evaluation board EVAL-TS201S-EZKIT [39]. CPLD: complex programmable logic device; DAC: digital-to-analog converter; ADC: analog-to-digital converter; JTAG: join test action group; LEDs: light-emitting diodes; PBs: push buttons; PLL: phase-locked loop; FLAGS: processor’s status register; IRQs: interrupt requests; SDRAM: synchronous dynamic random access memory. The experimental layout shown in Figure 11d (as well as in Figure 11c) is free from the signal limitations. The test signals were provided, at the same time, to the inputs of the examined E/A instrument and to the reference instrument. The reference instrument was based on the PCI eXtensions for Instrumentation (PXI) platform (National Instruments Corporation, Austin, TX, USA) equipped with suitable peripheries and the virtual instrument designed for measuring the power quality parameters (PCI stands for Peripheral Component Interconnect--personal computer bus). In Figure 13, the exemplary results of calibration of the phase voltage channels are presented. The differences between the rms values, measured by the tested instrument and also the PXI system, are shown. Table 3 contains the absolute errors \(\Delta\) representing the deviations between the rms values of the phase voltages, measured by the E/A instrument and the PXI system, obtained during the calibration of the instrument for different frequencies of the network voltage, as well as the relative (percentage) errors \(\delta\), adopting the value indicated by the PXI device as the actual value of the voltage, respectively. The values and course of the errors indicate that their main source were the systematic effects resulting from the incorrect calibration of the processing characteristics of the measurement channels. The random influences cause the dispersion of errors \(\Delta\) as a function of frequency (for L2 and L3 channels) not exceeding \(\Delta_{\text{max}}\) = 0.2 V. Assuming the uniform distribution of errors, the standard uncertainty can be calculated using Formula (1):  
\[u=\frac{\Delta_{max}}{\sqrt{3}}\cong 0.12\ V \tag{1}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Device** & **Size** & **Unit** & **L1** & **L2** & **L3** \\ \hline \multirow{2}{*}{E/A} & \(U_{rms}\) & (V) & 220.75 & 220.56 & 219.70 \\  & \(U_{1}\) & (V) & 219.13 & 218.93 & 218.10 \\  & THD & (\%) & 12.00 & 10.24 & 11.97 \\ \hline \multirow{2}{*}{PC} & \(U_{rms}\) & (V) & 220.80 & 220.020 & 220.24 \\  & \(U_{1}\) & (V) & 219.23 & 219.05 & 218.68 \\  & THD & (\%) & 12.18 & 12.23 & 12.14 \\ \hline \multirow{2}{*}{DST017} & \(U_{rms}\) & (V) & 220.00 & 220.00 & 220.00 \\  & \(U_{1}\) & (V) & 218.42 & 218.42 & 218.42 \\ \cline{1-1}  & THD & (\%) & 12.04 & 12.04 & 12.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The results obtained from the E/A and in the PC system for the standard signal DST017 from the Chroma Programmable AC Power Source. Figure 13: The calibration results of the voltage measurement channel of the instrument. In sum, all of the applied testing methods for the assessment of the measurement track characteristics are reliable for the specified instrument. The obtained results of the experimental verification are positive within an acceptable tolerance range. However, on the basis of the results, no conclusions about the degree of possible modification algorithms to improve the measurement accuracy can be drawn. What is the reason for the phenomena described in [15; 16]? Can these cases relate to the characteristics of the E/A instrument?